Crystal structure and synthesis of the bis­(anthracene)dicuprate dianion as the dipotassium salt, [K(tetra­hydro­furan)2]2[{Cu(9,10-η2-anthracene)}2], the first anionic arene com­plex of copper

Young, V.G.; Brennessel, W.W.; Ellis, J.E.

doi:10.1107/S2053229623008367

research papers

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 79| Part 11| November 2023| Pages 456-463

https://doi.org/10.1107/S2053229623008367

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Crystal structure and synthesis of the bis(anthracene)dicuprate dianion as the dipotassium salt, [K(tetrahydrofuran)₂]₂[{Cu(9,10-η²-anthracene)}₂], the first anionic arene complex of copper

Victor G. Young Jr,^a William W. Brennessel ^b ^* and John E. Ellis ^a ^*

^aDepartment of Chemistry, 207 Pleasant Street SE, University of Minnesota, Minneapolis, MN 55455, USA, and ^bDepartment of Chemistry, 120 Trustee Road, University of Rochester, Rochester, NY 14627, USA
^*Correspondence e-mail: william.brennessel@rochester.edu, ellis@umn.edu

Edited by E. Reinheimer, Rigaku Americas Corporation, USA (Received 9 June 2023; accepted 22 September 2023; online 3 October 2023)

Dedicated to Professors Marcetta and Donald Darensbourg on the occasion of their 80th birthdays.

Reactions of (tricyclohexylphosphane)copper(I) chloride with two equivalents of potassium anthracene (KAn) in tetrahydrofuran (THF) at 200 K provides air-sensitive but thermally stable (at 293 K) solutions from which yellow crystalline blocks of bis[bis(tetrahydrofuran-κO)potassium] bis(μ-anthracene-κ²C⁹:C¹⁰)dicopper, [K(THF)₂]₂[{Cu(9,10-η²-C₁₄H₁₀)}₂] or [K(C₄H₈O)₂]₂[Cu₂(C₁₄H₁₀)₂], 1, were isolated in about 50% yield. Single-crystal X-ray crystallographic analysis of 1 confirmed the presence of the first known (arene)cuprate. Also, unlike all previously known homoleptic (anthracene)metallates of d-block elements, which contain metals coordinated only to terminal rings, the organocuprate unit in 1 contains copper bound to the 9,10-carbons of the central ring of anthracene. No other d- or f-block metal is known to afford an anthracene or other aromatic hydrocarbon complex having the architecture of organodicuprate 1.

Keywords: anthracene; copper; arenecuprate; crystal structure; tetrahydrofuran.

CCDC reference: 2296812

1. Introduction

Our interest in the stabilization of `naked' atomic anions of d-block elements as homoleptic (arene)metallates (Ellis, 2019 ), where the arene is often a polycyclic aromatic hydrocarbon or polyarene, especially naphthalene or anthracene, led to an examination of `anionic copper' (Rieke et al., 1990 ) or `Cu¹⁻' (Stack et al., 1993 ), reported more than 30 years ago. In these studies, the assumed, but never isolated or characterized, cuprate species was generally prepared in tetrahydrofuran (THF) at subambient temperatures, ca 170 K, by addition of soluble Cu^I halide complexes to two equivalents of lithium naphthalene (LiNp). Although the cuprate was originally speculated to be a copper analog of the monoatomic gold anion, Au¹⁻, established to be present in cesium auride, CsAu (Knecht et al., 1978 ), and subsequently observed in single crystals of [Me₄N][Au], wherein Au¹⁻ has about the same ionic radius as Br¹⁻ (Dietzel & Jansen, 2001 ), the bona fide atomic copper anion has only been identified in the gas phase (Hotop et al., 1973 ). Indeed, to our knowledge, no substance containing copper in a formal negative oxidation state is known in a condensed phase, possibly except for the cryogenic species, [Cu(CO)_n]¹⁻ (n = 1, 2, or 3), which have been proposed to exist in solid neon at 4–10 K (Zhou & Andrews, 1999 ). Based on prior studies of compounds containing naphthalene-stabilized transition-metal anions (Ellis, 2006 ), we believed that these highly thermolabile solutions might contain presently unknown homoleptic (naphthalene)cuprates (Davies, 2011 ). Owing to the extreme thermal instability of these solutions above 170 K, our attempts to isolate or characterize products from these reactions have failed to date. However, recognition of the usual greater thermal stability in solution and/or the solid state of (anthracene)metallates of d-block elements, compared to formally analogous (naphthalene)metallates (Kucera et al., 2022 ), led to conducting previously unreported reactions of copper(I) halides with alkali metal anthracene radical anions, MAn (M = Li, Na, or K; An = anthracene), in THF. Also, because stoichiometrically analogous naphthalene and anthracene complexes of a given d-block element may possess very similar molecular structures, particularly in the solid state (Ellis, 2019), identification of an (anthracene)cuprate would be of substantial interest in shedding light on the possible nature of the previously reported `anionic copper' (Rieke et al., 1990) or `Cu⁻¹' (Stack et al., 1993).

Although `anionic copper' was often prepared by the reaction of the lithium naphthalene radical anion with triorganophosphane adducts of copper(I) halides, [CuX(PR₃)]_n (X = Cl, Br, or I; R = phenyl or n-butyl) (Rieke et al., 1990), owing to the particularly good solubility in THF and accessibility of [CuCl(PCy₃)]₂ (Cy = cyclohexyl) (Churchill & Rotella, 1979 ), this was the only copper precursor employed in our initial study reported herein. Also, we elected not to use triphenylphosphane (PPh₃) adducts of copper(I) halides due to the ease with which coordinated or free PPh₃ and mixed tertiary aryl–alkyl phosphanes undergo reductive cleavage of P—C(aryl) bonds, unlike trialkylphosphanes (Chou et al., 1986 ). Although reactions of [CuCl(PCy₃)]₂ with four equivalents of MAn (M = Li, Na, or K) in THF appear by NMR spectra to afford similar products in solution, owing to the facile isolation and crystallization of the potassium salt, only the latter will be described now. Thus, the addition of a colorless solution of [CuCl(PCy₃)]₂ in THF to a dark-blue solution of KAn (molar ratio: 2 KAn/Cu) in THF at 200 K, led to the formation of an air-sensitive but thermally stable (at 293 K) yellow–brown solution, from which yellow crystalline blocks of [K(THF)₂]₂[{Cu(9,10-η²-C₁₄H₁₀)}₂], 1, were isolated (Fig. 1).

Figure 1
Anisotropic displacement ellipsoid plot of 1, drawn at the 50% probability level with H atoms omitted. Symmetry-equivalent atoms (`A' label) were generated by inversion (−x, −y + 1, −z + 1). The K₂Cu₂ core is asymmetric (Å): Cu1⋯K1 = 3.6637 (15), Cu1⋯K1A = 3.3762 (9), and Cu1⋯Cu1A = 2.6172 (7).

Single-crystal X-ray diffraction (SCXRD) characterization of 1 confirmed the presence of an (anthracene)cuprate, the first anionic arene complex of copper. However, unlike all previously known homoleptic (anthracene)metallates of the d-block elements (Ellis, 2019), including the recently reported bis(anthracene)divanadate(1−) (Kucera et al., 2022), which contain metals coordinated only to terminal rings, the organocuprate unit in 1 contains Cu atoms bound to the 9,10-carbons of the central ring of anthracene. Mononuclear heteroleptic complexes of d- and f-block elements containing M(9,10-η²-anthracene) moieties have been structurally authenticated for the Group 3 elements scandium (Ellis et al., 2018 ; Ghana et al., 2020 ; Zhu et al., 2023 ) and lutetium (Roitershtein et al., 1992 , 1993 ), and the f-block elements thulium (Fedushkin et al., 2001 ) and thorium (Yu et al., 2020 ). Unique uranium anthracene complexes containing individual metals bound to both the terminal and central rings of different anthracene ligands have been published recently (Murillo et al., 2021 , 2022 ). Dinuclear complexes of scandium (Huang et al., 2011 , 2014 ), yttrium (Fryzuk et al., 2000 ), and iron (Hatanaka et al., 2012 ) containing bridging anthracenes, in which one metal binds to the terminal ring and the other anti to the central ring of anthracene, are also known. However, none of these species are of particular relevance to 1 and will not be discussed further. Although d-block complexes with η⁶-coordination of the central ring of untethered specially substituted anthracenes, for example, 2,3,6,7-tetramethoxy-9,10-dimethylanthracene, have been confirmed recently (Karslyan et al., 2017 ; Kuchuk et al., 2019 ), no d- or f-block metal is known to afford an anthracene or other arene complex having the architecture of the organodicuprate present in 1.

The structure of 1 (Fig. 1) consists of a contact ion-pair complex in which two anthracene ligands, distinctly folded about the 9,10-carbons [fold angle of 36.06 (6)°, calculated from all C atoms in the anthracene ligand] are present as centrosymmetric anthracene dianions bridging two equivalent Cu atoms in a near linear fashion across the 9,10-carbons of symmetry-related rings. Equivalent [K(THF)₂]¹⁺ counter-ions interact weakly with essentially planar terminal exo-benzene units (mean deviations from planarity of 0.011 and 0.006 Å for rings C1–C4/C14/C13 and C5–C8/C12/C11, respectively) on 1. Details of these interactions will be presented in Section 3.

To the best of our knowledge, only the long-known dimeric organoalanate complexes [{(AlR₂)(arene)}₂]²⁻ [R = methyl; arene = naphthalene, 2 (Brauer & Stucky, 1970 ), and anthracene, 3 (see Fig. 2; Brauer & Stucky, 1972 )] possess molecular structures in the solid state very similar to that observed for the organocuprate dimer in 1, vide infra. In particular, the coordinated anthracenes in both the cuprate, 1, and the alanate, 3, are effectively functioning as 9,10-dihydro-9,10-anthrylene dianionic units with about one negative charge on each of the mixed sp²/sp³-hybridized 9,10 bridgehead carbons. Thus, the respective copper and aluminium anthracene complexes contain formally Cu¹⁺ and Al³⁺, both closed-shell ions. One major difference in the molecular structures of the anionic components of 1, 2, and 3 is the coordination environment about the metals. Whilst the four-coordinated Al atoms in 2 and 3 adopt distorted tetrahedral geometries, the dimeric structure observed for organocuprate 1 contains identical two-coordinate Cu atoms with a nearly linear C—Cu—C angle of 174.74 (7)°. The substantially different steric impacts of the dimethylaluminium groups in 3 compared to the Cu atoms in 1 are responsible for some dramatic and surprising differences in the molecular structures of these two stoichiometrically similar contact ion-pair complexes (see Section 3). It should also be pointed out that dimeric neutral nonmetal or metalloid adducts of anthracene are known, which have molecular structures similar to the dimeric anion in 3, including anthracene-based macrocyclic diphosphanes, [{(PX₂)(9,10-η²-An)}₂], with X = Cl (Velian et al., 2014 ) and phenyl (Riu et al., 2020 ). Indeed, the oldest example, now known as the photodimer of anthracene, di-para-anthracene, was first reported nearly 160 years ago (see Bouas-Laurent et al., 2000 ) and forms as poorly soluble microcrystals when solutions of anthracene in benzene, toluene, etc., are exposed to sunlight/UV radiation. Structural characterization by SCXRD showed that the labile dimer arises by symmetrical coupling of the 9,10-carbons on two anthracenes, where the bridgehead C—C distance [1.624 (3) Å] is long (Choi & Marinkas, 1980 ), resulting in a low dissociation energy of the dimer, calculated to be 9 ± 3 kcal mol⁻¹ (Grimme et al., 2006 ). Interestingly, 1 may be considered formally to be a molecule in which atomic copper anions have been inserted into each of the two bridgehead C—C bonds of the anthracene dimer, thereby increasing the separation of the bridgehead C atoms from 1.624 (3) to 3.98 (1) Å.

Figure 2
The molecular plot of 3.

Unperturbed mononuclear homo-diorganocuprate complexes, [CuR₂]¹⁻ (R = alkyl, aryl, etc.), also have close to linear C—Cu—C units and are formulated to contain two carbanions bound to Cu^I by quite polar Cu—C σ bonds, where the Cu—C distance in 1 [1.989 (2) Å] is well within the range of 1.83–2.05 Å observed previously for homoleptic diorganocuprates (Davies, 2011). Although Cu^I commonly adopts coordination numbers 2–4 in mononuclear complexes, organodicuprate 1 contains two quite bulky dianionic hydrocarbyl units, which appear to favor the formation of the observed structure containing two-coordinated Cu^I with essentially linear C—Cu—C units, as expected for d¹⁰ Cu^I (Cotton et al., 1999 ). Owing to the latter, the separation of the 9,10-carbons on individual anthracene groups in 1 effectively defines the Cu⋯Cu distance of 2.6172 (7) Å. Prior studies suggest that d¹⁰Cu–d¹⁰Cu interactions are very weak to non-existent when the Cu⋯Cu separation is greater than ∼2.50 Å in molecular entities containing Cu^I complexes (Mehrotra & Hoffmann, 1978 ; Cotton et al., 1988 ; Merz & Hoffmann, 1988 ).

Although d¹⁰Cu–d¹⁰Cu or `cuprophilic' interactions (Harisomayajula et al., 2019 ) appear unlikely to stabilize the dimeric structure adopted by 1 in the solid state, the significant contact ion-pairing and resulting increase in its crystalline lattice stabilization may play a key role in the formation of the observed bis(anthracene)dicuprate(2−) complex, relative to unknown monomeric monoanions, i.e. [{Cu(THF)_x}(9,10-η²-An)]¹⁻ (x = 0–2), which would likely be strained metallacycles, vide infra. In the case of the structurally related organoaluminium complexes 2 and 3, it was proposed that the dimeric, rather than plausible monomeric structures, `are favored by smaller deviations from tetrahedral angles about the aluminum atoms in the dianions rather than about the aluminum atom in the hypothetical monoanions.' However, surprisingly, the possible importance of contact ion-pairing in contributing to the stabilization of the dimers in the solid state, and possibly also in solution, was not considered (Brauer & Stucky, 1972). Most interestingly, the bis(naphthalene)dialanate(2−) salt, 2, was originally prepared and proposed to be a monomer, [{AlMe₂}(1,4-η²-Np)]¹⁻ (Np = naphthalene), based only on a proton NMR spectrum in THF and identification of 1,4-dihydronaphthalene as a key hydrolysis product (Lehmkuhl, 1966 ). Later, the identical salt, as crystalline 2, dissolved in THF, was found to afford a proton NMR spectrum in good agreement with that of the purported monomer (Brauer & Stucky, 1970). In both SCXRD studies on 2 and 3, the possibility that they could be present as monomers in solution appears to have been implicitly rejected (Brauer & Stucky, 1970, 1972). However, the later structural authentication of an (anthracene)aluminium monomer, the neutral metallacycle [{AlEt(THF)}(9,10-η²-9,10-bis(trimethylsilyl)anthracene)], 4, strongly suggests that the natures of 2 and 3 in solution merit reinvestigation. It should also be emphasized that presently we cannot rule out the possibility that monomeric forms of 1 could be present in THF or other solvents (see Section 2).

The structure of the alane monomer 4 is consistent with that expected of a strained metallacycle, vide infra, i.e. a sharp C9—Al—C10 angle of 81.5° for four-coordinated aluminium and an average Al—C(bridgehead) distance of 2.057 (4) Å, which is significantly longer than the normal Al—C(Et) distance of 1.966 (4) Å present in 4 (Lehmkuhl et al., 1985 ). Structurally similar (anthracene)alane and (anthracene)alanate(1−) monomers have been prepared recently by novel additions of anthracene to an Al^I complex (Bakewell et al., 2020 ) and a dialkylaluminyl anion (Sugita et al., 2020 ), respectively.

A more well-known related complex is the monomeric (anthracene)Mg solvate in crystalline [{Mg(THF)₃}(9,10-η²-An)], 5, possessing a C9—Mg—C10 angle of 71.4°. This angle is significantly sharper than the corresponding angle in 4, likely owing in part to the higher coordination number of Mg in 5. The latter also contains a rather long Mg—C distance of 2.30 (2) Å (Engelhardt et al., 1988 ) compared to that present in [(9-anthracenyl)Mg(μ-Br)·di-n-butyl ether]₂, a dimeric Grignard reagent with bridging bromides and an essentially unstrained Mg—C bond with a distance of 2.132 (2) Å (Bock et al., 1996 ). For related reasons, 5 appears to be the first (anthracene)metal complex to be recognized as a strained metallacycle (Bogdanović et al., 1987 ). In solution, 5 is a metastable species, which following facile loss of THF in hexane or diethyl ether, readily eliminates free anthracene and is proposed to initially form `quasi-atomic' magnesium under strictly anaerobic conditions (Bönnemann et al., 1983 ). The latter rapidly forms a mirror of magnesium metal in the absence of other reactants (Alonso et al., 1987 ). Compound 5 has been found by the Cummins group (Velian & Cummins, 2012 ) and others to be a highly useful precursor to numerous new strained monomeric main group element adducts of anthracene, including the formal Ge^IV complex [{GeMe₂}(9,10-η²-An)], 6, or 2,3:5,6-dibenzo-7-dimethylgermanorbornadiene. X-ray structure characterization of 6, Me₂GeAn, revealed a sharp C9—Ge—C10 angle of 77.72 (5)°, and Ge—C(9,10 or bridgehead) distances [average 2.030 (1) Å] which are significantly longer than the Ge—C(Me) distance [average 1.943 (4) Å] (Velian et al., 2015 ). The latter is statistically identical to that observed for Me₄Ge [1.945 (3) Å; Hencher & Mustoe, 1975 ]. Compound 6 suffers thermal loss of anthracene at 373 K in toluene to produce in good yield an intriguing dimethylgermylene, Me₂Ge, adduct [{Ge₂Me₄}(9,10-η²-An)], 7, which may arise via insertion of highly reactive Me₂Ge into a strained Ge—C(bridgehead) bond of 6. However, also possible is an initial dimerization of Me₂Ge to the digermene, Me₄Ge₂, followed by its facile [4 + 2] cycloaddition to free anthracene, which was established previously to afford 7 (Sakurai et al., 1982 ). Also noteworthy is that the thermolysis of two equivalents of 6 to form the less strained 7 and free anthracene has been calculated to have a quite favorable free energy change (ΔG) of ca −37 kcal mol⁻¹ of 7 (Velian et al., 2015). Finally, under milder conditions, 6 has been shown to function as an Me₂Ge group transfer reagent (Geeson et al., 2019 ).

Of particular relevance to our discussion is that neutral 6 is isoelectronic and likely of similar structure to the presently unknown alanate, [{AlMe₂}(9,10-η²-An)]¹⁻, the monomer of structurally characterized dimeric 3 (Brauer & Stucky, 1972). To the best of our knowledge, none of the reported formally strained metallacyclic monomers, [{ML_n}(9,10-η²-An)]^z (z = 0 or −1), are presently known to form dimers (or oligomers) related to 1, 2, or 3. Calculations on the structures and relative stabilities of the monomeric forms of 1, 2, and 3, compared to the respective dimers, would be of considerable interest. Inclusion of contact ion-pairing could be of key importance in such a study, but might prove to be a nontrivial extension.

In contrast to 1, which contains only Cu—C σ-bonds, all prior (arene)copper compounds have been characterized as π-complexes, including the homoleptic cationic species, [Cu(arene)₂]¹⁺ [arene = 1,2-difluorobenzene (Santiso-Quiñones et al., 2009 ), 1,3,5-trimethylbenzene, and hexamethylbenzene (Wright et al., 2010 , 2015 )], which exhibit the long-known copper–η²-arene structural motif, first observed in [Cu(benzene)][(μ-Cl)₃AlCl] (Turner & Amma, 1966 ). More recently, unprecedented copper–arene π-complexes containing unsupported η⁶-arene binding modes in the 18-electron species [Cu(C₆Me₆)(PR₃)]PF₆ (R = phenyl or phenoxide) were described (Wright et al., 2015). Although unsupported naphthalene, anthracene, or related polyarene complexes of copper remain unknown, except in the case of 1 for anthracene, polyarenes bearing substituents which effectively bind to Cu^I can also coordinate to copper. For example, a cationic Cu–η²-naphthyl complex with a neutral 1-naphthyl-appended NS₂ macrocyclic ligand (Conry, 1998 ) and an unusual [Cu{η⁶-9,10-bis(N-n-propyl-N-diphenylphosphano)aminomethyl)anthracene}]¹⁺ complex, in which Cu^I is constrained via chelation with diphenylphosphanyl groups to lie over the central ring of nearly planar anthracene (Xu et al., 2003 ), have been characterized by SCXRD. Whereas the Cu–η²-naphthyl complex has unexceptional Cu—C distances [2.129 (6) and 2.414 (6) Å] for asymmetric π-bonding of the 1-naphthyl group, the Cu—C distances in the copper–η⁶-anthracene complex are in the range 2.773–3.021 Å. These are much longer than usual in (arene)copper complexes, indicative, at best, of a very weak copper–anthracene interaction (Xu et al., 2003). For example, in [Cu(η⁶-C₆Me₆)(PR₃)]PF₆, the Cu—C distances are in the range 2.253–2.300 Å (Wright et al., 2015).

2. Experimental

2.1. Synthesis and crystallization

All manipulations were carried out under argon in a standard glove-box and/or using Schlenk techniques to maintain strictly anaerobic conditions (Shriver, 1969 ; Wayda & Darensbourg, 1987 ). Solvents were dried by standard methods, as described previously (Brennessel & Ellis, 2012 ). Reagent-grade anthracene (99%) was sublimed in vacuo and [CuCl(PCy₃)]₂ (Cy = cyclohexyl) was prepared as described previously (Churchill & Rotella, 1979). NMR samples were sealed under argon into 5 mm tubes and analyzed on a Varian Unity 500 MHz or a Bruker Avance III 400 MHz spectrometer. ¹H and ¹³C chemical shifts are given with reference to residual ¹H and ¹³C solvent resonances relative to tetramethylsilane.

2.1.1. [K(THF)₂]₂[{Cu(C₁₄H₁₀)}₂] (1)

Sublimed anthracene (0.939 g, 5.27 mmol) and shiny pieces of potassium metal (0.211 g, 5.40 mmol) were transferred in an argon-filled glove-box to a round-bottomed Schlenk flask, along with a glass-enclosed magnetic stirrer bar. Subsequently, THF (100 ml) was added and the mixture was stirred vigorously in the dark for 6 h at 293 K to afford a deep-blue solution of potassium anthracene (KAn), which is susceptible to photo-oxidation by visible light. This solution/slurry was cooled to 200 K with stirring and to it was transferred via cannula a cold (200 K) colorless solution of [CuCl(PCy₃)]₂ (1.000 g, 1.318 mmol) in THF (50 ml) and stirring continued for 12 h at 200 K. The resulting yellow–brown solution was warmed over a ca 6 h period to near 290 K (room temperature) and filtered (medium or P4 porosity frit) to remove KCl. After careful evaporation of all but about 20 ml of solvent in vacuo at 273–293 K, pentane (100 ml) was added with stirring. The resulting slurry was filtered, washed vigorously with pentane (2 × 10 ml) and dried in vacuo to afford 0.59 g (53% yield, based on the copper precursor) of homogeneous yellow solid [K(THF)₂]₂[{Cu(C₁₄H₁₀)}₂], 1. No elemental analysis was conducted on the bulk solid 1, so its composition is based exclusively on the SCXRD study and NMR spectra. X-ray-quality yellow blocks of 1 were grown from a pentane-layered saturated solution in THF at 240 K over a 6 d period.

¹H NMR (500 MHz, 293 K, THF-d₈, δ, ppm): 1.77 (m, 4H, THF), 3.52 (s, 1H, H9), 3.63 (m, 4H, THF), 6.24 (m, 2H, H1), 6.35 (m, 2H, H2). ¹³C{¹H} NMR (125 MHz, 293 K, THF-d₈, δ, ppm): 24.2 (m, THF), 52.4 (s, C9), 66.3 (m, THF), 117.7 (s, C1), 117.9 (s, C2), 145.2 (s, C11).

It is interesting that the first structurally authenticated (by SCXRD) monomeric (anthracene)metal complex, [{Mg(THF)₃}(9,10-η²-An)], 5 (Engelhardt et al., 1988), was originally formulated to be a monomer based only on its NMR spectra in THF. Noteworthy is that the latter spectra, without THF, exhibit ¹H and ¹³C{¹H} resonances for the coordinated anthracene in 5 with quite similar values to those observed for 1; i.e. ¹H NMR (400 MHz, 293 K, THF-d₈, δ, ppm): 3.51 (s, 1H, H9), 5.95 (m, 2H, H1), 6.01 (m, 2H, H2); ¹³C{¹H} NMR (75.4 MHz, 293 K, THF-d₈, δ, ppm): 57.7 (s, C9), 114.1 (s, C1), 118.1 (s, C2), 145.9 (s, C11) (Bogdanović et al., 1984 ). However, based on available data, it would now be premature to suggest that 1 may also be present as a monomer in THF. Noteworthy is that the corresponding NMR spectra for the aluminium dimer 3 in THF apparently have not been reported for comparison. Also, studies of 1 in other solvents would be of interest, as well as further NMR spectral analyses of this cuprate. Unfortunately, this latter work must be carried out independently in another laboratory because we are no longer able to examine this intriguing species.

2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms on anthracene C atoms were found from difference Fourier maps and refined freely. H atoms on the tetrahydrofuran ligands were placed geometrically and treated as riding atoms, with C—H = 0.99 Å and U_iso(H) = 1.2U_eq(C).

Table 1
Experimental details

Crystal data
Chemical formula	[K(C₄H₈O)₂]₂[Cu(C₁₄H₁₀)₂]
M_r	850.13
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	173 (2)
a, b, c (Å)	9.6864 (19), 10.484 (2), 10.658 (2)
α, β, γ (°)	66.22 (3), 89.67 (3), 82.73 (3)
V (Å³)	981.2 (4)
Z	1
Radiation type	Mo Kα
μ (mm⁻¹)	1.34
Crystal size (mm)	0.40 × 0.40 × 0.20

Data collection
Diffractometer	Bruker SMART platform CCD
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996 )
T_min, T_max	0.630, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	11455, 4459, 3853
R_int	0.024
(sin θ/λ)_max (Å⁻¹)	0.650

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.029, 0.073, 1.04
No. of reflections	4459
No. of parameters	275
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.34, −0.31
Computer programs: SMART (Bruker, 2003 ), SAINT (Bruker, 2003), SHELXT2018 (Sheldrick, 2015a ), SHELXL2019 (Sheldrick, 2015b ), and SHELXTL (Sheldrick, 2008 ).

3. Results and discussion

The asymmetric unit of 1, which is one-half of the formula unit [K(THF)₂]₂[{Cu(9,10-η²-An)}₂], contains one copper center and one anthracene ligand in contact with one [K(THF)₂]¹⁺ counter-ion. A crystallographic inversion center generates full well-resolved 1 (Fig. 1). The potassium cations have normal ligated THF with K—O distances [average 2.74 (7) Å] within the range 2.62 (2)–2.78 (3) Å of those observed previously in [K(THF)₂]₂[ML_n], where ML_n is [V(η⁴-Np)(η⁶-Np)]²⁻ (Np = naphthalene; Kucera et al., 2022) and [U(NHDipp)₅]²⁻ (Dipp = 2,6-diisopropylphenyl; Nelson et al., 1992 ). To help understand the molecular structure of the contact ion-pair complex, 1, it is useful to first compare details of the metal–metal interactions in 1 with those in the only previously known (anthracene)metal dimer complex present in [Na(THF)₂]₂[{(AlMe₂)(9,10-η²-An)}₂], 3, (Brauer & Stucky, 1972). It is important to recognize that both metal atoms, K and Cu, in 1 are appreciably larger than the corresponding atoms, Na and Al, in 3. Thus, the sum of the covalent radii of K and Cu (3.35 Å) is greater than the corresponding sum for Na and Al (2.87 Å) (Cordero et al., 2008 ). However, the formally nonbonded distances (Table 2) between all of the metals in 1 are considerably shorter, i.e. K1⋯Cu1 = 3.6637 (15) Å, K1⋯Cu1A = 3.3762 (9) Å, K1⋯K1A = 6.542 (2) Å and Cu1⋯Cu1A = 2.6171 (7) Å [symmetry code: (A) −x, −y + 1, −z + 1], than the corresponding distances in 3, i.e. Na1⋯Al1 = 4.348 (6) Å, Na1⋯Al1A = 4.455 (7) Å, Na1⋯Na1A = 7.28 (1) Å and Al1⋯Al1A = 4.95 Å. As described in Section 1, the rather short, but formally nonbonded, Cu⋯Cu distance in 1 arises from the essentially linear C9—Cu—C10A angle, expected for two-coordinated d¹⁰ Cu^I (Cotton et al., 1999).

Table 2
Selected geometric parameters (Å, °)

Cu1—C9ⁱ	1.9873 (19)	C8—K1ⁱ	3.421 (2)
Cu1—C10	1.9906 (19)	C9—C13	1.480 (3)
Cu1—Cu1ⁱ	2.6172 (7)	C9—C12	1.482 (3)
Cu1—K1ⁱ	3.3762 (9)	C10—C14	1.478 (3)
Cu1—K1	3.6637 (15)	C10—C11	1.479 (3)
C1—K1	3.081 (2)	C11—K1ⁱ	3.158 (2)
C2—K1	3.158 (2)	C12—K1ⁱ	3.3324 (19)
C3—K1	3.338 (3)	C13—K1	3.170 (2)
C4—K1	3.446 (2)	C14—K1	3.364 (2)
C5—K1ⁱ	3.100 (2)	K1—O1	2.681 (2)
C6—K1ⁱ	3.203 (3)	K1—O2	2.8027 (16)
C7—K1ⁱ	3.360 (2)

C9ⁱ—Cu1—C10	174.74 (7)	C13—C9—C12	113.07 (15)
C9ⁱ—Cu1—Cu1ⁱ	91.87 (6)	C14—C10—C11	113.34 (15)
C10—Cu1—Cu1ⁱ	93.22 (6)
Symmetry code: (i) .

However, in 3, the considerably smaller C9—Al—C10A angle [120.2 (4)°], resulting from the distorted tetrahedral geometry of four-coordinated Al^III, causes the Al⋯Al distance to be much longer (Fig. 2). Of particular interest is that the relatively uncrowded linear Cu atoms in 1 permit both solvated potassium ions to approach the cuprate centers more closely than the smaller solvated sodium ions can with the bulkier distorted tetrahedral aluminate centers in 3. Whereas the Na⋯Al distances in 3 exhibit a small difference [0.107 (7) Å] and, as a result, its molecular structure, without the THF groups, is fairly symmetrical and deviates only slightly from D_2h symmetry (Brauer & Stucky, 1972), the two K⋯Cu distances in 1 differ by 0.287 (2) Å (Fig. 1), with one potassium ion having a surprisingly short K⋯Cu distance of 3.3762 (9) Å, close to the sum of the covalent radii of K and Cu (3.35 Å) (Cordero et al., 2008). As a consequence, 1 differs from 3 in having a slightly more compact but a much less symmetrical contact ion-pair structure, owing largely to the different coordination numbers of copper and aluminium, in otherwise quite similar species. Another key difference between 1 and 3 are the nonbonded bridgehead C9⋯C10A distances [3.974 (3) and 3.57 (1) Å, respectively], which show that the two formal 9,10-coordinated anthracene dianion units are slightly further apart in 1 than they are in 3, owing also to the different coordination numbers of copper and aluminium in these remarkable compounds, both of which are worthy of additional study.

Despite the aforementioned differences, the geometries of the central anthracene ring of 1 and 3 are similar. Thus, for 1, the bridgehead angles C11—C10—C14 [113.3 (2)°] and C12—C9—C13 [113.1 (2)°] (Table 2) do not differ significantly from the corresponding angles reported for 3 [114.1 (9) and 112 (1)°; Brauer & Stucky, 1972]. Similarly, the bridgehead C—C distances for 1 [C9—C12 = 1.482 (3) Å, C9—C13 = 1.480 (3) Å, C10—C11 = 1.479 (3) Å, and C10—C14 = 1.478 (3) Å, with average C—C = 1.480 (3) Å; Table 2], are statistically identical to corresponding C—C distances reported for 3 [average 1.49 (2) Å], which are both close to the value of 1.51 (5) Å observed previously for C(sp²)—C(sp³) distances (Jolly, 1976 ). Perhaps surprisingly, the geometry of the coordinated central ring of anthracene in the first reported structurally characterized anionic metallacyclic monomer of this type, [{Lu(η⁵-Cp)₂}(9,10-η²-An)]¹⁻, is structurally nearly identical, without the metal, to those observed in the dianions of 1 and 3, with an average bridgehead C—C distance of 1.485 (9) Å. The lutetium anion also has an average bridgehead C—C—C angle of 111.8 (5) Å, which is very close to the corresponding angles of 1 and 3. A key structural difference in the lutetium anion is the sharp C9—Lu—C10 angle of 67.1 (2)°, owing to the metallacyclopropane character of the complex and, likely also the large bulk of the bis(cyclopentadienyl)lutetium moiety, which may well be responsible for its stability towards dimerization or oligomerization in solution (THF) and in the solid state as a crystalline [Na(diglyme)₂]¹⁺ salt (diglyme = diethylene glycol dimethyl ether) at ca 293 K (Roitershtein et al., 1993).

Interactions of the alkali metal cations with the exo-benzene C atoms are consistent with the overall molecular structures of 1 and 3. In the less symmetrical cuprate 1, the K⋯C distances fall into a distinct 1:1 pattern, with the six C atom closest to the short K⋯Cu contact ion pairing (C1, C2, C5, C6, C11, and C13) having the shortest distances [average 3.14 (13) Å], whereas the K⋯C distances for the six C atoms closest to the long K⋯Cu contact (C3, C4, C7, C8, C12, and C14) are longer [average 3.38 (5) Å] (see Figs. 1 and 3). In contrast, for the aluminate 3, the Na—C distances for the eight outer C atoms are rather similar and range from 2.94 (1) to 3.24 (1) Å, but the Na—C distances of the four more crowded ring-junction C atoms are mostly longer [average 3.28 (4) Å; Brauer & Stucky, 1972]. Finally, in 1, the essentially planar exo-benzene units possess C—C distances [average 1.396 (3) Å] and C—C—C angles [average 119.9 (2)°] that are quite similar to those found in uncharged free benzene (Mitchell & Cross, 1965 ), indicating that the contact ion pairing is sufficiently weak to have no significant influence on the structure of the exo-benzene groups and that the negative charge on each anthracene ligand is essentially localized on the central ring and the appended metal center. Similar features were found for the exo-benzene groups in 3 (Brauer & Stucky, 1972). However, in both 1 and 3, the interactions of the counter-ions in these contact ion-paired complexes may play an important role in defining the structures of the anionic components and perhaps their existence in the solid state. In this respect, the isolation of the bis(anthracene)dicuprate(2−) with relatively weakly interacting cations, such as [K([2.2.2.]cryptand)]¹⁺, tetraalkylammonium(1+), etc., would be of considerable interest. As our laboratory will be irreversibly shuttered in 2023, others are encouraged to examine these possibilities and related issues, vide infra.

Figure 3
End views of 1 (left) and 3 (right) that highlight the much greater asymmetry of the dicuprate. Representative atom–atom distances are shown (Å). In 1, the six closest C atoms to the shorter Cu⋯K contact have an average K⋯C distance of 3.14 (13) Å, while those closest to the longer Cu⋯K contact have an average K⋯C distance of 3.38 (5) Å.

Since our initial report on tris(1,2,3,4-η⁴-naphthalene)zirconate(2−), the first confirmed homoleptic (polyarene)metallate of a d-block metal (Jang & Ellis, 1994 ), which was remarkably labile and functioned formally as a `masked' naked source of low-spin atomic Zr²⁻ in its facile reaction with carbon monoxide to afford [Zr(CO)₆]²⁻, our research group has been interested in discovering what other d-block elements, throughout the periodic table, would afford related and hopefully labile complexes. Thus began our exploration in a systematic fashion of the synthesis and reactivity patterns of transition-metal compounds containing metals in formal negative oxidation states (Ellis, 2006). Early on we wondered whether f-block elements would also `succumb' to this strategy, but unfortunately never examined these elements (Ellis, 2019). In this regard, we would like to point to the exciting recent results of Skye Fortier and co-workers in highly challenging uranium chemistry (Murillo et al., 2021, 2022). As mentioned in Section 1, we were also intrigued by early reports of `anionic copper' (Rieke et al., 1990) and this led to our synthesis and structural characterization of the totally unexpected dicuprate salt, 1, described herein. Owing to the early departure of a group member, extension of this study was not possible. For example, we had hoped to examine the reactivity of 1 with good acceptor ligands, such as CO, PF₃, and P(OR)₃, and particularly organic isocyanides, to determine whether the anthracenes would be displaced to produce new formal Cu(0,1−) complexes. Noteworthy is that although isolable Cu¹⁻ complexes remain unknown, very recently, the first unambiguous Cu⁰ complex was isolated, thoroughly characterized, and structurally authenticated (Graziano et al., 2022 ). Also, examination of Rieke's thermally unstable alleged cuprates, derived from naphthalene radical anion reductions remain of great interest because the possible `naphthalene stabilized cuprate' may be a more labile source of `naked Cu(1−)' than one derived from the anthracene radical anion. Extension of these studies to silver and gold promise to uncover exciting results. For example, could a bona fide gold anion (Jansen, 2008 ) be `tamed' by naphthalene or anthracene to provide labile complexes, enabling the study of new aurate chemistry? We mention these possible extensions because none of this research will be carried out by us at the University of Minnesota.

Supporting information

CCDC reference: 2296812

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2053229623008367/eq3012sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2053229623008367/eq3012Isup2.hkl

Computing details top

Bis(µ-anthracene-κ²C⁹:C¹⁰)dicopper bis[bis(tetrahydrofuran-κO)potassium] top

Crystal data top

[K(C₄H₈O)₂]₂[Cu(C₁₄H₁₀)₂]	Z = 1
M_r = 850.13	F(000) = 444
Triclinic, P1	D_x = 1.439 Mg m⁻³
a = 9.6864 (19) Å	Mo Kα radiation, λ = 0.71073 Å
b = 10.484 (2) Å	Cell parameters from 6461 reflections
c = 10.658 (2) Å	θ = 2.3–27.5°
α = 66.22 (3)°	µ = 1.34 mm⁻¹
β = 89.67 (3)°	T = 173 K
γ = 82.73 (3)°	Block, yellow
V = 981.2 (4) Å³	0.40 × 0.40 × 0.20 mm

Data collection top

Bruker SMART platform CCD diffractometer	3853 reflections with I > 2σ(I)
Radiation source: normal-focus sealed tube	R_int = 0.024
ω scans	θ_max = 27.5°, θ_min = 2.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −12→12
T_min = 0.630, T_max = 0.746	k = −13→13
11455 measured reflections	l = −13→13
4459 independent reflections

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.029	Hydrogen site location: mixed
wR(F²) = 0.073	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ²(F_o²) + (0.0327P)² + 0.3478P] where P = (F_o² + 2F_c²)/3
4459 reflections	(Δ/σ)_max < 0.001
275 parameters	Δρ_max = 0.34 e Å⁻³
0 restraints	Δρ_min = −0.30 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. The H atoms on the metal-coordinating C atoms were found from the difference Fourier map and refined freely.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Cu1	−0.05999 (2)	0.40243 (2)	0.48345 (2)	0.02155 (7)
C1	0.38363 (19)	0.4873 (2)	0.3784 (2)	0.0276 (4)
H1	0.430 (2)	0.559 (2)	0.390 (2)	0.026 (5)*
C2	0.4151 (2)	0.4501 (2)	0.2690 (2)	0.0343 (5)
H2	0.481 (2)	0.495 (2)	0.212 (2)	0.037 (6)*
C3	0.3490 (2)	0.3475 (2)	0.2528 (2)	0.0368 (5)
H3	0.371 (2)	0.321 (2)	0.184 (2)	0.042 (6)*
C4	0.2530 (2)	0.2823 (2)	0.3460 (2)	0.0320 (4)
H4	0.206 (2)	0.208 (2)	0.338 (2)	0.029 (5)*
C5	0.1116 (2)	0.1311 (2)	0.8108 (2)	0.0308 (4)
H5	0.068 (2)	0.058 (2)	0.797 (2)	0.033 (6)*
C6	0.1389 (2)	0.1233 (2)	0.9416 (2)	0.0366 (5)
H6	0.123 (2)	0.045 (2)	1.020 (2)	0.037 (6)*
C7	0.2012 (2)	0.2276 (2)	0.9571 (2)	0.0367 (5)
H7	0.222 (2)	0.223 (2)	1.046 (2)	0.042 (6)*
C8	0.2362 (2)	0.3400 (2)	0.8413 (2)	0.0306 (4)
H8	0.282 (2)	0.416 (2)	0.8515 (19)	0.024 (5)*
C9	0.23864 (18)	0.46989 (19)	0.58254 (19)	0.0236 (4)
H9	0.301 (2)	0.524 (2)	0.602 (2)	0.026 (5)*
C10	0.10924 (18)	0.26005 (19)	0.55160 (19)	0.0244 (4)
H10	0.086 (2)	0.175 (2)	0.5485 (19)	0.023 (5)*
C11	0.14273 (18)	0.24371 (19)	0.69295 (19)	0.0247 (4)
C12	0.20785 (17)	0.35061 (19)	0.70886 (19)	0.0241 (4)
C13	0.28346 (17)	0.42684 (18)	0.47075 (18)	0.0235 (4)
C14	0.21665 (18)	0.32051 (19)	0.45431 (19)	0.0245 (4)
K1	0.11852 (4)	0.63331 (5)	0.19219 (4)	0.03269 (11)
O1	0.1757 (2)	0.6849 (3)	−0.06891 (18)	0.0786 (7)
C15	0.0817 (3)	0.7024 (4)	−0.1778 (3)	0.0731 (9)
H15A	−0.014627	0.729703	−0.157488	0.088*
H15B	0.085162	0.613167	−0.189734	0.088*
C16	0.1226 (4)	0.8113 (3)	−0.3012 (3)	0.0745 (10)
H16A	0.063451	0.902048	−0.320983	0.089*
H16B	0.114022	0.786168	−0.380697	0.089*
C17	0.2715 (3)	0.8212 (4)	−0.2734 (3)	0.0713 (9)
H17A	0.334983	0.776688	−0.321839	0.086*
H17B	0.286732	0.920583	−0.303253	0.086*
C18	0.2948 (3)	0.7440 (4)	−0.1217 (3)	0.0709 (9)
H18A	0.375707	0.669418	−0.099890	0.085*
H18B	0.314465	0.809604	−0.080451	0.085*
O2	0.27673 (15)	0.82963 (15)	0.21520 (15)	0.0367 (3)
C19	0.4093 (2)	0.8595 (2)	0.1558 (2)	0.0414 (5)
H19A	0.395866	0.919108	0.056271	0.050*
H19B	0.469354	0.770940	0.168634	0.050*
C20	0.4758 (2)	0.9354 (3)	0.2282 (3)	0.0457 (6)
H20A	0.456244	1.038622	0.176450	0.055*
H20B	0.577920	0.906881	0.241359	0.055*
C21	0.4066 (3)	0.8884 (3)	0.3651 (2)	0.0464 (6)
H21A	0.453925	0.796853	0.431901	0.056*
H21B	0.404851	0.959285	0.404746	0.056*
C22	0.2617 (2)	0.8765 (2)	0.3231 (2)	0.0423 (5)
H22A	0.218169	0.808373	0.401707	0.051*
H22B	0.202466	0.968997	0.291007	0.051*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu1	0.01789 (11)	0.02101 (12)	0.02501 (12)	−0.00262 (8)	−0.00129 (8)	−0.00855 (9)
C1	0.0194 (9)	0.0277 (10)	0.0314 (10)	−0.0023 (7)	−0.0045 (7)	−0.0078 (8)
C2	0.0196 (9)	0.0443 (12)	0.0353 (11)	−0.0031 (9)	0.0026 (8)	−0.0128 (10)
C3	0.0284 (10)	0.0504 (13)	0.0385 (12)	−0.0019 (9)	0.0025 (9)	−0.0262 (11)
C4	0.0241 (9)	0.0358 (11)	0.0411 (11)	−0.0015 (8)	−0.0012 (8)	−0.0216 (9)
C5	0.0244 (9)	0.0240 (9)	0.0371 (11)	−0.0012 (8)	−0.0003 (8)	−0.0059 (8)
C6	0.0298 (10)	0.0339 (11)	0.0322 (11)	−0.0004 (9)	−0.0006 (9)	−0.0004 (9)
C7	0.0279 (10)	0.0486 (13)	0.0285 (11)	−0.0023 (9)	−0.0033 (8)	−0.0111 (10)
C8	0.0222 (9)	0.0360 (11)	0.0341 (11)	−0.0015 (8)	−0.0030 (8)	−0.0153 (9)
C9	0.0184 (8)	0.0223 (9)	0.0305 (9)	−0.0039 (7)	−0.0034 (7)	−0.0108 (8)
C10	0.0201 (8)	0.0200 (9)	0.0336 (10)	−0.0019 (7)	−0.0028 (7)	−0.0116 (8)
C11	0.0166 (8)	0.0229 (9)	0.0308 (10)	0.0009 (7)	−0.0023 (7)	−0.0078 (8)
C12	0.0164 (8)	0.0239 (9)	0.0295 (9)	0.0018 (7)	−0.0026 (7)	−0.0095 (8)
C13	0.0157 (8)	0.0225 (9)	0.0281 (9)	0.0014 (7)	−0.0054 (7)	−0.0072 (7)
C14	0.0176 (8)	0.0229 (9)	0.0319 (10)	0.0012 (7)	−0.0038 (7)	−0.0109 (8)
K1	0.0250 (2)	0.0396 (2)	0.0293 (2)	−0.00027 (18)	−0.00188 (17)	−0.01078 (19)
O1	0.0480 (11)	0.143 (2)	0.0373 (10)	−0.0145 (12)	0.0005 (8)	−0.0284 (12)
C15	0.0418 (15)	0.124 (3)	0.0574 (18)	0.0036 (16)	−0.0050 (13)	−0.0446 (19)
C16	0.114 (3)	0.0579 (18)	0.0592 (18)	−0.0113 (18)	−0.0295 (18)	−0.0309 (15)
C17	0.073 (2)	0.078 (2)	0.0529 (17)	0.0029 (17)	0.0111 (15)	−0.0209 (16)
C18	0.0525 (16)	0.119 (3)	0.0513 (16)	−0.0217 (17)	0.0036 (13)	−0.0419 (18)
O2	0.0299 (7)	0.0369 (8)	0.0394 (8)	−0.0077 (6)	0.0017 (6)	−0.0106 (7)
C19	0.0334 (11)	0.0436 (13)	0.0431 (13)	−0.0076 (10)	0.0080 (10)	−0.0129 (10)
C20	0.0276 (11)	0.0421 (13)	0.0650 (16)	−0.0074 (9)	0.0034 (10)	−0.0186 (12)
C21	0.0505 (14)	0.0396 (13)	0.0445 (13)	−0.0012 (11)	−0.0089 (11)	−0.0136 (11)
C22	0.0404 (12)	0.0394 (12)	0.0450 (13)	−0.0106 (10)	0.0119 (10)	−0.0134 (10)

Geometric parameters (Å, º) top

Cu1—C9ⁱ	1.9873 (19)	C10—H10	0.96 (2)
Cu1—C10	1.9906 (19)	C11—C12	1.420 (3)
Cu1—Cu1ⁱ	2.6172 (7)	C11—K1ⁱ	3.158 (2)
Cu1—K1ⁱ	3.3762 (9)	C12—K1ⁱ	3.3324 (19)
Cu1—K1	3.6637 (15)	C13—C14	1.426 (3)
C1—C2	1.391 (3)	C13—K1	3.170 (2)
C1—C13	1.398 (3)	C14—K1	3.364 (2)
C1—K1	3.081 (2)	K1—O1	2.681 (2)
C1—H1	0.97 (2)	K1—O2	2.8027 (16)
C2—C3	1.387 (3)	O1—C18	1.388 (3)
C2—K1	3.158 (2)	O1—C15	1.416 (3)
C2—H2	0.91 (2)	C15—C16	1.445 (4)
C3—C4	1.386 (3)	C15—H15A	0.9900
C3—K1	3.338 (3)	C15—H15B	0.9900
C3—H3	0.90 (2)	C16—C17	1.498 (4)
C4—C14	1.396 (3)	C16—H16A	0.9900
C4—K1	3.446 (2)	C16—H16B	0.9900
C4—H4	0.98 (2)	C17—C18	1.491 (4)
C5—C6	1.388 (3)	C17—H17A	0.9900
C5—C11	1.397 (3)	C17—H17B	0.9900
C5—K1ⁱ	3.100 (2)	C18—H18A	0.9900
C5—H5	0.98 (2)	C18—H18B	0.9900
C6—C7	1.379 (3)	O2—C22	1.422 (3)
C6—K1ⁱ	3.203 (3)	O2—C19	1.442 (2)
C6—H6	0.93 (2)	C19—C20	1.508 (3)
C7—C8	1.397 (3)	C19—H19A	0.9900
C7—K1ⁱ	3.360 (2)	C19—H19B	0.9900
C7—H7	0.95 (2)	C20—C21	1.521 (3)
C8—C12	1.397 (3)	C20—H20A	0.9900
C8—K1ⁱ	3.421 (2)	C20—H20B	0.9900
C8—H8	1.00 (2)	C21—C22	1.510 (3)
C9—C13	1.480 (3)	C21—H21A	0.9900
C9—C12	1.482 (3)	C21—H21B	0.9900
C9—H9	0.96 (2)	C22—H22A	0.9900
C10—C14	1.478 (3)	C22—H22B	0.9900
C10—C11	1.479 (3)

C9ⁱ—Cu1—C10	174.74 (7)	C2—K1—C3	24.46 (6)
C9ⁱ—Cu1—Cu1ⁱ	91.87 (6)	C11ⁱ—K1—C3	144.06 (6)
C10—Cu1—Cu1ⁱ	93.22 (6)	C13—K1—C3	51.09 (6)
C9ⁱ—Cu1—K1ⁱ	90.22 (6)	C6ⁱ—K1—C3	160.97 (6)
C10—Cu1—K1ⁱ	89.91 (6)	C12ⁱ—K1—C3	128.10 (6)
Cu1ⁱ—Cu1—K1ⁱ	74.15 (3)	O1—K1—C7ⁱ	80.71 (6)
C9ⁱ—Cu1—K1	91.13 (6)	O2—K1—C7ⁱ	114.16 (6)
C10—Cu1—K1	92.38 (6)	C1—K1—C7ⁱ	169.51 (5)
Cu1ⁱ—Cu1—K1	62.44 (2)	C5ⁱ—K1—C7ⁱ	43.22 (6)
K1ⁱ—Cu1—K1	136.592 (18)	C2—K1—C7ⁱ	161.18 (6)
C2—C1—C13	121.71 (18)	C11ⁱ—K1—C7ⁱ	50.92 (5)
C2—C1—K1	80.26 (12)	C13—K1—C7ⁱ	144.00 (6)
C13—C1—K1	80.68 (11)	C6ⁱ—K1—C7ⁱ	24.11 (6)
C2—C1—H1	119.5 (12)	C12ⁱ—K1—C7ⁱ	42.69 (5)
C13—C1—H1	118.7 (12)	C3—K1—C7ⁱ	138.90 (6)
K1—C1—H1	108.3 (12)	O1—K1—C14	122.94 (7)
C3—C2—C1	119.6 (2)	O2—K1—C14	108.40 (5)
C3—C2—K1	85.05 (13)	C1—K1—C14	43.96 (5)
C1—C2—K1	74.02 (11)	C5ⁱ—K1—C14	127.14 (6)
C3—C2—H2	123.3 (14)	C2—K1—C14	50.92 (6)
C1—C2—H2	117.1 (14)	C11ⁱ—K1—C14	102.00 (6)
K1—C2—H2	111.5 (14)	C13—K1—C14	24.99 (5)
C4—C3—C2	119.8 (2)	C6ⁱ—K1—C14	143.58 (6)
C4—C3—K1	82.63 (13)	C12ⁱ—K1—C14	92.71 (6)
C2—C3—K1	70.49 (12)	C3—K1—C14	42.52 (5)
C4—C3—H3	120.5 (16)	C7ⁱ—K1—C14	128.40 (6)
C2—C3—H3	119.7 (16)	O1—K1—Cu1ⁱ	174.34 (6)
K1—C3—H3	119.6 (15)	O2—K1—Cu1ⁱ	78.73 (4)
C3—C4—C14	121.72 (19)	C1—K1—Cu1ⁱ	69.88 (5)
C3—C4—K1	73.87 (13)	C5ⁱ—K1—Cu1ⁱ	70.12 (5)
C14—C4—K1	74.88 (11)	C2—K1—Cu1ⁱ	94.42 (5)
C3—C4—H4	121.4 (12)	C11ⁱ—K1—Cu1ⁱ	50.60 (4)
C14—C4—H4	116.9 (12)	C13—K1—Cu1ⁱ	50.52 (4)
K1—C4—H4	122.9 (12)	C6ⁱ—K1—Cu1ⁱ	94.30 (5)
C6—C5—C11	121.94 (19)	C12ⁱ—K1—Cu1ⁱ	60.61 (4)
C6—C5—K1ⁱ	81.44 (13)	C3—K1—Cu1ⁱ	100.40 (5)
C11—C5—K1ⁱ	79.43 (11)	C7ⁱ—K1—Cu1ⁱ	100.32 (5)
C6—C5—H5	120.9 (13)	C14—K1—Cu1ⁱ	60.72 (4)
C11—C5—H5	117.2 (13)	O1—K1—C8ⁱ	98.21 (6)
K1ⁱ—C5—H5	109.0 (12)	O2—K1—C8ⁱ	127.95 (5)
C7—C6—C5	119.6 (2)	C1—K1—C8ⁱ	146.66 (5)
C7—C6—K1ⁱ	84.35 (13)	C5ⁱ—K1—C8ⁱ	49.76 (6)
C5—C6—K1ⁱ	73.18 (12)	C2—K1—C8ⁱ	150.65 (6)
C7—C6—H6	118.5 (14)	C11ⁱ—K1—C8ⁱ	43.01 (5)
C5—C6—H6	121.7 (14)	C13—K1—C8ⁱ	120.92 (6)
K1ⁱ—C6—H6	117.5 (14)	C6ⁱ—K1—C8ⁱ	42.36 (6)
C6—C7—C8	119.8 (2)	C12ⁱ—K1—C8ⁱ	23.83 (5)
C6—C7—K1ⁱ	71.54 (12)	C3—K1—C8ⁱ	126.98 (6)
C8—C7—K1ⁱ	80.58 (12)	C7ⁱ—K1—C8ⁱ	23.75 (5)
C6—C7—H7	120.4 (14)	C14—K1—C8ⁱ	105.06 (6)
C8—C7—H7	119.8 (14)	Cu1ⁱ—K1—C8ⁱ	84.40 (5)
K1ⁱ—C7—H7	119.4 (14)	O1—K1—C4	99.52 (7)
C7—C8—C12	121.38 (19)	O2—K1—C4	118.02 (5)
C7—C8—K1ⁱ	75.67 (12)	C1—K1—C4	49.69 (6)
C12—C8—K1ⁱ	74.52 (11)	C5ⁱ—K1—C4	146.82 (5)
C7—C8—H8	120.4 (11)	C2—K1—C4	42.32 (6)
C12—C8—H8	118.2 (11)	C11ⁱ—K1—C4	121.11 (6)
K1ⁱ—C8—H8	121.2 (11)	C13—K1—C4	42.80 (5)
C13—C9—C12	113.07 (15)	C6ⁱ—K1—C4	150.73 (6)
C13—C9—Cu1ⁱ	106.80 (12)	C12ⁱ—K1—C4	105.07 (6)
C12—C9—Cu1ⁱ	106.01 (12)	C3—K1—C4	23.51 (5)
C13—C9—H9	113.5 (12)	C7ⁱ—K1—C4	127.46 (6)
C12—C9—H9	111.5 (12)	C14—K1—C4	23.63 (5)
Cu1ⁱ—C9—H9	105.3 (12)	Cu1ⁱ—K1—C4	84.31 (5)
C14—C10—C11	113.34 (15)	C8ⁱ—K1—C4	108.62 (6)
C14—C10—Cu1	104.68 (12)	O1—K1—Cu1	142.20 (6)
C11—C10—Cu1	106.65 (12)	O2—K1—Cu1	121.92 (4)
C14—C10—H10	112.3 (12)	C1—K1—Cu1	84.17 (5)
C11—C10—H10	112.5 (12)	C5ⁱ—K1—Cu1	84.94 (5)
Cu1—C10—H10	106.7 (12)	C2—K1—Cu1	96.93 (5)
C5—C11—C12	118.49 (17)	C11ⁱ—K1—Cu1	59.29 (4)
C5—C11—C10	123.83 (17)	C13—K1—Cu1	58.50 (4)
C12—C11—C10	117.67 (16)	C6ⁱ—K1—Cu1	97.51 (5)
C5—C11—K1ⁱ	74.79 (11)	C12ⁱ—K1—Cu1	46.67 (4)
C12—C11—K1ⁱ	84.33 (11)	C3—K1—Cu1	85.20 (5)
C10—C11—K1ⁱ	109.88 (11)	C7ⁱ—K1—Cu1	86.02 (5)
C8—C12—C11	118.77 (17)	C14—K1—Cu1	46.07 (4)
C8—C12—C9	123.59 (17)	Cu1ⁱ—K1—Cu1	43.409 (19)
C11—C12—C9	117.63 (16)	C8ⁱ—K1—Cu1	62.49 (5)
C8—C12—K1ⁱ	81.65 (11)	C4—K1—Cu1	61.88 (4)
C11—C12—K1ⁱ	70.58 (10)	C18—O1—C15	109.8 (2)
C9—C12—K1ⁱ	116.17 (11)	C18—O1—K1	119.35 (16)
C1—C13—C14	118.47 (17)	C15—O1—K1	127.81 (16)
C1—C13—C9	123.89 (17)	O1—C15—C16	107.8 (3)
C14—C13—C9	117.61 (16)	O1—C15—H15A	110.1
C1—C13—K1	73.53 (10)	C16—C15—H15A	110.1
C14—C13—K1	85.14 (11)	O1—C15—H15B	110.1
C9—C13—K1	109.69 (11)	C16—C15—H15B	110.1
C4—C14—C13	118.67 (17)	H15A—C15—H15B	108.5
C4—C14—C10	123.81 (17)	C15—C16—C17	105.7 (2)
C13—C14—C10	117.49 (16)	C15—C16—H16A	110.6
C4—C14—K1	81.49 (12)	C17—C16—H16A	110.6
C13—C14—K1	69.88 (10)	C15—C16—H16B	110.6
C10—C14—K1	116.86 (11)	C17—C16—H16B	110.6
O1—K1—O2	95.74 (7)	H16A—C16—H16B	108.7
O1—K1—C1	109.41 (6)	C18—C17—C16	104.6 (2)
O2—K1—C1	68.53 (5)	C18—C17—H17A	110.8
O1—K1—C5ⁱ	107.73 (7)	C16—C17—H17A	110.8
O2—K1—C5ⁱ	78.23 (5)	C18—C17—H17B	110.8
C1—K1—C5ⁱ	131.78 (6)	C16—C17—H17B	110.8
O1—K1—C2	85.77 (7)	H17A—C17—H17B	108.9
O2—K1—C2	80.06 (5)	O1—C18—C17	108.4 (2)
C1—K1—C2	25.72 (5)	O1—C18—H18A	110.0
C5ⁱ—K1—C2	155.40 (6)	C17—C18—H18A	110.0
O1—K1—C11ⁱ	128.99 (6)	O1—C18—H18B	110.0
O2—K1—C11ⁱ	91.18 (5)	C17—C18—H18B	110.0
C1—K1—C11ⁱ	120.03 (5)	H18A—C18—H18B	108.4
C5ⁱ—K1—C11ⁱ	25.78 (5)	C22—O2—C19	108.69 (16)
C2—K1—C11ⁱ	145.02 (5)	C22—O2—K1	122.52 (12)
O1—K1—C13	130.60 (6)	C19—O2—K1	125.62 (13)
O2—K1—C13	83.56 (5)	O2—C19—C20	107.12 (18)
C1—K1—C13	25.79 (5)	O2—C19—H19A	110.3
C5ⁱ—K1—C13	120.22 (6)	C20—C19—H19A	110.3
C2—K1—C13	45.27 (6)	O2—C19—H19B	110.3
C11ⁱ—K1—C13	100.38 (6)	C20—C19—H19B	110.3
O1—K1—C6ⁱ	84.40 (7)	H19A—C19—H19B	108.5
O2—K1—C6ⁱ	90.13 (6)	C19—C20—C21	102.91 (18)
C1—K1—C6ⁱ	155.17 (6)	C19—C20—H20A	111.2
C5ⁱ—K1—C6ⁱ	25.38 (6)	C21—C20—H20A	111.2
C2—K1—C6ⁱ	165.33 (6)	C19—C20—H20B	111.2
C11ⁱ—K1—C6ⁱ	45.02 (5)	C21—C20—H20B	111.2
C13—K1—C6ⁱ	144.82 (6)	H20A—C20—H20B	109.1
O1—K1—C12ⁱ	121.76 (6)	C22—C21—C20	101.36 (19)
O2—K1—C12ⁱ	116.27 (5)	C22—C21—H21A	111.5
C1—K1—C12ⁱ	126.83 (5)	C20—C21—H21A	111.5
C5ⁱ—K1—C12ⁱ	44.03 (5)	C22—C21—H21B	111.5
C2—K1—C12ⁱ	143.60 (5)	C20—C21—H21B	111.5
C11ⁱ—K1—C12ⁱ	25.09 (5)	H21A—C21—H21B	109.3
C13—K1—C12ⁱ	101.73 (6)	O2—C22—C21	106.58 (18)
C6ⁱ—K1—C12ⁱ	50.89 (6)	O2—C22—H22A	110.4
O1—K1—C3	82.10 (7)	C21—C22—H22A	110.4
O2—K1—C3	104.48 (5)	O2—C22—H22B	110.4
C1—K1—C3	43.70 (6)	C21—C22—H22B	110.4
C5ⁱ—K1—C3	169.66 (6)	H22A—C22—H22B	108.6

C13—C1—C2—C3	−2.0 (3)	C13—C9—C12—K1ⁱ	−118.00 (13)
K1—C1—C2—C3	−74.58 (19)	Cu1ⁱ—C9—C12—K1ⁱ	−1.31 (14)
C13—C1—C2—K1	72.59 (17)	C2—C1—C13—C14	2.5 (3)
C1—C2—C3—C4	−0.5 (3)	K1—C1—C13—C14	74.88 (15)
K1—C2—C3—C4	−68.9 (2)	C2—C1—C13—C9	−175.35 (17)
C1—C2—C3—K1	68.47 (17)	K1—C1—C13—C9	−102.99 (16)
C2—C3—C4—C14	2.4 (3)	C2—C1—C13—K1	−72.36 (17)
K1—C3—C4—C14	−60.13 (18)	C12—C9—C13—C1	−144.12 (17)
C2—C3—C4—K1	62.48 (19)	Cu1ⁱ—C9—C13—C1	99.66 (17)
C11—C5—C6—C7	−1.4 (3)	C12—C9—C13—C14	38.0 (2)
K1ⁱ—C5—C6—C7	−73.16 (19)	Cu1ⁱ—C9—C13—C14	−78.22 (17)
C11—C5—C6—K1ⁱ	71.80 (17)	C12—C9—C13—K1	132.91 (12)
C5—C6—C7—C8	0.0 (3)	Cu1ⁱ—C9—C13—K1	16.69 (13)
K1ⁱ—C6—C7—C8	−67.02 (19)	C3—C4—C14—C13	−1.8 (3)
C5—C6—C7—K1ⁱ	67.02 (18)	K1—C4—C14—C13	−61.43 (15)
C6—C7—C8—C12	0.9 (3)	C3—C4—C14—C10	176.36 (18)
K1ⁱ—C7—C8—C12	−61.42 (17)	K1—C4—C14—C10	116.72 (17)
C6—C7—C8—K1ⁱ	62.28 (18)	C3—C4—C14—K1	59.64 (19)
C6—C5—C11—C12	1.8 (3)	C1—C13—C14—C4	−0.6 (3)
K1ⁱ—C5—C11—C12	74.68 (15)	C9—C13—C14—C4	177.38 (16)
C6—C5—C11—C10	−176.87 (18)	K1—C13—C14—C4	67.67 (16)
K1ⁱ—C5—C11—C10	−104.01 (16)	C1—C13—C14—C10	−178.89 (16)
C6—C5—C11—K1ⁱ	−72.86 (18)	C9—C13—C14—C10	−0.9 (2)
C14—C10—C11—C5	−143.44 (18)	K1—C13—C14—C10	−110.59 (14)
Cu1—C10—C11—C5	101.91 (18)	C1—C13—C14—K1	−68.29 (15)
C14—C10—C11—C12	37.9 (2)	C9—C13—C14—K1	109.70 (15)
Cu1—C10—C11—C12	−76.79 (17)	C11—C10—C14—C4	144.80 (18)
C14—C10—C11—K1ⁱ	131.93 (13)	Cu1—C10—C14—C4	−99.38 (18)
Cu1—C10—C11—K1ⁱ	17.28 (13)	C11—C10—C14—C13	−37.0 (2)
C7—C8—C12—C11	−0.4 (3)	Cu1—C10—C14—C13	78.79 (17)
K1ⁱ—C8—C12—C11	−62.36 (15)	C11—C10—C14—K1	−117.18 (14)
C7—C8—C12—C9	177.95 (17)	Cu1—C10—C14—K1	−1.36 (14)
K1ⁱ—C8—C12—C9	115.96 (17)	C18—O1—C15—C16	−17.6 (4)
C7—C8—C12—K1ⁱ	61.99 (18)	K1—O1—C15—C16	142.1 (2)
C5—C11—C12—C8	−0.9 (2)	O1—C15—C16—C17	20.0 (4)
C10—C11—C12—C8	177.84 (16)	C15—C16—C17—C18	−15.0 (4)
K1ⁱ—C11—C12—C8	68.34 (16)	C15—O1—C18—C17	7.6 (4)
C5—C11—C12—C9	−179.36 (16)	K1—O1—C18—C17	−154.1 (2)
C10—C11—C12—C9	−0.6 (2)	C16—C17—C18—O1	4.8 (4)
K1ⁱ—C11—C12—C9	−110.09 (14)	C22—O2—C19—C20	−2.7 (2)
C5—C11—C12—K1ⁱ	−69.27 (15)	K1—O2—C19—C20	−162.90 (13)
C10—C11—C12—K1ⁱ	109.50 (15)	O2—C19—C20—C21	24.1 (2)
C13—C9—C12—C8	144.41 (17)	C19—C20—C21—C22	−34.7 (2)
Cu1ⁱ—C9—C12—C8	−98.91 (17)	C19—O2—C22—C21	−20.2 (2)
C13—C9—C12—C11	−37.3 (2)	K1—O2—C22—C21	140.69 (14)
Cu1ⁱ—C9—C12—C11	79.44 (17)	C20—C21—C22—O2	34.4 (2)

Symmetry code: (i) −x, −y+1, −z+1.

Acknowledgements

We thank Christopher Roberts for his preliminary assistance in this project.

Funding information

Funding for this research was provided by: US National Science Foundation; Donors of the Petroleum Research Fund, administered by the American Chemical Society; Research Gift Support, administered by the University of Minnesota Foundation.

References

Alonso, T., Harvey, S., Junk, P. C., Raston, C. L., Skelton, B. W. & White, A. H. (1987). Organometallics, 6, 2110–2116. CSD CrossRef CAS Web of Science Google Scholar
Bakewell, C., Garçon, M., Kong, R. Y., O'Hare, L., White, A. J. P. & Crimmin, M. R. (2020). Inorg. Chem. 59, 4608–4616. Web of Science CSD CrossRef CAS PubMed Google Scholar
Bock, H., Ziemer, K. & Näther, C. (1996). J. Organomet. Chem. 511, 29–35. CSD CrossRef CAS Web of Science Google Scholar
Bogdanović, B., Janke, N., Krüger, C., Schlichte, K. & Treber, J. (1987). Angew. Chem. Int. Ed. Engl. 26, 1025–1026. Google Scholar
Bogdanović, B., Liao, S., Mynott, R., Schlichte, K. & Westeppe, U. (1984). Chem. Ber. 117, 1378–1392. Google Scholar
Bönnemann, H., Bogdanović, B., Brinkmann, R., He, D.-W. & Spliethoff, B. (1983). Angew. Chem. Int. Ed. Engl. 22, 728. Google Scholar
Bouas-Laurent, H., Desvergne, J., Castellan, A. & Lapouyade, R. (2000). Chem. Soc. Rev. 29, 43–55. CAS Google Scholar
Brauer, D. J. & Stucky, G. D. (1970). J. Am. Chem. Soc. 92, 3956–3963. CSD CrossRef CAS Web of Science Google Scholar
Brauer, D. J. & Stucky, G. D. (1972). J. Organomet. Chem. 37, 217–232. CSD CrossRef CAS Web of Science Google Scholar
Brennessel, W. W. & Ellis, J. E. (2012). Inorg. Chem. 51, 9076–9094. Web of Science CSD CrossRef CAS PubMed Google Scholar
Bruker (2003). SAINT and SMART. Bruker AXS, Inc., Madison, Wisconsin, USA. Google Scholar
Choi, C. S. & Marinkas, P. L. (1980). Acta Cryst. B36, 2491–2493. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Chou, T.-S., Tsao, C.-H. & Chun Hung, S. (1986). J. Organomet. Chem. 312, 53–58. CrossRef CAS Web of Science Google Scholar
Churchill, M. R. & Rotella, F. J. (1979). Inorg. Chem. 18, 166–171. CSD CrossRef CAS Web of Science Google Scholar
Conry, R. R. (1998). Chem. Commun. pp. 555–556. CrossRef Google Scholar
Cordero, B., Gómez, V., Platero-Prats, A. E., Revés, M., Echeverría, J., Cremades, E., Barragán, F. & Alvarez, S. (2008). Dalton Trans. pp. 2832–2838. Web of Science CrossRef Google Scholar
Cotton, F. A., Feng, X., Matusz, M. & Poli, R. (1988). J. Am. Chem. Soc. 110, 7077–7083. CSD CrossRef CAS Web of Science Google Scholar
Cotton, F. A., Wilkinson, G., Murillo, C. A. & Bochmann, M. (1999). Advanced Inorganic Chemistry, 6th ed., pp. 854–876. New York: Wiley. Google Scholar
Davies, R. P. (2011). Coord. Chem. Rev. 255, 1226–1251. Web of Science CrossRef CAS Google Scholar
Dietzel, P. D. C. & Jansen, M. (2001). Chem. Commun. pp. 2208–2209. Web of Science CSD CrossRef Google Scholar
Ellis, J. E. (2006). Inorg. Chem. 45, 3167–3186. Web of Science CrossRef PubMed CAS Google Scholar
Ellis, J. E. (2019). Dalton Trans. 48, 9538–9563. Web of Science CrossRef CAS PubMed Google Scholar
Ellis, J. E., Minyaev, M. E., Nifant'ev, I. E. & Churakov, A. V. (2018). Acta Cryst. C74, 769–781. Web of Science CSD CrossRef IUCr Journals Google Scholar
Engelhardt, L. M., Harvey, S., Raston, C. L. & White, A. H. (1988). J. Organomet. Chem. 341, 39–51. CSD CrossRef CAS Web of Science Google Scholar
Fedushkin, I. L., Bochkarev, M. N., Dechert, S. & Schumann, H. (2001). Chem. Eur. J. 7, 3558–3563. CrossRef PubMed CAS Google Scholar
Fryzuk, M. D., Jafarpour, L., Kerton, F. M., Love, J. B. & Rettig, S. J. (2000). Angew. Chem. Int. Ed. 39, 767–770. CrossRef CAS Google Scholar
Geeson, M. B., Transue, W. J. & Cummins, C. C. (2019). Organometallics, 38, 3229–3232. Web of Science CSD CrossRef CAS Google Scholar
Ghana, P., Hoffmann, A., Spaniol, T. P. & Okuda, J. (2020). Chem. Eur. J. 26, 10290–10296. Web of Science CSD CrossRef CAS PubMed Google Scholar
Graziano, M. V., Scott, T. R., Vollmer, M. V., Dorantes, M. J., Young, V. G., Bill, E., Gagliardi, L. & Lu, C. C. (2022). Chem. Sci. 13, 6525–6531. Web of Science CSD CrossRef PubMed Google Scholar
Grimme, S., Diedrich, C. & Korth, M. (2006). Angew. Chem. Int. Ed. 45, 625–629. Web of Science CrossRef CAS Google Scholar
Harisomayajula, N. V. S., Makovetskyi, S. & Tsai, Y.-C. (2019). Chem. Eur. J. 25, 8936–8954. Web of Science CrossRef CAS PubMed Google Scholar
Hatanaka, T., Ohki, Y., Kamachi, T., Nakayama, T., Yoshizawa, K., Katada, M. & Tatsumi, K. (2012). Chem. Asian J. 7, 1231–1242. Web of Science CSD CrossRef CAS PubMed Google Scholar
Hencher, J. L. & Mustoe, F. J. (1975). Can. J. Chem. 53, 3542–3544. CrossRef CAS Web of Science Google Scholar
Hotop, H., Bennett, R. A. & Lineberger, W. C. (1973). J. Chem. Phys. 58, 2373–2378. CrossRef CAS Web of Science Google Scholar
Huang, W., Abukhalil, P. M., Khan, S. I. & Diaconescu, P. L. (2014). Chem. Commun. 50, 5221–5223. Web of Science CSD CrossRef CAS Google Scholar
Huang, W., Khan, S. I. & Diaconescu, P. L. (2011). J. Am. Chem. Soc. 133, 10410–10413. Web of Science CSD CrossRef CAS PubMed Google Scholar
Jang, M. & Ellis, J. E. (1994). Angew. Chem. Int. Ed. Engl. 33, 1973–1975. CSD CrossRef Web of Science Google Scholar
Jansen, M. (2008). Chem. Soc. Rev. 37, 1826–1835. Web of Science CrossRef PubMed CAS Google Scholar
Jolly, W. L. (1976). The Principles of Inorganic Chemistry, p. 35, Table 2.5. New York: McGraw–Hill. Google Scholar
Karslyan, E. E., Borissova, A. O. & Perekalin, D. S. (2017). Angew. Chem. Int. Ed. 56, 5584–5587. Web of Science CSD CrossRef CAS Google Scholar
Knecht, J., Fischer, R., Overhof, H. & Hensel, F. (1978). J. Chem. Soc. Chem. Commun. pp. 905–906. CrossRef Web of Science Google Scholar
Kucera, B. E., Young, V. G., Brennessel, W. W. & Ellis, J. E. (2022). Acta Cryst. C78, 148–163. Web of Science CSD CrossRef IUCr Journals Google Scholar
Kuchuk, E., Muratov, K., Perekalin, D. S. & Chusov, D. (2019). Org. Biomol. Chem. 17, 83–87. Web of Science CrossRef CAS Google Scholar
Lehmkuhl, H. (1966). Tetrahedron Lett. 7, 2817–2823. CrossRef Google Scholar
Lehmkuhl, H., Shakoor, A., Mehler, K., Krüger, C. & Tsay, Y.-H. (1985). Z. Naturforsch. B, 40, 1504–1510. CrossRef Google Scholar
Mehrotra, P. K. & Hoffmann, R. (1978). Inorg. Chem. 17, 2187–2189. CrossRef CAS Web of Science Google Scholar
Merz, K. M. Jr & Hoffmann, R. (1988). Inorg. Chem. 27, 2120–2127. CrossRef CAS Web of Science Google Scholar
Mitchell, A. D. & Cross, L. C. (1965). Tables of Interatomic Distances and Configurations in Molecules and Ions, Supplement 1956–1959, Special Publication 18, p. S15s. London: Chemical Society. Google Scholar
Murillo, J., Bhowmick, R., Harriman, K. L. M., Gomez-Torres, A., Wright, J., Meulenberg, R. W., Miró, P., Metta-Magaña, A., Murugesu, M., Vlaisavljevich, B. & Fortier, S. (2021). Chem. Sci. 12, 13360–13372. Web of Science CSD CrossRef CAS PubMed Google Scholar
Murillo, J., Bhowmick, R., Harriman, K. L. M., Gomez-Torres, A., Wright, J., Miró, P., Metta-Magaña, A., Murugesu, M., Vlaisavljevich, B. & Fortier, S. (2022). Chem. Commun. 58, 9112–9115. Web of Science CSD CrossRef CAS Google Scholar
Nelson, J. E., Clark, D. L., Burns, C. J. & Sattelberger, A. P. (1992). Inorg. Chem. 31, 1973–1976. CSD CrossRef CAS Web of Science Google Scholar
Rieke, R. D., Dawson, B. T., Stack, D. E. & Stinn, D. E. (1990). Synth. Commun. 20, 2711–2721. CrossRef CAS Web of Science Google Scholar
Riu, M. Y., Transue, W. J., Knopf, I. & Cummins, C. C. (2020). Organometallics, 39, 4187–4190. Web of Science CSD CrossRef CAS Google Scholar
Roitershtein, D. M. (1993). J. Organomet. Chem. 460, 39–45. CSD CrossRef CAS Web of Science Google Scholar
Roitershtein, D. M., Ellern, A. M., Antipin, M. Y., Rybakova, L. F., Struchkov, Y. T. & Petrov, E. S. (1992). Mendeleev Commun. 2, 118–120. CSD CrossRef Google Scholar
Sakurai, H., Nakadaira, Y. & Tobita, H. (1982). Chem. Lett. 11, 1855–1858. CrossRef Web of Science Google Scholar
Santiso-Quiñones, G., Higelin, A., Schaefer, J., Brückner, R., Knapp, C. & Krossing, I. (2009). Chem. Eur. J. 15, 6663–6677. Web of Science PubMed Google Scholar
Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Shriver, D. F. (1969). In The Manipulation Air-Sensitive Compounds, chs. 7 and 8, pp. 153–154. New York: McGraw–Hill. Google Scholar
Stack, D. E., Klein, W. R. & Rieke, R. D. (1993). Tetrahedron Lett. 34, 3063–3066. CrossRef CAS Web of Science Google Scholar
Sugita, K., Nakano, R. & Yamashita, M. (2020). Chem. Eur. J. 26, 2174–2177. Web of Science CSD CrossRef CAS PubMed Google Scholar
Turner, R. W. & Amma, E. L. (1966). J. Am. Chem. Soc. 88, 1877–1882. CSD CrossRef CAS Web of Science Google Scholar
Velian, A. & Cummins, C. C. (2012). J. Am. Chem. Soc. 134, 13978–13981. Web of Science CSD CrossRef CAS PubMed Google Scholar
Velian, A., Nava, M., Temprado, M., Zhou, Y., Field, R. W. & Cummins, C. C. (2014). J. Am. Chem. Soc. 136, 13586–13589. Web of Science CSD CrossRef CAS PubMed Google Scholar
Velian, A., Transue, W. J. & Cummins, C. C. (2015). Organometallics, 34, 4644–4646. Web of Science CSD CrossRef CAS Google Scholar
Wayda, A. L. & Darensbourg, M. Y. (1987). Editors. In Experimental Organometallic Chemistry: A Practicum in Synthesis and Characterization. Washington, DC: American Chemical Society. Google Scholar
Wright, A. M., Irving, B. J., Wu, G., Meijer, A. J. H. M. & Hayton, T. W. (2015). Angew. Chem. Int. Ed. 54, 3088–3091. Web of Science CSD CrossRef CAS Google Scholar
Wright, A. M., Wu, G. & Hayton, T. W. (2010). J. Am. Chem. Soc. 132, 14336–14337. Web of Science CSD CrossRef CAS PubMed Google Scholar
Xu, F.-B., Li, Q.-S., Wu, L.-Z., Leng, X.-B., Li, Z.-C., Zeng, X.-S., Chow, Y. L. & Zhang, Z.-Z. (2003). Organometallics, 22, 633–640. Web of Science CSD CrossRef CAS Google Scholar
Yu, C., Liang, J., Deng, C., Lefèvre, G., Cantat, T., Diaconescu, P. L. & Huang, W. (2020). J. Am. Chem. Soc. 142, 21292–21297. Web of Science CSD CrossRef CAS PubMed Google Scholar
Zhou, M. & Andrews, L. (1999). J. Chem. Phys. 111, 4548–4557. Web of Science CrossRef CAS Google Scholar
Zhu, M., Li, T., Chai, Z., Wei, J., Lv, Z.-J. & Zhang, W.-X. (2023). Inorg. Chem. Front. 10, 630–637. Web of Science CSD CrossRef CAS Google Scholar

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