Slow atmospheric oxidation of diphenyl­zinc: di-μ-phenoxido-bis­[(diethyl ether)phenyl­zinc(II)]

The title compound, [Zn₂(C₆H₅)₂(C₆H₅O)₂(C₄H₁₀O)₂], was isolated from a solution of diphenyl­zinc in diethyl ether that had been exposed to air. The mol­ecules are dinuclear, with a distorted tetra­hedral coordination geometry around the Zn atoms and with mol­ecules situated about a crystallographic inversion centre. Mol­ecules associate via three sets of C—H...π(arene) inter­actions, leading to a network structure.

S1. Comment

Organozinc reagents are known to be highly sensitive towards atmospheric O₂, as noted by Edward Frankland during his pioneering work on organozinc compounds (see, for example, Frankland, 1852, 1855; Seyferth, 2001). This forced Frankland to develop several ingenious apparatus in order to synthesize, purify and analyse the highly reactive compounds he had discovered (Frankland, 1855). Low molecular weight dialkylzinc compounds (ZnMe₂, ZnEt₂ and ZnPr₂) ignite spontaneously when exposed to air (Boersma, 1982a). Slow oxidation of organozinc reagents by low concentrations of O₂ is known to give rise to the corresponding alkoxides, with zinc organoperoxides as intermediates (Boersma, 1982b). The formation of alkoxides by the action of O₂ on dialkylzinc compounds was first reported in the case of diethylzinc by Frankland (1855), who identified zinc ethoxide as one of the products obtained in the reaction of diethyl zinc and oxygen.

The title compound, (I), was isolated from a diethyl ether solution of diphenylzinc (standing in a Schlenk tube) after a long time period (3.5 years), where the solution had partially attacked the silicon grease on the stopcock, causing a minute leak of atmospheric O₂ into the tube. Compound (I) is a dinuclear zinc complex, situated about a crystallographic inversion centre (Fig. 1). The coordination geometry around Zn1 is highly distorted tetrahedral with a Zn1—C1 distance of 1.964 (2) Å, Zn—O bond lengths of 1.9898 (14), 2.0008 (14) and 2.0939 (15) Å, and angles about the Zn centre ranging from 79.31 (6)° to 130.39 (7)°. The coordination of diethylether to zinc is, perhaps surprisingly, rare among the structures in the Cambridge Structural Database (CSD; Version 5.28 of November 2006; Allen 2002). Only 11 structures were found containing a Zn–OEt₂ fragment. Among these, two examples of organozinc complexes, bis[(µ₂-chloro)(1,1-dichloro-2,2,2-trifluoromethyl)(diethyl ether)zinc(II)] (Behm et al., 1993) and tris(diethyl ether)(ethyl)zinc(II) tetrakis(pentafluorophenyl)borate (Walker et al., 2001), as well as one example of a zinc aryloxide, bis[(diethyl ether)(2,6-diphenylphenoxy)]zinc(II) (Darensbourg et al., 1999), are to be found.

Several crystal structures for zinc aryloxides and organozinc aryloxides have been published and are reported in the CSD, but none of the structures are closely related to (I). A total of 146 structures are found where two Zn atoms are bridged by two aryloxide groups. Most of these structures include complex aryloxide groups, having for example N-donor substituents coordinating to Zn, e.g. bis{[µ₂-2-(diethylaminomethyl)phenoxo](ethyl)zinc(II)} (Hunger et al., 2005). Structures having a monodentate neutral ligand at Zn, as for (I), are rare. There is only one example of an organozinc aryloxide bearing a coordinating ligand at Zn, viz. bis[(µ₂-2,6-dimethylphenoxo)(ethyl)(pyridyl)zinc(II)] (Boyle et al., 2004). Two structures of bridged zinc aryloxides having monodentate neutral ligands at Zn are reported in the CSD, viz. bis[(µ₂-2,6-difluorophenoxo)(2,6-difluorophenoxo)(tetrahydrofuran)zinc(II)] and bis[(µ₂-2,6-difluorophenoxo)(2,6-difluorophenoxo)(tricyclohexylphosphine)zinc(II)] tetrahydrofuran solvate (Darensbourg et al., 2000). Another structure somewhat similar to (I) is bis[(µ₂-2,3-dihydro-2,2-dimethylbenzofuranoxide)(chloro)(pyridine)zinc(II)] (Sobota et al., 2000). In addition, there are a number of complexes with three-coordinate Zn atoms. In this category, there is one example of a base-free zinc aryloxide, viz. bis[(µ₂-2,6-di-t-butylphenoxo)(2,6-di-t-butylphenoxo)zinc(II)] n-pentane solvate (Kunert et al., 2000). Other examples include bis[(µ₂-2,6-di-t-butylphenoxo)(ethyl)zinc(II)] (Parvez et al., 1992) and [(µ₂-2,6-di-isopropylphenoxo)(trimethylsilylmethyl)zinc(II)] (Olmstead et al., 1991). There are no structures of Zn(OPh)₂ complexes in the CSD, but there are eight structures of derivatives bearing one phenoxo ligand at zinc, e.g. bis(µ₂-phenoxo)[N-isopropyl-2-(isopropylamino)troponiminato]zinc(II) (Herrmann et al., 2004) and bis(µ₃-phenoxo)tetrakis(µ₂-2,2-dimethyl-3,5-hexanedionato)(diphenyl)tetrazinc(II) (Boersma et al., 1974). The latter example is the only structure in the CSD of a phenylzinc–phenoxide complex (Fig. 2). The Zn···Zn distances in this structure are 3.177, 3.239 and 3.171 Å, slightly longer than that in (I) [3.0724 (6) Å].

The crystal structure of (I) displays three sets of C—H···π interactions (Nishio, 2004; Cantrill et al., 2000; Braga et al., 1998; Viswamitra et al., 1993). The shortest set of C—H···π interactions involves atom H14A and the (C1–C6)ⁱⁱ phenyl ring [symmetry code: (ii) x + 1, y, z] and gives rise to chains extending along the a axis. The second shortest set of C—H···π contacts involves atom H10 and the (C1–C6)ⁱ phenyl ring [symmetry code: (i) -x + 1/2, y - 1/2, -z + 1/2]. These interactions result in layers extending parallel to the (202) set of planes. A third set of interactions can be identified, viz. atom H15A interacts with the (C1–C6)ⁱⁱⁱ phenyl ring [symmetry code: (iii) x + 1/2, -y + 3/2, z + 1/2]. These interactions give rise to layers parallel to (202). The three sets of interactions result in a network structure, and these interactions are depicted in Fig. 3.

Zinc aryloxides have found use in carbon dioxide activation and may have future potential as an activator of this greenhouse gas. Darensbourg and co-workers reported that zinc aryloxides catalyse the copolymerization of carbon dioxide and epoxides (Darensbourg & Holtcamp, 1995; Darensbourg et al., 1999). Fixation of carbon dioxide by carboxylation of acetophenone using zinc aryloxide catalysts has also been reported (Kunert et al., 2000).

Related literature

For related literature, see: Allen (2002); Behm et al. (1993); Boersma (1982a, 1982b); Boersma et al. (1974); Boyle et al. (2004); Braga et al. (1998); Cantrill et al. (2000); Darensbourg & Holtcamp (1995); Darensbourg et al. (1999); Frankland (1852, 1855); Hunger et al. (2005); Kunert et al. (2000); Nishio (2004); Olmstead et al. (1991); Parvez et al. (1992); Seyferth (2001); Sobota et al. (2000); Viswamitra et al. (1993); Walker et al. (2001).

S2. Experimental

Bromobenzene (4.1 ml, 0.039 mol) was added to a stirred mixture of Mg (1.1 g, 0.045 mol) and diethyl ether (40 ml). The mixture was stirred overnight at ambient temperature. The solution was added dropwise to a suspension of ZnCl₂ (2.6 g, 0.019 mol) in diethyl ether (10 ml) at 273 K. The reaction mixture was stirred at ambient temperature overnight, evaporated and sublimated at 10^-2 mbar. The white product was dissolved in diethyl ether (4 ml). After 3.5 years of storage at 238 K, the silicon grease had been heavily attacked by the ZnPh₂ solution, resulting in leakage of atmospheric O₂ into the Schlenk tube. Large colourless hexagonal–prismatic crystals of (I) were isolated.

S3. Refinement

All H atoms were included in calculated positions (C—H = 0.93–0.97 Å) and refined using a riding model with U_iso(H) values of 1.2 or 1.5 times U_eq(C).

Computing details

Data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear (Rigaku, 2000); data reduction: CrystalClear (Rigaku, 2000); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

Figure 1. A view of (I), with the atomic numbering scheme; atoms with the suffix 'A' indicate symmetry-related equivalents. Displacement ellipsoids are drawn at the 30% probability level and H atoms are included with radii of an arbitrary size. Figure 2. A schematic drawing of the phenylzinc phenoxide derivative bis(µ3-phenoxo)tetrakis(µ2-2,2-dimethyl-3,5-ηexanedionato-)(diphenyl)tetrazinc(II) (Boersma et al., 1974). Figure 3. The structure of (I) has three sets of C—H···π(arene) interactions. The unit cell of (I) when viewed along the b axis (left, with H14A interaction) and along the c axis (right, with the H10 and H15A interactions).

(I)

Crystal data

[Zn2(C6H5)2(C6H5O)2(C4H10O)2]	F(000) = 648
Mr = 619.42	Dx = 1.356 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 2729 reflections
a = 8.5115 (13) Å	θ = 3.1–25.5°
b = 12.8018 (18) Å	µ = 1.61 mm^−1
c = 14.128 (2) Å	T = 100 K
β = 99.814 (5)°	Prism, colourless
V = 1516.9 (4) Å^3	0.30 × 0.25 × 0.15 mm
Z = 2

Data collection

Rigaku R-AXIS IIC image-plate system diffractometer	2729 independent reflections
Radiation source: rotating-anode X-ray tube, Rigaku RU-H3R	2540 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.030
Detector resolution: 105 pixels mm^-1	θmax = 25.5°, θmin = 3.1°
ϕ scans	h = −9→10
Absorption correction: multi-scan (CrystalClear; Rigaku, 2000)	k = −15→15
Tmin = 0.559, Tmax = 0.785	l = −17→17
9541 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.031	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.080	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0418P)^2 + 1.443P] where P = (Fo^2 + 2Fc^2)/3
2729 reflections	(Δ/σ)max < 0.001
172 parameters	Δρmax = 0.88 e Å^−3
0 restraints	Δρmin = −0.39 e Å^−3

Special details

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.3576 (2)	0.74388 (16)	−0.02054 (14)	0.0160 (4)
C2	0.1911 (3)	0.74190 (17)	−0.02415 (15)	0.0202 (4)
H2	0.1431	0.6799	−0.0099	0.024*
C3	0.0966 (3)	0.82957 (18)	−0.04825 (16)	0.0234 (5)
H3	−0.0130	0.8254	−0.0500	0.028*
C4	0.1645 (3)	0.92329 (18)	−0.06971 (16)	0.0230 (5)
H4	0.1013	0.9821	−0.0853	0.028*
C5	0.3284 (3)	0.92804 (16)	−0.06767 (15)	0.0199 (4)
H5	0.3754	0.9901	−0.0826	0.024*
C6	0.4220 (2)	0.83953 (16)	−0.04323 (14)	0.0170 (4)
H6	0.5314	0.8442	−0.0419	0.020*
C7	0.3473 (2)	0.45984 (16)	0.14165 (14)	0.0146 (4)
C8	0.2816 (3)	0.36151 (18)	0.15141 (18)	0.0247 (5)
H8	0.2841	0.3111	0.1043	0.030*
C9	0.2122 (3)	0.3385 (2)	0.2314 (2)	0.0342 (6)
H9	0.1683	0.2728	0.2371	0.041*
C10	0.2080 (3)	0.4126 (2)	0.30256 (17)	0.0317 (6)
H10	0.1633	0.3966	0.3565	0.038*
C11	0.2711 (3)	0.5101 (2)	0.29210 (17)	0.0333 (6)
H11	0.2665	0.5608	0.3387	0.040*
C12	0.3415 (3)	0.5337 (2)	0.21285 (17)	0.0285 (5)
H12	0.3850	0.5997	0.2075	0.034*
C13	0.7892 (3)	0.5633 (2)	0.16054 (18)	0.0317 (5)
H13A	0.7308	0.4979	0.1564	0.038*
H13B	0.8321	0.5762	0.2276	0.038*
C14	0.9211 (3)	0.5552 (3)	0.1052 (2)	0.0431 (7)
H14A	0.9908	0.4992	0.1304	0.065*
H14B	0.9797	0.6196	0.1102	0.065*
H14C	0.8784	0.5417	0.0390	0.065*
C15	0.6905 (3)	0.7359 (2)	0.18669 (17)	0.0305 (5)
H15A	0.6913	0.7114	0.2517	0.037*
H15B	0.5955	0.7781	0.1683	0.037*
C16	0.8334 (4)	0.8025 (2)	0.1854 (3)	0.0472 (7)
H16A	0.8320	0.8602	0.2287	0.071*
H16B	0.8323	0.8286	0.1215	0.071*
H16C	0.9281	0.7619	0.2051	0.071*
O1	0.41506 (17)	0.48186 (11)	0.06415 (10)	0.0167 (3)
O2	0.68260 (19)	0.64720 (13)	0.12344 (12)	0.0269 (4)
Zn1	0.48567 (3)	0.618065 (17)	0.016024 (16)	0.01466 (11)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0211 (10)	0.0147 (9)	0.0119 (9)	−0.0009 (8)	0.0019 (7)	−0.0005 (7)
C2	0.0237 (11)	0.0169 (10)	0.0208 (10)	−0.0041 (8)	0.0058 (8)	0.0011 (8)
C3	0.0194 (10)	0.0264 (12)	0.0235 (11)	0.0011 (9)	0.0012 (8)	−0.0012 (9)
C4	0.0272 (11)	0.0190 (11)	0.0204 (10)	0.0065 (9)	−0.0027 (9)	0.0007 (9)
C5	0.0293 (11)	0.0136 (10)	0.0156 (10)	−0.0037 (8)	0.0008 (8)	0.0009 (8)
C6	0.0195 (10)	0.0162 (10)	0.0151 (9)	−0.0017 (8)	0.0025 (8)	−0.0023 (8)
C7	0.0120 (9)	0.0180 (10)	0.0130 (9)	0.0009 (7)	0.0002 (7)	0.0031 (8)
C8	0.0292 (12)	0.0167 (10)	0.0313 (12)	0.0006 (9)	0.0136 (10)	0.0014 (9)
C9	0.0410 (14)	0.0239 (12)	0.0426 (15)	−0.0006 (11)	0.0217 (12)	0.0120 (11)
C10	0.0262 (12)	0.0511 (16)	0.0188 (11)	−0.0012 (11)	0.0069 (9)	0.0108 (11)
C11	0.0323 (13)	0.0509 (17)	0.0181 (11)	−0.0165 (11)	0.0081 (10)	−0.0141 (11)
C12	0.0337 (12)	0.0283 (12)	0.0259 (12)	−0.0165 (10)	0.0122 (10)	−0.0085 (10)
C13	0.0345 (13)	0.0266 (12)	0.0315 (13)	0.0047 (10)	−0.0015 (10)	0.0036 (10)
C14	0.0426 (16)	0.0519 (18)	0.0319 (14)	0.0050 (13)	−0.0018 (12)	−0.0006 (13)
C15	0.0368 (13)	0.0306 (13)	0.0222 (12)	−0.0023 (10)	−0.0006 (10)	−0.0055 (10)
C16	0.0458 (16)	0.0309 (14)	0.0620 (19)	−0.0107 (12)	0.0007 (14)	−0.0170 (14)
O1	0.0227 (7)	0.0126 (6)	0.0164 (7)	−0.0018 (6)	0.0076 (6)	0.0006 (6)
O2	0.0283 (8)	0.0166 (7)	0.0304 (9)	0.0028 (7)	−0.0105 (7)	−0.0052 (7)
Zn1	0.01876 (16)	0.01023 (15)	0.01496 (16)	−0.00033 (8)	0.00281 (10)	0.00062 (8)

Geometric parameters (Å, º)

C1—C6	1.401 (3)	C11—C12	1.390 (3)
C1—C2	1.410 (3)	C11—H11	0.9300
C1—Zn1	1.964 (2)	C12—H12	0.9300
C2—C3	1.389 (3)	C13—O2	1.446 (3)
C2—H2	0.9300	C13—C14	1.477 (4)
C3—C4	1.387 (3)	C13—H13A	0.9700
C3—H3	0.9300	C13—H13B	0.9700
C4—C5	1.392 (3)	C14—H14A	0.9600
C4—H4	0.9300	C14—H14B	0.9600
C5—C6	1.394 (3)	C14—H14C	0.9600
C5—H5	0.9300	C15—O2	1.440 (3)
C6—H6	0.9300	C15—C16	1.488 (4)
C7—O1	1.351 (2)	C15—H15A	0.9700
C7—C12	1.388 (3)	C15—H15B	0.9700
C7—C8	1.394 (3)	C16—H16A	0.9600
C8—C9	1.393 (3)	C16—H16B	0.9600
C8—H8	0.9300	C16—H16C	0.9600
C9—C10	1.387 (4)	O1—Zn1^i	1.9898 (14)
C9—H9	0.9300	O1—Zn1	2.0008 (14)
C10—C11	1.377 (4)	O2—Zn1	2.0939 (15)
C10—H10	0.9300	Zn1—Zn1^i	3.0724 (6)
C6—C1—C2	115.94 (19)	C14—C13—H13A	109.6
C6—C1—Zn1	123.78 (15)	O2—C13—H13B	109.6
C2—C1—Zn1	120.28 (15)	C14—C13—H13B	109.6
C3—C2—C1	122.1 (2)	H13A—C13—H13B	108.1
C3—C2—H2	119.0	C13—C14—H14A	109.5
C1—C2—H2	119.0	C13—C14—H14B	109.5
C4—C3—C2	120.4 (2)	H14A—C14—H14B	109.5
C4—C3—H3	119.8	C13—C14—H14C	109.5
C2—C3—H3	119.8	H14A—C14—H14C	109.5
C3—C4—C5	119.1 (2)	H14B—C14—H14C	109.5
C3—C4—H4	120.4	O2—C15—C16	113.3 (2)
C5—C4—H4	120.4	O2—C15—H15A	108.9
C4—C5—C6	119.9 (2)	C16—C15—H15A	108.9
C4—C5—H5	120.1	O2—C15—H15B	108.9
C6—C5—H5	120.1	C16—C15—H15B	108.9
C5—C6—C1	122.53 (19)	H15A—C15—H15B	107.7
C5—C6—H6	118.7	C15—C16—H16A	109.5
C1—C6—H6	118.7	C15—C16—H16B	109.5
O1—C7—C12	121.21 (19)	H16A—C16—H16B	109.5
O1—C7—C8	120.15 (19)	C15—C16—H16C	109.5
C12—C7—C8	118.6 (2)	H16A—C16—H16C	109.5
C9—C8—C7	120.3 (2)	H16B—C16—H16C	109.5
C9—C8—H8	119.9	C7—O1—Zn1^i	127.47 (13)
C7—C8—H8	119.9	C7—O1—Zn1	130.65 (13)
C10—C9—C8	120.7 (2)	Zn1^i—O1—Zn1	100.69 (6)
C10—C9—H9	119.7	C15—O2—C13	113.66 (18)
C8—C9—H9	119.7	C15—O2—Zn1	122.50 (14)
C11—C10—C9	118.9 (2)	C13—O2—Zn1	120.38 (14)
C11—C10—H10	120.6	C1—Zn1—O1^i	130.39 (7)
C9—C10—H10	120.6	C1—Zn1—O1	128.23 (7)
C10—C11—C12	120.9 (2)	O1^i—Zn1—O1	79.31 (6)
C10—C11—H11	119.6	C1—Zn1—O2	112.60 (7)
C12—C11—H11	119.6	O1^i—Zn1—O2	99.32 (6)
C7—C12—C11	120.6 (2)	O1—Zn1—O2	99.13 (6)
C7—C12—H12	119.7	C1—Zn1—Zn1^i	145.34 (6)
C11—C12—H12	119.7	O1^i—Zn1—Zn1^i	39.78 (4)
O2—C13—C14	110.3 (2)	O1—Zn1—Zn1^i	39.52 (4)
O2—C13—H13A	109.6	O2—Zn1—Zn1^i	102.02 (4)

Symmetry code: (i) −x+1, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C10—H10···Cg1^ii	0.93	2.76	3.542 (3)	143
C14—H14a···Cg2^iii	0.96	2.68	3.539 (3)	149
C15—H15a···Cg2^iv	0.97	2.88	3.834 (3)	167

Symmetry codes: (ii) −x+1/2, y−1/2, −z+1/2; (iii) x+1, y, z; (iv) x+1/2, −y+3/2, z+1/2.