Syntheses and crystal structures of [IrIII{C(CHCO2Et)(dppm)2-κ4 P,C,C′,P′}ClH]Cl·2.75CH2Cl2 and its derivatives, [IrIII{C(CHCO2Et)(dppm)2-κ4 P,C,C′,P′}(CH2CO2Et)Cl]Cl·CH3OH·0.5H2O, [IrIII{C(CHCO2Et)(dppm)2-κ4 P,C,C′,P′}Cl2]Cl·CH3OH·2H2O and [IrIII{C(CHCO2Et)(dppm)2-κ4 P,C,C′,P′}(CH2CO2Et)(CO)]Cl2·2CH2Cl2·1.5H2O

The common structural feature of the four title IrIII compounds is the octahedral coordination of the IrIII atom by a PCP pincer complex, a C atom of a (ethoxyoxoethanylidene)methane group and two variable ligands X (H, CH2CO2Et, Cl) and Y (Cl, CO).


Chemical context
Carbodiphosphoranes (CDP) in combination with transition metals initialize a huge variety of functionalities. As a result of the presence of two -electron-donor groups, preferred in the form of tertiary phosphines, the stabilization of two free- ISSN 2056-9890 electron pairs withand simultaneously -symmetry, the establishment of a localized electron octet and further the creation of a zero-valent, naked carbon atom in an excited singlet ( 1 D) state is possible (Petz & Frenking, 2010). The carbodiphosphorane C atom can be considered as a fourelectron donor, and accordingly enables the coordination of two Lewis acids, such as protons or different metal cations. Our interests focus on the combination of a carbodiphosphorane pincer ligand system, [CH(dppm) 2 ]Cl (dppm = 1,1-bis(diphenylphosphino)methane; Reitsamer et al., 2012), with reactive functionalities to enter new reaction pathways, to create new complexes and to analyse in detail the new properties obtained. In general, C-C coupling reactions can be induced via the use of diazo compounds such as ethyl diazoacetate. As a result of the presence of two nitrogen atoms acting together as an excellent leaving group, and an alkylidene group stabilized by different functionalities, the electrons are delocalized between three atoms and thus a positive and one negative charge theoretically allows by a disregard of the coordinating residuals and chemical conditions four different resonance structures to be gained in total. Therefore, the diazo compound can be regarded as both a nucleophilic and as an electrophilic reaction partner. By the use of this compound, a targeted synthesis of cyclopropanes or rather heterocyclopropanes, consisting of a transition metal, an electron-donor atom and a carbene carbon, is possible and has been reported several times in the literature (e.g. Nomura et al., 2011;Liu & Yan, 2015;Malisch et al., 1998;Strecker et al., 1991;Zhang et al., 2005, and references cited therein). An electrophilic reaction partner such as a transition metal establishes a nucleophilic attack of the diazo subunit and, according to the choice of the reaction conditions, the elimination of the nitrogen leaving group is supported. Consequently, the alkylidene carbon atom is stabilized by coordination of an electron-accepting atom and a reactive carbene intermediate complex is formed. The existence of a nucleophilic reaction partner in the vicinity of the carbene atom results in the formation of a ring including an alkylidene bridging subunit. In summary, the reaction of a diazo compound with an electrophilic and additionally a nucleophilic reaction partner initiates a mechanism that can be described as a cheletropic-like process. Inspired by this reaction sequence, we have synthesized a three-membered heterocycle by the combination of an ethyl diazoacetate and an iridium(III) PCP pincer carbodiphosphorane complex.
If the starting materials [CH(dppm) 2 ]Cl (Reitsamer et al., 2012) and [IrCl(cod)] 2 are mixed, a reaction sequence is initialized that consists of the following steps: Coordination of the iridium(I) atom, followed by deprotonation of the carbodiphosphorane carbon atom, the generation of a hydrido ligand caused by an oxidation of the iridium(I) atom and the formation of the [Ir{C(dppm) 2 -3 P,C,P'}ClH(MeCN)]Cl complex 1 (Schlapp-Hackl et al., 2018;Fig. 1). In summary, the iridium(III) transition metal is stabilized by the PCP pincer ligand system, and by a chlorido and a hydrido ligand and an acetonitrile solvent molecule. The addition of ethyl diazoacetate causes, via loss of the dinitrogen subunit, the formation of an Ir III -carbene bond. As a result of the presence of the second free lone-electron pair at the carbodiphosphorane carbon atom, a cyclization and further the creation of an alkylidene bridge is accomplished. The formation of the threemembered Ir-C CDP -C ring is accompanied by a surprising displacement of the hydrido ligand from a position perpendicular to the plane of the PCP pincer system to a meridional arrangement trans to the carbodiphosphorane carbon atom. Supported by the polar solvent mixture methanol/acetonitrile (v/v 5:1) an [Ir III {C(CHCO 2 Et)(dppm) 2 -4 P,C,C 0 ,P 0 }H-(MeCN)]Cl 2 precursor system (2) is generated in high yields (86%). Moreover, the preparation of complex 2 in a less polar solvent environment like chloroform/acetonitrile or in a solvent mixture of methylene chloride/acetonitrile (v/v 5:1) is not possible and quantitatively results in the substitution of one phosphine moiety of the carbodiphosphorane functionality against the carbene CHCO 2 Et subunit. An [Ir{C(CH-CO 2 Et)(dppm)-2 P,C}Cl(dppm)H]Cl complex 3 is generated, offering a phosphorus ylide carbon backbone (Schlapp-Hackl et al., 2018). To a lesser extent (14% yield), this complex is additionally obtained as by-product by the production of complex 2. Heating of complex 2 in methanol/acetonitrile (v/v 5:1) to 333 K for 2 h benefits the ring-opening reaction of the PCCP pincer ligand system. Therefore, a reorganization of the ligand system is supported, resulting in the quantitative formation of complex 3. Furthermore, evaporation of the reaction mixture of complex 2 causes an exchange of the acetonitrile solvent ligand with a chloride counter-ion and the creation of the desired [Ir III {C(CHCO 2 Et)(dppm) 2 -4 P,C,C 0 ,P 0 }ClH]Cl complex 4.
The stucture of this iridium(III) PCCP complex was completely determined by NMR spectroscopy and X-ray crystallography, but up to now crystallization attempts of the intermediates, 1 and 2, were unsuccessful. With regard to a ruthenium PCP pincer complex, a related cycloaddition was monitored (Zhang et al., 2005). Thereby, the ruthenium transition metal first stabilizes the phenyldiazomethane by coordination. After the elimination of the dinitrogen molecule, the formation of the corresponding carbene complex and finally a carbon-carbon coupling reaction between the central carbon atom of the phenyl-based PCP ligand and the carbene was detected. As a consequence, the arene backbone of the PCP ligand system is transformed to an arenium moiety. Treatment of complex 4 with an additional equivalent amount of ethyl diazoacetate causes an insertion reaction of the alkylidene to the iridium(III)-hydrido bond and the formation of the [Ir III {C(CHCO 2 Et)(dppm) 2 -4 P,C,C 0 ,P 0 }(CH 2 CO 2 Et)-Cl]Cl alkyl derivative 5. This reaction procedure is well known, and the mechanism of the intermolecular insertion reaction has been clarified via an intermediate carbene complex (Cohen et al., 2003). Moreover, treatment of complexes 4 and 5 with hydrochloric acid leads to a ligand substitution at the position trans to the central carbon atom of the PCP pincer ligand system with a chloride ion and to the formation of the [Ir III {C(CHCO 2 Et)(dppm) 2 -4 P,C,C 0 ,P 0 }-Cl 2 ]Cl complex 6. Besides, a replacement of the chlorido ligand of compound 5 by a carbonyl group is possible and results in the [Ir III {C(CHCO 2 Et)(dppm) 2 -4 P,C,C 0 ,P 0 }-(CH 2 CO 2 Et)(CO)]Cl 2 complex 7.
Here we report details of the syntheses and crystal structures of complexes 4-7.

Structural commentary
The asymmetric unit of compound 4, [Ir III {C(CHCO 2 Et)-(dppm) 2 -4 P,C,C 0 ,P 0 }ClH]Cl, comprises of one formula unit of 4 and additionally of 2.75 molecules of methylene chloride solvent molecules. The central iridium(III) transition metal is surrounded in a distorted octahedral fashion by a PCCP pincer-like ligand system, and anionic chlorido and hydrido ligands (Fig. 2). The neutral [C(CHCO 2 Et)(dppm) 2 -4 P,C,C 0 ,P 0 ] ligand coordinates the Ir III metal in a tetradentate fashion via two P and two C atoms under formation of two five-membered, dissimilar chelate rings [C4-C1-P3 = 120.2 (3) , C4-C1-P2 = 112.1 (3) ] and one three membered heterocycle. The PCP ligand exhibits a meridional arrangement with the hydrido ligand completing the equatorial plane trans to the C1 carbodiphosphorane atom. A cyclopropanelike chelate ring is positioned nearly normal (84.21 ) to the equatorial plane, and a chlorido ligand is positioned trans to the alkylidene carbon atom C4. The Ir-C1 [2.273 (4) Å ] and Ir-C4 [2.072 (5) Å ] distances differ significantly and consequently these values substantiate a strengthened interaction between the iridium(III) metal and the alkylidene carbon atom. The C1-C4 separation [1.515 (6) Å ] is slightly shorter in comparison to a typical C-C single bond but, in general, very close to that of cyclopropanes. However, in comparison with a cyclopropane molecule the C4-  ], C4-C1-Ir1 [62.6 (2) ] and C1-C4- Ir1 [76.9 (3) ] angles emphasise a significant distortion of the synthesized threemembered heterocycle. All mentioned geometric features of this strained Ir-C1-C4 metallacycle can be associated with the structural results of the Ru-C-C triangle reported by Zhang et al. (2005). Furthermore, the three-membered ring causes a distortion of the octahedral coordination geometry (Table 1). The P1-  ] atoms are less affected and show only a slight deviation from linearity. Though, the tetrahedral environment of the carbodiphosphorane C1 atom is strongly influenced and thus distorted, which is reflected by a P3-C1-P2 angle of 124.2 (3) . Overall, the transition metal and its ligand system present a cationic complex balanced by one chloride.
The asymmetric unit of compound 5, [Ir III {C(CHCO 2 Et)-(dppm) 2 -4 P,C,C 0 ,P 0 }(CH 2 CO 2 Et)Cl]Cl, is defined by one complex 5, one half-occupied water molecule and one disordered methanol solvent molecule. In comparison with the structural features discussed in detail for compound 4, significant differences pertain only to the equatorial position trans to C1. Here the hydrido ligand in 4 is exchanged by an ethyl acetate unit (Fig. 3).
The replacement of the hydrido ligand of compound 4 by a chlorido ligand led to formation of 6, [Ir III {C(CH-CO 2 Et)(dppm) 2 -4 P,C,C 0 ,P 0 }Cl 2 ]Cl. In its crystalline form, besides one formula unit of 6, one solvent molecule of MeOH and two water molecules in total are present in the asymmetric unit. Overall, this PCCP derivative shows very similar structural characteristics (Fig. 4) to complex 4.
Finally, an elimination of the chlorido ligand of complex 5 and its replacement by a carbonyl ligand results in compound 7, [Ir III {C(CHCO 2 Et)(dppm) 2 -4 P,C,C 0 ,P 0 }(CH 2 CO 2 Et)-(CO)]Cl 2 (Fig. 5). The asymmetric unit comprises one complex molecule of 7 and additionally of two methylene chloride solvent molecules and 1.5 molecules of water. In comparison with complex 5, the structural features have not changed dramatically, with some slight variations for bond lengths and angles (Table 1) Molecular structure of the complex cation in 5 and the counter-anion. Displacement ellipsoids are drawn at the 30% probability level. For clarity, only the ipso carbon atoms of the phenyl groups are presented and the solvent molecules are omitted. Table 1 Selected bond lengths (Å ) and angles ( ) of the compounds 4, 5, 6 and 7.

Figure 4
Molecular structure of the complex cation in 6 and the counter-anion. Displacement ellipsoids are drawn at the 30% probability level. For clarity, only the ipso carbon atoms of the phenyl groups are presented and the solvent molecules are omitted.

Supramolecular features
In all crystal structures, the complex cations and counter-ions are packed in a way that leaves voids for various types of solvent molecules. Weak non-classical hydrogen-bonding interactions are observed between complex cations, chloride counter-ions and solvent molecules. Numerical details of these interactions are given in Tables 2-5, and discussed briefly below.
Moreover, compound 5 shows C-HÁ Á ÁO and C-HÁ Á ÁCl interactions (Table 3)  A view along the c axis of the crystal packing of compound 4. Only the H atoms involved in the most significant intermolecular interactions (Table 2) are displayed and the intramolecular interaction is omitted.

Figure 5
Molecular structure of the complex cation in 7 and the two counter-ions. Displacement ellipsoids are drawn at the 30% probability level. For clarity, only the ipso carbon atoms of the phenyl groups are presented and the solvent molecules are omitted.  Table 3 Hydrogen-bond geometry (Å , ) for 5.  7).

Figure 8
A view along the a axis of the crystal packing of compound 6. Only the H atoms involved in the most significant intermolecular interactions (Table 4) are presented and the intramolecular interactions are omitted.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 6. Diffraction data for all crystals were measured by using multiple scans to increase the number of redundant reflections. We found the data of sufficient quality to proceed without semi-empirical absorption methods.
Unless noted otherwise, H atoms in the four structures were placed geometrically and refined in the riding-model approximation with U iso (H) = 1.2U eq (C) for phenyl and methylene H atoms and 1.5U eq (C) for methyl H atoms.
For compound 4, the two hydrogen atoms bound to the central Ir1 atom and the C4 atom of the ethoxyoxoethanylidene moiety were discernible from a difference-Fourier map. They were refined with bond-length restraints of 0.96 Å (C4) and 1.60 Å (Ir1) and with individual U iso values. Three of the four methylene chloride solvent molecules are disordered. One solvent molecule (C9, Cl3, Cl4) shows half-occupation, one (C12, Cl9, Cl10) is disordered around an inversion centre (occupancy 0.25) and for one (C11, Cl7, Cl8) the Cl atoms show a positional disorder over two sites (ratio 0.7:0.3). All H atoms of the solvent molecules were omitted from the final model.
The scattering power of the crystal of compound 5 was poor. Hence, it was possible to collect reflections only up to 45 /2. The H atom attached to the C4 position was treated as described above. The methanol (C13, O6) and water (O7) solvent molecules are disordered around an inversion centre and were refined with half-occupation. H atoms of the disordered solvent molecules were omitted from the model. Furthermore, one phenyl group shows a 1:1 positional disorder and was refined over two sets of sites (C401-C406; C41A-C46A). All atoms of the disordered phenyl ring were refined isotropically.
In compounds 6 and 7, the H atom attached to the C4 position was treated as described above. For 6, localization of the H atoms of the methanol and water solvent molecules was not possible and hence they were omitted from the model. For 7, H atoms of water molecule O6 were located from a differ-   (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: publCIF (Westrip, 2010) and CHEMDRAW (Cambridge Soft, 2001).

(Bis{[(diphenylphosphanyl)methyl]diphenylphosphanylidene}(ethoxyoxoethanylidene)methaneκ 4 P,C,C′,P′)chloridohydridoiridium(III) chloride methylene chloride 2.75-solvate (4)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.03 e Å −3 Δρ min = −0.86 e Å −3 Special details 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. Hyrogen atoms at Ir1 and C4 were localized and refined with bond restraints: 96 pm at C4 and 160 pm at Ir1, respectively. There are four solvent molecules into the asymmetric unit, which are partial disordered (C9 occupational disorder with factor 0.5, C11 positional disorder of chlorine atoms wiht ratio 7:3 and C12 occupational disorder with factor 0.25). Hydrogen atoms at solvent were omitted.

Special details
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. Small crystal with low diffraction, but good quality. Reflections were collected only until 45 degrees (2Theta). Hydrogen at C4 was found and refined isotropically with bond restraint (d=0.96 angs.). Solvent molecules methanole and water lies nearby an inversion centre and were all refined with multipicity of 0.5 (C12-O5, C13-O6 and O7). Hydrogens of these disordered molecules were not exact logalized and omitted. A 1:1 positional disorder occurs for one phenyl group of the phospane (C401-C406 and C41A-C46A). The distance of the carbon atoms between disordered rings are small and all atoms were refined isotropically.

Special details
Experimental. All data sets were measured with several scans to increase the number of redundant reflections. In our experience this method of averaging redundant reflections replaces in a good approximation semi-empirical absorptions methods (absorption correction programs like SORTAV lead to no better data sets). 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. Hydrogen at C4 was found and refined isotropically with bond restraint (d=96pm). Hydrogens at water O6 were found and refined isotropically with bond restraints (d=84pm). The water molecule O7 was half occupied and hydrogen of it were omitted. The chlorine atoms at solvent dichloromethane CL5-C14-Cl6 were positional disordered in ratio around 2:1 (CL5-6: Cl5A-6A). C14=C14A with equal coordinates and displacement parameters for hydrogen calculation.