Crystal structures of the [IrIII{C(C4H6O2)(dppm)-κ3 P,C,O}(dppm)H](CF3O3S)2 and [IrIII{C(C4H6O2)(dppm)-κ2 P,C}(CO)(dppm)H](CF3O3S)2 phosphorus ylide complexes, generated by a Wittig-type carbon–carbon coupling reaction of a carbodiphosphorane PCP ligand system

The reaction of [IrIII{C(dppm)2-κ3 P,C,P′}ClH(NH3C2)]Cl with ethyl diazoacetate, a well known C=C coupling reagent, leads to the formation of a C=C unit, accompanied by N2 abstraction, and reorganization of a dppm subunit and, considered as a whole, to the transformation of the PCP pincer carbodiphosphorane system to a phosphorus ylide ligand. After removal of the halogenides, the iridium center is stabilized by the carbonyl O atom through the formation of a five-membered chelate ring. A PCO pincer ligand system is thereby generated, which coordinates the iridium(III) atom threefold in a facial manner. The addition of carbon monoxide causes a replacement of the carbonyl O atom of the acetate subunit by a carbonyl ligand.


Chemical context
A divalent carbon(0) atom in an excited singlet ( 1 D) state, which may act as an electron-donor atom towards one or two Lewis acids, opens up a wide range of functionalities and chemical properties (Petz & Frenking, 2010). We decided to investigate these intriguing properties in detail and to explore this unusual donor species, generally known as a carbodiphosphorane (CDP) carbon atom, in combination with the transition metal iridium. We had earlier designed a new and innovative PCP pincer ligand system, which allows the ISSN 2056-9890 stabilization of a carbodiphosphorane atom by two dppm subunits or, more precisely, by two tertiary phosphines via donor-acceptor interactions (Stallinger et al., 2007). The central carbon atom exhibits two lone electron pairs and can also be referred to as a phosphorus double ylide.
Treatment of our PCP pincer ligand system [CH(dppm) 2 ]Cl (Stallinger et al., 2007) with [Ir I Cl(cod)] 2 causes a threefold coordination of the iridium(I) transition metal, a deprotonation of the carbodiphosphorane carbon atom, followed by a protonation and a subsequent oxidation of the iridium(I) center. Addition of ethyl diazoacetate (EDA) to [Ir{C(dppm) 2 -3 P,C,P 0 }ClH(MeCN)]Cl complex 1 (Scheme 1) leads to a carbon-carbon coupling reaction via extrusion of a dppm subunit, which is stabilized by two phosphorusiridium(III) electron donor-acceptor interactions under the formation of a four-membered chelate ring. This reaction sequence, produced by the interaction of the doubly ylidic carbon atom with an electrophile containing the extraordinarily good dinitrogen withdrawing group, may be described as Wittig-type carbon-carbon coupling reaction, which has rarely been reported in carbodiphosphorane chemistry (Kolodiazhnyi, 1999;Petz & Frenking, 2010). Furthermore, in analogy to Schmidbaur (1983), a specification of the process as a substitution reaction, during which one phosphine is replaced by a carbene ligand, is possible. The alkylidene C(dppm) unit coordinates the iridium(III) metal center in a 2 P,C manner. Overall, the carbodiphosphorane has been converted into a phosphorus ylide ligand. Perpendicularly located to the dppm and C(dppm) units, the iridium(III) center coordinates a hydrido and a chlorido ligand trans to each other. Reaction of the monocationic [Ir{C(C 4 H 6 O 2 )(dppm)-2 P,C}Cl(dppm)H]Cl complex 2 with two equivalents of thallium(I)trifluoromethanesulfonate (TfOTl) causes the removal of the chlorido ligand and the chloride counter-ion with concomitant coordination of the acetate carbonyl oxygen atom in a facial manner, resulting in formation of the dicationic [Ir{C(C 4 H 6 O 2 )(dppm)-3 P,C,O}-(dppm)H](CF 3 O 3 S) 2 complex 3.
A similar ligand arrangement in the coordination sphere of manganese(I) was previously mentioned by Ruiz et al. (2005). Protonation of the -alkynyl functionality of the [Mn I (C C-CO 2 Me)(CO) 3 (dppm)] complex at low temperature generates the corresponding vinylidene [Mn I (C CH-CO 2 Me)(CO) 3 (dppm)]BF 4 complex, which rearranges via insertion of the vinylidene ligand into the manganese-phosphorus bond upon warming to room temperature to an [Mn I {(dppm)C CH(CO 2 Me)}(CO) 3 ]BF 4 complex. Exposure of complex 3 to carbon monoxide gas cleaves the iridium(III) carbonyl oxygen bond under coordination of a carbonyl ligand. Up to now, we have been unable to obtain suitable single crystals of complexes 1 and 2; however, it proved possible to crystallize the [Ir{C(C 4 H 6 O 2 )(dppm)-3 P,C,O}(dppm)H](CF 3 O 3 S) 2 (3) and [Ir{C(C 4 H 6 O 2 )(dppm)-2 P,C}(CO)(dppm)H](CF 3 O 3 S) 2 (4) products, the latter as a mixed dichloromethane-ethyl acetate solvate.
The solvated complex 4 crystallizes in the monoclinic space group P2 1 /c and each asymmetric unit contains two closely related formula units. Complex 4 can be described as a bulky dicationic iridium(III) complex, which is stabilized by two trifluoromethanesulfonate counter-ions (Fig. 2). In comparison with complex 3, many structural characteristics are similar. The iridium(III) metal atom shows a distorted octahedral geometry. It coordinates a dppm unit and a PCO pincer ligand system in a meridional manner and, perpendicular to this plane, a hydrido ligand. The only difference is that the carbonyl oxygen atom of the PCO ligand system is uncoordinated and has been substituted by a carbonyl ligand. The carbonyl ligand reveals relatively long Ir1-C8 [1.965 (15) Å ] and C8-O3 [1.116 (14) Å ] distances, caused by the location trans to the hydrido ligand. Moreover, the substitution results in an overall lengthening of the Ir-P and the Ir-C separations (Table 1). This effect is especially pronounced for the Ir1-C1 value, which rises by an amount of 0.07 Å . Additionally, the substitution causes an approximation of the C1-Ir1-P1 angle [88.5 (3) ] to a regular octahedral angle of about 90 and an increase of the C4-C1-Ir1 angle to a value of 134.0 (9) . Notably, the coordination of the carbonyl functionality has almost no effect on the C1-C4 double bond (Table 1) and considered in total the planar environment of the C1 atom [sum of the angles (C4-C1-P2; C4-C1-Ir1; P2-C1-Ir1) = 359.2 ] is barely affected. The sequence of ligand replacements and reorganizations for 2, 3 and 4 are shown in Fig. 3.

Supramolecular features
In the crystal of 3, the counter-ions interact with the hydrido ligand and with the hydrogen atoms of the dppm methylene groups, leading to CÁ Á ÁO and CÁ Á ÁF separations of between 3.188 (11) and 3.473 (10) Å (Table 2). Such interactions are well known in connection with dppm and related ligand systems (Jones & Ahrens, 1998).
In the extended structure of 4, the complex shows additional interactions between the trifluoromethanesulfonate counter-ions and the hydrido ligand and the hydrogen atoms of the dppm methylene groups, respectively (Table 3).

Synthesis and crystallization
The [CH(dppm) 2 ]Cl compound was prepared by a previously reported procedure (Reitsamer et al., 2012); other starting materials and solvents were obtained from commercial suppliers. All preparations were carried out under an inert gas atmosphere of dinitrogen by the use of standard Schlenk techniques. The 1 H, 13 C and 31 P NMR spectra were recorded on a Bruker DPX 300 NMR spectrometer and were referenced against the solvent peaks of dichloromethane, chloro- Structure of one of the two independent units in complex 4 with displacement ellipsoids drawn at the 30% probability level. For clarity, only the ipso carbon atoms of the phenyl groups are shown and the counter-ions and solvent molecules are omitted. Table 1 Selected distances and angles (Å , ) in complexes 3 and 4.

Figure 3
The sequence of ligand replacements and reorganizations accompanying the transformation of 2 into 3 and then 4.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. The data for both 3 and 4 were processed without absorption corrections. In relation to the structure determination of complex 3, the hydrido ligand was detected and refined isotropically. One trifluoromethanesulfonate counter-ion shows positional disorder in a 2:1 ratio, caused by an overlying of the C9, O16 and F16 positions. These positions were also refined isotropically.  Table 2 Hydrogen-bond geometry (Å , ) for 3. Symmetry codes: (i) x À 1 2 ; Ày þ 3 2 ; Àz þ 1; (ii) x þ 1 2 ; Ày þ 3 2 ; Àz; (iii) x À 1 2 ; Ày þ 3 2 ; Àz; (iv) Àx þ 3 2 ; Ày þ 2; z þ 1 2 . Table 3 Hydrogen-bond geometry (Å , ) for 4. determination of complex 4 resulted in the detection of pseudo-merohedral twinning (matrix: 1 0 0 0 1 0 1 0 1). Furthermore, the hydrido ligand was determined and refined isotropically by the use of a bond restraint of 1.6 Å and a fixed U iso value. The solvent dichloromethane shows disorder over two orientations, which can be described with occupation factors 0.5 and 0.166. Refinement of this solvent molecule was carried out by the usage of bond restraints and isotropic displacement parameters. Furthermore, the ethyl acetate molecule was located and modelled with equal anisotropic displacement parameters for O21, C22 and C23. H atoms bound to Ir1 and C4 were located in a difference-Fourier map and refined isotropically. Other H atoms were positioned geometrically and refined using a riding model with C-H = 0.94-0.98 Å and U iso (H) = 1.2U eq (C).  (Nonius, 1999), DENZO and SCALEPACK (Otwinowski & Minor, 1997), XP in SHELXTL and SHELXS97 (Sheldrick, 2008), SHELXL2014/7 (Sheldrick, 2015) and ChemDraw (Cambridge Soft, 2001 For both structures, data collection: COLLECT (Nonius, 1999); cell refinement: DENZO and SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015). 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. Hydrogen atoms at C4 and Ir1 were found and isotropically refined. One trifat-anion is positional disordered in ratio 2:1 with overlying position for C9, O16 and F16. C, F and O atoms of this triflate were isotropically refined.