Crystal structures of the [IrIII{C(C4H6O2)(dppm)-κ3P,C,O}(dppm)H](CF3O3S)2 and [IrIII{C(C4H6O2)(dppm)-κ2P,C}(CO)(dppm)H](CF3O3S)2 phosphorus ylide complexes, generated by a Wittig-type carbon–carbon coupling reaction of a carbodiphosphorane PCP ligand system

Abstract

The reaction of [IrIII{C(dppm)2-κ3P,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, 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 phosphorus electron-donor atoms and the ylide carbon atom of the resulting [IrIII{C(C4H6O2)(dppm)-κ3P,C,O}(dppm)H](CF3O3S)2 complex, also termed as [bis(diphenylphosphanyl)methane]({[(diphenylphosphanyl)methyl]diphenylphosphanylidene}(ethoxyoxoethanylidene)methanylidene-κ3P,C,O)hydridoiridium(III) bis(trifluoromethanesulfonate), are in plane and the hydrido ligand and the carbonyl O atom are located trans to each other, perpendicular to the meridional plane. The addition of carbon monoxide causes a replacement of the carbonyl O atom of the acetate subunit by a carbonyl ligand, thereby creating [bis(diphenylphosphanyl)methane]carbonyl({[(diphenylphosphanyl)methyl]diphenylphosphanylidene}(ethoxyoxoethanylidene)methanylidene-κ2P,C}hydridoiridium(III) bis(trifluoromethanesulfonate)–dichloromethane–ethyl acetate (6/2/3) or, more simply, [IrIII{C(C4H6O2)(dppm)-κ2P,C}(CO)(dppm)H](CF3O3S)2·0.33CH2Cl2·0.5C4H8O2. One trifluoromethanesulfonate counter-ion of 3 shows positional disorder in a 2:1 ratio. Complex 4 shows pseudo-merohedral twinning (matrix: \overline{1} 0 0 0 \overline{1} 0 1 0 1). The dichloromethane solvent is disordered over two orientations with occupation factors of 0.5 and 0.166.

Keywords

• C=C coupling reaction
• carbodiphosphorane (CDP)
• iridium(III)
• PCP pincer
• ethyl diazoacetate
• crystal structure
• NMR