Abstract
After the successful creation of the newly designed PCP carbodi-phospho-rane (CDP) ligand [Reitsamer et al. (2012 ▸). Dalton Trans.41, 3503-3514; Stallinger et al. (2007 ▸). Chem. Commun. pp. 510-512], the treatment of this PCP pincer system with the transition metal iridium and further the analysis of the structures by single-crystal diffraction and by NMR spectroscopy were of major inter-est. Two different iridium complexes, namely (bis-{[(di-phenyl-phosphan-yl)meth-yl]di-phenyl-phosphanyl-idene}methane-κ3P,C,P')carbonyl-chlorido-hydridoiridium(III) chloride di-chloro-methane tris-olvate, [IrIII(CO){C(dppm)2-κ3P,C,P'}ClH]Cl·3CH2Cl2 (1) and the closely related (bis-{[(di-phenyl-phosphan-yl)meth-yl]di-phenyl-phosphanyl-idene}methanide(1+)-κ3P,C,P')carbonyl-chlorido-hy-dridoirid-ium(III) dichloride-hydro-chloric acid-water (1/2/5.5), [IrIII(CO){CH(dppm)2-κ3P,C,P')ClH]Cl}2 (2), have been designed and both complexes show a slightly distorted octa-hedral coordinated IrIII centre. The PCP pincer ligand system is arranged in a meridional manner, the CO ligand is located trans to the central PCP carbon and a hydride and chloride are located perpendicular above and below the P2C2 plane. With an Ir-CCDP distance of 2.157 (5) Å, an Ir-CO distance of 1.891 (6) Å and a quite short C-O distance of 1.117 (7) Å, complex 1 presents a strong carbonyl bond. Complex 2, the corresponding CH acid of 1, shows an additionally attached proton at the carbodi-phospho-rane carbon atom located anti-periplanar to the hydride of the metal centre. In comparison with complex 1, the Ir-CCDP distance of 2.207 (3) Å is lengthened and the Ir-C-O values indicate a weaker trans influence of the central carbodi-phospho-rane carbon atom.
Highlights
PCP carbon and a hydride and chloride are located perpendicular above and below the P2C2 plane
Diverse PCP pincer systems have been generated and these systems are, in general, classified according to the charge of the central carbon atom. Both an anionic sp2 or sp3 hybridization of the central carbon atom is possible (Table 1) and the charge arises from the metallation of the pertinent C—H functionalities of the non-coordinated ligand subunits
PCP pincer complexes based on tropylium backbones
Summary
Based on a great number of investigations of iridium complexes in organic synthesis (Oro & Claver, 2009), on the large variety of metal–pincer ligand interactions and reactivities (Morales-Morales & Jensen, 2007; Choi et al, 2011), the catalytic and stoichiometric organometallic chemistry of iridium PCP pincer complexes attracted our attention. Diverse PCP pincer systems have been generated and these systems are, in general, classified according to the charge of the central carbon atom. The central carbon is part of a carbodiphosphorane (CDP) functionality and can be described as a naked carbon atom or as a divalent carbon(0) atom in an excited singlet (1D) state stabilized by two tertiary phosphines via donor–acceptor interactions. This central atom disposes of two lone-electron pairs and is able to interact with one or two Lewis acids (Petz & Frenking, 2010)
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