We synthesized a PBP pincer ligand precursor 2 and demonstrated its complexation with iridium(I) to afford the coordinatively unsaturated [PBP](hydrido)chloroiridium complex 3 via B-H oxidative addition. The reaction of 3 with carbon monoxide produced [PBP](hydrido)chloro(carbonyl)iridium 7. The longer Ir-Cl bond length of 7 than that of 8 revealed a stronger sigma-donor ability of the PBP ligand than that of PCP. Complex 3 was also converted to [PBP](ethylene)iridium(I) complex 9 by the reaction with LiTMP under an ethylene atmosphere.
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Segawa et al. (2009) studied this question.