The Importance of Steric Factors in Iridium Pincer Complexes

POCOP ligands (POCOP = C6H4-1,3-[OPR2](2)) with R= Bu-t substituents on phosphorus react with Ir(CO)(2)Cl(p-toluidine) to afford square planar Ir(I) carbonyl complexes. Replacement of tBu groups with iPr groups results in the formation of six-coordinate hydrido-chloride carbonyl complexes of Ir(III). Analogous reactions of POCOP ligands with R groups smaller than iPr require meta-disubstitution in the aromatic ring to prevent precipitation of an insoluble polymer upon metalation with iridium. Structures of five-coordinate cationic hydrido carbonyl species show that a small change in steric demand of the alkyl groups on phosphorus can open the metal coordination sphere, with smaller alkyl groups favoring six-coordinate Ir(III) complexes.