The Importance of Steric Factors in Iridium Pincer Complexes

POCOP
ligands (POCOP = C6H4-1,3-[OPR2]2) with R= tBu substituents on phosphorus
react with Ir­(CO)2Cl­(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.