N-Aryl β-diiminate complexes of the platinum metals

This perspective summarizes the chemistry of platinum metal complexes of beta-diiminate ligands bearing aryl groups at the nitrogen atoms. While beta-diiminate ligands mostly coordinate in a kappa(2)-N, N' mode, palladium complexes have a tendency to rearrange to C-bound structures (kappa(2)-N, C or mu-N, N':C). Diiminate ligands are remarkably effective at stabilizing coordinatively unsaturated metal centers, and the resulting reactive complexes often activate C-H bonds even of relatively unreactive substrates (ethers, alkanes). However, the ligands are not completely innocent: addition of H-2, O-2, olefins, alkynes and phosphaalkynes across M-C beta has been observed for several of the platinum metals, and may even be relevant to catalytic activity. A comparison with related ligands (triazapentadienyl, formazanate, bis(phosphinimino)methanate) suggests that the beta-diiminate ligand represents a lucky combination of steric rigidity and strong sigma (and pi?) donor character, making it an ideal platform for mechanistic studies of catalytic reactions.