N-Aryl β-diiminate complexes of the platinum metals

This perspective summarizes the chemistry of platinum metal complexes of β-diiminate ligands bearing aryl groups at the nitrogen atoms. While β-diiminate ligands mostly coordinate in a κ(2)-N,N' mode, palladium complexes have a tendency to rearrange to C-bound structures (κ(2)-N,C or μ-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 H2, O2, olefins, alkynes and phospha-alkynes across M-Cβ 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 β-diiminate ligand represents a lucky combination of steric rigidity and strong σ (and π?) donor character, making it an ideal platform for mechanistic studies of catalytic reactions.