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 κ2-N,N′ mode, palladium complexes have a tendency to rearrange to C-bound structures (κ2-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.