Pt^II and Pd^II complexes with a trans-chelating bis(pyridyl) ligand

An atropisomeric bis(pyridyl) chelate ligand bis{3,3'-[N-Ph-2-(2'-py) indolyl]} (bpib) has been found to readily form trans-chelating Pd^II and Pt^II complexes. Two such complexes, Pt(bpib)Cl₂ and Pd(bpib)Cl₂ have been isolated and their structures were determined by single-crystal X-ray diffraction analysis. Both Pt(bpib)Cl₂ and Pd(bpib)Cl₂ have a chiral structure with C₂ symmetry. Pt(bpib)Cl₂ displays a long-lived phosphorescence with λ_em = 595 nm in a frozen CH₂Cl₂ solution at 77 K. To examine the potential use of the trans chelate bpib ligand in oxidative coupling reactions catalysed by Pd^II compounds, acetoxylation of benzene, chlorobenzene and toluene by PhI(OAc)₂ using Pd(OAc)₂/bpib (2:1) as the catalyst was examined and compared with the cis-chelating system Pd(OAc)₂/2,2'-bipyridine (bipy). The bpib system was found to accelerate the reaction but lower the overall yield.