Heterobimetallic catechol-phosphine complexes with palladium and a group-13 element: structural flexibility and dynamics

Abstract

Group-13 metal acetylacetonates [M(acac)₃] (M = Al, Ga, In) or Al(OiPr)₃ react with a complex [Pd(catphosH)₂] that may act as chelating ligand towards a second metal, or with a mixture of catechol phosphine (catphosH₂) and [PdCl₂(cod)], to give heterometallic complexes featuring either dinuclear M(catphos)₂Pd or trinuclear M{(catphos)₂Pd}₂ motifs. Characterisation of the products by crystallographic and solution NMR studies gives insight into the structural diversity and flexibility of the coordination environments of the group-13 elements and their impact on the stability of the multinuclear complexes. The results indicate that gallium and indium are the most suitable elements for the stabilisation of di- and trinuclear assemblies, respectively. Dynamic NMR spectroscopy allowed to follow the dynamic averaging of the coordination environments of the four distinguishable catechol phosphines in the indium complex [M{(catphos)₂Pd}₂]H. The results revealed that the isomerisation follows a complicated pathway involving several distinguishable proton transfer steps, and allowed to propose a mechanistic explanation for the observed isomerisation.