Lewis Acid Binding and Transfer as a Versatile Experimental Gauge of the Lewis Basicity of Fe0, Ru0, and Pt0 Complexes

A number of zerovalent ruthenium tri-and tetracarbonyl complexes of the form [Ru(CO)(5-n)L-n] (n=1, 2) with neutral phosphine or N-heterocyclic carbene donor ligands have been treated with the Lewis acids GaCl3 and Ag+ to form a range of metal-only Lewis pairs (MOLPs). The spectroscopic and structural parameters of the adducts are compared to each other and to related iron carbonyl based MOLPs. The Lewis basicity of the original Ru-0 complexes is gauged by transfer experiments, as well as through the degree of pyramidization of the bound GaCl3 units and the Ru-M bond lengths. The work shows the benefits of the MOLP concept as one of the few direct experimental gauges of metal basicity, and one that can allow comparisons between metal complexes with different metal centers and ligand sets.