Synthesis and Reactivity of Bimetallic 2-Phosphinoimidazole Complexes of Pt at the Pt(I/I) and Pt(III/III) Oxidation States

Abstract

Bimetallic transition metal complexes provide unique opportunities in catalysis over their monometallic counterparts because of their potential to benefit from direct metal–metal interactions. These interactions, which include the formation of M–M bonds, enable access to unique oxidation states that can impact reactivity and catalysis. In this work, we synthesize and characterize (single crystal X-ray analysis) dimeric Pt complexes at the Pt(I/I) and Pt(III/III) oxidation states scaffolded on a 2-phosphinoimidazole ligand framework. DFT-generated orbitals support the formation of metal–metal bonds in these complexes. We also compare the reactivity of these two new complexes to that of our previously reported Pt(I/III) dimer in Pt-catalyzed hydroamination, cycloisomerization, and amide reduction reactions. The Lewis acidic Pt(III/III) dimer provides the highest reactivity in reactions where the platinum complex serves as a π-acid (hydroamination, cycloisomerization). In contrast, the Pt(I/I) dimer is most active in silane-mediated amide reductions that involve the addition of Pt oxidatively into the Si–H bond.