Dinuclear Influence on the Mechanism, Reactivity, and Selectivity During Rh-Al Catalyzed Aryl Ether C-O Bond Reduction/Defunctionalization

Dinuclear metal complexes with a direct metal-metal interaction have the potential for unique mechanisms, intermediates, and selectivity during catalysis. Here we report density functional theory (DFT) calculations that directly evaluate the influence of a dinuclear metal-metal interaction during aryl C−O bond reduction/defunctionalization with either hydrosilane or bis(pinacolato)diboron (B2(pin)2) reagents catalyzed by a heterodinuclear Rh−Al complex. Our calculations demonstrate the critical Rh−Al cooperative behavior necessary for aryl C−O bond activation and catalytic turnover. However, only the Rh metal center is involved in hydrosilane Si−H bond activation to generate a defunctionalized arene or B−B bond activation of B2(pin)2 to form an aryl bornic acid pinacol ester. The calculations also reveal an unanticipated very strong ligand-to-substrate steric effect that controls reduction site selectivity.