Reactivity of TpRu(L)(NCMe)R (L = CO, PMe3; R = Me, Ph) systems with isonitriles: Experimental and computational studies toward the intra- and intermolecular hydroarylation of isonitriles

The Ru(II) phenyl complex TpRu(PMe3)(NCMe)Ph {Tp = hydridotris(pyrazolyl)borate} reacts with isonitriles to form complexes of the type TpRu(PMe3)(Ctriple bond; length of mdashNR)Ph (R = tBu, CH2Ph, CH2CH2Ph). Neither thermal nor photolytic reactions of these systems with excess isonitrile and benzene resulted in the production of corresponding imines. DFT studies that probed the energetics of the desired catalytic transformations revealed that (Tab)Ru(PH3)(Ctriple bond; length of mdashNCH2CH2Ph)Ph {Tab = tris(azo)borate} is the most stable species in a proposed catalytic cycle. Exclusive of calculated transition states, the highest points on the calculated free energy surface are 34 kcal/mol, for (Tab)Ru(PH3)(o,η2-C,C-CNCH2CH2Ph)Ph {relative to the starting material (Tab)Ru(PH3)(Ctriple bond; length of mdashNCH2CH2Ph)Ph}, and 27 kcal/mol for the C–H activation product (Tab)Ru(PH3)(o-C6H4CH2CH2NC) and benzene. The substantial increases in free energy result primarily from the loss of the stable ruthenium–η1-isonitrile interaction.