Kajjana Boonpalit,† Chayapat Uthayopas,† and Panida Surawatanawong*,†,‡
†Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
‡Center of Sustainable Energy and Green Materials, Mahidol University, Salaya, Nakhon Pathom 73170, Thailand
The Lewis acid−transition metal bifunctional complex has recently emerged as a new class of catalysts. The nickel-borane complex, Ni[(Mes)B(o-Ph2PC6H4)2], has been reported as the efficient catalyst for H2 activation and styrene hydrogenation. Herein, we performed density functional calculations to investigate the cooperativity between the nickel and the group 13 element (Z = B and Al) including the effect of its substituent (R = Mes, Ph, and C6F5) on Ni[(R)Z(o-Ph2PC6H4)2] toward H2 activation and styrene hydrogenation. We found that H2 activation by the nickel-borane complex is dominated by the charge transfer from the s-bonding orbital of H2 to the p-based vacant orbital of boron while H2 activation by the nickel-alane complex is governed by the charge transfer from the d-based orbital of Ni to the s*-antibonding orbital of H2. The resulting trans-dihydride nickel-alane complex has the higher negative charges on both terminal and bridging hydrogen atoms in comparison with the corresponding nickel-borane complex. These support the lower energy barriers for the nickel-alane complex toward both H2 activation and the subsequent hydrogenation of styrene. While the C6F5 electron withdrawing substituent on boron of the nickel-borane complex facilitates H2 activation and styrene hydrogenation better than the phenyl or mesityl substituent, the substituent on aluminum does not affect the reactivity of the nickel-alane complex. As the H2 activation and the styrene hydrogenation by nickel-alane complex proceed with lower energy barriers than those by the nickel-borane complex, the nickel-alane complex with [(R)Z(o-Ph2PC6H4)2] ligand scaffold is suggested to be more reactive than the nickel-borane counterpart. Insights into the role of Lewis acid in this Z-type s-acceptor ligand scaffold will assist with the development of metal ligand bifunctional catalysts.
Reference: Boonpalit, K.; Uthayopas, C.; Surawatanawong, P.* Organometallics 2022, 41, 259. https://pubs.acs.org/doi/abs/10.1021/acs.organomet.1c00620