Mechanistic Insight into H/D Exchange by a Pentanuclear Ni–H Cluster and Synthesis and Characterization of Structural Analogues of Potential Intermediates

Abstract

Experiments to gain mechanistic insight into catalytic H/D exchange of unactivated arenes by [(iPr3P)Ni]5H6 (1) are described. The reaction order with respect to 1, arene substrate, and added iPr3P were determined, as well as the temperature dependence of reaction rate. Site-selectivity data were obtained by monitoring the reaction of 1 with fluorobenzene and 2-methoxynaphthalene. H/D exchange competition reactions between arenes reacted with 1 were performed. The addition of an excess of Hg to a solution of 1 provided the new heterometallic cluster [(iPr3P)Ni]5H6(μ4-Hg) (2); this species also undergoes H/D exchange with C6D6, albeit more slowly than 1. Reaction of cluster 1 with TlCp (Cp = C5H5) gave (η5-Cp)Ni[(iPr3P)Ni]4(μ2-H)4(μ4-Tl) (3) with the loss of H2. A similar transfer of cyclopentadienyl to Ni occurred when 1 was reacted with MgCp2, to give (η5-Cp)Ni[(iPr3P)Ni]4H6(μ4-MgCp) (4), but not H2 loss. Reaction of 1 with cyclopentadiene gave the 5-coordinate hydride complex (η5-Cp)Ni[(iPr3P)Ni]4(μ2-H)...