C–N coupling in the gas-phase reactions of ammonia and [M(CH)]+ (M = Ni, Pd, Pt): a combined experimental/computational exercise

Abstract

Electrospray ionization (ESI) of methanolic solutions of monomeric nickel(II) acetate, [Ni(CH₃COO)₂], and tetrameric platinum(II) acetate, [Pt₄(CH₃COO)₈], leads to the formation of the corresponding methylidyne complexes [M(CH)]⁺ (M = Ni, Pt), which react with ammonia under C–N coupling. While the product couples M/[CH₄N]⁺ and [M(CH₂N)]⁺/H₂ are observed for both metals, hydrogen-atom expulsion to generate [M(CHNH₂)]⁺/H is only observed in the case of the nickel-containing system, and the proton transfer leading to M/[NH₄]⁺ is limited to platinum. Attempts to conduct related experiments with [Pd(CH)]⁺/NH₃ failed. The mechanisms that explain the experimentally observed reaction channels have been investigated computationally using the B3LYP functional for all metals of the nickel group (M = Ni, Pd, Pt). In line with labeling experiments using the reaction pairs [M(CD)]⁺/NH₃ and [M(CH)]⁺/ND₃ (M = Ni, Pt), two different mechanistic scenarios of the dehydrogenation process are operative for the Ni and Pt systems, respectively.