Cooperative metathesis of H–H/Sn–CAr bonds in stannylene-Ni0 systems

Abstract

The reaction of phosphine-appended (amido)(aryl)stannylenes (1) with Ni⁰ synthons leads to the facile formation of chelating-stannylene Ni⁰ complexes (2–4). Utilising the carbene-stabilised synthon IPr·Ni·(η⁶-toluene) (IPr = [(H)CN(Dipp)]₂C:; Dipp = 2,6-ⁱPr₂C₆H₃) leads to the high-yielding formation of targeted 16-electron Ni⁰ complexes. These systems activate H₂ under non-forcing conditions (1 bar, RT), all forming the same single product, 5, which is found to be a mono-hydrido stannylene complex. Alternative synthetic routes in combination with computational calculations demonstrate that this species features a bridging (i.e. [Sn-(µ-H)-Ni]) hydride ligand, and may be described either as an agostic [Sn–H–Ni] bonded hydrido-stannylene complex, or a formal nickelo-stannylene. The formation of compound 5 arises from the metathesis of the Sn–C^Ar bonds with H₂, leading to the elimination of Ar–H, which is detected by NMR and mass spectroscopic methods. The mechanism for this process, explored using DFT methods, proceeds through Ni-centre H₂ binding, Sn–Ni cooperative hydrogen activation, and subsequent Ar–H elimination via a cooperative C–H bond formation at the Ni and Sn centres. Finally, complex 5 is shown to undergo further Ph-H elimination of a single aryl group of the chelating phosphine arm with the bridging hydride ligand, forming a unique nickelo-stannylene complex 7, which features two formally Sn⁰ metallostannylene centres binding Ni^II.