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-CAr 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 NiII.