Synthesis and Catalytic Activity of Iron Hydride Ligated with Bidentate N-Heterocyclic Silylenes for Hydroboration of Carbonyl Compounds

We report the synthesis of a novel bidentate N-heterocyclic silylene (NHSi) ligand, N-(LSO-N-methy1-2-pyridin-amine (1) (L = PhC(NtBu)(2)), and the first bischelate disilylene iron hydride, [(Si,N)(Si,C)Fe(H)(PMe3)] (2), and monosilylene iron hydride, [(Si,C)Fe(H)(PMe3)(3)] (2'), through C-sp(2)-H activation of the NHSi ligand. Compounds 1 and 2 were fully characterized by spectroscopic methods and single-crystal X-ray diffraction analysis. Density functional theory calculations indicated the multiple-bond character of the Fe-Si bonds and the pi back-donation from Fe(II) to the Si(II) center. Moreover, the strong donor character of ligand 1 enables 2 to act as an efficient catalyst for the hydroboration reaction of carbonyl compounds at room temperature. Chemoselective hydroboration is attained under these conditions. This might be the first example of hydroboration of ketones and aldehydes catalyzed by a silylene hydrido iron complex. A catalytic mechanism was suggested and partially experimentally verified.