Iron complexes supported by silyl-NHC chelate ligands: synthesis and use for double hydroboration of nitriles.

Iron complexes bearing new silyl-NHC bidentate ligands were synthesised by treating Fe(CO) with a mixture of -(hydrosilyl)methyl imidazolium salts and a base. These complexes showed high performance in the catalytic double hydroboration of nitrile with pinacolborane (HBpin) to produce ,-bis(boryl)amine by a combination of UV irradiation and mild heating (60 °C). The product yields for the hydroboration of aromatic and aliphatic nitriles reached 85%-95% (NMR) using an iron complex (5 mol%). Reducing the loading amount of the iron complex to 0.5 mol% still afforded the products in high yields. An analogous ruthenium complex, which was similarly synthesised using Ru(CO), showed lower activity. Stoichiometric reactions of the iron complex with nitriles afforded Fe(0)--silylimine complexes, which may be dormant states in nitrile hydroboration. A catalytic mechanism including Fe(0) -silylimine species is proposed.