Catalysed and non-catalysed reaction between [Fe(CO)5] and isonitriles

Abstract

The reaction between [Fe(CO)₅] and isonitrile, RNC, is catalysed by CoCl₂·H₂O and readily yields the complexes [Fe(CO)_5–n(CNR)_n](n= 1–3, R = Me, C₆H₁₁, Bu^t, PhCH₂, Ph, 2,6-Me₂C₆H₃, or 2,4,6-Me₃C₆H₂; n= 4, R= Bu^t; n= 4 or 5, R = Ph, 2,6-Me₂C₆H₃, or 2,4,6-Me₃C₆H₂). The high-yield synthesis of [Fe(CO)₄(CNR)] from [Fe(CO)₅] and RNC in the absence of catalyst is also reported. Trimethylamine N-oxide has been used to synthesize [Fe(CO)₃(CNR)₂] from [Fe(CO)₄(CNR)] and RNC and results are compared with the CoCl₂ catalysed reaction. All products were characterized by i.r. and n.m.r. spectroscopy. The higher substituted derivatives were further characterized by reaction with l₂ and tetracyanoethylene (tcne) and gave [Fe(CO)_4–n(CNR)_n(tcne)](n= 2, R = Bu^t, PhCH₂, or 2,6-Me₂C₆H₃; n= 3, R = Bu^t or 2,6-Me₂C₆H₃; n= 4, R = 2,6-Me₂C₆H₃) and cis- and trans-[Fe(CNC₆H₃Me₂-2,6)₄I₂] from appropriate starting materials. Mechanistic data suggest that the reaction occurs via attack of catalyst at a co-ordinated CO ligand. Subsequent attack by unco-ordinated RNC in an intermolecular, non-bridging mechanism leads to the required isonitrile derivatives.