Isonitrile complexes of chromium(0) and molybdenum(0): characterisation and reactivity

The preparation of a series of isonitrile complexes, [(CO)6 –xM(CNR)x](x= 1–3; M = Cr, Mo; R = Me, Et, Pri, C6H11, But, p-tolyl, Ph, p-ClC6H4) is reported. The results of spectroscopic (i.r., u.v., mass, and n.m.r.— particularly aromatic solvent induced shifts) and electrochemical measurements are employed to assess the nature of the bonding in these systems. It is shown that the contribution of (d→π*)π-bonding is negligible and that variations in the donor strength of the isonitrile ligand are principally responsible for the changes observed. The compounds (RNC)Cr(CO)5 do not react with weak nucleophiles (amines, alcohols). Ketimine formation does not result from the reaction between (RNC)Cr(CO)5 and a silane in the presence of pyridine. The reaction between (RNC)2Cr(CO)4 and (Me2PCH2)2(dmpe) affords cis-(RNC)2(dmpe)Cr(CO)2 as the principal product, together with (dmpe)2Cr(CO)3.