Reactions of tert-butyl isocyanate and trimethylsilyl azide with imidoamido compounds of chromium, molybdenum and tungsten

Abstract

tert-Butyl isocyanate and Cr(NBu^t)₂(NHBu^t)₂ react to form a complex containing the dianion of N,N′,N″-tri-tert-butylbiuret Cr(NBu^t)₂{[Bu^tNC(O)]₂NBu^t}. The crystal structure of its hydrogen-bonded adduct with [Bu^t(H)NC(O)]₂NBu^t has been determined and the ligand found to bind its three N atoms, whereas in solution the ¹H NMR spectrum indicates a six-membered chromium metallacyclic structure. Interaction of Mo(NBu^t)₂(NHBu^t)₂ and of Cr(NBu^t)₂[NH(C₆H₃Cl₂-2,6]₂ with Bu^tNCO, gives [Graphic Omitted] (NHR)]₂-(NBu^t)₂(M = Cr, R = C₆H₃Cl₂-2,6; M = Mo, R = Bu^t) confirmed by the crystal structure of the molybdenum compound as having N,O bonding in a four-membered metallacycle. The previously described tungsten analogue has been reformulated as having the same structure. In all these reactions Bu^tNCO is inserted into the M–N bond of the MNHR groups and not into that of the MNR imido groups. The tungsten ureato(1–)-N,O compound reacts with HCl in Et₂O to give WCl₃(NBu^t)(NHBu^t)-[OC(NHBu^t)₂] and the crystal structure confirms an octahedral structure with unidentate O-bonded di-tert-butylurea. Interaction of M(NBu^t)₂(NHBu^t)₂, M = Cr or W, with SiMe₃(N₃) gives, respectively, the azido species Cr(NBu^t)₂(N₃)₂ and [W(NBu^t)₂(N₃)(NH₂Bu^t)]₂(µ-N₃)₂. The structure of the latter has been confirmed by X-ray crystallography.