REACTIONS OF TERT-BUTYL ISOCYANATE AND TRIMETHYLSILYL AZIDE WITH IMIDOAMIDO COMPOUNDS OF CHROMIUM, MOLYBDENUM AND TUNGSTEN

tert-Butyl isocyanate and Cr(NBut)2(NHBut)2 react to form a complex containing the dianion of N,N',N''-tri-tert-butylbiuret Cr(NBut)2{[ButNC(O)]2NBut}. The crystal structure of its hydrogen-bonded adduct with [But(H)NC(O)]2NBut has been determined and the ligand found to bind its three N atoms, whereas in solution the 1 H N M R spectrum indicates a six-membered chromium metallacyclic structure. Interaction of Mo(NBut)2(NHBut)2 and of Cr(NBut)2[NH(C6H3Cl2-2,6)]2 with Bu(t)NCO, gives M[N(But)C(O)(NHR)]2-(NBut)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(t)NCO 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 HCI in Et2O to give WCl3(NBut)(NHBut)-[OC(NHBut)2] and the crystal structure confirms an octahedral structure with unidentate O-bonded di-tert-butylurea. Interaction of M(NBut)2(NHBut)2, M = Cr or W, with SiMe3(N3) gives, respectively, the azido species Cr(NBut)2(N3)2 and [W(NBut)2(N3)(NH2But)]2(mu-N3)2. The structure of the latter has been confirmed by X-ray crystallography.