METAL-ASSISTED UNORTHODOX REACTIONS OF FORMAMIDINES - COUPLING, CLEAVAGE AND INSERTIONS

The purpose of this report is to call attention to the wide range of r eactions that an amidine or amidinium may undergo in the presence of r educed metal ions, other than simple ligation of the metal ions. Cryst al structures of five examples are presented. In Tol)(mu-eta(2)-HC=NTo l)(mu-dmpm)TaCl(eta(2)-DTolF) (I), both fragments from a C-N bond clea vage of the di-p-tolylformamidinate anion, DTolF(-), namely tolylimido and tolylformimidoyl groups, are found forming bridges between the me tal atoms. An amido group is also found in TaCl2(NPh)(DPhF)(HDPhF) (II ), in which a six-coordinated tantalum atom is surrounded also by two chlorine atoms, a chelating diphenylformamidinate, DPhF(-) and a neutr al HDPhF molecule. A new neutral chelating ligand forms during the syn thesis of CoCl2(PhNCHNPhCHNPh) (III), in which the divalent cobalt ato m is in a pseudo-tetrahedral environment. The six-membered metallocycl e formed by th Co-N-C-N-C-N atoms is essentially planar. Reaction of K with crude Ta-2(mu(2)-eta(4)-B2H6)(mu-DTolF)(4) produces -NTol)(2)(mu (2)-DTolF)(2)Ta[(Tol)NC(H)N(Tol)B2H5]. 2Et(2)O (IV), in which a ditant alum unit is bridged by two DTolF and two tolylimido groups. A new lig and formed by fusion of a B2H5- unit to a DTolF(-) anion chelates to e ach of the metal atoms. In the crystals, 50% of the B2H5 moieties are BH3 groups. Coupling of two DPhF anions is observed in PhNC(H)N(Ph)C(H )(NPh)(2)Ta(DPhF)(3) . Et(2)O (V). The new dianion chelates the metal center, to which three other DPhF groups are attached giving an eight- coordinated compound. Copyright (C) 1997 Elsevier Science Ltd.