Metal-assisted unorthodox reactions of formamidines: Coupling, cleavage and insertions

The purpose of this report is to call attention to the wide range of reactions that an amidine or amidinium may undergo in the presence of reduced metal ions, other than simple ligation of the metal ions. Crystal structures of five examples are presented. In (eta-dmpm)Cl2Ta(mu-NTol)(mu-eta(2)-HC=NTol)(mu-dmpm)TaCl(eta(2)-DTolF) (I), both fragments from a C-N bond cleavage of the di-p-tolylformamidinate anion, DTolF(-), namely tolylimido and tolylformimidoyl groups, are found forming bridges between the metal 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 neutral HDPhF molecule. A new neutral chelating ligand forms during the synthesis of CoCl2(PhNCHNPhCHNPh) (III), in which the divalent cobalt atom is in a pseudo-tetrahedral environment. The six-membered metallocycle 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 [(B2H5)N(Tol)C(H)N(Tol)]Ta(mu(2)-NTol)(2)(mu(2)-DTolF)(2)Ta[(Tol)NC(H)N(Tol)B2H5]. 2Et(2)O (IV), in which a ditantalum unit is bridged by two DTolF and two tolylimido groups. A new ligand formed by fusion of a B2H5- unit to a DTolF(-) anion chelates to each 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.