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

Article abstract of DOI:10.1016/S0277-5387(96)00366-X

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 (η-dmpm)Cl₂Ta(μ-NTol)(μ-η ²-HC=NTol)(μ-dmpm)TaCl(η²-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 the Co-N-C-N-C-N atoms is essentially planar. Reaction of K with crude Ta₂(μ₂-η⁴-B₂H ₆)(μ-DTolF)₄ produces [(B₂H₅)N(Tol)C(H)N(Tol)]Ta(μ₂NTol) ₂(μ₂-DTolF)₂Ta[(Tol)NC(H)N(Tol)B ₂H₅]·2Et₂O (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)₂Ta(DPhF)₃·Et₂O (V). The new dianion chelates the metal center, to which three other DPhF groups are attached giving an eight-coordinated compound. Copyright