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

Abstract

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 ( ηdmpm)Cl 2Ta(μ-NTol)(μ-η 2-HC=NTol)(μ-dmpm)taCl(n 2DtolF) ( I), both fragments from a CN bond cleavage of the di- p-toloformamidinate anion, DTolF −, namely tolylimido and tolylformomidoyl groups, are found forming bridges between the metal atoms. An amido group is also found in TaCl 2(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 CoCl 2(PhNCHNPhCHNPh) ( III), in which the divalent cobalt atom is in a pseudo-tetrahedral environment. The six-membered metallocycle formed by the C–N–C–N–C–N atoms is essentially planar. Reaction of K with crude Ta 2( μ 2- η 4-B 2H 6)( μ-DTolF) 4 produces [(B 2H 5)N(Tol)C(H)N(Tol)]Ta( μ 2-NTol) 2( μ 2-DTolF) 2Ta[(Tol)NC(H)N(Tol)B 2H 5] · 2Et 2O ( IV), in which a ditantalum unit is bridged by two DTolF and two tolylimido groups. A new ligand formed by fusion of a B 2H 5 − unit to a DTolF − anion chelates to each of the metal atoms. In the crystals, 50% of the B 2H 5 moieties are BH 3 groups. Coupling of two DPhF anions is observed in PhNC(H)N(Ph)C(H) (NPh) 2Ta(DPhF) 3·Et 2O ( V). The new dianion chelates the metal center, to which three other DPhF groups are attached giving an eight-coordinated compound.