Direct access to non-symmetric lithium nitriloamidinate and disymmetric dilithium bisamidinate complexes from 1,3- or 1,4- dicyanobenzene and lithium amides

Abstract

Non-symmetric lithium nitriloamidinate complexes of composition 3- or 4-(N≡C)C6H4[C(NSiMe3)(NAr)]Li(D)n where Ar is phenyl, 2,6-(CH3)2C6H3 (Dmp) or 2,6-[(CH3)2CH]2C6H3 (Dipp); D means coordinated solvent - THF or diethylether and n = 1 or 2, were prepared from 1,3- or 1,4-dicyanobenzene and one molar equivalent of appropriate trimethylsilylated lithium amide. Disymmetric dilithium bisamidinate complexes of 1, 3- or 1, 4-{[(NSiMe3)(NAr)C]Li(D)n}2C6H4 type were prepared by the same procedure using two molar equivalents of lithium amides. When the isolated lithium nitriloamidinate complexes were reacted with lithium amide of another type, asymmetric dilithium bisamidinates 3- or 4-{[(NSiMe3)(NAr)C]Li(D)n}{[(NSiMe3)(NAr')C]Li(D)n}C6H4 were obtained and characterized. The reaction period for essentially quantitative conversion of the starting material to desired bisamidinates is strongly dependent on the substitution pattern of parent lithium amides as well as the dinitrile going from hours to more than forty days in the case of Dipp-substituted amide and 1,3-dicyanobenzene combination. In the solid state, complexes bearing less bulky substituent - phenyl - tend to aggregate to dinuclear species for lithium nitriloamidinates or linear polymers for bisamidinates. Presence of more sterically demanding substituents directed the structure of prepared compounds to mononuclear species with isobidentate bonding fashion of amidinates and two molecules of solvent being extra-coordinated to the lithium atom. For all lithium amidinates prepared, the central lithium atom has distorted tetrahedral coordination geometry with ligands being in an anisobidenate or bidentate-bridging bonding fashion.