EVIDENCE OF REVERSIBLE N-H EXCHANGE IN A 3-COORDINATE AMIDOZINC COMPLEX - SYNTHESES AND STRUCTURES OF 1-METHYL-2-((N-TERT-BUTYLAMINO)METHYL)BENZIMIDAZOLE COMPLEXES OF ZINC

1-Methyl-2-((N-tert-butylamino)methyl)benzimidazole 1 reacts with 1 equiv of Zn[N(SiMe(3))(2)](2) in nonpolar solvents (benzene, toluene) yielding the monomeric, 3-coordinate, planar amidozinc complex 3 and HN(SiMe(3))(2). Compound 3 has been characterized by H-1 and C-13 NMR spectroscopy, elemental. analysis, and X-ray crystallography. The crystal structure of this complex at -100 degrees C (monoclinic, P2(1)/n, a = 8.468(2) Angstrom, b = 18.700(4) Angstrom, c = 15.551-(2) Angstrom, beta = 98.10(2)degrees, Z = 4, R = 4.43%, R(W) 5.35%) shows two short, equivalent amidozinc bonds of 1.874(4) Angstrom and 1.887(4) Angstrom and a longer Zn-N coordinate covalent bond of 2.067(4) Angstrom to the benzimidazole N atom. No evidence of Zn- = N+ double bond character is found even though a N lone pair and an ''empty'', p-like Zn orbital are geometrically arranged for favorable overlap. Magnetization transfer studies show reversible, degenerate exchange between 3 and 1 at 40 degrees C. Compound 3 undergoes rapid, irreversible protonolysis with HNMe(2) to produce 1, HN(SiMe(3))(2), and a white precipitate. Addition of 1 to a Et(2)O solution of ZnCl2 immediately forms a white precipitate of 2. Single crystals of 2 were grown from CH2Cl2 solutions. The molecular structure of 2, determined by X-ray crystallography at -100 degrees C (monoclinic, P2(1)/n, a = 7.622(2) Angstrom, b = 14.378 (3) Angstrom, c 14.476(3) Angstrom, beta = 104.91(2)degrees, Z = 4, R = 3.14%, R(W) = 3.61%), shows the Zn atom in a distorted tetrahedral environment. Bonding between Zn and N atoms in four-coordinate 2 and three-coordinate 3 is compared.