Syntheses and Structures of Mg(C5H5BMe)2, Mg(3,5-Me2C5H3BNMe2)2, the 2,2‘-Bipyridine Adduct Mg(C5H5BMe)2(bipy), and the N-Bonded Aminoboratabenzene Species Mg(3,5-Me2C5H3BNMe2)2(THF)21

Abstract

The donor-free magnesocene analogues bis(1-methylboratabenzene)magnesium (1) and bis[3,5-dimethyl-1- (dimethylamino)boratabenzene]magnesium (2) are synthesized in good yields by the reactions of dimethylmagnesium with (trimethylstannyl)dihydroborinine precursors 3 and 4. In the crystalline state, both 1 and 2 possess sandwich structures with eta 6-coordinated boratabenzene ligands and display crystallographic centrosymmetry. Compound 1 reacts with the nitrogen donor 2,2'-bipyridine to give the Lewis base adduct (1)(bipy) (identical to 5). In the crystal structure of 5, one boratabenzene ligand is eta 6-bonded to the central metal while the other ligand adopts an eta 1-bonding mode. Crystallization of compound 2 from THF produces the solvate (2)(THF)2 (identical to 6), which exhibits a distorted tetrahedral N2O2 coordination environment around the magnesium atom. The average Mg-N bond distance is 2.141(3) A, and the N-Mg-N angle is 148.0(1) degrees. The observation of an aminoboratabenzene that is solely sigma-bonded to a metal is without precedent.