AMINOBORATABENZENES - AN EVALUATION OF THE EXOCYCLIC B-N INTERACTION

The reaction of 1-chloro-1-boracyclohexa-2,5-diene with diisopropylami ne or N-benzyl-N-methylamine followed by reaction with LDA in THF affo rds lithium N,N-diisopropyl-1-aminoboratabenzene (9b) or lithium N-ben zyl-N-methyl-1 -aminoboratabenzene (9c), respectively. The reaction of 9b with FeCl2 affords bis(N,N-diisopropyl-1-aminoboratab enzene)iron (18b), while the reaction of 9b or 9c with Mn(CO)(3)(CH3CN)(3)PF6 affo rds nyl[N,N-diisopropyl-1-aminoboratabenzene)manganese (19b) or tricar bonyl-1-(N-benzyl-N-methylamino) boratabenzene manganese (19b), respec tively. Photochemical displacement of CO by PMe(3) from 19b affords di carbonyl(trimethylphosphine) (N-benzyl-N-methyl-1-aminoboratabenzene)m anganese (20b). The rates of bond rotation about the B-N bonds of 9c, 18b, 19b,c, and 20b have been determined using variable-temperature NM R spectroscopy. The rates depend markedly on the electron-withdrawing power of the coordinating metal group. The boron atom is weakly coordi nated to manganese (B-Mn = 2.485(3) Angstrom) and strongly bound to ni trogen (B-N = 1.417 (3) Angstrom).