Syntheses of 4-benzyl-3,5-dimethylpyrazolylborato complexes of molybdenum and tungsten nitrosyls: molecular structure of [Mo(CO)2(NO){HB(3,5-Me2-4-PhCH2C3N2)3}], a complex with an ‘inverted’ bowl-like structure
Abstract
Reaction of [HB(bdmpz)3]–, obtained by reaction of 4-benzyl-3,5-dimethylpyrazole (Hbdmpz) with KBH4, with [M(CO)6](M = Mo or W) and p-MeC6H4SO2N(NO)Me afforded [M(CO)2(NO)-{HB(bdmpz)3}](M = Mo or W). The molybdenum carbonyl was converted into [Mo(NO)-{HB(bdmpz)3}X(Y)](X = Y = Cl, I or OC6H4Me-p; X = Cl, Y = OMe or OC6H4Me-p) the spectral and electrochemical properties of which are virtually identical to those of [Mo(NO){HB(dmpz)3}X(Y)](Hdmpz = 3,5-dimethylpyrazole), indicating that the addition of a benzyl group has no significant electronic effect in the new species. However, a crystal and molecular structure determination of [Mo(CO)2(NO){HB(bdmpz)3}] revealed that the molecule has a highly symmetrical structure, the CH2groups of the benzyl groups in the tris(pyrazolyl)borate ligand being disposed in a star-shaped configuration where the phenyl rings adopt an ‘inverted’ bowl-like structure with the BH group inside and the Mo(CO)2(NO) group outside the bowl. The arrangement of the 4-benzyl groups with respect to the pyrazolyl rings and the H–B ⋯ Mo three-fold axis is strongly reminiscent of an inverted three-legged ‘Isle of Man’ symbol.