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.