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

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 CH, groups 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.