SYNTHESIS AND CHARACTERIZATION OF NEW D0 TUNGSTEN AND MOLYBDENUM IMIDO COMPLEXES WITH HETEROATOMIC BIFUNCTIONAL O-N CHELATE LIGANDS

New tungsten d0 bis(imido) compounds of formula W(NCMe3)2(O-N)2 (2a-e) (HO-N = 2-hydroxypyridine, 2-pyridinecarboxylic acid, 8-hydroxyquinoline, 8-hydroxyquinaldine, 2-(2-hydroxyphenyl)benzothiazole, and 2-(2-hydroxyphenyl)benzoxazole) have been prepared from the bis(amido) bis(imido) compound W(NCMe3)2(NHCMe3)2 (1) by protonation and subsequent replacement of the amido groups with heteroatomic chelate ligands of the type HO-N which are weak acids and strong nitrogen bases. Solution spectroscopic data suggest that the new hexacoordinate tungsten(VI) imido complexes are monomeric and six-coordinate with equivalent imido ligands. The four-coordinate molybdenum bis(imido) complex Mo(NCMe3)2(OSiMe3)2 (3) reacts with 1,2-dihydroxybenzene (CatH-2) in the presence of pyridine, yielding the six-coordinate compound of formula Mo(NCMe3)(Cat)(OSiMe3)2(PY) (4), while the reaction with 2 equiv of the heteroatomic chelate ligand 8-hydroxyquinoline yields the six-coordinate mixed oxo imido compound of formula Mo(NCMe3)(O)(N-O)2 (5) (HO-N = 8-hydroxyquinoline) by elimination of tert-butylamine and hexamethyldisiloxane. In a different manner, the protonation of the isoelectronic organomolybdenum species Mo(NCMe3)2(Mes)2 (6) (Mes = 2,4,6-trimethylphenyl) with 1 equiv of 8-hydroxyquinoline or 8-hydroxyquinaldine results in the cleavage of one mesityl group, leading to the formation of five-coordinate compounds of formula Mo(NCMe3)2(Mes)(O-N) (7a,b).