IMIDO AND OXO COMPOUNDS OF CHROMIUM-(V) AND CHROMIUM-(VI) AND OF MOLYBDENUM-(VI) AND TUNGSTEN-(VI)

The interaction of 1,1,1,3,3,3-hexamethyldisilazane and CrO2Cl2 gives the amido complex CrO2[N(SiMe3)2] whereas MoO2Cl2 gives the imido complex Mo(NSiMe3)2(OSiMe3)2 and WOCl2(dme) (dme = 1,2-dimethoxyethane) gives a red oil that reacts with pyridine (py) to give WCl(NSiMe3)(OSiMe3)3(py). Interaction of CrO2[N(SiMe3)2] with pyridine and 4-methylpyridine (L) leads to reduction to the chromium(v) species [CrO(NSiMe3)L]2(mu-OSiMe3)2. Interaction of CrO2Cl2 with 2,2,6,6-tetramethylpiperidine gives the amido species CrO2Cl(NC9H18) while SiMe2(NHBut)2 gives Cr(NBut)2Cl2(NH2But). The crystal structures of the compounds [CrO(NSiMe3)(py)]2(mu-OSiMe3)2, CrO2Cl(NC9H16) and WCl(NSiMe3)(OSiMe3)3(py) have been determined. In the centrosymmetric dimeric complex the Cr atom is five-co-ordinate with a geometry intermediate between trigonal bipyramidal and square pyramidal. The crystals of CrO2Cl(NC9H18) contain two chemically equivalent tetrahedral molecules, while WCl(NSiMe3)(OSiMe3)(py) is octahedral with the pyridine ligand trans to the imido group.