High oxidation state chromium, molybdenum and tungsten imido metallasiloxanes

Abstract

Reactions between the bis-imido compounds [M(NBu^t)₂X₂] (M = Cr or Mo, X = Cl, M = W, X = NHBu^t) and tetraphenyldisiloxanediol (1∶1) in the presence of two equivalents of added py where X = Cl gave the products [{CrO(NBu^t)(O(Ph₂SiO)₂)}₂] 1, [Mo(NBu^t)(py)(O(Ph₂SiO)₂)₂] 2 and [W(NBu^t)(NH₂Bu^t)(O(Ph₂SiO)₂)₂] 3 showing a marked variation from Cr to Mo and W. Single crystal X-ray studies of 1·C₆H₅Me, 2·py and 3·C₆H₅Me were made. Compound 1 is the first chromium(VI) oxo-imido compound to be structurally characterised and the first example of a chromium(VI) monocyclic metallasiloxane. Compounds 2 and 3 incorporate the first examples of six-membered metallasiloxane rings for compounds of Mo or W. The compounds were also characterised by multinuclear NMR and mass spectroscopy.