High oxidation state imido metallasiloxanes: synthesis and structural characterisation of novel bis-imido chromium(VI) and molybdenum(VI) compounds

Abstract

For reactions between [M(NBu^t)₂Cl₂] (M = Cr or Mo) or [Mo(NAr)₂Cl₂]·dme, Ar = 2,6-Prⁱ₂C₆H₃, dme = 1,2-dimethoxyethane, and tetraphenyldisiloxanediol, [O(Ph₂SiOH)₂] (2∶1), in the presence of a nitrogen donor base, changing the nitrogen donor from pyridine, py, to triethylamine, NEt₃, inhibited the protonation of imido groups and facilitated the formation of bis-imido compounds. Thus the compounds [Cr(NBu^t)₂(O(Ph₂SiO)₂)]₂1, [Mo(NBu^t)₂(O(Ph₂SiO)₂)₂] 2 and [Mo(NAr)₂(O(Ph₂SiO)₂)]₂3 were isolated when NEt₃ was used as base. Compound 3 was also formed when the dilithium reagent [O(Ph₂SiOLi)₂] was used. The pyridine adduct [Mo(NAr)₂Cl₂]·2py 4 was isolated from the reaction between [Mo(NAr)₂Cl₂] and O(Ph₂SiOH)₂ and py (1∶1∶2 molar ratio). Compounds 2, 3·C₆H₆ and 4·0.5C₆H₅Me have been characterised by X-ray crystallography. The dimeric composition of 1 in the gas phase and in benzene was confirmed by mass spectroscopy and cryoscopic molecular weight determination respectively. All compounds were characterised by NMR spectroscopy.