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Reactions involving TaCl5 and LiX (where X = NMe2, NEt2, NPr2n, NBu2n, NMeBun, and NC5H10) were shown to produce substantially the pentaderivatives TaX5. The thermal decomposition of TaX5 (X = NMe2, NEt2, NPr2n, NBu2n, and NMeBun) was studied and only Ta(NMe2)5 could be sublimed unchanged. In other cases the main product of decomposition was a quinquevalent compound RN=Ta(NR2)3 and the secondary amine R2NH. Some olefin and quadrivalent Ta(NR2)4 were also detected and it is believed that decomposition involves the following sequence:[Formula: see text]This is in contrast to the behavior of niobium compounds, which appears to be:[Formula: see text]

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or 0, M = Ti, Zr, Nb, or Ta, and n is the valency of M, have been prepared by various methods. Their physicochemical properties have been studied and are compared with the corresponding metal tertiary alkoxides. The organosilyloxy-metal compounds appear to be less susceptible to hydrolysis or thermal decomposition than the metal tertiary alkoxides.TETRAKISTRIMETHYLSILYLOXYTITANIUM Ti(O*SiMe,), was first reported by English and Sommerl in 1955. Although other authors2*3*4s5 have since prepared this and other trialkylsilyloxytitanium compounds, the yields were often low and little was known about them when our systematic studies began. Furthermore we have extended these studies to cover other transition metals whose trialkylsilyloxy-derivatives are more difficult to prepare. Now we report the preparation of derivatives of titanium, zirconium, niobium, and tantalum together with the results of molecular-weight studies (ebulliometrically in benzene) and boiling points under reduced pressure.Preparative Methods.-English and Sommer's synthesis of tetrakistrimethylsilyloxytitanium involved the reaction between titanium tetrachloride and trimethylsilanol in benzene in the presence of ammonia, and they inferred that the low yield (18%) was caused by water produced in the acid-catalysed condensation of the silanol. Zeitler and Brown obtained a better yield (56%) by the silanolysis of titanium tetra-n-butoxide in boiling toluene :They isolated butoxytrimethylsilane among the products and it was thus clear that condensation of the silanol with the butyl alcohol liberated by silanolysis also produced water which hydrolysed the titanium compounds. This behaviour confirmed our independent experiences with the trimethylsilanolysis of titanium or zirconium isopropoxides and it was clear that good yields of these trimethylsilyloxy-derivatives would only result under conditions which suppressed the condensation reactions of the silanol. Obviously the concentrations of silanol and liberated alcohol (in the silanolysis) must be minimised. By

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