Monocyclopentadienyl(niobium) Compounds with Imido and Silsesquioxane Ligands: Synthetic, Structural and Reactivity Studies

Anew half-sandwich imido compound, [Nb{η5-C 5H3(SiMe3)2}Cl2(NrBu)] (1), was isolated by treatment of [Nb{η5C5H 3(SiMe3)2)Cl4] with 1 equiv. LiNHtBu in hexane. Alkylimido derivatives [Nb[η5-C5H 3(SiMe3)2)RR′(NiBu)] (R = Cl, R′ = Me 2; R = R′ = Me 3, CH2SiMe3 4) can be prepared by reaction of 1 with the appropriate alkylating reagent. Silsesquioxane ligand [Si8O12Cl(JBu)7] (5a) can be obtained by treatment of [Si7O9(OH)3(JBu)7] with 1 equiv. silicon tetrachloride in the presence of triethylamine. Ligand 5a reacts with NH3 (g) at low temperatures to yield an amido derivative, [Si8O12(NH2)(JBu)7] (5b), whereas the reaction of the trisilanol with excess BuLi leads to the corresponding lithium salt [Li3Si7O12(JBu)7] (5c), A dichlorido(silsesquioxanylimido)niobium compound [Nb{η5-C 5H3(SiXMe2)(SiMe3)}Cl 2[NSi8O12(IBu)7)] (X = Cl 6a, Me 6b) can be prepared by reaction of 1 equiv. tetrachloridoniobium complex [Nb{η5C5H3(SiXMe2)(SiMe 3)JCl4] (X = Cl, Me) and amidosilsesquioxane 5b. From 6b, three new alkyl derivatives, [Nb(η5C5H 3(SiMe3J2)XY(NSi8O 12R7)] (R = i'Bu, X = Cl, Y. = Me 7; X = Y. = Me 8, CH2SiMe3 9), were isolated by usual alkylation reactions. Alternatively, protonolysis reaction of trisilanol [Si7O 9R7(OH)3] with [Nb{η5-C 5H3(SiXMe2)(SiMe3))Cl4] (X = Cl) in the presence of triethylamine produces a dichlorido derivative, [Nb[η5-C5H3(SiMe3)(Me 2SiOSi7O11R7-K20,0)} Cl2] (R = iBu 10), which can be transformed into an imido complex, [Nb{η5-C5H3(SiMe3)(Me 2SiOSi7O11R7-K2O,O)} (NtBu)] (R = iBu 11), by reaction with LiNHiBu, whereas for X = Me, a chlorido complex, [Nb[η5-C5H3(SiMe3) 2}Cl(Si7O12R7K3O,O,O)] (R = iBu 12), can be isolated. Alkylation of 10 and 12 leads to dimethyl, trimethylsilylmethylidene and methyl derivatives 13, 14 and 15, respectively. AlkyUmidoniobium complexes 2-4 react with carbon monoxide or xylyl isocyanide at room temperature to give acylimidoniobium [Nb[η5C 5H3(SiMe3)2)R(NiBu){C(R′)O- K2C,O}] (R = Cl, R′ = Me 16; R = R′= Me 17, CH 2SiMe3 18) and iminoacylimidoniobium [Nb[η 5-C5H3(SiMe3)2}R(NtBu) {C(Me)NAr-K2C,N}] (Ar = 2,6Me2C6H3; R = Cl 21, Me 22) compounds by simple insertion reactions. However, compound 13 reacts with CO and 2,6Me2C6H3NC, leading to enediolato [Nb{η5-C5H3(SiMe 3)(Me2SiOSi7O11R7-K 2O,O)}{O(Me)C=C(Me)O-K2O,O}] (R = iBu 19) and azaniobacyclopropane [Nb[η5-C5H3(SiMe 3)(Me2SiOSi7O11R7-K 2O,O)J(CMe2NAr-K2CN)] (R = iBu, Ar = 2,6-Me2C6H3 20) derivatives through intermolecular coupling between two acyl groups and by a double methyl migration processes, respectively. All new compounds have been characterized by IR spectrophotometry, 1H, 13C{1H} and 29Si{1H} NMR spectroscopy and elemental analysis. © Wiley-VCH Verlag GmbH & Co. KGaA.