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

A new half‐sandwich imido compound, [Nb{η 5 ‐C 5 H 3 (SiMe 3 ) 2 }Cl 2 (N t Bu)] ( 1 ), was isolated by treatment of [Nb{η 5 ‐C 5 H 3 (SiMe 3 ) 2 }Cl 4 ] with 1 equiv. LiNH t Bu in hexane. Alkylimido derivatives [Nb{η 5 ‐C 5 H 3 (SiMe 3 ) 2 }RR′(N t Bu)] (R = Cl, R′ = Me 2 ; R = R′ = Me 3 , CH 2 SiMe 3 4 ) can be prepared by reaction of 1 with the appropriate alkylating reagent. Silsesquioxane ligand [Si 8 O 12 Cl( i Bu) 7 ] ( 5a ) can be obtained by treatment of [Si 7 O 9 (OH) 3 ( i Bu) 7 ] with 1 equiv. silicon tetrachloride in the presence of triethylamine. Ligand 5a reacts with NH 3  (g) at low temperatures to yield an amido derivative, [Si 8 O 12 (NH 2 )( i Bu) 7 ] ( 5b ), whereas the reaction of the trisilanol with excess BuLi leads to the corresponding lithium salt [Li 3 Si 7 O 12 ( i Bu) 7 ] ( 5c ). A dichlorido(silsesquioxanylimido)niobium compound [Nb{η 5 ‐C 5 H 3 (SiXMe 2 )(SiMe 3 )}Cl 2 {NSi 8 O 12 ( i Bu) 7 }] (X = Cl 6a , Me 6b ) can be prepared by reaction of 1 equiv. tetrachloridoniobium complex [Nb{η 5 ‐C 5 H 3 (SiXMe 2 )(SiMe 3 )}Cl 4 ] (X = Cl, Me) and amidosilsesquioxane 5b . From 6b , three new alkyl derivatives, [Nb{η 5 ‐C 5 H 3 (SiMe 3 ) 2 }XY(NSi 8 O 12 R 7 )] (R = i Bu, X = Cl, Y = Me 7 ; X = Y = Me 8 , CH 2 SiMe 3 9 ), were isolated by usual alkylation reactions. Alternatively, protonolysis reaction of trisilanol [Si 7 O 9 R 7 (OH) 3 ] with [Nb{η 5 ‐C 5 H 3 (SiXMe 2 )(SiMe 3 )}Cl 4 ] (X = Cl) in the presence of triethylamine produces a dichlorido derivative, [Nb{η 5 ‐C 5 H 3 (SiMe 3 )(Me 2 SiOSi 7 O 11 R 7 ‐κ 2 O,O )}Cl 2 ] (R = i Bu 10 ), which can be transformed into an imido complex, [Nb{η 5 ‐C 5 H 3 (SiMe 3 )(Me 2 SiOSi 7 O 11 R 7 ‐κ 2 O,O )}(N t Bu)] (R = i Bu 11 ), by reaction with LiNH t Bu, whereas for X = Me, a chlorido complex, [Nb{η 5 ‐C 5 H 3 (SiMe 3 ) 2 }Cl(Si 7 O 12 R 7 ‐κ 3 O,O,O )] (R = i Bu 12 ), can be isolated. Alkylation of 10 and 12 leads to dimethyl, trimethylsilylmethylidene and methyl derivatives 13 , 14 and 15 , respectively. Alkylimidoniobium complexes 2 – 4 react with carbon monoxide or xylyl isocyanide at room temperature to give acylimidoniobium [Nb{η 5 ‐C 5 H 3 (SiMe 3 ) 2 }R(N t Bu){C(R′)O‐κ 2 C , O }] (R = Cl, R′ = Me 16 ; R = R′ = Me 17 , CH 2 SiMe 3 18 ) and iminoacylimidoniobium [Nb{η 5 ‐C 5 H 3 (SiMe 3 ) 2 }R(N t Bu){C(Me)NAr‐κ 2 C , N }] (Ar = 2,6‐Me 2 C 6 H 3 ; R = Cl 21 , Me 22 ) compounds by simple insertion reactions. However, compound 13 reacts with CO and 2,6‐Me 2 C 6 H 3 NC, leading to enediolato [Nb{η 5 ‐C 5 H 3 (SiMe 3 )(Me 2 SiOSi 7 O 11 R 7 ‐κ 2 O,O )}{O(Me)C=C(Me)O‐κ 2 O , O }] (R = i Bu 19 ) and azaniobacyclopropane [Nb{η 5 ‐C 5 H 3 (SiMe 3 )(Me 2 SiOSi 7 O 11 R 7 ‐κ 2 O,O )}(CMe 2 NAr‐κ 2 C , N )] (R = i Bu, Ar = 2,6‐Me 2 C 6 H 3 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, 1 H, 13 C{ 1 H} and 29 Si{ 1 H} NMR spectroscopy and elemental analysis.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)