(Alkyl)‐ and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes

Alkylation of [TaCp*Cl 4 ] (Cp* = η 5 ‐C 5 Me 5 ) with 3 equiv. of MgCl(CH 2 SiMe 3 ) gives the chloridotris(trimethylsilylmethyl) complex [TaCp*Cl(CH 2 SiMe 3 ) 3 ] ( 1 ). TaCp*Cl 2 Me 2 reacts with 2 equiv. of LiR (R = CH 2 Ph, CH 2 SiMe 3 ) to give the mixed alkyl derivatives [TaCp*Me 2 R 2 ] (R = CH 2 Ph, 2 ; CH 2 SiMe 3 , 3 ). The dimethyldineopentyl complex [TaCp*Me 2 (CH 2 CMe 3 ) 2 ] ( 4 ) was obtained by reaction of TaCp*Cl 2 (CH 2 CMe 3 ) 2 with 2 equiv. of LiMe. The treatment of a toluene solution of TaCp*Cl 2 Me 2 with 2 equiv. of neophyllithium in a standard vacuum line gave a mixture of three compounds, [{TaCp*Me 2 (CH 2 CMe 2 Ph)} 2 ( μ ‐O)] ( 5 ), [TaCp*Me 2 (CH 2 CMe 2 – o ‐C 6 H 4 ‐κ 2 C , C )] ( 6 ) and [TaCp*Me(CH 2 CMe 2 Ph)(CH 2 )] ( 7 ), which were identified by NMR spectroscopy. However, when the reaction was carried out under rigorously anhydrous conditions, only complexes 6 and 7 were isolated. A chlorido(trimethylsilylmethyl)(trimethylsilylmethylidene) complex [TaCp*Cl(CH 2 SiMe 3 )(CHSiMe 3 )] ( 8 ) was prepared by heating 1 at 60 °C, or by leaving it at room temperature for a long time. A 3:2 ( 9 / 10 ) mixture of [TaCp*MeR(CHSiMe 3 )] (R = CH 2 SiMe 3 , 9 ; Me, 10 ) was obtained by thermal treatment of 3 , which was accompanied by the evolution of CH 4 and SiMe 4 . However, irradiation of a [D 6 ]benzene solution of 3 with a sun lamp gave a mixture of 9 and [TaCp*(CH 2 SiMe 3 )R(CH 2 )] (R = Me, 11 ; CH 2 SiMe 3 , 12 ) in a 2:1:1 ( 9 / 11 / 12 ) ratio. When a [D 6 ]benzene solution of 4 was heated at 60 °C, a mixture of the (alkyl)(neopentylidene) derivatives [TaCp*MeR(CHCMe 3 )] (R = Me, 13 ; CH 2 CMe 3 , 14 ) in a 4:1 ( 13 / 14 ) ratio was detected by NMR spectroscopy, while irradiation with a sun lamp produced a mixture ofalkylidene complexes [TaCp*(CH 2 CMe 3 )R(CH 2 )] (R = Me, 15 ; CH 2 CMe 3 , 16 ) in a 3:1 ( 15 / 16 ) ratio. On the other hand, the alkylation of TaCp*Cl 2 (CH 2 CMe 3 ) 2 with 2 equiv. of LiCH 2 SiMe 3 gave the (alkyl)(alkylidene) complex [TaCp*(CH 2 CMe 3 )(CH 2 SiMe 3 )(CHCMe 3 )] ( 17 ) with the elimination of SiMe 4 , whereas the treatment of TaCp*Cl 2 (CH 2 SiMe 3 ) 2 with the appropriate reagent gave [TaCp*(CH 2 R)(CH 2 SiMe 3 )(CHR′)] (R = R′ = Ph, 18 ; R = CMe 2 Ph, R′ = SiMe 3 , 19 ) with the elimination of SiMe 4 and CMe 3 Ph, respectively. All compounds were studied by IR and NMR spectroscopy, and the molecular structures of complexes 1 , 4 and 5 were determined by X‐ray diffraction methods. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)