Synthesis of Novel Mono(pentamethylcyclopentadienyl)tantalacycloalkyl and -tantalacycloalkylidene Complexes. Crystal Structure of [TaCp*Cl2{η3-C6H4(2-CH2NMeCH2)}]

TaCp*Cl 4 reacts with 1 equiv of Li[2-(CH 2 NMe 2 )C 6 H 4 ] to give the trichloroaryltantalum(V) complex [TaCp*Cl 3 {η 2 -C 6 H 4 (2-CH 2 NMe 2 )}] ( 1 ), containing the chelated arylamine ligand. Reaction of complex 1 with an additional 1 equiv of the lithium reagent causes C−H bond activation at one of the methylamino groups with β-H elimination, leading to the formation of the cyclometalated species [TaCp*Cl 2 {η 3 -C 6 H 4 (2-CH 2 NMeCH 2 )}] ( 2 ). Complex 2 reacts with a further 2 equiv of the lithium reagent giving the cyclometalated alkylidene complex [TaCp*{η 2 -C 6 H 4 (2-CH 2 NMe 2 )}{η 2 -C 6 H 4 (2-CH 2 NMeCH)}] ( 3 ), via α-H elimination. Thermally stable complex 2 reacts with 1 equiv of LiNMe 2 and LiNH t Bu to give the new chloroamidotantalacycloalkyl complexes [TaCp*Cl{η 2 -C 6 H 4 (2-CH 2 NMeCH 2 )}(NMe 2 )] ( 4 ) and [TaCp*Cl{η 2 -C 6 H 4 (2-CH 2 NMeCH 2 )}(NH t Bu)] ( 5 ). The imido complex [TaCp*{η 2 -C 6 H 4 (2-CH 2 NMeCH 2 )}(N t Bu)] ( 6 ) is obtained by reacting the monoamido derivative 5 with an additional 1 equiv of LiNH t Bu, whereas the related reaction of complex 4 with LiNMe 2 leads, via α-H elimination, to the tantalacycloalkylidene complex [TaCp*{η 2 -C 6 H 4 (2-CH 2 NMeCH)}(NMe 2 )] ( 7 ). A similar reaction is also observed when complex 2 is treated with 1 equiv of LiN(SiMe 3 ) 2, giving the chlorotantalacycloalkylidene complex [TaCp*Cl{η 2 -C 6 H 4 (2-CH 2 NMeCH)}] ( 8 ); no amido complex was isolated in this case. All compounds were characterized by IR and NMR spectroscopy. The structure of 2 was solved from diffractometer data by a combination of direct and Fourier methods and refined by full-matrix least squares.