Synthesis of novel mono(pentamethylcyclopentadienyl)tantalacycloalkyl and -tantalacycloalkylidene complexes. Crystal structure of [TaCp*Cl-2{eta(3)-C6H4(2-CH(2)NMeCH(2))}]

TaCp*C-4 reacts with 1 equiv of Li[2-(CH(2)NMe(2))C6H4] to give the trichloroaryltantalum(V) complex [TaCp*Cl-3{eta(2)-C6H4(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 methylnmino groups with B-H elimination, leading to the formation of the cyclometalated species [TaCp*Cl-2{eta(3)-C6H4(2-CH(2)NMeCH(2))}] (2). Complex 2 reacts with a further 2 equiv of the lithium reagent giving the cyclometalated alkylidene complex [TaCp*{eta(2)-C6H4(2-CH(2)NMe(2))}{eta(2)-C6H4(2-CH(2)NMeCH)}] (3), via alpha-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{eta(2)-C6H4(2-CH(2)NMeCH(2))}(NMe(2))] (4) and [TaCp*Cl{eta(2)-C6H4(2-CH(2)NMeCH(2))}(NH(t)Bu)] (5). The imido complex [TaCp*{eta(2)-C6H4(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 alpha-H elimination, to the tantalacycloalkylidene complex [TaCp*{eta(2)-C6H4(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{eta(2)-C6H4(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.