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

Abstract

TaCp*Cl4 reacts with 1 equiv of Li[2-(CH2NMe2)C6H4] to give the trichloroaryltantalum(V) complex [TaCp*Cl3{η2-C6H4(2-CH2NMe2)}] (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*Cl2{η3-C6H4(2-CH2NMeCH2)}] (2). Complex 2 reacts with a further 2 equiv of the lithium reagent giving the cyclometalated alkylidene complex [TaCp*{η2-C6H4(2-CH2NMe2)}{η2-C6H4(2-CH2NMeCH)}] (3), via α-H elimination. Thermally stable complex 2 reacts with 1 equiv of LiNMe2 and LiNHtBu to give the new chloroamidotantalacycloalkyl complexes [TaCp*Cl{η2-C6H4(2-CH2NMeCH2)}(NMe2)] (4) and [TaCp*Cl{η2-C6H4(2-CH2NMeCH2)}(NHtBu)] (5). The imido complex [TaCp*{η2-C6H4(2-CH2NMeCH2)}(NtBu)] (6) is obtained by reacting the monoamido derivative 5 with an additional 1 equiv of LiNHtBu, whereas the related reaction of complex 4 with LiNMe2 leads, via α-H elimination, to the tantalacycloalkylidene complex [TaCp*{η2-C6H4(2-CH2NMeCH)}(NMe2)] (7). A similar reaction is also observed when complex 2 is treated with 1 equiv of LiN(SiMe3)2, giving the chlorotantalacycloalkylidene complex [TaCp*Cl{η2-C6H4(2-CH2NMeCH)}] (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.