Competitive insertion of isocyanide into tantalum-amido and tantalum-methyl bonds

The (amido)methyl complexes [Ta(η5-C5Me5)(NtBu)Me(NR2)] [R = Ph (3), SiMe3 (4)] were prepared by reaction of [Ta(η5-C5Me5)(NtBu)ClMe] (1) with the appropriate lithium amides. Attempts to isolate the analogous NHMe derivative afforded a mixture of complexes [Ta(η5-C5Me5)(NtBu)Me(NHMe)] (5) and [Ta(η5-C5Me5)(NMe)Me(NHtBu)] (6), resulting from hydrogen exchange between the amido and imido ligands. Insertion of CN(2,6-Me2C6H3) into the Ta−Me bond of complexes 3 and 4 gave the η1-iminoacyl derivatives [Ta(η5-C5Me5)(NtBu)(NR2){η1-C(Me)=N(2,6-Me2C6H3)}] [R = Ph (7), SiMe3 (8)], while insertion into the Ta−NRMe (R = H, Me) bond of the complexes [Ta(η5-C5Me5)(NtBu)Me(NRMe)] [R = H (5), Me (2)] gave the η2-iminocarbamoyl compounds [Ta(η5-C5Me5)(NtBu)Me{η2-C(NRMe)=N(2,6-Me2C6H3)}] [R = H (10), Me (9)]. All of the new compounds were characterized by 1H and 13C NMR spectroscopy. The X-ray crystal structure of 9 is reported. DFT calculations were carried out to justify the preference of the insertion either into the Ta−C or the Ta−N bond. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)