Oxo and imido/imido exchange and C–H activation reactions based on pentamethylcylopentadienyl imido tantalum complexes

Reactions of [TaCp*Cl4] with two, three and four equivalents of LiNH Bu give the haloand amido-imido complexes [TaCp*Cl2(N Bu)] (1a), [TaCp*Cl(NBu)(NHBu)] (2) and [TaCp*(NBu)(NHBu)2] (3), respectively. The related complex [TaCp*Cl2{N(2,6-Me2C6H3)}] (1b) is prepared by a similar reaction using two equivalents of Li[NH(2,6-Me2C6H3)]. Complex 3 can be transformed into 2 and further into 1a by reaction with SiClMe3. Complex 1a reacts with CNBu to give the 18-electron adduct [TaCp*Cl2(N Bu)(CNBu)] (4) whereas addition of excess CN(2,6-Me2C6H3) results in reductive elimination of the carbodiimide BuN C N(2,6-Me2C6H3) (5) to give [TaCp*Cl2{CN(2,6-Me2C6H3)}3]. However complex 1b does not react with any of the isocyanide ligands. Both complexes 1a and 1b react with PhCHO undergoing imido/oxo exchange to give the imines PhCH NR (R= Bu, 2,6-Me2C6H3 (6)) and dimeric [TaCp*Cl2(O)]2 or trimeric [(TaCp*Cl)3(m2-Cl)(m2-O)3(m3-O)] oxo-complexes, whereas only 1a reacts with CO2, PhCH NR% (R%=Ph, Me) and (2,6-Me2C6H3)N C NBu producing BuN CO, PhCH NBu and BuN C NBu, respectively and the corresponding oxo or imido tantalum derivative. None of the complexes reacts with CO or NCR (R=Me, Ph). The complex [TaCp*Me(NBu)(NHBu)] activates C–H bonds when heated in benzene and toluene affording [TaCp*Ph(NBu)(NHBu)] (7) and a mixture of [TaCp*(m-MeC6H4)(NBu)(NHBu)] 8a and [TaCp*(pMeC6H4)(N Bu)(NHBu)] (8b). All of the reported organic compounds and tantalum complexes were characterized by Hand C-NMR spectroscopy. © 2000 Elsevier Science S.A. All rights reserved.