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

Reactions of [TaCp*Cl-4] with two, three and four equivalents of (LiNHBu)-Bu-t give the halo- and amido-imido complexes [TaCp*Cl-2((NBu)-Bu-t)] (la), [TaCp*Cl((NBu)-Bu-t)((NHBu)-Bu-t)] (2) and [TaCp*((NBu)-Bu-t)((NHBu)-Bu-t)(2)] (3), respectively. The related complex [TaCp*Cl-2{N(2,6-Me2C6H3)}] (Ib) 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 la by reaction with SiClMe3. Complex la reacts with (CNBu)-Bu-t to give the 18-electron adduct [TaCp*Cl-2((NBu)-Bu-t)((CNBu)-Bu-t)] (4) whereas addition of excess CN(2,6-Me2C6H3) results in reductive elimination of the carbodiimide (BuN)-Bu-t=C=N(2,6-Me2C6H3) (5) to give [TaCp*Cl-2{CN(2,6-Me2C6H3)}(3)]. However complex Ib does not react with any of the isocyanide ligands. Both complexes la and Ib react with PhCHO undergoing imido/oxo exchange to give the imines PhCH=NR (R = Bu-t, 2,6-Me2C6H3 (6)) and dimeric [TaCp*Cl-2(O)](2) or trimeric [(TaCp*Cl)(3)(mu(2)-Cl)(mu(2)-O)(3)(mu(3)-O)] oxo-complexes, whereas only la reacts with CO2, PhCH=NR' (R' = Ph, Me) and (2,6-Me2C6H3)N=C=(NBu)-Bu-t producing (BuN)-Bu-t=CO, PhCH=(NBu)-Bu-t and (BuN)-Bu-t=C=(NBu)-Bu-t, 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)-Bu-t)((NHBu)-Bu-t)] activates C-H bonds when heated in benzene and toluene affording [TaCp*Ph((NBu)-Bu-t)((NHBu)-Bu-t)] (7) and a mixture of [TaCp*(m-MeC6H4)((NBu)-Bu-t)((NHBu)-Bu-t)] 8a and [TaCp*(p-MeC6H4)((NBu)-Bu-t)((NHBu)-Bu-t)] (8b). All of the reported organic compounds and tantalum complexes were characterized by H-1- and C-13-NMR spectroscopy. (C) 2000 Elsevier Science S.A. All rights reserved.