Insertion of isocyanides into tantalum-methyl and tantalum-amido bonds

The imido-amido complex [TaCp*((NBu)-Bu-t)Cl((NHBu)-Bu-t)], 1, was isolated from the reaction of [TaCp*XCl4] with 3 equiv of (LiNHBu)-Bu-t. The dimeth yl [TaCp*((NBu)-Bu-t)Me-2], 2, and chloro-methyl [TaCp*((NBu)-Bu-t)ClMe], 3 , complexes were obtained by methylation of [TaCp*((NBu)-Bu-t)Cl-2] with 2 equiv of LiMe and 1 equiv of ZnMe2, respectively. Metathetical reactions of complex 3 with alkali metal salts MX (M = Na, X = OMe; M = Li, X = (OBu)-B u-t, NHtBu) afforded the new imido-methyl compounds [TaCp*((NBu)-Bu-t)MeX] (X = OMe 4, (OBu)-Bu-t 5, (NHBu)-Bu-t 6). Insertion of CNR (R = 2,6-Me2C6H3 ) into the Ta-(NHBu)-Bu-t and Ta-Me bonds of the imido-pentamethylcyclopent adienyl complexes 1-6 gave the eta(2)-iminocarbamoyl compound [TaCp*((NBu)- Bu-t)Cl{eta(2)-C((NHBu)-Bu-t)=NR}], 7, and the eta(2)-iminoacyl compounds [ TaCp*((NBu)-Bu-t)X(eta(2)-C(Me)=NR}] (X = Me 8, Cl 9, OMe 10, (OBu)-Bu-t 11 , (NHBu)-Bu-t 12), which under appropriate thermal conditions react with a second equivalent of CNR (R = 2,6-Me2C6H3) to give the double insertion imi ne-eta(2)-iminoacyl products [TaCp*((NBu)-Bu-t)X{eta(2)-C[C(Me)=NR]=NR}] (X = Me 13, Cl 14, OMe 15, (OBu)-Bu-t 16, (NHBu)-Bu-t 17). When compound 17 w as heated at 140 degrees C for 3 days, an intramolecular proton migration o ccurred to give the eta(2)-diamidoalkene complex [TaCp*((NBu)-Bu-t){eta-(NB u)-Bu-t-C(NHR)=C(Me)-eta-NR}], 18. All of the new compounds were characteri zed by IR, H-1 NMR; and C-13 NMR spectroscopy, and the molecular structures of 14 and 18 were studied by X-ray diffraction methods.