Successive Protonation And Methylation Of Bridging Imido And Nitrido Ligands At Titanium Complexes

The reactions of nitrido complexes [{Ti(eta(5)-C5Me5)(mu-NH)}(3)(mu(3)-N)] (1) and [{Ti(eta(5)-C5Me5)}(4)(mu(3)-N)(4)] (2) with electro-philic reagents ROTf (R = H, Me; OTf = OSO2CF3) in different molar ratios have allowed the structural characterization of a series of titanium intermediates en route to the formation of the ammonium salts [NR4]OTf and [NR4][Ti(eta(5)-C5Me5)(OTf4]. The treatment of the trinuclear imido-nitrido complex 1 with 5.5 equiv of triflic acid in toluene at room temperature led to the dinuclear complex [Ti-2(eta(5)-C5Me5)(2)(mu-N)(NH3)(mu-O2SOCF3)(2) (OTf)] (3) and [NH4]OTf. Compound 3, along with the ammonium salts [NMe4]OTf and [NMe4][Ti(eta(5)-C5Me5)(OTf4] (5), was also obtained in the reaction of 1 with 8 equiv of methyl triflate in toluene at 100 degrees C. The trinuclear complex [Ti-3(eta(5)-C5Me5)(3)(mu-N)(mu-NH)(2)(mu-O2SOCF3)(OTf)] (4), an intermediate in the formation of 3, was isolated in the treatment of 1 with 4 equiv of MeOTf, although compound 4 was prepared in better yield by treatment of 1 with Me3SiOTf (2 equiv). Addition of a large excess of MeOTf or HOTf reagents to solutions of 3 resulted in the clean formation of ammonium salts [NR4][Ti(eta(5)-C5Me5)(OTf4] (R = Me (5), H (6)). Treatment of the tetranuclear nitrido complex [{Ti(eta(5)-C5Me5)}(4)(mu(3)-N)(4)] (2) with 1 equiv of ROTf in toluene afforded the precipitation of the ionic compounds [{Ti(eta(5)-C5Me5)}(4)(mu(3)-N)(3)(mu(3)-NR)][OTf] (R = H (8), Me (9)), while a large excess of HOTf led to the formation of [{Ti(eta(5)-C5Me5))(4)(mu(3)-N)(3)(mu(3)-NH)][Ti(eta(5)-C5Me5)(OTf)(4)(NH3)] (10) by rupture of a fraction of tetranuclear molecules. Complex 2 reacted with 1 equiv of [M(eta(5)-C5H5)(CO)(3)H] (M = Mo, Cr) via hydrogenation of one nitrido ligand to give the molecular derivative [{Ti(eta(5)-C5Me5)}(4)(mu(3)-N)(3)(mu(3)-NH)] (11) and [{M eta(5)-C5H5)(CO)(3))(2)], while a second 1 equiv of [M(eta(5)-C5H5)(CO)(3)H] produced the ionic compounds [{Ti(eta(5)-C5Me5)}(4)(mu(3)-N)(2)(mu(3)-NH)(2)][M(eta(5)-C5H5)(CO)(3)] (M = Mo (12), Cr (13)) by protonation of another nitrido group. The X-ray crystal structures of 3-5, 9, 10, and 13 were determined.