Studies on the chemical reduction of polynuclear titanium(IV) nitrido complexes.

The redox chemistry of cube-type titanium(IV) nitrido complexes [{Ti(η-CMe)(R)}(μ-N)] (R = η-CMe (1), N(SiMe) (2), η-CHSiMe (3), and η-CH (4)) was investigated by electrochemical methods and chemical reactions. Cyclic voltammetry studies indicate that 1-4 undergo a reversible one-electron reduction at -1.8 V . ferrocenium/ferrocene. Thus, complex 1 reacts with sodium sand in tetrahydrofuran to produce the highly reactive ionic compound [Na(thf)][{Ti(η-CMe)}(μ-N)] (5). The treatment of complexes 1-4 in toluene with one equivalent of [K(CMe)] in the presence of macrocycles (L) leads to CMe and the formation of more stable derivatives [K(L)][{Ti(η-CMe)(R)}(μ-N)] (R = η-CMe, L = 18-crown-6 (6), crypt-222 (7); R = N(SiMe), L = 18-crown-6 (8), crypt-222 (9); R = η-CHSiMe, L = 18-crown-6 (10), crypt-222 (11); R = η-CH, L = crypt-222 (12)). However, the analogous reaction of 4 with [K(CMe)] and 18-crown-6 affords [{(18-crown-6)K}(μ-η:η-CH)][{Ti(η-CMe)(η-CH)}(μ-N)] (13) abstraction of one cyclopentadienide group from a putative intermediate [(18-crown-6)K(μ-η:η-CH)Ti(η-CMe)(μ-N)]. In contrast to the cube-type nitrido systems 1-4, the cyclic voltammogram of the trinuclear imido-nitrido titanium(IV) complex [{Ti(η-CMe)(μ-NH)}(μ-N)] (14) does not reveal any reversible redox event and 14 readily reacts with [K(CMe)] to afford CMeH and the diamagnetic derivative [{K(μ-N)(μ-NH)Ti(η-CMe)(μ-N)}] (15). The treatment of 15 with two equiv. of 18-crown-6 polyethers produces the molecular species [(L)K{(μ-N)(μ-NH)Ti(η-CMe)(μ-N)}] (L = 18-crown-6 (16), dibenzo-18-crown-6 (17)). Complex 17 further reacts with one equiv. of dibenzo-18-crown-6 to yield the ion-separated compound [K(dibenzo-18-crown-6)][Ti(η-CMe)(μ-N)(μ-N)(μ-NH)] (18) similar to the ion pair [K(crypt-222)][Ti(η-CMe)(μ-N)(μ-N)(μ-NH)] (19) obtained in the treatment of 15 with cryptand-222.