(TRI-TERT-BUTYLSILYL)IMIDO COMPLEXES OF TITANIUM - BENZENE C-H ACTIVATION AND STRUCTURE OF [(TERT-BU3SINH)TI]2(MU-NSI-TERT-BU3)2

Treatment of TiCl4(THF)2 with 3.0 equiv of (t)Bu3SiNHLi in Et2O produced ((t)Bu3SiNH)3TiCl (1; 82%). An attempt to alkylate 1 with MeMgBr led to ((t)Bu3SiNH)3TiBr (2), alternatively prepared from 1 and MgBr2 (41%), and addition of MeLi to 1 yielded ((t)Bu3SiNH)2(Et2O)Ti = NSi(t)Bu3 (4; 55%) and CH4 via dehydrochlorination and Et2O trapping of transient [((t)Bu3SiNH)2Ti = NSi(t)Bu3] (3). The amido protons of 4 are deuterated through addition/elimination of a benzene-d6 C-D bond to the imido ligand of transient 3. A similar deuteration of 1, 2, and ((t)Bu3SiNH)4Ti (12) in C6D6 occurs via other reactive intermediates, [((t)Bu3SiNH)XTi = NSi(t)Bu3] (X = Cl (7), Br (8), (t)Bu3SiNH (3)), produced by loss of (t)Bu3SiNH2. Thermolysis of 1, 2, and 12 in C6D6/THF or THF afforded ((t)Bu3SiNH)(THF)XTi = NSi(t)Bu3 (X = Cl (9), Br (11), (t)Bu3SiNH (13)) and (t)Bu3SiNH2. Kinetic studies in C6D6/THF-d8 revealed that formation of 9 is THF independent, amine elimination is rate determining (k = 1.03 (1) x 10(-4) s-1 at 80.5-degrees-C; DELTA-H double-ended dagger = 23.3 (8) kcal/mol, DELTA-S double-ended dagger = -11 (2) eu; k(NH)3/k(ND)3 = 5.9 (6) at 90.4-degrees-C), and the rate of (t)Bu3SiNH2 loss increases 10-fold when 12 is thermolyzed, consistent with an amide abstraction mechanism. Alkylation of 9 with MeLi or (t)BuLi provided ((t)Bu3SiNH)(THF)RTi = NSi(t)Bu3 (R = Me (15), 55%; (t)Bu (16), 76%), respectively. Hydrogenation of either produced [((t)Bu3SiNH)Ti]2(mu-NSi(t)Bu3)2 (17; 61% (97% by H-1 NMR)) through dimerization of transient hydride [((t)Bu3SiNH)(THF)HTi = NSi(t)Bu3] (18), generated via sigma-bond metathesis of Ti-R, according to labeling experiments. Crystal data for 17: monoclinic, P2(1)/n, a = 12.033 (3) angstrom, b = 23.309 (5) angstrom, c = 22.741 (4) angstrom, beta = 99.314 (15)-degrees, V = 6294 (2) angstrom3, Z = 4, T = -80-degrees-C, R = 6.64%, R(w) = 7.75% (7806 reflections where ((F(o)) greater-than-or-equal-to 4-sigma(F(o)))). Dimer 17 has an unusual C2 structure with an extremely short Ti-Ti bond (2.442 (1) angstrom) and titanium atoms 0.58 and 0.60 angstrom exo to their respective amido and both mu-NSi(t)Bu3 ligands. EHMO calculations of 17 rationalize this geometry in terms of constraints imposed by the bridges and a single Ti-Ti bond of mixed composition.