中性和阳离子二(叔丁基)环戊二烯基钛,锆和铪配合物的无配体的阳离子的动态NMR研究[M(1,3-吨卜2 - η 5 -C 5 H ^ 3)(η 5 -C 5 H 5)(CH 3)] +(M = Zr,Hf)
摘要:
含有二第4族金属配合物(叔丁基)环戊二烯基配位体(1,3-吨卜2 - η 5 -C 5 H ^ 3)已经被合成。1,3-和1,4-二(叔丁基)环戊二烯异构体的混合物与KH在THF中在-78°C下反应,得到盐K + [(1,3- t Bu 2 C 5 H 3)] -(THF)1-3 2为白色固体。用氯三甲基硅烷以1:1的摩尔比处理2,得到空气稳定的三甲基甲硅烷基环戊二烯基衍生物Si(1,3-t Bu 2 C 5 H 3)(CH 3)3 3。的甲硅烷基衍生物3是一个极好的前体的单环戊二烯三氯和锆化合物M(1,3-吨卜2 - η 5 -C 5 H ^ 3)氯3 [M =的Ti(4),锆(5)]。在NEt 3存在下将化学计量的水添加到4的甲苯溶液中,得到羰基三聚体化合物[Ti(1,3- t Bu 2 - η5 -C 5 H 3)Cl(μ- O)] 3 6。4与2equiv的反应。石灰,得到氯甲基衍生物的Ti(1
Catalyst structural effects in titanocene-catalyzed pinacol coupling: activity, stereoselectivity and mechanistic implications
摘要:
The effects of catalyst structural variation on the activity and selectivity of titanocene-catalyzed pinacol coupling of cyclohexane carboxaldehyde by Mn/TMSCl have been evaluated. Complexes which have been tested include: Cp2TiCl2 (1), Cp2TiBr2 (2), (C5Me5)(2)TiCl2 (3), (1,3-t-Bu2C5H3)(2)TiCl2 (4), (1,3-t-Bu2C5H3)(Cp)TiCl2 (5), ansa-[(eta (5)-tetrahydroindenyl)CH2CH2(eta (5)-tetrahydroindenyl)]TiCl2 (6), and ansa-[(eta (5)-Cp)CH2CH2(eta (5)-fluorenyl)]TiCl2 (7). Cp2TiCl2 (1) is the most active (pre)catalyst for pinacol silylether (8a) formation, but Brintzinger's complex 6 provides the best DL/meso diastereoselectivity (5:1). Complexes 2, 4 and 7 slowly catalyze the predominant formation of the corresponding pinacol acetal 9a as a secondary product. Comparative stoichiometric reactions of benzaldehyde/Me3SiCl with [Cp2TiCl . -MnCl2(THF)(2). Cp2TiCl] (10) and [Cp2TiCl](2) (11) result in highly diastereoselective pinacol silylether formation with binuclear 11 (29:1), but primarily the production of pinacol acetal (9b) from trimetallic 10, suggesting a dominant role for the binuclear complex (or derived mononuclear species) in the catalytic systems employing Cp2TiCl2/M/TMSCl, contrary to previous suggestions. (C) 2001 Elsevier Science B.V. All rights reserved.