Hydrophenylation of ethylene using a cationic Ru(<scp>ii</scp>) catalyst: comparison to a neutral Ru(<scp>ii</scp>) catalyst
作者:Samantha A. Burgess、Evan E. Joslin、T. Brent Gunnoe、Thomas R. Cundari、Michal Sabat、William H. Myers
DOI:10.1039/c4sc01665c
日期:——
Charge neutral Ru(II) complexes of the type TpRu(L)(NCMe)Ph [Tp = hydridotris(pyrazolyl)borate; L = CO, PMe3, P(OCH2)3CEt or P(OCH2)2(OCCH3)] have been previously reported to catalyze the hydrophenylation of ethylene (Organometallics, 2012, 31, 6851–6860). However, catalyst longevity for the TpRu(L)(NCMe)Ph complexes is inhibited by competitive ethylene C–H activation. For example, ethylene C–H activation limits catalysis using TpRu(P(OCH2)3CEt)(NCMe)Ph to a maximum of 20 turnover numbers for conversion of benzene and ethylene to ethylbenzene. In contrast, reaction of the cationic Ru(II) complex [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr′4] [HC(pz5)3 = tris(5-methyl-pyrazolyl)methane; BAr′4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate] (0.025 mol% relative to benzene) in benzene with C2H4 (15 psi) at 90 °C gives 565 turnover numbers of ethylbenzene after 131 hours. The production of 565 turnovers of ethylbenzene corresponds to an approximate one-pass 95% yield with ethylene is the limiting reagent and is a 28-fold improvement compared to the charge neutral catalyst TpRu(P(OCH2)3CEt)(NCMe)Ph. Under identical conditions, the activity of [(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr′4] is only 1.3 times less than TpRu(P(OCH2)3CEt)(NCMe)Ph, but the increased stability of the cationic Ru(II) catalyst allows reactivity at much higher temperatures (up to 175 °C) and significantly enhanced rates.
电荷中性的 TpRu(L)(NCMe)Ph 型 Ru(II) 复合物[Tp = 三(吡唑基)硼酸氢化物;L = CO、PMe3、P(OCH2)3CEt 或 P(OCH2)2(OCCH3)]先前已被报道可催化乙烯的氢苯化反应(Organometallics,2012,31,6851-6860)。然而,TpRu(L)(NCMe)Ph 复合物的催化剂寿命受到乙烯 C-H 竞争性活化的抑制。例如,乙烯 C-H 活化限制了使用 TpRu(P(OCH2)3CEt)(NCMe)Ph 将苯和乙烯转化为乙苯的催化作用,最多只能达到 20 个周转数。相反,阳离子 Ru(II) 复合物[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr′4][HC(pz5)3 = 三(5-甲基吡唑基)甲烷;BAr′4 = 四[3,5-双(三氟甲基)苯基]硼酸酯](相对于苯 0.025摩尔%)与 C2H4(15 磅/平方英寸)在 90 °C的苯中反应,131 小时后可得到 565 个周转数的乙苯。与电荷中性催化剂 TpRu(P(OCH2)3CEt)(NCMe)Ph 相比,565 次乙苯翻转相当于约 95% 的单程产率,乙烯是限制性试剂,提高了 28 倍。在相同条件下,[(HC(pz5)3)Ru(P(OCH2)3CEt)(NCMe)Ph][BAr′4]的活性仅比 TpRu(P(OCH2)3CEt)(NCMe)Ph 低 1.3 倍,但阳离子 Ru(II) 催化剂稳定性的提高使得反应温度更高(高达 175 °C),反应速率也显著提高。