Probing substituent effects on the activation of H2 by phosphorus and boron frustrated Lewis pairs
作者:Rebecca C. Neu、Eva Y. Ouyang、Stephen J. Geier、Xiaoxi Zhao、Alberto Ramos、Douglas W. Stephan
DOI:10.1039/c001133a
日期:——
The impact of substituent changes on phosphorus and boron-containing frustrated Lewis pairs (FLPs) has been examined. The phosphites (RO)3P R = Me, Ph form classical Lewis acid–base adducts of the formula (RO)3PB(C6F5)3 R = Me 1; R = Ph 2, whereas P(O-2,4-tBu2C6H3)3 and P(O-2,6-Me2C6H3)3 generate FLPs. Nonetheless, these latter combinations do not react with H2. The more basic phosphinite tBu2POR, R = tBu 3 reacts with B(C6F5)3 to give (tBu2(H)PO)B(C6F5)36. The related species tBu2POR, R = Ph 4; 2,6-Me2C6H35 showed no reaction with B(C6F5)3 but the FLPs react under H2 (4 atm) to give [tBu2P(OR)H][HB(C6F5)3] R = Ph 7 and 2,6-Me2C6H38. Similarly, tBu2PCl in combination with B(C6F5)3, generates an FLP that upon addition of H2, gives [tBu2PH2][ClB(C6F5)3] 9 albeit in low yield. The diborane 1,4-(C6F5)2B(C6F4)B(C6F5)2 in combination with either tBu3P or (C6H2Me3)3P generates FLPs that react with H2 to give [R3PH]2[1,4-(C6F5)2HB(C6F4)BH(C6F5)2] (R = tBu 11, C6H2Me312). Similarly PhB(C6F5)2 and tBu3P react with H2 giving [tBu3PH][HBPh(C6F5)2] 13. The combination of B(OC6F5)3 and PtBu3 also generate an FLP which reacts with H2 to give [HPtBu3][B(OC6F5)4] 14, the product of substituent redistribution. The boronic esters, (C6H4O2)BC6F515, (C6H3FO2)BC6F516 and (C6F4O2)BC6F517, and the borate esters B(OC6H3(CF3)2)318, B(OC6H2F3)319 and B(OC6H4CF3)320 were prepared and shown to generate FLPs with tBu3P or (C6H2Me3)3P. Nonetheless, no reaction with H2 was observed for 15-17. Collectively these data suggest that there is a threshold of combined Lewis acidity and basicity that is required to effect the splitting of H2.
替代基变化对含磷和硼的挫折路易斯对(FLPs)的影响进行了研究。磷酸酯 (RO)3P(R = Me,Ph)形成经典的路易斯酸碱加合物,化学式为 (RO)3PB(C6F5)3(R = Me 1;R = Ph 2),而 P(O-2,4-tBu2C6H3)3 和 P(O-2,6-Me2C6H3)3 则生成 FLPs。然而,这些后者组合不与 H2 反应。更基本的磷酸亚酯 tBu2POR(R = tBu 3)与 B(C6F5)3 反应生成 (tBu2(H)PO)B(C6F5)36。相关物种 tBu2POR(R = Ph 4;2,6-Me2C6H35)与 B(C6F5)3 不反应,但在 H2(4 atm)下 FLPs 反应生成 [tBu2P(OR)H][HB(C6F5)3](R = Ph 7 和 2,6-Me2C6H38)。类似地,tBu2PCl 与 B(C6F5)3 组合生成一个 FLP,该 FLP 在添加 H2 后生成 [tBu2PH2][ClB(C6F5)3] 9,尽管产率较低。二硼烷 1,4-(C6F5)2B(C6F4)B(C6F5)2 与 tBu3P 或 (C6H2Me3)3P 组合生成 FLPs,这些 FLPs 与 H2 反应生成 [R3PH]2[1,4-(C6F5)2HB(C6F4)BH(C6F5)2](R = tBu 11,C6H2Me312)。同样,PhB(C6F5)2 和 tBu3P 与 H2 反应生成 [tBu3PH][HBPh(C6F5)2] 13。B(OC6F5)3 和 PtBu3 的组合也生成一个 FLP,该 FLP 与 H2 反应生成 [HPtBu3][B(OC6F5)4] 14,这是取代基重新分布的产物。已制备以下硼酸酯:(C6H4O2)BC6F515、(C6H3FO2)BC6F516 和 (C6F4O2)BC6F517,以及硼酸盐酯 B(OC6H3(CF3)2)318、B(OC6H2F3)319 和 B(OC6H4CF3)320,表明这些酯与 tBu3P 或 (C6H2Me3)3P 可以生成 FLPs。然而,对于 15-17 号化合物未观察到与 H2 的反应。综合这些数据表明,实现 H2 分裂所需的路易斯酸度和碱度的结合存在一个阈值。