The tetrahydroborate ligand in [Ru(η2-BH4)(CO)H(PMe2Ph)2], 1, allows conversion under very mild conditions to [Ru(CO)(Et)H(PMe2Ph)3], 7, by way of [Ru(η2-BH4)(CO)Et(PMe2Ph)2], 4. Deprotection of the hydride ligand in 7
(by BH3 abstraction) occurs only in the final step, thus preventing premature ethane elimination. A deviation from the route from 4 to 7 yields [Ru(η2-BH4)(COEt)(PMe2Ph)3], 6, but does not prevent ultimate conversion to 7. Modification of the treatment of 4 yields an isomer of 7, 10. Both isomers eliminate ethane at temperatures above 250 K: the immediate product of elimination, thought to be [Ru(CO)(PMe2Ph)3], 11, can be trapped as [Ru(CO)(PMe2Ph)4], 12, [Ru(CO)H2(PMe2Ph)3], 3a, or [Ru(CO)(CCCMe3)H(PMe2Ph)3], 13. The elimination is a simple first-order process with negative ΔS‡ and (for 7) a normal kinetic isotope effect (kH/kD
= 2.5 at 287.9 K). These results, coupled with labelling studies, rule out a rapid equilibrium with a σ-ethane intermediate prior to ethane loss.
[Ru(η2-
BH4)(CO)H(PMe2Ph)2], 1 中的四氢
硼酸盐
配体可以在非常温和的条件下通过以下方式转化为 [Ru(CO)(Et)H(PMe2Ph)3], 7 [Ru(η2- )(CO)Et(PMe2Ph)2], 4. 7 中
氢化物配体的脱保护
(通过
BH3 提取)仅发生在最后一步,从而防止
乙烷过早消除。从 4 到 7 的路线偏离会产生 [Ru(η2- )(COEt)(PMe2Ph)3], 6,但不会阻止最终转化为 7。对 4 的处理进行修改会产生 7, 10 的异构体两种异构体在温度高于 250 K 时都会消除
乙烷:消除的直接产物被认为是 [Ru(CO)(PMe2Ph)3], 11,可以被捕获为 [Ru(CO)(PMe2Ph)4], 12, [Ru(CO)H2(PMe2Ph)3], 3a 或 [Ru(CO)(CCCMe3)H(PMe2Ph)3], 13. 消除是一个简单的一阶过程,ΔS‡ 为负且(对于 7)正常的动力学同位素效应 (kH/kD
= 2.5 (287.9 K)。这些结果与标记研究相结合,排除了
乙烷损失之前与 σ-
乙烷中间体的快速平衡。