Reactivity of the 4-coordinate molecule (PNP)RhO (PNP is (tBu2PCH2SiMe2)2N) towards CO proceeds stepwise, first forming an η2-CO2 complex, by a mechanism which involves a preliminary adduct of CO on Rh, then a second CO displaces CO2. Reaction of the oxo complex with CO2 occurs in time of mixing even at low temperature to form (PNP)Rh(η2-CO3), with no intermediate detectable. DFT calculations indicate an initial bond formation between the oxo center and the CO2 carbon. Reaction of (PNP)RhO with H2 occurs only at a 1 : 2 molar stoichiometry, to ultimately form (PNP)Rh(H)2 and free H2O. No intermediate reaches detectable population even at −60 °C, but DFT mapping of various possible mechanisms on the singlet energy surface shows that the nearly equi-energetic (PNP)Rh(H2O) and (PNP)RhH(OH) are formed, but only the latter readily adds the second molecule of H2 to proceed to the observed products; these reactions thus both involve heterolytic splitting of H2.
4 配位分子 (
PNP)RhO(
PNP 为 (tBu2PCH2SiMe2)2N)与 CO 的反应是逐步进行的,首先形成一个 η2-
CO2 复合物,其机理是 CO 与 Rh 发生初步加成,然后第二个 CO 取代 。即使在低温条件下,氧化络合物与 也会在混合过程中发生反应,形成 (
PNP)Rh(η2-
CO3) ,没有检测到中间产物。DFT 计算表明,氧化中心与 碳之间形成了初始键。(
PNP)RhO 与 H2 的反应仅以 1 : 2 的摩尔
化学计量发生,最终形成 (
PNP)Rh(H)2 和游离
H2O。即使在-60 °C时,也没有中间产物达到可检测的数量,但对单线能表面各种可能机制的 DFT 绘图显示,形成了能量几乎相等的 (
PNP)Rh( ) 和 (
PNP)RhH(OH),但只有后者容易加入第二个 H2 分子,从而生成观察到的产物;因此,这些反应都涉及 H2 的异质裂解。