Exceptionally Facile CO Addition to a Saturated Ruthenium Complex

Synthesis and characterization of Cp*Ru[η3-HC(PPh2NPh)2], 1, reveals it to have a “piano stool” structure with the ligand bound to Ru(II) via two N and the unique, sp3 hybridized carbon. While the analogous (cymene) Ru[η3-HC(PPh2NPh)2]+ does not react with CO, under the same conditions, 1 adds one CO rapidly (25 °C, 1 atm CO). Characterization, including an X-ray structure determination, shows that CO has displaced one chelate ligand nitrogen, which then hangs off the molecule, free of Ru. DFT calculations reveal a possible mechanism via a remarkably low energy (+9.3 kcal/mol) intermediate, pendant N, but with one phenyl on phosphorus stabilizing Ru via donation from a C(ipso)C(ortho) bond. DFT calculations show that the electronic energy change for binding CO is over 20 kcal/mol less favorable for cymene than for C5Me5- as ligand; the reactivity difference is thus thermodynamic in origin.

对Cp*Ru[η³-HC(PPh₂NPh)₂]（记为1）的合成与表征结果显示，该配合物具有“钢琴凳型”结构，配体通过两个氮原子与钌(II)中心结合，同时连接一个独特的sp³杂化碳原子。尽管类似的（伞花烃）Ru[η³-HC(PPh₂NPh)₂]⁺配合物在相同条件下不与一氧化碳（CO）发生反应，但配合物1却能在25℃、1个标准大气压的CO氛围中快速结合一分子CO。包括X射线晶体结构测定在内的表征结果表明，CO取代了一个螯合配体的氮配位位点，该氮原子随后脱离钌中心，以悬挂基团的形式存在于分子中。密度泛函理论（Density Functional Theory，DFT）计算揭示了一条可能的反应机理：反应经历了一个能量极低（+9.3千卡/摩尔）的悬挂氮中间体，此时磷原子上的一个苯基可通过C(ipso)与C(ortho)之间的π键电子捐赠作用稳定钌中心。DFT计算还显示，以伞花烃为配体时，CO结合的电子能量变化比以五甲基环戊二烯基负离子（C₅Me₅⁻）为配体时高出20千卡/摩尔以上，因此该反应活性差异源于热力学本质。