杂双核(H)Rh-Cr配合物中乙烯插入RhI—H键反应的密度泛函研究

采用密度泛函理论B3LYP方法研究了配体和配位数对乙烯插入杂双核(CO)₄Cr(m-PH₂)₂RhH(L_n) (L＝CO或PH₃, n＝1或2)配合物中Rh—H键反应的影响. 计算结果表明, 六配位乙烯复合物中乙烯与铑之间轨道相互作用主要为乙烯到铑中心的s供体相互作用; 而五配位乙烯复合物中乙烯与铑中心间相互作用涉及乙烯到铑中心的s供体相互作用和铑到乙烯的p反馈作用. PH₃配体在热力学上不利于该反应. 处于氢配体对位的膦配体能加速乙烯插入反应. 乙烯插入的五配位反应途径占优势. Cr(CO)₄部分的引入降低了乙烯插入反应的活化能.

DFT Study on Ethylene Insertion into RhI-H Bond of Heterobinuclear (H)Rh-Cr Complexes

A theoretical study was carried out at the B3LYP level of theory to study the impact of the ligand and coordinate number on the ethylene insertion into the Rh—H bond of heterobinuclear (CO)₄Cr(m-PH₂)₂RhH(L_n) (L＝CO or PH₃, n＝1 or 2) complexes. It is shown that the bonding between ethylene and rhodium in the hexa-coordinate ethylene complexes is mainly the s-donation from ethylene to rhodium center, while the bonding between ethylene and rhodium in the penta-coordinate ethylene complexes involves the s-donation and p-back-donation. The PH₃ ligand inhibits the ethylene insertion thermodynamically. The phosphine ligand cis to the hydride ligand can enhance the ethylene insertion kinetically. The penta-coordinate pathway of the ethylene insertion is predominant. The introduction of Cr(CO)₄ moiety lowers the activation energy of the ethylene insertion.