Dynamic coordinative exchange in rhodium(I) complexes of chiral diphosphines bearing pendant pyridyl donor groups
作者:Jonathan L. Bookham、Darren M. Smithies、Mark Thornton Pett
DOI:10.1039/a908984e
日期:——
meso-Ph2PCH(Ph)CH(Ph)PPh2}, meso-Ph2PCH(pyr)CH(pyr)PPh2}, erythro-Ph2PCH(Ph)CH(pyr)PPh2}, rac-Ph2PCH(pyr)CH(pyr)PPh2}, threo-Ph2PCH(Ph)CH(pyr)PPh2}, and threo-Ph2PCH(Ph)CH(pym)PPh2}, [pyr = 2-pyridyl, pym = 2-pyrimidyl] reacted with [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) to give cationic rhodium(I) complexes [Rh(COD)L}]+ (L = diphosphine ligand), which were isolated as their PF6− salts, 1–6 respectively. In 2 and in 3 the phosphine ligand adopts a P,P′,N-coordination mode whereas 1, and 4–6 exhibit simple P,P′-coordination for the parent ligands and no evidence for N-coordination is observed. In solution 2 undergoes a fluxional process involving interchange of the coordinated and non-coordinated pyridyl environments. Variable temperature NMR studies revealed an enthalpy of activation (ΔH‡) of 64.3 kJ mol−1 and an entropy of activation (ΔS‡) of 0.005 kJ K−1 mol−1 for this process in ortho-dichlorobenzene solution. Complex 3 exhibits no similar fluxional behaviour. A single-crystal X-ray analysis of 2 revealed a nitrogen–rhodium distance of 2.369(3) Å for the coordinated pyridyl group, which is slightly longer than each of the phosphorus–rhodium distances [2.2868(7) Å and 2.3649(8) Å]. This suggests a relatively weak nitrogen–rhodium bonding interaction.
介-Ph2PCH(Ph)CH(Ph)PPh2}、介-Ph2PCH(PYR)CH(PYR)PPh2}、赤-Ph2PCH(Ph)CH(PYR)PPh2}、rac-Ph2PCH(PYR)CH(PYR)PPh2}、threo-Ph2PCH(Ph)CH(PYR)PPh2}和threo-Ph2PCH(Ph)CH(PYM)PPh2},[PYR = 2-吡啶基、pym = 2-嘧啶基]与[Rh(COD)Cl]2(COD = 1,5-环辛二烯)反应生成阳离子铑(I)配合物[Rh(COD)L}]+(L = 二膦配体),这些配合物分别以其 PF6 盐的形式分离出来,即 1-6。在 2 和 3 中,膦配体采用了 P、P′、N 配位模式,而 1 和 4-6 中的母配体则表现出简单的 P、P′配位,没有观察到 N 配位的迹象。在溶液中,2 经历了一个涉及配位和非配位吡啶基环境互换的流动过程。变温核磁共振研究显示,在正二氯苯溶液中,这一过程的活化焓(ΔH‡)为 64.3 kJ mol-1,活化熵(ΔS‡)为 0.005 kJ K-1 mol-1。络合物 3 没有类似的通量行为。2 的单晶 X 射线分析表明,配位吡啶基的氮铑距离为 2.369(3) Å,比磷铑距离[2.2868(7) Å 和 2.3649(8) Å]稍长。这表明氮-铑成键作用相对较弱。