Water-Soluble Mo3S4 Clusters Bearing Hydroxypropyl Diphosphine Ligands: Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions

The [Mo3S4Cl3(dhprpe)3]+ (1+) cluster cation has been prepared by reaction between Mo3S4Cl4(PPh3)3 (solvent)2 and the water-soluble 1,2-bis­(bis­(hydroxypropyl)­phosphino)­ethane (dhprpe, L) ligand. The crystal structure of [1]2[Mo6Cl14] has been determined by X-ray diffraction methods and shows the typical incomplete cuboidal structure with a capping and three bridging sulfides. The octahedral coordination around each metal center is completed with a chlorine and two phosphorus atoms of the diphosphine ligand. Depending on the pH, the hydroxo group of the functionalized diphosphine can substitute the chloride ligands and coordinate to the cluster core to give new clusters with tridentate deprotonated dhprpe ligands of formula [Mo3S4(dhprpe-H)3]+ (2+). A detailed study based on stopped-flow, 31P­{1H} NMR, and electrospray ionization mass spectrometry techniques has been carried out to understand the behavior of acid–base equilibria and the kinetics of interconversion between the 1+ and the 2+ forms. Both conversion of 1+ to 2+ and its reverse process occur in a single kinetic step, so that reactions proceed at the three metal centers with statistically controlled kinetics. The values of the rate constants under different conditions are used to discuss on the mechanisms of opening and closing of the chelate rings with coordination or dissociation of chloride.[Mo3S4Cl3(dhprpe)3]+（1+）簇阳离子通过Mo3S4Cl4(PPh3)3(溶剂)₂与水溶性1,2-双(双(羟丙基)膦基)乙烷（dhprpe，记为L）配体反应制得。通过X射线衍射法解析了[1]₂[Mo6Cl14]的晶体结构，结果显示其具有典型的带帽类立方结构，包含1个盖帽硫原子与3个桥连硫原子。每个金属中心的八面体配位环境由1个氯原子与双膦配体的2个磷原子共同完成。根据pH值的不同，功能化双膦配体的羟基层团可取代氯配体并与簇核配位，生成通式为[Mo3S4(dhprpe-H)3]+（2+）的、由三齿去质子化dhprpe配体修饰的新型簇合物。本研究采用停流技术、³¹P{¹H}核磁共振波谱法及电喷雾电离质谱法开展了详细的实验表征，以探究1+与2+两种簇阳离子之间的酸碱平衡行为及转化动力学。1+向2+的转化及其逆反应均仅通过单步动力学过程进行，因此三个金属中心上的反应均遵循统计控制的动力学规律。不同条件下测得的速率常数被用于讨论氯配体配位与解离过程中螯合环开合的反应机理。