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

摘要

The [Mo3S4Cl3(dhprpe)3]+ (1+) cluster cation has beennprepared by reaction between Mo3S4Cl4(PPh3)3 (solvent)2 and the watersolublen1,2-bis(bis(hydroxypropyl)phosphino)ethane (dhprpe, L) ligand.nThe crystal structure of [1]2[Mo6Cl14] has been determined by X-rayndiffraction methods and shows the typical incomplete cuboidal structurenwith a capping and three bridging sulfides. The octahedral coordinationnaround each metal center is completed with a chlorine and two phosphorusnatoms of the diphosphine ligand. Depending on the pH, the hydroxo groupnof the functionalized diphosphine can substitute the chloride ligands andncoordinate to the cluster core to give new clusters with tridentatendeprotonated dhprpe ligands of formula [Mo3S4(dhprpe-H)3]+ (2+). Andetailed study based on stopped-flow, 31P{1H} NMR, and electrospraynionization mass spectrometry techniques has been carried out to understandnthe behavior of acid−base equilibria and the kinetics of interconversion between the 1+ and the 2+ forms. Both conversion of 1+nto 2+ and its reverse process occur in a single kinetic step, so that reactions proceed at the three metal centers with statisticallyncontrolled kinetics. The values of the rate constants under different conditions are used to discuss on the mechanisms of openingnand closing of the chelate rings with coordination or dissociation of chloride.