Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions in a Water-Soluble Mo3S4 Cluster Bearing Hydroxymethyl Diphosphine Ligands

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• 作者：André ; s G. Algarra ; Manuel G. Basallote ; M. Jesú ; s Ferná ; ndez-Trujillo ; Eva Guillam&oacute ; n ; Rosa Llusar ; M. Dolores Segarra ; Cristian Vicent
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：September 3, 2007
• 年：2007
• 卷：46
• 期：18
• 页码：7668 - 7677
• 全文大小：287K
• 年卷期：v.46,no.18(September 3, 2007)
• ISSN：1520-510X

文摘

The [Mo₃S₄Cl₃(dhmpe)₃]Cl ([1]Cl) cluster has been prepared from [Mo₃S₇Cl₆]^2- and the water-soluble 1,2-bis(bis(hydroxymethyl)-phosphino)ethane (dhmpe, L) ligand. The crystal structure has been determined by X-ray diffractionmethods and shows the incomplete cuboidal structure typical of the M₃Q₄ clusters (M = Mo, W; Q = S, Se), witha capping sulfide ligand to the three metal centers and the other three sulfides acting as bridges between two Moatoms. The octahedral coordination around each metal center is completed with a chlorine and two phosphorusatoms of one L ligand. The chemistry of aqueous solutions of [1]Cl is dominated by the formation of the [Mo₃S₄L(L-H)₂(H₂O)]²⁺ complex ([2]²⁺), where the three chlorides have been replaced by one water molecule and twoalkoxo groups of two different dhmpe ligands, thus leading to a solution structure where the three metal centersare not equivalent. A detailed study based on stopped-flow, ³¹P{¹H} NMR, and electrospray ionization massspectrometry techniques has been carried out to understand the behavior of [2]²⁺ in aqueous solution. In this way,it has been established that the addition of an excess of X^- (Cl^-, SCN^-) leads to [Mo₃S₄X₃(dhmpe)₃]⁺ complexesin three resolved kinetic steps that correspond to the sequential coordination of X^- at the three metal centers.However, whereas the first two steps involve the opening of the chelate rings formed with the alkoxo groups of thedhmpe ligands, the third one corresponds to the substitution of the coordinated water molecule. These resultsdemonstrate that the asymmetry introduced by the closure of chelate rings at only two of the three Mo centersmakes the kinetics of the reaction deviate significantly from the statistical behavior typically associated with M₃Q₄clusters. The results obtained for the reaction of [2]²⁺ with acid and base are also described, and they completethe picture of the aqueous speciation of this cluster.