Rational Design and Assembly of M2M'3L6 Supramolecular Clusters with C3h Symmetry by Exploiting Incommensurate Symmetry

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• 作者：Xiankai Sun ; Darren W. Johnson ; Dana L. Caulder ; Kenneth N. Raymond ; and Edward H. Wong
• 刊名：Journal of the American Chemical Society
• 出版年：2001
• 出版时间：March 28, 2001
• 年：2001
• 卷：123
• 期：12
• 页码：2752 - 2763
• 全文大小：412K
• 年卷期：v.123,no.12(March 28, 2001)
• ISSN：1520-5126

文摘

A rational approach to heterometallic cluster formation is described that uses incommensuratesymmetry requirements at two different metals to control the stoichiometry of the assembly. Critical to thisstrategy is the proper design and synthesis of hybrid ligands with coordination sites selective toward eachmetal. The phosphino-catechol ligand 4-(diphenylphosphino)benzene-1,2-diol (H₂L) possesses both hardcatecholate and soft phosphine donor sites and serves such a role, using soft (C₂-symmetric) and hard (C₃-symmetric) metal centers. The ML₃ catecholate complexes (M = Fe^III, Ga^III, Ti^IV, Sn^IV) have been preparedand characterized as C₃-symmetry precursors for the stepwise assembly (aufbau) of heterometallic clusters.While the single-crystal X-ray structure of the Cs₂[TiL₃] salt shows a C₁ mer-configuration in the solid -state,room-temperature solution NMR data of this and related complexes are consistent with either exclusive formationof the C₃-fac-isomer with all PPh₂ donor sites syn to each other or facile fac/mer isomerization. Coordinationof these [ML₃]^2- (M = Ti^IV, Sn^IV) metallaligands via their soft P donor sites to C₂-symmetric PdBr₂ unitsgives exclusively pentametallic [M₂Pd₃Br₆L₆]^4- (M = Ti, Sn) clusters. These clusters have been fullycharacterized by spectral and X-ray structural data as C_3h mesocates with Cs⁺ or protonated 1,4-diazabicyclo[2.2.2]octane (DABCO·H⁺) cations incorporated into deep molecular clefts. Exclusive formation of this typeof supramolecular species is sensitive to the nature of the counterions. Alkali cations such as K⁺, Rb⁺, andCs⁺ give high-yield formation of the respective clusters while NEt₃H⁺ and NMe₄⁺ yield none of the desiredproducts. Extension of the aufbau assembly to produce related [M₂Pd₃Cl₆L₆]^4-, [M₂Pd₃I₆L₆]^4-, and[M₂Cr₃(CO)₁₂L₆]^4- (M = Ti, Sn) clusters has also been realized. In addition to this aufbau approach, self-assembly of several of these [M₂Pd₃Br₆L₆]^4- clusters from all eleven components (two M^IV, three PdBr₂, sixH₂L) was also accomplished under appropriate reaction conditions.