- and -Cyclodextrin Rotaxanes of http:/

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• 作者：Andrew J. Baer and Donal H. Macartney
• 刊名：Inorganic Chemistry
• 出版年：2000
• 出版时间：April 3, 2000
• 年：2000
• 卷：39
• 期：7
• 页码：1410 - 1417
• 全文大小：118K
• 年卷期：v.39,no.7(April 3, 2000)
• ISSN：1520-510X

文摘

The kinetics and mechanism of the self-assemblies of hars/alpha.gif" BORDER=0>- and hars/beta2.gif" BORDER=0 ALIGN="middle">-cyclodextrin (CD) [2]rotaxanes, [(NC)₅Fe{pyRpy·CD}Fe(CN)₅]^6-, containing pentacyanoferrate(II)-stoppered 4,4'-bis(pyridyl) threads pyRpy (R = -CH=CH-, -N=N-, -CH=N-N=CH-, and -C(CH₃)=N-N=C(CH₃)-) have been investigated in aqueous solutionby using visible and ¹H NMR spectroscopy. The rotaxanes may be formed rapidly by the addition of the[Fe(CN)₅OH₂]^3- ion to the CD-included pyRpy thread or slowly by the addition of an excess of CD to the dimeric[(NC)₅Fe(pyRpy)Fe(CN)₅]^6- complex. In the latter method, the mechanism involves a rate-determining dissociationof a [Fe(CN)₅]^3- center to form the monomeric complex, which subsequently includes the coordinated pyRpy inthe CD cavity to yield the semirotaxane, which is rapidly recomplexed by the [Fe(CN)₅OH₂]^3- ion, generatingthe [2]rotaxane. Rate and activation parameters and CD inclusion stability constants have been determined forthe ligand substitution reactions involving the formations and dissociations of the semirotaxanes and rotaxanes.The extents of the decreases in the formation (k_f) and dissociation (k_d) rate constants upon CD inclusions of thefree and coordinated ligands, respectively, are related to the natures of the CD hosts and the R linkage on thepyRpy guests. The semirotaxanes and rotaxanes exhibit significant bathochromic shifts in their visible MLCTtransitions compared with the corresponding monomeric and dimeric iron complexes. A correlation between theextent of the decrease in k_d and the change in the MLCT energy upon hars/alpha.gif" BORDER=0>-CD inclusions of [Fe(CN)₅L]^3-, whereL is an aromatic N-heterocyclic 4-Rpy or pyRpy ligand, has been observed.