Synthesis and Reactivity of the Methoxozirconium Pentatungstate (nBu4N)6[{(-MeO)ZrW5O18}2]: Insights into Proton-Tra
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- 作者：R. John Errington ; Sagar S. Petkar ; Paul S. Middleton ; William McFarlane ; William Clegg ; Robert A. Coxall ; Ross W. Harrington
- 刊名：Journal of the American Chemical Society
- 出版年：2007
- 出版时间：October 10, 2007
- 年：2007
- 卷：129
- 期：40
- 页码：12181 - 12196
- 全文大小：758K
- 年卷期：v.129,no.40(October 10, 2007)
- ISSN：1520-5126
文摘
The methoxo-bridged, dimeric, ZrIV-substituted Lindqvist-type polyoxometalate (POM) (nBu4N)6[{(-MeO)ZrW5O18}2], (TBA)61, has been synthesized by stoichiometric hydrolysis of Zr(OnPr)4, [{Zr(OiPr)3(-OnPr)(iPrOH)}2], or [{Zr(OiPr)4(iPrOH)}2] and [{WO(OMe)4}2] in the presence of (nBu4N)2WO4,providing access to the systematic nonaqueous chemistry of ZrW5 POMs for the first time and an efficientroute to 17O-enriched samples for 17O NMR studies. 1H NMR provided no evidence for dissociation of 1 insolution, although exchange with MeOH was shown to be slow by an EXSY study. Reactions with HX atelevated temperatures gave a range of anions [{XZrW5O18}n]3n- (X = OH, 3; OPh, 4; OC6H4Me-4, 5; OC6H4(CHO)-2, 6; acac, 7; OAc, 8), where n = 2 for 3 and n = 1 for 4-8, while 1H and 17O NMR studies ofhydrolysis of 1 revealed the formation of an intermediate [(-MeO)(-HO)(ZrW5O18)2]6-. Electrosprayionization mass spectrometry of 1 and 3 illustrated the robust nature of the ZrW5O18 framework, and X-raycrystal structure determinations showed that steric interactions between ligands X and the ZrW5O18 surfaceare important. The coordination number of Zr is restricted to six in aryloxides 4 and 5, while seven-coordination is achieved in the chelate complexes 6-8. Given the inert nature of the methoxo bridges in1, protonation of ZrOW sites is proposed as a possible step in reactions with HX. The diphenylphosphinateligand in [(Ph2PO2)ZrW5O18]3- was found to be labile and upon attempted recrystallization the aggregate[(3-HO)2(ZrW5O18)3H]7- 9 was formed, which was found to be protonated at ZrOZr and ZrOW sites. Thiswork demonstrates the flexibility of the {ZrW5O18}2- core as a molecular platform for modeling catalysis bytungstated zirconia surfaces.