Alkoxides of Trivacant Lacunary Polyoxometalates

作者：Minato Takuo; Suzuki Kosuke^*; Yamaguchi Kazuya; Mizuno Noritaka^*

来源：Chemistry - A European Journal, 2017, 23(57): 14213-14220.

DOI：10.1002/chem.201702883

• alkoxides
• hydrolysis
• organic-inorganic hybrid composites
• polyoxometalates
• protecting groups

Lacunary polyoxometalates (POMs) are useful rigid multidentate inorganic ligands to construct multinuclear metal oxo clusters and inorganic-organic hybrid materials. However, the use of multivacant lacunary POMs often suffers from their undesired condensation reactions at the highly reactive vacant sites. Herein, the introduction of alkoxy protecting groups into the vacant sites of lacunary POMs in organic media is reported for the first time. By reacting organic solvent-soluble trivacant lacunary Keggin-type POMs with methanol, six methoxy groups were successfully introduced into the vacant sites, resulting in the formation of the alkoxides TBA(4)[A-alpha-XW9O28(OCH3)(6)] (I-x-OMe; X = Si, Ge). These methoxy groups could protect the reactive vacant sites and suppress the undesired dimerization reaction into the corresponding alpha-Dawson-type POMs. Since the introduced monodentate methoxy groups could easily be dissociated by hydrolysis, I-Si-OMe could be utilized as the precursor for the synthesis of metal-substituted POMs. In addition, by using pentaerythritol as the multidentate alkoxy ligand, the monomeric alkoxide TBA(4)[A-alpha-SiW9O28{(OCH2)(2)C(CH2OH)(2)}(3)] (I-Si-PE) was successfully synthesized. In particular, these multidentate alkoxy groups showed high resistance against hydrolysis. Moreover, by reacting I-Si-PE with trivacant lacunary Keggin-type POMs, the dimeric inorganic-organic-inorganic hybrid structures TBA(n)H(8-n)[(A-alpha-SiW9O28){(OCH2)(2)C(CH2O)(2)}(3)-(A-alpha-XW9O28)] (IISiX-PE; X = Si, Ge) with the same or different heteroatoms (Si and Ge) were successfully synthesized.

• 出版日期2017-10-12