Recent advances in controllable alkoxylation chemistry of Anderson-type polyoxometalates from synthetic strategies perspective

Abstract

Polyoxometalates (POMs) are an exceptional family of inorganic oxide anions consisting of Mo, W, V, etc. early transition metal ions at their highest oxidization states with structural versatility. The Anderson-type hetreopolyanions are one of the most important subclass since their most flexibility benefited from the central heteroatom. Among the frontier of current POMs investigations, organic modification and functionalization of POMs stands for one of most hot topics. The organic modification of POMs can incorporate POMs with advanced functional organic moieties on their surfaces to make the structure versatility more accessible and the design of advanced functional materials more rational. In this review, recent advances in controllable alkoxylation chemistry of Anderson-type polyoxometalates are briefly summarized into 9 parts as following: (1) the synthesis strategy development of direct modification protocol for the synthesis of single-side triol-functionalized Anderson δ isomer organic hybrids. (2) Based on direct modification protocol, the synthesis strategy development of μ 2-O atom pronation and activation chemistry in Anderson cluster to afford single-side triol-functionalized Anderson χ and ψ isomer organic hybrids. The proton-controlled isomer transformation between the δ , χ and ψ isomer was discovered. This will open up a new era for developing chemical reactivity of μ 2-O atoms in the Anderson cluster. (3) By precise proton control, the synthesis strategy development to obtain diol functionalized Anderson organic hybrids. Such diol functionalization mode not only works for some specific triol ligands but also can readily be extended to the diol ligands, which will greatly enrich the species of alkoxo-derivatized Anderson POM clusters. (4) Based on direct modification protocol, extending special tripodal ligands with carboxyl group to symmetrically functionalized the Anderson cluster. Such Anderson organic hybrids cannot be obtained for the traditional reconstruction protocol. This has extended the versatility of tripodal ligands applied for Anderson-type POMs modification. (5) Through stepwise synthesis strategy, single-side δ isomer was utilized as a precursor to efficiently synthesized asymmetrically triol-functionalized Anderson organic hybrids. (6) The synthesis strategy development of direct parent Anderson alkoxylation protocol for triol-functionalized butterfly-shaped β isomers of Anderson POMs hybrids. (7) The synthesis strategy development to extend the triol-functionalized Anderson from polymolybdates(Mo6O24) to polyoxotungstates(W6O24). (8) The newly development and revised synthesis strategy of Mo8 reconstruction protocol. (9) The original concept proposed by our group, organic ligand protected and inorganic-ligand supported atomically precise Anderson nanocluster based molecular armor hybrid material design as effective catalysts for green aerobic oxidation catalysis applications. In summary, the synthetic strategies and structures of novel alkoxyl-functionalized Anderson cluster have been discussed in this review. These newly developed synthesis strategies have greatly enriched the category of organoalkoxylation derivatives of Anderson cluster, providing a reliable and convenient synthetic methodology for the controllable design of triol-functionalized Anderson organic hybrids with specific and desirable functionalization modes. The extension of triol ligands with functional groups to other POMs units are still need to be developed. One of the important application fields for POMs is catalysis, however, the exploration of catalysis of alkoxyl-functionalized Anderson nanoclusters is quite limited to the recent cases we mentioned in this review. It is worth exploring to develop more alkoxyl-functionalized Anderson nanoclusters as catalysts for useful reactions, because alkoxyl-functionalized Anderson nanoclusters have multiple active sites and special properties derived from functional groups of alkoxyl ligands as well as cooperativities. The charge transfer properties between POMs and organic moieties in alkoxyl-functionalized Anderson nanoclusters have also attracted widely attentions. Using alkoxyl ligands with conjugated groups to functionalize Anderson nanoclusters may enhance the ability of electron transfer to improve the intrinsic redox properties of Anderson nanoclusters. It can be concluded with confidence that the persistent and dedicated efforts of chemists have revealed a vast advance in alkoxylation of Anderson nanoclusters, which may in fact just be the reason why the alkoxylation chemistry of Anderson nanoclusters research field has flourished in recent years. Of course, more Anderson nanoclusters-based materials with novel structures, interesting and functional properties remain to be explored and the alkoxylation chemistry of Anderson nanoclusters still has great growing opportunities in the future.