A collection of robust methodologies for the preparation of asymmetric hybrid Mn–Anderson polyoxometalates for multifunctional materials

Abstract

Here we report a suite of approaches for the isolation of asymmetrically grafted organic-inorganic hybrid Mn-Anderson polyoxometalate compounds (TBA) 3 [MnMo 6 O 18 ((OCH 2) 3 CNHR 1)((OCH 2) 3 CNHR 2)] (where TBA ¼ tetrabutylammonium). Both a "pre-functionalization" route (for compound 1-R 1 ¼-COC 14 H 9 , R 2 ¼-H) using two different TRIS-based ligands ((HOCH 2) 3 CNHR), and a "post-functionalization" of the preformed TRIS Mn-Anderson compound (R 1 ¼ R 2 ¼-H) were demonstrated. Compounds 2 (R 1 ¼-COC 15 H 31 , R 2 ¼-CO(CH 2) 2 COOH) and 3 (R 1 ¼-COC 15 H 31 , R 2 ¼-H) are some of the first reported examples of asymmetric Mn-Anderson compounds to have been synthesized by the latter route. The reliable and broadly applicable chromatographic method used to isolate these compounds relies on the difference in affinity of compounds' organic moieties for reverse phase (RP) media; the target asymmetric cluster will have an intermediate affinity, between that of the two symmetric by-products. For instances where this is not the case, we have prepared and isolated a "universal" asymmetric Mn-Anderson precursor 4 (R 1 ¼-C(O)OC 14 H 11 , R 2 ¼-H), which can be used as a precursor to synthesize practically any asymmetric Mn-Anderson system. The use of 4 as an "universal" precursor was successfully demonstrated in the synthesis and isolation of compound 5 (R 1 ¼-COC 2 H 5 , R 2 ¼-H), which would not be accessible by a simple 'one pot' approach. In addition to removing a significant barrier to the exploitation of asymmetric Mn-Anderson clusters as new functional materials, the methods presented here should be applicable to a range of other hybrid organic-inorganic clusters.

The Anderson–Evans polyoxometalate: From inorganic building blocks via hybrid organic–inorganic structures to tomorrows “Bio-POM”

“…Instead asymmetric products were formed in both cases. Compared with previously reported methods for the isolation of asymmetric products explored for the Mn III Mo 6 system [85,184], this and similar procedures [171] are more controllable since it does not rely on re-arrangement of octamolybdate, save time, give high purity and good yield [188]. Further post-functionalization on asymmetrically functionalized POMs (Figure 7, B5) can be selective depending on e.g.…”

“…-NH 2 , -OH, -CH 2 OH, and further derivatization with imine and amide bonds either before or after attachment to the POM) [83,84]. The tris-ligands can be synthesized first and then be grafted onto the POM (pre-functionalization) or trisligands can further be modified by organic reactions after attachment onto the POM (postfunctionalization) [85]. They may cap either a tetrahedral cavity by connecting to two μ 3 -O atoms and one μ 2 -O atom (χ-isomer, Figure 4A) or by capping the templating heteroatom and connecting to three μ 3 -O atoms (δ-isomer, Figure 4B) [86].…”

“…By separating crystals from the mother liquor every six hours and applying ESI-MS the three different products were isolated. More recent methods take advantage of the difference in polarity between the three products and were therefore separated by means of RP-HPLC [85]. If the difference in polarity is too small, protective groups may be used to allow proper separation with the possibility of subsequent post-functionalization once isolated [85].…”

“…More recent methods take advantage of the difference in polarity between the three products and were therefore separated by means of RP-HPLC [85]. If the difference in polarity is too small, protective groups may be used to allow proper separation with the possibility of subsequent post-functionalization once isolated [85]. The only report of an asymmetric post-functionalization (Figure 7, A2) involves the attachment of SP to [MnMo 6 O 18 {(OCH 2 ) 3 CNH 2 } 2 ] 3-.…”

Polyoxometalate Clusters Integrated into Peptide Chains and as Inorganic Amino Acids: Solution‐ and Solid‐Phase Approaches

“…[14] Herein, we present a set of synthetic approaches to the insertion of these hybrid Mn-Anderson building blocks into peptide sequences, both by liquid-phase reactions with preformed peptides and by integration into solid-phase peptide synthesis (SPPS; see Scheme 1). [14] Herein, we present a set of synthetic approaches to the insertion of these hybrid Mn-Anderson building blocks into peptide sequences, both by liquid-phase reactions with preformed peptides and by integration into solid-phase peptide synthesis (SPPS; see Scheme 1).…”