Synthesis of highly sterically hindered niobium and tantalum alkoxides and their microhydrolysis in strongly basic medium

Crystal Engineering of Nanomorphology for Complex Oxide Materials via Thermal Decomposition of Metal−Organic Frameworks. Case Study of Sodium Tantalate

“…Formation of an oxo-complex with high yield even on rigorous protection against moisture is not surprising for this system (see and refs therein) and could even be promoted by Bradley reaction, the ether elimination from metal alkoxides in solution, that even was first described for Nb(V) and Ta(V) complexes with bulky ligands and is known to be facilitated in the basic medium …”

“…21 It is worth noting that the structure of 1 should definitely not be considered as derived from an oxoalkoxide dimer of tantalum pinacolate, having as an individual homometallic compound Ta 2 O(OCMe 2 CMe 2 O) 2 (HOCMe 2 CMe 2 O) 4 completely different structure and composition. 19 Formation of an oxo-complex with high yield even on rigorous protection against moisture is not surprising for this system (see 19 and refs therein) and could even be promoted by Bradley reaction, the ether elimination from metal alkoxides in solution, that even was first described for Nb(V) and Ta(V) complexes with bulky ligands 22 and is known to be facilitated in the basic medium. 23 The crystal structure of 1 is composed of these distinct bimetallic molecules (Figure 1) with elongated shape, forming linear chain-like packing along the volume diagonal of the triclinic cell.…”

“…It is worth noting that the structure of 1 should definitely not be considered as derived from an oxoalkoxide dimer of tantalum pinacolate, having as an individual homometallic compound Ta 2 O(OCMe 2 CMe 2 O) 2 (HOCMe 2 CMe 2 O) 4 completely different structure and composition …”

“…17 An attractive approach to insoluble and moisture insensitive materials is application of bidentate aryloxide ligands as it has been demonstrated earlier for Ti-derivatives by Wolczansky et al 18 The recently characterized homometallic tantalum pinacolates revealed, however, extremely high solubility and moisture sensitivity, resulting apparently from chelating mode in attachment of the [OCMe 2 CMe 2 O] 2ligands. 19 Introduction of bulky sodium cations had then a prospect to interconnect the alkoxo-tantalate units and lead to denser packing and stronger interactions, having a chance to produce insoluble and stable material. Application of a bulky and hydrophobic pinacolate ligand remained preferable as the hydrolysis of metal alkoxides occurs as a proton-assisted S N 1 mechanism and hydrophobicity had to hinder the diffusion of protons or water.…”

“…The bimetallic alifatic alkoxide complexes NaTa(OR) 6 , R = Me, Et, iPr, tBu, are highly soluble in organic solvents, easily melt and are strongly moisture sensitive . An attractive approach to insoluble and moisture insensitive materials is application of bidentate aryloxide ligands as it has been demonstrated earlier for Ti-derivatives by Wolczansky et al The recently characterized homometallic tantalum pinacolates revealed, however, extremely high solubility and moisture sensitivity, resulting apparently from chelating mode in attachment of the [OCMe 2 CMe 2 O] 2− ligands . Introduction of bulky sodium cations had then a prospect to interconnect the alkoxo-tantalate units and lead to denser packing and stronger interactions, having a chance to produce insoluble and stable material.…”