Studies in Niobium (V) - Schiff Base Complexes

Prashar, P.; Tandon, J. P.

doi:10.1515/znb-1971-0105

Cited by 7 publications

(3 citation statements)

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Section: ■ Results and Discussionmentioning

confidence: 98%

“…The metathesis reaction between M(OEt) 5 (M = Nb or Ta) and the ligand to form the desired catalyst is likely driven by the relative basicity of ethoxide as compared with the resulting phenoxide as well as by the chelate effect. This procedure is similar to the synthesis of analogous group IV and group V phenoxyimine chelates , and provides a straightforward route to a variety of ROP catalysts containing ethoxide initiating groups. Starting from commercially available metal alkoxides and proceeding through an alcohol metathesis route has advantages over salt metathesis reactions with metal halides, as this approach eliminates the need to first deprotonate the ligand and does not require the separation of metal salts from the final reaction mixture, simplifying the synthesis and increasing atom economy.…”

Section: Resultsmentioning

confidence: 99%

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Investigating the Ring-Opening Polymerization Activity of Niobium and Tantalum Ethoxides Supported by Phenoxyimine Ligands

Plaman

Durr

2022

ACS Omega

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A variety of metal catalysts from around the periodic table have been studied for the ring-opening polymerization (ROP) of cyclic esters. Within this field, group V catalysts have been rarely explored. To better understand the effect the choice of metal and ligand has on ROP activity, a series of 10 niobium and tantalum alkoxide catalysts, supported by a range of phenoxyimine ligands, were synthesized. The electronics and steric bulk of the ligands were varied on the phenoxy group ( t Bu, Cl, and OMe) and the imine group (Ph; 2,6-diMePh; 2,6-di i PrPh; and 2,4,6-tri t BuPh) to probe their effect on the catalyst structure and activity. Catalysts were characterized with 1D, 2D, and variable-temperature NMR techniques to determine their structure in solution. Single crystal X-ray diffraction studies were conducted to establish their solid-state structure. The 10 catalysts are pseudo-octahedral, and each shows ligand coordination through phenoxy-oxygen and imine-nitrogen (O,N). In the case of the o -vanillin ligand set, however, evidence was found for O,O-coordination of the ligand when the steric encumbrance of the imine-nitrogen was increased. Each catalyst was active for the ring-opening polymerization of both rac -lactide (LA) and ε-caprolactone (CL) in the absence of solvent at 140 °C. In the case of CL, the catalysts supported by chloro-containing ligands showed the most polymerization control based on final polymer molecular weight and dispersity. Ligand trends were less clear for the polymerization of LA, though in all cases the catalysts were more controlled than the parent homoleptic alkoxide [M(OEt) 5 ; M = Nb or Ta]. The most promising catalyst in the family was tested for copolymerization activity of LA and CL in one pot. Copolymerization of the two monomers was successful and yielded random poly(caprolactone- co -lactide).

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Section: ■ Results and Discussionmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Investigating the Ring-Opening Polymerization Activity of Niobium and Tantalum Ethoxides Supported by Phenoxyimine Ligands

Plaman

Durr

2022

ACS Omega

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“…The present study details a niobium(V) ethoxide derivative of 8-hydroxyquinoline. The parent compound, niobium(V) ethoxide, Nb(OC 2 H 5 ) 5 is a liquid which reacts with various monofunctional bidentate and bifunctional, tri and tetradentate ligands [15][16][17]. Niobium(V) ethoxide, when reacted with 8-hydroxyquinoline, affords the title compound, whose structure in solution and in solid state is detailed in this study.…”

Section: Introductionmentioning

confidence: 97%

Synthesis, single crystal structure determination, and solution behavior of an 8-hydroxyquinoline derivative of niobium(V) ethoxide

Amini

Mirzaee

Yaganeh

et al. 2007

Transition Met Chem

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An 8-hydroxyquinoline derivative of niobium(V) ethoxide was synthesized and characterized by elemental analysis, mass spectrometry, infrared, electronic, and 1 H, 13 C, and 93 NMR spectroscopies. Tetraethoxy(8-quinolinato)niobium(V), as shown by the single crystal structure determination, exists as an octahedral compound in the solid state in which the 8-quinolinato group chelates to the metal atom. In solution, this group partially becomes unidentate; the six-coordinate species is in equilibrium with the five-coordinate species, as shown by 93 Nb and variable-temperature 1 H NMR spectroscopy.

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