The room temperature reactions of a series of 1,2-dialkoxyalkanes ROCH2CH(R')OR" with MX5 (M = Nb, Ta; X = Br, I) in 1:1 ratio result in single C-O bond cleavage and high-yield formation of the halo-alkoxides MBr4[K-2-OCH2CH(R')OR"] or [Nbl(4){K-1-OCH2CH(R')OR")](2), and equimolar amounts of the corresponding alkyl halides RX. The reaction of NbBr5 with 1,2-climethoxyethane, dme, proceeds with preliminary formation of the ionic species (NbBr4(K-2-dme)(K-1-dme)][NbBr6], 3b, which has been identified by solution NMR at low temperature and conductivity analyses. The gas-phase structure of 3b has been optimized by DFT calculations, confirming that the dme ligands adopt bidentate and monodentate coordination, respectively. Although the formation of NbOBr3(dme), 4b, 1,4-dioxane and MeBr from NbBr5/dme (ratio 1:2) is an exoergonic process (calculated Delta G(r)(degrees) = -115.96 kcal mol(-1)), it is inhibited at room temperature. High temperature conditions enhance the production of 1,4-dioxane at the expense of selectivity. The dinuclear species NbOBr3(dme)NbBr5 (Nb-O-Nb), 5b, (X-ray) has been isolated in modest yield as byproduct of the room temperature reaction of NbBr5 with dme. In general, the 1:2 molar reactions of NbX5 (X = Br. I) with ROCH2CH(R')OR" occur with the exclusion of nearly one equivalent of organic reactant.

R. Bini, F. Marchetti, G. Pampaloni, S. Zacchini (2011). Further insights into the Chemistry of Niobium and Tantalum Pentahalides with 1,2-Dialkoxyalkanes: Synthesis of Bromo- and Iodoalkoxides, Spectroscopic and Computational Studies. POLYHEDRON, 30, 1412-1419 [10.1016/j.poly.2011.03.005].

Further insights into the Chemistry of Niobium and Tantalum Pentahalides with 1,2-Dialkoxyalkanes: Synthesis of Bromo- and Iodoalkoxides, Spectroscopic and Computational Studies

ZACCHINI, STEFANO
2011

Abstract

The room temperature reactions of a series of 1,2-dialkoxyalkanes ROCH2CH(R')OR" with MX5 (M = Nb, Ta; X = Br, I) in 1:1 ratio result in single C-O bond cleavage and high-yield formation of the halo-alkoxides MBr4[K-2-OCH2CH(R')OR"] or [Nbl(4){K-1-OCH2CH(R')OR")](2), and equimolar amounts of the corresponding alkyl halides RX. The reaction of NbBr5 with 1,2-climethoxyethane, dme, proceeds with preliminary formation of the ionic species (NbBr4(K-2-dme)(K-1-dme)][NbBr6], 3b, which has been identified by solution NMR at low temperature and conductivity analyses. The gas-phase structure of 3b has been optimized by DFT calculations, confirming that the dme ligands adopt bidentate and monodentate coordination, respectively. Although the formation of NbOBr3(dme), 4b, 1,4-dioxane and MeBr from NbBr5/dme (ratio 1:2) is an exoergonic process (calculated Delta G(r)(degrees) = -115.96 kcal mol(-1)), it is inhibited at room temperature. High temperature conditions enhance the production of 1,4-dioxane at the expense of selectivity. The dinuclear species NbOBr3(dme)NbBr5 (Nb-O-Nb), 5b, (X-ray) has been isolated in modest yield as byproduct of the room temperature reaction of NbBr5 with dme. In general, the 1:2 molar reactions of NbX5 (X = Br. I) with ROCH2CH(R')OR" occur with the exclusion of nearly one equivalent of organic reactant.
2011
R. Bini, F. Marchetti, G. Pampaloni, S. Zacchini (2011). Further insights into the Chemistry of Niobium and Tantalum Pentahalides with 1,2-Dialkoxyalkanes: Synthesis of Bromo- and Iodoalkoxides, Spectroscopic and Computational Studies. POLYHEDRON, 30, 1412-1419 [10.1016/j.poly.2011.03.005].
R. Bini; F. Marchetti; G. Pampaloni; S. Zacchini
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/103528
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