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Issue 19, 2016
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Niobium tetrahalide complexes with neutral diphosphine ligands

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Abstract

The reactions of NbCl4 with diphosphine ligands o-C6H4(PMe2)2, Me2PCH2CH2PMe2 or Et2PCH2CH2PEt2 in a 1 : 2 molar ratio in MeCN solution produced eight-coordinate [NbCl4(diphosphine)2]. [NbBr4(diphosphine)2] (diphosphine = o-C6H4(PMe2)2 or Me2PCH2CH2PMe2) were made similarly from NbBr4. X-ray crystal structures show that [NbCl4{o-C6H4(PMe2)2}2] has a dodecahedral geometry, but the complexes with dimethylene-backboned diphosphines are distorted square antiprisms. The Nb–P distances and <P–Nb–P angles are very similar in the two types, but Nb–Cl distances are ∼0.1 Å longer in the square antiprismatic complexes. These paramagnetic (d1) complexes were also characterised by microanalysis, magnetic measurements, IR and UV-visible spectroscopy. Using a 1 : 1 molar ratio of NbCl4 : diphosphine (diphosphine = Me2PCH2CH2PMe2, Et2PCH2CH2PEt2, Cy2PCH2CH2PCy2 and Ph2PCH2CH2CH2PPh2) afforded [NbCl4(diphosphine)], and [NbBr4(Me2PCH2CH2PMe2)] was obtained similarly. These 1 : 1 complexes are unstable in solution, preventing X-ray crystallographic study, but based upon their diamagnetism, IR, UV-visible and 31P{1H} NMR spectra, they are formulated as halide-bridged dimers [(diphosphine)X2Nb(μ-X)4NbX2(diphosphine)], with single Nb–Nb bonds and chelating diphosphines. The Nb(IV) complexes are prone to hydrolysis and oxidation in solution and the structures of the Nb(V) complexes [NbBr4(Me2PCH2CH2PMe2)2][NbOBr4(MeCN)] with a dodecahedral cation, and [{NbOCl3{Et2P(CH2)2PEt2}}2{μ-Et2P(CH2)2PEt2}] which contains seven-coordinate Nb(V) centres with a symmetrical diphosphine bridge, are reported. The structure of niobium tetrabromide, conveniently made from NbCl4 and BBr3, is a chain polymer with edge-linked NbBr6 octahedra and alternating long and short Nb–Nb distances, the latter ascribed to Nb–Nb bonds.

Graphical abstract: Niobium tetrahalide complexes with neutral diphosphine ligands

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Supplementary files

Article information


Submitted
21 Mar 2016
Accepted
08 Apr 2016
First published
12 Apr 2016

Dalton Trans., 2016,45, 8192-8200
Article type
Paper

Niobium tetrahalide complexes with neutral diphosphine ligands

S. L. Benjamin, Y. Chang, A. L. Hector, M. Jura, W. Levason, G. Reid and G. Stenning, Dalton Trans., 2016, 45, 8192
DOI: 10.1039/C6DT01099G

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