Article: Metallkomplexe von Heteroarenen, VII: Bis(2,3,5,6-tetramethyl-η6-pyrazin)vanadium, der erste Bis(aren)metall-Komplex mit vier N-Atomen in der Koordinationssphäre / Metal Complexes of Heteroarenes, VII: Bis(2,3,5,6-tetramethyl-η6-pyrazine)vanadium, the First Bis(arene)metal Complex with Four N Atoms in the Coordination Sphere
Zeitschrift für Naturforschung. 2014 June 2, v. 48, no. 11
2014
Abstract: Cocondensation of 2,3,5,6-tetramethyl-pyrazine with vanadium atoms affords [2,3,5,6-(CH₃)₄-η⁶-1,4-C4N₂]₂V (6) which has been studied by X-ray crystallography, EPR-spectro-scopy and cyclic voltammetry. As shown by unequal metal ring-atom distances (V—C = ... ...
| Abstract | Cocondensation of 2,3,5,6-tetramethyl-pyrazine with vanadium atoms affords [2,3,5,6-(CH₃)₄-η⁶-1,4-C4N₂]₂V (6) which has been studied by X-ray crystallography, EPR-spectro-scopy and cyclic voltammetry. As shown by unequal metal ring-atom distances (V—C = 219.6, V—N = 210.9 pm) the ligand in 6 is folded along the N—N axis (dihedral angle 13.6°). The conformation adopted by the cyclic ligands in the crystal has a torsional angle of 44.2° which comes close to the angle of 45° expected for maximum back-bonding, the filled vanadium orbitals 3 dₓ₂₋ᵧ₂and 3 dₓy interacting separately with unoccupied b₃ᵤ(π*) orbitals of the individual pyrazine rings. The hyperfine coupling constant a(⁵¹V) = 4.45 mT attests to comparatively small spin density at the metal nucleus. It is proposed, that substantial transfer of spin density is effected by V 3dz²→ag(σⁿ⁺) overlap, the latter function representing the in-phase combination of the nitrogen “lone pair” orbitals. Contrary to bis(η⁶-phosphinine)vanadium 8, for the pyrazine complex 6 only the anion 6⁻ is formed reversibly in cyclovoltammetry, oxidation to 6⁺ being irreversible. However, in common with 8, the redox potentials for 6 show pronounced anodic shifts. Attempts towards η⁶-coordination of 2,4,6-trimethyl-1,3,5-triazine failed. Apparently, the 1:1 ratio of CH₃/N is insufficient to furnish the triazine ring with the appropriate combination of π-donor and δ-acceptor properties essential for synergetic bond formation. |
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| Keywords | X-ray diffraction ; aromatic hydrocarbons ; ligands ; nitrogen ; oxidation ; pyrazines ; redox potential ; triazines ; vanadium | ||||||||||
| Language | English | ||||||||||
| Dates of publication | 2014-0602 | ||||||||||
| Size | p. 1581-1588. | ||||||||||
| Publishing place | Verlag der Zeitschrift für Naturforschung | ||||||||||
| Document type | Article | ||||||||||
| ZDB-ID | 124635-5 | ||||||||||
| ISSN | 0340-5087 ; 0044-3174 ; 0932-0776 ; 0341-0447 ; 0341-0420 | ||||||||||
| ISSN | 0340-5087 ; 0044-3174 ; 0932-0776 ; 0341-0447 ; 0341-0420 | ||||||||||
| DOI | 10.1515/znb-1993-1117 | ||||||||||
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| Database | NAL-Catalogue (AGRICOLA) |
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