Radical Anions and Radical Trianions of a Phosphabenzene and Some Diphospha Derivatives of Biphenyl, p-Terphenyl and p,p′-Quaterphenyl: an ESR and ENDOR Study
✍ Scribed by Fabian Gerson; Pascal Merstetter; Susanne Pfenninger; Gottfried Märkl
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 321 KB
- Volume
- 35
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
The radical anions and radical trianions of 2,4,6-triphenylphosphabenzene (1), 3,3º,5,5º-tetraphenyl-4k3,4ºk3diphosphabiphenyl-1,1º (2), 3,3/,5,5/-tetraphenyl-4k3,4/k3-diphosphaterphenyl-1,1º : 4º,1/ (3) and 3,3Ó,5,5Ótetraphenyl-4k3,4Ók3-diphosphaquaterphenyl-1,1º : 4º,4/ : 1/,1Ó (4) were studied by ESR and (in part) ENDOR spectroscopy. The singly occupied orbital in the radical anions is symmetric with respect to the vertical mirror plane passing through the phosphorus atom in 1Õ-or two such atoms in 2Õ--4Õ-. Accordingly, the prominent feature of these species is the large and positive 31P coupling constant (1Õ-, + 3.31 ; 2Õ-, + 2.62 ; 3Õ-, + 2.02 ; and 4Õ-, + 1.67 mT), which gives rise to a pronounced hyperÐne anisotropy. The anions 1Õ--4Õ-can thus be regarded as "P-centred radicalsÏ (g = 2.0045 » 0.0003). In contrast, the trianions 1Õ3--4Õ3-have to be classiÐed as "hydrocarbon radicalsÏ (g = 2.0027 » 0.0001). For 1Õ3-, the hyperÐne data could be precisely analysed with the use of the ENDOR technique. As the nodal plane of the singly occupied orbital in this trianion passes through the phosphorus atom, the 31P coupling constant is small and negative ( Ô 0.267 mT) ; the largest value ( Ô 0.473 mT) belongs to the two protons in the 3,5-positions of the phosphabenzene ring. The hyperÐne patterns of the radical trianions 2Õ3--4Õ3-resemble that of 1Õ3-with the p-spin population being thus restricted to one phosphabenzene ring and its two phenyl substituents. Such a "localizationÏ is considered to be due to a degeneracy or near-degeneracy of the singly occupied orbital and to a perturbation caused by the association with three alkali metal counterions. 1997 ( by John Wiley & Sons, Ltd.