RADICAL-ANIONS AND RADICAL TRIANIONS OF A PHOSPHABENZENE AND SOME DIPHOSPHA DERIVATIVES OF BIPHENYL, P-TERPHENYL AND P,P'-QUATERPHENYL - ANESR AND ENDOR STUDY

The radical anions and radical trianions of 2,4,6-triphenylphosphabenz ene (1), 3,3',5,5'-tetraphenyl-4 lambda(3),4'lambda(3)-diphosphabiphen yl-1,1' (2), 3,3 '',5,5 ''-tetraphenyl-4 lambda(3),4 ''lambda(3)-dipho sphaterphenyl-1,1':4',1 '' (3) and 3,3''',5,5'''-tetraphenyl-4 a(3),4' ''lambda(3)-diphosphaquaterphenyl-1,1':4',4 '':1 '',1''' (4) were stud ied by ESR and (in part) ENDOR spectroscopy. The singly occupied orbit al in the radical anions is symmetric with respect to the vertical mir ror plane passing through the phosphorus atom in 1(.-) or two such ato ms in 2(.-)-4(.-). Accordingly, the prominent feature of these species is the large and positive P-31 coupling constant (1(.-), + 3.31; 2(.- ), + 2.62; 3(.-), + 2.02; and 4(.-), + 1.67 mT), which gives rise to a pronounced hyperfine anisotropy. The anions 1(.-)-4(.-) can thus be r egarded as 'P-centred radicals' (g = 2.0045 +/- 0.0003). In contrast, the trianions 1(.3-)-4(.3-) have to be classified as 'hydrocarbon radi cals' (g = 2.0027 +/- 0.0001). For 1(.3-), the hyperfine 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 t he phosphorus atom, the P-31 coupling constant is small and negative ( -0.267 mT); the largest value (-0.473 mT) belongs to the two protons i n the 3,5-positions of the phosphabenzene ring. The hyperfine patterns of the radical trianions 2(.3-)-4(.3-) resemble that of 1(.3-) with t he pi-spin population being thus restricted to one phosphabenzene ring and its two phenyl substituents. Such a 'localization' is considered to be due to a degeneracy or near-degeneracy of the singly occupied or bital and to a perturbation caused by the association with three alkal i metal counterions. (C) 1997 by John Wiley & Sons, Ltd.