Chemistry of metal-bound anion radicals. A family of mono- and bis(azopyridine) chelates of bivalent ruthenium.
The reaction of the dihydride [RuII(H)2(CO)(PPh3)3], 3, with excess azo-2,2'-bipyridine (abp) in boiling dry benzene has afforded the diradical bischelate [RuII(abp.-)2(CO)(PPh3)], 4, and the hydridic monochelate monoradical [RuII(abp.-)(H)(CO)(PPh3)2], 5. A similar reaction between 3 and 2-(p-chlorophenylazo)pyridine (Clpap) did not yield a bischelate, but the hydridic monoradical [RuII(Clpap.-)(H)(CO)(PPh3)2], 6, has been isolated. Upon treatment of 4-6 with NH4PF6 in a wet dichloromethane-acetonitrile medium, the one-electron-oxidized salts 4+PF6-, 5+PF6-, and 6+PF6- are isolated, H+ being the oxidizing agent. The X-ray structures of 4+PF6-.CH2Cl2, 5+PF6-.H2O, and 6+PF6- have been determined. In the monoradical 4+ the azo N-N bond lengths in the two chelate rings are 1.284(6) and 1.336(6) A, showing that the radical electron is localized in the latter ring. The half-filled extended Hückel HOMO is indeed found to be so localized, and it has a large azo character. Complexes 4-6 display radical redox couples with E1/2 in the range -0.5 to +0.10 V vs SCE. The E1/2 values qualitatively correlate with corresponding vco values (1900-2000 cm-1). The monoradicals (S = 1/2) 4+, 5, and 6 uniformly display a strong EPR signal near g = 2.00. Metal-mediated magnetic interaction makes the EPR-silent diradical 4 strongly antiferromagnetic with J = -299 cm-1. Crystal data are as follows: (4+PF6-.CH2Cl2, C40H33Cl2F6N8-OP2Ru) monoclinic, space group P2(1)/c (no. 14), a = 14.174(6) A, b = 16.451(4) A, c = 18.381(4) A, beta = 98.00(3) degrees, Z = 4; (5+PF6-.H2O, C47H41F6N4O2P3Ru) monoclinic, space group P2(1)/n (no. 14), a = 9.433(2) A, b = 38.914(17) A, c = 13.084(3) A, beta = 103.47(2) degrees, Z = 4; (6+PF6-, C48H39ClF6N3OP3Ru) monoclinic, space group P2(1)/n (no. 14), a = 10.496(5) A, b = 22.389(8) A, c = 19.720(6) A, beta = 90.53(3) degrees, Z = 4.
Shivakumar
M
M
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India.
Pramanik
K
K
Bhattacharyya
I
I
Chakravorty
A
A