| Abstract
| - The reaction of the dihydride [RuII(H)2(CO)(PPh3)3], 3, with excess azo-2,2‘-bipyridine (abp) in boiling dry benzenehas 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 notyield a bischelate, but the hydridic monoradical [RuII(Clpap•-)(H)(CO)(PPh3)2], 6, has been isolated. Upon treatmentof 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 twochelate rings are 1.284(6) and 1.336(6) Å, showing that the radical electron is localized in the latter ring. Thehalf-filled extended Hückel HOMO is indeed found to be so localized, and it has a large azo character. Complexes4−6 display radical redox couples with E1/2 in the range −0.5 to +0.10 V vs SCE. The E1/2 values qualitativelycorrelate with corresponding νCO values (1900−2000 cm-1). The monoradicals (S = 1/2) 4+, 5, and 6 uniformlydisplay a strong EPR signal near g = 2.00. Metal-mediated magnetic interaction makes the EPR-silent diradical4 strongly antiferromagnetic with J = −299 cm-1. Crystal data are as follows: (4+PF6-·CH2Cl2, C40H33Cl2F6N8OP2Ru) monoclinic, space group P21/c (no. 14), a = 14.174(6) Å, b = 16.451(4) Å, c = 18.381(4) Å, β =98.00(3)°, Z = 4; (5+PF6-·H2O, C47H41F6N4O2P3Ru) monoclinic, space group P21/n (no. 14), a = 9.433(2) Å, b= 38.914(17) Å, c = 13.084(3) Å, β = 103.47(2)°, Z = 4; (6+PF6- , C48H39ClF6N3OP3Ru) monoclinic, spacegroup P21/n (no. 14), a = 10.496(5) Å, b = 22.389(8) Å, c = 19.720(6) Å, β = 90.53(3)°, Z = 4.
- The radical complexes [RuII(abp•-)2(CO)(PPh3)], 4, [RuII(abp•-)(H)(CO)(PPh3)2], 5, and [RuII(Clpap•-)(H)(CO)(PPh3)2], 6, are afforded via homolytic Ru−H cleavage in the reaction between [RuII(H)2(CO)(PPh3)3] and azo-2,2‘-bipyridine (abp) or 2-(p-chlorophenylazo)pyridine (Clpap). Protic oxidation of antiferromagnetic (J = −299 cm-1) 4 furnishes [RuII(abp)(abp•-)(CO)(PPh3)]PF6, which displays radical localization as shown below (N-N distances 1.34 and 1.28 Å). The geometries of 5 and 6 are isomeric.
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