Di-carbonyl-o-semiquinonato rhodium complexes

Abstract

Two novel dicarbonyl-semiquinonato rhodium complexes were synthesized and studied. Complexes are analogues of (CO)2Rh(3,6-DBSQ) (3,6-DBSQ-3,6-di-tert-butyl-o-benzosemiquinone) which thread-like crystals can bend reversibly under light or heat activation (G.A. Abakumov, V.I. Nevodchikov, Dokl. Acad. Nauk SSSR 1982, 266, 1407–1410). Complexes differ from (CO)2Rh(3,6-DBSQ) by substituents in 3,6-positions of quinonato ring (cyclohexyl (1) and isopropyl (2) instead of tert-butyl). Single crystal structural study indicates that both complexes are the derivatives of Rh(I) with o-semiquinonato anion-radical. Molecules form pairs due the short contacts in contrast to (CO)2Rh(3,6-DBSQ) and other similar compounds which form the endless alternated chains with direct Rh-Rh bond. At that, complex 1 molecules form isolated pairs, whereas molecules of 2 can be united in the chain. Both compounds 1 and 2 have the array of intensive bands in IR spectrum in the region 1350 cm−1 which is closer to bond stretch vibrations of C–O ordinary bond but not sesquilateral. EPR of solutions of complexes indicates presence of monomeric complex molecules where the single unpaired electron is localized in o-semiquinonato ligand. The drop of EPR signal intensity with cooling of solutions of 1 and 2 evidence that the association process takes place.