Electronic effects of (N2S2)M(NO) complexes (M = Fe, Co) as metallodithiolate ligands.

Heterobimetallic complexes comprised of W(CO)4 adducts of (N2S2)M(NO) have been isolated and characterized by nu(CO) and nu(NO)IR spectroscopies and X-ray diffraction. The molecular structures of (N2S2)M(NO) compounds (bme-dach)Co(NO), [(bme-dach)Co(NO)]W(CO)4, and [(bme-dach)Fe(NO)]W(CO)4 [bme-dach = N, N'-bis(2-mercaptoethyl)-1,4-diazacycloheptane)] find the square-pyramidal (bme-dach)M(NO) unit to serve as a bidentate ligand via the cis-dithiolato sulfurs, with a hinge angle of the butterfly bimetallic structures of ca. 130 degrees . The W(CO)4 moiety is used as a probe of the electron-donor ability of the nitrosyl complexes through CO stretching frequencies that display a minor increase as compared to analogous [(N2S2)Ni]W(CO)4 complexes. These findings are consistent with the electron-withdrawing influence of the {Co(NO)}(8) and {Fe(NO)}(7) units on the bridging thiolate sulfurs relative to Ni(2+). Also sensitive to derivatization by W(CO)4 is the NO stretch, which blue shifts by ca. 30 and 50 cm(-1) for the Co and Fe complexes, respectively. Cyclic voltammetry studies find similar reduction potentials (-1.08 V vs NHE in N, N-dimethylformamide solvent) of the (bme-dach)Co(NO) and (bme-dach)Fe(NO) free metalloligands, which are positively shifted by ca. 0.61 and 0.48 V, respectively, upon complexation to W(CO)4.