Coupling of CpCr(CO)₃ and Heterocyclic Dithiadiazolyl Radicals. Synthetic, X-ray Diffraction, Dynamic NMR, EPR, CV, and DFT Studies

The reaction of the 1,2,3,5-dithiadiazolyls (4-R-C6H4CN2S2)2 (R = Me, 2a; Cl, 2b; OMe, 2c; and CF3, 2d) and (3-NC-5-tBu-C6H3CN2S2)2 (2e) with [CpCr(CO)3]2 (Cp = η5-C5H5) (1) at ambient temperature respectively yielded the complexes CpCr(CO)2(η2-S2N2CC6H4R) (R = 4-Me, 3a; 4-Cl, 3b; 4-OMe, 3c; and 4-CF3, 3d) and CpCr(CO)2(η2-S2N2CC6H3-3-(CN)-5-(tBu)) (3e) in 35−72% yields. The complexes 3c and 3d were also synthesized via a salt metathesis method from the reaction of NaCpCr(CO)3 (1B) and the 1,2,3,5-dithiadiazolium chlorides 4-R-C6H4CN2S2Cl (R = OMe, 8c; CF3, 8d) with much lower yields of 6 and 20%, respectively. The complexes were characterized spectroscopically and also by single-crystal X-ray diffraction analysis. Cyclic voltammetry experiments were conducted on 3a−e, EPR spectra were obtained of one-electron-reduced forms of 3a−e, and variable temperature 1H NMR studies were carried out on complex 3d. Hybrid DFT calculations were performed on the model system [CpCr(CO)2S2N2CH] and comparisons are made with the reported CpCr(CO)2(π-allyl) complexes.