Coupling of CpCr(CO)3 and heterocyclic dithiadiazolyl radicals: synthetic, X-ray diffraction, dynamic NMR, EPR, CV and DFT studies

Abstract

The reaction of 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, yielded respectively the complexes CpCr(CO)2(η2-S2N2CC6H4R) (R = 4-Me, 3a; 4Cl, 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.