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

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posted on 21.01.2008, 00:00 by Hiu Fung Lau, Pearly Chwee Ying Ang, Victor Wee Lin Ng, Seah Ling Kuan, Lai Yoong Goh, Alexey S. Borisov, Paul Hazendonk, Tracey L. Roemmele, René T. Boeré, Richard D. Webster
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)22-S2N2CC6H4R) (R = 4-Me, 3a; 4-Cl, 3b; 4-OMe, 3c; and 4-CF3, 3d) and CpCr(CO)22-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 3ae, EPR spectra were obtained of one-electron-reduced forms of 3ae, 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.