An oxidorhenium(v) complex with an electron-withdrawing ligand: benefits and drawbacks for a dual role catalyst.

One very unique feature of oxidorhenium(v) complexes is their dual catalytic activity in both reduction of stable oxyanions like perchlorate ClO and nitrate NO as well as epoxidation of olefins. In our ongoing research efforts, we were interested to study how an electron-withdrawing ligand would affect both these catalytic reactions. Hence, we synthesized the novel bidentate dimethyloxazoline-dichlorophenol ligand HL1 and synthesized oxidorhenium(v) complex [ReOCl(L1)] (1). Then, catalytic experiments were conducted showing that non-redox epoxidation activity is indeed enhanced, but redox catalysis oxygen atom transfer (OAT) activity was reduced for ClO and NO reductions. From one nitrate reduction experiment, a small amount of the singly-oxidized dioxidorhenium(vi) complex [ReO(L1)] (2) could be isolated, confirming the successful reduction sequence of nitrate to nitrite NO (2e reduction) to NO (1e reduction). Furthermore, ligand L1 displayed a richer than usually observed coordination chemistry, allowing for the isolation of complexes [ReOCl(SMe)(L1)] (-3a), [ReOCl(OPPh)(L1)] (3b) and [ReCl(OPPh)(L1)] (3c). Complexes 1 and 3a-b were tested in cyclooctene epoxidation, 1 was additionally investigated as an oxyanion reduction catalyst of perchlorate and nitrate. All compounds HL1, 1, 2 and 3a-c could be characterized by single-crystal X-ray diffraction, besides other routine analyses.