The rhenium(V) monooxo complexes (hoz)2Re(O)Cl (1) and [(hoz)2Re(O)(OH2)][OTf] (2) have been synthesized and fully characterized (hoz = 2-(2'-hydroxyphenyl)-2-oxazoline). A single-crystal X-ray structure of 2 has been solved: space group = P1, a = 13.61(2) A, b = 14.76(2) A, c = 11.871(14) A, alpha = 93.69(4) degrees, beta = 99.43(4) degrees, gamma = 108.44(4) degrees, Z = 4; the structure was refined to final residuals R = 0.0455 and Rw = 0.1055. 1 and 2 catalyze oxygen atom transfer from aryl sulfoxides to alkyl sulfides and oxygen-scrambling between sulfoxides to yield sulfone and sulfide. Superior catalytic activity has been observed for 2 due to the availability of a coordination site on the rhenium. The active form of the catalyst is a dioxo rhenium(VII) intermediate, [Re(O)2(hoz)2]+ (3). In the presence of sulfide, 3 is rapidly reduced to [Re(O)(hoz)2]+ with sulfoxide as the sole organic product. The transition state is very sensitive to electronic influences. A Hammett correlation plot with para-substituted thioanisole derivatives gave a reaction constant rho of -4.6 +/- 0.4, in agreement with an electrophilic oxygen transfer from rhenium. The catalytic reaction features inhibition by sulfides at high concentrations. The equilibrium constants for sulfide binding to complex 2 (cause of inhibition), K2 (L x mol(-1)), were determined for a few sulfides: Me2S (22 +/- 3), Et2S (14 +/- 2), and tBu2S (8 +/- 2). Thermodynamic data, obtained from equilibrium measurements in solution, show that the S=O bond in alkyl sulfoxides is stronger than in aryl sulfoxides. The Re=O bond strength in 3 was estimated to be about 20 kcal x mol(-1). The high activity and oxygen electrophilicity of complex 3 are discussed and related to analogous molybdenum systems.

Recently recognized as a water contaminant in the United States, perchlorate (ClO4−) has been added to the Environmental Protection Agency's “Contaminant Candidate List” (CCL) and “Unregulated Contaminants Monitoring Rule” (UCMR). Removal of perchlorate from water is difficult because of its high solubility and kinetic inertness. Oxorhenium(V) oxazoline complexes catalyze the reduction of perchlorate to chloride with organic sulfides [Eq. (1)] at exceptionally fast rates with no sign of deactivation. Tf=trifluoromethanesulfonyl, TON=turn‐over number.

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The measured 13 C chemical shifts of over forty carborane compounds correlate very well with ab-initio/ IGLO/NMR calculated values at both the DZ//3-21G and DZ//6-31G* (IGLO-NMR//Gaussian-geometry-optimized) levels of theory as well as with the ab-initio/GIAO/NMR values at the 6-31G*//6-31G* level of theory. For the carboranes in this study, the linear relationships δ( 13 C-IGLO-DZ//6-31G*) ) 0.941δ( 13 C-exp) -1.897 (r 2) 0.990) and δ( 13 C-GIAO-6-31G*//6-31G*) ) 0.893δ( 13 C-exp) -2.554 (r 2) 0.991) are derived. Combined together with recently reported 11 B NMR correlations between experiment and theory, a significant means is added to the arsenal of carborane NMR structure proof methods available to the experimentalist having access to only modest computational resources. And this procedure, of course, also has the additional feature of yielding reasonably good structural information (bond distances, angles, etc.).