Controlled Sulfur Oxygenation of the Ruthenium Dithiolate (4,7-Bis-(2′-methyl-2′-mercaptopropyl)-1-thia-4,7-diazacyclononane)RuPPh₃ under Limiting O₂ Conditions Yields Thiolato/Sulfinato, Sulfenato/Sulfinato, and Bis-Sulfinato Derivatives

Abstract

The ruthenium(II) dithiolate complex (bmmp-TASN)RuPPh(3) (1) reacts with O(2) under limiting conditions to yield isolable sulfur oxygenated derivatives as a function of reaction time. With this approach, a family of sulfur-oxygenates has been prepared and isolated without the need for O-atom transfer agents or column chromatography. Addition of 5 equiv of O(2) to 1 yields the thiolato/sulfinato complex (bmmp-O(2)-TASN)RuPPh(3) (2) in 70% yield within 5 min. Increasing the reaction time to 12 h yields the sulfenato/sulfinato derivative (bmmp-O(3)-TASN)RuPPh(3) (3) in 82% yield. Longer reaction times and/or additional O(2) exposure yield the bis-sulfinato complex (bmmp-O(4)-TASN)RuPPh(3) (4). All products remain in the Ru(II) oxidation state under the conditions employed. Stoichiometric hydrolysis of acetonitrile to acetamide by 2 and 3 is observed in mixed acetonitrile, methanol, PIPES buffer (pH = 7.0) mixtures. The Ru(III)/(II) reduction potential of -0.85 V (versus ferrocenium/ferrocene) for 1 shifts to -0.39 and -0.26 V for 2 and 3, respectively, because of the decreased donor ability of sulfur upon oxygenation. X-ray diffraction studies reveal a decrease in Ru-S bond distances upon oxygenation by 0.045(1) and 0.158(1) Å for the sulfenato and sulfinato donors, respectively. Conversely, sulfur-oxygenation increases the Ru-P bond distance by 0.061(1) Å from 1 to 2 and an additional 0.027(1) Å from 2 to 3. Density functional theory investigations using the BP86 and B3LYP functionals with a LANL2DZ basis set for Ru and the 6-31G(d) basis set for all other atoms reveal a direct correlation between the oxygenation level and the Ru-P distance with an increase of 0.031 Å per O-atom.

Kinetic Effects of Sulfur Oxidation on Catalytic Nitrile Hydration: Nitrile Hydratase Insights from Bioinspired Ruthenium(II) Complexes

“…However, this is more than offset by the substantial decrease in the enthalpy of activation upon S-oxidation. Notably, the enhanced Lewis acidity of the metal center upon S-oxidation, as noted in electrochemical studies (positive shift of half potential as result of sulfur oxidation) and XAS and DFT studies on L n RuPPh 3 , 19,26 is also expected to lower the enthalpic barrier. The further lowering of the enthalpy of activation of Co-NHase relative to L 2 RuPPh 3 and L 3 RuPPh 3 can be attributed to the greater Lewis of acidity of Co(III) as compared to Ru(II).…”

Sequential Oxidations of Thiolates and the Cobalt Metallocenter in a Synthetic Metallopeptide: Implications for the Biosynthesis of Nitrile Hydratase

“…16–22 However, few of these have even modest nitrile hydrolysis activity, and most of those that utilize oxidized sulfur contain bis-sulfinate ligands since controlling the extent of oxidation of the metal-bound thiolates has proven difficult. 23 This has been especially true for reactions of thiolates with oxygen, as opposed to O-atom transfer reagents, which tend to yield sulfinato complexes. 18, 23–34 Nonetheless, oxygen is believed to be the oxidant in vivo for modification of the sulfur atoms of NHase.…”

Sulfur-oxidation enhances nitrile hydration in bioinspired ruthenium complexes : catalytic, kinetic, and DFT investigations.

“…Preliminary studies using acetonitrile as substrate showed that complex 48 did not hydrate the nitrile, whereas with both 49 and 50 sub-stoichiometric activity was noticed. 81 These results further inspired detailed studies to determine effect of sulfur-oxidation, temperature, inhibitor, substrate ratio, and metal-centered oxidation state on catalytic activity that are the focus of Chapter 3 in this dissertation. Chapter 4 extends the study to include kinetic assays and Chapter 5 includes DFT studies.…”

“…The ligand H2(bmmp-TASN) and precatalysts L 2-3 RuPPh3 were prepared as described in the literature and precatalyst L 1 RuPPh3 was prepared through a slight modification to the procedure reported in literature. 74,[80][81]83 A 0.500 mL aliquot of stock solution of L 1-3 RuPPh3 in benzonitrile (5.4 X 10 -4 M), measured using an automatic micropipette was transferred to 3 mL screw-top vial containing the desired quantities of benzonitrile and water to make a total volume of 2.000 mL. The vial was capped using an air-tight teflon screw cap under argon atmosphere.…”

“…3.9). [80][81] Preliminary room temperature catalytic assays using acetonitrile as the substrate revealed no activity for complexes L 1-2 RuPPh3 with sub-stoichiometric nitrile hydration for L 3 RuPPh3. We anticipated that elevated temperature would lead to phosphine dissociation opening a vacant site for substrate binding and promoting hydration activity.…”