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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

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posted on 06.12.2010, 00:00 by César A. Masitas, Manoj Kumar, Mark S. Mashuta, Pawel M. Kozlowski, Craig A. Grapperhaus
The ruthenium(II) dithiolate complex (bmmp-TASN)RuPPh3 (1) reacts with O2 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 O2 to 1 yields the thiolato/sulfinato complex (bmmp-O2-TASN)RuPPh3 (2) in 70% yield within 5 min. Increasing the reaction time to 12 h yields the sulfenato/sulfinato derivative (bmmp-O3-TASN)RuPPh3 (3) in 82% yield. Longer reaction times and/or additional O2 exposure yield the bis-sulfinato complex (bmmp-O4-TASN)RuPPh3 (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.

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