Dirhodium(II)-Catalyzed Sulfide Oxygenations: Catalyst Removal by Coprecipitation with Sulfoxides

Abstract

The dirhodium(II) carboxylate complex Rh2(esp)2 (esp = α,α,α',α'-tetramethyl-1,3-benzenedipropanoate) was shown to catalyze the sulfoxidation of organic sulfides using tert-butyl hydroperoxide as the oxidant. Due to the unique structure of Rh2(esp)2 and its stable Rh2(II,II) catalyst resting state, the rhodium catalyst is able to precipitate as a Rh2(esp)2-sulfoxide complex following the reaction which makes separation of the catalyst from the products very convenient. The precipitated Rh2(esp)2-sulfoxide complexes could be reused to catalyze sulfide oxygenation reactions without considerable loss of activity. Mechanistic studies suggest that the axial ligands fine-tune the redox potential of the dirhodium(II,II) compounds and determine the predominant catalyst species in the oxidation reaction.

Dirhodium(II,II) Paddlewheel Complexes

“…Photochemical and thermal evolution of molecular hydrogen from water [111] can be catalyzed with dirhodium paddlewheel complexes with electron withdrawing carboxylate ligands [112] . Rh(II) to Rh(III) redox transitions of dirhodium complexes are used in reduction/oxidation processes (e. g. sulfide oxygenations catalyzed by Rh 2 (esp) 2 ( W1 , Figure 24) [275] or allylic oxidations of alkenes with hydrogen peroxide as an oxidant catalyzed by caprolactam dirhodium complex ( C1 , Figure 5) [113] or by Rh 2 (esp) 2 ( W1 , Figure 24)) [276] …”

Visible light sensitizer-catalyzed highly selective photo oxidation from thioethers into sulfoxides under aerobic condition

“…Oxidation of thioethers into sulfoxides was the most straightforward pathway for the synthesis of sulfoxides 9 – 11 . Several methods in this field were developed during the past decades, including hydrogen peroxide oxidation 12 – 14 , metal complexes-catalyzed oxidation 15 – 20 , organocatalytic oxidation 21 , photo oxidation 22 – 27 , etc. However, stoichiometric external organic or inorganic oxidants were generally required in those reactions.…”

“…Another issue of those methods were the low selectivity between sulfoxides and over-oxidized by-product sulfones in many cases 14 . Although some catalytic system showed high selectivity, but the catalyst was too expensive to practical applications 15 , 17 . With the consideration of “Green Chemistry”, an environmentally friendly, energy-saving, atom-economical, and highly selective oxidation from thioethers to sulfoxides is required.…”

Oxidation of sulfides using recyclable pseudocyclic benziodoxole triflate

“…p-Nitrophenyl methyl sulfoxide (4i). 35 Reaction of p-nitrophenyl methyl sulfide 3i (21 mg, 0.125 mmol) according to general procedure afforded 22 mg (96%) of product 4i as a white solid: mp 150.5-150.8 °C (lit. 35 ; mp 153.0-155.0 o C): 1 H NMR (500 MHz, CDCl3):  8.38 (d, J 9.0 Hz, 2H), 7.83 (d, J 9.0 Hz, 2H), 3.79 (s, 3H).…”