Mechanistic Insights into the C–S Bond Breaking in Dibenzothiophene Sulfones

Abstract

The reactivity of Grignard reagents in the presence of nickel catalysts is known to be highly efficient in the deoxydesulfurization of dibenzothiophene sulfone (DBTO 2 ), 4-methyldibenzothiophene (4-MeDBTO 2 ), and 4,6-dimethyldibenzothiophene (4,6-Me 2 DBTO 2 ), to yield sulfur-free biphenyls via cross-coupling reactions. However, the mechanistic details involved in the process remained unknown. In this report the reactivity of [(dippe)Pt(μ-H)] 2 with DBTO 2 turned out to be catalytically less efficient compared with [(dippe)Ni(μ-H)] 2 , but the first allowed the isolation and full characterization of several reaction intermediates, such as [(dippe)Pt(κ 2 -C,S-DBTO 2 )]. It was demonstrated that this is a key intermediate in all the deoxydesulfurization reactions of the above-mentioned aromatic sulfones (DBTsO 2 ).

Transition-metal mediated carbon–sulfur bond activation and transformations

“…Desulfonylation of TsCl by a transition metal complex has been known for quite a long time. Treatment of complex Ir(CO)(PPh 3 ) 3 (176) with TsCl formed complex 177 which was decomposed to desulfitative complex 178 by loss of SO 2 upon heating (eqn ( 64)). 136 Although the C-S bond in a sulfonyl chloride can be considered as an activated bond, only limited work has been directed towards the catalytic desulfitative carbon-carbon cross-couplings of sulfonyl chlorides, i.e., their relevant Stille, Suzuki, Sonogashira, Heck and Negishi reactions.…”

Nickel‐Catalyzed Kumada Reaction of Tosylalkanes with Grignard Reagents to Produce Alkenes and Modified Arylketones

“…Intermediate B is readily formed from intermediate A with MeMgBr base, followed by oxidative addition of the active Ni 0 species to the C vinyl S bond affords intermediate C 8. Transmetalation of intermediate C with MeMgBr ( 2 a ) furnishes intermediate D 8a,b. Finally, reductive elimination of intermediate E affords the desired alkenes and the active Ni 0 species.…”

Nickel‐Catalyzed Kumada Reaction of Tosylalkanes with Grignard Reagents to Produce Alkenes and Modified Arylketones

“…Pathway (c) is also proposed to generate intermediate I from tosylalkane 1 through a-deprotonation, oxidative addition, and b-deprotonation. [8] As shown in Table 2 and Equation (2), some experiments were conducted to trap the proposed intermediates. Initially, we rechecked the GC-MS data from the reaction between substrate 1 a and MeMgBr ( Table 2, entry 1 and Table 1, entry 20).…”

“…Based on our experiments, we propose the mechanisms shown in Scheme 4. [1][2][3][7][8][9][10][11] Initially, the ligand exchange of NiI 2 (PPh 3 ) 2 with PCy 3 gives more reactive NiI 2 (PCy 3 ) 2 , followed by conversion of NiI 2 (PCy 3 ) 2 in situ FTIR analysis), [9,10] 4,4'-dimethylbiphenyl, and toluene. [1] Intermediate B is readily formed from intermediate A with MeMgBr base, followed by oxidative addition of the active Ni 0 species to the C vinyl À S bond affords intermediate C. [8] Transmetalation of intermediate C with MeMgBr (2 a) furnishes intermediate D. [8a,b] Finally, reductive elimination of intermediate E affords the desired alkenes and the active Ni 0 species.…”

“…Intermediate E undergoes b-hydrogen elimination leading to a nickel-hydride complex intermediate F. [2,3,7] An addition reaction takes place on intermediate F to furnish intermediate G. Pathway (c) is also proposed to generate intermediate I from tosylalkane 1 through a-deprotonation, oxidative addition, and b-deprotonation. [8] As shown in Table 2 and Equation (2), some experiments were conducted to trap the proposed intermediates. Initially, we rechecked the GC-MS data from the reaction between substrate 1 a and MeMgBr ( Table 2, entry 1 and Table 1, entry 20).…”