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C(sp 3 )–Cl Bond Activation Promoted by a POP-Pincer Rhodium(I) Complex

2019; American Chemical Society; Volume: 38; Issue: 15 Linguagem: Inglês

10.1021/acs.organomet.9b00409

1520-6041

Sheila G. Curto, Laura A. de las Heras, Miguel A. Esteruelas, Montserrat Oliván, Enrique Oñate,

Organometallic Complex Synthesis and Catalysis

The complex [RhCl(κ3P,O,P-{xant(PiPr2)2})] (1; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) activates C(sp3)–Cl bonds of mono- and dichloroalkanes and catalyzes the dehalogenation of chloroalkanes and the homocoupling of benzyl chloride. Complex 1 reacts with chlorocyclohexane to give [RhHCl2(κ3P,O,P-{xant(PiPr2)2})] (2) and cyclohexene and promotes the dehalogenation of the chlorocycloalkane to cyclohexane using 2-propanol solutions of sodium formate as the reducing agent. The oxidative addition of benzyl chloride to 1 leads to [Rh(CH2Ph)Cl2(κ3P,O,P-{xant(PiPr2)2})] (4). The dehalogenation of this chloroalkane with 2-propanol solutions of sodium formate, in the presence of 1, gives toluene and 1,2-diphenylethane. The latter is selectively formed with KOH instead of sodium formate. Complex 1 also reacts with trans-1,2-dichlorocyclohexane and dichloromethane. The reaction with the former gives [RhCl3(κ3P,O,P-{xant(PiPr2)2})] (5) and cyclohexene, whereas complex 1 undergoes oxidative addition of dichloromethane to afford cis-dichloride-[Rh(CH2Cl)Cl2(κ3P,O,P-{xant(PiPr2)2})] (6a), which evolves into its trans-dichloride isomer 6b. The kinetic study of the overall process suggests that the oxidative addition is cis-concerted and the isomerization an intramolecular reaction which takes place through a σ-C–Cl intermediate with two conformations.