title: Development of an improved rhodium catalyst for z-selective anti-markovnikov addition of carboxylic acids to terminal alkynes.
abstract: To develop more active catalysts for the rhodium-catalyzed addition of carboxylic acids to terminal alkynes furnishing anti-Markovnikov Z enol esters, a thorough study of the rhodium complexes involved was performed. A number of rhodium complexes were characterized by NMR, ESI-MS, and X-ray analysis and applied as catalysts for the title reaction. The systematic investigations revealed that the presence of chloride ions decreased the catalyst activity. Conversely, generating and applying a mixture of two rhodium species, namely, [Rh(DPPMP)2][H(benzoate)2] (DPPMP=diphenylphosphinomethylpyridine) and [{Rh(COD)(μ2-benzoate)}2], provided a significantly more active catalyst. Furthermore, the addition of a catalytic amount of base (Cs2CO3) had an additional accelerating effect. This higher catalyst activity allowed the reaction time to be reduced from 16 to 1-4 h while maintaining high selectivity. Studies on the substrate scope revealed that the new catalysts have greater functional-group compatibility.
authors.affiliation: Leibniz-Institut für Katalyse e.V. Albert-Einstein-Strasse 29a, 18059 Rostock (Germany).
authors.forename: Siping
authors.initials: S
authors.lastname: Wei
authors.forename: Julia
authors.initials: J
authors.lastname: Pedroni
authors.forename: Antje
authors.initials: A
authors.lastname: Meißner
authors.forename: Alexandre
authors.initials: A
authors.lastname: Lumbroso
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Drexler
authors.forename: Detlef
authors.initials: D
authors.lastname: Heller
authors.forename: Bernhard
authors.initials: B
authors.lastname: Breit
keywords: N,P ligands; chemoselectivity; enol esters; homogeneous catalysis; rhodium