- Synthesis and Catalytic Applications of Heterobimetallic Carbene Complexes Obtained via Sequential Metalation of Two Bisazolium Salts
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A simple sequential metalation approach starting from the imidazolium/benzimidazolium salt 4(I)2 yielded the heterobimetallic RhIII/M (M = PdII, IrI, AuI, RuII) complexes [6]-[9]. Alternatively, a symmetrical 1,3-imidazolium substituted benzene was used for the preparation of the heterobimetallic M′/PdII (M′ = RhIII, IrIII) complexes [12] and [13]. The versatile stepwise approach used for the preparation of complexes [6]-[9] involved the deprotonation reaction of the bisazolium salt 4(I)2 in the presence of [RhCp?(Cl)2]2 to afford the monometallic complex [5]I featuring a chelating coordinated bidentate CNHC^Cphenyl ligand. Complex [5]I was reacted with Ag2O to give a nonisolated RhIII/AgI complex which in a subsequent transmetalation reaction yielded the heterobimetallic RhIII/M bis-NHC complexes (M = PdII [6], IrI [7], AuI [8], RuII [9]). Similarly, heterobimetallic M′/PdII bis-NHC complexes [12] (M′ = RhIII) and [13] (M′ = IrIII) have been prepared from a symmetrical bisazolium salt by generating first the monometallic M′ complexes followed by a transmetalation reaction of the in situ generated M′/AgI complexes with [Pd(dmba)(μ-Cl)]2. The RhIII/PdII complexes [6] and [12] and the IrIII/PdII complex [13] were used as catalysts for two orthogonal tandem reactions, namely, the Suzuki-Miyaura coupling/transfer hydrogenation and the Suzuki-Miyaura-coupling/α-alkylation of ketones. The catalytic activity of the heterobimetallic complexes was compared to mixtures of the related monometallic analogues [14]-[17], with the heterobimetallic complexes generally showing a higher catalytic activity. In addition, nBuOH was found to play a dual role as an alkylating and reducing agent in the Suzuki-Miyaura coupling/α-alkylation of ketones.
- B?hmer, Maximilian,Guisado-Barrios, Gregorio,Kampert, Florian,Roelfes, Florian,Tan, Tristan Tsai Yuan,Peris, Eduardo,Hahn, F. Ekkehardt
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p. 2120 - 2131
(2019/05/21)
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- Well-defined Ir/Pd complexes with a triazolyl-diylidene bridge as catalysts for multiple tandem reactions
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The ligand 1,2,4-trimethyl-triazolyl-diylidene has been used for the preparation of a series of three iridium/palladium heterometallic complexes that have been fully characterized. The presence of the two different metals allows tandem processes to be designed by combining reactions that are typically catalyzed by Ir and Pd. Three tandem reactions have been studied: dehalogenation/transfer hydrogenation of haloacetophenones, Suzuki-coupling/ transfer hydrogenation of p-bromoacetophenone, and Suzukicoupling/ α-alkylation of p-bromoacetophenone. All three reactions yielded excellent outcomes to the corresponding final products, with the relevant feature that the heterodimetallic complexes are more active than the sum of the corresponding homodimetallic species. All three catalytic reactions reported here constitute unprecedented examples of tandem approaches to complex organic molecules.
- Zanardi, Alessandro,Mata, Jose A.,Peris, Eduardo
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experimental part
p. 14531 - 14537
(2010/02/28)
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