52359-16-7Relevant academic research and scientific papers
Synthesis and reactivity of a cationic palladium complex as possible intermediate in a Suzuki-Miyaura cross-coupling reaction
Kohlmann, Johannes,Braun, Thomas
, p. 140 - 145 (2017)
A stoichiometric reaction of a palladium fluorido complex with an aromatic boronic ester yielded a fluorinated 4-aryl phenylalanine derivative (aryl = 4-C6H4SF5) as Suzuki-Miyaura cross-coupling product. Due to the high reactivity of the metal complex, the reaction proceeded smoothly at ambient temperature. Low-temperature NMR investigations revealed a possible role of trans‐[Pd{BF(4-C6H4SF5)(pin)}(PheEt)(PiPr3)2] (5, PheEt = bound phenylalanine derivative = 4-C6H4CH2C{NHC(O)CH3}(CO2Et)2, pin = pinacolato = O2C2Me4) as a potential intermediate of the transmetallation step. Compound 5 resulted from fluoride transfer from palladium to boron. The similar complex trans-[Pd(BF4)(PheEt)(PiPr3)2] (7) was generated on treatment of the fluorido complex with NaBF4. Complex 7 is not stable at room temperature. Degradation gave the phosphonium salt [PiPr3PheEt][BF4] (4). Interestingly, the same compound was also found in the initially mentioned cross-coupling reaction as minor product.
Structural, Kinetic, and Computational Characterization of the Elusive Arylpalladium(II)boronate Complexes in the Suzuki-Miyaura Reaction
Thomas, Andy A.,Wang, Hao,Zahrt, Andrew F.,Denmark, Scott E.
supporting information, p. 3805 - 3821 (2017/03/20)
The existence of the oft-invoked intermediates containing the crucial Pd-O-B subunit, the “missing link”, has been established in the Suzuki-Miyaura cross-coupling reaction. The use of low-temperature, rapid injection NMR spectroscopy (RI-NMR), kinetic studies, and computational analysis has enabled the generation, observation, and characterization of these highly elusive species. The ability to confirm the intermediacy of Pd-O-B-containing species provided the opportunity to clarify mechanistic aspects of the transfer of the organic moiety from boron to palladium in the key transmetalation step. Specifically, these studies establish the identity of two different intermediates containing Pd-O-B linkages, a tri-coordinate (6-B-3) boronic acid complex and a tetra-coordinate (8-B-4) boronate complex, both of which undergo transmetalation leading to the cross-coupling product. Two distinct mechanistic pathways have been elucidated for stoichiometric reactions of these complexes: (1) transmetalation via an unactivated 6-B-3 intermediate that dominates in the presence of an excess of ligand, and (2) transmetalation via an activated 8-B-4 intermediate that takes place with a deficiency of ligand.
