It Is Not All about the Ligands: Exploring the Hidden Potentials of <i>t</i>Bu<sub>3</sub>P through Its Oxidative Addition Complex as the Precatalyst
Yam N. Timsina, Guolin Xu, Thomas J. Colacot
Abstract
A series of oxidative addition complexes with a general formula ( t Bu 3 P)Pd(Ar)X, as a class of precatalysts, were synthesized for challenging Suzuki–Miyaura coupling involving coupling partners, such as (i) sensitive polyfluorinated arylboronic acids or their corresponding boronic esters, (ii) sterically hindered electrophiles, and (iii) sterically hindered nucleophiles. A total of 89 examples are reported, of which 39 examples are in the Supporting Information. These precatalysts, in particular ( t Bu 3 P)Pd(4-CF 3 Ph)Br, were demonstrated to be powerful catalytic systems in general for cross coupling reactions in comparison to the in situ systems created by mixing t Bu 3 P ligand with a palladium precursor. The precatalysts are also superior to the other monoligated systems, such as Buchwald’s biaryl based G3 or G4 palladacycles. In addition, the ( t Bu 3 P)Pd(4-CF 3 Ph)Br precatalyst is also highly effective for the second most popular coupling reaction, namely the Buchwald–Hartwig coupling. In this study, hindered and electron-deficient amines were coupled with hindered (hetero)aryl bromides and chlorides with 34 examples, of which 8 are in the Supporting Information. Interestingly, the results obtained for both C–C and C–N couplings were on par with or superior to that of the “state-of-the-art” catalysts containing Ad 3 P and Np 3 P ligands for the same or similar substrates, suggesting that it is not all about the ligands.