Pd(η ~3-1-PhC 3H 4)(η ~5- C 5H 5), an unusually effective catalyst precursor for Suzuki-Miyaura cross-coupling reactions catalyzed by bis-phosphine palladium(0) compounds

摘要

It has previously been shown that the easily handled, heat- and air-stable compound Pd(η ~3-1-PhC_3H_4)(η ~5- C_5H_5) (Vb) reacts rapidly with a wide variety of tertiary phosphines L to produce near-quantitative yields of the corresponding Pd(0) compounds PdL_2, which are widely believed to be the active species in many often-used cross-coupling catalyst systems based on Pd(PPh_3)_4 (I), Pd_2(dba)_3 (II), PdCl_2 (III), and Pd(OAc)_2 (IV). However, catalyst precursors I-IV are in fact known to preferentially generate sterically hindered, three-coordinate Pd(0) species rather than two-coordinate PdL_2, and thus Vb is hypothetically expected to be a better catalyst precursor for e.g. Suzuki-Miyaura cross-coupling reactions. Utilizing the conventional Suzuki-Miyaura cross-coupling reaction of phenylboronic acid with bromoanisole, comparisons are made of the efficacies of catalyst systems based on Vb with those based on compounds I-IV (L = the representative phosphines PPh_3, PCy_3, PBu ~t_3). As anticipated, catalysts generated from Vb are significantly more competent and, as a bonus, Vb makes palladium(0) complexes PdL_2 available under rigorously anhydrous conditions.