A new synthetic route towards stable molecular-weight enlarged monodentate phosphine ligands via click chemistry was developed. These ligands were applied in the Pd-catalyzed SuzukiMiyaura coupling of aryl halides and phenyl boronic acid. The supported systems show very similar activities compared to the unsupported analogues. Moreover, recycling experiments by means of nanofiltration using ceramic nanofiltration membranes demonstrate that these systems can be recovered and reused efficiently.
On the basis of deuterium labeling experiments and an equal 1,2-/1,4-product distribution, the reductive elimination of the product has been established to be the enantioselective step in the nickel-catalyzed hydrocyanation of 1,3-cyclohexadiene. This could be achieved by successfully exploiting the rather unique features of this reaction: identical product formation for 1,2- and 1,4-addition, cis addition over the diene, and high enantiomeric excess.
The straightforward synthesis of cationic complex 1, [Ag(PNP
tBu
)]BF4 (PNPtBu = 1,2-bis[(di-tert-butylphosphino)methyl]pyridine), and its facile transmetalating properties toward gold and palladium are described. The corresponding Au complex [Au(PNPtBu)]2(BF4)2 (2) exists as a dimer in the solid state, as deduced by X-ray crystallography. The transmetalating properties were expanded to include the formation of Pd-alkyl species. Reaction of 1 with 0.5 equiv of Pd(allyl)(μ-Cl) dimer led to clean formation of the [Pd(PNPtBu)(η1-allyl)]BF4 complex 3. The analogous cationic methyl (4), cyanophenyl (5), and chloro species (6) could also be prepared in good yields from appropriate Pd precursors via this transmetalation methodology. The molecular structures for complexes 3−5 were established by X-ray crystallography. Reaction of complexes 4 and 6 with NaN(SiMe3)2 led to deprotonation and dearomatization of the PNP backbone with formation of the neutral Pd species 7 and 8, which can be regarded as the diphosphino-monoamido N-ligated analogues of well-studied Pd(PCPtBu) complexes. These neutral Pd(PN
−
PtBu) complexes 7 and 8 displayed reasonable activity in the Suzuki−Miyaura coupling of phenylboronic acid pinacol ester and bromoarenes.
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