Stability and Unimolecular Reactivity of Palladate(II) Complexes [L_nPdR₃]⁻ (L=Phosphine, R=Organyl, n=0 and 1)

Abstract

The reduction of Pd precatalysts to catalytically active Pd species is a key step in many palladium-mediated cross-coupling reactions. Besides phosphines, the stoichiometrically used organometallic reagents can afford this reduction, but do so in a poorly understood way. To elucidate the mechanism of this reaction, we have treated solutions of Pd(OAc) and a phosphine ligand L in tetrahydrofuran with RMgCl (R=Ph, Bn, Bu) as well as other organometallic reagents. Analysis of these model systems by electrospray- ionization mass spectrometry found palladate(II) complexes [L PdR ] (n=0 and 1), thus pointing to the occurrence of transmetallation reactions. Upon gas-phase fragmentation, the [L PdR ] anions preferentially underwent a reductive elimination to yield Pd species. The sequence of the transmetallation and reductive elimination, thus, constitutes a feasible mechanism for the reduction of the Pd(OAc) precatalyst. Other species of interest observed include the Pd complex [PdBn ] , which did not fragment via a reductive elimination but lost BnH instead.

Rapid Room‐Temperature, Chemoselective C−C Coupling of Poly(pseudo)halogenated Arenes Enabled by Palladium(I) Catalysis in Air

“…CÀOTfa ddition is predicted to be even less favored (see the Supporting Information). In contrast, an anionic palladium(0) species [Pd 0 (PtBu 3 )X À ] with X = halogen or aryl, which may form under conditions with nucleophilic additives, [2a, 3a,f, 9] particularly Grignard reagents, [22] is predicted to add preferentially to CÀOTf( by DDG°! 3.5 kcal mol À1 for X = Ph and 2.8 kcal mol À1 for X = Cl).…”

Electronic and Steric Effects on the Reductive Elimination of Anionic Arylferrate(III) Complexes

“…[6a] Indeed, both complexes were found to undergor eductive elimination. [8] In the presentw ork, we extend our studies to as eries of heteroleptic arylferrate(III) model complexes.B ys ystematically varying the electronic and steric properties of the aryl substituents,w eare able to probe the competition betweenc ross-couplinga nd homo-coupling in unprecedentedd etail.…”

Rapid Room‐Temperature, Chemoselective C−C Coupling of Poly(pseudo)halogenated Arenes Enabled by Palladium(I) Catalysis in Air

“…Yield is that of isolated product. In contrast, an anionic palladium(0) species [Pd 0 (PtBu 3 )X À ] with X = halogen or aryl, which may form under conditions with nucleophilic additives, [2a, 3a,f, 9] particularly Grignard reagents, [22] is predicted to add preferentially to CÀOTf( by DDG°! [21] Thec omputational data suggest ac lear preference for oxidative addition at C À Br for both, am onoligated [Pd 0 PtBu 3 ]and aPd I -Pd I derived species (by DDG°!…”