Anionic Palladium(0) and Palladium(II) Ate Complexes

Abstract

Palladium ate complexes are frequently invoked as important intermediates in Heck and cross-coupling reactions, but so far have largely eluded characterization at the molecular level. Here, we use electrospray-ionization mass spectrometry, electrical conductivity measurements, and NMR spectroscopy to show that the electron-poor catalyst [L Pd] (L=tris[3,5-bis(trifluoromethyl)phenyl]phosphine) readily reacts with Br ions to afford the anionic, zero-valent ate complex [L PdBr] . In contrast, more-electron-rich Pd catalysts display lower tendencies toward the formation of ate complexes. Combining [L Pd] with LiI and an aryl iodide substrate (ArI) results in the observation of the Pd ate complex [L Pd(Ar)I ] .

Palladium–Borane Cooperation: Evidence for an Anionic Pathway and Its Application to Catalytic Hydro‐/Deutero‐dechlorination

“…Anionic Pd 0 species are generally formed by addition of nucleophiles,typically halides,toPd 0 centers. [17] In the case of complex 1,t he borane moiety present in the coordination sphere of Pd can serve as an acceptor to give access to anionic Pd 0 borate species.T his chemical behavior was realized by reacting 1 with KH at 60 8 8Ci nt he presence of [2.2.2]cryptand. TheP d 0 borohydride complex 2 was thereby obtained in 43 %isolated yield after workup.…”

Second Comes First: Switching Elementary Steps in Palladium‐Catalyzed Cross‐Coupling Reactions

“…Thea ddition of LiI to the sample solution ensured that anyf ormed neutral heteroleptic palladium(II) products would have been readily ionized by the coordination of I À . [12] We then examined the reactions of [L 2 PdBu] À with further substrates. With PrBr,t he heteroleptic product complex [LPdBu 2 Pr] À was formed again, although more slowly than in the reaction with PrI as ac omparison of the signal intensity of the product ion relative to that of [L 2 PdBu] À indicated (Figures S60 andS 61).…”

“…As we have shown previously,e lectron-poorp hosphines, such as La nd,t oal esser extent L Ph1 (Figure 1) palladate(0) complexes of the type L n PdX À ,X = Cl, Br,I , OAc. [12,13] Here, we investigate whether these ligands also stabilize anionic organopalladates formed upon the reactiono fL 3 Pd with RMgX and other organometallic reagents and whether such anionic complexes reactw ith alkyl halides to afford crosscoupling products. To identify palladate intermediates, we use negative-ion mode electrospray-ionization (ESI) mass spectrometry.T his methodh as proven wells uitable for the detection of these and other anionic organometallate complexes.…”

“…To identify palladate intermediates, we use negative-ion mode electrospray-ionization (ESI) mass spectrometry.T his methodh as proven wells uitable for the detection of these and other anionic organometallate complexes. [12,[14][15][16][17][18] By combiningE SI mass spectrometry with gasphase experiments on mass-selected species,w ec an also determinet he microscopic reactivity of species of interesta nd directly probe their catalytic competence.…”

The Intermediates in Lewis Acid Catalysis with Lanthanide Triflates

“…[7] Examples of reactions catalysed by these metals include Friedel-Crafts acylations, [8] Michael additions, [9,10] aldol condensations [11] and cycloadditions. [18,19,28,29,[20][21][22][23][24][25][26][27] Electrospray ionization mass spectrometry (ESI-MS) is a highly sensitive technique for monitoring complex reaction mixtures. [17] The growing use and applications of lanthanides as catalysts calls for detailed understanding of their speciation in solution and their reactivity modes.…”