Ylide‐Functionalized Phosphines: Strong Donor Ligands for Homogeneous Catalysis

Abstract

Phosphines are important ligands in homogenous catalysis and have been crucial for many advances, such as in cross‐coupling, hydrofunctionalization, or hydrogenation reactions. Herein we report the synthesis and application of a novel class of phosphines bearing ylide substituents. These phosphines are easily accessible via different synthetic routes from commercially available starting materials. Owing to the extra donation from the ylide group to the phosphorus center the ligands are unusually electron‐rich and can thus function as strong electron donors. The donor capacity surpasses that of commonly used phosphines and carbenes and can easily be tuned by changing the substitution pattern at the ylidic carbon atom. The huge potential of ylide‐functionalized phosphines in catalysis is demonstrated by their use in gold catalysis. Excellent performance at low catalyst loadings under mild reaction conditions is thus seen in different types of transformations.

Mono- and diylide-substituted phosphines (YPhos): impact of the ligand properties on the catalytic activity in gold(i)-catalysed hydroaminations

“…30% conversion after 24 h under the same reaction conditions. 10 At higher temperatures (70°C), the reaction with 6 as catalyst is also completed within less than 3 h reaction time. Overall, Y CN PtBu 2 and (Y CN ) 2 PCy are the most active catalysts and comparable to CyJohnPhos under these reaction conditions (see the ESI, † Table S1).…”

“…The synthesis of the mono-ylide substituted phosphines 1 and 2 was previously reported via reaction of Y CN -M with one equivalent of the corresponding chlorophosphine (Scheme 1). 10 Analogous treatment of Y CN -Na with di-tert-butylchlorophosphine, tBu 2 -PCl, selectively produced the ylide-substituted phosphine Y CN PtBu 2 (3) as evidenced by 31 P{ 1 H} NMR spectroscopy. Work-up delivered the ligand as colorless solid in 46% yield.…”

“…9 Recently, our group reported on the synthesis of ylidesubstituted phosphines (YPhos) and their application in goldcatalyzed hydroamination reactions as well as palladium catalyzed Buchwald-Hartwig aminations and α-arylations. 10,11 The molecular architecture of the triphenylphosphoniumsubstituted YPhos ligands is somewhat reminiscent to biarylphosphines due to the possible interaction of the metal with one of the phosphonium bound phenyl groups (Fig. 1).…”

“…However, due to the carbanionic centre next to the phosphorus atom, these ligands possess an increased donor capacity, whichdepending on the substitution patternmay reach or even surpass that of N-heterocyclic carbenes. 10 Given the efficiency of mono-ylide substituted phosphines, we now became interested in the impact of two ylide moieties on the ligand synthesis and their efficiency in catalytic applications. Owing to their enhanced donor properties as well as increased steric demand, we expected these ligands to be particularly suited for the stabilization of the cationic AuIJI) species and the production of highly effective catalysts for hydroamination reactions.…”

Pyridinylidenaminophosphines: Facile Access to Highly Electron‐Rich Phosphines

“…More recently, the family of highly electron‐rich phosphines with π‐donor substituents has been extended by the groups of Gessner and Sundermayer using phosphoniumylidyl (R 3 P=CR−) and phosphazenyl (R 3 P=N−) groups, respectively . Although strongly donating phosphines have great potential as ligands in coordination chemistry and catalysis, their broad application as ligands, but more importantly in stoichiometric reactions, is often hampered by their rather difficult synthesis.…”