A Highly Active Ylide‐Functionalized Phosphine for Palladium‐Catalyzed Aminations of Aryl Chlorides

Abstract

Ylide‐functionalized phosphine ligands (YPhos) were rationally designed to fit the requirements of Buchwald–Hartwig aminations at room temperature. This ligand class combines a strong electron‐donating ability comparable to NHC ligands with high steric demand similar to biaryl phosphines. The active Pd species are stabilized by agostic C−H⋅⋅⋅Pd rather than by Pd–arene interactions. The practical advantage of YPhos ligands arises from their easy and scalable synthesis from widely available, inexpensive starting materials. Benchmark studies showed that YPhos‐Pd complexes are superior to the best‐known phosphine ligands in room‐temperature aminations of aryl chlorides. The utility of the catalysts was demonstrated by the synthesis of various arylamines in high yields within short reaction times.

Palladium Complexes Based on Ylide‐Functionalized Phosphines (YPhos): Broadly Applicable High‐Performance Precatalysts for the Amination of Aryl Halides at Room Temperature

“…The buried volumes were calculated from the geometries of the isolated L⋅ AuCl complexes (XRD analysis, Figure ), which were prepared by treatment of the YPhos ligands with [(tht)AuCl] (tht=tetrahydrothiophene). With % V bur =47.9 %, L2 holds an intermediate position between the smaller L1 (%V bur =45.2 %) and bulkier L3 (% V bur =51.3 %). The increased size of L2 compared to L1 can be explained by the increased steric demand of the phenyl substituent in the ylide backbone, which results in a smaller P‐C‐P angle (114.1(1)° in L2 compared to 119.1(2) L1 ) thus forcing the PCy 3 moiety closer towards the metal.…”

“…[20] Surprisingly,d etermination of the TEP value of L2 by measuremento ft he CO stretching frequencyi nt he rhodiumc omplexes [Rh(acac)(CO)(L)] (acac = acetylacetone)r evealed that L2 is more electron-rich than expected. With aT EP of 2049.3 cm À1 it is comparable to L1 (TEP = 2050.1 cm À1 ) [10] and the N-heterocyclic carbene IMes (IMes = 1,3-dimesitylimidazol-2-ylidene, IMes:T EP = 2050.7 cm À1 ). [21] This can be explained by the molecular structures of L2 as well as its AuCl complex.…”

“…(tht = tetrahydrothiophene). With %V bur = 47.9 %, L2 holds an intermediate positionb etween the smaller L1 (%V bur = 45.2 %) [10] and bulkier L3 (%V bur = 51.3 %). The increased size of L2 compared to L1 can be explained by the increased steric demando ft he phenyls ubstituent in the ylide backbone, which resultsi nasmaller P-C-P angle (114.1(1)8 in L2 compared to 119.1(2) L1)t hus forcing the PCy 3 moiety closer towards the metal.O verall, all YPhos ligands are sterically bulky ligands, which are more demanding than classical phosphines (e.g.…”

“…Recently, we reported on the ylide‐functionalized phosphine (YPhos) Y Me PCy 2 ( L1 , keYPhos) as an excellent ligand for Buchwald–Hartwig aminations of aryl chlorides at room temperature . In combination with [Pd 2 (dba) 3 ] (dba=dibenzylideneacetone) or Pd(OAc) 2 as metal sources, high activities were observed also with challenging substrates without elaborate tailoring of the ligand design.…”

“…Recently,w er eported on the ylide-functionalizedp hosphine (YPhos) Y Me PCy 2 (L1,k eYPhos) as an excellent ligand for Buchwald-Hartwig aminationso fa ryl chlorides at room temperature. [10] In combination with [Pd 2 (dba) 3 ]( dba = dibenzylideneacetone) or Pd(OAc) 2 as metal sources, high activities were observeda lso with challengings ubstrates withoute laborate tailoring of the ligand design.T of urther evaluatet he potential and improvet he designo fY Phos ligands for broader applications, we becamei nterested in the impact of the ylide moiety and phosphine substituent on the catalytic activity.B oth moieties determine the electron density at the phosphorusa tom and thus the donor property of the ligand. [11] Furthermore, we were also interested in the effect of the use of defined palladium complexesa sp recatalysts in the coupling reactions.…”