Synthesis and X-ray structure determination of highly active Pd(II), Pd(I), and Pd(0) complexes of di(tert-butyl)neopentylphosphine (DTBNpP) in the arylation of amines and ketones.
The air-stable complex Pd(η(3)-allyl)(DTBNpP)Cl (DTBNpP = di(tert-butyl)neopentylphosphine) serves as a highly efficient precatalyst for the arylation of amines and enolates using aryl bromides and chlorides under mild conditions with yields ranging from 74% to 98%. Amination reactions of aryl bromides were carried out using 1-2 mol % Pd(η(3)-allyl)(DTBNpP)Cl at 23-50 °C without the need to exclude oxygen or moisture. The C-N coupling of the aryl chlorides occurred at relatively lower temperature (80-100 °C) and catalyst loading (1 mol %) using the Pd(η(3)-allyl)(DTBNpP)Cl precatalyst than the catalyst generated in situ from DTBNpP and Pd(2)(dba)(3) (100-140 °C, 2-5 mol % Pd). Other Pd(DTBNpP)(2)-based complexes, (Pd(DTBNpP)(2) and Pd(DTBNpP)(2)Cl(2)) were ineffective precatalysts under identical conditions for the amination reactions. Both Pd(DTBNpP)(2) and Pd(DTBNpP)(2)Cl(2) precatalysts gave nearly quantitative conversions to the product in the α-arylation of propiophenone with p-chlorotoluene and p-bromoanisole at a substrate/catalyst loading of 100/1. At lower substrate/catalyst loading (1000/1), the conversions were lower but comparable to that of Pd(t-Bu(3)P)(2). In many cases, the tri-tert-butylphosphine (TTBP) based Pd(I) dimer, [Pd(μ-Br)(TTBP)](2), stood out to be the most reactive catalyst under identical conditions for the enolate arylation. Interestingly, the air-stable Pd(I) dimer, Pd(2)(DTBNpP)(2)(μ-Cl)(μ-allyl), was less active in comparison to [Pd(μ-Br)(TTBP)](2) and Pd(η(3)-allyl)(DTBNpP)Cl. The X-ray crystal structures of Pd(η(3)-allyl)(DTBNpP)Cl, Pd(DTBNpP)(2)Cl(2), Pd(DTBNpP)(2), and Pd(2)(DTBNpP)(2)(μ-Cl)(μ-allyl) are reported in this paper along with initial studies on the catalyst activation of the Pd(η(3)-allyl)(DTBNpP)Cl precatalyst.
Hill
Lensey L
LL
Department of Chemistry, The University of Alabama, Box 870336, Tuscaloosa, Alabama 35487-0336, USA.
Crowell
Jason L
JL
Tutwiler
Strudwick L
SL
Massie
Nicholas L
NL
Hines
C Corey
CC
Griffin
Scott T
ST
Rogers
Robin D
RD
Shaughnessy
Kevin H
KH
Grasa
Gabriela A
GA
Johansson Seechurn
Carin C C
CC
Li
Hongbo
H
Colacot
Thomas J
TJ
Chou
Joe
J
Woltermann
Christopher J
CJ
D000588:Amines / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D007659:Ketones / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010720:Phosphines / Q000737:chemistry*; D013237:Stereoisomerism
D000588:Amines; D007659:Ketones; D009942:Organometallic Compounds; D010720:Phosphines; C554650:di(tert-butyl)neopentylphosphine; D010165:Palladium