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. 2014 Jan 13;33(1):249-253.
doi: 10.1021/om4009873. Epub 2013 Dec 31.

Equilibrium Study of Pd(dba)2 and P(OPh)3 in the Pd-Catalyzed Allylation of Aniline by Allyl Alcohol

Supaporn Sawadjoon  1 , Andreas Orthaber  2 , Per J R Sjöberg  1 , Lars Eriksson  3 , Joseph S M Samec  1
Affiliations

Equilibrium Study of Pd(dba)2 and P(OPh)3 in the Pd-Catalyzed Allylation of Aniline by Allyl Alcohol

Supaporn Sawadjoon et al. Organometallics. .

Abstract

Reaction of Pd(dba)2 and P(OPh)3 shows a unique equilibrium where the Pd[P(OPh)3]3 complex is favored over both Pd(dba)[P(OPh)3]2 and Pd[P(OPh)3]4 complexes at room temperature. At a lower temperature, Pd[P(OPh)3]4 becomes the most abundant complex in solution. X-ray studies of Pd[P(OPh)3]3 and Pd(dba)[P(OPh)3]2 complexes show that both complexes have a trigonal geometry with a Pd-P distance of 2.25 Å due to the π-acidity of the phosphite ligand. In solution, pure Pd(dba)[P(OPh)3]2 complex equilibrates to the favored Pd[P(OPh)3]3 complex, which is the most stable complex of those studied, and also forms the most active catalytic species. This catalyst precursor dissociates one ligand to give the reactive Pd[P(OPh)3]2, which performs an oxidative addition of nonmanipulated allyl alcohol to generate the π-allyl-Pd[P(OPh)3]2 intermediate according to ESI-MS studies.

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Figures

Scheme 1
Scheme 1. Palladium-Catalyzed Allylic Amination with Allyl Substrates
Figure 1
Figure 1
31P{1H} NMR spectra (121 MHz) performed in 0.6 mL of C6D6 with H3PO4 as an external standard: (a) P(OPh)3 (b) Pd[P(OPh)3]3, (c) Pd(dba)[P(OPh)3]2, (d) Pd(dba)2 (15 mM) + P(OPh)3 (30 mM), (e) Pd(dba)2 (15 mM) + P(OPh)3 (60 mM), (f) Pd(dba)2 (15 mM) + P(OPh)3 (120 mM).
Figure 2
Figure 2
VT-31P{1H} NMR spectra (121 MHz) performed in 0.6 mL of C7D8 Pd(dba)2 (15 mM) + P(OPh)3 (60 mM) with H3PO4 as an external standard at temperatures between 25 and −60 °C.
Figure 3
Figure 3
ORTEP representation of Pd(dba)[P(OPh)3]2 at thermal ellipsoids of 50%. Hydrogen atoms and CH2Cl2 solvent molecules are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Pd1–C97 2.126(15), Pd1–C98 2.159(15), Pd1–P1 2.247(5), Pd1–P2 2.254(5), C97–C98 1.348(19), C97–Pd1–C98 36.7(5), P1–Pd1–P2 105.14(17), C97–Pd1–P2 102.7(5), C98–Pd1–P1 115.4(5).
Figure 4
Figure 4
ORTEP representation of Pd[P(OPh)3]3 at thermal ellipsoids of 50%. Only one of the two independent units is displayed. Hydrogen atoms and acetone solvent molecules are omitted for clarity. Selected bond lengths [Å] and angles [deg]: P1–Pd1 2.2498(14), P2–Pd1 2.2525(14), P3–Pd1 2.2573(14), P1–Pd1–P2 116.03(5), P1–Pd1–P3 120.93(5), P2–Pd1–P3 122.94(5).
Figure 5
Figure 5
Pd(dba)[P(OPh)3]2 and Pd[P(OPh)3]3 complexes in the allylation of aniline by allyl alcohol. Reaction conditions: allyl alcohol (0.840 M), aniline (0.209 M), Pd catalyst (2 mol %), C6D6, 60 °C.
Figure 6
Figure 6
ESI mass spectrum of reaction of Pd(dba)[P(OPh)3]2 + allyl alcohol after 5 min at 60 °C.
Figure 7
Figure 7
ESI mass spectrum of reaction of Pd[P(OPh)3]3 + allyl alcohol after 5 min at 60 °C.
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