N-Heterocyclic Benzhydrylamines as Ligands in Palladium Complexes: Catalytic Activity in Suzuki Coupling Reaction

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N-Heterocyclic Benzhydrylamines as Ligands in Palladium Complexes: Catalytic Activity in Suzuki

Coupling Reaction

Vincent Terrasson, D. Prim, J. Marrot

To cite this version:

Vincent Terrasson, D. Prim, J. Marrot. N-Heterocyclic Benzhydrylamines as Ligands in Palladium

Complexes: Catalytic Activity in Suzuki Coupling Reaction. BOSS, 2008, Ghent, Belgium. �hal-

02913341�

N-Heterocyclic Benzhydrylamines as Ligands in Palladium Complexes:

Catalytic Activity in Suzuki Coupling Reaction

Institut Lavoisier de Versailles, UMR CNRS 8180, Université de Versailles – Saint-Quentin-en-Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles, France. E-mail: terrasson@chimie.uvsq.fr; prim@chimie.uvsq.fr

References

[1] a) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457. b) A. Suzuki, J. Organomet. Chem. 1999, 576, 147.

[2] a) B. Puget, J.-P. Roblin, D. Prim, Y. Troin, Tetrahedron Lett. 2008, 49, 1706. b) S. Haneda, Z. Gan, K.

Eda, M. Hayashi, Organometallics 2007, 26, 6551. c) S. Haneda, C. Ueda, K. Eda, M. Hayashi, Adv.

Synth. Catal. 2007, 349, 833.

[3] V. Terrasson, S. Marque, A. Scarpacci, D. Prim, Synthesis 2006, 11, 1858.

[4] V. Terrasson, D. Prim, J. Marrot, Eur. J. Inorg. Chem. 2008, 2739.

Vincent Terrasson, Damien Prim, Jérome Marrot

Table 1

1. Synthesis of palladium (II) complexes:

N-heterocyclic benzhydrylamines 1a-c were obtained according to our previously described one-pot procedure (Figure 1).

This strategy was applied to three different

-deficient heterocycles in order to modulate the electronic effects in the new N,N-bidentate ligand series.

Benzylation of 1 a-c to obtain the secondary amines 2 a-c proved judicious in increasing solubility of the complexes in common solvents, making purification and characterization easier.

Further alkylation of the nitrogen atom of 2a leading to tertiary amine 2d was also envisioned to study the influence of steric effects over catalytic activity (Figure 1).

Institut Lavoisier de Versailles

Over the last decades, the Suzuki-Miyaura coupling reaction has become one of the most popular way to create carbone-carbone bounds and found widespread applications in organic synthesis.

This Pd-assisted process offers many advantages over other metal-catalyzed reactions such as commercial availability of a large panel of boronic acids, easy handling and high functional group tolerance, explaining the increasing interest in the scientific community. N,N-bidentate ligands recently proved to efficiently compete with classical phosphine-based ligands and to overcome some of their known drawbacks such as their cost and low air-stability.

Development of new series of N,N-bidentate palladium complexes more efficient and easier to prepare is therefore of great interest.

Acknowledgments : CNRS, Université de Versailles (financial support) and MENRT (grant to V.T.)

R¹ X R² Cat.

(mol.%) Time (h) Conv*

4-NO2 Br 4-CF3 0.01 – A 5 quant. (95)

4-CHO Br 2-Me 0.01 – A 3 quant. (95)

4-CHO Br 3-NO2 0.01 – A 5 quant. (97)

4-OMe Br H 0.1 - A 72 85 %

4-OMe Br H 0.1 - B 18 quant. (89)

2-CN Br 2-Me 0.05 - A 12 quant. (89)

4-CN Cl 2-Me 0.2 - A 24 quant. (89)

2-CHO Cl 4-OMe 0.2 - A 24 quant. (89)

Figure 1

N YX

CN N

YX

NH2 2/ NaBH₄

1/ Ph-MgCl

N YX

HN 1/ Ph-CHO

2/ NaBH₄

Yields over 2 steps:

2a R = H, X = Y = CH, 81 % 2b R = H, X = N, Y = CH, 46 % 2c R =H, X = CH, Y = N, 47 %

2 a-c

N N 2d 76 %

K₂CO₃ MeI 1 a-c

Complexation reactions were next examined (Figure 2). Diamines 2a-d were treated with Na

PdCl

to give the expected palladium (II) complexes 3a-d in high yields after simple filtration through a silica gel pad. These complexes are perfectly air-stable during months, both in the solid state and in solution.

Figure 2

3a R = H, X = Y = CH, 92 % 3b R = H, X = N, Y = CH, 95%

3c R =H, X = CH, Y = N, 93 % 3d R =Me, X = Y = CH, 99 % N

YX

RN

N Y X

N Pd

R Cl

Cl Na2PdCl4

2 a-d MeOH

3 a-d

2. Catalytic activities in Suzuki reaction:

Cat. Time (h)

Conv.

(%)

3a 0.5 34

3d 0.5 28

3b 0.5 50

3c 0.5 70

3c 1 quant.

(92)*

These complexes were fully characterized by NMR spectroscopy and X-ray structure determination (Figure 3).

Figure 3 : X-ray structures.

Catalytic activities of these Pd-complexes in the Suzuki coupling reaction were next studied.

Comparison of our four different complexes in a model reaction proved complex 3c bearing a pyrazine heterocycle was the most efficient (Figure 4, Table1). Catalyst loadings as low as 0.01 mol.% could be successfully used.

The substitution on both boronic acids and aromatic halides were surveyed (Figure 5). Results are gathered in Table 2.

Table 2 Good results are obtained with halides and boronic acids bearing either electron donating or withdrawing groups. It is also worth noting that the use of pure water as a solvent seemed to afford increased yields of biphenyl products in some cases. Our catalytic system also proved efficient in the coupling reaction of aromatic chlorides.

Figure 4

O₂N Br

B(OH)₂

+ NO₂

cat. (0.01 mol.%) Cs₂CO₃ DMF / H₂O

100°C

Figure 5

X

B(OH)₂ +

cat. 3c conditions A or B R¹

R²

R¹ R²

A : DMF / H2O, Cs2CO3, 100°C B : H2O, K2CO3, 100°C

Complex 3a Complex 3d

* Isolated yields (%) are within brackets

* Isolated yield