Synthesis of chiral mono(N-heterocyclic carbene) palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis.

Lian-Jun Liu,Wenfeng Wang,Min Shi,Feijun Wang,Mei-Xin Zhao

doi:10.3762/bjoc.7.64

Lian-Jun Liu, Wenfeng Wang + Show 3 more

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https://doi.org/10.3762/bjoc.7.64

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Abstract

Axially chiral mono(NHC)–Pd(II) and mono(NHC)–Au(I) complexes with one side shaped 1,1'-biphenyl backbone have been prepared from chiral 6,6'-dimethoxybiphenyl-2,2'-diamine. The complexes were characterized by X-ray crystal structure diffraction. The Pd(II) complex showed good catalytic activities in the Suzuki–Miyaura and Heck–Mizoroki coupling reactions, and the (S)-Au(I) complexes also showed good catalytic activities in the asymmetric intramolecular hydroamination reaction to give the corresponding product in moderate ee.

Highlights

N-heterocyclic carbene (NHC) ligands, which have intrinsic characteristics such as strong σ-donor but poor π-acceptor abilities, easy preparation, air and thermal stability of their metal complexes, and convenient introduction of chiral elements, have been widely used as promising ligands in metal-catalyzed transformations [1-13]
Synthesis of the NHC–Pd(II) and NHC–Au(I) complexes The synthesis of the chiral benzimidazolium salt (S)-5a is shown in Scheme 1
(S)-6,6'-dimethoxybiphenyl-2,2'-diamine was reacted with acetic anhydride in the presence of acetic acid at room temperature (25 °C) in DCM to afford the corresponding amide (S)-1a in 56% yield

Summary

Introduction

N-heterocyclic carbene (NHC) ligands, which have intrinsic characteristics such as strong σ-donor but poor π-acceptor abilities, easy preparation, air and thermal stability of their metal complexes, and convenient introduction of chiral elements, have been widely used as promising ligands in metal-catalyzed transformations [1-13]. Many monodentate NHCs (Figure 1) with sterically hindered R1, R2 groups have been designed, and these have been shown to be good to excellent catalysts in chiral induction reactions [19-25]. Synthesis of the NHC–Pd(II) and NHC–Au(I) complexes The synthesis of the chiral benzimidazolium salt (S)-5a is shown in Scheme 1.

Results

Conclusion