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Synlett 2006(10): 1621-1622  
DOI: 10.1055/s-2006-944228
SPOTLIGHT
© Georg Thieme Verlag Stuttgart · New York

Biphenyl-Based Phosphine Ligands

Padmaja Gunda*
City College of CUNY, Department of Chemistry, Marshak Hall, 138th Street at Convent Ave, New York, NY-10031, USA
e-Mail: padmaja@sci.ccny.cuny.edu;

Further Information

Publication History

Publication Date:
12 June 2006 (online)

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Biographical Sketches

Padmaja Gunda was born in Mancherial, India in 1977 and received her BSc degree in 1997 from Osmania University (India). She completed her MSc degree (Chemical Sciences) and MPhil (Chemistry) in 1999 and 2000, respectively, at the University of Hyderabad ­(India). She is currently working towards her PhD with Prof. ­Mahesh K. Lakshman at the City University of New York in the area of palladium-catalyzed C-C and C-N bond formation reactions of nucleoside derivatives. Her research interests include the development of new transition-metal-mediated reactions with an emphasis on the elucidation of reaction mechanisms. She thanks Prof. Mahesh K. Lakshman for valuable suggestions and constant encouragement.

Introduction

A family of biphenyl ligands for transition-metal-catalyzed cross-coupling reactions is becoming well documented in the literature. [1-5] Buchwald and colleagues invented and developed ligands 1 and 2, which have found utility in C-C,2 C-N [2a] [3a] [3c] and C-O [3b] bond formation.

Figure 1 Biphenyl-based phosphine ligands

Palladium complexes supported by ligands 1 and 2 are ­efficient catalysts for C-C, and C-heteroatom (C-N and C-O) bond formation of aryl halides, [2] [3] triflates [3a] and ­sulfonates. [4] Catalysts supported by the ligands shown in Figure 1 are reactive, efficient and operationally simple to generate. Ligand 1 is effective for hindered substrates at very low catalyst loadings (0.000001 mol%) [2] compared with ligand 2. The efficiency of catalysts derived from ligands 1 and 2 is most likely due to a combination of ­several factors such as steric and electronic properties, ­basicity of the phosphorus and their abilities to form ­palladacycles. [2]

Preparation of the ligands 1 and 2

Ligands 1 and 2 were prepared in high yields in a one-pot transformation (Scheme 1) and are also now commer­cially available. [2b] They are generally air-stable, white, crystalline solids that require no special handling. These ligands interact in unusual and interesting manners with the metal and thereby modulate the reactivity of the metal for various transformations. There is also a balance ­between steric and electronic properties among these compounds. [2b]

Scheme 1

Abstracts

(A) Buchwald and co-workers have used biphenyl ligands 1 and 2 for palladium-catalyzed Suzuki reactions of arylhalides at room temperature. [2b]

(B) Lakshman et al. extended the utility of these phosphine ligands to the class of nucleosides. [4] Use of ligand 1 for palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of nucleosides resulted in the C-6 aryl derivatives and yielded 80-90%. Ligand 2 was less effective.

(C) Ligands 1 and 2 yield efficient catalytic systems for palladium-mediated amination of aryl chlorides, bromides and triflates. [3a]

(D) Recently it was reported by Echavarren and co-workers that ligand 1 in a complex with Au(I) acts as an efficient catalyst to give a variety of cycloisomerization and addition derivatives. 1,3-Enynes or arylalkynes react at room temperature with alkenyl or an aryl groups in intramolecular [4+2] cycloaddition of to give hydrindanes or linearly fused tricyclic systems. [5]

(E) Ligand 2 was also utilized in rhodium-catalyzed additions of alkynes to activated 1,2-diketones and aldehydes. [6]

(F) Ligand 1 was used in Pd-mediated Suzuki coupling reaction of resin-bound monomethylated tryptamine and arylboronic acid. [7]

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Figure 1 Biphenyl-based phosphine ligands

Scheme 1