In situ generation chiral palladium complexes

Cammidge s group [37] reported the first asymmetric SM reaction of 1-iodo naphthalene (632) with 2-methylnaphthalene-l-boronic acid (633) catalysed by the complex in situ generated from palladium(ll) chloride and the chiral phosphine ligand (S)-213 resulting with formation of biaryl (/ )-634 in 44% yield and 63Vo e.e., Scheme 17. 

Among a numerous number of chiral palladium complexes, those applied to organic synthesis, either catalytically or stoichiometrically, will be a central subject of this section. This section will cover only the chiral palladium complexes whose X-ray crystal structures and/or NMR data have been reported. Thus, chiral palladium catalysts that are generated in situ in the reaction media are excluded from discussion. Because of recent progress of the X-ray crystallographic and NMR techniques/instruments, examples of well-characterized chiral palladium species are growing rapidly. 

In 2003, Sigman et al. reported the use of a chiral carbene ligand in conjunction with the chiral base (-)-sparteine in the palladium(II) catalyzed oxidative kinetic resolution of secondary alcohols [26]. The dimeric palladium complexes 51a-b used in this reaction were obtained in two steps from N,N -diaryl chiral imidazolinium salts derived from (S, S) or (R,R) diphenylethane diamine (Scheme 28). The carbenes were generated by deprotonation of the salts with t-BuOK in THF and reacted in situ with dimeric palladium al-lyl chloride. The intermediate NHC - Pd(allyl)Cl complexes 52 are air-stable and were isolated in 92-95% yield after silica gel chromatography. Two diaster corners in a ratio of approximately 2 1 are present in solution (CDCI3). 

When the Pd bears chiral ligands, these reactions can be enantioselective.1448 ir-Allylmo-lybdenum compounds behave similarly.1449 Because palladium compounds are expensive, a catalytic synthesis, which uses much smaller amounts of the complex, was developed. That is, a substrate such as an allylic acetate, alcohol, amine, or nitro compound1450 is treated with the nucleophile, and a catalytic amount of a palladium salt is added. The rr-allylpal-ladium complex is generated in situ. Alkene-palladium complexes (introducing the nucleophile at a vinylic rather than an allylic carbon) can also be used.1451... 

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