Monophosphine ligands, biaryl

Air-stable biaryl monophosphine ligands developed by Buchwald and co-workers have played a central role in the advancement of palladium-catalyzed cross-coupling reactions, including BHA chemistry the utility of appropriately configured ancillary ligands of this type in the selective monoarylation of ammonia has been examined. Following on preliminary experimentation that established the capability of the Pd2(dba)j/L3 catalyst system (dba=dibenzylideneacetone) to promote the monoarylation of ammonia at elevated temperature Tsvelikhovsky... 

Heller et al. applied the methodology above to the enantioselective synthesis of axially chiral biaryl monophosphine ligands. The reactions of alkynylphosphine oxides 11 with acetylene in the presence of the chiral cyclopentadienyl cobalt(I) catalyst... 

Optically active Cr-complexed arylphosphines 57 can be prepared in three steps from achiral arene-Cr(CO)3 precursors 56. A successful addition of PPh2Li to the complex 56a with concomitant carbamate displacement has been suggested, giving rise to the desired phosphine complex 57a as an air-stable crystalline solid in 96 % yield (R = H) (Scheme 26). Therefore, efficient C-P bond construction can be achieved by reacting, for example, the biaryl complex 56b with PPh2Li, providing the optically active monophosphine ligand 57b in 87 % yield, which has been used in Pd-catalyzed allylic alkylation reactions (Scheme 26) [42]. 

Suzuki reactions of the more easily handled but relatively unreactive tosyloxyquinolines are also possible using bulky biaryl monophosphines as supporting ligands in the presence of palladium(II) acetate <2003JA11818>. 

Discovery of biaryl monophosphine ancillary ligand modification... 

Scheme 13 Previously unobserved aryl transfer from palladium to a coordinated biaryl monophosphine ancillary ligand resulting in lower ring dearomatization...

Various palladium(O) monophosphine complexes of 1,6-diene have been prepared from tmedaPd(CHj)2, PRj, and the corresponding 1,6-dienes. These molecularly defined Pd complexes catalyzed the Suzuki coupling of aryl chlorides with phenyl-boronic acid more efficiently than traditional Pd(Il)-PRj pre-catalysts. Best results were achieved with the 1,6-diene complex containing Buchwald s ligand (26). With only 0.05 mol% of the catalyst, good to excellent yields of biaryls were obtained from activated (2-chlorobenzonitrile, 97%), non-activated (4-chlorotoluene, 82%, chlorobenzene, 87%) and deactivated (4-chloroanisole, 72%) aryl chlorides (Equation 54) [66]. 

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