2,2′-bis(diphenylphosphino)-1,1′-biphenyl:: New entry of bidentate triarylphosphine ligand to transition metal catalysts

The bidentate triaryl phosphine 2,2'-bis(diphenylphosphino)-1,1'-bipheny (dpbp) was examined as a supporting ligand in several transition metal catalysts. The dpbp complexes showed superior catalytic activity to the corresponding complexes of other bisphosphines in Pd-catalyzed Grignard cross-coupling and Rh-catalyzed Michael addition of boronic acid. In the Pd-catalyzed Grignard cross-coupling of sec-BuMgCl, the Pd-dpbp catalyst showed nearly perfect secondary selectivity in the product. This selectivity is much higher than that of Pd catalysts with other standard bisphosphines and is comparable only with that of the corresponding Pd-dppf catalyst. Dpbp was also applied to Rh-catalyzed conjugate addition of boronic acids to enones, and the Rh(acac)(C2H4)(2)/dpbp catalyst exhibited excellent catalytic activity, which is far better than the corresponding catalyst with dppb. The structure of the dpbp complex PdCl2(dpbp) was studied by X-ray single-crystal structure determination, which clarified the bite angle of dpbp in the complex being 92.24 degrees.