Biphosphole: A<i>C</i>₂Symmetry Chiral Bidentate Ligand. Synthesis and Characterization Of Nickel, Palladium, Platinum, and Rhodium Complexes

Abstract

Owing to the C2 symmetry structure of 1,1‘-diphenyl-3,3‘,4,4‘-tetramethyl-2,2‘-biphosphole, 1 (BIPHOS), we investigated the coordination of this chiral bidentate ligand to transition metals in order to explore the potential of these complexes in asymmetric catalysis. Nickel, palladium, and platinum complexes [M(BIPHOS)X2] (2 (M = Ni, X = Br), 3 (M = Pd, X = Cl), 4 (M = Pt, X = Cl) were synthesized and fully characterized. Their structures were determined by X-ray crystallography. The cationic palladium complexes [Pd(BIPHOS)(CH3CN)2](BF4)2, 6, and [Pd(BIPHOS)(η3-C3H5)]Cl, 7, were also synthesized. The π-allyl−palladium complex 7 reveals a potential interest for catalytic allylic substitution. The reaction of 1 with [Pd(CH3CN)4](BF4)2 leads to the formation of the meso diastereoisomer [Pd(BIPHOS)2] (BF4)2, 5, which was fully characterized. Its structure was determined by X-ray crystallography. A bis(BIPHOS) complex of Rh(I), 8, was also obtained by reaction of 1 with [Rh(COD)Cl]2 or [Rh(COD)2]BF4.