Room-temperature hydrodebromination of 4,4'-dibromobiphenyl catalyzed by 1,1'-bis(diphenylphosphino) ferrocene complexes of palladium

Abstract

Hydrodebromination of 4,4'-dibromobiphenyl to 4-bromobiphenyl and biphenyl was studied by using a variety of metal complexes of Ru(II), Ni(II), Pd(II), Pt(II) and Cu(I) under different ligand environments. Palladium complexes are most effective in giving biphenyl whereas other complexes give 4-bromobiphenyl. 1,1'-Bis(dipbenylphosphino)ferrocene (dppf) is the best phosphine ligand whereas NaBH4 and N,N,N',N'-tetramethylethylenediamine are the best reductant and base, respectively. The use of catalytic PdCl2(CH3CN)2 and PdCl2(dppf) gives 4-bromobiphenyl (86%) and bipbenyl (100%) respectively. PdCl2(dppf) is effective even at a low concentration of 3.5 mol.% and at room temperature (r.t.) with a short reaction time (10 min) and performs better than Pd on charcoal (5%). It also leads to a complete breakdown of 4-monobromobiphenyl and decabromobiphenyl giving 100% of biphenyl in 4 min and 40 h, respectively.