Palladium Chemistry Related to Benzyl Bromide Carbonylation: Mechanistic Studies

Summary.

 Palladium(II) complexes of the general formula PdCl₂ (PR₃)₂ with PR₃ = { P(OPh)₃}, P(O-4-MeC₆H₄)₃, P(O-2-MeC₆H₄)₃, and PPh₂(OBu) were reduced by NEt₃ in chloroform or benzene to Pd(0) complexes Pd(PR₃)₄ and Pd(PR₃)_x(NEt₃) _4−x . The same reaction performed in the presence of air gave CH₃CHO or CH₃CH₂CHO when NPr₃ was used instead of NEt₃. Pd(P(OPh)₃)₄ reacted with benzyl bromide affording the oxidative addition product cis-PdBr(CH₂Ph)(P(OPh)₃)₂. The reaction of PdCl₂(P(OPh)₃)₂ with benzyl bromide was observed only in the presence of NEt₃, and a dimeric complex of [PdBr(CH₂Ph)(P(OPh)₃)]₂ was identified as the reaction product. Both benzyl complexes reacted fast with CO (1 atm) to form acyl complexes exhibiting ν(CO) bands at 1709 and 1650 cm⁻¹.