Stepwise displacement of the tertiary phosphine ligand in square-planar [PdR2L2]-type complexes by organolithium reagents with stereochemical retention affording organopalladate complexes

Article abstract of DOI:10.1021/om00074a007

Reactions of trans- and cis-[PdR₂L₂] (R = Me, Et, Ph; L = tertiary phosphine) with R′Li (R′ = Me, Ph) in ether or THF solution lead to stepwise displacement of L by R′ with stereochemical retention to afford alkylpalladate complexes Li[PdR₂R′L] and Li₂[PdR₂R′₂], as established by means of ¹H, ³¹P, and ¹³C NMR spectroscopy. The displacement of PEt₃ in trans-[PdPh₂(PEt₃)₂] by MeLi is a slow process, and the rate is independent of the MeLi concentration with indication of a dissociative mechanism generating a three-coordinate, T-shaped intermediate, whereas the reaction of PdR₂L₂ (R = Me, Et) with MeLi is much faster. Displacement of PEt₂Ph in Li[PdMe₃(PEt₂Ph)] by MeLi is a slow process and first order in concentrations of the complex and MeLi and independent of L. An associative mechanism involving a five-coordinate intermediate is proposed for the second displacement to account for the stereochemical retention. Factors influencing the ¹H and ¹³C NMR chemical shifts of the neutral and palladate complexes are discussed.