Substitution reactions on sterically hindered square-planar trans-[NiBr(R)(PR′3)2](R = aryl) complexes. Effects of the substituents of the aryl ligand

Abstract

Substitution reactions of sterically hindered trans-[NiBr(R)(PPh₃)₂] complexes (R = C₆Cl₅, C₆F₅,C₆H₂Me₃-2,4,6, C₆HCl₄-2,3,5,6, C₆HCl₄-2,3,4,6, C₆HCl₄-2,3,4,5, C₆H₂Cl₃-2,3,4, C₆H₃Cl₂-2,4, or C₆H₄Cl-2) and of trans-[NiBr(R)(PR′₃)₂](PR′₃= PEtPh₂ or PMePh₂; R = C₆Cl₅ C₆F₅, C₆H₂Me₃-2,4,6, or C₆H₂Cl₃-2,3,4) have been studied in acetone solution. The reaction rates obey the well established two-term rate law k_obs=k_S+k_an[anion] and seem to be solely controlled by steric factors; namely, the existence of one or two substituents on the R ligand, in an ortho position with respect to the Ni–C bond. The different donor ability of the ligand might be considered only for R = C₆H₂Me₃-2,4,6. The effects of the para and meta chloro substituents of the R ligand on the reaction rates are negligible. Steric strain in the molecule, as a whole, is also considered by studying the effect of a decrease in the phosphine size on the reaction rate.