RATES OF SUBSTITUTION REACTIONS OF TETRAKIS(TRIETHYL PHOSPHITE)METAL(0) COMPOUNDS OF NICKEL TRIAD

The rate of ligand substitution between tetrakis (triethyl phosphite) nickel (0) and cyclohexyl isocyanide has been studied in n-hexane and benzene solutions by infrared spectroscopy. The reaction is first order in complex concentration and independent of the isocyanide concentration. The activation parameters are ΔH≠ = 32 keal/mol and ΔS≠ = +19 eu in n-hexane solution and ΔH≠ = 27 keal/mol and ΔS≠ = +2 eu in benzene. Tetrakis (triethyl phosphite)palladium(0) and tetrakis (triethyl phosphite) platinum (0) were prepared and the rates of ligand exchange between these complexes and free triethyl phosphite were studied in toluene solution by proton magnetic resonance. For both complexes the exchange reaction is first order in complex concentration and independent of the concentration of free phosphite. The activation parameters [ΔH≠ = 22 kcal/mol and ΔS≠ = +30 eu for the exchange reaction between Pd[P(OC2H5)3]4 and P(OC2H5)3; ΔH≠ = 26 keal/mol and ΔS≠ = +24 eu for the reaction between Pt[P(OC2H5)3]4 and P(OC2H5)3] are compatible with a dissociative (Sn1) mechanism. These results show that the activation energies for M-P bond rupture in the compounds M[P(OC2H5)3]4 vary in the order Ni > Pd < Pt. © 1969, American Chemical Society. All rights reserved.