Electronic Effect of Substituents on Cyclopalladation of the Solvated Palladium(II) Complexes with N-Benzyl Triamine [Pd(Sol){(4-XC6H4CH2)NH(CH2) 3NR(CH2)3NH2}]2+ (Sol = Solvent; R = Ph, H, and Me; X = H, Et, Me, MeO, Cl, and NO2)

Article abstract of DOI:10.1246/bcsj.71.1857

The solvated palladium(II) complexes with the potentially cyclopalladating monobenzyl triamine ligand, [Pd(CH₃CN)(BnPhdptn)](BF₄) ₂(1)(BnPhdptn=N-(3-aminopropyl)-N' -benzyl- 1,3-propanediamine), [Pd(CH₃CN)(4-XC₆H₄CH₂dptn)](BF ₄)₂ (4-XC₆H₄CH₂dptn = N-(3-aminopropyl)-N'-(4-substituted benzyl)-1,3-propanediamine; X = Me (3), MeO (4), Cl (5), and NO₂ (6)), and [Pd(CH₃CN)(4-XC₆H₄CH ₂Medptn)](BF₄)₂ (4-XC₆H₄CH₂Medptn = N-(3-aminopropyl)-N'-(4substituted benzyl)-methyl-1,3-propanediamine; X = Et (8), Me (9), MeO (10), Cl (11), and NO₂ (12)) have been synthesized. The kinetics for the cyclopalladation of 1-6, [Pd(CH₃CN)(BnMedptn)](BF₄)₂ (7) (BnMedptn = N-(3-aminopropyl)-N'-benzyl-N-methyl- 1,3-propanediamine), 8-12 in N,N-dimethylformamide (DMF), and 7,9,11, and 12 at 25 °C in dimethyl sulfoxide (DMSO) have been investigated. The Hammett p values for the rate constants at 25 °C obtained by variation of the 4-substituent on the benzyl group were -0.73 for 2 - 6 and -0.87 for 7 - 12 in DMF, and -0.67 for 7, 9, 11, and 12 in DMSO using the substituent constants for the meta position, σ_m. The difference in the rate constants for 1, 2, and 7 at 25 °C in DMF and the negative p values confirmed that the present cyclopalladation proceeds by the electrophilic attack of the palladium(II) center on the ortho benzyl carbon. We have also discussed the electronic effects of the solvent and the N-substituent of the bound triamine on the p values to arrive at a conclusion for the reaction mechanism of [Pd(solvent)(N-benzyltriamine)]-type complexes.