Effect of N-alkylation on the rate of β-amine elimination from transients with CuII–carbon σ bonds

Abstract

The rates of β-amine elimination from Cu^II—CH(CH₂NH₃)³⁺₂ and Cu^II—CH₂CH₂NH²⁺₃ have been found to be about two orders of magnitude lower than those from Cu^II—CH[CH₂N(CH₃)₂H]³⁺₂ and Cu^II—CH₂CH₂N(C₂H₅)₂H²⁺ in aqueous solutions. The results indicate that N-alkylation increases the rate of β-amine elimination, whereas previous results demonstrated that O-alkylation decreases the rate of β-elimination of HOR′ from (H₂O)₅Cr^III—CH₂CH₂OR^′2+(R′= H, C₂H₅). These opposite trends are in accord with expectations based on the assumption that the rate of β elimination of X^– from L_mM^{(n+ 1)}—CR¹R²CR³R⁴Xⁿ⁺ is correlated to the C—X bond strength. A mechanism of activation from the reaction is formulated, based on the Shaik–Pross curve-crossing model. The model provides a basis for the assumption of bond strength controlled rates.