Effect of N-alkylation on the rate of β-amine elimination from transients with Cu^II-carbon σ bonds

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.