Intermolecular Electron-Transfer Reactions Involving Hydrazines

Abstract

The self-exchange electron-transfer (ET) rate constant k22 for 1,2,3,4,5-pentamethylferrocene was determined by NMR line broadening to be 8.5(±0.8) × 106 M-1 s-1 (25 °C, CD3CN/0.09 M Et4NBF4) and k11 for the bis-N,N-bicyclic hydrazine, 9,9‘-bi-9-azabicyclo[3.3.1]nonane, to be 8.7(0.5) × 103 M-1 s-1 (25 °C, CH2Cl2). These self-exchange rate constants are used to analyze cross reactions of these molecules with hydrazines, ferrocenes, and tetramethyl-p-phenylenediamine (TMPD) using Marcus theory. Cross-reaction rate constants for eight reactions are reported. Included are six cross-reactions between methylferrocenes and four cyclic hydrazines, one hydrazine, hydrazine−reaction, and the reduction of TMPD+ by a cyclic hydrazine. These are the first cross-reaction rate constants reported for hydrazine−hydrazine and hydrazine−TMPD+ ET reactions. The cross-reaction rate constants are used to test the application of Marcus theory to hydrazine ET reactions and to extract estimates of hydrazine self-exchange ET rate constants in systems for which direct measurement is presently impossible.