The rate of electron exchange between tris(3,4,7,8-tetramethyl-l,10-phenanthroline)iron(II) and -(III) ions in acetonitrile has been measured by the nmr line-broadening method in the temperature range from -5 to 35°. For a total reactant concentration of 0.035 M, the second-order rate constant at 25°is (1.7 ± 0.1) X 107 M-1 sec-1, and the experimental activation energy is 2 ± 1 kcal/mol.

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The exchange of trimethylgallium with trimethylgallium-dimethylamine (I), trimethylgallium-monomethylamine (II), trimethylgallium-ammonia (III), and trimethylgallium-dimethyl ether (IV) addition compounds has been investigated. This exchange proceeds through a dissociation step for I, but has been shown to proceed by an electrophilic displacement reaction for II and III. Activation energies were determined to be 19, 10, and 8.5 kcal/mole, respectively, for I, II, and III. The reaction of IV was too fast to follow by the techniques available. An explanation for this drastic change in mechanism is given, and the results are compared with those observed for similar exchange reactions of boron trifluoride addition compounds.