Solvent-Based Reactivity of a Rhenium Carbonyl and Ethylene Diamines: Activating a Bond by Making It Stronger

This report presents the reaction chemistry of Re(CO)₅Br with a series of simple chelating aliphatic diamines. While this chemistry is typically highly predictable, we observed different products depending on the reaction medium. In a nonpolar solvent (toluene), ethylene diamine engages in simple bidentate chelation with the replacement of two carbonyls. However, in neat ethylene diamine, we observe carbamoyl formation upon nucleophilic attack by one of the diamine nitrogen atoms on a carbonyl. We explored a series of methylated ethylene diamines and observed several different medium-dependent reactivities. These data support the notion that these products result from the differential relative stabilization of the bromide bound versus bromide unbound intermediate, which affects carbamoyl formation.