Dinuclear iron carbonyl complexes of 3H-1,2-diazepines

3H-1,2-Diazepines ($\text{1}\text{2}$) give dinuclear complexes ($\text{3}\text{4}$) on reaction with diiron nonacarbonyl. Complexation much reduces the rate of the [1,5] sigmatropic hydrogen shift across the diazepine ring and also reduces the activation energy for ring inversion.