Formation of di-iron hexacarbonyl complexes of 3H-1,2-diazepines and the effects of complexation on ring inversion and the rate of sigmatropic hydrogen migration

Abstract

A number of 3H-1,2-diazepines [(9)/(10)(a–f)] have been synthesised by the reactions of 6,7-dihydro-1-tosyl-1,2-diazepines with base. These diazepines are in dynamic equilibrium at room temperature via[1,5] sigmatropic hydrogen migrations but in some cases could be separated by h.p.l.c. at 0 °C. The reactions of 1H-2,3-benzodiazepines, 3H-1,2-benzodiazepines and the monocylic 3H-1,2-diazepines (9)/(10) with di-iron nonacarbonyl gave the dinuclear iron hexacarbonyl complexes (12), (14), and (15)/(16), respectively, in moderate yield. The complexes were found to undergo ring inversion more easily than their precursors, and activation energies were determined. The complexation of the azo group also stopped the easy [1,5] sigmatropic hydrogen shift observed for (9)/(10) and this is discussed in terms of changes in electronic effect and in the structural geometry of the diazepine ring.