Kinetic Study of the Interconversion of the Regio-isomeric Iron Tricarbonyl Complexes Derived from 4-Bromotropone

Abstract

The title complexes, 1 and 2, have been prepared and their interconversion has been studied by 1H NMR spectroscopy; the activation enthalpies and entropies as well as the equilibrium constants for these reversible intramolecular first-order processes have been determined. The iron tricarbonyl complex 3 of 3-bromotropone has also been prepared, but this does not isomerize to regio-isomer 4.

Bond Shift Isomerization in Cyclic and Acyclic (triene)Fe(CO)3 Complexes. A Density Functional Study

“…The interconversion between these structures is possible in solution. Experimental studies have shown that this bond shift isomerization is much faster for complexes of cyclic polyenes than for acyclic derivatives. − …”

Thermodynamic and kinetic parameters associated with the fluxional behavior of 2-methyl- and 2,6-dimethyltroponeiron tricarbonyl complexes

“…In both of these latter studies, the activation enthalpies and entropies as well as the equilibrium constants for these reversible intramolecular first-order processes were determined. In contrast to the fluxional behavior of these complexes, the iron tricarbonyl complex of 3-bromotropone does not isomerise to its regioisomer [14].…”

“…Similar kinetic studies have been carried out on 2-acetoxy-and 2-benzoyloxy-derivatives of tricarbonyl[g 4 -tropone]iron regioisomers by Morita and Asao [13]. Kinetic studies of the interconversion of the regioisomeric iron tricarbonyl complexes derived from 4-bromotropone have also been carried out [14]. In both of these latter studies, the activation enthalpies and entropies as well as the equilibrium constants for these reversible intramolecular first-order processes were determined.…”

Fluxional behavior of methyl-substituted tricarbonyl(tropone)iron complexes and their different reactivity

“…The equilibrium ratio of regioisomers has not been published. In the equilibrated mixture of (4-bromotropone)tricarbonyliron complex thermodynamically more stable form is (g 4 -4,5,6,7) isomer in which the peripheral carbon of the coordinated diene fragment is substituted [16].…”

“…While the equilibrium distribution of tricarbonyl(3-methyltropone)iron complexes 2a and 2b (Chart 1) is 34:66 at 323 K in CDCl 3 [17], the tricarbonyliron complexes of 3-methoxytropone [15] and 3-bromotropone [16] occur exclusively in the (g 4 -4,5,6,7) form due to a large energetic difference between the two possible regioisomers. Density functional computations were employed to explain the differences in the equilibrium compositions of regioisomers of the tricarbonyliron complexes of 3-bromotropone and 4-bromotropone [18].…”