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The mechanism of the reactions of (η4-cycloheptatrien-1-al)Fe(CO)3 and its ethyleneglycol acetal with tetracyanoethylene (TCNE) was studied. The aldehyde undergoes a fast reversible 3+2 cycloaddition involving the free aldehyde-substituted double bond, and a slow irreversible 3+2 cycloaddition at the coordinated site. The latter, σ,π-allylic complex undergoes a slow interconversion with the corresponding 5 +2 isomer via the pericyclic [3,3]-sigmahaptotropic rearrangement. In contrast, the acetal reacts with TCNE at the free acetal-substituted double bond to give a single kinetic 3+2 adduct, which, under thermodynamic conditions, undergoes a [4,4]-sigmahaptotropic rearrangement to the 6 + 2 adduct. The reaction kinetics was followed by 1H NMR. The effect of substituents on the reaction course is discussed, and the detailed mechanism of both the cycloadditions and rearrangements is described.

Variable temperature NMR studies have established equilibrium constants and/or activation parameters for the exo2↔exo3 equilibrium in the series M(o-tolyl)3(M = P, As), XM (o-tolyl)3(M = P, X = O, S, Se; M = As, X = O, S) and [MeM(o-tolyl)3]n+(n= 0, M = Si; n= 1, M = P, As). The crystal structure of OAs(o-tolyl)3H2O is reported. Molecular mechanics studies of P(o-tolyl)3 reproduce correctly the ground state exo3 conformation and provide an analysis of the lowest energy two-ring flip exchange mechanism.

The mechanism of the reactions of (η4-cycloheptatrien-1-al)Fe(CO)3 and its ethyleneglycol acetal with tetracyanoethylene (TCNE) was studied. The aldehyde undergoes a fast reversible 3+2 cycloaddition involving the free aldehyde-substituted double bond, and a slow irreversible 3+2 cycloaddition at the coordinated site. The latter, σ,π-allylic complex undergoes a slow interconversion with the corresponding 5 +2 isomer via the pericyclic [3,3]-sigmahaptotropic rearrangement. In contrast, the acetal reacts with TCNE at the free acetal-substituted double bond to give a single kinetic 3+2 adduct, which, under thermodynamic conditions, undergoes a [4,4]-sigmahaptotropic rearrangement to the 6 + 2 adduct. The reaction kinetics was followed by 1H NMR. The effect of substituents on the reaction course is discussed, and the detailed mechanism of both the cycloadditions and rearrangements is described.

Variable temperature NMR studies have established equilibrium constants and/or activation parameters for the exo2↔exo3 equilibrium in the series M(o-tolyl)3(M = P, As), XM (o-tolyl)3(M = P, X = O, S, Se; M = As, X = O, S) and [MeM(o-tolyl)3]n+(n= 0, M = Si; n= 1, M = P, As). The crystal structure of OAs(o-tolyl)3H2O is reported. Molecular mechanics studies of P(o-tolyl)3 reproduce correctly the ground state exo3 conformation and provide an analysis of the lowest energy two-ring flip exchange mechanism.