Mechanism of the reaction of [Mo(η-C6H6)(Me2PCH2CH2PMe2)(η-C2H4)H]+with PMe3giving [Mo(η-C6H5Et)(dmpe)(PMe3)H]+: metal-to-ring migration of an ethyl group

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Abstract
The cis-ethylenehydride compounds [Mo(η-C6H6)(L2)(η-C2H4)H]PF6[L2= Me2PCH2CH2PMe2(dmpe) or o-C6H4(EMe2)2(E = P, pdmp, or As, pdma)] react with trimethylphosphine to give the η-ethylbenzene compounds [Mo(η-C6H5Et)(L2)(PMe3)H]PF6. Detailed studies of the mechanism of this reaction show that there is an initial reaction, at low temperatures, giving isomeric mixtures of thermally unstable η-cyclohexadienyl derivatives [Mo(η-C6H7)(dmpe)(PMe3)(η-C2H4)]+. The combined evidence from n.m.r. spectra, including kinetic studies, and from the preparation and reactions of intermediates shows that the η-ethylbenzene compound is formed by the sequence [Mo(η-C6H6)(dmpe)(η-C2H4)H]+→[Mo(η-C6H6)(dmpe)(PMe3)Et]+→[Mo(η-C6H6Et-endo)(dmpe)(PMe3)(solvent)]+→[Mo(η-C6H5Et)(dmpe)(PMe3)]+ H+→[Mo(η-C6H5Et)(dmpe)(PMe3)H]+. The following new compounds have been prepared and characterised: [Mo(η-C6H6){P(OMe)3}2(η-C3H5)] PF6, [Mo(η-C6H6)(pdmp)(η-C3H5)]PF6, [Mo(η-C6H6)(pdma)(η-C3H5)]PF6, [Mo(η-C6H6)(pdmp)(η-C2H4)], [Mo(η-C6H6)(pdma)(η-C2H4)], [Mo(η-C6H6)(pdmp)(η-C2H4)H]PF6, [Mo(η-C6H6)(pdma)(η-C3H5)]PF6, [Mo(η-C6H6)(pdmp)(η-C2H4)], [Mo(η-C6H6)(pdma)(η-C2H4)], [Mo(η-C6H6)(pdmp)(η-C2H4)H]PF6, [Mo(η-C6H6)(pdma)(η-C2H4)H]PF6, [Mo(η-C6H5Et)(pdmp)(PMe3)H]PF6, [Mo(η-C6H5Et)(pdma)(PMe3)H]PF6, [Mo(η-C6H6)(dmpe)(PMe3)D]PF6, [Mo(η-C6H6)(dmpe)(η-C2H4)], [Mo(η-C6H6Et-endo)(dmpe)2]PF6, [Mo(η-C6H6)(dmpe){P(OMe)3}H]PF6, [Mo(η-C6H6)(dmpe)(CO)H]PF6, [Mo(η-C6H6)(dmpe)(2,6-Me2C6H3 NC)]PF6, [Mo(η-C6H5Me)(dmpe)(η-C2H4)H]PF6, [Mo(C6H4Me-2-Et-1)(dmpe)(PMe3)H]PF6, [Mo(C6H4Me-3-Et-1)(dmpe)(PMe3)H]PF6, [Mo(C6H5Me-1-Et-6-endo)(dmpe)2]PF6, [Mo(C6H5Me-2-Et-6-endo)(dmpe)2]PF6, and [Mo(η-C6H6Et-endo)(pdmp)2]PF6.

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