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Issue 43, 2010
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Insights into the intramolecular acetate-mediated formation of ruthenium vinylidene complexes: a ligand-assisted proton shuttle (LAPS) mechanism

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Abstract

The ruthenium bis-acetate complex Ru(κ2-OAc)2(PPh3)2 reacts with HC[triple bond, length as m-dash]CPh to afford the vinylidene-containing species Ru(κ1-OAc)(κ2-OAc)([double bond, length as m-dash]C[double bond, length as m-dash]CHPh)(PPh3)2. An experimental study has demonstrated that this reaction occurs under very mild conditions, with significant conversion being observed at 255 K. At lower temperatures, evidence for a transient metallo-enol ester species Ru(κ1-OAc)(OC{Me}O–C[double bond, length as m-dash]CHPh)(PPh3)2 was obtained. A comprehensive theoretical study to probe the nature of the alkyne/vinylidene tautomerisation has been undertaken using Density Functional Theory. Calculations based on a number of isomers of the model system Ru(κ1-OAc)(κ2-OAc)([double bond, length as m-dash]C[double bond, length as m-dash]CHMe)(PH3)2 demonstrate that both the η2(CC) alkyne complex Ru(κ1-OAc)(κ2-OAc)(η2-HC[triple bond, length as m-dash]CMe)(PH3)2 and the C–H agostic σ-complex Ru(κ1-OAc)(κ2-OAc)(η2{CH}-HC[triple bond, length as m-dash]CMe)(PH3)2 are minima on the potential energy surface. The lowest energy pathway for the formation of the vinylidene complex involves the intramolecular deprotonation of the σ-complex by an acetate ligand followed by reprotonation of the subsequently formed alkynyl ligand. This process is thus termed a Ligand-Assisted Proton Shuttle (LAPS). Calculations performed on the full experimental system Ru(κ1-OAc)(κ2-OAc)([double bond, length as m-dash]C[double bond, length as m-dash]CHPh)(PPh3)2 reinforce the notion that lowest energy pathway involves the deprotonation/reprotonation of the alkyne by an acetate ligand. Inclusion of the full ligand substituents in the calculations are necessary to reproduce the experimental observation of Ru(κ1-OAc)(κ2-OAc)([double bond, length as m-dash]C[double bond, length as m-dash]CHPh)(PPh3)2 as the thermodynamic product.

Graphical abstract: Insights into the intramolecular acetate-mediated formation of ruthenium vinylidene complexes: a ligand-assisted proton shuttle (LAPS) mechanism

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Publication details

The article was received on 06 May 2010, accepted on 01 Jul 2010 and first published on 12 Oct 2010


Article type: Paper
DOI: 10.1039/C0DT00431F
Citation: Dalton Trans., 2010,39, 10432-10441
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    Insights into the intramolecular acetate-mediated formation of ruthenium vinylidene complexes: a ligand-assisted proton shuttle (LAPS) mechanism

    D. G. Johnson, J. M. Lynam, J. M. Slattery and C. E. Welby, Dalton Trans., 2010, 39, 10432
    DOI: 10.1039/C0DT00431F

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