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

TY - JOUR

T1 - Insights into the intramolecular acetate-mediated formation of ruthenium vinylidene complexes

T2 - a ligand-assisted proton shuttle (LAPS) mechanism

AU - Johnson, David G.

AU - Lynam, Jason M.

AU - Slattery, John M.

AU - Welby, Christine E.

PY - 2010/11/21

Y1 - 2010/11/21

N2 - The ruthenium bis-acetate complex Ru(kappa(2)-OAc)(2)(PPh3)(2) reacts with HC CPh to afford the vinylidene-containing species Ru(kappa(1)-OAc)(kappa(2)-OAc)(=C=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(kappa(1)-OAc)(OC{Me}O-C=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(kappa(1)-OAc)(kappa(2)-OAc)(=C=CHMe)(PH3)(2) demonstrate that both the eta(2)(CC) alkyne complex Ru(kappa(1)-OAc)(kappa(2)-OAc)(eta(2)-HC CMe)(PH3)(2) and the C-H agostic sigma-complex Ru(kappa(1)-OAc)(kappa(2)-OAc)(eta(2){CH}-HC 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 s-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(kappa(1)-OAc)(kappa(2)-OAc)(=C=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(kappa(1)-OAc)(kappa(2)-OAc)(=C=CHPh)(PPh3)(2) as the thermodynamic product.

AB - The ruthenium bis-acetate complex Ru(kappa(2)-OAc)(2)(PPh3)(2) reacts with HC CPh to afford the vinylidene-containing species Ru(kappa(1)-OAc)(kappa(2)-OAc)(=C=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(kappa(1)-OAc)(OC{Me}O-C=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(kappa(1)-OAc)(kappa(2)-OAc)(=C=CHMe)(PH3)(2) demonstrate that both the eta(2)(CC) alkyne complex Ru(kappa(1)-OAc)(kappa(2)-OAc)(eta(2)-HC CMe)(PH3)(2) and the C-H agostic sigma-complex Ru(kappa(1)-OAc)(kappa(2)-OAc)(eta(2){CH}-HC 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 s-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(kappa(1)-OAc)(kappa(2)-OAc)(=C=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(kappa(1)-OAc)(kappa(2)-OAc)(=C=CHPh)(PPh3)(2) as the thermodynamic product.

KW - ANTI-MARKOVNIKOV HYDRATION

KW - APPROXIMATE COULOMB POTENTIALS

KW - AUXILIARY BASIS-SETS

KW - TERMINAL ALKYNES

KW - METAL VINYLIDENES

KW - BIFUNCTIONAL CATALYST

KW - BIDENTATE LIGANDS

KW - TRANSITION-METAL

KW - DIRECT ARYLATION

KW - HYDROGEN-BOND

UR - http://www.scopus.com/inward/record.url?scp=78049335765&partnerID=8YFLogxK

U2 - 10.1039/c0dt00431f

DO - 10.1039/c0dt00431f

M3 - Article

SN - 1477-9226

VL - 39

SP - 10432

EP - 10441

JO - Dalton Transactions

JF - Dalton Transactions

IS - 43

ER -