Kinetics and mechanism of the hydrogenolysis of a ruthenium(II) acyl complex
- Univ. of British Columbia, Vancouver (Canada)
N,N{prime}-Dimethylacetamide (DMA) and toluene solutions of the acyl complex dicarbonylchloronorbornenoylbis(triphenylphosphine)ruthenium(II), RuCl(COC{sub 7}H{sub 9})(CO){sub 2}(PPh{sub 3}){sub 2}, react with 1 mol equiv of H{sub 2} to give RuHCl(CO){sub 2}(PPh{sub 3}){sub 2} (2) and the unsaturated aldehyde product 2-norbornene-5-carboxaldehyde, C{sub 7}H{sub 9}CHO (3). A subsequent, relatively slow hydrogenation of C{sub 7}H{sub 9}CHO by a further 1 mol of H{sub 2} to give the saturated aldehyde norbornane-2-carboxaldehyde, C{sub 7}H{sub 11}CHO (4), is catalyzed by 2. A detailed kinetic study on the hydrogenolysis of 1 in DMA at 65{degree}C reveals a first-order rate dependence on total Ru concentration, an inverse dependence on added PPh{sub 3} ligand concentration, and a first- to zero-order dependence on H{sub 2} pressure. A mechanism involving PPh{sub 3} dissociation as the first step followed by hydrogenolysis of the resulting intermediate accounts for these observations. Values of k{sub 1} and k{sub {minus}1}/k{sub 2} in DMA have been evaluated at 65{degree}C (k{sub 1} = 4.5 {times} 10{sup {minus}5} s{sup {minus}1}, k{sub {minus}1}/k{sub 2} = 1.6) and the activation parameters for the k{sub 1} step determined ({Delta}H{sup {double dagger}} = 69 {plus minus} 7 kJ mol{sup {minus}1}, {Delta}S{sup {double dagger}} = {minus}126 {plus minus} 13 J K{sup {minus}1} mol{sup {minus}1}); k{sub 1} and k{sub {minus}1} are the rate constants for the dissociation and reassociation of PPh{sub 3}, and k{sub 2} is the rate constant for the hydrogenolysis step. The activation parameters for the corresponding k{sub 1} step in toluene solution are very different; {Delta}H{sup {double dagger}} = 128 {plus minus} 13 kJ mol{sup {minus}1}, {Delta}S{sup {double dagger}} = +62 {plus minus} 6 J K{sup {minus}1} mol{sup {minus}1}. Association of DMA in the transition state is proposed to account for the differences.
- OSTI ID:
- 6654593
- Journal Information:
- Organometallics; (USA), Journal Name: Organometallics; (USA) Vol. 9:1; ISSN 0276-7333; ISSN ORGND
- Country of Publication:
- United States
- Language:
- English
Similar Records
Water exchange of the (o-phenylenediamine-N,N,N prime ,N prime -tetraacetato)ferrate(III) complex in aqueous solution as studied by variable-temperature, -pressure, and -frequency oxygen-17 NMR techniques
Separation by /sup 23/Na NMR of the unimolecular and bimolecular components of the dissociation kinetics of 18-crown-6-Na/sup +/ in some nonaqueous solvents
Related Subjects
400200* -- Inorganic
Organic
& Physical Chemistry
ACYLATION
CHEMICAL REACTIONS
COMPLEXES
DATA
DATA ANALYSIS
ENZYMES
EXPERIMENTAL DATA
HYDROGENASES
INFORMATION
KINETICS
MEASURING INSTRUMENTS
MEASURING METHODS
MECHANICS
NUMERICAL DATA
OXIDOREDUCTASES
REACTION KINETICS
RUTHENIUM COMPLEXES
TRANSITION ELEMENT COMPLEXES