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Catalytic Hydrogenation by Triruthenium Clusters: A Mechanistic Study with Parahydrogen‐Induced Polarization
Author(s) -
Blazina Damir,
Duckett Simon B.,
Dyson Paul J.,
Lohman Joost A. B.
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200390098
Subject(s) - heterolysis , chemistry , ruthenium , alkyne , hydride , catalysis , medicinal chemistry , reactivity (psychology) , ligand (biochemistry) , homogeneous catalysis , frustrated lewis pair , photochemistry , cluster chemistry , spin isomers of hydrogen , stereochemistry , hydrogen , metal , lewis acids and bases , organic chemistry , medicine , biochemistry , alternative medicine , receptor , pathology
The reactivity of the cluster family [Ru 3 (CO) 12− x (L) x ] (in which L=PMe 3 , PMe 2 Ph, PPh 3 and PCy 3 , x =1–3) towards hydrogen is described. When x =2, three isomers of [Ru 3 (H)( μ ‐H)(CO) 9 (L) 2 ] are formed, which differ in the arrangement of their equatorial phosphines. Kinetic studies reveal the presence of intra‐ and inter‐isomer exchange processes with activation parameters and solvent effects indicating the involvement of ruthenium‐ruthenium bond heterolysis and CO loss, respectively. When x =3, reaction with H 2 proceeds to form identical products to those found with x =2, while when x =1 a single isomer of [Ru 3 (H)( μ ‐H)(CO) 10 (L)] is formed. Species [Ru 3 (H)( μ ‐H)(CO) 9 (L) 2 ] have been shown to play a kinetically significant role in the hydrogenation of an alkyne substrate through initial CO loss, with rates of H 2 transfer being explicitly determined for each isomer. A less significant secondary reaction involving loss of L yields a detectable product that contains both a pendant vinyl unit and a bridging hydride ligand. Competing pathways that involve fragmentation to form [Ru(H) 2 (CO) 2 (L)(alkyne)] are also observed and shown to be favoured by nonpolar solvents. Kinetic data reveal that catalysis based on [Ru 3 (CO) 10 (PPh 3 ) 2 ] is the most efficient although [Ru 3 (H)( μ ‐H)(CO) 9 (PMe 3 ) 2 ] corresponds to the most active of the detected intermediates.