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(Arene)ruthenium(II) Complexes Containing Substituted Bis(pyrazolyl)methane Ligands – Catalytic Behaviour in Transfer Hydrogenation of Ketones
Author(s) -
Carrión M. Carmen,
Jalón Félix A.,
Manzano Blanca R.,
Rodríguez Ana M.,
Sepúlveda Francisco,
Maestro Miguel
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200700267
Subject(s) - chemistry , ruthenium , benzophenone , substituent , medicinal chemistry , steric effects , metallacycle , transfer hydrogenation , catalysis , biphenyl , benzene , pyrazole , stereochemistry , photochemistry , organic chemistry , x ray crystallography , physics , diffraction , optics
A new and safer methodology has been developed for the synthesis of bis(pyrazol‐1‐yl)methane ligands (NN). Several ligands containing different phenyl groups on the central carbon atom have been obtained. Ruthenium derivatives of the type [Ru(arene)Cl(NN)]BPh 4 (arene = benzene, p ‐cymene) have been synthesised using these ligands. One or two isomers that differ regarding the axial or equatorial disposition of the phenyl group on the metallacycle have been obtained. Their formation is rationalised by considering steric effects. The structures of five derivatives were determined by X‐ray diffraction. In four complexes the phenyl substituent is in the axial disposition of the metallacycle and in one case in the equatorial orientation. The dihedral angle formed by the planes of the two pyrazole rings is always bigger for the complexes containing unsubstituted pyrazolyl heterocycles. The behaviour of the new derivatives in the transfer hydrogenation of benzophenone in the presence of KOH was studied. The benzene derivatives showed higher activity than the p ‐cymene complexes. A marked and positive effect of the methyl groups on the pyrazolyl rings was observed. The effect of the substituents on the benzyl carbon atom was also important. It has been observed that the benzophenone hydrogenation was possible without the addition of complexes. The effect of the KOH concentration was evaluated and a concentration that leads to negligible conversion in a base‐only process was chosen. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)