Metallacarbonares containing exo-thio and exo-phosphinocarbonare ligands. Tehir application in catalysis

Abstract

Metallacarboranes containing exo-thioether or exo-phosphinocarboranes were synthesized and characterized. These complexes were obtained from the reaction of tetramethylammonium or cesium salt of the nido ligand with Rh(I), Pd(II) or Ru(II) complexes incorporating ancillary ligands. Although two molecular structures were possible, the closo and the exo-nido, generally only the exo-nido tautomer was formed. The cluster was coordinated with the metal through the S or P atom and one or two B-HM interactions, depending on the metal. These exo-nido rhoda and ruthenacarboranes catalyzed the hydrogenation of terminal alkenes in very good yield but were not active in the hydrogenation of internal alkenes. Ruthenamonophosphinocarboranes were also active in the hydrogenation of the 1-hexene, with a higher selectivity than the respective rhodacarboranes. On the other hand, while [Rh(7-PPh2-8-R-7,8- C2B9H10)(PPh3)2] (R= H, Me) catalyzed the hydrogenation of methacycline to doxycycline with high yield (ca. 100%) and very high diastereoselectivity (> 99%), ruthenacarboranes were not active. The closo species [closo-3-(C8H13)-1-SR-2- R-3,2,1-RhC2B9H9] (R= Ph; R= Me, Ph) obtained from exonido-[ Rh(7-SR-8-R-7,8-C2B9H10)(cod)] were very efficient catalysts in the hydrogenation of cyclohexene exhibiting higher activity than the parent exo-nido isomers. All these complexes were recoverable after completion of the catalytic reaction. In addition to hydrogenation, exo-nido rhoda and ruthenamonothio and monophosphinocarboranes were also tested as catalyst precursors in the insertion of carbenes into C=C and O-H bonds.