Homogeneous Hydrogenation of Tri‐ and Tetrasubstituted Olefins: Comparison of Iridium‐Phospinooxazoline [Ir‐PHOX] Complexes and Crabtree Catalysts with Hexafluorophosphate (PF 6 ) and Tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (BAr F ) as Counterions
2007; Wiley; Volume: 350; Issue: 1 Linguagem: Inglês
10.1002/adsc.200700438
ISSN1615-4169
AutoresBettina Wüstenberg, Andreas Pfaltz,
Tópico(s)Chemical Synthesis and Analysis
ResumoAbstract Four iridium complexes with achiral phosphino‐oxazoline (PHOX) ligands were readily prepared in two steps starting from commercially available phenyloxazolines. The air‐stable complexes with tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (BAr F ) as counterion showed high reactivity in the hydrogenation of a range of tri‐ and tetrasubstituted olefins. The best results were obtained with an iridium complex ( 11 ) derived from a dicyclohexylphosphino‐oxazoline ligand bearing no additional substituents in the oxazoline ring. With several substrates, which gave only low conversion with the Crabtree catalyst, [Ir(Py)(PCy 3 )(COD)]PF 6 , full conversion was observed. The productivity of the Crabtree catalyst could be strongly increased by replacing the hexafluorophosphate anion with tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate. In one case, in the hydrogenation of a tetraalkyl‐substituted CC bond, [Ir(Py)(PCy 3 )(COD)]BAr F gave higher conversion than catalyst 11 . However, with several other substrates complex 11 proved to be superior.
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