posted on 2006-03-27, 00:00authored byDaniel Carmona, Cristina Vega, Néstor García, Fernando J. Lahoz, Sergio Elipe, Luis A. Oro, M. Pilar Lamata, Fernando Viguri, Rosana Borao
The synthesis and characterization of optically active phosphinooxazoline chloride complexes (SM and
RM)-[(η6-p-MeC6H4iPr)MCl(PN)]A (M = Ru, Os; PN = phosphinooxazoline ligand; A = counteranion)
and the derived aqua complexes (RM and SM)-[(η6-p-MeC6H4iPr)M(PN)(H2O)](A)2 are reported. The
OPOF2-containing compounds (RM and SM)-[(η6-p-MeC6H4iPr)M(OPOF2)(PNiPr)][PF6] (M = Ru, Os;
PNiPr = (4S)-2-(2-diphenylphosphinophenyl)-4-isopropyl-1,3-oxazoline) have been also prepared and
characterized. The molecular structures of (SM)-[(η6-p-MeC6H4iPr)MCl(PNiPr)][SbF6] (M = Ru, Os),
(SRu)-[(η6-p-MeC6H4iPr)RuCl(PNInd)][SbF6] (PNInd = (3aS,8aR)-2-(2-diphenylphosphinophenyl)-3a,8a-dihydroindane [1,2-d]oxazole), and (RRu)-[(η6-p-MeC6H4iPr)Ru(PNiPr)(H2O)][SbF6] and that of the
OPOF2-containing compounds (RRu and SRu)-[(η6-p-MeC6H4iPr)Ru(OPOF2)(PNiPr)][PF6] have been
determined by X-ray diffractometric methods. Dichloromethane solutions of the aqua complexes [(η6-p-MeC6H4iPr)M(PN)(H2O)][SbF6]2 are active catalysts for the Diels−Alder reaction between methacrolein
and cyclopentadiene. The reaction occurs rapidly at room temperature with good exo:endo selectivity
(from 85:15 to 96:4) and moderate enantioselectivity (up to 47%). The intermediate Lewis acid−dienophile
compound (RRu and SRu)-[(η6-p-MeC6H4iPr)Ru(PNInd)(methacrolein)][SbF6]2 was isolated, and the
molecular structure of the S epimer was determined by diffractometric means. The osmium complexes
(SOs and ROs)- [(η6-p-MeC6H4iPr)Os(PN)(H2O)][A]2 (PN = PNiPr, A = SbF6, BF4; PN = PNInd, A =
SbF6) evolve to the phenyl-containing compounds (SOs and ROs)-[(η6-p-MeC6H4iPr)OsPh(PN‘)][SbF6]
(PN‘ = (4S)-2-(2-hydroxyphenylphosphinophenyl)-4-isopropyl-1,3-oxazoline (PNOHiPr), PN‘ = (3aS,8aR)-2-(2-hydroxyphenylphosphinophenyl)-3a,8a-dihydroindane[1,2d]oxazole] (PNOHInd)) and (SOs and ROs)-[(η6-p-MeC6H4iPr)OsPh(PNFiPr)][BF4] (PNFiPr = (4S)-2-(2-fluorophenylphosphinophenyl)-4-isopropyl-1,3-oxazoline), respectively, in which the phosphinooxazoline ligand incorporates a hydroxy or fluoro
functionality. On the basis of spectroscopic and crystallographic observations, a common pathway for
these reactions is proposed.