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Article

Chiral Phosphinooxazoline−Ruthenium(II) and −Osmium(II) Complexes as Catalysts in Diels−Alder Reactions

Supporting Info

Daniel Carmona,* Cristina Vega, Néstor García, Fernando J. Lahoz, Sergio Elipe, and Luis A. Oro

Departamento de Qumica Inorgnica, Instituto Universitario de Catlisis Homognea, Instituto de Ciencia de Materiales de Aragn, Universidad de Zaragoza-Consejo Superior de Investigaciones Cientficas, 50009 Zaragoza, Spain

M. Pilar Lamata,* Fernando Viguri, and Rosana Borao

Departamento de Qumica Inorgnica, Escuela Universitaria de Ingeniera Tcnica Industrial, Instituto Universitario de Catlisis Homognea, Instituto de Ciencia de Materiales de Aragn, Universidad de Zaragoza-Consejo Superior de Investigaciones Cientficas, 50018 Zaragoza, Spain

Organometallics, 2006, 25 (7), pp 1592–1606

DOI: 10.1021/om050973d

Publication Date (Web): February 21, 2006

To whom correspondence should be addressed. E-mail: dcarmona@unizar.es; plamata@unizar.es. Fax: 34 + 976 761187.

Abstract

The synthesis and characterization of optically active phosphinooxazoline chloride complexes (S_M and R_M)-[(η⁶-p-MeC₆H₄iPr)MCl(PN)]A (M = Ru, Os; PN = phosphinooxazoline ligand; A = counteranion) and the derived aqua complexes (R_M and S_M)-[(η⁶-p-MeC₆H₄iPr)M(PN)(H₂O)](A)₂ are reported. The OPOF₂-containing compounds (R_M and S_M)-[(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 (S_M)-[(η⁶-p-MeC₆H₄iPr)MCl(PNiPr)][SbF₆] (M = Ru, Os), (S_Ru)-[(η⁶-p-MeC₆H₄iPr)RuCl(PNInd)][SbF₆] (PNInd = (3aS,8aR)-2-(2-diphenylphosphinophenyl)-3a,8a-dihydroindane [1,2-d]oxazole), and (R_Ru)-[(η⁶-p-MeC₆H₄iPr)Ru(PNiPr)(H₂O)][SbF₆] and that of the OPOF₂-containing compounds (R_Ru and S_Ru)-[(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 (R_Ru and S_Ru)-[(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 (S_Os and R_Os)- [(η⁶-p-MeC₆H₄iPr)Os(PN)(H₂O)][A]₂ (PN = PNiPr, A = SbF₆, BF₄; PN = PNInd, A = SbF₆) evolve to the phenyl-containing compounds (S_Os and R_Os)-[(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 (S_Os and R_Os)-[(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.