Abstract
Ruthenium complexes of formula [(η^6^‐arene)Ru(LL*)(H~2~O)][SbF~6~]~2~ (arene = C~6~H~6~, p‐MeC~6~H~4~i__Pr, C~6~Me~6~; LL* = bidentate chelate chiral ligand with PN, PP or NN donor atoms) have been tested as catalyst precursors for the asymmetric 1,3‐dipolar cycloaddition of nitrones to methacrolein. The reaction occurs quantitatively with perfect endo selectivity and moderate enantioselectivity (up to 74 % ee). The ruthenium aqua complexes can be prepared from the corresponding chlorides, [(η^6^‐arene)RuCl(LL*)][SbF~6~]. Dipolarophile intermediates [(η^6^‐arene)Ru(PN__i__Pr)(methacrolein)][SbF~6~]~2~ {PN__i__Pr = (4__S)‐2‐(2‐diphenylphosphanylphenyl)‐4‐isopropyl‐1,3‐oxazoline} as well as nitrone‐containing complexes [(p‐MeC~6~H~4~i__Pr)Ru(PN__i__Pr)(nitrone)][SbF~6~]~2~ (nitrone = N‐benzylidenephenylamine N‐oxide, N‐benzylidenemethylamine N‐oxide, 3,4‐dihydroisoquinoline N‐oxide) have been also isolated and characterised. The crystal structures of the chlorides (R~Ru~)‐[(η^6^‐C~6~Me~6~)RuCl(PN__i__Pr)][SbF~6~], (R~Ru~)‐[(η^6^‐C~6~H~6~)RuCl(PNInd)][SbF~6~] {PNInd = (3a__R,8a__S__)‐2‐[2‐(diphenylphosphanyl)phenyl]‐3a,8a‐dihydroindane[1,2‐d]oxazole} and those of the aqua solvates (R~Ru~)‐[(η^6^‐arene)Ru(PN__i__Pr)(H~2~O)][SbF~6~]~2~ (arene = C~6~H~6~, C~6~Me~6~) were determined by X‐ray diffraction methods. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)