Cp*Rh complexes with pyridyloxazolines: synthesis, fluxionality and applications as asymmetric catalysts for Diels–Alder reactions
Abstract
Half-sandwich complexes [RhCl(pymox)Cp*][SbF6] (1–7) (pymox = pyridyloxazoline) have been synthesised as single diastereomers. Treatment of these with AgSbF6 generates dications [Rh(OH2)(pymox)Cp*]2+ which are fluxional at room temperature and which are enantioselective catalysts for the Diels–Alder reaction of methacrolein and cyclopentadiene. Treatment of the dication [Rh(OH2)(iPr-pymox)Cp*]2+ with [X]− gives [RhX(iPr-pymox)Cp*][SbF6] (X = Br, I) as single diastereomers whilst reaction with 4-Mepy (4-methylpyridine) gives [Rh(4-Mepy)(iPr-pymox)Cp*][SbF6] as a mixture of diastereomers. Two complexes, [RhCl(iPr-pymox)Cp*][SbF6] (3) and [RhCl(Bz-pymox)Cp*][SbF6] (6) have been characterised by X-ray crystallography.