Showing papers by "Penny A. Chaloner published in 1991"

Enantioselective reaction of diethylzinc with arenecarbaldehydes in the presence of ephedrine derivatives

Abstract: The reaction of diethylzinc with a range of arenecarbaldehydes has been catalysed by N-alkyl ephedrines to give 1-arylpropan-1-ols with good to excellent optical yields. The enantioselectivity of the reaction was substantially improved by the use of a 4 molar excess of the organozinc reagent.

Synthesis of µ-carbene and µ-carbyne complexes of rhodium and cobalt from substituted diazirines. Crystal structures of [Rh2(η5-C5Me5)2(CO)2{µ-C(C6H4F-4)(OMe)}] and [Rh2(η5-C5Me5)2(µ-CO)(µ-C6H4Me-4)][BPh4]

Abstract: The reaction of aryl(methoxy)diazirines with [M2(η5-C5Me5)2(µ-CO)2](M = Rh or Co) affords the µ-carbene complexes [M2(η5-C5Me5)(CO)2{µ-CR(OMe)}](R = aryl) in excellent yield. The carbonyl groups are terminal in the rhodium complexes, as demonstrated conclusively in an X-ray diffraction study, but bridging for the cobalt complex. Thermolysis of the rhodium complexes results in loss of CO and the formation of [Rh2(η5-C5Me5)2(µ-CO){µ-CR(OMe)}]. Protonation of either the mono- or di-carbonyl rhodium complex with HBF4 led to the formation of a stable cationic carbyne complex, [Rh2(η5-C5Me5)2(µ-CO)(µ-CR)][BF4]; the structure of the related [BPh4]– salt was established in a diffraction study. Dynamic processes in the complexes were investigated by variable-temperature NMR spectroscopy.