(1 R,2S,5R)-Menthyl-substituted ruthenium(II) phthalocyanines: How many chiral inductors are required for enantioselective catalysis?

Ruthenium chiral phthalocyanine complexes bearing (1[Formula: see text],2[Formula: see text],5[Formula: see text]-menthyl groups orthogonal to the aromatic macrocycle plane (M) and 15-crown-5 ether moieties (C) provide promising efficiency in asymmetric catalysis. The complexes bearing one, two and three chiral isoindoline motifs RuPc[MC[Formula: see text]](CO), RuPc[MCMC](CO) and RuPc[M 3 C](CO) have been evaluated in asymmetric catalytic cyclopropanation of olefins by ethyl diazoacetate as a benchmark reaction. Unexpectedly, the complex RuPc[MC 3 ](CO) having only one chiral fragment showed dia- and enantioselectivity close to those achieved by RuPc[MCMC](CO) possessing two chiral isoindoline motifs in the symmetrical arrangement. Importantly, RuPc[MC 3 ](CO) afforded a higher chiral induction than RuPc[M 3 C](CO) carrying three chiral isoindoline units. Although the enantiomeric excess (e.e.) values obtained are still moderate, this counter-intuitive result opens new perspectives for the development of low-symmetrical chiral phthalocyanine complexes for asymmetric catalysis which should be more accessible in terms of straightforward preparation and yield.