Synthesis, characterization and aggregation properties of non-peripherally (1R,2R)-1,2-di(naphthalen-1-yl)ethane-1,2-diol substituted optically active zinc phthalocyanine and its catalytic application in enantioselective ethylation of aldehydes

Abstract

The novel optically active zinc(II) phthalocyanine having four (1R,2R)-1,2-di(naphthalen-1-yl)ethane-1,2-diol 1 at non-peripheral positions has been synthesized in a condensation using optically active phthalonitrile 2, and characterized by 1H NMR, IR, UV–Vis, Circular Dichroism (CD) and HRMS-TOF spectral data. The spectral and aggregation properties of novel optically active zinc(II) phthalocyanine 3 were investigated. The aggregation behavior of phthalocyanine 3 was investigated at different concentrations in N,N-dimethylformamide and tetrahydrofuran. No aggregation behavior was observed in both solvents at concentrations between 10 × 10−6 and 2 × 10−6 mol dm−3. The applicability of these chiral ligands 1–3 was evaluated in the enantioselective diethyl zinc addition of aldehydes. The addition of diethylzinc to 2-methoxybenzaldehyde was achieved with excellent enantioselectivity (87% ee, 80% yield) under catalysis with (1R,2R)-1,2-di(naphthalen-1-yl)ethane-1,2-diol 1. At the same condition, optically active zinc(II) phthalocyanine 3 afforded the corresponding chiral secondary alcohol with the enantiomeric excess of 11%.