Synthesis and catalytic activity of ruthenium complexes modified with chiral racemic per- and polyfluorooxaalkanoates

Abstract

Silver salts of racemic 2H-perfluoro(3-oxahexanoic) (3a), perfluoro(2-methyl-3-oxahexanoic) (3b) and 2,3,3,3-tetrafluoro-2-methoxypropanoic acid (3c) gave with Hoveyda-Grubbs 2nd generation catalyst 4 or its bis(polyfluoroalkylated) analogue 5 the corresponding bis(polyfluoroacylated) ruthenium complexes 1a–1c or 2a, 2b as mixtures of three diastereoisomers. Their catalytic activity in model ring-closing metathesis (RCM) reactions decreased in the order 1b–2b>1a–2a>1c due to increased steric hindrance around the catalytic centre in complexes 1a, 1c and 2a, as well as due to lower acidity of acid 3c resulting in lower electrophilicity of the complex 1c. Thus, the complexes 1b and 2b displayed high activity in RCM of bis-unsaturated malonates forming disubstituted (RCM2) or trisubstituted (RCM3) double bond and were even significantly active in the formation of tetrasubstituted bond (RCM4), while complexes 1a, 1c were active in RCM2 but inactive in RCM3. Moreover, the yield of RCM2 catalyzed with complex 1c was rather low.