Manganese- and Lanthanide-Based 1D Chiral Coordination Polymers as an Enantioselective Catalyst for Sulfoxidation

The chiral 1D-coordination
polymers (CP) {[Ln2­(MnLCl)2­(NO3)2­(dmf)6­(H2O)2]·xH2O}n [Ln = Pr (1), Nd (2), Sm (3), and Gd (4)] were synthesized
by the reaction of N,N′-bis­(4-carboxy­salicylidene)­cyclo­hexane­di­amine
(H4L) with [MnCl2·4­(H2O)] and
[Ln­(NO3)3·x(H2O)] in the presence of dmf/pyridine at 90 °C. The polymers consist
of manganese-salen-based moieties having carboxylate linkers connected
to rare earth atoms in a 1D-chain structure. The polymers are very
easily accessible. A one-step synthesis for the ligand and a second
step for the preparation of the 1D coordination polymers starting
from commercially available material are needed. The solid state structures
of 1–4 were established by single-crystal
X-ray diffraction. Compounds 1–4 were
investigated as heterogeneous catalysts for the sulfoxidation reaction
of various alkyl and aryl sulfides. The influence of various solvents
and oxidizing agents on the catalytic reaction was examined. It was
found that the catalysts were active for more than one reaction cycle
without significant loss of activity. For phenylsulfide with 1 mol
% of the catalyst 4, a maximum conversion 100% and a
chemoselectivity 88% were observed.