Multipoint Coordinative Capture of Olefinic Substrates Utilizing Metal-Carbon Bonds by Macrocyclic Complex.

Terpenoids and unsaturated fatty acids containing C=C double bonds are biologically and synthetically important compounds. The transformation of these substrates catalyzed by proteins relies on precise molecular capture. However, achieving precise molecular recognition of C=C double bonds using synthetically designed hosts remains a significant challenge. We now report a macrocyclic palladium tetranuclear complex that functions as a synthetic receptor featuring coordination sites within its inner cavity. This receptor selectively binds specific double bonds of unsaturated hydrocarbon substrates. Squalene (C30H50), a linear triterpene with chemically similar six isoprenoid units, was captured by the macrocyclic complex through the coordination of four out of the six C=C double bonds, leading to a unique host-guest complex with a folded-squalene structure. Furthermore, the macrocyclic complex exhibited stronger binding affinity for methyl linolenate compared to methyl oleate or methyl linoleate through multipoint coordinative capture. This unprecedented approach to multipoint coordination of specific unsaturated bonds contrasts sharply with biological and traditional artificial receptors, which typically rely on intermolecular interactions such as hydrogen bonding or hydrophobic effects. By achieving precise capture and folding of flexible olefinic substrates, this study establishes a new paradigm for the design of artificial host molecules and a novel platform for enzyme-like reaction vessels.