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Content available remote H/D exchange of β-carbonyl esters inhibited by cucurbit[7]uril
Hydrogen/deuterium (H/D) exchange at the α-H of β-carbonyl esters has been used as a useful probe to demonstrate the kinetic aspects of cucurbit[7]uril-catalyzed processes. The rate constants for H/D exchange of ethyl acetoacetate (1), methyl acetoacetate (2) and dimethyl malonate (3) have been determined in the absence and presence of cucurbit[7] uril by 1H NMR spectroscopy. H/D exchange at the α-H of β-carbonyl esters is inhibited by cucurbit[7]uril in D2O, where the inhibitory factor order methyl acetoacetate > ethyl acetoacetate > dimethyl malonate, is in good agreement with the order of their binding constants. In the previous research, the models are oftentimes restricted to positively charged substrate. We now extend this research to neutral substrates, hence demonstrating further the versatile applications of cucurbiturils in the field of supramolecular catalysis.
Content available remote Bidentate ligands templated by a convex trimetallic bis(salphen) platform
A Zn3-bis(salphen) compound was used as a template for the construction of bidentate phosphine ligands by self-assembly with phosphines containing a carboxyl group. The convex shape of the template, exposing the three zinc atoms, ensured the correct orientation of the assembled diphosphine, such that it can coordinate to a single metal atom. The strong zinc-carboxylate bond guaranteed the integrity of the final assembly at the low concentrations (1 mM) used in catalysis. Depending on the substitution pattern of the benzoic acid phosphines, either monometallic chelates or dimeric complexes were formed. Coordination studies were carried out for Pt and Rh. A modest chelate effect in the rhodium catalyzed hydroformylation of 1-octene (l/b=4.7) confirmed the formation of the bidentate assemblies.
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