Mesoscale Metallocycles

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Science  18 Jun 2004:
Vol. 304, Issue 5678, pp. 1721
DOI: 10.1126/science.304.5678.1721a

Entropy causes the formation of large metallocycles, in which alternating metal centers and bridging ligands form a ring structure, to become more difficult as the rings become larger. Metallocycles are typically limited to triangular or square topologies. Jiang and Lin have reported on a synthetic method that yields larger rings, up to octomers. They now report on an alternative approach that reduces the entropic penalty by starting with longer oligomers that can fuse into chiral metallocyclic rings of up to 47 units (or a diameter of 22 nm).

The ligand L that they use is 2,2'-deacetoxy-1,1'-binaphthyl-3,3'-bis(ethyne). Longer oligomers were made by reacting L[Pt]2Cl2, where [Pt] is trans-Pt(P(CH2CH3)3)2, with L-H2. Reaction of metal-terminated Lm[Pt]m+1Cl2 species with the ligand-terminated [Pt]nLn+1H2 species afforded cyclic species in [1+1], [2+2], or even [3+3] cyclization processes. These compounds were characterized by a variety of methods, including mass spectrometry and circular dichroism spectroscopy. Size-exclusion chromatography indicates that metallocycles are more compact and rigid than linear oligomers with the same number of units. — PDS

J Am. Chem. Soc. 125, 8084 (2003).

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