Polyyne bridges

Kawabata, S. Yamazaki, L Nishimura, Y. Synthesis and photochemical properties of anthracene-polyyne-porphyrin assemblies. Bull. Chem. Soc. Jpn. 1997, 70, 1125-1133 Kawabata, S. Tanabe, N. Osuka, A. A convenient synthesis of polyyne-bridged porphyrin dimmers. Chem. Lett. 1994, (10), 1797-1800. 

Osuka and co-workers (Osuka et al, 1995) have compared polyynes (9) and polyenes (10) as mediators for electronic interaction between porphyrin electron donors and acceptors. Transient absorption spectra were recorded to confirm ET by the observation of the charge-separated state (ZnP ). However, the charge-separated state was difficult to detect and fast charge recombination was discussed as one possible explanation. The ET is approximately two times more efficiently mediated by polyene-bridges than polyyne-bridges. The attenuation factor P (Eq. 12) was found to be 0.08 and 0.1 for the polyene and polyyne series, respectively. The conclusion drawn from the small attenuation factor is that the electronic coupling between the donor and acceptor is efficiently... 

ESR has been used to study new polyyne derivatives of (157), in particular spin conduction through the diethynyl and mercury bridges in (161) (80IZV128). Radicals from aromatic iV-oxides may also be useful as spin labels in this context the anion radical (162) of azobispyridine N- oxide was studied by ESR (750MR(7)33). 

The synthesis of several high molecular-weight platinum polyyne polymers carrying chiral (R)-l,l -bi-2-naphthol bridge, P17, was described.48 These represent the first examples of metal acetylide polymer with an optically active backbone. They display much larger specific negative optical rotations than both the metal-free alkyne precursors and their corresponding dinuclear model compounds. These results support the fact that the main chain of P17 adopts a one-handed helical conformation and induces the helical chirality of the polymers. 

FIGURE 13.50 Molecules with Polyyne and Polyene Bridges. 

Dinuclear complexes in which the two metal atoms are bridged by polyyne, unsaturated elemental carbon chains (15-17), have received considerable attention due to their unique properties. For example, upon oxidation, these complexes form metallacumulenes of the general formula [L M=(C=C)p=ML ] +, where L includes pentamethyl-cyclopentadienyl, [Cp, C5(CH3)5], triarylphosphine, [Ar3 , Ar = Ph, C6H5, and Tol, P-CH3C6H4], aryl, CO, and NO. With the fragment [C5(CH3)5]Re(NO)[P (05115)3] as the capping, complex molecules with chains containing up to 20 carbon atoms have been synthesized. For compound 17 a rhenium-rhenium distance of 2.87 nm was estimated. These complexes can be considered the first step toward metal-capped, one-dimensional carbon allotropes. 

Osuka A, Tanabe N, Kawabata S, Yamazaki I, Nishimura Y. Synthesis and Intramolecular Electron- and Energy-Transfer Reactions of Polyyne- or Polyene-Bridged Diporphyrins. 7. Org. Chem. 1995 60 7177-7185. 

Dinuclear complexes with a bridging polyynediyl ligand and diphosphine ligands with long methylene chains between the two P atoms show a structure in which the alkylene chains are double-helixed around the polyyne ligand... 

The chemistry of polymetallic complexes featuring bridging alkyne and alkynyl (M-G=GR) ligands has been an intense area of study in recent years, which has also been expanded to polyynes and polyynyl moieties linking the metal centers. Recent developments in the chemistry and also materials properties of these complexes have been the subject of several reviews and highlight articles. " " " " In this section, we only present complexes featuring 77 -alkyne-platinum bonding interactions. 

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