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Phosphorus-Bridged [1.1]Ferrocenophane with syn and anti Conformations

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journal contribution
posted on 28.02.2005, 00:00 by Tsutomu Mizuta, Yuki Imamura, Katsuhiko Miyoshi, Hideki Yorimitsu, Koichiro Oshima
Photolysis of PPh-bridged [1]ferrocenophane (1) in THF gave PPh-bridged [1.1]ferrocenophane (2) as a minor dimer along with major polymeric products. After subsequent sulfurization of the reaction mixture with elemental sulfur, both syn and anti isomers of P(S)Ph-bridged [1.1]ferrocenophane (3) were successfully isolated and characterized by X-ray analysis. syn-3 thus obtained was desulfurized stereoretentively to syn-2 with Si2Cl6 in refluxing benzene, while anti-3 primarily gave the isomerized product, syn-2. Stereoretentive desulfurization of anti-3 to anti-2 was achieved with CF3SO3Me/P(NMe2)3 at room temperature. anti-2 thus obtained could be converted almost completely to syn-2 upon simple heating in toluene, indicative of the thermal instability of the anti isomer over the syn isomer. The yield of syn-2 was improved from 9% to 32% when THF used in the photolysis was replaced with ether and the reaction mixture was heated so as to isomerize anti-2, which had been formed concomitantly. A potential utility of syn-2 as a ligand was demonstrated by the formation of [CoCl2(syn-2)] (5) through a reaction of syn-2 with CoCl2.