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

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 Si 2 Cl 6 in refluxing benzene, while anti - 3 primarily gave the isomerized product, syn - 2 . Stereoretentive desulfurization of anti - 3 to anti - 2 was achieved with CF 3 SO 3 Me/P(NMe 2 ) 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 [CoCl 2 ( syn - 2 )] ( 5 ) through a reaction of syn - 2 with CoCl 2 .