Structure and properties of the macrocyclic tridentate ferrocenylphosphine ligand (-PhPC5H4FeC5H4-)3

Isolation and characterization were carried out for a novel tridentate ferrocenylphosphine macrocycle, (-PhPC5H4FeC5H4-)(3), as follows. A photolytic ring-opening reaction of PPh-bridged [1]ferrocenophane in ether gave a mixture of its oligomers. After their sulfurization, GPC separation of low-molecular-weight species afforded two isomers of a macrocyclic trimer, 1,1 '':1',1:1 ',1'-tris(phenylthiophosphinidene)tris(ferrocene), in which three 1,1'-ferrocenediyl units and three P(S)Ph groups were alternately linked to form a macrocyclic ring. Although yields of both isomers were low (17% in total), they were successfully desulfurized in good yields without configurational inversion at their phosphorus centers by treatment with MeOTf/P(NMe2)(3) (OTf = CF3SO3), to give the respective tridentate macrocyclic phosphine ligands. The molecular structure of one isomer (C-3 isomer) with C-3 symmetry was determined by X-ray analysis, while the other was identified as the C, isomer on the basis of H-1, C-13, and P-31 NMR data. When the C-3 isomer was heated in toluene at around 80 degrees C, it isomerized gradually but almost completely to the C-S isomer with the activation energy Delta G(350)(double dagger) = 26.2 +/- 0.6 kcal mol(-1). The reaction of AgOTf with the C-3 isomer in CH2Cl2 gave a mononuclear silver complex in which the C-3 isomer encircled the Ag+ ion as a tridentate ligand. To our surprise, a similar reaction using the C-S isomer gave the same silver complex as above, indicating that a facile conversion of the C-S isomer to the C-3 isomer took place upon coordination to the Ag+ ion at room temperature.