Abstract
Ferrocenophosphines have a long history. The first phosphorus compound having a ferrocenyl group had appeared only 10 years after the discovery of ferrocene. Since then, a vast number of ferrocenophosphines have been reported, but those having cyclic structures were relatively limited in number. This Account highlights cyclic dimers and trimers as well as monomers of ferrocenophosphine, (C5H4FeC5H4PR)n n = 1-3, because of their fascinating structures and properties. The dimers and trimers were obtained by a photolysis of the monomer which was structurally strained and thus readily underwent a ring opening reaction. The dimer was also prepared by multi-step reactions starting from ferrocene. The cyclic monomer, dimer, and trimer all worked as phosphorus ligands. Metal complexes having the strained monomer as the ligand could be oligomerized by the photolysis. The dimer has a [1.1]ferrocenophane framework, the syn configuration of which was thermodynamically favored to make the dimer useful as the bidentate ligand. The trimer had two configurational isomers bearing the C3 or Cs symmetry. The former isomer firmly bound to an Ag+ center as a tridentate ligand. In addition, the Cs isomer was found to be transformed to the C3 isomer upon coordination at ambient temperature, indicating that both isomer were practically available as the tridentate ligand.
