THE SYNTHESIS AND PROPERTIES OF FACE-TO-FACE METALLOCENE POLYMERS

Polymerization of 1,1'-bis(8-cyclopentadienyl-1-naphthyl)ferrocene (8) and its alkylated analogs 13a-d, through base-assisted, metal complexation, gives a new class of metallocene polymer 14 in which contiguous metallocene rings are held in a stacked, face-to-face orientation. The monomers are prepared in three steps from 1,8-diiodonaphthalene (2) through coupling with cyclopentadienylcopper reagents to give 1-cyclopentadienyl-8-iodonaphthalenes 4 or 11, conversion to the ferrocene derivative by metal complexation with ferrous chloride, and then cyclopentadienylation. Polymers incorporating only ferrocene units as well as copolymers of ferrocene and nickelocene or cobaltocene, in which the metallocenes alternate within the chain, have been prepared. These have been characterized by GPC analysis and by their infrared and H-1 NMR spectra. Polymerization of 1,8-bis(cyclopentadienyl)naphthalene (15) and its alkylated derivative 17 by base-assisted complexation provides a new pathway to a broader range of metallocene polymers. These monomers have been polymerized through base-assisted metal complexation with nickel(II) salts to gives low molecular weight, stacked nickelocene polymers. Electrical conductivity of compressed pellets of the ferrocene polymer 14b, which is less than 10(-12) S cm(-1) for the unoxidized material, is greatly increased on oxidative doping with iodine, and reaches a maximum of 6.7 x 10(-3) at a nominal oxidation level of 37%. The conductivity data are best accounted for in terms of a phonon-assisted electron-hopping mechanism between Fe(II) and Fe(III) centers, The behavior of the doped ferrocene polymer as a weakly interacting mixed-valence system is supported by Mossbauer spectra of oxidized polymer, which show trapped valence states over a broad temperature range and slow paramagnetic relaxation for the Fe(III) sites at lower temperatures. Bulk susceptibility measurement of paramagnetic polymers shows room temperature magnetic moments for the iron-cobalt copolymer 14i of 5.2 mu(B) and for the nickel polymer 18 of 5.3 mu(B). These values are significantly larger than the moments of either cobaltocene or nickelocene.