STRUCTURE AND ELECTROCHEMISTRY OF FERROCENYLOLIGOSILANES - ALPHA,OMEGA-BIS(FERROCENYL)OLIGOSILANES AND ALPHA,OMEGA-(1,1'-FERROCENEDIYL)OLIGOSILANES

The structures and electrochemical properties of 1,2-bis(ferrocenyl)-1 ,1,2,2-tetramethyldisilane (Fc-(SiMe2)nFc, n = 2, Ib) and (1,1'-ferroc enediyl)tetramethyldisilane ((C5H4)2(SiMe2)nFe, n = 2, IIb), a ferroce nophane, are reported together with the electrochemical behavior of th eir analogs (n = 1 (a), 3 (c)). Complex Ib exhibited a Si-Si bond leng th of 2.340(2) angstrom and two distinctive reversible redox processes (E(ox) = 0.56 and 0.67 V, E(red) = 0.50 and 0.61 V). Complex IIb exhi bited an elongated Si-Si bond length of 2.351(1) angstrom and an elong ated C(cyciopentadienyl)-Si bond length compared to Ib (1.881(3) versu s 1.862(4) angstrom). These bond length elongations result in minimal cyclopentadienyl dihedral angle strain, 4.3-degrees, in IIb. Electroch emically IIb exhibited a single oxidation process (E(ox) = 0.67 V, E(r ed) = 0.59 V). The ferrocenophane redox behavior disappeared after a f ew cycles because of decomposition. Themonosilyl-bridged ferrocenophan e IIa underwent decomposition upon electrochemical oxidation, while (1 ,1'-ferrocenediyl)heptamethyltrisilane (IIc) exhibited a completely re versible oxidation process. This trend reflects the capacity of the th ree bridges, Si, Si2 and Si3, to incorporate the increase in Fe-cyclop entadienyl ring distance upon oxidation. Electrochemical investigation of the alpha,omega-bis-(ferrocenyl) complexes Ia-c, and complexes wit h n = 0 (biferrocene) and n = 6 (If), showed that the two redox system s are most separated when the two Fe atoms are adjacent (n = 0) and pr ogressively become closer as the inter-ferrocene distance increases, u ntil at n = 6 only a single process is observed. Complexes IIb,c did n ot undergo simple linear polymerization at temperatures below 350-degr ees-C, and above this temperature cross-linking polymerization occurre d to produce insoluble materials. Both Ib and IIb undergo Si-Si bond c leavage upon photolysis in MeOH to produce the methoxysilane derivativ es, and in the case of IIb the major product (>95%) was (1,1'-ferrocen ediyl)tetramethyldisiloxane.