HIGHLY STRAINED, RING-TILTED [1]FERROCENOPHANES CONTAINING GROUP-16 ELEMENTS IN THE BRIDGE - SYNTHESIS, STRUCTURES, AND RING-OPENING OLIGOMERIZATION AND POLYMERIZATION OF [1]THIAFERROCENOPHANE AND [1]SELENAFERROCENOPHANE

The first chalcogen-bridged [1]ferrocenophanes Fe(eta-C5H3R)(2)E (6, E = S, R = H; 7, E = Se, R = H; 12, E = S, R = Me) have been synthesize d and characterized both structurally and spectroscopically. Synthesis of sulfur- and selenium-bridged species 6 and 7 was achieved by the r eaction of dilithioferrocene.TMEDA (TMEDA = tetramethylethylenediamine ) with bis(phenylsulfonyl) sulfide S(O2SPh)(2) and selenium diethyldit hiocarbamate Se(S2CNEt2)(2), respectively, in 20-30% yields. Structura l characterization of both 6 and 7 revealed highly strained structures with tilt-angles between the cyclopentadienyl ligands of 31.05(10)deg rees and 26.4(2)degrees, respectively. Compounds 6 and 7 are purple an d red-purple, respectively; comparison of the structures of known [1]f errocenophanes 1 showed that when the second period (from group 14-16) is traversed, there is a substantial increase in cyclopentadienyl rin g-tilting in main group element bridged [1]ferrocenophanes, and the lo west energy UV/vis absorption peaks become increasingly red-shifted. E xtended Huckel MO calculations were performed and, consistent with thi s observation, predicted a decrease in the HOMO-LUMO gap as the ring-t ilt increases. Thermal ring-opening polymerization (ROP) of both 6 and 7 afforded the insoluble poly(ferrocenyl sulfide) [Fe(eta-C5H4)(2)S]( n) 8 and poly(ferrocenyl selenide) [Fe(eta-C5H4)(2)Se](n) 9, respectiv ely. Differential scanning calorimetry studies of the ROP process prov ided estimates of the strain energies of 6 and 7 which were ca. 130(+/ -20) and 110(+/-20) kJ mol(-1), respectively. Anionic ROP of 6 also yi elded the insoluble poly(ferrocenyl sulfide) 8, However, linear solubl e dimeric and trimeric trimethylsilyl-capped oligo(ferrocenyl sulfides ) 10b and 11b were synthesized by the reaction of 6 with dilithioferro cene.TMEDA followed by the addition of Me3SiCl and were characterized spectroscopically, electrochemically, and, for 11b, by X-ray diffracti on, and provide useful models for the analogous high polymer. The dime thylated sulfur-bridged species 12 was prepared as a mixture of isomer s from the reaction between dilithiodimethylferrocene.TMEDA and S(O2SP h)(2). and X-ray structural characterization of a single isomer 12a sh owed the presence of a large tilt-angle of 31.46(8)degrees. Thermal an d anionic ROP of the isomer mixture 12 afforded the first soluble poly (ferrocenyl sulfide) [Fe(eta-C5H3Me)(2)S](n) 13 which was characterize d by H-1 and C-13 NMR, elemental analysis, thermogravimetric analysis, and gel permeation chromatography. Cyclic voltammetric studies of 13 showed the presence of two reversible oxidation waves with a redox cou pling Delta E = ca. 0.32 V, which is consistent with the presence of s ignificantly stronger M...M interactions compared to those present in other ring-opened poly(ferrocenes) derived from [1]ferrocenophanes.