Thermal Ring-Opening Polymerization of Planar-Chiral Sila[1]ferrocenophanes

The new Me2Si-bridged [1]ferrocenophane ([1]FCP) with one iPr group in a position on a Cp ring was synthesized in an enantiopure (S-p-4) and a racemic form (rac-4). The molecular structure of rac-4 was determined by single-crystal X-ray analysis (tilt angle alpha = 20.15(14)degrees). Experimental and calculated molecular structures of the related [1]FCPs with one (S-p-4 and rac-4) or two iPr groups (S-p,S-p-4) are compared to that of the nonsubstituted [1]FCP Me(2)Sifc. Differential scanning calorimetry (DSC) measurements resulted in Delta H-ROP of -72(+/- 2) kJ mol(-1) for rac-4 and 62(+/- 2) kJ mol(-1) for the known S-p,S-p-4. While thermal ring-opening polymerization of S-p,S-p-4 gave insoluble material, the monosubstituted monomers S-p-4 and rac-4 resulted in soluble polymers with molecular weights (M-w) of 5.3 X 10(6) and 2.6 X 10(6) Da, respectively. Investigation of the polymer structures by Si-29 NMR spectroscopy gave further evidence that the breakage of Si-Cp bonds occurs in the thermal ROP process of sila[1]ferrocenophanes.