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

The new Me2Si-bridged [1]­ferrocenophane ([1]­FCP) with one iPr group in α position on a Cp ring was synthesized in an enantiopure (Sp-4) and a racemic form (rac-4). The molecular structure of rac-4 was determined by single-crystal X-ray analysis (tilt angle α = 20.15(14)°). Experimental and calculated molecular structures of the related [1]­FCPs with one (Sp-4 and rac-4) or two iPr groups (Sp,Sp-4) are compared to that of the nonsubstituted [1]­FCP Me2Sifc. Differential scanning calorimetry (DSC) measurements resulted in ΔHROP of −72(±2) kJ mol–1 for rac-4 and −62(±2) kJ mol–1 for the known Sp,Sp-4. While thermal ring-opening polymerization of Sp,Sp-4 gave insoluble material, the monosubstituted monomers Sp-4 and rac-4 resulted in soluble polymers with molecular weights (Mw) of 5.3 × 106 and 2.6 × 106 Da, respectively. Investigation of the polymer structures by 29Si NMR spectroscopy gave further evidence that the breakage of Si–Cp bonds occurs in the thermal ROP process of sila[1]­ferrocenophanes.