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.