Synthesis, Cyclization, and Migration Insertion Oligomerization of CpFe(CO)2(CH2)3PPh2 in Solution

Cyclopentadienyldicarbonyl­[(diphenylphosphino)­propyl]­iron (CpFe­(CO)2(CH2)3PPh2, FpP), containing both Fp and phosphine groups, was synthesized as a difunctional monomer for migration insertion polymerization (MIP). FpP underwent either intra- or intermolecular reactions in solution. When a solution with low FpP concentration (ca.1% by weight) was left at 25 °C, FpP was quantitatively converted to the five-membered-ring species 1 via CO release. On the other hand, when a solution at the same low concentration was heated to 70 °C in the dark, an intramolecular migration insertion reaction was promoted, leading to a high conversion of FpP (ca. 70%) to the six-membered cyclic Fp acyl derivatives 2. At the same temperature with an increase in the concentration of FpP to 10% by weight, intermolecular MIR became predominant (ca. 90%) with a low yield of ring molecules (ca. 10%). Solution polymerization of FpP (ca. 20% by weight) was therefore performed at 70 °C, which generated both THF-soluble and -insoluble macromolecules via intermolecular migration insertion reactions. The resulting macromolecules were fully characterized by using FT-IR, solution- and solid-state 31P, and 13C NMR. The soluble macromolecules exhibit a molecular weight of ca. 4200 with a PDI value of ca. 1.24, as characterized by GPC. A kinetic study shows that the polymerization follows a step-growth mechanism.