Influence of the Metal (Al, Cr, and Co) and Substituents of the Porphyrin in Controlling Reactions Involved in Copolymerization of Propylene Oxide and Carbon Dioxide by Porphyrin Metal(III) Complexes. 3. Cobalt Chemistry

A series of cobalt(III) complexes LCoX, where L = 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20- tetrakis(pentafluorophenyl)porphyrin (TFPP), and 2,3,7,8,12,13,17,18-octaethylporphyirn (OEP) and X = Cl or acetate, has been investigated for homopolymerization of propylene oxide (PO) and copolymerization of PO and CO2 to yield polypropylene oxide (PPO) and polypropylene carbonate (PPC) or propylene carbonate (PC), respectively. These reactions were carried out both with and without the presence of a cocatalyst, namely, 4-dimethylaminopyridine (DMAP) or PPN+Cl- (bis(triphenylphosphine)iminium chloride). The PO/CO2 copolymerization process is notably faster than PO homopolymerization. With ionic PPN+Cl- cocatalyst the TPPCoOAc catalyst system grows two chains per Co center and the presence of excess [Cl-] facilitates formation of PC by two different backbiting mechanisms during copolymerization. Formation of PPC is dependent on both [Cl-] and the CO2 pressure employed (1-50 bar). TPPCoCl and PO react to form TPPCo(II) and ClCH2CH(Me)OH, while with DMAP, TPPCoCl yields TPPCo(DMAP)2+Cl-. The reactions and their polymers and other products have been monitored by various methods including react-IR, FT-IR, GPC, ESI, MALDI TOF, EXAFS, and NMR (1H, 13C{1H}) spectroscopy. Notable differences are seen in these reactions with previous studies of (porphyrin)M(III) complexes (M = Al, Cr) and of the (salen)M(III) complexes where M = Cr, Co.