A series of single-component cobalt salen complexes, N,N0-bis(salicylidene)-1,2phenylenediaminocobaltX were prepared for alternating copolymerization of carbon dioxide and propylene oxide(PO) under mild condition. The axial anion X group of the SalenphCoX played important role in tailoring the catalytic activity, polymeric/ cyclic carbonate selectivity, as well as stereochemistry of carbonate unit sequence in the polymer chain. SalenphCoX with an electron-withdrawing axial X group (complex 1c) was an ideal catalyst for the copolymerization of CO2 and PO to selectively produce polycarbonate with w99% carbonate linkage and over 81% head-to-tail structure.