Abstract: The present invention relates to the field of polymerisation catalysts, and systems comprising said catalysts for polymerising carbon dioxide and an epoxide, a lactide and/or lactone, and/or an epoxide and an anhydride. The catalyst is of formula (I): Wherein M1 and M2 are independently selected from Zn(II), Cr(II), Co(II), Cu(II), Mn(II), Ni(II), Mg(II), Fe(II), Ti(II), V(II), Cr(III)-X, Co(III)-X, Ni(III)-X, Mn(III)-X, Fe(III)-X, Ca(II), Ge(II), Al(III)-X, Ti(III)-X, V(III)-X, Ge(IV)-(X)2 or Ti(IV)-(X)2. R3A is different from R3B; and/or at least one occurrence of E3, E4, E5 and E6 is different to a remaining occurrence of E3, E4, E5 and E6. A ligand, a process of asymmetric N-substitution of a symmetrical ligand and a process for the reaction of: (i) carbon dioxide with an epoxide; (ii) an epoxide and an anhydride; and/or (iii) a lactide and/or a lactone, in the presence of a catalyst is also described.