A catalyst of formula: wherein: M 1 and M 2 are independently selected from Zn, Cr, Co, Cu, Mn, Ni, Mg, Fe, Ti, V, Cr -X, Co -X, Ni -X, Mn -X, Fe -X, Ca, Ge, Al -X, Ti -X, V -X, Ge - 2 or Ti - 2; R 1 and R 2 are independently selected from hydrogen, halide, a nitro group, a nitrile group, an imine, an amine, an ether group, a silyl group, a silyl ether group, a sulfoxide group, a sulfonyl group, a sulfinate group or an acetylide group or an optionally substituted alkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy, alkylthio, arylthio, alicyclic or heteroalicyclic group; R 3A and R 3B are independently selected from optionally substituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene, arylene, heteroarylene or cycloalkylene, wherein alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene and heteroalkynylene, may optionally be interrupted by aryl, heteroaryl, alicyclic or heteroalicyclic; R 5 is independently selected from H, or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl; E 1 is C, E 2 is O; E 3, E 4, E 5 and E 6 are each independently selected from N, NR 4, O and S, wherein when any of E 3, E 4, E 5 or E 6 are N, - - - - - - is, and wherein when any of E 3, E 4, E 5 or E 6 are NR 4, O or S, - - - - - - is; R 4 is independently selected from H, or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl; X is independently selected from OC R x, OSO 2 R x, OSOR x, OSO(R x) 2, S R x, OR x, phosphinate, halide, nitrate, hydroxyl, carbonate, amino, amido or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl; R x is independently hydrogen, or optionally substituted aliphatic, haloaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, alkylaryl or heteroaryl; and G is absent or independently selected from a neutral or anionic donor ligand which is a Lewis base; and wherein at least one occurrence of E 3, E 4, E 5 and E 6 is different to a remaining occurrence of E 3, E 4, E 5 and E 6. M 1 and M 2 are independently selected from Zn, Cr, Co, Cu, Mn, Ni, Mg, Fe, Ti, V, Cr -X, Co -X, Ni -X, Mn -X, Fe -X, Ca, Ge, Al -X, Ti -X, V -X, Ge - 2 or Ti - 2; R 1 and R 2 are independently selected from hydrogen, halide, a nitro group, a nitrile group, an imine, an amine, an ether group, a silyl group, a silyl ether group, a sulfoxide group, a sulfonyl group, a sulfinate group or an acetylide group or an optionally substituted alkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy, alkylthio, arylthio, alicyclic or heteroalicyclic group; R 3A and R 3B are independently selected from optionally substituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene, arylene, heteroarylene or cycloalkylene, wherein alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene and heteroalkynylene, may optionally be interrupted by aryl, heteroaryl, alicyclic or heteroalicyclic; R 5 is independently selected from H, or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl; E 1 is C, E 2 is O; E 3, E 4, E 5 and E 6 are each independently selected from N, NR 4, O and S, wherein when any of E 3, E 4, E 5 or E 6 are N, - - - - - - is, and wherein when any of E 3, E 4, E 5 or E 6 are NR 4, O or S, - - - - - - is; R 4 is independently selected from H, or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl; X is independently selected from OC R x, OSO 2 R x, OSOR x, OSO(R x) 2, S R x, OR x, phosphinate, halide, nitrate, hydroxyl, carbonate, amino, amido or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl; R x is independently hydrogen, or optionally substituted aliphatic, haloaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, alkylaryl or heteroaryl; and G is absent or independently selected from a neutral or anionic donor ligand which is a Lewis base; and wherein at least one occurrence of E 3, E 4, E 5 and E 6 is different to a remaining occurrence of E 3, E 4, E 5 and E 6.