The invention provides a polyimidazolium salt and poly N-heterocyclic carbene metal complexes. In particular, the invention provides a polymeric salt wherein a monomer unit of the polymeric salt has a structure (I) shown in the description, wherein a ring is optionally substituted at C4 and/or C5, R and R' are linker groups, R' may be a rigid linker group, X- is counterions, and a group shown in the description represents either a single or a double bond, and wherein the nitrogen atoms of the heterocyclic groups are disposed so as to enable a polymeric carbene formed by from the polymeric salt to complex with a metal atom. The invention also provides a method for producing the polymeric salt with the structure (I), which comprises: treating imidazolium or imidazolidine with a compound of structure Y-R'-Y' to form a bisimidazole or a bisimidazolidine; and copolymerising the bisimidazole or bisimidazolidine with a compound of structure X-R-X'; wherein X, X', Y and Y' are leaving groups and R and R' are linker groups, at least one of the R and R' is the rigid linker group. The polymeric salt may be sued as a heterogeneous organic catalyst for cyanation reaction.