Burstein, C., Lehmann, C. W., & Glorius, F. (2005). Imidazo[1,5-a]pyridine-3-ylidenes - pyridine derived N-heterocyclic carbene ligands. Tetrahedron, 61(26), 6207-6217. doi:10.1016/j.tet.2005.03.115.