N-heterocyclic carbene complexes can formally be derived from any kind of heterocycle. So in order to get unusual carbenes, Manuel developed a synthesis for the appropriate heterocycles. I could help with a structure.
“A new, mild one-pot synthesis of iodinated heterocycles as suitable precursors for N-heterocyclic carbene complexes” M. Iglesias, O. Schuster, M. Albrecht, Tetrahedron Lett. 2010, 51, 5423-5425.
Article and abstract available from Elsevier here, or open access on the institutional rero servers here.