N-heterocyclic carbenes (NHCs) have played a dominant role in organometallic chemistry for decades and revolutionized the field of homogenous catalysis. NHCs have been thoroughly studied, both experimentally and theoretically, and have shown unique reactivity towards transition metals, chalcogens, azides and pnictogens. This thesis is aimed at utilizing the unique reactivity of N-heterocyclic carbenes to develop novel, robust catalysts to mediate organic transformations. The multi-faceted work within this thesis explores the use of NHCs as ancillary ligands on early and late transition metals as potential catalysts for olefin polymerization and ring-closing metathesis, respectively. This work also includes exploring the synthesis and coordination of ancillary ligands derived from the unique reactivity of NHCs towards azides, chalcogens and pnictinidenes. The reactivity of a novel aryl-substituted acyclic imino-N-heterocyclic carbene to early transition metals, cyclooctasulfur and Grubbs-type ruthenium benzylidene complexes was explored. The reactivity of imidazol-2-imide towards Grubbs-type ruthenium benzylidene complexes and the synthesis and coordination of a novel group of ligands bearing an imidazol-2-imine scaffold were also explored. Lastly, this work will include the reactivity of IMes=PPh to Grubbs-type ruthenium benzylidene complexes.