Spin transitions in bis(amidinato)-N-heterocyclic carbene iron(ii) and iron(iii) complexesThis paper is dedicated in memoriam to Gregory L. Hillhouse.Electronic supplementary information (ESI) available: General considerations, computational methods, synthetic procedures and characterization for all new complexes. CCDC 900881, 927786-927788 for 2a, 927790-927794 for 3. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt02440d

In contrast to high spin pyridyl diimine iron( ii ) dichloride complexes, analogous bis(amidinato)-N-heterocyclic carbene iron( ii ) and iron( iii ) complexes demonstrate complex magnetic behaviour. In the solid state, they are best described as intermediate spin complexes at low temperatures that demonstrate gradual spin transitions beginning near or below room temperature. Treating the bis(amidinato)-N-heterocyclic carbene iron( ii ) complex with an aryl azide revealed enhanced reactivity compared to analogous complexes supported by pyridyl diimine ligands. In contrast to high spin pyridyl diimine iron( ii ) dichloride complexes, analogous bis(amidinato)-N-heterocyclic carbene iron( ii ) and iron( iii ) complexes demonstrate complex magnetic behaviour.