High-Spin Iron(II) Alkynyl Complexes with N-Heterocyclic Carbene Ligation: Synthesis, Characterization, and Reactivity Study

Abstract

High-spin iron(II) alkynyl complexes [(IPr2Me2)2Fe(C≡CBut)2] (1) and [(IPr2Me2)2Fe(C≡CR)(NHMes)] (R = But 2, SiMe3 3) bearing a monodentate N-heterocyclic carbene ligand IPr2Me2 (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) have been prepared by salt metathesis and/or amine elimination methods and characterized by various spectroscopic methods. Complex 1 reacts with PMe3 (4 equiv) and ButNC (4 equiv) to form trans-[(PMe3)4Fe(C≡CBut)2] (4) and [η3-{(ButC≡C)(But)CC(IPr2Me2)C(NBut)}Fe(NCBut)3] (5), respectively. In contrast, the reactions of 1 with 4-Pri-C6H4NCO and PriNCNPri lead to the formation of the zwitterionic salts 4-Pri-C6H4NC(O)(IPr2Me2) and (PriN)2C(IPr2Me2), respectively. The interaction of 1 with I2 gives ButC≡CC≡CBut and (IPr2Me2)2FeI2. The C(sp)–C(sp3) cross-coupling products n-C8H17C≡CBut and c-C6H11C≡CBut are formed in high yields when 1 is treated with the corresponding alkyl halides n-C8H17X and c-C6H11X (X = Br, Cl). The formation of the ring-opening product 7,7-dimethyloct-1-en-5-yne ...