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

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 in the reaction of 1 with cyclopropylmethyl bromide supports the radical character of the cross-coupling reaction.