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CBu^t)₂] (1) and [(IPr₂Me₂)₂Fe­(CCR)­(NHMes)] (R = Bu^t 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 Bu^tNC (4 equiv) to form trans-[(PMe₃)₄­Fe­(CCBu^t)₂] (4) and [η³-{(Bu^tCC)­(Bu^t)­CC­(IPr₂Me₂)­C­(NBu^t)}­Fe­(NCBu^t)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 Bu^tCCCCBu^t and (IPr₂Me₂)₂FeI₂. The C­(sp)–C­(sp³) cross-coupling products n-C₈H₁₇CCBu^t and c-C₆H₁₁CCBu^t 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.