Mono‐ and Bis‐Alkynyl Iron Complexes Supported by a “Softened” Tetraaza Macrocycle

• Published in: European journal of inorganic chemistry Vol. 2022; no. 7
• Main Authors: Clendening, Reese A., Ren, Tong
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 09.03.2022
• Subjects: Acetonitrile; Alkynyl; Coordination compounds; Crystal structure; Dehydrogenation; Density functional theory; Inorganic chemistry; Iron; Iron(II/III); Redox-noninnocence; Tetraimine-macrocycle
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.202101021

A pair of novel Fe‐alkynyl complexes, [FeIII(HMTI)(C2SiEt3)2]ClO4 (2) and [FeII(HMTI)(C2SiEt3)(NCCH3)]ClO4 (3), is described herein. Reaction of Fe(meso‐HMC)Cl(ClO4)]ClO4 (1) with lithiated triethylsilylacetylene and subsequent exposure to oxygen yielded the bis‐alkynyl 2 containing the dehydrogenated tetraimine macrocycle (HMTI). Reduction of 2 by mossy zinc in acetonitrile yielded the mono‐alkynyl 3. The structures of 2 and 3 were determined using single‐crystal X‐ray diffraction. Analysis of visible absorption and electrochemical data establishes the redox‐active nature of the HMTI macrocycle, and indicates significant interactions between the Fe dπ and tetraimine π* orbitals. These deductions are further supported by density functional theory calculations. Reported herein are bis‐ (2) and mono‐alkynyl (3) iron complexes supported by a tetraimine macrocycle. The tetraimine macrocycle engages in significant π‐interactions with the Fe center as evidenced by both experimental and computational studies, revealing a significantly softened macrocycle compared to the parental cyclams.