Exploring C(sp3)–C(sp3) reductive elimination from an isolable iron metallacycle. (1st February 2019)

• Record Type: Journal Article
• Authors: Joannou, Matthew V.; Darmon, Jonathan M.; Bezdek, Máté J.; Chirik, Paul J.
• Is Part Of: Polyhedron. Volume 159(2019)
• Page Start: 308
• Page End: 317
• Publication Date: 2019-02-01
• Subjects: Iron -- Metallocycle -- Redox active -- Reductive elimination -- Spectroscopy; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2018.11.047
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: The TOC graphic, and accompanying article, detail the solid, solution, and electronic structure of a 6-coordinate ferracyclopentane. The article also explores conditions that selectively lead to C-C bond formation, where one of these conditions is pictured in the graphical abstract. While addition of 5 equivalents of CO to the ferracyclopentane leads to exclusive C( sp 3 )-C( sp 3 ) reductive elimination of cyclobutane, addition of only 2 equivalents exclusively forms cyclopentanone. The latter product is formed from initial insertion of the metallacyclopentane into a coordinated CO ligand, followed by C( sp 3 )-C( sp 2 ) reductive elimination. Abstract: A six-coordinate iron metallacyclopentane, (phen)2 Fe(CH2 )4, supported by two 1, 10-phenanthroline (phen) ligands, has been synthesized and structurally and spectroscopically characterized. The complex is diamagnetic and an idealized octahedral geometry was observed in the solid state. The electronic structure of (phen)2 Fe(CH2 )4 was determined by a combination of X-ray diffraction, Mössbauer spectroscopy, and DFT analyses and is best described as a low-spin Fe(III) center antiferromagnetically coupled to a radical anion delocalized equally over both phen ligands. The reactivity of (phen)2 Fe(CH2 )4 under different conditions was explored. Thermolysis or photolysis promoted elimination reactions and mixtures of isomeric butenes and butane were observed. Reactions of (phen)2 Fe(CH2 )4 with ethylene and isoprene yielded 3% and 11% of reductive elimination product cyclobutane, respectively, along with butane and butene isomers. Addition of π-accepting ligands such as carbon monoxide, maleic anhydride, or 1, 4-benzoquinone to (phen)2 Fe(CH2 )4 promoted C( sp 3 )-C( sp 3 ) reductive elimination as judged by high selectivity for cyclobutane formation. Two electron oxidation of (phen)2 Fe(CH2 )4 with two equivalents of ferrocenium tetraphenylborate also exclusively yielded cyclobutane in 95% yield. The electronic structure and reactivity of related bis(bipyridine) iron dialkyl compounds previously isolated by Kochi and co-workers were also revisited and their electronic structures revised based on structural, spectroscopic and computational data.