Co(cyclam) alkynyl complexes of gem-DEE-aryl: Synthesis, molecular and electronic structures

Publication date: Available online 27 June 2019Source: Journal of Organometallic ChemistryAuthor(s): Tyler J. Azbell, Susannah D. Banziger, Brandon L. Mash, Tong RenAbstractReported in this contribution are the syntheses of mono-alkynyl complexes [Co(cyclam)(gem-DEE-Ar)Cl]Cl (cyclam = 1,4,8,11-tetraazacycloctetradecane; gem-DEE = geminal-diethynylethene) with Ar as either –C6H4-4-NO2 (1) or –C6H4-4-NMe2 (2) from the reactions between [Co(cyclam)Cl2]Cl and H-gem-DEE-Ar under weak base conditions. Further reaction between compound 1 and Li-gem-DEE–C6H4–4-NMe2 at −78 °C afforded the unsymmetric complex trans-[Co(cyclam)(gem-DEE–C6H4–4-NO2)(gem-DEE–C6H4–4-NMe2)]Cl (3). Providing structural features observed for other Co(cyclam) alkynyls, X-ray diffraction study also reveals the influence of the aryl substituent on the first coordination sphere of the Co(III) center. The presence of an aryl substituent also shifts the Co-based redox couples, and enables intense LMCT transitions that are absent in complexes of unsubstituted gem-DEE. These contrasts can be rationalized based on DFT calculations.Graphical abstractNew unsymmetric species utilizing a Co(cyclam)(gem-DEE) motif were synthesized and studied, where gem-DEE (geminal-diethynylethene) acts as an unique iso-electronic partition. Density functional theory (DFT) analysis of unsymmetric trans-[Co(cyclam)(gem-DEE–C6H4–4-NO2)(gem-DEE–C6H4–4-NMe2)]Cl revealed that the HOMO and LUMO+1 orbitals lie...

Source: Journal of Organometallic Chemistry - June 28, 2019 Category: Chemistry Source Type: research