Acyclic diaminocarbene-based Thiele, Chichibabin, and Müller hydrocarbons. Issue 43 (12th October 2020)

• Record Type: Journal Article
• Authors: Maiti, Avijit; Chandra, Shubhadeep; Sarkar, Biprajit; Jana, Anukul
• Is Part Of: Chemical science. Volume 11:Issue 43(2020)
• Page Start: 11827
• Page End: 11833
• Publication Date: 2020-10-12
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0sc03622f
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : We report the synthesis of acyclic diaminocarbene (ADC)-scaffold based Thiele, Chichibabin, and Müller hydrocarbons. Studies support that the singlet-triplet energy gap depends on the π-conjugated spacer between the ADC scaffolds. Abstract : Thiele, Chichibabin and Müller hydrocarbons are considered as classical Kekulé diradicaloids. Herein we report the synthesis and characterization of acyclic diaminocarbene (ADC)-based Thiele, Chichibabin, and Müller hydrocarbons. The calculated singlet–triplet energy gaps are Δ E S–T = −27.96, −3.70, −0.37 kcal mol −1, respectively, and gradually decrease with the increasing length of the π-conjugated spacer ( p -phenylene vs. p, p ′-biphenylene vs. p, p ′′-terphenylene) between the two ADC-scaffolds. In agreement with the calculations, we also experimentally observed the enhancement of paramagnetic diradical character as a function of the length of the π-conjugated spacer. ADC-based Thiele's hydrocarbon is EPR silent and exhibits very well resolved NMR spectra, whereas ADC-based Müller's hydrocarbon displays EPR signals and featureless NMR spectra at room temperature. The spacer also has a strong influence on the UV-Vis-NIR spectra of these compounds. Considering that our methodology is modular, these results provide a convenient platform for the synthesis of an electronically modified new class of carbon-centered Kekulé diradicaloids.