Dianionic and Neutral Diboron-Centered Classical Diradicaloids
Ayan Das, Benedict J. Elvers, Nicolas Chrysochos, Sk Imraj Uddin, Tejaswinee Gangber, Ivo Krummenacher, Dipanti Borah, Anshika Mishra, Maheswaran Shanmugam, Cem B. Yildiz, Holger Braunschweig, Carola Schulzke, Anukul Jana
Abstract
Herein, we report the syntheses and electronic structures of crystalline dianionic as well as neutral diboron-centered classical diradicaloids as boron analogues of classical Thiele, Chichibabin, and Müller (this only for dianionic diradicaloids!) hydrocarbons. These are based on borane radical anion and NHC-stabilized boryl radical spin carriers, respectively. All these dianionic diboron-centered diradicaloids exhibit triplet population at room temperature regardless of the π-conjugated spacer: p -phenylene, p, p′ -biphenylene, or p, p″ -terphenylene. In the case of neutral diboron-centered diradicaloids, the employed π-conjugated spacer plays a crucial role for the triplet population at room temperature: EPR inactive for p -phenylene vs EPR active for p, p′ -biphenylene. The findings emphasize the importance of the spin carriers for the resulting ground-state: borane radical anion vs NHC-stabilized boryl radical along with the pivotal role of the π-conjugated spacer as spin-coupler between two spins. Notably, 100 years (a century) after the first report by Krause of the triphenyl borane radical-anion, being isoelectronic to the triphenylmethyl radical, we convey borane radical anion-based diradicaloids. Furthermore, while donor-stabilized boryl radicals were introduced in the 1980s by Giles and Roberts, said concept is herewith being extended to NHC-stabilized boryl radical-based diradicaloids.