Doubly zwitterionic, di-reduced, highly electron-rich, air-stable naphthalenediimides: redox-switchable islands of aromatic–antiaromatic states. Issue 26 (30th May 2019)

• Record Type: Journal Article
• Authors: Kumar, Sharvan; Shukla, Jyoti; Mandal, Kalyanashis; Kumar, Yogendra; Prakash, Ravi; Ram, Panch; Mukhopadhyay, Pritam
• Is Part Of: Chemical science. Volume 10:Issue 26(2019)
• Page Start: 6482
• Page End: 6493
• Publication Date: 2019-05-30
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c9sc00962k
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The synthesis and isolation of two-electron reduced naphthalenediimides is reported. A doubly zwitterionic structure is observed for the first time in a naphthalene moiety, which aids in its stabilization. Abstract : The di-reduced state of the naphthalene moiety and its congeners have long captivated chemists as it is elusive to stabilize these intrinsically reactive electron-rich π-systems and for their emergent multifaceted properties. Herein we report the synthesis and isolation of two-electron (2e − ) reduced, highly electron-rich naphthalenediimides (NDIs). A doubly zwitterionic structure is observed for the first time in a naphthalene moiety and validated by single crystal X-ray crystallography and spectroscopic methods. The synthesis avoids hazardous reducing agents and offers an easy, high-yielding route to bench-stable di-reduced NDIs. Notably, we realized high negative first oxidation potentials of up to −0.730 V vs. Fc/Fc + in these systems, which establish these systems to be one of the strongest ambient stable electron donors. The study also provides the first insights into the NMR spectra of the di-reduced systems revealing a large decrease in diatropicity of the naphthalene ring compared to its 2e − oxidized form. The NICS, NICS- XY global ring current, gauge-including magnetically induced current (GIMIC) and AICD ring current density calculations revealed switching of the antiaromatic and aromatic states at the naphthalene and the imide rings, respectively, in the di-reduced system compared to the 2e − oxidized form. Notably, the substituents at the phosphonium groups significantly tune the antiaromatic–aromatic states and donor ability, and bestow an array of colors to the di-reduced systems by virtue of intramolecular through-space communication with the NDI scaffold. Computational studies showed intramolecular noncovalent interactions to provide additional stability to these unprecedented doubly zwitterionic systems.