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Catalytic cross‐coupling between aryl halides and alkynes is considered an extremely important organic transformation (popularly known as the Sonogashira coupling) and it requires a transition metal‐based catalyst. Accomplishing such transformation without any transition metal‐based catalyst in the absence of any external stimuli such as heat, photoexcitation or cathodic current is highly challenging. This work reports transition‐metal‐free cross‐coupling between aryl halides and alkynes synthesizing a rich library of internal alkynes without any external stimuli. A chemically double‐reduced phenalenyl (PLY)‐based molecule with the super‐reducing property was employed for single electron transfer to activate aryl halides generating reactive aryl radicals, which subsequently react with alkyne. This protocol covers not only various types of aryl, heteroaryl and polyaryl halides but also applies to a large variety of aromatic alkynes at room temperature. With a versatile substrate scope successfully tested on more than 75 entries, this radical‐mediated pathway has been explained by several control experiments. All the key reactive intermediates have been characterized with spectroscopic evidence. Detailed DFT calculations have been instrumental in portraying the mechanistic pathway. Furthermore, we have successfully extended this transition‐metal‐free catalytic strategy for the first time towards solvent‐free cross‐coupling between solid aryl halide and alkyne substrates. [ABSTRACT FROM AUTHOR]

An extended class of organic multi‐redox systems was derived from bicyclic(alkyl)amino carbenes (BICAACs). The highly‐conjugated system undergoes a total of 4 redox events spanning a 1.8 V redox range. These organic compounds exhibited four different stable redox states (dication, radical cation, neutral and radical anion), and all of them were characterized either by single crystal X‐ray study and/or various spectroscopic studies. Three of the four redox states are stable to air and moisture. The availability of stable multiple redox states demonstrated promise towards their efficacy in the symmetric H‐cell charge/discharge cycling. Among various redox states, the dication/neutral state works efficiently and continuously for 1500 cycles in 2e− charge/discharge process outside glovebox in commercially available DMF with minimum capacity loss (retaining nearly 90 % Coulombic efficiency). Surprisingly, the efficiency of the redox cycle was retained even if the system was exposed to air for 30 days when it slowly regenerated to the initial deep blue radical cation, and it exhibited another 100 charge/discharge cycles with a minimal capacity loss. Such a stable H‐cell cycling ability is not well known among organic molecule‐based systems. [ABSTRACT FROM AUTHOR]

A redox‐active phenalenyl ligand coordinated Mn(III)‐complex can be reduced chemically to generate an active catalyst containing a ligand‐centered radical. This chemically reduced Mn‐catalyst shows excellent catalytic reactivity for silylative dehydration of a wide range of primary amides (including late‐stage diversification of various bio‐active molecules) to synthesize nitriles using an inert and inexpensive silane, polymethylhydrosiloxane (PMHS), under mild conditions. Control experiments suggest a radical pathway for the present catalytic reaction, initiated by the ligand‐centered radical. [ABSTRACT FROM AUTHOR]

Organic photoredox catalysis is a versatile tool for accessing a wide range of synthetic transformations. Towards the development of a new class of organophotoredox catalysts, we have employed phenalenyl, an odd alternant hydrocarbon (OAH), for reductive C−C coupling reactions. Phenalenyl can adopt a stable open‐shell state (radical), using its non‐bonding molecular orbital. To date, chemically induced phenalenyl‐based radicals have been extensively explored in designing various intriguing organic materials and recently towards electron transfer catalysis. However, the photochemical generation of phenalenyl‐based radicals is rare. In this work, we report the photoinduced generation of phenalenyl‐based radicals with detailed mechanistic studies such as steady‐state absorption, time‐resolved transient absorption spectroscopy, and in‐situ absorption kinetic experiments to authenticate the generation of photo‐induced phenalenyl radicals. In addition, we present results demonstrating that this novel catalytic species can be applied to reductive pinacol coupling catalysis and reductive alkylation of terminal alkynes. [ABSTRACT FROM AUTHOR]

A MnI catalyst featuring redox‐active tridentate phenalenyl (PLY) ligand has been used for catalytic N‐formylation of secondary amides and lactams under 1 atm CO2 as a C1 source at room temperature for the first time. The protocol is applicable to a wide range of secondary amides including heterocycles, bio‐active cinnamide derivatives and the diversification of therapeutic molecules. In‐depth mechanistic investigations based on experimental outcomes and DFT calculations suggested an unconventional metal‐ligand cooperation, where a ligand‐centred radical plays a crucial role in initiating the reaction process. [ABSTRACT FROM AUTHOR]

An extended class of stable mesoionic N‐heterocyclic imines (mNHIs), containing a highly polarized exocyclic imine moiety, were synthesized. The calculated proton affinities (PA) and experimentally determined Tolman electronic parameters (TEPs) reveal that these synthesized mNHIs have the highest basicity and donor ability among NHIs reported so far. The superior nucleophilicity of newly designed mNHIs was utilized in devising a strategy to incorporate CO2 as a bridging unit under reductive conditions to couple inert primary amides. This strategy was further extended to hetero‐couplings between amide and amine using CO2. These hitherto unknown catalytic transformations were introduced in the diversification of various biologically active drug molecules under metal‐free conditions. The underlying mechanism was explored by performing a series of control experiments, characterizing key intermediates using spectroscopic and crystallographic techniques. [ABSTRACT FROM AUTHOR]

An extended class of stable mesoionic N‐heterocyclic imines (mNHIs), containing a highly polarized exocyclic imine moiety, were synthesized. The calculated proton affinities (PA) and experimentally determined Tolman electronic parameters (TEPs) reveal that these synthesized mNHIs have the highest basicity and donor ability among NHIs reported so far. The superior nucleophilicity of newly designed mNHIs was utilized in devising a strategy to incorporate CO2 as a bridging unit under reductive conditions to couple inert primary amides. This strategy was further extended to hetero‐couplings between amide and amine using CO2. These hitherto unknown catalytic transformations were introduced in the diversification of various biologically active drug molecules under metal‐free conditions. The underlying mechanism was explored by performing a series of control experiments, characterizing key intermediates using spectroscopic and crystallographic techniques. [ABSTRACT FROM AUTHOR]

The use of molecular spin state as a quantum of information for storage, sensing and computing has generated considerable interest in the context of next-generation data storage and communication devices [...]

The preparation, crystallization and solid-state characterization of the first two members of the family of spiro-bis(1,9-disubstituted phenalenyl)boron neutral radicals based solely on oxygen functionalization, significantly lowers the electrochemical disproportionation potentials, in comparison with other salts. These two radical molecular conductors do not exist as isolated free radicals, but exhibit a spin-spin interaction, best rationalized by the resonating valence bond model.