Quick Access to 2,2’-Bipyridines from Halopyridines and Pyridines Using Transition Metals: A Short Review N.S. Kumar, A. Adhikary Letters in Organic Chemistry, 2025 Over the past decades, 2,2’-bipyridines and their derivatives have significantly contributed to the field of advanced materials, synthesis, and catalysis. In particular, the structural ability of bipyridines to accommodate numerous types of functional groups with varying electronic and steric properties resulted in their diverse applications. In this regard, developing novel and cost-effective preparative methodologies for 2,2’-bipyridines having various substituents has always been a popular area of research. Starting from pyridine derivatives, the simplest route to these molecules includes homo-, hetero-, and cross-coupling reactions. This review concentrated on transition metal-mediated one-step procedures for 2,2’-bipyridines from inexpensive and abundant starting materials, specifically, pyridines and 2-halopyridines. Although this report focuses on self-coupling techniques, convenient hetero-coupling methods are included. Special attention is given to the substrate scope details of the existing methodologies.
Transition metal pincer catalysts for formic acid dehydrogenation: a mechanistic perspective N. Sai Kumar, Anubendu Adhikary Frontiers in Chemistry, 2024 The storage and transportation of hydrogen gas, a non-polluting alternative to carbon-based fuels, have always been challenging due to its extreme flammability. In this regard, formic acid (FA) is a promising liquid organic hydrogen carrier (LOHC), and over the past decades, significant progress has been made in dehydrogenating FA through transition metal catalysis. In this review, our goal is to provide a detailed insight into the existing processes to expose various mechanistic challenges associated with FA dehydrogenation (FAD). Specifically, methodologies catalyzed by pincer-ligated metal complexes were chosen. Pincer ligands are preferred as they provide structural rigidity to the complexes, making the isolation and analysis of reaction intermediates less challenging and consequently providing a better mechanistic understanding. In this perspective, the catalytic activity of the reported pincer complexes in FAD was overviewed, and more importantly, the catalytic cycles were examined in detail. Further attention was given to the structural modifications, role of additives, reaction medium, and their crucial effects on the outcome.
Using CS2 to Probe the Mechanistic Details of Decarboxylation of Bis(phosphinite)-Ligated Nickel Pincer Formate Complexes Qiang-Qiang Ma, Ting Liu, Anubendu Adhikary, Jie Zhang, Jeanette A. Krause, et al. Organometallics, 2016 The reaction of the formate complex {2,6-(R2PO)2C6H3}Ni(OCHO) (R = tBu, 5; R = iPr, 6) with CS2 shows first-order kinetics in nickel concentration and zero-order in [CS2] when CS2 is used in large excess. Rate measurement at different temperatures gives activation parameters ΔH⧧ = 22.6 ± 0.9 kcal/mol and ΔS⧧ = −5.2 ± 3.0 eu for the decarboxylation of 5 and ΔH⧧ = 22.6 ± 1.0 kcal/mol and ΔS⧧ = −4.3 ± 3.2 eu for the decarboxylation of 6. Comparing the decarboxylation rate constants for 6 and {2,6-(iPr2PO)2C6H3}Ni(OCDO) (6-d) yields KIE values of 1.67–1.90 within the temperature range 30–45 °C. On the basis of these experimental results and DFT calculations, an ion pair mechanism has been proposed for the decarboxylation process. The CS2 insertion products {2,6-(R2PO)2C6H3}Ni(SCHS) (R = tBu, 3; R = iPr, 4) have been characterized by X-ray crystallography.
Catalysis Involving Phosphinite-Based Metallacycles Anubendu Adhikary, Hairong Guan ACS Catalysis, 2015 Phosphinite-based metallacycles are important intermediates, catalyst precursors, or catalysts for a variety of chemical transformations. Facile, reversible formation of P–O bonds allows phosphinites to act as catalytic directing groups that lead to more efficient and selective metal-catalyzed processes. Relatively low costs and convenient syntheses make metallacyclic phosphinite complexes attractive compounds for catalytic studies. Given the high interest in developing the related phosphine- and phosphite-based catalysts, this Perspective focuses specifically on the comparisons between these different metallacyclic complexes in catalytic reactions. In a number of examples, phosphinite-based metallacycles are more efficient catalysts due to better-matched ligand properties for rate-limiting steps or faster conversion of the complexes to catalytically active species.
Configurational Stability and Stereochemistry of P-Stereogenic Nickel POCOP-Pincer Complexes Anubendu Adhikary, Jeanette A. Krause, Hairong Guan Organometallics, 2015 The P-stereogenic nickel complex {2,6-[(t-Bu)(Ph)PO]2C6H3}NiCl (2) has been synthesized via cyclometalation of the POCOP-pincer ligand 1,3-[(t-Bu)(Ph)PO]2C6H4 (1) with NiCl2. The initially isolated 2 consists of a 1:1 mixture of racemic and meso isomers that are separable through repeated crystallization and is configurationally stable even at 110 °C. Upon mixing with t-BuOK, the meso isomer (2-meso) displays a higher ligand substitution rate than the racemic isomer (2-rac), likely because its nickel center is sterically more accessible. Complex 2, as either pure 2-rac or a 2-rac/2-meso mixture, can be converted to the nickel triflate complex {2,6-[(t-Bu)(Ph)PO]2C6H3}NiOTf (3) or the nickel formate complex {2,6-[(t-Bu)(Ph)PO]2C6H3}NiOCHO (7) without epimerization at the phosphorus centers. Under a dynamic vacuum at 90 °C, decarboxylation of 7-meso is faster than that of 7-rac, suggesting that in the transition state the formato hydrogen approaches the nickel center from the axial site rather than the equa...
How does the carbon hybridization impact the rate of metal-carbon bond cleavage by an alkyne? A case study with POCOP-pincer ligated palladium hydrocarbyl complexes A Adhikary, JA Krause, H Guan Journal of Organometallic Chemistry 845, 151-156 , 2017 2017 Citations: 6
Palladium POCOP-pincer complexes: Catalysis in reduction of CO2 with boranes A Adhikary, J Krause, H Guan ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 253 , 2017 2017
Using CS 2 to Probe the Mechanistic Details of Decarboxylation of Bis(phosphinite)-Ligated Nickel Pincer Formate Complexes QQ Ma, T Liu, A Adhikary, J Zhang, JA Krause, H Guan Organometallics 35 (24), 4077-4082 , 2016 2016 Citations: 31
Metathesis reactivity of bis (phosphinite) pincer ligated nickel chloride, isothiocyanate and azide complexes H Li, W Meng, A Adhikary, S Li, N Ma, Q Zhao, Q Yang, NA Eberhardt, ... Journal of Organometallic Chemistry 804, 132-141 , 2016 2016 Citations: 27
Catalysis Involving Phosphinite-Based Metallacycles A Adhikary, H Guan ACS Catalysis 5 (11), 6858-6873 , 2015 2015 Citations: 41
Configurational Stability and Stereochemistry of P-Stereogenic Nickel POCOP-Pincer Complexes A Adhikary, JA Krause, H Guan Organometallics 34 (14), 3603-3610 , 2015 2015 Citations: 21
Synthesis and Catalytic Applications of Nickel and Palladium Pincer Complexes A Adhikary University of Cincinnati , 2015 2015
Kinetics of CO2 deinsertion from bis (phosphinite)-ligated nickel and palladium pincer formate complexes A Adhikary, H Guan ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 248 , 2014 2014
Interaction of alkynes with palladium POCOP-pincer hydride complexes and its unexpected relation to palladium-catalyzed hydrogenation of alkynes A Adhikary, JR Schwartz, LM Meadows, JA Krause, H Guan Inorganic Chemistry Frontiers 1 (1), 71-82 , 2014 2014 Citations: 49
H. Guan in Pincer and Pincer-Type Complexes, Vol. 7 A Adhikary Wiley-VCH, Weinheim, Germany , 2014 2014 Citations: 6
Nickel-Catalyzed Cross-Coupling Reactions A Adhikary, H Guan 2014) Pincer and pincer-type complexes: applications in organic synthesis … , 2014 2014 Citations: 5
New and convenient method for the synthesis of nickel and palladium pincer fluoride complexes A Adhikary, JA Krause, H Guan ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 246 , 2013 2013
Synthesis of new palladium hydride complexes and their reactivity with alkynes A Adhikary, JA Krause, H Guan ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 245 , 2013 2013
Substituent effects on Ni–S bond dissociation energies and kinetic stability of nickel arylthiolate complexes supported by a bis (phosphinite)-based pincer ligand J Zhang, A Adhikary, KM King, JA Krause, H Guan Dalton Transactions 41 (26), 7959-7968 , 2012 2012 Citations: 44
Tetrabutylammonium tribromide (TBATB): a mild and efficient catalyst for O-isopropylidenation of carbohydrates AT Khan, MM Khan, A Adhikary Carbohydrate research 346 (5), 673-677 , 2011 2011 Citations: 36
MOST CITED SCHOLAR PUBLICATIONS
Interaction of alkynes with palladium POCOP-pincer hydride complexes and its unexpected relation to palladium-catalyzed hydrogenation of alkynes A Adhikary, JR Schwartz, LM Meadows, JA Krause, H Guan Inorganic Chemistry Frontiers 1 (1), 71-82 , 2014 2014 Citations: 49
Substituent effects on Ni–S bond dissociation energies and kinetic stability of nickel arylthiolate complexes supported by a bis (phosphinite)-based pincer ligand J Zhang, A Adhikary, KM King, JA Krause, H Guan Dalton Transactions 41 (26), 7959-7968 , 2012 2012 Citations: 44
Catalysis Involving Phosphinite-Based Metallacycles A Adhikary, H Guan ACS Catalysis 5 (11), 6858-6873 , 2015 2015 Citations: 41
Tetrabutylammonium tribromide (TBATB): a mild and efficient catalyst for O-isopropylidenation of carbohydrates AT Khan, MM Khan, A Adhikary Carbohydrate research 346 (5), 673-677 , 2011 2011 Citations: 36
Using CS 2 to Probe the Mechanistic Details of Decarboxylation of Bis(phosphinite)-Ligated Nickel Pincer Formate Complexes QQ Ma, T Liu, A Adhikary, J Zhang, JA Krause, H Guan Organometallics 35 (24), 4077-4082 , 2016 2016 Citations: 31
Metathesis reactivity of bis (phosphinite) pincer ligated nickel chloride, isothiocyanate and azide complexes H Li, W Meng, A Adhikary, S Li, N Ma, Q Zhao, Q Yang, NA Eberhardt, ... Journal of Organometallic Chemistry 804, 132-141 , 2016 2016 Citations: 27
Configurational Stability and Stereochemistry of P-Stereogenic Nickel POCOP-Pincer Complexes A Adhikary, JA Krause, H Guan Organometallics 34 (14), 3603-3610 , 2015 2015 Citations: 21
How does the carbon hybridization impact the rate of metal-carbon bond cleavage by an alkyne? A case study with POCOP-pincer ligated palladium hydrocarbyl complexes A Adhikary, JA Krause, H Guan Journal of Organometallic Chemistry 845, 151-156 , 2017 2017 Citations: 6
H. Guan in Pincer and Pincer-Type Complexes, Vol. 7 A Adhikary Wiley-VCH, Weinheim, Germany , 2014 2014 Citations: 6
Nickel-Catalyzed Cross-Coupling Reactions A Adhikary, H Guan 2014) Pincer and pincer-type complexes: applications in organic synthesis … , 2014 2014 Citations: 5
Palladium POCOP-pincer complexes: Catalysis in reduction of CO2 with boranes A Adhikary, J Krause, H Guan ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 253 , 2017 2017
Synthesis and Catalytic Applications of Nickel and Palladium Pincer Complexes A Adhikary University of Cincinnati , 2015 2015
Kinetics of CO2 deinsertion from bis (phosphinite)-ligated nickel and palladium pincer formate complexes A Adhikary, H Guan ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 248 , 2014 2014
New and convenient method for the synthesis of nickel and palladium pincer fluoride complexes A Adhikary, JA Krause, H Guan ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 246 , 2013 2013
Synthesis of new palladium hydride complexes and their reactivity with alkynes A Adhikary, JA Krause, H Guan ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 245 , 2013 2013
