@article {42716, title = {New CNN-type ruthenium pincer NHC complexes. synthesis and catalytic activity. mild, efficient hydrogenation of esters}, journal = {Organometallics}, volume = {30}, year = {2011}, month = {JUN}, pages = {3826{\textendash}3833}, abstract = {

New pincer ruthenium complexes (2{\textendash}6) based on the new bipyridine-NHC ligand 1 were prepared and studied, resulting in an efficient catalytic hydrogenation of esters to the corresponding alcohols under mild conditions. Reaction of the ligand 1 with RuH(Cl)CO(PPh3)3, followed by reaction with one equivalent of the base KHMDS, gave the mixed phosphine-NHC complex 2, incorporating a C{\textendash}H-activated bipyridine ligand. Complex 2 has an octahedral structure containing two phosphorus atoms trans to each other, a hydride trans to the NHC ligand, and CO trans to the C{\textendash}H-activated carbon of the bipyridine ligand. Using the precursor complex Ru(p-cymene)Cl2(CO), reaction with 1 followed by treatment of the intermediate product with one equivalent of KHMDS resulted in formation of the dichloride pincer complexes 3a and 3b, which are in equilibrium, as indicated by variable-temperature 1H NMR. Complex 3a is an octahedral, neutral, and symmetric complex with the CO ligand positioned trans to the central pyridine group of the pincer ligand and the two chlorides trans to each other, as indicated by single-crystal X-ray diffraction. Complex 3b is cationic, with an outer-sphere chloride. Reaction of the NHC ligand 1 with LiHMDS at low temperature followed by addition of RuH(Cl)CO(PPh3)3 resulted in the mixed phosphine-NHC complex 4, which has an octahedral structure containing phosphorus trans to the hydride, a CO trans to the NHC ligand, and an outer-sphere chloride. Chloride substitution by BArF{\textendash} gave the X-ray-characterized complex 5. Deprotonation of complex 4 with KHMDS resulted in formation of the dearomatized complex 6. The in situ prepared 6 (from complex 4 and an equivalent of base) is among the best catalysts known for the hydrogenation of nonactivated esters to the corresponding alcohols under mild conditions.

}, doi = {10.1021/om200367j}, author = {Fogler, Eran and Balaraman, Ekambaram and Ben-David, Yehoshoa and Leitus, Gregory and Shimon, Linda J. W. and Milstein, David} } @article {42707, title = {Novel ruthenium complexes and their uses in processes for formation and/or hydrogenation of esters, amides and derivatives thereof}, number = {US 14/702,641}, year = {2012}, month = {OCT}, chapter = {US20150284417 A1}, abstract = {

The present invention relates to novel Ruthenium complexes and related borohydride complexes, and their use for (1) hydrogenation of amides (including polyamides) to alcohols and amines; (2) preparing amides from alcohols with amines (including preparing polyamides (e.g., polypeptides) by reacting dialcohols and diamines or by polymerization of amino alcohols); (3) hydrogenation of esters to alcohols (including hydrogenation of cyclic esters (lactones), cyclic di-esters (di-lactones) or polyesters); (4) hydrogenation of organic carbonates (including polycarbonates) to alcohols and of carbamates (including polycarbamates) or urea derivatives to alcohols and amines; (5) dehydrogenative coupling of alcohols to esters; (6) hydrogenation of secondary alcohols to ketones; (7) amidation of esters (synthesis of amides from esters and amines); (8) acylation of alcohols using esters; (9) coupling of alcohols with water to form carboxylic acids; and (10) dehydrogenation of beta-amino alcohols to form pyrazines. The present invention further relates to novel uses of certain pyridine Ruthenium complexes.

}, author = {Milstein, David and Balaraman, Ekambaram and Gunanathan, Chidambaram and Gnanaprakasam, Boopathy and Zhang, Jing} } @article {42696, title = {Nickel-catalyzed direct alkynylation of C(sp2)-H bonds of amides: an {\textquotedblleft}inverse sonogashira strategy{\textquotedblright} to ortho-alkynylbenzoic acids. just accepted}, journal = {Catalysis Science \& Technology}, volume = {6}, year = {2016}, month = {OCT}, pages = {1946-1951}, abstract = {

Nickel-catalyzed direct alkynylation of C(sp2){\textendash}H bonds of amides using commercially available, inexpensive 8-aminoquinoline as a removable bidentate directing group is described. The present ortho-alkynylation has a broad substrate scope, functional group tolerance and high regiocontrol, and can be scaled up. The efficiency and selectivity of this strategy provide sustainable routes to a diverse array of ortho-alkynylbenzoic acids under Ni(II)-catalyzed conditions.

}, doi = {10.1039/C5CY01299F}, author = {Landge, Vinod Gokulkrishna and Shewale, Chinmay H. and Jaiswal, Garima and Sahoo, Manoj Kumar and Midya, Siba Prasad and Balaraman, Ekambaram} } @article {44403, title = {Nickel-catalyzed direct synthesis of dialkoxymethane ethers}, journal = {Journal of Chemical Sciences}, volume = {129}, year = {2017}, month = {AUG}, pages = {1153-1159}, abstract = {A simple and efficient method for the preparation of dialkoxymethane ethers (oxymethylene ethers) from alcohols and paraformaldehyde in the presence of commercially available nickel(II) salt is described. The reaction proceeds readily under neutral, solvent-free conditions using paraformaldehyde as a C-1 source. The present strategy has a broad substrate scope including aliphatic (both primary and secondary) and aromatic alcohols and provides a benign method for the preparation of symmetrical dialkoxymethanes in good yields (up to 89\%).}, doi = {10.1007/s12039-017-1339-6}, author = {Subaramanian, Murugan and Bera, Abhijit and Prasad, Bhagavatula L. V. and Balaraman, Ekambaram} } @article {43883, title = {Nickel-catalyzed N-vinylation of heteroaromatic amines via C-H bond activation}, journal = {Organic \& Biomolecular Chemistry}, volume = {15}, year = {2017}, month = {SEP}, pages = { 6896-6900}, type = {Article}, abstract = {

Here, we report a ligand- and reductant-free nickel-catalyzed N-vinylation of heteroaromatic amines using biorenewable p-cymene as a solvent. This unprecedented cross-coupling strategy has high functional group tolerance (halides, alkoxy, cyano, chiral motif, etc.) and proceeded via C-H bond activation.

}, keywords = {Alkylation, Amination Reactions, Anilines, Aryl Chlorides, halides, Monoarylation, O Bonds, Precatalyst, Pyrimidines, Removeble Directing Group}, issn = {1477-0520}, doi = {10.1039/c7ob01791j}, author = {Landge, Vinod G. and Rana, Jagannath and Subaramanian, Murugan and Balaraman, Ekambaram} } @article {45471, title = { Ni-catalyzed alpha-alkylation of unactivated amides and esters with alcohols by hydrogen auto-transfer strategy }, journal = {CHEMSUSCHEM}, volume = {11}, year = {2018}, month = {NOV}, pages = {3911-3916}, type = {Article}, abstract = {A transition-metal-catalyzed borrowing hydrogen/hydrogen auto-transfer strategy allows the utilization of feedstock alcohols as an alkylating partner, which avoids the formation of stoichiometric salt waste and enables a direct and benign approach for the construction of C-N and C-C bonds. In this study, a nickel-catalyzed alpha-alkylation of unactivated amides and ester (tert-butyl acetate) is carried out by using primary alcohols under mild conditions. This C-C bond-forming reaction is catalyzed by a new, molecularly defined nickel(II) NNN-pincer complex (0.1-1 mol \%) and proceeds through hydrogen auto-transfer, thereby releasing water as the sole byproduct. In addition, N-alkylation of cyclic amides under Ni-catalytic conditions is demonstrated.}, doi = {10.1002/cssc.201801443}, author = {Midya, Siba P. and Rana, Jagannath and Pitchaimani, Jayaraman and Nandakumar, Avanashiappan and Madhu, Vedichi and Balaraman, Ekambaram} } @article {45479, title = {Ni-catalyzed dehydrogenative coupling of primary and secondary alcohols with methyl-N-heteroaromatics}, journal = {Organic Chemistry Frontiers}, volume = {5}, year = {2018}, month = {NOV}, pages = {3250-3255}, type = {Article }, abstract = {Here we report the first base-metal catalyzed dehydrogenative coupling of primary (aromatic, heteroaromatic, and aliphatic) and secondary alcohols with methyl-N-heteroaromatics to form various C(sp(3))-alkylated N-heteroaromatics. The reaction is enabled by Earth abundant, non-precious NiBr2 as a transition metal catalyst and N,N,N,N-tetramethylethylenediamine (TMEDA) as a ligand system. Mechanistic studies reveal that a hydrogen auto-transfer process is involved in the direct C(sp(3))-alkylation and the reaction proceeds through an -olefination process.}, doi = {10.1039/c8qo00764k}, author = {Rana, Jagannath and Babu, Reshma and Subaramanian, Murugan and Balaraman, Ekambaram} } @article {46099, title = {Nickel(ii)-catalyzed direct olefination of benzyl alcohols with sulfones with the liberation of H-2}, journal = {Chemical Communications}, volume = {55}, year = {2019}, month = {MAY }, pages = {6130-6133}, type = {Article}, abstract = {

A nickel(II)-catalyzed direct olefination of benzyl alcohols with sulfones to access various terminal and internal olefins with the liberation of hydrogen gas is reported.

}, issn = {1359-7345}, doi = {10.1039/c9cc02603g}, author = {Landge, Vinod G. and Yadav, Vinita and Subaramanian, Murugan and Dangarh, Pragya and Balaraman, Ekambaram} } @article {48343, title = {Nickel-catalyzed direct synthesis of N-substituted indoles from amino alcohols and alcohols}, journal = {Organic Letters}, volume = {24}, year = {2022}, month = {DEC}, pages = {9054-9059}, type = {Article}, abstract = {

A one-pot cascade approach for the synthesis of N substituted indoles from amino alcohols and alcohols under additive and base-free conditions with the liberation of water as the only stoichiometric byproduct is reported. The commercially available bench-stable Ni(OTf)2 salt in combination with 1,2-bis(dicyclohexylphosphino)ethane (dcype) is very effective for this unprecedented catalytic transformation. A broad range of substrates including aromatic and aliphatic primary alcohols, cyclic and acyclic secondary alcohols, and various substituted 2-aminophenyl ethyl alcohols are employed in the reaction conditions to provide a diverse range of N-alkylated indoles. Mechanistic studies revealed that the reaction proceeds through tandem N-alkylation via hydrogen autotransfer followed by the cyclization of N-alkylated alcohol intermediate.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.2c03617}, author = {Yadav, Vinita and Jagtap, Sayali G. and Balaraman, Ekambaram and Mhaske, Santosh B.} } @article {49009, title = {Nickel-catalyzed tandem conversion of paraformaldehyde : methanol to hydrogen and formate/chemo- and stereoselective hydrogenation of alkynes under neutral conditions}, journal = {Catalysis Science and Technology }, volume = {14}, year = {2024}, month = {MAY}, pages = {2779-2793}, type = {Article}, abstract = {

The development of new catalytic protocols for clean and COx-free hydrogen generation from fundamental feedstocks is always interesting and challenging. Herein, we disclose nickel-catalyzed dihydrogen generation from a mixture of paraformaldehyde-methanol under base-free and activator-free conditions. The dihydrogen generation from this redox combination under neutral, oxidative coupling conditions has been integrated with the hydrogen transfer reactions such as chemo- and stereoselective hydrogenation of alkynes in a tandem manner. This unprecedented strategy provides diverse highly stereoselective olefins with excellent tolerance of reducible functional groups such as ether, silyl ether, aldehyde, keto, ester, nitrile, halides including bromo and iodo groups, and heteroarenes. Additionally, we demonstrated catalytic stereo-interconversion of alkenes under benign conditions. The affordable gram-scale synthesis of some important pharmaceutical bioactive molecules has further enhanced their synthetic value. A tandem dihydrogen generation from a mixture of paraformaldehyde-methanol under base-free conditions followed by semihydrogenation of alkynes is reported.

}, issn = {2044-4753}, doi = {10.1039/d3cy01699d}, author = {Subaramanian, Murugan and Padhy, Subarna Sukanya and Gouda, Chandrakanth and Das, Tamal and Vanka, Kumar and Balaraman, Ekambaram} }