@article {46716, title = {Amidinato germylene-zinc complexes: synthesis, bonding, and reactivity}, journal = {Chemistry-An Asian Journal}, volume = {15}, year = {2020}, month = {OCT }, pages = {3116-3121}, type = {Article}, abstract = {

Despite the explosive growth of germylene compounds as ligands in transition metal complexes, there is a modicum of precedence for the germylene zinc complexes. In this work, the synthesis and characterization of new germylene zinc complexes [PhC(NtBu)(2)Ge{N(SiMe3)(2)}-\> ZnX2](2)(X= Br (2) and I (3)) supported by (benz)-amidinato germylene ligands are reported. The solid-state structures of2and3have been validated by single-crystal X-ray diffraction studies, which revealed the dimeric nature of the complexes, with distorted tetrahedral geometries around the Ge and Zn center. DFT calculations reveal that the Ge-Zn bonds in2and3are dative in nature. The reaction of2with elemental sulfur resulted in the first structurally characterized germathione stabilized ZnBr(2)complexes PhC(NtBu)(2)Ge(=S){N(SiMe3)(2)}-\> ZnBr2(5). Therefore, the Ge=S in5is in-between Ge-S single and Ge=S double bond length, owing to the coordination of a sulfur lone pair of electrons to ZnBr2.

}, keywords = {DFT, Germathione, Germylene, X-ray Structure, zinc}, issn = {1861-4728}, doi = {10.1002/asia.202000807, Early Access Date = SEP 2020}, author = {Yadav, Sandeep and Kumar, Rohit and Raj, K. Vipin and Yadav, Prashant and Vanka, Kumar and Sen, Sakya S.} } @article {46956, title = {Tale of biphenyl and terphenyl substituents for structurally diverse ketiminato magnesium, calcium and germanium complexes}, journal = {Chemistry-An Asian Journal}, volume = {15}, year = {2020}, month = {MAR}, pages = {820-827}, type = {Article}, abstract = {

In this paper, we have used two N,O-ketiminato ligands (L1 and L2) with biphenyl and terphenyl substituent on the nitrogen atom. Deprotonation of L1 with KN(SiMe3)(2) and subsequent reaction with MgI2 led to a homoleptic dinuclear magnesium complex (1) with a Mg2O2 four-membered ring. Deprotonation with nBuLi and subsequent reaction with MgI2 afforded a unusual dinuclear magnesium complex (2) with a Mg2O2 ring. Extension of the ligand for calcium resulted in a trinuclear calcium complex (3) with six four-membered Ca2O2 rings. We could not isolate any chelating complex when L2 was used as a ligand, and only oxygen bound magnesium (4) and calcium (5) adducts were isolated. DFT studies were performed to understand this dissimilar behavior. More diverse results were obtained when lithiated L1 and L2 were treated with germanium dichloride. We were able to stabilize a monomeric germylene monochloride (7) with L1. However, with L2, an unusual ligand scrambling, and a C-C coupling take place, leading to the formation of a secondary carbocation with GeCl3- as a counter-anion (8). Besides, a germanium dichloride adduct (9) bound to the oxygen center of the ligand was obtained as the minor product.

}, keywords = {calcium, Germylene, ligand, Magnesium, X-ray Structure}, issn = {1861-4728}, doi = {10.1002/asia.201901801, Early Access Date = FEB 2020}, author = {Kumar, Rohit and Yadav, Sandeep and Gour, Kritika and Sangtani, Ekta and Ranjan Dash, Soumya and Raja, Abhishekram and Vanka, Kumar and Gonnade, Rajesh G. and Sen, Sakya S.} } @article {47644, title = {Deoxygenative hydroboration of primary and secondary amides: a catalyst-free and solvent-free approach}, journal = {Chemical Communications}, volume = {57}, year = {2021}, month = {OCT }, pages = {10596-10599}, type = {Article}, abstract = {In contrast to the recent reports on catalytic hydroboration of amides to amines with pinacolborane (HBpin), a simple catalyst-free and solvent-free method for the hydroboration of a variety of amides has been realized. To get the mechanistic insights, DFT calculations have been performed.}, issn = {1359-7345}, doi = {10.1039/d1cc04148g}, author = {Kumar, Rohit and Bisai, Milan Kumar and Jain, Shailja and Vanka, Kumar and Sen, Sakya S.} } @article {47038, title = {Phosphorus ligands in hydroformylation and hydrogenation: a personal account}, journal = {Chemical Record}, year = {2021}, month = {MAR}, type = {Article; Early Access}, abstract = {

Metal-catalyzed hydroformylation and hydrogenation heavily rely on ligands, among which phosphorous ligands play a pivotal role. This personal account presents a selection of three distinct classes of phosphorous ligands, namely, monodentate meta-substituted phosphinites, bis-phosphites, and P-chiral supramolecular phosphines, developed in our group. The synthesis of these ligands, isolation, characterization, and their performance in transition metal-catalyzed hydroformylation, isomerizing hydroformylation, and asymmetric hydrogenation of olefins is summarized. The state of the art development in iron-catalyzed hydroformylation of alkenes and our contributions to the field is discussed. Use of phosphines enabled iron-catalyzed hydroformylation of alkenes under mild conditions. Thus, this account demonstrates the central role of phosphorus ligands in industrially relevant transformations such as hydrogenation and hydroformylation. The seemingly matured field of ligand discovery still holds significant potential and will steer the field of homogeneous catalysis.

}, keywords = {Homogeneous catalysis, Hydroformylation, Hydrogenation, Olefins, Phosphorus ligands}, issn = {1527-8999}, doi = {10.1002/tcr.202100007, Early Access Date = MAR 2021}, author = {Tewari, Tanuja and Kumar, Rohit and Chandanshive, Amol C. and Chikkali, Samir H.} } @article {47805, title = {Hydroformylation of olefins by metals other than rhodium}, journal = {Journal of Organometallic Chemistry}, volume = {960}, year = {2022}, month = {FEB}, pages = {122231}, type = {Article}, abstract = {Metal catalyzed hydroformylation of alkenes is an atom economic transformation to construct useful aldehydes and is being industrially practiced for decades. The most commonly used metal for this transformation on an industrial scale is rhodium. However, rhodium is rare, costly, and is depleting at a skyrocketing rate. Therefore, finding a suitable alternative to rhodium for metal-catalyzed hydroformylation has been on the radar of many academic and industrial researchers. This review presents the scientific advancements reported in the hydroformylation reaction using metals other than rhodium. An overview of recent progress in palladium, iridium, ruthenium, cobalt, platinum, and iron-catalyzed hydroformylation is presented. Hydroformylation of alkenes and alkynes, using syngas as well as syngas surrogates is examined. The evaluation of the current status of non-rhodium metals in hydroformylation suggests that the field is still in a nascent stage and, except cobalt, no other metal poses a significant challenge to the dominance of rhodium. Deep mechanistic understanding of rate-limiting elementary steps in the non-rhodium metals is largely missing and thus only limited success is reported. Intense research on ligand design, mechanistic understanding, and choice of non-rhodium metal precursors may change this scenario in near future.}, keywords = {aldehydes, alkenes, catalysis, Hydroformylation, Non-rhodium metals}, issn = {0022-328X}, doi = {10.1016/j.jorganchem.2021.122231}, author = {Kumar, Rohit and Chikkali, Samir H.} } @article {48154, title = {Luminescent magnesium complexes with intra- and inter-ligand charge transfer}, journal = {Chemical Communications}, volume = {58}, year = {2022}, month = {OCT}, pages = {11843-11846}, type = {Article}, abstract = {

Herein, we report two 2,2{\textquoteright}-pyridylpyrrolide (PyPyrH) ligand supported magnesium complexes (1 and 2), which demonstrate bright luminescence with a quantum yield of 22\% and 14\% in the solid state, respectively. Theoretical calculations reveal that their emissive properties originate from the intra- and inter-ligand charge transfer.

}, issn = {1359-7345}, doi = {10.1039/d2cc04142a}, author = {Kumar, Rohit and Pahar, Sanjukta and Chatterjee, Joy and Dash, Soumya Ranjan and Gonnade, Rajesh G. and Vanka, Kumar and Sen, Sakya S.} } @article {47899, title = {Mechanistically guided one pot synthesis of phosphine-phosphite and its implication in asymmetric hydrogenation}, journal = {European Journal of Organic Chemistry}, volume = {2022}, year = {2022}, month = {JAN}, pages = {e202101447}, type = {Article}, abstract = {

Although hybrid bidentate ligands are known to yield highly enantioselective products in asymmetric hydrogenation (AH), synthesis of these ligands is an arduous process. Herein, a one pot, atom-economic synthesis of a hybrid phosphine-phosphite (L1) is reported. After understanding the reactivity difference between an 0-nucleophile versus C-nucleophile, one pot synthesis of Senphos (L1) was achieved (72\%). When L1 was treated with [Rh], P-31 NMR revealed bidentate coordination to Rh. Senphos, in the presence of rhodium, catalyzes the AH of Methyl-2-acetamido-3-phenylacrylate and discloses an unprecedented turn over frequency of 2289, along with excellent enantio-selectivity (92\%). The generality is demonstrated by hydrogenating an array of alkenes. The AH operates under mild conditions of 1-2 bar H-2 pressure, at room temperature. The practical relevance of Ll is demonstrated by scaling-up the reaction to 1 g and by synthesizing DOPA, a drug widely employed for the treatment of Parkinson{\textquoteright}s disease. Computational insights indicate that the R isomer is preferred by 3.8 kcal/mol over the S isomer.

}, keywords = {asymmetric hydrogenation, catalysis, DOPA synthesis, One pot synthesis, Phosphine-phosphite ligand}, issn = {1434-193X}, doi = {10.1002/ejoc.202101447}, author = {Sen, Anirban and Kumar, Rohit and Pandey, Swechchha and Raj, K. Vipin and Kumar, Pawan and Vanka, Kumar and Chikkali, Samir H.} } @article {48141, title = {Monomeric magnesium catalyzed alkene and alkyne hydroboration}, journal = {Chemistry-A European Journal}, volume = {28}, year = {2022}, month = {OCT }, type = {Article}, abstract = {

In this work, two monomeric magnesium alkyl complexes (1 and 2) were prepared using bis(phosphino)carbazole framework and among them 1 has been used as a catalyst for hydroboration of alkenes and alkynes with pinacolborane (HBpin). A broad variety of aromatic and aliphatic alkenes and alkynes were efficiently reduced. Anti-Markovnikov regioselective hydroboration of alkenes and alkynes was achieved, which was confirmed by deuterium-labelling experiments. The work represents the first example of the use of magnesium in homogeneous catalytic hydroboration of alkene with broad substrate scope. Experimental mechanistic investigations and DFT calculations provided insights into the reaction mechanism. Finally, the hydroboration protocol was extended to terpenes.

}, keywords = {carbazole, Magnesium, monomeric complexes, phosphorous, X-ray Structure}, issn = {0947-6539}, doi = {10.1002/chem.202201896}, author = {Kumar, Rohit and Dutta, Sayan and Sharma, Vishal and Singh, Praval P. and Gonnade, Rajesh G. and Koley, Debasis and Sen, Sakya S.} } @article {48032, title = {Well-defined calcium compound catalyzes trimerization of arylisocyanates into 1,3,5-triarylisocyanurates}, journal = {ChemCatChem}, volume = {14}, year = {2022}, month = {JUN }, pages = {e202101788}, type = {Article}, abstract = {

We report the synthesis of a calcium complex (2) bearing a tetradentate monoanionic ligand with a diaminoethane core and phenolate and pyridine peripheral donors. Single crystal X-ray studies on 2 revealed that LiI was also co-crystallized, leading to a four-membered ring with four different elements. 2 was found to be an efficient catalyst for the cyclotrimerization of a variety of aromatic isocyanates under mild conditions.

}, keywords = {calcium, Cyclotrimerization, Isocyanurates, Tetradentate ligand}, issn = {1867-3880}, doi = {10.1002/cctc.202101788}, author = {Kumar, Rohit and Sharma, Vishal and Jain, Shailja and Sharma, Himanshu and Vanka, Kumar and Sen, Sakya S.} } @article {48263, title = {Controlled reduction of isocyanates to formamides using monomeric magnesium}, journal = {Chemical Communications}, volume = {59}, year = {2023}, month = {FEB}, pages = {2255-2258}, type = {Article}, abstract = {

This work describes a transition metal-free methodology involving an efficient and controlled reduction of isocyanates to only formamide derivatives using pinacolborane (HBpin) as the hydrogenating agent and a bis(phosphino)carbazole ligand stabilized magnesium methyl complex (1) as the catalyst. A large number of substrates undergo selective hydroboration and give exclusively N-boryl formamides.

}, issn = {1359-7345}, doi = {10.1039/d3cc00036b}, author = {Kumar, Rohit and Sharma, Vishal and Banerjee, Subhrashis and Vanka, Kumar and Sen, Sakya S.} } @article {48693, title = {Iron-catalysed highly selective hydroalkoxycarbonylation of alkynes using CO as C1 source}, journal = {Catalysis Science \& Technology}, volume = {13}, year = {2023}, month = {OCT }, pages = {5549-5555}, type = {Article}, abstract = {

Though precious and rare, late-transition metals have been extensively used in metal-catalysed carbonylation reactions in organic transformations. On the other hand, base metals are abundant and cheap, but their practical utilization in carbonylation reactions is rarely explored. Here, we report iron-catalysed hydroalkoxycarbonylation of alkynes to alpha,beta-unsaturated esters in one pot. A readily available iron precursor [Fe2(CO)9] in the presence of a diimine ligand L7 catalyzes the conversion of alkynes to alpha,beta-unsaturated esters under 10 bar CO pressure. This operationally simple protocol tolerates various functional groups and allows facile access to about 40 alpha,beta-unsaturated esters. The synthetic utility of the reaction has been demonstrated by scaling up the reaction to 1 g and by preparing sunscreen/antifungal agents. The kinetic study suggests that the reaction is an approximate 1st order with respect to the iron catalyst, and the initial rate of the reaction is 3.6 x 10-2 M h-1. Mechanistic investigations using NMR spectroscopy indicated the existence of an [Fe-H] intermediate, and control experiments using a radical trapping reagent and EPR revealed the absence of any radical species in the reaction. Precious and rare, late transition metals have been extensively used in carbonylation. An earth abundant iron-catalyst is reported here for hydroalkoxycarbonylation of alkynes in the presence of CO as C1 source.

}, issn = {2044-4753}, doi = {10.1039/d3cy00843f}, author = {Tewari, Tanuja and Kumar, Rohit and Chikkali, Samir H.} } @article {48311, title = {Iron-catalyzed magnesium-mediated formal hydroformylation of alkynes and alkenes}, journal = {ChemCatChem}, volume = {15}, year = {2023}, month = {FEB }, type = {Article}, abstract = {

Alkynes and alkenes are routinely converted to corresponding synthetically versatile aldehydes using rhodium-catalyzed hydroformylation. However, rhodium is rare, precious, costly, and depleting at a considerably high rate. Reported here is iron-catalyzed, magnesium-mediated, formal hydroformylation of alkynes and alkenes in the absence of syngas. Readily available FeCl2 in the presence of alkyl magnesium halide, and dimethyl formamide, catalyzes hydroformylation of various alkynes and selectively produces alpha,beta-unsaturated aldehydes in good to excellent conversion. Mechanistic investigations revealed the presence of vinyl magnesium intermediate, the kinetic study disclosed the first-order dependence of the reaction on iron loading, and the control experiment authenticated the iron catalyst{\textquoteright}s homogeneous nature. The scope of this methodology was amplified, and 20 alkenes were examined. [Fe(acac)(3)] in the presence of ligand, alkyl magnesium halide, and dimethyl formamide catalyzed the hydroformylation of alkenes and displayed good to excellent conversion. An earth-abundant iron catalyst offering a syngas cylinder-free safe alternative to high-pressure hydroformylation has been reported.

}, keywords = {aldehydes, alkenes, Alkynes, Hydroformylation, iron catalysis}, issn = {1867-3880}, doi = {10.1002/cctc.202201394}, author = {Tewari, Tanuja and Kumar, Rohit and Chikkali, Samir H.} }