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The presence of an aromatic additive has been seen to enhance, often significantly, the enantioselectivity and yield in asymmetric organocatalysis. Considering their success across a dizzying range of organocatalysts and organic transformations, it would seem unlikely that a common principle exists for their functioning. However, the current investigations with DFT suggest a general principle: the phenolic additive sandwiches itself, through hydrogen bonding and π⋅⋅⋅π stacking, between the organocatalyst coordinated electrophile and nucleophile. This is seen for a wide range of experimentally reported systems. That such complex formation leads to enhanced stereoselectivity is then demonstrated for two cases: the cinchona alkaloid complex (BzCPD), catalysing thiocyanation (2‐naphthol additive employed), as well as for L‐pipecolicacid catalysing the asymmetric nitroaldol reaction with a range of nitro‐substituted phenol additives. These findings, indicating that dual catalysis takes place when phenolic additives are employed, are likely to have a significant impact on the field of asymmetric organocatalysis. [ABSTRACT FROM AUTHOR]

The great success of asymmetric organocatalysis has made it one of the most important advancements made in chemistry in the past two decades. A significant achievement in this context is the asymmetric organocatalysis of the thiocyanation reaction. In the current study, computational studies with density functional theory have been done in order to understand an interesting experimental finding: the reversal of enantioselectivity from R to S when the electrophile is changed from β‐keto ester to oxindole for the thiocyanation reaction with the cinchona alkaloid complex catalyst. The calculations reveal an unusual fact – the principal reason for the reversal is the presence of the C−H⋅⋅⋅S noncovalent interaction, which is present only in the major transition states in each of the two nucleophile cases. Only recently has it been realized that the supposedly weak C−H⋅⋅⋅S noncovalent interaction has the properties of a hydrogen bond, and the fact that this interaction is the cause of enantioselectivity has relevance, because of the large number of asymmetric transformations involving the sulphur heteroatom. [ABSTRACT FROM AUTHOR]

The single-site activation of strong σ bonds (such as that of H−H, P−H, and N−H) remains a significant challenge in main-group chemistry, with only a few cases reported to date. In this regard, recent exciting experiments performed with aluminumI complexes hold significance because they have been seen to activate a variety of strong σ bonds. Such chemistry is generally seen to occur in aromatic solvents. Current computational studies with DFT reveal the interesting reason for this: an explicit aromatic solvent molecule acts as a catalyst by converting the aluminumI complex into aluminumIII during the process. Different cases of σ-bond activation by aluminumI complexes have been investigated and the efficiency of H−X (X=H, NH tBu, PPh2) bond activation in the presence of an explicit benzene solvent molecule is orders of magnitude higher than that in its absence. The current work therefore reveals the chemistry of aluminumI complexes to be richer and more complex than that previously realized, and shows it to be dependent on metal-solvent cooperativity; the first known example of its kind in main-group chemistry. [ABSTRACT FROM AUTHOR]

The field of frustrated Lewis pair (FLP) chemistry has seen rapid development in only a few years. FLPs have performed most spectacularly in hydrogenation catalysis: a wide variety of FLP-based systems can catalyze the hydrogenation of a range of different substrates, including imines, enamines, ketones, alkynes, and alkenes. However, FLP-based hydrogenation catalysts are yet to match the efficiency of their transition-metal counterparts. The current investigation reveals an important aspect of FLPs that can be exploited to improve their efficiency, that is, the more sterically hindered the FLP catalyst is, the lower is its turnover frequency. Full quantum chemical calculations with DFT for a family of different, experimentally known hydrogenation FLP catalysts shows that superior FLP catalysts can be designed by reducing the frustration (by reducing the steric demand and acid/base strength) in the FLP. However, as lowering the steric demand without reduction in the frustration can result in unwanted side reactions, the design of the most efficient FLP catalysts depends on tuning the system so that both the steric demand and the frustration are reduced appropriately. [ABSTRACT FROM AUTHOR]

A new mechanism has been proposed for the hydroboration of aldehydes by germylene and stannylene complexes, with the aid of the hydroborating agent, pinacolborane (HBpin). This new mechanism is demonstrated with computational studies with density functional theory (DFT), not only for existing systems, but also for newly designed germylene and stannylene systems. [Display omitted] The chemistry of low valent main group compounds has grown as an alternative to the chemistry of less abundant and less green transition metal complexes. It has been found that low valent compounds such as carbenes, silylenes, stannylenes and germylenes are efficient for activating small molecules and for catalysis. However, the reaction mechanism and the factors that affect the rate of reaction are not completely understood. In this computational investigation with density functional theory (DFT), we investigate and demonstrate the efficiency of a new mechanism for the hydroboration of aldehydes by germylenes and stannylenes, in the presence of the common hydroborating agent, pinacolborane, HBpin. This mechanism involves an HBpin molecule as an additional catalyst that cooperates with the germylene or stannylene catalyst to efficiently carry out the hydroboration. This mechanism is first demonstrated to work for experimentally reported systems, and then shown to be efficient for newly proposed germylene and stannylene systems. These new systems are α-Borylamido-germylene ((2,6- i Pr 2 C 6 H 3 NBCy 2) 2 Ge(II)) and α-Borylamido-stannylene((2,6- i Pr 2 C 6 H 3 NBCy 2) 2 Sn(II)). These new insights will help researchers look into low valent germylene and stannylene chemistry from a new perspective. [ABSTRACT FROM AUTHOR]

Carbon–carbon coupling in CO molecules is a challenging proposition, and very few main group complexes have been shown to effect this process. A recently reported triply bonded diboryne system (1) is notable for coupling four CO molecules to produce a (bis)boralactone species. The current full quantum chemical computational investigation with density functional theory (DFT) provides important insights into the nature of the CO coupling process by triply bonded diboryne systems. The complete reaction pathway leading to the formation of the (bis)boralactone has been determined. Factors that make this system so successful in coupling CO groups have been elucidated, and pertinent issues, such as why the coupling process stops after four CO additions, have been explored. Also, importantly, insights have been gained through the natural bond orbital (NBO) analysis into how the back-donation from diboryne activates CO. [ABSTRACT FROM AUTHOR]

The protolytic cleavage of the O–H bond in water and alcohols is a very important reaction, and an important method for producing dihydrogen. Full quantum chemical studies with density functional theory (DFT) reveal that germanium based complexes, such as HC{CMeArB}2GeH (Ar = 2,6-iPr2C6H3), with the assistance of silicon based compounds such as SiF3H, can perform significantly better than the existing state-of-the-art post-transition metal based systems for catalyzing dihydrogen generation from water and alcohols through the protolysis reaction. [ABSTRACT FROM AUTHOR]

An exciting new development in main group chemistry has been the use of a constrained, "flat", phosphorus-based complex to mediate in reactions such as the dehydrogenation of ammonia borane (AB), and the activation of the N-H bond in primary amines. Its importance is based on the fact that it shows that main group compounds, when properly designed, can be as effective as transition metal complexes for doing significant chemical transformations. What the current computational study, employing density functional theory (DFT), reveals is that a common, general mechanism exists that accounts for the behavior of the flat phosphorus compound in the different reactions that have been experimentally reported to date. This mechanism, which involves the mediation by a base as a proton transfer agent, is simpler and energetically more favorable than the previous mechanisms that have been proposed for the same reactions in the literature. It is likely that the knowledge gained from the current work about the chemical behavior of this phosphorus compound can be utilized to design new constrained phosphorus-based compounds. [ABSTRACT FROM AUTHOR]

The combination of 6-SIDipp·AlH3 (1) and 5-IDipp resulted in the ring expansion of 6-NHC, while the five-membered NHC remained unchanged, which was subsequently explained by DFT studies. Besides, the substitution chemistry of 1 was also studied with TMSOTf and I2, which gave rise to the substitution of a hydride by triflate or iodide ligands. [ABSTRACT FROM AUTHOR]

There is considerable interest presently in the chemistry of allenes. The current computational investigation looks into the possibility of using allenes and their derivatives as leaving groups. As it is well known, leaving groups are significant in catalytic processes for generating the active site. A full quantum mechanical study using density functional theory shows that allenes and their derivatives can function as excellent leaving groups. Indeed, the calculations show that they can be several orders of magnitude more effective than existing ligands for this purpose. The modification of second generation Grubbs' catalysts with these ligands suggests that the allene ligand cases that would be most effective are those having electron withdrawing groups, especially those that have the potential for supramolecular interactions between the substituent groups in the free state. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Full quantum chemical calculations with density functional theory (DFT) show that bond-strengthening back-donation to a π-diborene, recently discovered for transition metal systems (Braunschweig and co-workers, Nat. Chem., 2013, 5, 115-121), would be just as favored for Main Group silylene complexes. This result not only shows the range and applicability of the bond-strengthening back-bonding interaction, but also showcases the capacity of silylene complexes to do new chemistry, such as the cooperative activation of carbon monoxide and carbon dioxide. [ABSTRACT FROM AUTHOR]

Recently synthesized acyclic silylenes have the potential to rival transition metal complexes in performing single site small molecule activation, which is significant because of the need to find cheap and green alternatives to transition metal complexes for this important class of reactions. However, the current computational study, a full quantum chemical investigation with density functional theory, demonstrates that undesired side reactions would be competitive in these systems during small molecule activation. The current investigation, in addition to shedding light on this problem, also provides solutions on how the undesired side reactions during small molecule activation can be avoided. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT)/Becke-Lee-Yang-Parr (B3LYP) and gauge-including atomic orbital (GIAO) calculations were performed on a number of 1,2,4-triazole derivatives, and the optimized structural parameters were employed to ascertain the nature of their predominant tautomers. 13C and 15N NMR chemical shifts of 3-substituted 1,2,4-triazole-5-thiones and their propargylated derivatives were calculated via GIAO/DFT approach at the B3LYP level of theory with geometry optimization using a 6-311++G** basis set. A good agreement between theoretical and experimental 13C and 15N NMR chemical shifts could be found for the systems investigated. The data generated were useful in predicting 15N chemical shifts of all the nitrogen atoms of the triazole ring, some of which could not be obtained in solution state 15N HMBC/HSQC NMR measurements. The energy profile computed for the dipropargylated derivatives was found to follow the product distribution profile of regioisomers formed during propargylation of 1,2,4-triazole thiones. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

There has been considerable interest in recent times to develop transition metal complex systems that can demonstrate metal–ligand cooperativity. It has recently been shown (Wass et al., J. Am. Chem. Soc., 2011, 133, 18463) that early transition metals can cooperate with ligands carrying phosphines as pendant groups, working as metal analogues to frustrated Lewis pairs (FLPs) to mediate in a variety of important reactions. What the current work attempts to do is to show how this concept of metal containing FLPs can be expanded to include late transition metal complexes as well: complexes that have been modified from existing systems that serve as efficient catalysts for homogeneous polymerization. A modified palladium complex has been considered in this regard as an example of a potential late transition metal FLP and studied with full quantum mechanical calculations. The calculations indicate that this complex would be effective at catalyzing ammonia borane dehydrogenation. The possibility of competing side reactions such as reductive elimination have also been considered, and it has been found that such processes would also yield stable products which could act as an FLP in catalyzing reactions such as the dehydrogenation of ammonia borane. The current work therefore expands the scope of metal containing FLPs to include late transition metals and demonstrates computationally the potential of such complexes for exhibiting metal–ligand cooperativity. [ABSTRACT FROM AUTHOR]

Several approaches have been investigated in recent years in the area of small molecule activation. The current work introduces a new concept in this field: that of molecular cages, containing only main group elements, serving to activate small molecules. Full quantum mechanical calculations employing DFT/SCS-MP2 methods indicate that recently synthesized Ga--N cage compounds would be excellent candidates for mediating in important reactions such as the catalysis of ammonia borane dehydrogenation. The current work therefore opens up exciting new possibilities in small molecule activation research. [ABSTRACT FROM AUTHOR]

Methods based on the stochastic formulation of chemical kinetics have the potential to accurately reproduce the dynamical behavior of various biochemical systems of interest. However, the computational expense makes them impractical for the study of real systems. Attempts to render these methods practical have led to the development of accelerated methods, where the reaction numbers are modeled by Poisson random numbers. However, for certain systems, such methods give rise to physically unrealistic negative numbers for species populations. The methods which make use of binomial variables, in place of Poisson random numbers, have since become popular, and have been partially successful in addressing this problem. In this manuscript, the development of two new computational methods, based on the representative reaction approach (RRA), has been discussed. The new methods endeavor to solve the problem of negative numbers, by making use of tools like the stochastic simulation algorithm and the binomial method, in conjunction with the RRA. It is found that these newly developed methods perform better than other binomial methods used for stochastic simulations, in resolving the problem of negative populations. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Xanthates of 1,3-benzylidene acetal derivatives of myo- and neo-inositols undergo dideoxygenation under Barton-McCombie conditions, as a result of intramolecular abstraction of the benzylidene acetal hydrogen and subsequent cleavage of the acetal ring. Scrutiny of structure of these bicyclic inositol derivatives shows that although the conformation of the two rings can vary depending on the configuration of the inositol ring and the phase in which the molecules are present, both the xanthates lead to the formation of the same dideoxyinositol. DFT calculations on these molecular systems suggest that neo-inositol derivatives undergo conformational change prior to radical formation while myo-inositol derivatives undergo conformational change subsequent to radical formation, during the deoxygenation reaction. A low barrier for intramolecular hydrogen transfer supports the extreme facility of this deoxygenation reaction. [Copyright &y& Elsevier]

We have developed two new approximate methods for stochastically simulating chemical systems. The methods are based on the idea of representing all the reactions in the chemical system by a single reaction, i.e., by the 'representative reaction approach' (RRA). Discussed in the article are the concepts underlying the new methods along with flowchart with all the steps required for their implementation. It is shown that the two RRA methods {with the reaction $ 2A \rightarrow B $ as the representative reaction (RR)} perform creditably with regard to accuracy and computational efficiency, in comparison to the exact stochastic simulation algorithm (SSA) developed by Gillespie and are able to successfully reproduce at least the first two moments of the probability distribution of each species in the systems studied. As such, the RRA methods represent a promising new approach for stochastically simulating chemical systems. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2012 [ABSTRACT FROM AUTHOR]

Abstract: Cp2Zr(CH3)R and its derivatives can serve as powerful olefin polymerization catalysts after activation by a Lewis acid A to form the ion-pair [Cp2ZrR]+[CH3A]– (I) which is held together by a Zr-μ-CH3A– bridge. It is generally assumed that the cation Cp2ZrR+ (II) of I is the active species whereas the influence of the anion CH3A– (III) is less well understood. We have conducted an extensive study based on density functional theory (DFT) of ethylene polymerization catalyzed by both I and II in order to probe the influence of the anion CH3A– for the case where A=B(C6F5)3. The reaction between ethylene and the cation II leads in the first place to a π−complex in a highly exothermic and exogonic reaction without any (uptake) barrier. Even the subsequent insertion process has a transition state that is lower in energy than II and C2H4 at full separation. The only (internal) barrier is the modest energy required to proceed from the π-complex to the insertion transition state. For the reaction between the ion-pair and ethylene the monomer can approach cis or trans to the Zr-μ-CH3A– bridge. In addition with R = Pr, cis and trans approaches are possible for 4 different orientations of the propyl chain. We find for all of these approaches that the rate determining step is the (partial) displacement of the anion CH3A–. For the first insertion (R=Me) the total insertion barrier is 13.0 kcal/mol for the most favorable (trans) approach. The second (R=Pr) insertion (which likely also is a good model for subsequent propagation steps) prefer a cis-approach in which the ethylene uptake barrier of 9.5 kcal/mol is rate determining whereas the barrier for the subsequent insertion process only is 6.8 kcal/mol. Displacement of the anion was found to be more pronounced for R=Pr than R=Me and larger for the insertion transition state than the uptake transition state. Solvation effects were seen to stabilize anion displacement and thus reduce especially insertion barriers. Thus for the favored cis-path of the second propagation, the insertion was the rate determining step in the gas-phase with a barrier of 10.0 kcal/mol whereas the corresponding uptake process became the rate determining step in solution with a barrier of 8.6 kcal/mol. After the insertion, the ion-pair was found to recombine completely so that ethylene will have to displace the anion in the next propagation step. Considerations were also given to the chain termination step by transfer of hydrogen to the monomer. Here the rate determining step is again cis-uptake off ethylene with a barrier of 12.5 kcal/mol whereas the subsequent hydrogen transfer barrier only is 10.6 kcal/mol. To cite this article: T. Ziegler, C. R. Chimie 8 (2005) . [Copyright &y& Elsevier]

Calculations have been carried out to investigate the insertion of the ethylene monomer into the Ti–alkyl bond for the systems CpNC(t-Bu)2RTi-µ-Me-B(C6F5)3 (R = Me and Pr), using density functional theory. A validated QM/MM model was used to represent the counterion. The tertiary butyl groups in the ligands were modeled with QM/MM, with hydrogens being used as the capping atoms. Solvent effects were incorporated with single point solvent calculations done with cyclohexane (epsilon= 2.023) as the solvent. With R = Me (the initiation step), approach of the ethylene cis and trans to the -µ-Me bridge was considered. Insertion was found to be endothermic, with ΔHtot being 12.7 kcal/mol (cis) and 15.5 kcal/mol (trans). The propagation step was then studied for the contact ion pair CpNC(t-Bu)2PrTi-µ-Me-B(C6F5)3 (4). Different conformations of the propyl chain in 4 were considered by altering theta, the dihedral angle formed between the Cβ-Cα-Ti and the Cα-Ti-µC planes. The resting states were found to be at theta = –69° (4a), 177° (4b), and 53° (4c). A maxima was found near theta = 0° (4d). The cis and trans approaches of the ethylene monomer were considered for each of the four cases. The cis approach towards 4a and trans approach towards 4d led to insertion, with displacement of the counterion from the metal centre. The insertion barriers were found to be 17.8 kcal/mol, for the cis approach towards 4b and 16.4 kcal/mol for the trans approach towards 4d. The cis approaches towards conformers 4a and 4c showed common characteristics, with uptake barriers being higher than the subsequent insertion barriers in the two cases. Uptake barriers were 13.6 kcal/mol {TS(4a–7a)} and 10.7 kcal/mol {TS(4c–8a)}. The corresponding insertion barriers were 11.8 kcal/mol {TS(7a–13a)} and 8.4 kcal/mol {TS(8a–13a)}. The trans approaches towards conformers 4a and 4c led to insertion barriers of about 15.1 kcal/mol (lower than for the 4b and 4d cases). The cis approach towards 4d and trans approach towards 4b were found to lead to hydrogen transfer from the propyl chain to monomer, terminating the chain. Termination barriers were high — greater than 19.0 kcal/mol. This suggested that ethylene insertion would be favoured over termination during the propagation step. [ABSTRACT FROM AUTHOR]

A series of 21 sulfoester and sulfonamide derivatives comprising two aromatic rings was synthesized to investigate the effect of the presence of either electron-donating (ED) or electron-withdrawing (EW) groups on the intramolecular π-stacking assembly. The positioning of ED or EW moieties was carried out directly on one of the aromatic rings linked to the sulfonyl or sulfonamide moieties. In contrast, the other aromatic ring (phenyl or pyridine) was connected by a –CH2–CH2– spacer with the sulfonyl or sulfonamide moiety. The purpose of having an ethyl spacer between the two aromatic rings was to achieve conformational flexibility, facilitating the intramolecular π-stacking assembly between the two aromatic rings. The use of sulfoester/sulfonamide groups allowed more conformational flexibility to attain desired orientations in solids with the interplay of the hydrogen-bonding interactions. Between the two functional groups, sulfonamides offered a more hydrogen-rich environment due to the amine moiety and may exhibit higher H-bonding propensity than the sulfoester moiety. The central idea here was to study the interplay between the hydrogen-bonding and π⋯π interactions. The substituent groups chosen were categorized as strong electron-withdrawing (–CF3 and –CN), weak electron-withdrawing (–Cl and –Br), neutral (–H), and good electron-donating (–CH3 and –OCH3) groups. Crystal structure analysis revealed the syn conformation for all the derivatives, enabling intramolecular π⋯π interactions between the two aromatic rings, whereas in the sulfonamide derivatives, the molecule takes either midway or anti conformations, except for one pyridine sulfonamide derivative, which showed the syn orientation but lacked intramolecular π-stacking interactions. The absence of any conventional H-bond forming functional groups in the sulfoester derivatives may have resulted in the syn geometry facilitated by intramolecular π-stacking interactions. Conversely, H-bond-forming functional groups in the sulfonamide derivatives could have prevented the syn conformation. The conformational analysis carried out employing density functional theory (DFT) calculations confirmed the higher stability of the syn conformation over the midway and anti orientations. [ABSTRACT FROM AUTHOR]

Full DFT based quantum mechanical studies reveal that zero dimensional porous structures, especially the newly proposed phosphorus incorporated organic cages, can be excellent catalysts for the dehydrogenation of ammonia borane. [ABSTRACT FROM AUTHOR]

The reaction of a nickel(II) chloride complex containing a tridentate β‐diketiminato ligand with a picolyl group [2,6‐iPr2‐C6H3NC(Me)CHC(Me)NH(CH2py)]Ni(II)Cl (1)] with KSi(SiMe3)3 conveniently afforded a nickel(I) radical with a T‐shaped geometry (2). The compound's metalloradical nature was confirmed through electron paramagnetic resonance (EPR) studies and its reaction with TEMPO, resulting in the formation of a highly unusual three‐membered nickeloxaziridine complex (3). When reacted with disulfide and diselenide, the S−S and Se−Se bonds were cleaved, and a coupled product was formed through carbon atom of the pyridine‐imine group. The nickel(I) radical activates dihydrogen at room temperature and atmospheric pressure to give the monomeric nickel hydride. [ABSTRACT FROM AUTHOR]

Disilenes with differently coordinated silicon atoms are not known. Here, we have shown the high yield synthesis of a range of disilenes (2–4 and 6) upon reaction of a hypersilyl silylene PhC(NtBu)2SiSi(SiMe3)3 (1) with aliphatic chlorophosphines. The most striking characteristic of these disilenes is the presence of two differently coordinated Si atoms (one is three‐coordinated, the other four‐coordinated). The analogous reaction with Ph2PCl did not afford the desired disilene, but, surprisingly, led to the first tetraphosphinosilane (8). DFT calculations were performed to understand the bonding in disilenes and differences in reactivity of the complexes. [ABSTRACT FROM AUTHOR]

Disilenes with differently coordinated silicon atoms are not known. Here, we have shown the high yield synthesis of a range of disilenes (2–4 and 6) upon reaction of a hypersilyl silylene PhC(NtBu)2SiSi(SiMe3)3 (1) with aliphatic chlorophosphines. The most striking characteristic of these disilenes is the presence of two differently coordinated Si atoms (one is three‐coordinated, the other four‐coordinated). The analogous reaction with Ph2PCl did not afford the desired disilene, but, surprisingly, led to the first tetraphosphinosilane (8). DFT calculations were performed to understand the bonding in disilenes and differences in reactivity of the complexes. [ABSTRACT FROM AUTHOR]

Squaraine dyes possess sharp far‐red active transition with high extinction coefficient and form aggregates on TiO2 surface. Aggregation of dyes on TiO2 has been considered as a detrimental factor for DSSC device performance, which can be controlled by appending alkyl groups to the dye structures. Hence by integrating alkylated (alkyl groups with both in‐plane and out‐of‐plane) aryl group with indoline moiety to make it compatible with other electrolytes and for controlling the dye‐aggregation, a series of squaraine acceptor‐based dyes SQA4‐6 have been designed and synthesized. SQA4‐6 dyes showed absorption between 642 and 653 nm (λmax), photophysical and electrochemical studies indicated that the HOMO energy levels of this sets of dyes are well aligned with the potentials of I−/I3−$$ {\mathrm{I}}_3^{-} $$ and [Co(bpy)3]2+/3+ redox shuttles for better dye regeneration process. DSSC device efficiency of 3% has been achieved for SQA5 dye with iodolyte (I−/I3−$$ {\mathrm{I}}_3^{-} $$) electrolyte in the presence of 0.3 mM of chenodeoxycholic acid (CDCA). The IPCE profile of DSSC device fabricated with SQA4‐6 dyes indicated the contribution of aggregated structures for the photocurrent generation. [ABSTRACT FROM AUTHOR]

In the last decade, magnesium complexes have emerged as a viable alternative to transition‐metal catalysts for the hydrofunctionalization of unsaturated bonds. However, their potential for advanced catalytic reactions has not been thoroughly investigated. To address this gap, we have developed a novel magnesium amide compound (3) using a PNP framework that is both bulky and flexible. Our research demonstrates that compound 3 can effectively catalyze the synthesis of biologically significant oxazolidinone derivatives. This synthesis involves a tandem reaction of hydroalkoxylation and cyclohydroamination of isocyanate using propargyl alcohol. Furthermore, we conducted comprehensive theoretical calculations to gain insights into the reaction mechanism. It is important to note that these types of transformations have not been reported for magnesium and would significantly enhance the catalytic portfolio of the 7th most abundant element. [ABSTRACT FROM AUTHOR]

Treatment of trans-[Ir(H)(N)2(iPr)4(POCOP)(DMAP)][BAr4f] (2) with H2 (1 bar) under ambient conditions (298 K) results in the formation of a trans-[Ir(H)(η2-H2)(iPr)4(POCOP)(DMAP)][BAr4f] (3) complex. Complex 3 exhibits H-atom site exchange between the bound H2 and the hydride ligands which are mutually trans to one another. A plausible mechanism of this exchange involves metal–ligand cooperativity as studied by computations. [ABSTRACT FROM AUTHOR]

A 12‐membered zwitterionic tetrastanna(II) cycle 1 having a crown ether‐like topology has been isolated from the deprotonation of 1,1′‐methylenediimidazole (B) with two equivalents of Sn[N(SiMe3)2]2 (A). The solid‐state structure and NMR analysis confirms the tetrastanna(II) cycle 1 to be comprised of two stannate(II) and two stannyliumylidene ion pairs in alternating positions of the heterocycle. Computational analysis shows greater nucleophilicity at the proximally located stannate(II) centers. Nonetheless, the tetrastanna(II) cycle 1 remains poorly reactive due to engagement of SnII lone pair electrons in intramolecular donor‐acceptor interactions. Simple deprotonation reaction between Sn[N(SiMe3)2]2 (A) and N‐(diisopropylphenyl)imidazole (C) in equimolar ratio has led to a stannylene 2, involving the formation of a Sn−C covalent bond with the anionic imidazol‐2‐yl carbon center along with the release of NH(SiMe3)2. Compound 2 exists as a dimer, where the unsubstituted ring nitrogen atom coordinated intermolecularly to the other stannylene center. [ABSTRACT FROM AUTHOR]

In this work, 5‐SIDipp [SIDipp=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene] (1) derived Chichibabin's hydrocarbon with an octafluorobiphenylene spacer (3) has been reported. The addition of two equivalents of 5‐SIDipp with decafluorobiphenyl in presence of BF3 gives the double C−F bond activated imidazolium salt with two tetrafluoroborate anions, 2. Further reduction of 2 gives the fluorine substituted 5‐SIDipp based Chichibabin's hydrocarbon, 3. Quantum chemical calculations suggested a singlet state of 3 with a singlet–triplet energy gap (ΔES‐T) of 3.7 kcal mol−1, which is substantially lower with respect to the hydrogen substituted NHC‐based Chichibabin's hydrocarbons (10.7 kcal mol−1, B3LYP). As a result, the diradical character (y) of 3 (y=0.62) is also noticeably higher than the hydrogen substituted CHs (y=0.41–0.43). The ▵ES‐T was found to be higher in CASSCF (22.24 kcal mol−1) and CASPT2 (11.17 kcal mol−1) for 3 and the diradical character (d) is 44.6 %. [ABSTRACT FROM AUTHOR]

The addition of HBpin to PhC(NtBu)2SiN(SiMe3)2 (1) results in the cleavage of the B–H bond in a cooperative fashion across the Si and amidinate-C sites. The reaction of 1 with benzaldehyde led to C–H bond activation with amidinate ring expansion leading to a five-membered heterocycle. In case of 4-fluorobenzaldehyde, a C–C bond coupling takes place leading to a dioxasilolane derivative as the major product. [ABSTRACT FROM AUTHOR]

This paper describes the rare use of a 6‐membered saturated N‐heterocyclic carbene (NHC) known as 1,3‐di(2,6‐diisopropylphenyl) tetrahydropyrimidine‐2‐ylidene (abbreviated as 6‐SIDipp) as a ligand in zinc chemistry. We report on the investigation of the reactions between 6‐SIDipp and ZnX2, which resulted in a range of new monomeric 6‐SIDipp⋅ZnX2 complexes (X=Et (1), Cl (2), Br (3), and I (4)). We also prepared a new NHC zinc complex where the two substituents of the zinc atom are different, 6‐SIDipp⋅Zn(Et)Br (7) through the reaction of the proligand [6‐SIDippH]Br with ZnEt2. We have observed that the reactions of complex 1 with sulfur and HBpin led to the removal of the ZnEt2 moiety, resulting in the formation of a C=S double bond and a B−H activation product, respectively. Lastly, the reaction of 1 with five‐membered NHCs led to the exchange of carbene and the formation of either 5‐IDipp⋅ZnEt2 (8) or 5‐SIDipp⋅ZnEt2 (9). [ABSTRACT FROM AUTHOR]

Rivaroxaban (RXB) is a direct factor Xa inhibitor used for the treatment of deep vein thrombosis (DVT, a blood clot in the leg) and pulmonary embolism (PE, a blood clot in the lung) and to prevent blood clots in atrial fibrillation following hip or knee surgery. However, RXB suffers from poor solubility that hinders its broader application. Although its cocrystals are reported for solubility enhancement, the methodology used to prepare multi-component crystals is complex. Also, it uses hazardous solvents to develop cocrystals. We have prepared eutectics of RXB with caffeic acid (CAA), coumaric acid (CA), fumaric acid (FA), succinic acid (SA), mandelic acid (MA) and trimesic acid (TA) and analyzed them using hot stage microscopy (HSM), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and fourier transform infrared spectroscopy (FTIR) techniques. The saturation solubility and dissolution rate profiles were also obtained to investigate the effect of eutectics on these parameters. Amongst all the coformers tested, coformers CAA, CA, and FA showed significant enhancement in the solubility of RXB. The powder dissolution rate of the eutectics showed considerable enhancement compared to that of RXB. In vivo pharmacokinetic study was carried out for RXB–CAA, RXB–CA and RXB–FA in rats and compared with RXB, which showed 1.5 and 1.4 times enhancement in relative bioavailability for RXB–CAA and RXB–CA, respectively. Stability studies were carried out as per ICH guidelines for all the eutectics, which revealed excellent stability over six months under accelerated (40 °C and 75%) conditions and twelve months under long-term (30 °C and 60% RH) conditions. The DFT studies carried out using the B3LYP/TZVP level of theory revealed higher Gibbs free interaction energy (ΔGint) for homosynthons (drug⋯drug and coformer⋯coformer) than heterosynthons (drug⋯coformer). [ABSTRACT FROM AUTHOR]

A series of alkyl‐group‐functionalized, aniline‐ and indoline‐donor‐based, unsymmetrical visible‐light‐active squaraine dyes, AM1‐3, were designed and synthesized. Dye‐sensitized solar cell (DSSC) devices were fabricated with both I−/I3− and [Cu(tmby)2]+/2+ electrolytes. DSSC devices sensitized with the AM1 and AM2 dyes showed relatively high‐power conversion efficiency of 7.44 % and 7.22 %, respectively with I−/I3− in the absence of chenodeoxycholic acid (CDCA) than those of the AM3 dye (5.41 %). The [Cu(tmby)2]+/2+ electrolyte along with poly(3,4‐ethylenedioxythiophene) (PEDOT) as cathode material showed excellent open‐circuit potentials (VOC) of 1030, 1025, and 1001 mV with the DSSC efficiency of 8.05 %, 7.96 %, and 5.84 %, respectively, for the AM1, AM2, and AM3 dyes in the absence of CDCA. Here, the AM1 dye exhibited the maximum DSSC efficiency of 8.05 % and VOC of 1030 mV, which is the highest obtained efficiency and VOC for the visible‐light active zwitterionic unsymmetrical‐squaraine dye with copper‐based electrolyte. [ABSTRACT FROM AUTHOR]

Compared to H 2 SO 4 , Brønsted acidic ionic liquid (BAIL, [C 3 SO 3 HMIM][HSO 4 ]) catalyzed depolymerization of lignin yielded higher concentration of low molecular weight products under mild conditions (120 °C) as proven by GC and GC–MS. To comprehend this disparity in catalytic activity among H 2 SO 4 and BAIL (at similar H + concentration), experimental techniques [1D( 1 H) NMR, 2D( 15 N/ 1 H HMBC) NMR and RAMAN] have been employed. Based on these studies, it has been proven that the transfer of electron density from substrate to the electron deficient imidazolium ring via formation of hydrogen bond between O H/ O CH 3 (substrate) and N 1 C 2 H 2 N 3 − (cation) is possible, while the anion plays an important role. Further, density functional theory (DFT) calculations also corroborated this fact by showing a change in the bond angle and decrease in bond length (C 2 H 2 in imidazole), due to the presence of weak and strong hydrogen bonding between the substrate and IL. [ABSTRACT FROM AUTHOR]

Abstract: Organocalcium compounds have been reported as efficient catalysts for various transformations, for cases in which one of the substrates contained an E−H (E=B, N, Si, P) bond. Here, we look at the possibility of employing an organocalcium compound for a transformation in which none of the precursors has a polar E−H bond. This study demonstrates the utilization of a well‐defined amidinatocalcium iodide, [PhC(NiPr)2CaI] (1) for cyanosilylation of a variety of aldehydes and ketones with Me3SiCN under ambient conditions without the need of any co‐catalyst. The reaction mechanism involves a weak adduct formation between 1 and Me3SiCN leading to the activation of the Si−C bond, which subsequently undergoes σ‐bond metathesis with a C=O moiety. Such a mechanistic pathway is unprecedented in alkaline earth metal chemistry. Experimental and computational studies support the mechanism. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The reaction of PhC(NtBu)2SiSi(SiMe3)3 (1) with Me3SiCH2Cl afforded an unsymmetrical sp2–sp3 disilene, 2, with concomitant elimination of Me3SiCl. The analogous reaction with PhC(NtBu)2SiCl resulted in the oxidative addition of the C–Cl bond at the Si(II) atom (3). The reactions of 2 with sulfur and selenium led to compounds with Si＝E (E＝S (4) and Se (5)) double bonds. Tellurium reacted differently with 2 and furnished a zwitterionic compound, 6. [ABSTRACT FROM AUTHOR]

Herein, we report two 2,2′-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. [ABSTRACT FROM AUTHOR]

The NHC·borane chemistry has been majorly restricted to imidazol-2-ylidene classes of carbenes. In our previous communication, we reported the synthesis of 6-SIDipp·BH3 [6-SIDipp = 1,3-di(2,6-diisopropylphenyl) tetrahydropyrimidine-2-ylidene] and its electrophilic substitution reaction with iodine. Here, we have shown selective bromination of a 6-SIDipp stabilized sp3 B–H bond. Treatment of 1.2 equivalents of N-bromosuccinamide with 6-SIDipp·BH3 gives a mixture of mono- and disubstituted products 6-SIDipp·BH2Br (1) and 6-SIDipp·BHBr2 (2). However, the reactions with alkyl bromides or carbon tetrabromide resulted in 6-SIDipp·BH2Br (1) selectively. Exploration of the chemistry of 6-SIDipp with BHCl2 and 9-BBN (9-borabicyclo[3.3.1]nonane) led to mono-6-SIDipp adducts 3 and 6a. Furthermore, 6a undergoes ring expansion to afford a seven-membered product, 6b, under mild conditions. Unlike BHCl2 or 9-BBN, the B–H bond of HBpin undergoes oxidative addition upon reaction with 6-SIDipp, epitomizing the first example (7) of a B–H bond insertion at NHCs. The analogous reactivity with HBcat led to a tetrahydropyrimidinium salt with B(cat)2 as a counteranion (8). [ABSTRACT FROM AUTHOR]

Full quantum chemical calculations, using density functional theory (DFT), have been conducted to explain the effect of donors on the 'activation mechanism' in the Ziegler-Natta (Z-N) catalyst system. In the activation mechanism, the inactive TiIVCl4 catalyst converts into the active TiIIICl2Et catalyst with the help of the AlEt3 present in the system. The donors that have been considered in this study are: ethyl benzoate ( eb), two representative diether cases, a phthalate donor, and a silyl ester donor. The results indicate that eb and the diether donor cases donor have a negative effect on the barriers for the activation mechanism. However, the eb donor can be displaced from the MgCl2 surface by AlEt3, which matches experimental observations. For the phthalate, silyl ester and TiCl3-OC4H8Cl cases, the results indicate that a significant induction period would be present in Z-N systems employing such donors or having such a catalytic center, before catalysis could commence. [ABSTRACT FROM AUTHOR]

• Oxidative addition of dihydrogen molecule has been studied using four coordinate iridium pincer [Ir(iPr)4(POCOP)(PPh 3)] complex. • A complete isomerization of oxidatively added kinetic product, cis-[Ir(H) 2 (iPr)4(POCOP)(PPh 3)] to thermodynamically stable product, trans-[Ir(H) 2 (iPr)4(POCOP)(PPh 3)] complex was noted at 298 K. • A kinetics and mechanistic studies of cis-trans isomerization was discussed and further investigated computationally. • Protonation of trans-[Ir(H) 2 (iPr)4(POCOP)(PPh 3)] complex resulted in a novel trans-dihydrogen hydride, trans-[Ir(H)(η2–H 2)(iPr)4(POCOP)(PPh 3)]+complex at 183 K. • Cis-[Ir(H) 2 (iPr)4(POCOP)(PPh 3)] complex is found to be a catalytically active species towards the hydrogenation of ethylene at ambient conditions. Reaction of a four coordinate, 16-electron Ir complex, [Ir(iPr)4(POCOP)(PPh 3)] (4) ((iPr)4(POCOP = 2,6-bis(di-isopropyl phosphinito)benzene, κ 3-C 6 H 3 -1,3-[OP(iPr) 2 ] 2), with H 2 resulted in an oxidative addition product, cis-dihydride complex, cis-[Ir(H) 2 (iPr)4(POCOP)(PPh 3)] (cis-5) presumably via the intermediacy of a sigma complex, [Ir(η2-H 2)(iPr)4(POCOP)(PPh 3)]. The cis-dihydride complex completely isomerizes to the trans-dihydride complex trans-[Ir(H) 2 (iPr)4(POCOP)(PPh 3)] (trans-5) under ambient conditions in about 3 h. It was found that the steric and electronic features on the iridium center have significant influence on the approach of H 2 onto the metal center followed by oxidative addition and isomerization. The isomerization process was studied in detail and all the mechanistic aspects have been elucidated using a combination of both experimental work and computation. The cis-dihydride complex isomerizes to the trans-dihydride by compensating the trans influence of the strongly trans-directing hydride ligand. A mechanism involving the exchange of the position of PPh 3 with a hydride ligand cis to itself via PPh 3 dissociation and re-coordination thereby resulting in the formation of the trans-dihydride complex, has been proposed for the isomerization. The cis-dihydride was found to be a highly active catalyst for hydrogenation of ethylene. A competing reactivity study of cis-dihydride between isomerization versus insertion of C 2 H 4 into the Ir—H bond, was studied experimentally and computationally. [Display omitted] [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The catalysis of acceptorless alcohol dehydrogenation (AAD) is an important area of research. Transition metal-based systems are known to be effective catalysts for this reaction, but developing metal free catalytic systems would lead to highly desirable cheaper and greener alternatives. With this in mind, this computational study investigates design strategies than can lead to metal free frustrated Lewis pairs (FLPs) that can be employed for AAD catalysis. A careful study of 36 different proposed FLP candidates reveals that several new FLPs can be designed from existing, experimentally synthesized FLPs that can rival or be even better than state-of-the-art transition metal-based systems in catalyzing the alcohol dehydrogenation process. [ABSTRACT FROM AUTHOR]

The catalytic enantioselective hydroamination-hydroarylation of alkynes under the catalysis of (R3P)AuMe /( S)-3,3′-bis(2,4,6-triisopropylphenyl)-1,1′-binaphthyl-2,2′-diyl hydrogenphosphate (( S)-TRIP) is reported. The alkyne was reacted with a range of pyrrole-based aromatic amines to give pyrrole-embedded aza-heterocyclic scaffolds bearing a quaternary carbon center. The presence of a hydroxyl group in the alkyne tether turned out to be very crucial for obtaining products in high yields and enantioselectivities. The mechanism of enantioinduction was established by carefully performing experimental and computational studies. [ABSTRACT FROM AUTHOR]

Full quantum chemical calculations with density functional theory (DFT) show that a principal role of donors in Ziegler-Natta (ZN) olefin polymerization catalysts is to coordinate to the metal center at the active sites on the MgCl2 surface. Thereby, the behavior of the catalyst is modulated to favor insertion over termination and, thus, polymerization occurs. This is shown to be true for a range of different donors. The calculations indicate that active sites that feature anionic chloride ligands at the titanium center (the conventional model for the active site) would lead to lower-molecular-weight polymers. If an -OC2H5 group were present instead of a chloride ligand, the active site would much more effectively produce long chain polymers. Therefore, the current work provides important new insights into the nature of the ZN polymerization process. [ABSTRACT FROM AUTHOR]

The development of new donors (Lewisbases, usually containingoxygen atoms) is one of the chief areas of research in Ziegler–Natta(ZN) olefin polymerization systems. The addition of such donors hasled to improvement in the activity and selectivity of ZN systems.However, in order for the donor to be effective, it has to be chemicallystable and resistant to decomposition by Lewis acidic species suchas AlEt3. Discussed in the current work is the chemicalstability of different ester donors, including aromatic benzoate donorsand the silyl estera promising new donor class in ZN systems.Full quantum chemical calculations with density functional theory(DFT) indicate that esters can undergo decomposition through differentpathways upon interaction with species such as the AlEt3dimer: Al2Et6. Moreover, the studies showthat the active, supported titanium catalyst species can cause donordecomposition and, in fact, is likely to be the greater threat todonor decomposition than Al2Et6. This explainswhy the addition of excess donors can lead to the poisoning of theactive site in ZN systems. We have also computationally investigatedmeans of improving the silyl ester donors in order to make them morerobust and resilient to donor decomposition by Al2Et6and the supported active titanium species. [ABSTRACT FROM AUTHOR]

Herein, we have undertaken the synthesis and investigated the reactivity of a 6-membered saturated NHC borane adduct (1). Direct electrophilic halogenation of 1 with a stoichiometric amount of I2 led to NHC boryl iodides, 6-SIDipp·BH2I (2) and 6-SIDipp·BHI2 (3), which were further reacted with various nucleophiles to give novel 6-SIDipp based mono and disubstituted boranes with OTf (4 and 6) or ONO2 (5 and 7) functional groups. The addition of Br2/H2O to 1 smoothly results in a dihydroxyborenium cation (8). [ABSTRACT FROM AUTHOR]

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 O‐nucleophile versus C‐nucleophile, one pot synthesis of Senphos (L1) was achieved (72 %). When L1 was treated with [Rh], 31P 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 H2 pressure, at room temperature. The practical relevance of L1 is demonstrated by scaling‐up the reaction to 1 g and by synthesizing DOPA, a drug widely employed for the treatment of Parkinson's disease. Computational insights indicate that the R isomer is preferred by 3.8 kcal/mol over the S isomer. [ABSTRACT FROM AUTHOR]

The possibility of metal-metal cooperativity in improving the yield of the homogeneous water gas shift reaction (WGSR) has been investigated through full quantum mechanical density functional theory calculations. The calculations indicate that bimetallic catalysts would be likely to be more highly active than mononuclear metal-based catalysts for the WGSR. The results have implications for the design of improved WGSR catalysts in the future [ABSTRACT FROM AUTHOR]