F:Highly flammable;
498-66-8Relevant academic research and scientific papers
Structure and reactivity of lithium diisopropylamide solvated by polyamines: Evidence of monomer- and dimer-based dehydrohalogenations
Remenar, Julius F.,Collum, David B.
, p. 4081 - 4086 (1998)
6Li and 15N NMR spectroscopic studies show that hexane solutions of LDA containing 1.0 equiv of PMDTA per lithium, monomer is the dominant species. Addition of PMDTA to LDA in toluene affords open dimer at low [PMDTA] and a mixture of LDA monomer and benzyllithium (resulting from toluene deprotonation) at high [PMDTA]. The results are compared and contrasted with previous investigations of LDA solvated by N,N,N',N'-tetramethylethylenediamine (TMEDA) and (±)-trans- N,N,N',N'-tetramethylcyclohexanediamine (TMCDA). The reactivities of LDA solvated by TMEDA, TMCDA, and PMDTA were probed by investigating the dehydrohalogenation of (±)-2-exo-bromonorbornane. All three ligands afford qualitatively similar behavior: (1) a maximum reactivity at low ligand concentrations ascribed to monosolvated LDA dimers and (2) ligand- concentration-independent rates at high ligand concentrations ascribed to monosolvated LDA monomers. Structure and rate differences in hexane and toluene solutions are noted.
Homogeneous hydrogenation of norbornadiene with parahydrogen and phosphonic ester phosphine rhodium complexes studied by in situ NMR spectroscopy
Harthun,Woelk,Bargon,Weigt
, p. 11199 - 11206 (1995)
Homogeneous hydrogenation of norbornadiene with enriched parahydrogen (p-H2) and phosphonic ester phosphine rhodium complexes is detected using in situ NMR spectroscopy. The obtained polarization spectra remain unchanged during the catalysis of thf-d8 as a solvent but change with time when the hydrogenation is executed in acetone-d6. The observed phenomenon is attributed to a change of the phase correlation of the transferred parahydrogen nuclei via nuclear singlet-triplet (S/T0) mixing during the reaction. Simultaneously, 31P NMR spectra change indicating a change in the nature of the original rhodium complex when the hydrogenation is carried out in acetone-d6.
Chelation-based stabilization of the transition structure in a lithium diisopropylamide mediated dehydrobromination: Avoiding the 'universal ground state' assumption
Remenar, Julius F.,Collum, David B.
, p. 5573 - 5582 (1997)
Dehydrobrominations of (±)-2-exo-bromonorbornane (RBr) by lithium diisopropylamide (LDA) were investigated to determine the roles of aggregation and solvation. Elimination with LDA/n-BuOMe occurs by deaggregation of disolvated dimers via a monosolvated monomer transition structure (e.g., [i-Pr2NLi·n-BuOme·-RBr]. In contrast, elimination by LDA- THF displays THF concentration dependencies that are consistent with parallel reaction pathways involving both mono- and disolvated monomer transition structures. Elimination is markedly faster by LDA-DME than by LDA with monodentate ligands and follows a rate law consistent with a transition structure containing a chelated monomeric LDA fragment. A number of hemilabile amino ethers reveal the capacity of different coordinating functionalities to chelate. A protocol based upon kinetic methods affords the relative ligand binding energies in the LDA dimer reactants. Separating contributions of ground state from transition state stabilization allows us to attribute the stabilizing effects of chelation exclusively to the transition structure. The importance of chelating ligands in LDA-mediated dehydrobrominations, but not in previously studied reactions of LDA, sheds light on lithium ion chelation.
Reactions of Sodium Diisopropylamide: Liquid-Phase and Solid-Liquid Phase-Transfer Catalysis by N, N, N′, N″, N″-Pentamethyldiethylenetriamine
Algera, Russell F.,Collum, David B.,Ma, Yun,Woltornist, Ryan A.
supporting information, p. 13370 - 13381 (2021/09/03)
Sodium diisopropylamide (NaDA) in N,N-dimethylethylamine (DMEA) and DMEA-hydrocarbon mixtures with added N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDTA) reacts with alkyl halides, epoxides, hydrazones, arenes, alkenes, and allyl ethers. Comparisons of PMDTA with N,N,N′,N′-tetramethylethylenediamine (TMEDA) accompanied by detailed rate and computational studies reveal the importance of the trifunctionality and κ2-κ3 hemilability. Rate studies show exclusively monomer-based reactions of 2-bromooctane, cyclooctene oxide, and dimethylresorcinol. Catalysis with 10 mol % PMDTA shows up to >30-fold accelerations (kcat > 300) with no evidence of inhibition over 10 turnovers. Solid-liquid phase-transfer catalysis (SLPTC) is explored as a means to optimize the catalysis as well as explore the merits of heterogeneous reaction conditions.
Aqueous Microdroplets Capture Elusive Carbocations
Kumar, Anubhav,Mondal, Supratim,Banerjee, Shibdas
supporting information, p. 2459 - 2463 (2021/02/16)
Carbocations are short-lived reactive intermediates in many organic and biological reactions that are difficult to observe. This field sprung to life with the discovery by Olah that a superacidic solution allowed the successful capture and nuclear magnetic resonance characterization of transient carbocations. We report here that water microdroplets can directly capture the fleeting carbocation from a reaction aliquot followed by its desorption to the gas phase for mass spectrometric detection. This was accomplished by employing desorption electrospray ionization mass spectrometry to detect a variety of short-lived carbocations (average lifetime ranges from nanoseconds to picoseconds) obtained from different reactions (e.g., elimination, substitution, and oxidation). Solvent-dependent studies revealed that aqueous microdroplets outperform organic microdroplets in the capture of carbocations. We provide a mechanistic insight demonstrating the survival of the reactive carbocation in a positively charged aqueous microdroplet and its subsequent ejection to the gas phase for mass spectrometric analysis.
Iridium-Catalyzed Asymmetric Hydroalkenylation of Norbornene Derivatives
Sun, Xin,Bai, Xiao-Yan,Li, An-Zhen,Li, Bi-Jie
supporting information, p. 2182 - 2187 (2021/03/01)
Transition-metal-catalyzed asymmetric hydroalkenylation of alkenes provides an atom-economical method to build molecular complexity from easily available materials. Herein we report an iridium-catalyzed asymmetric hydroalkenylation of unconjugated alkenes with acrylamides and acrylates. The catalytic hydroalkenylation of norbornene derivatives occurred to form products with allylic stereocenters with high chemo-, regio-, and stereoselectivities. DFT calculations revealed that the migratory insertion is irreversible and the enantiodetermination step.
Understanding the roles of variable Pd(II)/Pd(0) ratio supported on conjugated poly-azobenzene network: From characteristic alteration in properties to their cooperation towards visible-light-induced selective hydrogenation
Nath, Ipsita,Chakraborty, Jeet,Zhang, Gaoke,Chen, Cheng,Chaemchuen, Somboon,Park, Jihae,Zhuiykov, Serge,Han, Taejun,Verpoort, Francis
, p. 120 - 128 (2020/04/15)
Selective hydrogenation of organic functionalities at environmentally benign conditions using visible light is of great industrial and economic significance. Herein we report visible-light-induced rapid, almost quantitative and selective hydrogenation of olefins to respective mono-reduced products using cooperative performance of Pd(0) nanoparticles (NPs) and Pd(II) ions evenly distributed on a newly synthesized conjugated mesoporous poly-azobenzene network. Role of variable Pd(0)/Pd(II) ratio on the properties of polymeric networks and their overall catalytic abilities is critically investigated. This is the first proposed example of cooperative hydrogenation by simultaneous activation of H2 and unsaturated substrates using Mott-Schottky heterojunction between Pd NPs and the semiconducting polymer, with the help of Pd(II)-site-mediated η-coordination. A control over selective mono-reduction of diene with identical double bonds was also obtained. The catalytic activity retained for other non-olefinic functionalities as well.
Simple Alkaline-Earth Metal Catalysts for Effective Alkene Hydrogenation
Bauer, Heiko,Alonso, Mercedes,Fischer, Christian,R?sch, Bastian,Elsen, Holger,Harder, Sjoerd
supporting information, p. 15177 - 15182 (2018/10/24)
Alkaline earth metal amides (AeN′′2: Ae=Ca, Sr, Ba, N′′=N(SiMe3)2) catalyze alkene hydrogenation (80–120 °C, 1–6 bar H2, 1–10 mol % cat.), with the activity increasing with metal size. Various activated C=C bonds (styrene, p-MeO-styrene, α-Me-styrene, Ph2C=CH2, trans-stilbene, cyclohexadiene, 1-Ph-cyclohexene), semi-activated C=C bonds (Me3SiCH=CH2, norbornadiene), or non-activated (isolated) C=C bonds (norbornene, 4-vinylcyclohexene, 1-hexene) could be reduced. The results show that neutral Ca or Ba catalysts are active in the challenging hydrogenation of isolated double bonds. For activated alkenes (e.g. styrene), polymerization is fully suppressed due to fast protonation of the highly reactive benzyl intermediate by N′′H (formed in the catalyst initiation). Using cyclohexadiene as the H source, the first Ae metal catalyzed H-transfer hydrogenation is reported. DFT calculations on styrene hydrogenation using CaN′′2 show that styrene oligomerization competes with styrene hydrogenation. Calculations also show that protonation of the benzylcalcium intermediate with N′′H is a low-energy escape route, thus avoiding oligomerization.
Reactions of Fluoroalkenes with an Aluminium(I) Complex
Bakewell, Clare,White, Andrew J. P.,Crimmin, Mark R.
supporting information, p. 6638 - 6642 (2018/05/05)
A series of industrially relevant fluoroalkenes react with a monomeric AlI complex. These reactions break strong sp2 and sp3 C?F bonds, and result in the formation of a diverse array of organoaluminium compounds. Mechanistic studies show that two mechanisms are likely in operation: 1) direct oxidative addition of the C?F bond to AlI occurs with retention of alkene stereochemistry, and 2) stepwise formation and decomposition of a metallocyclopropane intermediate occurs with inversion of alkene stereochemistry. As part of this mechanistic analysis, we have isolated the first aluminium metallocyclopropane complex from oxidative addition of an alkene to AlI. Remarkably this reaction is reversible and reductive elimination of the alkene occurs at higher temperature reforming AlI. Furthermore, in selected cases the organoaluminium products are susceptible toward β-fluoride elimination to yield a double C?F activation pathway.
Simple Access to the Heaviest Alkaline Earth Metal Hydride: A Strongly Reducing Hydrocarbon-Soluble Barium Hydride Cluster
Wiesinger, Michael,Maitland, Brant,F?rber, Christian,Ballmann, Gerd,Fischer, Christian,Elsen, Holger,Harder, Sjoerd
supporting information, p. 16654 - 16659 (2017/12/07)
Reaction of Ba[N(SiMe3)2]2 with PhSiH3 in toluene gave simple access to the unique Ba hydride cluster Ba7H7[N(SiMe3)2]7 that can be described as a square pyramid spanned by five Ba2+ ions with two flanking BaH[N(SiMe3)2] units. This heptanuclear cluster is well soluble in aromatic solvents, and the hydride 1H NMR signals and coupling pattern suggests that the structure is stable in solution. At 95 °C, no coalescence of hydride signals is observed but the cluster slowly decomposes to undefined barium hydride species. The complex Ba7H7[N(SiMe3)2]7 is a very strong reducing agent that already at room temperature reacts with Me3SiCH=CH2, norbornadiene, and ethylene. The highly reactive alkyl barium intermediates cannot be observed and deprotonate the (Me3Si)2N? ion, as confirmed by the crystal structure of Ba14H12[N(SiMe3)2]12[(Me3Si)(Me2SiCH2)N]4.
