Isolasi Senyawa Fenolat dari Fraksi Etil Asetat Kulit Batang Tumbuhan Gandaria

Telah dilakukan isolasi senyawa fenolat dari fraksi etil asetat kulit batang tumbuhan Gandaria (Bouea macrophylla Griff). Ekstraksi dilakukan dengan metode maserasi dan pemisahan senyawa hasil isolasi dilakukan dengan teknik kromatografi. Hasil isolasi berupa kristal berwarna putih dengan titik leleh 185-187_C. Spektrum UV dalam pelarut etil asetat menunjukkan serapan maksimum pada 289 nm, mengindikasikan adanya ikatan rangkap terkonjugasi yang lazimnya merupakan cincin aromatis. Analisa spektrum IR menunjukkan adanya gugus −OH, C−H alifatik, C=O, C=C, C−H, C−O, C=C−H. Berdasarkan data-data spektrum UV, IR, serta berdasarkan uji fitokimia diduga senyawa hasil isolasi ini merupakan senyawa golongan fenolat yang tersubtitusi gugus alifatik dan gugus karbonil

Coinage-Metal Mediated Ring Opening of <i>cis</i>-1,2-Dimethoxy­cyclo­propane: Trends from the Gold, Copper, and Silver Fischer Carbene Bond Strength

N-heterocyclic carbene (NHC) supported coinage metal cations proved to react in the gas phase with the electron-rich <i>cis</i>-1,2-dimethoxy­cyclo­propane. Upon Collision Induced Dissociation (CID), several spectrometric fragment-ion signals were observed, one corresponding to the recovery of the bare cation IMes-M⁺ (IMes = 1,3-bis­(2,4,6-trimethyl­phenyl)­imidazol-2-ylidene) and the second to the methoxy­methylidene metal complex IMes–M–[HCOCH₃]⁺. The gold and copper complexes appear to stabilize the carbene sufficiently enough to promote the latter channel. On the contrary, the silver complex binds weakly to the methoxy­methylidene moiety as observed by the predominance of the bare cation IMes–M⁺ channel. Density Functional Theory (DFT) investigations of the Potential Energy Surface and Bond Energy Decomposition Analyses provided results that correlate well with the experimental data. In the case of the bare cation channel, two distinct reaction pathways were found: a straightforward decoordination of the cyclopropane and a cationic rearrangement of the three-membered ring into a dimethoxy­propylene isomer before dissociation. However, for the abstraction of the methoxy­methylidene moiety by the metal cation, only one pathway was found. In analogy to earlier studies by other groups, we found the trend Au > Cu > Ag for the metal–carbene bond strength

A Heterobimetallic Pd–Zn Complex: Study of a d⁸–d¹⁰ Bond in Solid State, in Solution, and in Silico

A heterobimetallic Pd­(II)–Zn­(II) complex has been prepared and characterized by X-ray diffraction analysis. An accompanying computational study shows that the bimetallic complex is predominantly stabilized by a short metal–metal bond; Δ<i>G</i> for the reversible dissociation of that bond in solution could be quantified by NMR-titration experiments. A comparison of the experimental crystal structure with previously calculated structures of intermediates and transition states for transmetalation in the Negishi coupling reveals close similarity

Elementary Reactions at Organocopper(III): A Gas-Phase and Theoretical Study

The role of copper­(III) in copper-catalyzed coupling reactions is a topic of much debate in the literature, in large part due to the difficulty in isolating the typically reactive species. Advanced mass spectrometry experiments allow the isolation and interrogation of reactive species in the absence of any solvent, counterions, or competing species. Macrocyclic aryl-X-copper­(III) complexes were isolated in the gas phase and subjected to collision-induced dissociation experiments to examine their unimolecular reactivity both qualitatively and quantitatively. When X = Cl or Br, the complexes fragment solely by deprotonation of nitrogen and concomitant loss of HX. The experimentally determined energies of activation are 33.4 ± 0.9 kcal mol^–1 (X = Cl) and 35.8 ± 0.9 kcal mol^–1 (X = Br). This process is analogous to nucleophile activation at a copper­(III) center, and it is observed preferentially over C-X reductive elimination in the gas phase due to the strong ligating ability of the employed macrocyclic ligand. The measured activation energies for the observed nucleophile activation were used to test the performance of a range of popular DFT functionals for predicting reactivity at Cu^III. Most dispersion-corrected functionals reproduced the experimental results with reasonable errors (D3bj-corrected TPSSh performed best), whereas the uncorrected values tended to significantly underestimate the activation energies. When X = I, a second fragmentation pathway becomes competitive, which involves loss of I^• and reduction of copper from Cu^III to Cu^II. The relative energetics of one-electron versus two-electron processes at Cu^III are discussed

Structure and Gas-Phase Thermochemistry of a Pd/Cu Complex: Studies on a Model for Transmetalation Transition States

A heterobimetallic Pd­(II)/Cu­(I) complex was prepared and characterized by X-ray diffraction analysis. The crystal structure shows a remarkably short Pd–Cu bond and a trigonal ipso carbon atom. The Pd–Cu interaction, as determined by energy-resolved collision-induced dissociation cross-section experiments, models the net stabilizing energy of the Pd–Cu interaction in the transition state of the transmetalation step in Pd/Cu-catalyzed cross-coupling reactions. The bonding situation in the bimetallic dinuclear complex has been studied by atoms-in-molecules analysis

Trends in Metallophilic Bonding in Pd–Zn and Pd–Cu Complexes

Metallophilic interactions stabilize the bond between closed-shell metal centers, which electrostatically repel one another. Since their introduction, the origin of these interactions has been argued to be either London dispersion forces or dative bonding, but as yet, there is no definitive answer. Insight into the nature of metallophilic bonding would provide the key for rational tuning of the stabilizing interaction, for example, in specific transmetalation transition states. We now report on a computational study focused on the metallophilic d⁸–d¹⁰ bond in recently published families of Pd­(II)–Cu­(I) and Pd­(II)–Zn­(II) heterobimetallic compexes. We show that dative bonding outweighs dispersion interaction in controlling the metallophilic bonding energy in the studied heterobimetallic complexes, and elucidate the governing orbital interactions

Trends in Metallophilic Bonding in Pd–Zn and Pd–Cu Complexes

Metallophilic interactions stabilize the bond between closed-shell metal centers, which electrostatically repel one another. Since their introduction, the origin of these interactions has been argued to be either London dispersion forces or dative bonding, but as yet, there is no definitive answer. Insight into the nature of metallophilic bonding would provide the key for rational tuning of the stabilizing interaction, for example, in specific transmetalation transition states. We now report on a computational study focused on the metallophilic d⁸–d¹⁰ bond in recently published families of Pd­(II)–Cu­(I) and Pd­(II)–Zn­(II) heterobimetallic compexes. We show that dative bonding outweighs dispersion interaction in controlling the metallophilic bonding energy in the studied heterobimetallic complexes, and elucidate the governing orbital interactions

Manuscripta Medica Tom. III

Pp. 141-176 Table, with 4 columns: (from interior of page) running number, author of experiment, short description, and keywords of experiment

Experimental Gas-Phase and <i>in Silico</i> Investigation of β‑Methyl Elimination from Cationic Palladium Alkyl Species

Herein we disclose experimental and <i>in silico</i> gas-phase studies of β-methyl and β-hydride elimination from cationic diphosphine palladium­(II) neopentyl and isobutyl complexes. In particular, we have determined activation barriers for these transformations through mass-spectrometric threshold collision-induced dissociation (T-CID) studies. These systems can undergo at least one of the several competitive processes: (1) β-methyl elimination, (2) Pd–C bond homolysis, or (3) β-hydride elimination. We also confirm that qualitative trends in the branching ratios between these processes depend on the diphosphine bite angle, whereas electronic modifications of phosphine electron-donating ability have no significant effect on the barriers for β-methyl elimination within the experimental error. The full reaction manifold has been investigated with density functional theory (DFT) and affords a valuable experimental benchmark for types of organometallic transformations described herein

Gas-Phase Investigations on the Transmetalation Step in Sonogashira Reactions

The microscopic reverse of the transmetalation step in the Pd/M (M = Cu, Ag, Au) catalyzed Sonogashira-type reactions has been observed in the gas phase upon collision-induced dissociation (CID) of the heterobimetallic complexes. Measuring the activation energies by quantitative energy-resolved CID experiments provides an upper bound for the internal rearrangement energies. The potential-energy surface is investigated by density functional theory calculations and compared to the experimental values