Synthesis of polyacetylenic acids isolated from Heisteria acuminata

Four linear polyacetylenic compounds were synthesized. Pentadeca-6,8,10-triynoic acid 1 and octadeca-8,10,12-triynoic acid 2 were synthesized by using acetylene coupling reactions. The syntheses of (Z)-hexadec-11-en-7,9-diynoic acid 3 and (Z)-octadec-12-en-7,9-diynoic acid 4 by using vinylic telluride coupling reactions were accomplished.     

Intramolecular Dynamics of Tetranuclear Carbonyliridium Cluster Compounds. Part II. Disubstituted complexes with one chelating ligand. Crystal structure of [Ir4(CO)7(μ-CO)3(1,5-cyclooctadiene)]

The two complexes [Ir₄(CO)₁₀(diarsine)] (1) and [Ir₄(CO)₁₀(1,5-cyclooctadiene)] (2) bear a bidentate ligand chelating one metal atom of the basal face of the Ir₄ tetrahedron. However, they differ in fluxional behaviour as observed by 2D-exchange and variable-temperature ¹³C-NMR. The CO-site exchange with lowest activation energy proceeds via an unbridged intermediate in 2 , whereas that in 1 occurs via a concerted edge-bridging of CO's to an alternative face of the metal core. This difference is apparently related to different ground-state geometries: the basal CO's are symmetrically bridging in 2 , whereas two CO's are semi-bridging in 1 . The molecular structure of 2 was determined by single crystal X-ray diffractometry. The crystals are orthorhombic, space group Pbca, a = 11.651(4), b = 13.118(3), c = 28.64(1)Å. The idealized molecular symmetry is C_s. The diolefin chelates a basal Ir-atom replacing an axial and a radial CO group on the tetrahedral metal-atom framework.     

Catalytic enantioselective arylation of aldehydes: boronic acids as a suitable source of transferable aryl groups

The catalytic enantioselective arylation of several aldehydes using boronic acids as the source of transferable aryl groups is described; the reaction is found to proceed in excellent yields and high enantioselectivities (up to 97% ee) in the presence of a chiral amino alcohol.     

A fluorous chiral dirhodium(II) complex as a recyclable asymmetric catalyst

[reaction: see text] The chiral fluorous complex tetrakis-dirhodium(II)-(S)-N-(n-perfluorooctylsulfonyl)prolinate has been prepared and used as a catalyst in homogeneous or fluorous biphasic fashion. The catalyst displays good chemo- and enantioselectivity in intermolecular cyclopropanation and C-H bond activation reactions. The catalyst can be simply and thoroughly separated from the reaction mixture and is recyclable.     

Semiempirical study on the electronic structure of antitumor drugs ellipticines, olivacines and isoellipticines

Ellipticine [5,11-dimethyl-6H-pyrido[4,3]carbazole] is a planar organic compound isolated from the plant extract of Ochrosia elliptica, with a high degree of antitumor and cytotoxic activity. Ellipticine and its derivatives have different modes of action, which may include intercalation or covalent binding to DNA and interference with the activity of topoisomerase II. In the present work we studied the electronic, geometrical and spectroscopic properties of 31 ellipticine derivatives and analogue compounds, using the semiempirical methods Parametric Method 3 and Zerner's Intermediate Neglect of Differential Overlap. The Zero Differential Overlap semiempirical Molecular Electrostatic Potential (MEP) was also calculated in order to interpret the electronic structure of the molecules. For the biologically tested ellipticines and olivacines we have observed a rule based on the dipole moment values and a selective distribution of active sites (coming from the MEP calculations) that can be used to identify the active molecules. These results provide a pattern which can be used to select potentially active molecules from the untested group of molecules and to design new ellipticine derivatives with improved antitumor activity.     

2,5-Bis-(butyltelluro) thiophene as a convenient precursor for the synthesis of 2,5-bis-(acetylenic) thiophenes

Both symmetrically and unsymmetrically substituted 2,5-bis-(acetylenic) thiophene derivatives were obtained in good yields under mild conditions through palladium-catalyzed cross coupling reaction of 2,5-bis-(butyltelluro) thiophene 2 and terminal alkynes. The methodology represents a general and efficient protocol for carrying out the synthesis of thiophene derivatives with potential biological activities.     

Reactions between or within molecular crystals

Reactions that occur within or between molecular crystals, in particular those reactions that are activated by mechanical methods, are reviewed. The focus is on processes (whether intrasolid or intersolid) that are controlled primarily by supramolecular bonding, such as template cycloadditions, formation of inclusion compounds, reactions between molecular crystals by the reassembling of noncovalent bonds, and the formation of complexes and coordination compounds. It is proposed that solvent-free mechanochemical methods, for example, cogrinding, milling, and kneading, represent viable "green" routes for the preparation of novel molecular and supramolecular solids.     

Computational characterization of the role of the base in the Suzuki-Miyaura cross-coupling reaction

The role of the base in the transmetalation step of the Suzuki-Miyaura cross-coupling reaction is analyzed computationally by means of DFT calculations with the Becke3LYP functional. The model system studied consists of Pd(CH=CH2)(PH3)2Br as the starting catalyst complex, CH2=CHB(OH)2 as the organoboronic acid, and OH- as the base. The two main mechanistic proposals, consisting of the base attacking first either the palladium complex or the organoboronic acid, are evaluated through geometry optimization of the corresponding intermediates and transition states. Supplementary calculations are carried out on the uncatalyzed reaction and on a process where the starting complex is Pd(CH=CH2)(PH3)2(OH). These calculations, considered together with available experimental data, strongly suggest that the main mechanism of transmetalation in the catalytic cycle starts with the reaction of the base and the organoboronic acid.     

Synthesis,XRD, spectral (IR,UV–Vis,NMR) characterization and quantum chemical exploration of benzoimidazole‐based hydrazones: A synergistic experimental‐computational analysis

Present study advocates the joint experimental and computational studies of two potent benzoimidazole‐based hydrazones with chemical formula C₂₃H₁₈F₂N₄O ( 5a ) and C₂₅H₂₂FN₅O₃ ( 5b ). Both 5a and 5b were synthesized and resolved into their crystal structures using SC‐XRD for the assessment of bond lengths, bond angles, unit cells and space groups. The structures of 5a and 5b were chemically characterized using infrared (FT‐IR), UV–Visible, nuclear magnetic resonance (¹H‐NMR and ¹³C‐NMR), EIMS and elemental analysis. DFT at M06‐2X/6‐31G(d,p) level of theory was performed to get optimized structures and countercheck the experimental findings. Overall, DFT findings show excellent concurrence with the experimental data which confirms the purity of both compounds. FMO, NBO analysis, MEP surfaces and nonlinear optical (NLO) properties were explored at same level of theory. UV–Vis analysis at TDDFT/M06‐2X/6‐31G(d,p) level of theory showed that 5b is red shifted with λ_max 331.69 nm as compared to 5a with λ_max 240.25 nm. Global reactivity parameters were estimated using energy of FMOs indicated the greater harness value than the softness values of 5a and 5b . NBO analysis confirmed that the presence of non‐covalent interactions, hydrogen bonding and hyper conjugative interactions are pivotal cause for the existence of 5a and 5b in the solid‐state. NLO results of 5a and 5b were observed better than standard molecule recommended the NLO activity of said molecules for optoelectronic applications.