The first total synthesis of waihoensene, a tetracyclic diterpene containing an angular triquinane and a six-membered ring, with four contiguous quaternary carbon atoms, was achieved through the tandem cycloaddition reaction of an allenyl diazo substrate containing a six-membered ring via trimethylenemethane (TMM) diyl intermediate. 相似文献
The equilibrium geometries and first bond dissociation energies of the homoleptic complexes M(EMe)4 and M(CO)4 with M = Ni, Pd, Pt and E = B, Al, Ga, In, Tl have been calculated at the gradient corrected DFT level using the BP86 functionals. The electronic structure of the metal‐ligand bonds has been examined with the topologial analysis of the electron density distribution. The nature of the bonding is revealed by partitioning the metal‐ligand interaction energies into contributions by electrostatic attraction, covalent bonding and Pauli repulsion. The calculated data show that the M‐CO and M‐EMe bonding is very similar. However, the M‐EMe bonds of the lighter elements E are much stronger than the M‐CO bonds. The bond energies of the latter are as low or even lower than the M‐TlMe bonds. The main reason why Pd(CO)4 and Pt(CO)4 are unstable at room temperature in a condensed phase can be traced back to the already rather weak bond energy of the Ni‐CO bond. The Pd‐L bond energies of the complexes with L = CO and L = EMe are always 10 — 20 kcal/mol lower than the Ni‐L bond energies. The calculated bond energy of Ni(CO)4 is only Do = 27 kcal/mol. Thus, the bond energy of Pd(CO)4 is only Do = 12 kcal/mol. The first bond dissociation energy of Pt(CO)4 is low because the relaxation energy of the Pt(CO)3 fragment is rather high. The low bond energies of the M‐CO bonds are mainly caused by the relatively weak electrostatic attraction and by the comparatively large Pauli repulsion. The σ and π contributions to the covalent M‐CO interactions have about the same strength. The π bonding in the M‐EMe bonds is less than in the M‐CO bonds but it remains an important part of the bond energy. The trends of the electrostatic and covalent contributions to the bond energies and the σ and π bonding in the metal‐ligand bonds are discussed. 相似文献
[Cp°MoCl4] (Cp° = C5EtMe4) reacts with primary phosphines PH2R to give the paramagnetic phosphine complexes [Cp°MoCl4(PH2R)] [Cp° = C5EtMe4, R = But ( 1 ), 1‐Ad (1‐Ad = 1‐adamantyl; 2 ), Cy ( 3 ), Ph ( 4 ), Mes (Mes = 2, 4, 6‐Me3C6H2; 5 ), Tipp (Tipp = 2, 4, 6‐Pri3C6H2; 6 )]. 1 — 6 were characterized spectroscopically (IR, MS), and X‐ray crystal structures were determined for 1 — 4 and 6 . EPR investigations in liquid and frozen solution confirmed the presence of MoV species, and the data were used to analyze the spin‐density distribution in the first coordination sphere. Complexes 3 and 4 react with two equivalents of NEt3 with formation of [Cp°MoCl2(η3‐P4Cy4H)] ( 7 ) and [Cp°2Mo2(μ‐Cl)2(μ‐P4Ph4)] ( 8 ), respectively, in low yield. Complexes 7 and 8 were characterized by X‐ray crystallography. 相似文献
In dimethylformamide containing tetramethylammonium tetrafluoroborate, cyclic voltammograms for reduction of 4,4′‐(2,2,2‐trichloroethane‐1,1‐diyl)bis(chlorobenzene) (DDT) at a glassy carbon cathode exhibit five waves, whereas three waves are observed for the reduction of 4,4′‐(2,2‐dichloroethane‐1,1‐diyl)bis(chlorobenzene) (DDD). Bulk electrolyses of DDT and DDD afford 4,4′‐(ethene‐1,1‐diyl)bis(chlorobenzene) (DDNU) as principal product (67–94%), together with 4,4′‐(2‐chloroethene‐1,1‐diyl)bis(chlorobenzene) (DDMU), 1‐chloro‐4‐styrylbenzene, and traces of both 1,1‐diphenylethane and 4,4′‐(ethane‐1,1‐diyl)bis(chlorobenzene) (DDO). For electrolyses of DDT and DDD, the coulometric n values are essentially 4 and 2, respectively. When DDT is reduced in the presence of a large excess of D2O, the resulting DDNU and DDMU are almost fully deuterated, indicating that reductive cleavage of the carbon–chlorine bonds of DDT is a two‐electron process that involves carbanion intermediates. A mechanistic scheme is proposed to account for the formation of the various products. 相似文献
2,5‐Bis(chloromethyl)‐1,3,4‐oxadiazole was synthesized and dehydrohalogenation of this model compound was investigated under various base conditions. The formation of an intermediate with quinodimethane‐type structure is suggested for reaction in EtONa/EtOH. Polymerization of this intermediate proceeds via an anionic mechanism to form poly(1,3,4‐oxadiazole‐2,5‐diyl‐1,2‐vinylene). Polymerization at a toluene/water interface results in shorter polymerization times, milder conditions, higher molecular weights, higher yields and fewer defects in the polymer as compared to the corresponding polycondensation route.
Three isotypic rare earth complexes, catena‐poly[[aquabis(but‐2‐enoato‐κ2O,O′)yttrium(III)]‐bis(μ‐but‐2‐enoato)‐κ3O,O′:O;κ3O:O,O′‐[aquabis(but‐2‐enoato‐κ2O,O′)yttrium(III)]‐μ‐4,4′‐(ethane‐1,2‐diyl)dipyridine‐κ2N:N′], [Y2(C4H5O2)6(C12H12N2)(H2O)2], the gadolinium(III) analogue, [Gd2(C4H5O2)6(C12H12N2)(H2O)2], and the gadolinium(III) analogue with a 4,4′‐(ethene‐1,2‐diyl)dipyridine bridging ligand, [Gd2(C4H5O2)6(C12H10N2)(H2O)2], are one‐dimensional coordination polymers made up of centrosymmetric dinuclear [M(but‐2‐enoato)3(H2O)]2 units (M = rare earth), further bridged by centrosymmetric 4,4′‐(ethane‐1,2‐diyl)dipyridine or 4,4′‐(ethene‐1,2‐diyl)dipyridine spacers into sets of chains parallel to the [20] direction. There are intra‐chain and inter‐chain hydrogen bonds in the structures, the former providing cohesion of the linear arrays and the latter promoting the formation of broad planes parallel to (010). 相似文献
d‐glucosamine propane‐1,3‐diyl dithioacetal is a versatile synthetic building block, especially when being incorporated with the Corey‐Seebach method. Hence, exploring compatible protecting group patterns on this compound mainly for use with the Corey‐Seebach method is a fundamental work. Various protecting group strategies were applied. Typically, N‐protection of d‐glucosamine propane‐1,3‐diyl dithioacetal yielded N‐phthaloyl, N‐Boc, and N‐Ac derivatives. On the N‐Ac derivative, experiments differentiating 3,4‐ and 5,6‐hydroxyls by basic stable protecting groups yielded useful intermediates. Selective protections of the 6‐hydroxyl of the N‐Ac derivative were also applied. The remaining secondary hydroxyls of the resulting N‐Ac‐6‐O‐acyl d‐glucosamine propane‐1,3‐diyl dithioacetals could be methoxymethylated to tri‐O‐MOM derivatives or protected by a unique one‐pot discriminating protection to form the N‐acyl‐6‐O‐acyl‐ 3,4‐O‐methylene‐5‐O‐methoxymethyl d‐glucosamine propane‐1,3‐diyl dithioacetals as useful intermediates. 相似文献
A novel three‐dimensional coordination polymer, {[Pb(C14H8N2O4)(H2O)]·0.5C12H10N2}n, has been synthesized by hydrothermal reaction of Pb(OAc)2·3H2O (OAc is acetate), 2,2′‐(diazene‐1,2‐diyl)dibenzoic acid (H2L) and 1,2‐bis(pyridin‐4‐yl)ethylene (bpe). The asymmetric unit contains a crystallographically independent PbII cation, one L2− ligand, an aqua ligand and half a bpe molecule. Each PbII centre is seven‐coordinated by six O atoms of bridging–chelating carboxylate groups from L2− ligands and by one O atom from a coordinated water molecule. The PbII cations are bridged by L2− ligands, forming [PbO2]n chains along the a axis. These chains are further connected by L2− ligands along the b and c axes to give a three‐dimensional framework with a 41263 topology. The channel voids are occupied by bpe molecules. 相似文献
In the title coordination polymer, {[Cd(C6H8O4S)(C13H14N2)]·H2O}n, the CdII atom displays a distorted octahedral coordination, formed by three carboxylate O atoms and one S atom from three different 3,3′‐thiodipropionate ligands, and two N atoms from two different 4,4′‐(propane‐1,3‐diyl)dipyridine ligands. The CdII centres are bridged through carboxylate O atoms of 3,3′‐thiodipropionate ligands and through N atoms of 4,4′‐(propane‐1,3‐diyl)dipyridine ligands to form two different one‐dimensional chains, which intersect to form a two‐dimensional layer. These two‐dimensional layers are linked by S atoms of 3,3′‐thiodipropionate ligands from adjacent layers to form a three‐dimensional network. 相似文献
In the title coordination polymer, [Pb(C14H8N2O4)(CH3OH)2]n, the asymmetric unit contains half of a PbII cation, half of a 2,2′‐(diazene‐1,2‐diyl)dibenzoate dianionic ligand (denoted L2−) and one methanol ligand. Each PbII centre is eight‐coordinated by six O atoms of chelating/bridging carboxylate groups from four L2− ligands and two O atoms from two terminal methanol ligands, forming a distorted dodecahedron. The [PbL2(MeOH)2] subunits are interlinked via the sharing of two carboxylate O atoms to form a one‐dimensional [PbL2(MeOH)2]n chain. Adjacent chains are further connected by L2− ligands, giving rise to a two‐dimensional layer, and these layers are bridged by L2− linkers to afford a three‐dimensional framework with a 41263 topology. 相似文献