Three characteristic reactions of alkynes with metal compounds in organic synthesis

Alkynes have two sets of mutually orthogonal π‐bonds that are different from the π‐bonds of alkenes. These π‐bonds are able to bond with transition metal compounds. Alkynes easily bond with the various kinds of compounds having a π‐bond such as carbon monoxide, alkenes, other alkynes and nitriles in the presence of the transition metal compounds. The most representative reaction of alkynes is called the Pauson–Khand reaction. The Pauson–Khand reactions include the cyclization of alkynes with alkenes and carbon monoxide in the presence of cobalt carbonyls. Similar Pauson–Khand reactions also proceed in the presence of other transition metal compounds. These reactions are the first type of characteristic reaction of alkynes. Other various kinds of cyclizations with alkynes also proceed in the presence of the transition metal compounds. These reactions are the second type of characteristic reaction of alkynes. These include cyclooligomerizations and cycloadditions. The cyclooligomerizations include mainly cyclotrimerizations and cyclotetramerizations, and the cycloadditions are [2 + 2], [2 + 2 + 1], [2 + 2 + 2], [3 + 2], [4 + 2], etc., type cycloadditions. Alkynes are fairly reactive because of the high s character of their σ‐bonds. Therefore, simple coupling reactions with alkynes also proceed besides the cyclizations. The coupling reactions are the third type of characteristic reactions of alkynes in the presence of, mainly, the transition metal compounds. These reactions include carbonylations, dioxycarbonylations, Sonogashira reactions, coupling reactions with aldehydes, ketones, alkynes, alkenes and allyl compounds. Copyright © 2008 John Wiley & Sons, Ltd.     

Three characteristic reactions of organocobalt compounds in organic synthesis

Organocobalt compounds in organic synthesis have three characteristic reactions. The first occurs because cobalt has a high affinity to carbon–carbon π‐bonds or carbon–nitrogen π‐bonds. The second occurs because cobalt has a high affinity to carbonyl groups. The third is due to cobalt easily tending to form square‐planar bipyramidal six‐coordination structures with four nitrogen atoms or two nitrogen atoms and two oxygen atoms at the square‐planar position, and to bond with one or two carbon atoms at the axial position. The first characteristic reactions are the representative reactions of organocobalt compounds with a mutually bridged bond between the two π‐bonds of acetylene and the cobalt–cobalt bond of hexacarbonyldicobalt. These are reactions with a Co₂(CO)₆ protecting group to reactive acetylene bond, the Nicholas reactions, the Pauson–Khand reactions ([2 + 2 + 1] cyclizations), [2 + 2 + 2] cyclizations, etc. These reactions are applied for the syntheses of many kinds of pharmaceutically useful compounds. The second reactions are carbonylations that have been used or developed as industrial processes such as hydroformylation for the manufacture of isononylaldehyde, and carbonylation for the production of phenylacetic acid from benzyl chloride. The third reactions are those reactions with the B₁₂‐type catalysts, and they have recently been used in organic syntheses and are utilized as catalysts for stereoselective syntheses. These reactions have been used as new applications for organic syntheses. Copyright © 2007 John Wiley & Sons, Ltd.     

Well‐Defined Models for the Elusive Dinuclear Intermediates of the Pauson–Khand Reaction

The mechanism of the Pauson–Khand reaction has attracted significant interest due to the unusual dinuclear nature of the Co₂(CO)_x active site. Experimental and computational data have indicated that the intermediates following the initial Co₂(CO)₆(alkyne) complex are thermodynamically unstable and do not build up in appreciable concentrations during the course of the reaction. As a consequence, the key steps that control the scope of viable substrates and various aspects of selectivity have remained largely uncharacterized. Herein, a direct experimental investigation of the dinuclear metallacycle‐forming step of the Pauson–Khand reaction is reported. These studies capitalize on well‐defined d⁹–d⁹ dinickel complexes supported by a naphthyridine–diimine (NDI) pincer ligand as functional surrogates of Co₂(CO)₈.     

Application of the NDDO method to transition metal compounds

The NDDO method has been extended to include elements withd-orbitals. A parametrization for the first-row transition metals is given, which has been worked out to describe structural properties of transition metal complexes. Applications of the method to the Jahn-Teller distortions of tetrachloro complexes are presented. The NDDO results are compared with those from CNDO and INDO calculations. It turns out that the NDDO method seems to be the most sensitive among the ZDO procedures.     

Carbonylation of acetaldehyde in the presence of transition metal compounds

The carbonylation of acetaldehyde to give butyl lactate has been carried out in the presence of rhodium and cobalt compounds atP _CO=5–9 MPa andT=383–483 K.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 570–571, March, 1995.     

相转移条件下过渡金属促进有机反应的一些新进展

本文综述了近年来，在相转移条件下，过渡金属催化氧化、还原、羰基化以及偶合反应及其在有机合成中应用新进展。     

Metal–metal bonding in biscycloheptatrienyl dimetal compounds of the second‐row transition metals

Density functional theory has been used to examine the dimetallocene‐like dicycloheptatrienyl dimetal compounds of the second‐row transition metals (C₇H₇)₂M₂ (M = Ru, Tc, Mo, Nb, Zr). The lowest energy (C₇H₇)₂Mo₂ structure is a coaxial structure with terminal η⁷? C₇H₇ rings, whereas the lowest energy (C₇H₇)₂M₂ structures (M = Ru, Tc, Nb, Zr) are perpendicular structures with bridging η⁴,η⁴? C₇H₇ rings except for the perpendicular (η⁴,η³? C₇H₇)₂Ru₂ structure. The metal–metal bond orders in the (C₇H₇)₂M₂ structures (M = Ru, Tc, Mo, Nb), as determined by analysis of their frontier molecular orbitals, suggest preferred 16‐ rather than 18‐electron configurations for the central metal atoms. Thus, in the coaxial (η⁷? C₇H₇)₂M₂ structures the formal bond orders are two for M = Tc and three for M = Mo. For the perpendicular structures both (η⁴,η³? C₇H₇)₂Ru₂ and (η⁴,η⁴? C₇H₇)₂Tc₂ have 16‐electron configurations with metal–metal single bonds owing to the different modes of bonding of the bridging C₇H₇ rings in the two structures. For the (C₇H₇)₂Zr₂ system the perpendicular structure has a formal Zr?Zr double bond and the coaxial structure has a very long (～3.5 Å) Zr? Zr bond indicating only 12‐ to 14‐electron configurations for the zirconium atoms.     

New approaches in radical carbonylation chemistry: fluorous applications and designed tandem processes by species-hybridization with anions and transition metal species

New approaches in radical carbonylation chemistry are described. We have successfully integrated tin mediated radical carbonylation chemistry into modern fluorous applications and separation techniques. We revealed that radical carbonylation reactions can be performed using fluorous tin mediators, such as fluorous tin hydride and fluorous allyltin reagents. Fine tuning of the reaction conditions resulted in a good efficiency equivalent to conventional tin mediators. The tedious procedure of removing organotin byproducts can be circumvented through the use of fluorous/organic liquid-liquid extraction or fluorous liquid-solid phase extraction with fluorous reverse phase silica (FRPS). Also described are newly developed tandem carbonylation reactions that are based on species hybridization approaches. Using a radical/anionic hybrid system based on zinc-induced one-electron reduction, we achieved a three-component coupling reaction consisting of 4-alkenyl iodides, carbon monoxide, and electron-deficient alkenes. We observed two types of annulations processes, namely [4 + 1](radical)/[3 + 2](anionic) and [5 + 1](radical)/[3 + 2](anionic), which lead to the production of bicyclo[3.3.0]octanols and bicyclo[3.2.1]octanols, respectively. We found a radical/palladium hybrid system to be useful in the construction of new cyclic systems that incorporate two or three molecules of carbon monoxide.     

离子液体在有机反应中的应用

室温离子液体，由含氮的有机阳离子和无机阴离子组成，可溶解各种有机、无 机、金属有机化合物。它们没有蒸气压、不易燃、容易循环使用。近年已发现，离 子液体可广泛地用于许多过渡金属化合物和酶催化的反应。着重讨论这方面的发展 状况。     

A general synthesis of transition metal oxides with assistance of organic amines and their electrocatalytic properties

Several transition metal oxides,including α-Fe2O3,Fe3O4,Co3O4,NiO,CuO and ZnO,were synthesized via an easily controlled hydrothermal method at assistance of organic amine(cyclohexylamine or triethylamine).The synthesized samples were identified and characterized by X-ray diffraction(XRD),Transmission Electron Microscopy(TEM),High-resolution Electron Microscopy(HR-TEM),Field Emission Scanning Electron Microscopy(FE-SEM),N2 adsorption/desorption measurement.The resultant metal oxides displayed various morphol...     

Pentafluorophenyl carbonyl compounds in the Reformatsky-type reactions promoted with Fe(CO)5-based metal complex systems

Iron pentacarbonyl is an effective promoter for additions of halogenated acid esters and nitriles to pentafluorophenyl carbonyl compounds 1, 4, and 5 by the Reformatsky-type reaction and reductive coupling of compound 1. The electron-withdrawing character of the pentafluorophenyl group has a significant effect on the reaction pathway and the type of the reaction products. The reactions involving metal complex systems derived from Fe(CO)₅ have a number of advantages such as a simple procedure for carrying out, the lack of necessity to use anhydrous solvents and an inert atmosphere. The schemes of the reactions have been proposed and the conditions for preparative syntheses of most products have been optimized.     

Design of hydroxyapatite-bound transition metal catalysts for environmentally-benign organic syntheses

Novel heterogeneous catalysts, which were designed with atomic precision, easy to prepare, and recyclable, have been developed using a unique inorganic support hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂. The introduction of a Ru cation into the apatite framework can generate a stable monomeric phosphate complex, which exhibits prominent catalytic performances for various oxidation reactions using molecular oxygen as a primary oxidant. Treatment of the RuHAP with an aqueous solution of AgX affords cationic Ru phosphate complexes as Lewis acid catalysts, promoting Diels–Alder and aldol reactions under mild and neutral conditions. Furthermore, two classes of heterogeneous Pd catalysts were synthesized with both stoichiometric and Ca-deficient hydroxyapatites, which show specific functions for aerobic oxidation of alcohols and carbon–carbon bond-forming reactions with extremely high turnover numbers. The catalytic systems described here are simple, efficient, and general for practical organic syntheses; thus meeting the increasing demands for environmentally-benign chemical processes.     

Transformations of cycloalkanes under the action of organoaluminum compounds and transition metal complexes in the presence of polychloromethanes

A catalytic system comprising an organoaluminum compound, polychloromethane, and a transition metal complex transforms cyclohexane into dimethyldecalins, cyclooctane into dimethyl- and ethylcyclohexanes, and endo-tricyclo[5.2.1.0^2,6]decane into its exo-isomer under mild conditions.