Characteristic reactions of group 9 transition metal compounds in organic synthesis

Group 9 metal compounds in organic synthesis have two characteristic reactions. The first occurs because the group 9 metals have a high affinity to carbon–carbon or carbon–nitrogen π‐bonds. The first type of characteristic reactions in these group 9 metal compounds includes Pauson–Khand reactions, the Pauson–Khand‐type reactions ([2 + 2 + 1] cyclization), the other cyclizations and coupling reactions. The second occurs because the group 9 metals have a high affinity to carbonyl groups. The second type of characteristic reactions includes carbonylations such as hydroformylations, the carbonylations of methanol, amidocarbonylations and other carbonylations. The first characteristic reactions are applied for the synthesis of fine chemicals such as pharmaceuticals and agrochemicals. However, the second characteristic reactions are utilized not only for fine chemicals but also for important bulk commodity chemicals such as aldehydes, carboxylic acids and alcohols. Copyright © 2009 John Wiley & Sons, Ltd.     

Designing catalysts for nitrene transfer using early transition metals and redox-active ligands

In this Forum Article, we discuss the use of redox-active pincer-type ligands to enable multielectron reactivity, specifically nitrene group transfer, at the electron-poor metals tantalum and zirconium. Two analogous ligand platforms, [ONO] and [NNN], are discussed with a detailed examination of their similarities and differences and the structural and electronic constraints they impose upon coordination to early transition metals. The two-electron redox capabilities of these ligands enable the transfer of organic nitrenes to tantalum(V) and zirconium(IV) metal centers despite formal d(0) electron counts. Under the correct conditions, the resulting metal imido complexes can participate in further multielectron reactions such as imide reduction, nitrene coupling, or formal nitrene transfer to an isocyanide.     

Electrophilic Activation of Silicon–Hydrogen Bonds in Catalytic Hydrosilations

Hydrosilation reactions represent an important class of chemical transformations and there has been considerable recent interest in expanding the scope of these reactions by developing new catalysts. A major theme to emerge from these investigations is the development of catalysts with electrophilic character that transfer electrophilicity to silicon by Si‐H activation. This type of mechanism has been proposed for catalysts ranging from Group 4 transition metals to Group 15 main group species. Additionally, other electrophilic silicon species, such as silylene complexes and η³‐H₂SiRR′ complexes, have been identified as intermediates in hydrosilation reactions. In this Review, different types of catalysts are compared to highlight the range of hydrosilation mechanisms that feature electrophilic silicon centers. The importance of these catalysts to the development of new hydrosilation reactions is also discussed.     

d^0过渡金属化合物对氧气反应性：合成和反应机理研究

众所周知,过渡金属如卟啉中的铁与氧气的结合和反应对许多生物功能和催化氧化至关重要．在这些反应中,过渡金属一般含d价电子,并且金属被氧化往往是其中一个重要的反应步骤．近年来,氧气与d^0过渡金属化合物如Hf（NR2）4（R=烷基）的反应被广泛用来制备金属氧化物薄膜以作为新型微电子器件中的栅（门）绝缘材料．这篇专题文章讨论我们近期对这些反应以及TiO2薄膜形成的研究．在许多氧气与d^0过渡金属化合物的反应中,总是金属被氧化．然而,在d^0过渡金属化合物如Hf（NMe2）4和Ta（NMe2）4（SiR3）与氧气的反应中通常是配体被氧化．如-NMe2和--SIR3配体分别形成了-0NMe2和--OSiR3配体．反应机理和理论方面的研究显示了微电子金属氧化物薄膜形成的途径．     

环钯化合物合成及其在催化中的应用

环钯化合物由于丰富的结构、高度的稳定性和卓越的催化性能,已成为钯化学研究的热点之一。迄今已开发出了C-H键活化、氧化加成、转金属化、亲核加成和配体交换等多种方法,可制备出从三元环到十一元环的CY型环钯化合物和多种YCY型环钯化合物。环钯化合物目前已应用于偶联、烯烃氢化和不对称催化等反应中。本文简单介绍了环钯化合物的种类,重点介绍了环钯化合物的合成方法和催化应用情况,最后提出了环钯化合物在今后合成研究和催化应用中的发展建议。     

Stable dimeric magnesium(I) compounds: from chemical landmarks to versatile reagents

The chemistry of the s-block metals is dominated by the +1 oxidation state for the Alkali metals (group 1) and the +2 oxidation state for the Alkaline Earth metals (group 2). In recent years, a series of stable dimeric magnesium(I) compounds has been prepared and their chemistry has started to develop. These complexes feature "deformable" Mg-Mg single bonds and are stabilised by sterically demanding and chelating anionic N-ligands that prevent their disproportionation. They have rapidly proven useful in organic and organometallic/inorganic reduction reactions as hydrocarbon soluble, stoichiometric, selective and safe reducing agents. The scope of this perspective focuses on stable molecular compounds of the general type LMgMgL and describes their synthesis, structures, theoretical and spectroscopic studies as well as their further chemistry. Also, comparisons are drawn with related complexes including magnesium(II) hydrides and dimeric zinc(I) compounds.     

Microwave Assisted Cross-Coupling Reaction of Sodium Tetraphenylborate with Aroyl Chlorides on Palladium-Doped KF/Al2O

The palladium-catalyzed cross-coupling reaction of organoborate compounds with organic electrophiles is very attractive method for organic synthesis. These coupling reactions offer a powerful tool for the formation of carbon-carbon bonds. 1 In the past few years a number of methods have been devoloped which permit the use of organoboron compounds that are thermally stable and inert to water and oxygen. Further these coupling reactions have been used successfully for the synthesis of natural products, pharmaceutical intermediates, and combinatiorial libraries of organic compounds. Sodium tetraphenylborate is a stable, non-toxic and has been used as a phenylating agent affording σ-phenyl complexes of various transition metals by the transfer of a phenyl group from boron to metals. Phenyl transfer from this reagent to some organopalladium complexes making a new carbon-carbon bond has also been noted. Uemura and Huang reported respectively that Pd(0) or Si-P-Pd(0)-catalyzed reaction of acyl chlorides and NaBPh4 proceeded in THF to give the corresponding phenyl ketones. However, only one phenyl group out of four in the borate was available for transfer. Recently, Bumagin reported that the cross-coupling reaction of NaBPh4 with acyl chlorides in the presence of Pd(OAc)2 and Na2CO3 in dry or aqueous acetone to give high yields of unsymmetric ketones. However, the reaction time is long(1-6 h).     

Titanocene and zirconocene σ-alkynyl complexes in C---C single bond coupling and cleavage reactions

Group 4 metallocene mono- and bis-σ-alkynyl complexes of the type L₂M(σ-CCR) and L₂M(σ-CCR)₂ with M=titanium and zirconium in the oxidation states +3 and +4 and L=Cp (η⁵-cyclopentadienyl) and Cp^* (η⁵-pentamethylcyclopentadienyl) are important compounds for stoichiometric and catalytic C---C single bond coupling and cleavage reactions. Detailed investigations show five-membered metallacyclocumulenes L₂M(η⁴-1,2,3,4-RC₄R) as the key intermediates in both reactions of a C---C single bond cleavage of different 1,4-substituted 1,3-butadiynes RCC---CCR to alkynyl groups and the opposite reaction of C---C single bond formation starting from alkynyl groups under the formation of 1,4-substituted 1,3-butadiynes. Depending on different metals M and ligands L, coupling or cleavage is favoured. Combination of both reactions offered the first C---C single bond metathesis in homogeneous solution, which is photocatalyzed and titanocene-mediated. It proceeds via titanocene–mono-alkynyl complexes, which are interesting species also for other stoichiometric and catalytic C---C coupling reactions. Some similarities regarding the σ-to-π conversion exist between the coupling of the alkynyl groups at titano- and zirconocenes to complexed 1,3-butadiynes on one side and the coupling of phenyl groups at chromium to complexed diphenyl on the other side.     

Cobalt–Pincer Complexes in Catalysis

Non-noble metal catalysts based on pincer type compounds are of special interest for organometallic chemistry and organic synthesis. Next to iron and manganese, currently cobalt–pincer type complexes are successfully applied in various catalytic reactions. In this review the recent progress in (de)hydrogenation, transfer hydrogenation, hydroboration and hydrosilylation as well as dehydrogenative coupling reactions using cobalt–pincer complexes is summarised.     

Manganese-Catalyzed Sustainable Synthesis of Pyrroles from Alcohols and Amino Alcohols

The development of reactions that convert alcohols into important chemical compounds saves our fossil carbon resources as alcohols can be obtained from indigestible biomass such as lignocellulose. The conservation of our rare noble metals is of similar importance, and their replacement by abundantly available transition metals, such as Mn, Fe, or Co (base or nonprecious metals), in key technologies such as catalysis is a promising option. Herein, we report on the first base-metal-catalyzed synthesis of pyrroles from alcohols and amino alcohols. The most efficient catalysts are Mn complexes stabilized by PN₅P ligands whereas related Fe and Co complexes are inactive. The reaction proceeds under mild conditions at catalyst loadings as low as 0.5 mol %, and has a broad scope and attractive functional-group tolerance. These findings may inspire others to use Mn catalysts to replace Ir or Ru complexes in challenging dehydrogenation reactions.     

以N-杂环卡宾为配体的金属络合物催化有机合成的反应

综述了近几年来以N-杂环卡宾为配体的金属络合物催化有机合成的反应。     

Design of organometallic group IV heteroallylic complexes and their catalytic properties for polymerizations and olefin centered transformations

The use of metallocenes in many stoichiometric and catalytic processes has been the impetus for the development of new organometallic complexes, especially those containing early transition metals. The formation of coordinative unsaturated complexes using allylic, benzamidinate and aminopyridine families is presented. The synthesis and structural parameters of the new complexes, their activation and use in the polymerization of alpha-olefins and dienes, in the dehydrogenative coupling of silanes and in the hydroamination reactions comprise the objectives of this review.     

Catalytic thermal and photo-induced CH and CC activation reactions of alkanes with ansa amido functionalized half-sandwich complexes and methylalumoxane

In the literature most of the dehydrogenation reactions of alkanes are described as CH activation reactions of cyclooctane. The best results of CH activation reactions have been found for the reaction of MAO activated metallocene complexes and cyclooctane at temperatures over 300 °C.The application of ansa amido functionalized half sandwich compounds of the type Ind′Si(Me)2NtBuMCl2 (Ind′= monosubstituted indenyl); M = Ti, Zr, Hf) for CH and CC activation reactions is completely unknown in the literature.In contrast to the dehydrogenation reactions of cyclooctane and the metallocene complexes of the group 4 metals, where the zirconocene complexes give higher TONs than the titanocene complexes the ansa amido functionalized titanium complexes give more than two times higher TONs than the corresponding Zr or Hf complexes. The ansa amido functionalized ligand increases the TONs for the Ti complexes and decreases the TONs of the Zr complexes.In contrast to the metallocene complexes, the ansa amido functionalized dichloride complexes of Ti show also a higher activity than the corresponding Zr complexes. It is known that the photolysis of organometallic titanium, zirconium and hafnium (IV) compounds can give M(III) radicals. The formation of the active Ti metal centre is easier than in the case of the corresponding Zr and Hf metal compounds.     

Molecular Rare‐Earth‐Metal Hydrides in Non‐Cyclopentadienyl Environments

Molecular hydrides of the rare‐earth metals play an important role as homogeneous catalysts and as counterparts of solid‐state interstitial hydrides. Structurally well‐characterized non‐metallocene‐type hydride complexes allow the study of elementary reactions that occur at rare‐earth‐metal centers and of catalytic reactions involving bonds between rare‐earth metals and hydrides. In addition to neutral hydrides, cationic derivatives have now become available.     

Carbon–Carbon Cross‐Coupling Reactions Catalyzed by a Two‐Coordinate Nickel(II)–Bis(amido) Complex via Observable NiI,NiII, and NiIII Intermediates

Recently, the development of more sustainable catalytic systems based on abundant first‐row metals, especially nickel, for cross‐coupling reactions has attracted significant interest. One of the key intermediates invoked in these reactions is a Ni^III–alkyl species, but no such species that is part of a competent catalytic cycle has yet been isolated. Herein, we report a carbon–carbon cross‐coupling system based on a two‐coordinate Ni^II–bis(amido) complex in which a Ni^III–alkyl species can be isolated and fully characterized. This study details compelling experimental evidence of the role played by this Ni^III–alkyl species as well as those of other key Ni^I and Ni^II intermediates. The catalytic cycle described herein is also one of the first examples of a two‐coordinate complex that competently catalyzes an organic transformation, potentially leading to a new class of catalysts based on the unique ability of first‐row transition metals to accommodate two‐coordinate complexes.     

Carbon–Carbon Cross‐Coupling Reactions Catalyzed by a Two‐Coordinate Nickel(II)–Bis(amido) Complex via Observable NiI,NiII, and NiIII Intermediates

Recently, the development of more sustainable catalytic systems based on abundant first‐row metals, especially nickel, for cross‐coupling reactions has attracted significant interest. One of the key intermediates invoked in these reactions is a Ni^III–alkyl species, but no such species that is part of a competent catalytic cycle has yet been isolated. Herein, we report a carbon–carbon cross‐coupling system based on a two‐coordinate Ni^II–bis(amido) complex in which a Ni^III–alkyl species can be isolated and fully characterized. This study details compelling experimental evidence of the role played by this Ni^III–alkyl species as well as those of other key Ni^I and Ni^II intermediates. The catalytic cycle described herein is also one of the first examples of a two‐coordinate complex that competently catalyzes an organic transformation, potentially leading to a new class of catalysts based on the unique ability of first‐row transition metals to accommodate two‐coordinate complexes.     

The Transition Metal-Nitrogen Multiple Bond

Numerous nitrido complexes of transition metals show very short metal-nitrogen bond lengths, suggesting M?N-triple bonds. At present, compounds of this type are being intensively investigated. In particular the molybdenum complexes are considered as model substances for the study of at least an intermediate step of N₂-assimilation. This article contains a review of the structure and bonding, as well as syntheses and reactions of these complexes.     

Visible‐Light‐Induced Nickel‐Catalyzed Negishi Cross‐Couplings by Exogenous‐Photosensitizer‐Free Photocatalysis

The merging of photoredox and transition‐metal catalysis has become one of the most attractive approaches for carbon–carbon bond formation. Such reactions require the use of two organo‐transition‐metal species, one of which acts as a photosensitizer and the other one as a cross‐coupling catalyst. We report herein an exogenous‐photosensitizer‐free photocatalytic process for the formation of carbon–carbon bonds by direct acceleration of the well‐known nickel‐catalyzed Negishi cross‐coupling that is based on the use of two naturally abundant metals. This finding will open new avenues in cross‐coupling chemistry that involve the direct visible‐light absorption of organometallic catalytic complexes.     

Reactivities of d<Superscript>0</Superscript> transition metal complexes toward oxygen: Synthetic and mechanistic studies

Transition metals such as Fe in porphyrin complexes are known to bind or react with O₂, and such reactions are critical to many biological functions and catalytic oxidation using O₂. The transition metals in these reactions often contain valence d electrons, and oxidation of metals is an important step. In recent years, reactions of O₂ with d⁰ transition metal complexes such as Hf(NR₂)₄ (R = alkyl) have been used to make metal oxide thin films as insulating gate materials in new microelectronic devices. This feature article discusses our recent studies of such reactions and the formation of TiO₂ thin films. In contrast to the reactions of many d ⁿ complexes where metals are often oxidized, reactions of d⁰ complexes such as Hf(NMe₂)₄ and Ta(NMe₂)₄(SiR₃) with O₂ usually lead to the oxidation of ligands, forming, e.g., -ONMe₂ and -OSiR₃ from -NMe₂ and -SiR₃ ligands, respectively. Mechanistic and theoretical studies of these reactions have revealed pathways in the formation of the metal oxide thin films as microelectronic materials.     

锰配合物催化加氢反应的研究进展

过渡金属催化不饱和有机化合物的加氢反应具有原子经济性高、绿色环保等优点,一直是有机化学研究的重点和难点.当前加氢反应中最常用的催化剂主要是铑、钌、铱、钯等贵金属,以储量丰富的金属锰作为催化剂更符合可持续发展的要求,在过去的几年中,锰催化的醛、酮、酯、腈、酰胺等不饱和化合物的氢化反应得以实现.我们系统地总结了锰配合物在加...