Synthesis and reactivity of saturated hydrocarbon-bridged dinuclear complexes

Casey, Charles P.; Audett, Jay D.

doi:10.1021/cr00072a003

Cited by 89 publications

(16 citation statements)

References 27 publications

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“…A final facet of the system described herein is the insertion of CO into a metal–carbon bond, which is an important organometallic transformation 9. In particular, metal ketene complexes (which can formally be considered as the derivatives of such insertion processes) are considered to play important roles in industrial Fischer–Tropsch syntheses1e, 10 as well as in CO 2 fixation and functionalization,11 and may be intermediates in the thermal and photochemical reactions of carbene/CO complexes 12. In most cases, the existence of the intermediate ketene complex is only inferred because the general instability of such complexes hampers direct observation.…”

Section: Methodsmentioning

confidence: 99%

A Bimetallic, Coordinated‐Ketene Complex Formed from a Bimetallic Lithium–Carbon Spirocycle by Lithium‐Mediated Insertion of CO into a Rhodium–Carbon Bond

et al. 2006

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Section: Methodsmentioning

confidence: 99%

A Bimetallic, Coordinated‐Ketene Complex Formed from a Bimetallic Lithium–Carbon Spirocycle by Lithium‐Mediated Insertion of CO into a Rhodium–Carbon Bond

et al. 2006

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“…Accordingly, we set out to prepare compounds of this type. [49][50][51] Alkylation of [(i-Pr 2 Ph) 2 nacnacCr(μ-I)] 2 with 1,ω-dilithioalkanes indeed yielded such compounds, after some optimization (see Scheme 3). The required dilithioalkyl reagents were synthesized using a procedure reported by Negishi.…”

Section: Dalton Transactions Papermentioning

confidence: 99%

A well-defined model system for the chromium-catalyzed selective oligomerization of ethylene

et al. 2013

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The chromium(I) dinitrogen complex [(i-Pr2Ph)2nacnacCr]2(μ-η(2):η(2)-N2) catalyzes the selective trimerization of ethylene to 1-hexene at ambient pressure and temperature, and in the absence of any cocatalyst. After the conversion of the substrate, the catalyst cleanly converts to another chromium(I) species, namely [(i-Pr2Ph)2nacnacCr]2(μ-η(2):η(2)-C2H4), which is not catalytically active. Binuclear metallacycles containing Cr(II) have been prepared as candidates for catalytically active intermediates; however they are not kinetically competent to explain the catalysis. Turning thus to mononuclear metallacycles featuring Cr(III), a chromacyclopentane, chromacyclopentene and chromacyclopentadiene have been prepared as models of catalytic intermediates. Of these, the latter also catalyzes the trimerization of ethylene. These results support the proposal that selective ethylene oligomerization catalysis involves an interplay between Cr(I) ethylene complexes and mononuclear Cr(III) metallacycles.

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“…6 lists some reactions described by Casey et al in which electrophilic m-methylidynes form C-C bonds by reaction with nucleophiles. [135][136][137][138][139] Even more pertinent to the proposals presented here was the discovery that three C 1 ligands in the dirhodium complexes 7; the Z 5 -C 5 Me 5 -ligand was shown to play no direct part in the reaction. 94,95 A reaction scheme for the FT reaction based upon these ideas has therefore been suggested and is depicted in Fig.…”

Section: Charged Surface Species: Analogies To Electrophiles and Nucl...mentioning

confidence: 99%

The role of electrophilic species in the Fischer–Tropsch reaction

2009

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The heterogeneously catalysed Fischer-Tropsch (FT) synthesis converts syngas (CO+H2) into long chain hydrocarbons and is a key step in the economically important transformation of natural gas, coal, or biomass into liquid fuels, such as diesel. Catalyst surface studies indicate that the FT reaction starts when CO is activated at imperfections on the surfaces of late transition metals (Fe, Ru, Co, or Rh) and at interfaces with "islands" of promoters (Lewis acid oxides such as alumina or titania). Activation involves CO cleavage to generate a surface carbide, C(ad), which is sequentially hydrogenated to CHx(ad) species (x=1-4). An overview of practical aspects of the FT synthesis is followed by a discussion of the chief mechanisms that have been proposed for the formation of 1-alkenes by polymerisation of surface C1 species. These mechanisms have traditionally postulated rather non-polar intermediates, such as CH2(ad) and CH3(ad). However, electrophiles and nucleophiles are well-known to play key roles in the reactions of organic and organometallic compounds, and also in many reactions homogeneously catalysed by soluble metal complexes, including olefin polymerisation. We have now extended these concepts to the Fischer-Tropsch reaction, and show that the polymerisation reactions at polarising surfaces, such as oxide-metal interfaces, can be understood if the reactive chain carrier is an electrophilic species, such as the cationic methylidyne, CH(delta+)(ad). It is proposed that the key coupling step in C-C bond formation involves the interaction of the electrophilic methylidyne with an alkylidene (RCH(ad), R=H, alkyl), followed by an H-transfer to generate the homologous alkylidene: CHdelta+(ad)+RCH(ad)-->RCHCH(ad) and RCHCH(ad)+H(ad)-->RCH2CH(ad). If the reactions occur on non-polarising surfaces, an alternative C-C bond forming reaction such as the alkenyl+methylene, RCH=CH(ad)+CH2(ad)-->RCH=CHCH2(ad), can take place. This approach explains important aspects of the enigmatic Fischer-Tropsch reaction, and allows new predictions.

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Synthesis and reactivity of saturated hydrocarbon-bridged dinuclear complexes

Cited by 89 publications

References 27 publications

A Bimetallic, Coordinated‐Ketene Complex Formed from a Bimetallic Lithium–Carbon Spirocycle by Lithium‐Mediated Insertion of CO into a Rhodium–Carbon Bond

A Bimetallic, Coordinated‐Ketene Complex Formed from a Bimetallic Lithium–Carbon Spirocycle by Lithium‐Mediated Insertion of CO into a Rhodium–Carbon Bond

A well-defined model system for the chromium-catalyzed selective oligomerization of ethylene

The role of electrophilic species in the Fischer–Tropsch reaction

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