Agostic interactions in transition metal compounds

Brookhart, Maurice; Green, Malcolm L. H.; Parkin, Gerard

doi:10.1073/pnas.0610747104

Cited by 1,024 publications

(912 citation statements)

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“…a three-center-twoelectron Mo-H-C interaction, in which the electron density given to the Mo atom is given by the C-H bond. 56 As said above, the present quality of the electron density maps does not allow a clear identification of the chemical form of the alcohol molecule, and additional crystallographic and/or spectroscopic studies would be therefore necessary in order to unambiguously determine the binding modes of EDO in DgAOR. Interestingly, the structure of the Mo-EDO complex resembles in some way that proposed by Bray and Lowe for the paramagnetic "very rapid" intermediate of the reaction (Figure 1e).…”

Section: Discussionmentioning

confidence: 99%

Kinetic, Structural, and EPR Studies Reveal That Aldehyde Oxidoreductase from Desulfovibrio gigas Does Not Need a Sulfido Ligand for Catalysis and Give Evidence for a Direct Mo−C Interaction in a Biological System

et al. 2009

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Aldehyde oxidoreductase from Desulfovibrio gigas (DgAOR) is a member of the xanthine oxidase (XO) family of mononuclear Mo-enzymes that catalyzes the oxidation of aldehydes to carboxylic acids. The molybdenum site in the enzymes of the XO family shows a distorted square pyramidal geometry in which two ligands, a hydroxyl/water molecule (the catalytic labile site) and a sulfido ligand, have been shown to be essential for catalysis. We report here steady-state kinetic studies of DgAOR with the inhibitors cyanide, ethylene glycol, glycerol, and arsenite, together with crystallographic and EPR studies of the enzyme after reaction with the two alcohols. In contrast to what has been observed in other members of the XO family, cyanide, ethylene glycol, and glycerol are reversible inhibitors of DgAOR. Kinetic data with both cyanide and samples prepared from single crystals confirm that DgAOR does not need a sulfido ligand for catalysis and confirm the absence of this ligand in the coordination sphere of the molybdenum atom in the active enzyme. Addition of ethylene glycol and glycerol to dithionite-reduced DgAOR yields rhombic Mo(V) EPR signals, suggesting that the nearly square pyramidal coordination of the active enzyme is distorted upon alcohol inhibition. This is in agreement with the X-ray structure of the ethylene glycol and glycerolinhibited enzyme, where the catalytically labile OH/OH 2 ligand is lost and both alcohols coordinate the Mo site in a η 2 fashion. The two adducts present a direct interaction between the molybdenum and one of the carbon atoms of the alcohol moiety, which constitutes the first structural evidence for such a bond in a biological system.

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Section: Discussionmentioning

confidence: 99%

Kinetic, Structural, and EPR Studies Reveal That Aldehyde Oxidoreductase from Desulfovibrio gigas Does Not Need a Sulfido Ligand for Catalysis and Give Evidence for a Direct Mo−C Interaction in a Biological System

et al. 2009

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“…151 Agostic interactions in metal alkyl complexes are a case of 3-centre-2-electron bonds, and are related to important chemical transformations including insertion reactions related to polymerization catalysis or C-H activation. 152 Computational studies of agostic interactions in early and late transition metal complexes have been reported in the last years. [153][154] Characterization of such interactions may in some cases, particularly with α-agostic interactions, require NMR and theoretical analysis, in addition to X-ray diffraction data, since the latter technique may not be precise enough to reveal the activation of the bridging C-H bond.…”

Section: Scheme 29 Examples Of Methyl Bridged Homobimetallic Complexementioning

confidence: 99%

Methyl Complexes of the Transition Metals

Campos

López‐Serrano

Peloso

et al. 2016

Chemistry A European J

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Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, i.e. based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition metal complexes containing M-CH3 fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last 5 years. After a panoramic overview on M-CH3 compounds of groups 3 to 11 which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity.

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“…A feature of high oxidation state M=CHR complexes of the type shown in Figure 1 is that they form two isomers, a syn alkylidene isomer in which the R group points toward the oxo or imido ligand and an anti alkylidene isomer in which the R group points away from the oxo or imido ligand ( Figure 4); the CHα bond of the syn isomer is engaged in an "agostic" interaction 44 …”

Section: Syn and Anti Isomers And Alternating Ab Copolymersmentioning

confidence: 99%

Metathesis by Molybdenum and Tungsten Catalysts

Schrock¹

2015

Chimia

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IntroductionIn the early 1970's organometallic, organic, and polymer chemists were attracted to a new type of catalytic reaction called Olefin Disproportionation by Banks and Bailey, who published results in the open literature in 1964; 1 the reaction also was reported by Natta in 1964 2 and had appeared in patents filed at duPont 3 and Standard Oil 4 several years earlier. The basic process, which was shown to be catalyzed by various molybdenum or tungsten, and later rhenium, compounds of unknown type, resulted in an "exchange" of alkylidene (usually CHR, where R = H or alkyl) units in alkenes with one another, e.g., propylene could be equilibrated with ethylene and cis and trans-2-butenes (equation 1) or norbornene could be polymerized through a "ringopening" of its double bonds (equation 2). Although several mechanisms were proposed, the correct one appeared first in a publication by Hérrison and Chauvin in 1971, 5 namely the reversible reaction between a metal complex that contains a metal-carbon double bond (M=CHR) and a C=C bond to yield an intermediate that contains a metallacyclobutane (MC 3 ) ring. A related reaction that involves alkynes was discovered to be catalyzed by a heterogeneous catalyst in 1968 6 and a homogeneous catalyst in 1972. 7 This "alkyne disproportionation" reaction was proposed to consist of a reversible reaction between a M≡CR bond (R≠H) and a C≡C bond to give all possible alkynes via a metallacyclobutadiene intermediate. 8 Neither process resulted in any positional isomerization of the C=C or C≡C bonds. Although Fischer-type "low oxidation state" carbene 9 complexes were known at the time, and the synthesis of carbyne complexes soon followed, 10 they did not promote what came to be known as alkene metathesis 11 and alkyne metathesis, respectively, in the rapid manner often observed for what are now known as "classical" alkene and alkyne metathesis catalysts. However, experiments first published in 1976 showed that polymerization of cyclic olefins, metathesis of linear olefins, enyne metathesis, and polymerization of acetylenes could be initiated by certain Fischer-type carbene complexes, although new alkylidenes of the same type as the initiator were not observed. 12 Classical metathesis catalysts often are formed from metal oxides on silica or alumina 13 or in solution from a variety of metal complexes. An alkylating agent is often required, but simply exposing the supported metal oxide to alkenes or alkynes at high temperatures will generate the catalyst through some unknown mechanism of mechanisms.

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Agostic interactions in transition metal compounds

Abstract: The impact of agostic interactions (i.e., 3-center-2-electron M-H-C bonds) on the structures and reactivity of organotransition metal compounds is reviewed.

Cited by 1,024 publications

References 89 publications

Kinetic, Structural, and EPR Studies Reveal That Aldehyde Oxidoreductase from Desulfovibrio gigas Does Not Need a Sulfido Ligand for Catalysis and Give Evidence for a Direct Mo−C Interaction in a Biological System

Kinetic, Structural, and EPR Studies Reveal That Aldehyde Oxidoreductase from Desulfovibrio gigas Does Not Need a Sulfido Ligand for Catalysis and Give Evidence for a Direct Mo−C Interaction in a Biological System

Methyl Complexes of the Transition Metals

Metathesis by Molybdenum and Tungsten Catalysts

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