Preparation and characterization of two unsubstituted hydrazido(1-) complexes, W(.eta.5-C5Me5)Me4(.eta.2-NHNH2) and [W(.eta.5-C5Me5)Me3(.eta.2NHNH2)]+[SO3CF3]-

Schrock, Richard R.; Liu, A. H.; O’Regan, Marie B.; Finch, William C.; Payack, Joseph F.

doi:10.1021/ic00293a027

Cited by 44 publications

(39 citation statements)

References 2 publications

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“…The higher energy process interconverts H B and H C and is thought to occur through the h 1 -NHNH 2 geometry (Scheme 6, R H, M {W(Cp*)Me 4 }, DG = 53 kJ mol À1 ). [43] A similar site-exchange mechanism was reported for [MoCp(NMeNMe 2 )I(NO)] (R Me, M {MoCpI(NO)}, DG = 59 kJ mol À1 , Scheme 6). [44] If similar fluxional processes take place for [Mo 2 Cp 2 -(m-SMe) 3 (m-N 2 H 2 Ph)], species A and B would be related by a proton 1,2-shift, while C would arise from a MoÀNÀNÀMo ring opening analogous to the one depicted in Scheme 6.…”

Section: Introductionsupporting

confidence: 60%

“…Interconversion of protons [43] or of alkyl groups [44] on the nitrogen atoms of mononuclear side-on bonded hydrazido(1 À ) complexes has been reported. In [W(Cp*)Me 4 (h 2 -NHNH 2 )], two different fluxional processes take place.…”

Section: Introductionmentioning

confidence: 99%

“…In [W(Cp*)Me 4 (h 2 -NHNH 2 )], two different fluxional processes take place. [43] The lower energy one consists in a proton shift from one N atom to the other. The higher energy process interconverts H B and H C and is thought to occur through the h 1 -NHNH 2 geometry (Scheme 6, R H, M {W(Cp*)Me 4 }, DG = 53 kJ mol À1 ).…”

Section: Introductionmentioning

confidence: 99%

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Electrochemical Cleavage of NdN Bonds at a Mo2(μ-SMe)3 Site Relevant to the Biological Reduction of Dinitrogen at a Bimetallic Sulfur Centre

et al. 2002

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Section: Introductionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

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Electrochemical Cleavage of NdN Bonds at a Mo2(μ-SMe)3 Site Relevant to the Biological Reduction of Dinitrogen at a Bimetallic Sulfur Centre

et al. 2002

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“…Although this information can be interpreted in a variety of ways, one reasonable interpretation is that an N 2 reduction intermediate binds at the same place and in the same way as determined here for propargyl-OH and propargyl-NH 2 . In this context there is ample evidence in the chemical literature for metal-hydrazine complexes having the same configuration as the metallacyclopropane ring structure proposed for alkyne reduction intermediates (36). Future work will focus on testing whether or not N 2 or its reduction intermediates can be trapped and characterized using the genetic, biochemical, and biophysical approaches described for characterizing alkyne reduction intermediates.…”

Section: Appearance Of a Propargyl-nh 2 Reductionmentioning

confidence: 99%

Localization of a Catalytic Intermediate Bound to the FeMo-cofactor of Nitrogenase

Igarashi

Santos

Niehaus

et al. 2004

Journal of Biological Chemistry

104

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Nitrogenase catalyzes the biological reduction of N 2 to ammonia (nitrogen fixation) as well as the reduction of a number of alternative substrates, including acetylene (HCϵCH) to ethylene (H 2 C‫؍‬CH 2 ). It is known that the metallocluster FeMo-cofactor located within the nitrogenase MoFe protein component provides the site of substrate reduction, but the exact site where substrates bind and are reduced on the FeMo-cofactor remains unknown. We have recently shown that the ␣-70 residue of the MoFe protein plays a significant role in defining substrate access to the active site; ␣-70 approaches one face of the FeMo-cofactor, and when valine is substituted by alanine at this position, the substituted nitrogenase is able to accommodate a reduction of the larger alkyne propargyl alcohol (HCϵCCH 2 OH, propargyl-OH). During this reduction, a substrate-derived intermediate can be trapped on the FeMo-cofactor resulting in an S ‫؍‬ 1/2 spin system with a novel electron paramagnetic resonance spectrum. In the present work, trapping of the propargyl-OH-derived or propargyl amine (HCϵCCH 2 NH 2 , propargyl-NH 2 )-derived intermediates is shown to be dependent on pH and the presence of histidine at position ␣-195. It is concluded that these catalytic intermediates are stabilized and thereby trapped by H-bonding interactions between either the -OH group or the -NH 3 ؉ group and the imidazole ⑀-NH of ␣-195 His . Thus, for the first time it is possible to establish the location of a bound substrate-derived intermediate on the FeMo-cofactor. Refinement of the binding mode and site was accomplished by the use of density functional and force field calculations pointing to an 2 coordination at Fe-6 of the FeMo-cofactor.Nitrogenase is comprised of two component proteins, called the iron protein and the MoFe protein, which together catalyze the nucleotide-dependent reduction of N 2 to ammonia (Equation 1). N 2 ϩ 8e Ϫ ϩ 16MgATP ϩ 8H ϩ 3 2NH 3 ϩ H 2 ϩ 16MgADP ϩ 16P i (Eq. 1) During catalysis, electrons are delivered one at a time from the iron protein to the MoFe protein in a reaction coupled to the hydrolysis of 2 eq of MgATP for each equivalent of electrons transferred (1, 2). The MoFe protein contains two metalloclusters called the P-cluster [8Fe-7S] and the FeMo-cofactor [7Fe-9S-Mo-X-homocitrate], where X is proposed to be nitrogen, carbon, or oxygen (3). The P-clusters are thought to mediate electron transfer from the iron protein to the FeMo-cofactor, which in turn provides the site for substrate binding and reduction. The structure of the FeMo-cofactor has been elucidated from the solution of x-ray structures of MoFe proteins (3-7), yet where and how substrates interact with the FeMocofactor is still unknown. Different models for where substrates bind to the FeMo-cofactor have been developed; they were built on evidence from model compounds, theoretical calculations, and kinetic and biophysical studies on the wildtype (WT) 1 and genetically altered MoFe proteins (8). Some models propose binding and reduction of substrates at th...

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“…If H-atom transfer instead occurs to the a-N-atom the hydrazine adduct Mo(0)-N 2 H 4 is generated, accounting for the alternative byproduct of protonation, hydrazine. The secondary pathway has been suggested to be more prevalent in related tungsten phosphine systems that have been studied [2], and also in the Cp*MMe 3 (N 2 ) (M = Mo, W) systems discussed below [33][34][35][36][37][38][39].…”

Section: The Originally Proposed "Chatt Cycle"mentioning

confidence: 99%

Bio‐organometallic Approaches to Nitrogen Fixation Chemistry

Peters

Mehn

2006

Activation of Small Molecules

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Preparation and characterization of two unsubstituted hydrazido(1-) complexes, W(.eta.5-C5Me5)Me4(.eta.2-NHNH2) and [W(.eta.5-C5Me5)Me3(.eta.2NHNH2)]+[SO3CF3]-

Cited by 44 publications

References 2 publications

Electrochemical Cleavage of NdN Bonds at a Mo2(μ-SMe)3 Site Relevant to the Biological Reduction of Dinitrogen at a Bimetallic Sulfur Centre

Electrochemical Cleavage of NdN Bonds at a Mo2(μ-SMe)3 Site Relevant to the Biological Reduction of Dinitrogen at a Bimetallic Sulfur Centre

Localization of a Catalytic Intermediate Bound to the FeMo-cofactor of Nitrogenase

Bio‐organometallic Approaches to Nitrogen Fixation Chemistry

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