The hydride route to the preparation of dinitrogen complexes

Ballmann, Joachim; Munhá, Rui F.; Fryzuk, Michael D.

doi:10.1039/b922853e

Cited by 122 publications

(121 citation statements)

References 163 publications

(202 reference statements)

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“…1 H NMR (C 6 D 6 , 300 MHz, 298 K): δ 14.70 (t, 2 J HP = 3.2 Hz, 4H, Ta(μ-H) 4 Ta), 7.57 (m, 4H, ArH), 7.20 (bs, 4H, ArH), 7.13 (m, 6H, ArH), 6.99 (s, 4H, ArH), 6.93 (s, 2H, ArH), 6.60 ( 2 bd, J HH = 8. 7 …”

Section: ■ Experimental Sectionmentioning

confidence: 97%

Hydrogenolysis of Tantalum Hydrocarbyl Complexes: Intermediates on the Road to a Dinuclear Tantalum Tetrahydride Derivative

2015

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The synthesis, characterization, and reactivity with H 2 of a series of tantalum hydrocarbyl complexes are reported. The reaction of [NPN*]TaMe 3 (4, where NPN* = PhP(2-(Nmesityl)-5-Me-C 6 H 3 ) 2 ) with dihydrogen (H 2 , 4 atm) results in the formation of the dinuclear tetrahydride ([NPN*]Ta) 2 (μ-H) 4 (5), without the observation of intermediates. The preparations of two alkyne benzyl complexes of the formula [NPN*]Ta(alkyne)-(CH 2 Ph) (where alkyne = BTA = bis(trimethylsilyl)acetylene ( 6), 3-hexyne ( 7)) are reported starting from the respective chloroalkyne complexes [NPN*]Ta(alkyne)Cl, by addition of benzylpotassium. Hydrogenation of these two alkyne benzyl complexes ultimately results in the formation of the same dinuclear tetrahydride 5; however, using lower pressures of H 2 and shorter reaction times results in the isolation of an intermediate in each case. Hydrogenation of 6 generates the alkene hydride complex [NPN*]Ta(trans-1,2-C 2 H 2 (SiMe 3 ) 2 )H (8); addition of H 2 to 7 gives [NPN*]Ta(1-hexene)H ( 9), in which the 3-hexyne moiety has been partially hydrogenated and isomerized to the 1-hexene regioisomer. Both of these alkene hydride complexes can be converted to the dinuclear tetrahydride complex 5 by addition of H 2 . A mechanism is proposed for the formation of the intermediates that involves hydrogenolysis of the alkyne moiety prior to the benzyl ligand; the formation of the trans-alkene units is suggested to be a result of a zwitterionic alkylidene intermediate that allows free rotation of a C−C single bond.

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Section: ■ Experimental Sectionmentioning

confidence: 97%

Hydrogenolysis of Tantalum Hydrocarbyl Complexes: Intermediates on the Road to a Dinuclear Tantalum Tetrahydride Derivative

2015

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“…[96,[106][107][108] The dinitrogen compounds are relatively unstable in contrast to its lighter group 8 homologues [109] and their formation did not proceed via reactions with N 2 , but rather as a result of N···N coupling of osmium nitrides [104] , dissociation of azides [97] or the diazotization of an osmium ammine species by nitrous acid. [94,101] Consequently, there is hardly any system known that is capable of binding a more extended series of intermediate species to one scaffold.…”

Section: Osmiummentioning

confidence: 98%

Late Metal Scaffolds that Activate Both, Dinitrogen and Reduced Dinitrogen Species N_xH_y

Köthe

Limberg

2014

Zeitschrift anorg allge chemie

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Abstract. In the context of biological nitrogen fixation, the question whether molybdenum or iron is the site for substrate binding and reduction is still discussed controversially. Therefore, the development of relevant model compounds containing early or late transition metals is essential in understanding the nature and behavior of intermediates bound to the FeMo-cofactor. Ligated early transition metal atoms are known to strongly activate N 2 and mediate its cleavage, but the resulting complexes contain metal-nitrogen bonds, which often elude

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“…One model, involving protonation of one of the hydrides to form H 2 , and its replacement by N 2 , was shown to violate the turnover constraints, and was therefore rejected. In the second model, H 2 is produced by reductive elimination (re) (17)(18)(19)(20) of the two bridging hydrides of E 4 during N 2 binding (Fig. 1B and Scheme S1).…”

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On reversible H ₂ loss upon N ₂ binding to FeMo-cofactor of nitrogenase

Yang

Khadka

Lukoyanov

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Nitrogenase is activated for N 2 reduction by the accumulation of four electrons/protons on its active site FeMo-cofactor, yielding a state, designated as E 4 , which contains two iron-bridging hydrides [Fe-H-Fe]. A central puzzle of nitrogenase function is an apparently obligatory formation of one H 2 per N 2 reduced, which would "waste" two reducing equivalents and four ATP. We recently presented a draft mechanism for nitrogenase that provides an explanation for obligatory H 2 production. In this model, H 2 is produced by reductive elimination of the two bridging hydrides of E 4 during N 2 binding. This process releases H 2 , yielding N 2 bound to FeMocofactor that is doubly reduced relative to the resting redox level, and thereby is activated to promptly generate bound diazene (HN=NH). This mechanism predicts that during turnover under D 2 /N 2 , the reverse reaction of D 2 with the N 2 -bound product of reductive elimination would generate dideutero-E 4 [E 4 to two ammonia (NH 3 ) molecules-is primarily catalyzed by the Mo-dependent nitrogenase. This enzyme comprises an electron-delivery Fe protein and MoFe protein, which contains the active site FeMo-cofactor ( Fig. 1A) (1, 2). The nitrogenase catalyzed reaction is generally thought to have the limiting stoichiometry shown in Eq. 1 (3),This equation conveys one of the most puzzling aspects of nitrogenase function, for it incorporates an obligatory formation of one mole of H 2 per mole of N 2 reduced, which requires the waste of two reducing equivalents and four ATP (1, 2). A kinetic framework for nitrogenase function that incorporates the stoichiometry of Eq. 1 is provided by the Lowe-Thorneley model (1, 2, 4), which describes transformations among catalytic intermediates (denoted E n ), where n is the number of electrons and protons (n = 0-8) delivered to MoFe protein. N 2 reduction requires activation of the MoFe protein to the E 4 state in which FeMo-cofactor has accumulated four electrons and four protons stored as two hydrides that bridge Fe atoms [Fe-H-Fe] and two protons presumably bound to sulfides of FeMo-cofactor (Fig. 1B) (5-8). The binding of N 2 to the E 4 state is coupled to the stoichiometric evolution of one H 2 per N 2 reduced.We recently presented a draft mechanism for N 2 reduction by nitrogenase that incorporates a mechanistic explanation for obligatory, reversible H 2 loss upon N 2 binding (5). We considered two models for this process, both built on our characterization of the key E 4 state, and tested them against the numerous constraints imposed by turnover under N 2 plus D 2 or T 2 (5, 9-16). In particular, these constraints include the key findings that during catalytic reduction of N 2 (see Scheme S1), a molecule of D 2 or T 2 will reduce two protons to form two HD or HT without D + /T + exchange with solvent, even though neither D 2 nor T 2 by themselves reacts with nitrogenase during turnover under Ar (5). One model, involving protonation of one of the hydrides to form H 2 , and its replacement by N 2 , was shown to violate ...

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The hydride route to the preparation of dinitrogen complexes

Cited by 122 publications

References 163 publications

Hydrogenolysis of Tantalum Hydrocarbyl Complexes: Intermediates on the Road to a Dinuclear Tantalum Tetrahydride Derivative

Hydrogenolysis of Tantalum Hydrocarbyl Complexes: Intermediates on the Road to a Dinuclear Tantalum Tetrahydride Derivative

Late Metal Scaffolds that Activate Both, Dinitrogen and Reduced Dinitrogen Species N_xH_y

On reversible H ₂ loss upon N ₂ binding to FeMo-cofactor of nitrogenase

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The hydride route to the preparation of dinitrogen complexes

Cited by 122 publications

References 163 publications

Hydrogenolysis of Tantalum Hydrocarbyl Complexes: Intermediates on the Road to a Dinuclear Tantalum Tetrahydride Derivative

Hydrogenolysis of Tantalum Hydrocarbyl Complexes: Intermediates on the Road to a Dinuclear Tantalum Tetrahydride Derivative

Late Metal Scaffolds that Activate Both, Dinitrogen and Reduced Dinitrogen Species NxHy

On reversible H 2 loss upon N 2 binding to FeMo-cofactor of nitrogenase

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Late Metal Scaffolds that Activate Both, Dinitrogen and Reduced Dinitrogen Species N_xH_y

On reversible H ₂ loss upon N ₂ binding to FeMo-cofactor of nitrogenase