Molybdenum and Tungsten Catalysts for Hydrogenation, Hydrosilylation and Hydrolysis

Bullock, R. Morris

doi:10.1002/9783527631582.ch3

Cited by 72 publications

(66 citation statements)

References 103 publications

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“…3 These enzymes have attracted attention as proven motifs for the processing of hydrogen. 4,5 A key goal in this area is the elucidation of catalytic mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Synthetic Models for the Active Site of the [FeFe]-Hydrogenase: Catalytic Proton Reduction and the Structure of the Doubly Protonated Intermediate

et al. 2012

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This report compares biomimetic HER catalysts with and without the amine cofactor (adtNH): Fe2(adtNH)(CO)2(dppv)2 (1NH) and Fe2(pdt)(CO)2(dppv)2 (2; (adtNH)2− = (HN(CH2S)22−, pdt2− = 1,3-(CH2)3S22−). These compounds are spectroscopically, structurally, and stereodynamically very similar but exhibit very different catalytic properties. Protonation of 1NH and 2 each give three isomeric hydrides beginning with the kinetically favored terminal hydride, which converts sequentially to sym and unsym isomers of the bridging hydrides. In the case of the amine, the corresponding ammonium-hydrides are also observed. In the case of the terminal amine hydride [t-H1NH]BF4, the ammonium/amine-hydride equilibrium is sensitive to counteranions and solvent. The species [t-H1NH2](BF4)2 represents the first example of a crystallographically characterized terminal hydride produced by protonation. The NH--HFe distance of 1.88(7) Å indicates dihydrogen bonding. The bridging hydrides [µ-H1NH]+ and [µ-H2]+ reduce near −1.8 V, about 150 mV more negative than the reductions of the terminal hydride [t-H1NH]+ and [t-H2]+ at −1.65 V. Reductions of the amine hydrides [t-H1NH]+ and [t-H1NH2]2+ are irreversible. For the pdt analog, the [t-H2]+/0 couple is unaffected by weak acids (pKaMeCN 15.3) but exhibits catalysis with HBF4•Et2O, albeit with a TOF around 4 s−1 and an overpotential greater than 1 V. The voltammetry of [t-H1NH]+ is strongly affected by relatively weak acids and proceeds at 5000 s−1 with an overpotential of 0.7 V. The ammonium-hydride [t-H1NH2]2+ is a faster catalyst with an estimated TOF of 58,000 s−1 and an overpotential of 0.5 V.

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“…3 These enzymes have attracted attention as proven motifs for the processing of hydrogen. 4,5 A key goal in this area is the elucidation of catalytic mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Synthetic Models for the Active Site of the [FeFe]-Hydrogenase: Catalytic Proton Reduction and the Structure of the Doubly Protonated Intermediate

et al. 2012

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“…In this regard, the design of catalytic systems based on abundant and biocompatible metals is an important goal for the implementation and progress of green and sustainable chemistry. Hence, transition metals such as Fe, Co and Cu are ideal candidates, which meet these requirements [7][8][9][10]. As a matter of fact, these elements are among the most abundant metals in the Earth's upper crust, thus being readily accessible [11].…”

Section: Introductionmentioning

confidence: 99%

Co-based heterogeneous catalysts from well-defined α-diimine complexes: Discussing the role of nitrogen

Formenti

Ferretti

Topf

et al. 2017

Journal of Catalysis

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‡ These authors contributed equally to this work.Abstract: Ar-BIANs and related α-diimine Co complexes were wet impregnated onto Vulcan® XC 72 R carbon black powder and used as precursors for the synthesis of heterogeneous supported nanoscale catalysts by pyrolysis under argon at 800 °C. The catalytic materials feature a core-shell structure composed of metallic Co and Co oxides decorated with nitrogen-doped graphitic layers (NGr). These catalysts display high activity in the liquid phase hydrogenation of aromatic nitro compounds (110 °C, 50 bar H2) to give chemoselectively substituted aryl amines. The catalytic activity is closely related to the amount and type of nitrogen atoms in the final catalytic material, which suggests a heterolytic activation of dihydrogen.Keywords: cobalt, hydrogenation, nitro compounds, kinetic, heterolytic activation IntroductionCatalysis is a key-technology for the manufacturing of all kinds of bulk and fine chemical products. It allows for producing chemicals avoiding the formation of undesired and useless stoichiometric side products which leads to additional cost and energy consumption [1][2][3]. Many of the industrially relevant catalytic processes in the fine chemical industry are still based on expensive and rare late transition metals such as Pd, Pt, Rh, Ru and Ir [4,[1][2][3][4][5]. Although these metals exhibit very good catalytic performance for advanced organic substrates, the decreasing availability of these elements requires the development of efficient alternative metal-based catalysts [6]. In this regard, the design of catalytic systems based on abundant and biocompatible metals is an important goal for the implementation and progress of green and sustainable chemistry. Hence, transition metals such as Fe, Co and Cu are ideal candidates, which meet these requirements [7][8][9][10]. As a matter of fact, these elements are among the most abundant metals in the Earth's upper crust, thus being readily accessible [11]. Recently, heteroatom-doped carbon materials attracted major interest in the field of metal supported heterogeneous catalysts for both chemical synthesis [12][13][14] and/or energy-relevant transformations [15,16]. Indeed, doping graphene with heteroatoms such as N, B, P, or S leads to a radical modification of the electronic properties of both the support and the supported metal [17][18][19]. Consequently, it is possible to modify the activity and adjust the selectivity of the final catalytic material towards the desired transformation. Among the various dopants, nitrogen attracted most interest [15,[20][21][22]. and applications of transition metal/N-doped graphene (NGr) based catalytic systems ranges from oxygen reduction reactions (ORR) [23][24][25][26], hydrogen evolving reactions (HER) [27,28], photocatalysis [29,30], oxidation [31][32][33][34][35][36][37][38], and reduction [39][40][41][42][43][44] reactions of organic

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“…1 There is growing interest in developing catalysts for bond forming/cleavage reactions based on earth abundant mid-to-late first-row transition metals, a goal that presents a unique set of challenges. 2 First-row transition metal catalysts that can circumvent undesirable one electron processes in favor of concerted two electron reaction steps present one plausible design criterion. 3 …”

Section: Introductionmentioning

confidence: 99%

Heterolytic H₂ Cleavage and Catalytic Hydrogenation by an Iron Metallaboratrane

et al. 2013

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Reversible, heterolytic addition of H2 across an iron-boron bond in a ferraboratrane with formal hydride transfer to the boron gives iron-borohydrido-hydride complexes. These compounds catalyze the hydrogenation of alkenes and alkynes to the respective alkanes. Notably, the boron is capable of acting as a shuttle for hydride transfer to substrates. The results are interesting in the context of heterolytic substrate addition across metal-boron bonds in metallaboratranes and related systems, as well as metal-ligand bifunctional catalysis.

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Molybdenum and Tungsten Catalysts for Hydrogenation, Hydrosilylation and Hydrolysis

Cited by 72 publications

References 103 publications

Synthetic Models for the Active Site of the [FeFe]-Hydrogenase: Catalytic Proton Reduction and the Structure of the Doubly Protonated Intermediate

Synthetic Models for the Active Site of the [FeFe]-Hydrogenase: Catalytic Proton Reduction and the Structure of the Doubly Protonated Intermediate

Co-based heterogeneous catalysts from well-defined α-diimine complexes: Discussing the role of nitrogen

Heterolytic H₂ Cleavage and Catalytic Hydrogenation by an Iron Metallaboratrane

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Molybdenum and Tungsten Catalysts for Hydrogenation, Hydrosilylation and Hydrolysis

Cited by 72 publications

References 103 publications

Synthetic Models for the Active Site of the [FeFe]-Hydrogenase: Catalytic Proton Reduction and the Structure of the Doubly Protonated Intermediate

Synthetic Models for the Active Site of the [FeFe]-Hydrogenase: Catalytic Proton Reduction and the Structure of the Doubly Protonated Intermediate

Co-based heterogeneous catalysts from well-defined α-diimine complexes: Discussing the role of nitrogen

Heterolytic H2 Cleavage and Catalytic Hydrogenation by an Iron Metallaboratrane

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Heterolytic H₂ Cleavage and Catalytic Hydrogenation by an Iron Metallaboratrane