Alkane dehydrogenation by iridium complexes

Crabtree, Robert H.; Mellea, Michelle F.; Mihelcic, Jean M.; Quirk, Jennifer M.

doi:10.1021/ja00365a021

Cited by 210 publications

(77 citation statements)

References 1 publication

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“…This dissociation is consequently quite different from the dissociation of NiH2, where the H-H bond strength can grow continuously all the way to dissociation. The splitting of a C-H bond in methane is expected to be an intermediate case with a much lower barrier than in the case of breaking the C-C bond in ethane, which also agrees with recent experimental evidence [20].…”

Section: A Nih2 and Ni(ch3)2supporting

confidence: 90%

Contracted CI calculations of models for catalytic reactions involving transition metals

Blomberg

Brandemark

Pettersson

et al. 1983

Int J of Quantum Chemistry

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Theoretical models for reductive elimination from transition metal containing molecules have been studied using large scale contracted CI calculations. Four different models were treated, namely, NiH2, PdH2, Ni(CH3)2, and Pd(H20)zHz. in order to study the effects of adding ligands, exchanging hydrogens with methyl groups, and comparing nickel and palladium. The most interesting result already appeared for the simplest system NiH2. A closed-shell-type ' A 1 state with a small bond angle of only 57O is bound compared to Ni and H2 with only a very small barrier for formation. The bond distance is short, shorter than in NiH, and the d orbitals are strongly involved in the binding. The hydrogen atoms bind both to nickel and to each other. With methyl groups rather than hydrogens, this double sided bonding situation is destroyed and Ni(CH3)Z has a negative binding energy with the carbon bonds pointing towards nickel. For PdH2 only a weakly bound complex between an essentially unchanged H Z and Pd was found. ThePond distance is very long. Adding H 2 0 ligands to Pd shortens the bond distance and significantly opens up the bond angle. The methods used in the investigation and the chemical implications of the results are discussed.

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Section: A Nih2 and Ni(ch3)2supporting

confidence: 90%

Contracted CI calculations of models for catalytic reactions involving transition metals

Blomberg

Brandemark

Pettersson

et al. 1983

Int J of Quantum Chemistry

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“…[60] DLS is able to detect particles of 1t o% 250 nm, even at concentrations in the nM range. [10,21,24,61,62] Although its main task is to show the presenceo ra bsence of scattering particles, this technique also provides information about the average size of the particles, assuming single scattering conditions, which is generally the case in catalytic reactions. Another advantage is that DLS is as imple and fast technique:i tt akes abouta sl ong as recording an NMR spectrum.…”

Section: Design Of the Protocolmentioning

confidence: 99%

Pd‐Catalyzed Z‐Selective Semihydrogenation of Alkynes: Determining the Type of Active Species

et al. 2015

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A protocol was developed to distinguish between well‐defined molecular and nanoparticle‐based catalysts for the Pd‐catalyzed semihydrogenation reaction of alkynes to Z‐alkenes. The protocol applies quantitative partial poisoning and dynamic light scattering methods, which allow the institution of additional validation experiments. For the quantitative partial poisoning method, tetramethylthiourea (TMTU) was developed as an alternative for the standard poison ligand CS2, and was found to be superior in its applicability. The protocol and the TMTU poison ligand were validated using the well‐described [PdII(phenanthroline)]‐catalyzed copolymerization of styrene and CO, confirming that this system is clearly operating as a well‐defined molecular catalyst. The protocol was subsequently applied to three catalyst systems used for the semihydrogenation of alkynes. The first was proposed to be a molecular [Pd0(IMes)] catalyst that uses molecular hydrogen, but the data gathered for this system, following the new protocol, clearly showed that nanoparticles (NPs) are catalytically active. The second catalyst system studied was an N‐heterocyclic carbene (NHC) Pd system for transfer semihydrogenation using formic acid as the hydrogen source, which was proposed to operate through an in situ generated molecular [Pd0(IMes)] catalyst in earlier studies. The investigations showed that only a small fraction of the Pd added becomes active in the catalytic reaction and that NPs are formed. However, despite these findings, a clear distinction between catalytic activity of NPs versus a molecular catalyst could not be made. The third investigated system is based on a [PdII(IMes)(η3‐allyl)Cl] precatalyst with additive ligands. The combined data gathered for this system are multi‐interpretable, but suggest that a partially deactivated molecular catalyst dominates in this reaction.

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“…The major problem of the dehydrogenation reaction is the very unfavourable thermodynamics [3,4]. Strategies to overcome this difficulty include: (i) the use of hydrogen acceptors [5], (ii) photochemical stimulation via UV-Vis irradiation [6], (iii) continuous removal of dihydrogen from the catalytic phase [7].…”

Section: Introductionmentioning

confidence: 99%

Direct in situ synthesis of cationic N-heterocyclic carbene iridium and rhodium complexes from neat ionic liquid: Application in catalytic dehydrogenation of cyclooctadiene

Hintermair

Gutel

Slawin

et al. 2008

Journal of Organometallic Chemistry

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Alkane dehydrogenation by iridium complexes

Cited by 210 publications

References 1 publication

Contracted CI calculations of models for catalytic reactions involving transition metals

Contracted CI calculations of models for catalytic reactions involving transition metals

Pd‐Catalyzed Z‐Selective Semihydrogenation of Alkynes: Determining the Type of Active Species

Direct in situ synthesis of cationic N-heterocyclic carbene iridium and rhodium complexes from neat ionic liquid: Application in catalytic dehydrogenation of cyclooctadiene

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