Alkane Complexation

Crabtree, Robert H.

doi:10.1002/9781119379256.ch26

Cited by 3 publications

(2 citation statements)

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“…It follows that the equilibrium between a σ-alkane complex and its alkyl/hydride tautomer will be influenced by changing the ancillary ligands. The stabilities of known σ-alkane complexes, which feature a variety of ancillary ligands, support this view, as do computational studies of methane addition and elimination from a series of rhenium complexes. − …”

Section: Introductionmentioning

confidence: 84%

Steric and Electronic Analyses of Ligand Effects on the Stability of σ-Methane Coordination Complexes: A DFT Study

et al. 2022

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Developing efficient catalysts for methane functionalization is a longstanding goal in inorganic chemistry. Here, we present theoretical calculations to support efforts to synthesize σmethane complexes that can be studied by NMR spectroscopy. The systems studied are osmium complexes of stoichiometry (C 5 R 5 )Os(diphosphine)(CH 3 )(H) + : when both cyclopentadienyl and diphosphine are relatively strong electron donors, the methyl/ hydride structure is in rapid equilibrium with its σ-methane tautomer at low temperatures, as shown experimentally some years ago. Here, using density functional theory, we examine how changing the steric and electronic properties of the ancillary cyclopentadienyl and diphosphine ligands affects the relative energies of the two tautomers, with the goal of identifying a ligand set for which the σ-methane structure, rather than the methyl/hydride form, is the predominant species in equilibrium. We also examine how varying the ancillary ligands affects the barrier for methane dissociation. The calculations suggest that osmium complexes bearing weakly donating and sterically undemanding ligands stabilize the σ-methane structure both relative to its methyl/hydride tautomer and toward dissociation of the methane ligand. More specifically, osmium σ-methane complexes of fluorinated diphosphines (CF 3 ) 2 PCH 2 P(CF 3 ) 2 and (CF 3 ) 2 PCF 2 P(CF 3 ) 2 are predicted to be stable enough to be observed by variable-temperature NMR spectroscopy.

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Section: Introductionmentioning

confidence: 84%

Steric and Electronic Analyses of Ligand Effects on the Stability of σ-Methane Coordination Complexes: A DFT Study

et al. 2022

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“…One mechanism by which alkane C─H bonds can be activated by a transition metal complex involves, as a first step, coordination of the alkane to the metal center. Such compounds, which are known as σ-alkane complexes, were initially studied by matrix isolation methods (22,23) and have subsequently been studied by a variety of other techniques (24)(25)(26)(27)(28)(29)(30)(31). Despite these advances, there is little detailed experimental information about exactly how the alkane binds to the metal, especially in solution.…”

Section: Introductionmentioning

confidence: 99%

An osmium(II) methane complex: Elucidation of the methane coordination mode

et al. 2023

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The activation of inert C─H bonds by transition metals is of considerable industrial and academic interest, but important gaps remain in our understanding of this reaction. We report the first experimental determination of the structure of the simplest hydrocarbon, methane, when bound as a ligand to a homogenous transition metal species. We find that methane binds to the metal center in this system through a single M···H-C bridge; changes in the 1 J CH coupling constants indicate clearly that the structure of the methane ligand is significantly perturbed relative to the free molecule. These results are relevant to the development of better C─H functionalization catalysts.

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