Spectroscopic characterization of alumina-supported bis(allyl)iridium complexes

Site-isolation, reactivity, and decomposition studies

Ryan Trovitch, Neng Guo, Michael T. Janicke, Hongbo Li, Christopher L. Marshall, Jeffrey T. Miller, Alfred P. Sattelberger, Kevin D. John, R. Thomas Baker

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

The covalent attachment of tris(allyl)iridium to partially dehydroxylated γ-alumina is found to proceed via surface hdroxyl group protonation of one allyl ligand to form an immobilized bis(allyl)iridium moiety, (=AIO)lr(allyl)2, as characterized by CP-MAS 13C NMR, inductively coupled plasma-mass spectrometry, and lr L3 edge X-ray absorption spectroscopy. Extended X-ray absorption fine-structure (EXAFS) measurements taken on unsupported lr(allyl)3 and several associated tertiary phosphine addition complexes suggest that the η3-allyl ligands generally account for an Ir-C coordination number of 2 rather than 3, with an average Ir-C distance of 2.16 Å. Using this knowledge, combined EXAFS and X-ray absorption near-edge structure studies reveal that a small amount of Iro is also formed upon reaction of lr(allyl)3 with the surface. It was found that the addition of either 2,6-dimethylphenyl isocyanide or carbon monoxide to the supported complex allows spectroscopic identification of the supported bis(allyl)iridium complexes, (=AIO)lr(allyl)2(CNAr) [Ar=2,6-(CH3)2C6H4] and (=AIO)lr(allyl)2(CO)2, respectively. Although samples of the supported bis(allyl)iridium complex are active for the dehydrogenation of cyclohexane to benzene at temperatures between 180 and 220 °C, in situ temperature-programmed reaction XAFS and continuous-flow reactor studies suggest that Iro nanoparticles, rather than a well-defined lr3+ complex, are responsible for the observed activity.

Original languageEnglish (US)
Pages (from-to)2247-2258
Number of pages12
JournalInorganic Chemistry
Volume49
Issue number5
DOIs
StatePublished - Mar 1 2010
Externally publishedYes

Fingerprint

Iridium
Aluminum Oxide
iridium
isolation
X ray absorption
reactivity
aluminum oxides
Decomposition
decomposition
phosphine
Carbon Monoxide
x rays
fine structure
Ligands
Inductively coupled plasma mass spectrometry
ligands
X ray absorption spectroscopy
inductively coupled plasma mass spectrometry
Protonation
Dehydrogenation

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Spectroscopic characterization of alumina-supported bis(allyl)iridium complexes : Site-isolation, reactivity, and decomposition studies. / Trovitch, Ryan; Guo, Neng; Janicke, Michael T.; Li, Hongbo; Marshall, Christopher L.; Miller, Jeffrey T.; Sattelberger, Alfred P.; John, Kevin D.; Thomas Baker, R.

In: Inorganic Chemistry, Vol. 49, No. 5, 01.03.2010, p. 2247-2258.

Research output: Contribution to journalArticle

Trovitch, R, Guo, N, Janicke, MT, Li, H, Marshall, CL, Miller, JT, Sattelberger, AP, John, KD & Thomas Baker, R 2010, 'Spectroscopic characterization of alumina-supported bis(allyl)iridium complexes: Site-isolation, reactivity, and decomposition studies', Inorganic Chemistry, vol. 49, no. 5, pp. 2247-2258. https://doi.org/10.1021/ic9021036
Trovitch, Ryan ; Guo, Neng ; Janicke, Michael T. ; Li, Hongbo ; Marshall, Christopher L. ; Miller, Jeffrey T. ; Sattelberger, Alfred P. ; John, Kevin D. ; Thomas Baker, R. / Spectroscopic characterization of alumina-supported bis(allyl)iridium complexes : Site-isolation, reactivity, and decomposition studies. In: Inorganic Chemistry. 2010 ; Vol. 49, No. 5. pp. 2247-2258.
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AU - Li, Hongbo

AU - Marshall, Christopher L.

AU - Miller, Jeffrey T.

AU - Sattelberger, Alfred P.

AU - John, Kevin D.

AU - Thomas Baker, R.

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AB - The covalent attachment of tris(allyl)iridium to partially dehydroxylated γ-alumina is found to proceed via surface hdroxyl group protonation of one allyl ligand to form an immobilized bis(allyl)iridium moiety, (=AIO)lr(allyl)2, as characterized by CP-MAS 13C NMR, inductively coupled plasma-mass spectrometry, and lr L3 edge X-ray absorption spectroscopy. Extended X-ray absorption fine-structure (EXAFS) measurements taken on unsupported lr(allyl)3 and several associated tertiary phosphine addition complexes suggest that the η3-allyl ligands generally account for an Ir-C coordination number of 2 rather than 3, with an average Ir-C distance of 2.16 Å. Using this knowledge, combined EXAFS and X-ray absorption near-edge structure studies reveal that a small amount of Iro is also formed upon reaction of lr(allyl)3 with the surface. It was found that the addition of either 2,6-dimethylphenyl isocyanide or carbon monoxide to the supported complex allows spectroscopic identification of the supported bis(allyl)iridium complexes, (=AIO)lr(allyl)2(CNAr) [Ar=2,6-(CH3)2C6H4] and (=AIO)lr(allyl)2(CO)2, respectively. Although samples of the supported bis(allyl)iridium complex are active for the dehydrogenation of cyclohexane to benzene at temperatures between 180 and 220 °C, in situ temperature-programmed reaction XAFS and continuous-flow reactor studies suggest that Iro nanoparticles, rather than a well-defined lr3+ complex, are responsible for the observed activity.

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