Dihydrogen/dihydride or tetrahydride? an experimental and computational investigation of pincer iridium polyhydrides

Travis J. Hebden, Karen I. Goldberg, Michael D. Heinekey, Xiawei Zhang, Thomas J. Emge, Alan S. Goldman, Karsten Krogh-Jespersen

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Abstract

The iridium pincer complexes (PCP)IrH4 (1; PCP = [ 3-1, 3-(CH2PtBu2)2C 6H3]) and (POCOP)IrH4 (2; POCOP = [κ 3-1, 3-(OPtBu2)2C6H 3]) have proven to be effective catalyst precursors for dehydrogenation of alkanes. The complex (POCOP)IrH2 has also been applied successfully as a catalyst for release of H2 from ammonia borane. Investigation of the "tetrahydride" forms of these complexes by solution NMR methods suggests their formulation as dihydrogen/dihydride species. This is in contrast to the solid state structure of 1, determined by neutron diffraction (at 100 K), which indicates a compressed tetrahydride structure with only weak H-H interactions. Complex 1 (C24H 47IrP2) crystallizes in the space group P42, tetragonal, (Z = 2) with a = 11.7006 (19) Å, c = 9.7008(27) Å, and V = 1328.1(5) Å 3. Electronic structure calculations on 1 and 2 indicate that the global minima on the potential energy surfaces in the gas phase are tetrahydride structures; however, the dihydrogen/dihydride forms are only slightly higher in energy (1-3 kcal/mol). A dihydrogen/dihydride species is calculated to be the global minimum for 2 when in solution. The barriers to interconversion between the tetrahydride and dihydrogen/dihydride species are almost negligible.

Original languageEnglish
Pages (from-to)1733-1742
Number of pages10
JournalInorganic Chemistry
Volume49
Issue number4
DOIs
Publication statusPublished - Feb 15 2010

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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    Hebden, T. J., Goldberg, K. I., Heinekey, M. D., Zhang, X., Emge, T. J., Goldman, A. S., & Krogh-Jespersen, K. (2010). Dihydrogen/dihydride or tetrahydride? an experimental and computational investigation of pincer iridium polyhydrides. Inorganic Chemistry, 49(4), 1733-1742. https://doi.org/10.1021/ic902163w