Solid-state synthesis and characterization of σ-alkane complexes, [Rh(L2)(η22-C7H12)][BArF 4] (L2 = bidentate chelating phosphine)

Sebastian D. Pike, F. Mark Chadwick, Nicholas H. Rees, Mark P. Scott, Andrew S. Weller, Tobias Kraemer, Stuart A. Macgregor

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Abstract

The use of solid/gas and single-crystal to single-crystal synthetic routes is reported for the synthesis and characterization of a number of σ-alkane complexes: [Rh(R2P(CH2)nPR2)(η22-C7H12)][BArF 4]; R = Cy, n = 2; R = iPr, n = 2,3; Ar = 3,5-C6H3(CF3)2. These norbornane adducts are formed by simple hydrogenation of the corresponding norbornadiene precursor in the solid state. For R = Cy (n = 2), the resulting complex is remarkably stable (months at 298 K), allowing for full characterization using single-crystal X-ray diffraction. The solid-state structure shows no disorder, and the structural metrics can be accurately determined, while the 1H chemical shifts of the Rh⋯H-C motif can be determined using solid-state NMR spectroscopy. DFT calculations show that the bonding between the metal fragment and the alkane can be best characterized as a three-center, two-electron interaction, of which σCH → Rh donation is the major component. The other alkane complexes exhibit solid-state 31P NMR data consistent with their formation, but they are now much less persistent at 298 K and ultimately give the corresponding zwitterions in which [BArF 4]- coordinates and NBA is lost. The solid-state structures, as determined by X-ray crystallography, for all these [BArF 4]- adducts are reported. DFT calculations suggest that the molecular zwitterions within these structures are all significantly more stable than their corresponding σ-alkane cations, suggesting that the solid-state motif has a strong influence on their observed relative stabilities.

Original languageEnglish
Pages (from-to)820-833
Number of pages14
JournalJournal of the American Chemical Society
Volume137
Issue number2
DOIs
Publication statusPublished - 21 Jan 2015

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

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