Cationic Tris N-Heterocyclic Carbene Rhodium Carbonyl Complexes: Molecular Structures and Solution NMR Studies

Suzanne Burling, Susie Douglas, Mary F Mahon, Devendrababu Nama, Paul S Pregosin, Michael K Whittlesey

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

The cationic N-heterocyclic carbene (NHC) Rh complexes [Rh(NHC)3(CO)]+ (NHC = ICy (1), IiPr2Me2 (2)) were isolated from the reactions of RhH(PPh3)3(CO) with the free NHCs. The hexafluorophosphate salts of both compds., 1[PF6] and 2[PF6], were characterized by x-ray diffraction. The obsd. temp. dependences of the 1H NMR spectra for 1[PF6] and 2[PF6] are a consequence of restricted rotation assocd. with the three Rh-CNHC bonds. Line shape analyses from the NMR studies on 1[PF6], 1[BAr4F], and 2[PF6] (BAr4F = B(3,5-C6H3(CF3)2)4) afford activation barriers for the two trans-positioned Rh-CNHC bonds of 35, 38, and 40 kJ mol-1, resp. Pulsed-gradient spin-echo (PGSE) NMR measurements show that there is only a relatively small amt. of ion pairing for these salts in CH2Cl2 soln. 1H-19F HOESY data help to place the anions relative to the cations. Preliminary mechanistic studies on the formation of 1 and 2 suggest a role for neutral dinuclear precursors, as revealed by the reaction of (PPh3)2Rh(micro -CO)2Rh(IiPr2Me2)2 with ICy, which affords the structurally characterized mixed NHC complex [Rh(IiPr2Me2)2(ICy)(CO)][PF6] (3[PF6]).
Original languageEnglish
Pages (from-to)2642-2648
Number of pages7
JournalOrganometallics
Volume25
Issue number10
Publication statusPublished - 2006

Keywords

  • Potential barrier
  • Rh heterocyclic carbene imidazolylidene complex prepn crystal mol structure
  • RACT (Reactant or reagent) (reaction of imidazolylidene derivs. with Rh hydride to give cationic tris N-heterocyclic carbene rhodium carbonyl complexes)
  • imidazolylidene reaction Rh hydride
  • Internal rotation (hindered
  • restricted rotation activation barrier Rh heterocyclic carbene imidazolylidene complex
  • Molecular structure (of imidazolylidene N-heterocyclic carbene rhodium carbonyl complexes)
  • Molecular rotation (internal
  • Carbenes Role
  • PRP (Properties)
  • hindered
  • RCT (Reactant)
  • PREP (Preparation)
  • Spin echo (reaction of imidazolylidene derivs. with Rh hydride to give cationic tris N-heterocyclic carbene rhodium carbonyl complexes)
  • Overhauser spectroscopy (heteronuclear
  • Crystal structure
  • Heterocyclic compounds Role
  • Ion pairs
  • reaction of imidazolylidene derivs. with Rh hydride to give cationic tris N-heterocyclic carbene rhodium carbonyl complexes)
  • SPN (Synthetic preparation)

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