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Synthesis and structural characterisation of rhodium hydride complexes bearing N-heterocyclic carbene ligands

Journal of Organometallic Chemistry
Publication Date
  • {Activation
  • {Addition
  • Bond
  • Bond} {Activation
  • Carbenes
  • C-H
  • C-H Activation
  • Oxidative Addition
  • Imidazolium Salts
  • Bond Activation
  • Complexes
  • Dehydrogenation
  • {Dehydrogenation
  • Hydride
  • Hydride Ligands
  • Imidazolium
  • Imidazolium} {Salts
  • Irh5(Pph3)(2)
  • {Irh5(Pph3)(2)
  • Temperature
  • Ligands
  • Molecular-Structure
  • {Molecular-Structure
  • Ruthenium
  • Reactivity
  • N-Heterocyclic
  • N-Heterocyclic Carbenes
  • Rhodium Complexes
  • Oxidative
  • Oxidative} {Addition
  • {Reactivity
  • Rhodium
  • {Ruthenium
  • {Salts


Addition of excesses of N-heterocyclic carbenes ({NHCs)} {IEt2Me2}, {I'Pr2Me2} or {ICy} ({IEt2Me2} = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene; {I'Pr2Me2} = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; {ICy} = 1,3-dicyclohexylimidazol-2-ylidene) to [{HRh(PPh3)(4)]} (1) affords an isomeric mixture of [{HRh(NHC)(PPh3)(2)]} ({NHC} = {IEt2Me2} (cis-/trans-2), {I'Pr2Me2} (cis-/trans-3), {ICy} (cis-/trans-4)) and [{HRh(NHC)(2)(PPh3)]} ({IEt2Me2} (cis-/trans-5), {I'Pr2Me2} (cis-/trans-6), {ICy} (cis-/trans-7)). Thermolysis of 1 with the aryl substituted {NHC}, 1,3-dimesityl-4,5-dihydroimidazol-2-ylideiie ({IMesH(2))}, affords the bridging hydrido phosphido dimer, [\{({PPh3)(2)Rh\}(2)-(mu-H)(mu-PPh2)]} (8), which is also the reaction product formed in the absence of carbene. When the rhodium precursor was changed from 1 to [{HRh(CO)(PPh3)(3)]} (9) and treated with either {INIes} (=1,3-dimesitylimidazol-2-ylidene) or {ICy}, the bis-{NHC} complexes trans-[{HRh(CO)(IMeS)(2)]} (10) and trans-[{HRh(CO)(ICY)(2)]} (11) were formed. In contrast, the reaction of 9 with {I'Pr2Me2} gave [{HRh(CO)(I'Pr2Me2)(2)]} (cis-/trans-12) and the unusual unsymmetrical dimer, [({PPh3)(2)Rh(mu-CO)(2)Rh(I'Pr2Me2)(2)]} (13). The complexes trans-3, 8, 10 and 13 have been structurally characterised. (c) 2005 Elsevier {B.V.} All rights reserved.

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