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Reaction intermediates in the synthesis of new hydrido, N-heterocyclic dicarbene iridium(III) pincer complexes

(2009) ORGANOMETALLICS. 28(14). p.4028-4047
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Abstract
The reactivity of the potential pincer ligands (1,3-phenylene)bis(1-butylimidazolium) diiodide ((n-Bu)(CHimdCHCHimid)I-2, 1) and (4,6-dimethyl-1,3-phenylene)bis(1-butylimidazolium) diiodide ((n-Bu)((CHimidCHCHimid)-C-Me)I-2, 3) toward [Ir(mu-Cl)(cod)](2), in the presence of a weak base, was compared. Performing the reaction with a stoichiometric amount of NEt3 led to three complexes from 1, [IrI2n-Bu(CNHCCCNHC)(NCMe)] (4, 50%), [Ir(H)In-Bu(CNHCCCNHC)(NCMe)] (6, 10%), and {[Ir(mu-I)(n-Bu)((CNHCCCHimid)-C-4)(2)]I-2}(2) (7,40%) and to five complexes from 3, [IrI2n-Bu((CNHCCCNHC)-C-Me)(NCMe)] (8, 30%), [Ir(H)In-Bu((CNHCCCNHC)-C-Me)(NCMe)] (9, 30%), IrI(cod)(n-Bu)((CNHCCHCHimid)-C-Me)I (10, 34%), [{IrI(cod)}(2)(n-Bu)(mu-(CNHCCHCNHC)-C-Me)] (11, < 5%), and [Irn-Bu((CNHCCCNHC)-C-Me)(2)]I (12, < 5%). In both cases, the amount of CNHCCCNHC and C-NHC (CCNHC)-C-Me pincer complexes formed (4 and 6 from 1; 8 and 9 from 3) was almost the same. Replacing NEt3 by Cs2CO3 or using an excess of NEt3 allowed the formation of the pincer iridium(III) hydride complexes 6 and 9 as the main products (isolated yields of ca. 70%). In contrast, base-free oxidative addition of the bis(imidazolium) salt 1 toward [Ir(mu-Cl(cod)](2) unexpectedly yielded the complex [IrI2n-Bu((CNHCCCHimid)-C-4)(NCMe)(2)]I (17), in which aromatic metalation has occurred in the C-4 or C-6 position. Cationic complexes [Ir(H)(n-Bu)(CNHCCCNHC)(NCMe)(2)](PF6) (13) and [Ir(H)(n-Bu)((CNHCCCNHC)-C-Me)(NCMe)(2)](PF6) (14) were prepared by iodide ligand abstraction from 6 and 9, respectively, with TIPF6. The cyclometalated complex [Ir(H)In-Bu((CNHCCCHimid)-C-4)(cod)]I (15) and 10, obtained from 1 and 3, respectively, were shown to be effective intermediates in the synthesis of 6 and 9. On the basis of these experimental results, we suggest possible mechanisms for the formation of 6 and 9 and a plausible explanation of the equilibrium observed between the iridium diiodo pincer complexes (4 and 8) and the iridium hydride complexes (6 and 9). A new dinuclear iridium(II) complex, [Ir-2(mu-I)(mu(2)-eta(1)-CHCH=NEt2)I-2(cod)(2)] (18), containing a ligand derived from activation of NEt3 was obtained, albeit in low yields, which could be involved in the transformation of 4 and 8 into 6 and 9, respectively. Finally, three polyhydride NHC ifidium complexes were generated from [IrI2n-Bu-(CNHCCCNHC)(DMSO)] (21) and 6. All these compounds were characterized by spectroscopic and spectrometric analysis, and the structures of 6, 8, 11, 12, 17, and 18 were determined by X-ray diffraction.
Keywords
C-H ACTIVATION, CARBENE COMPLEXES, CATALYTIC-ACTIVITY, ALKANE DEHYDROGENATION, OXIDATIVE ADDITION, RHODIUM COMPLEXES, TRANSFER HYDROGENATION, CRYSTAL-STRUCTURE, STABLE CATALYSTS, BOND ACTIVATION

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Chicago
Raynal, Matthieu, Roberto Pattacini, Catherine Cazin, Christophe Vallee, Helene Olivier-Bourbigou, and Pierre Braunstein. 2009. “Reaction Intermediates in the Synthesis of New Hydrido, N-heterocyclic Dicarbene iridium(III) Pincer Complexes.” Organometallics 28 (14): 4028–4047.
APA
Raynal, M., Pattacini, R., Cazin, C., Vallee, C., Olivier-Bourbigou, H., & Braunstein, P. (2009). Reaction intermediates in the synthesis of new hydrido, N-heterocyclic dicarbene iridium(III) pincer complexes. ORGANOMETALLICS, 28(14), 4028–4047.
Vancouver
1.
Raynal M, Pattacini R, Cazin C, Vallee C, Olivier-Bourbigou H, Braunstein P. Reaction intermediates in the synthesis of new hydrido, N-heterocyclic dicarbene iridium(III) pincer complexes. ORGANOMETALLICS. 2009;28(14):4028–47.
MLA
Raynal, Matthieu, Roberto Pattacini, Catherine Cazin, et al. “Reaction Intermediates in the Synthesis of New Hydrido, N-heterocyclic Dicarbene iridium(III) Pincer Complexes.” ORGANOMETALLICS 28.14 (2009): 4028–4047. Print.
@article{8536920,
  abstract     = {The reactivity of the potential pincer ligands (1,3-phenylene)bis(1-butylimidazolium) diiodide ((n-Bu)(CHimdCHCHimid)I-2, 1) and (4,6-dimethyl-1,3-phenylene)bis(1-butylimidazolium) diiodide ((n-Bu)((CHimidCHCHimid)-C-Me)I-2, 3) toward [Ir(mu-Cl)(cod)](2), in the presence of a weak base, was compared. Performing the reaction with a stoichiometric amount of NEt3 led to three complexes from 1, [IrI2n-Bu(CNHCCCNHC)(NCMe)] (4, 50\%), [Ir(H)In-Bu(CNHCCCNHC)(NCMe)] (6, 10\%), and \{[Ir(mu-I)(n-Bu)((CNHCCCHimid)-C-4)(2)]I-2\}(2) (7,40\%) and to five complexes from 3, [IrI2n-Bu((CNHCCCNHC)-C-Me)(NCMe)] (8, 30\%), [Ir(H)In-Bu((CNHCCCNHC)-C-Me)(NCMe)] (9, 30\%), IrI(cod)(n-Bu)((CNHCCHCHimid)-C-Me)I (10, 34\%), [\{IrI(cod)\}(2)(n-Bu)(mu-(CNHCCHCNHC)-C-Me)] (11, {\textlangle} 5\%), and [Irn-Bu((CNHCCCNHC)-C-Me)(2)]I (12, {\textlangle} 5\%). In both cases, the amount of CNHCCCNHC and C-NHC (CCNHC)-C-Me pincer complexes formed (4 and 6 from 1; 8 and 9 from 3) was almost the same. Replacing NEt3 by Cs2CO3 or using an excess of NEt3 allowed the formation of the pincer iridium(III) hydride complexes 6 and 9 as the main products (isolated yields of ca. 70\%). In contrast, base-free oxidative addition of the bis(imidazolium) salt 1 toward [Ir(mu-Cl(cod)](2) unexpectedly yielded the complex [IrI2n-Bu((CNHCCCHimid)-C-4)(NCMe)(2)]I (17), in which aromatic metalation has occurred in the C-4 or C-6 position. Cationic complexes [Ir(H)(n-Bu)(CNHCCCNHC)(NCMe)(2)](PF6) (13) and [Ir(H)(n-Bu)((CNHCCCNHC)-C-Me)(NCMe)(2)](PF6) (14) were prepared by iodide ligand abstraction from 6 and 9, respectively, with TIPF6. The cyclometalated complex [Ir(H)In-Bu((CNHCCCHimid)-C-4)(cod)]I (15) and 10, obtained from 1 and 3, respectively, were shown to be effective intermediates in the synthesis of 6 and 9. On the basis of these experimental results, we suggest possible mechanisms for the formation of 6 and 9 and a plausible explanation of the equilibrium observed between the iridium diiodo pincer complexes (4 and 8) and the iridium hydride complexes (6 and 9). A new dinuclear iridium(II) complex, [Ir-2(mu-I)(mu(2)-eta(1)-CHCH=NEt2)I-2(cod)(2)] (18), containing a ligand derived from activation of NEt3 was obtained, albeit in low yields, which could be involved in the transformation of 4 and 8 into 6 and 9, respectively. Finally, three polyhydride NHC ifidium complexes were generated from [IrI2n-Bu-(CNHCCCNHC)(DMSO)] (21) and 6. All these compounds were characterized by spectroscopic and spectrometric analysis, and the structures of 6, 8, 11, 12, 17, and 18 were determined by X-ray diffraction.},
  author       = {Raynal, Matthieu and Pattacini, Roberto and Cazin, Catherine and Vallee, Christophe and Olivier-Bourbigou, Helene and Braunstein, Pierre},
  issn         = {0276-7333},
  journal      = {ORGANOMETALLICS},
  keyword      = {C-H ACTIVATION,CARBENE COMPLEXES,CATALYTIC-ACTIVITY,ALKANE DEHYDROGENATION,OXIDATIVE ADDITION,RHODIUM COMPLEXES,TRANSFER HYDROGENATION,CRYSTAL-STRUCTURE,STABLE CATALYSTS,BOND ACTIVATION},
  language     = {eng},
  number       = {14},
  pages        = {4028--4047},
  title        = {Reaction intermediates in the synthesis of new hydrido, N-heterocyclic dicarbene iridium(III) pincer complexes},
  url          = {http://dx.doi.org/10.1021/om900226c},
  volume       = {28},
  year         = {2009},
}

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