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Journal of the American Chemical Society
Volumn 131, Issue 5, 2009, Pages 1847-1861
Catalytic hydrodefluorination of aromatic fluorocarbons by ruthenium N-heterocyclic carbene complexes
Author keywords

[No Author keywords available]
Indexed keywords

ALKYLSILANES; C-F ACTIVATION; CATALYTIC ACTIVITY; CATALYTIC REACTIONS; FIRST-ORDER DEPENDENCE; HEXAFLUOROBENZENE; IMIDAZOL; IMIDAZOLIN-2-YLIDENE; N-HETEROCYCLIC CARBENE; N-HETEROCYCLIC CARBENE COMPLEX; TURNOVER FREQUENCY; TURNOVER NUMBER;
EID: 67749095019     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja806545e     Document Type: Article
Times cited : (139)
References (136)
  • 7
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    • Braun, T.; Perutz, R. N.; Sladek, M. 1. Chem. Commun. 2001, 2254- 2255.
    • (d) Braun, T.; Perutz, R. N.; Sladek, M. 1. Chem. Commun. 2001, 2254- 2255.
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    • For other catalytic transformations involving C-F cleavage, see
    • For other catalytic transformations involving C-F cleavage, see:
  • 60
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    • Klahn, M.; Fischer, C; Spannenberg, A.; Rosenthal. U.; Krossing, 1. Tetrahedron Lett. 2007, 48, 8900-8903.
    • (e) Klahn, M.; Fischer, C; Spannenberg, A.; Rosenthal. U.; Krossing, 1. Tetrahedron Lett. 2007, 48, 8900-8903.
  • 67
    • 84891738728 scopus 로고    scopus 로고
    • There are relatively few examples of NHC metal fluoride complexes known. See refs 10. 18, and 23 along with:
    • There are relatively few examples of NHC metal fluoride complexes known. See refs 10. 18, and 23 along with:
  • 73
    • 84891739532 scopus 로고    scopus 로고
    • H-F coupling on either the hydride or fluoride resonances. As any coupling would be < 10 Hz, we assume it
    • We see no may be lost in the line width of the signals
    • We see no H-F coupling on either the hydride or fluoride resonances. As any coupling would be < 10 Hz, we assume it may be lost in the line width of the signals.
  • 76
    • 84891737105 scopus 로고    scopus 로고
    • 3 complex. See:
    • 3 complex. See:
  • 78
    • 84891747740 scopus 로고    scopus 로고
    • 2HF (NHC = SIMes 17, SIPr 18, IPr 19, IMes 20), which were analytically and structurally characterized (CCDC 697992-697995). See Supporting Information for details.
    • 2HF (NHC = SIMes 17, SIPr 18, IPr 19, IMes 20), which were analytically and structurally characterized (CCDC 697992-697995). See Supporting Information for details.
  • 79
    • 84891742720 scopus 로고    scopus 로고
    • 2 to isolate clean samples of 6 and 7 proved unsuccessful, as the addition of 1 equiv of the Pd complex turned yellow solutions of both Ru complexes brown (to black after 12 h at room temperature) and generated a mixture of four new hydride containing species.
    • 2 to isolate clean samples of 6 and 7 proved unsuccessful, as the addition of 1 equiv of the Pd complex turned yellow solutions of both Ru complexes brown (to black after 12 h at room temperature) and generated a mixture of four new hydride containing species.
  • 80
    • 84891738591 scopus 로고    scopus 로고
    • Complexes 5-7 could also be formed the same way starting with complexes 13-15.
    • Complexes 5-7 could also be formed the same way starting with complexes 13-15.
  • 81
    • 84891745247 scopus 로고    scopus 로고
    • -1. See ref 28 for a comparison of other 16- and 18e ruthenium monocarbonyl complexes.
    • -1. See ref 28 for a comparison of other 16- and 18e ruthenium monocarbonyl complexes.
  • 82
    • 84891738540 scopus 로고    scopus 로고
    • X-ray and neutron structures of Ru(IMes)2(CO)HF yielded Ru-F distances of 2.0326(15) and 2.042(6) A, respectively. See ref 25b
    • 2(CO)HF yielded Ru-F distances of 2.0326(15) and 2.042(6) A, respectively. See ref 25b.
  • 84
    • 67849109287 scopus 로고    scopus 로고
    • PhD Thesis, University of Bath
    • Jazzar, R. F. R. PhD Thesis, University of Bath, 2003.
    • (2003)
    • Jazzar, R.F.R.1
  • 93
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    • 5.
    • 5.
  • 95
    • 84891747277 scopus 로고    scopus 로고
    • 3)(CO)HF complexes as catalytic precursors as they were simply transformed into complexes 13-16 under the reaction conditions.
    • 3)(CO)HF complexes as catalytic precursors as they were simply transformed into complexes 13-16 under the reaction conditions.
  • 96
    • 84891746070 scopus 로고    scopus 로고
    • ON is defined as (the number of moles of fluoroaromatic product(s) multiplied by no. of HDF steps)/number of moles of catalyst
    • ON is defined as (the number of moles of fluoroaromatic product(s) multiplied by no. of HDF steps)/number of moles of catalyst.
  • 98
    • 84891738059 scopus 로고    scopus 로고
    • Kinetic experiments were run in THF at 339 K, the boiling point of the solvent.
    • Kinetic experiments were run in THF at 339 K, the boiling point of the solvent.
  • 99
    • 84891740560 scopus 로고    scopus 로고
    • Turnover numbers of up to 90 have been recorded by Braun and co-workers for the conversion of hexafluoropropene into 3,3-trifluoro- propylsilanes. See ref 17j
    • Turnover numbers of up to 90 have been recorded by Braun and co-workers for the conversion of hexafluoropropene into 3,3-trifluoro- propylsilanes. See ref 17j.
  • 100
    • 0242607648 scopus 로고    scopus 로고
    • We and others have shown previously that Ru-NHC complexes can bring about bond activation of aromatic solvents. Thus, in ref 36 we reported that thermolvsis of 16 in C6D6 led to a mixture of products including 16-HD, Ru(lMes)2(PPh3)(CO)H 2, Ru(1Mes)2(PPh3)(CO)HD, Ru(PPh 3)3(CO)H2, and Ru(PPh3) 3(CO)HD. Leitner and co-workers subsequently showed that the dihydrogen dihydride complex Ru(IMes)(P-Cy3)(η2-H 2)2H2 was able to induce H/D exchange of C 6D5CD3 at room temperature. The resulting organometallic complex, which was now labeled Ru-D, Ru(η2-D 2) and at the ortho-mesityl groups, was subsequently used to introduce deuterium into a range of aromatic substrates including benzene, aniline, and anisole. Giunta, D, Hölscher
    • 2) and at the ortho-mesityl groups, was subsequently used to introduce deuterium into a range of aromatic substrates including benzene, aniline, and anisole. Giunta, D.; Hölscher, M.; Lehmann, C. W.; Mynott, R.; Wirtz. C; Leitner. W. Adv. Synth. Catal. 2003, 345, 1139-1145.
  • 101
    • 84891742717 scopus 로고    scopus 로고
    • This contrasts with an earlier report (ref 16) employing (η5-C5H5)2ZrCl 2/Mg/HgCl2 in which deuterium could be extracted from THF-d8
    • 8.
  • 102
    • 84891739630 scopus 로고    scopus 로고
    • Analysis of the 1H NMR spectrum at longer times (ca. 85 h) showed the presence of a new ruthenium species assigned as the ?uoroaryl hydride complex Ru(IPr)(PPh3)(CO)(C6F4CF 3)H. This displayed a hydride resonance at δ-25.83 (JHP, 24.01, JHF, 5.95 Hz) with a doublet of triplets multiplicity and a singlet 31P signal at δ 55.0. The presence of a 2,3,5,6-C6F4CF3 ligand was inferred from a 19F-1H HMBC experiment which showed a correlation from the hydride signal to two 19F signals at δ-111.1 (dd, J, 34.10, J, 15.62 Hz) and δ-117.6 (multiplet, 19F-19F COSY con?rmed the presence of a further three 19F resonances, two multiplets at δ-146.3 and-148.6, and a triplet at δ-57.6 JFF, 21.68 Hz, The proton spectrum also displaye
    • 2.
  • 103
    • 84891744869 scopus 로고    scopus 로고
    • Similarly, analysis of the 1H NMR spectrum at the end of the catalytic reaction with pentafluoropvridine showed a broad doublet hydride signal at (δ-25.62 (2JHP, 23.50 Hz, which showed an HMQC correlation to a broad 31P resonance at δ 47.0. We assign these signals as arising from Ru(IPr)(PPh3)(CO)(C 5F4N)H on the grounds that the ,9F NMR showed four signals in a 1:1:1:1 ratio, which was correlated by 19F- 19F COSY. The appearance of a singlet at δ 4.3 in the proton spectrum for H2 is consistent with formation of the 2,3,5,6-tetrafluo- ropyridyl ligand by C-H activation of 2,3,5,6- tetrafluoropyridine
    • 2 is consistent with formation of the 2,3,5,6-tetrafluo- ropyridyl ligand by C-H activation of 2,3,5,6- tetrafluoropyridine.
  • 104
    • 84891735934 scopus 로고    scopus 로고
    • 2.
    • 2.
  • 108
    • 84891743071 scopus 로고    scopus 로고
    • 2 (Wolf, J.; Stüer, W.;Grünwald, C; Gevert, O.; Laubender, M.; Werner, H. Eur. J. Inorg. Chem. 1998, 1827-1834)
    • 2 (Wolf, J.; Stüer, W.;Grünwald, C; Gevert, O.; Laubender, M.; Werner, H. Eur. J. Inorg. Chem. 1998, 1827-1834)
  • 109
    • 0000589279 scopus 로고    scopus 로고
    • 3 (Rodriguez. V.; Donnadieu, B.; Sabo- Etienne, S.; Chaudret, B. Organometallics 1998, 17, 3809-3814),
    • 3 (Rodriguez. V.; Donnadieu, B.; Sabo- Etienne, S.; Chaudret, B. Organometallics 1998, 17, 3809-3814),
  • 110
    • 84891740951 scopus 로고    scopus 로고
    • Kubas has noted that σ-coordination vs oxidation (e.g, M(η2-H2) vs H-M-H) is highly ligand dependent and that CO ligands tend to favor cr-complexes. For this reason, we feel that cr-coordination of, for example, C6F6 to afford the Ru(II) species Ru(NHC)(PPh3)(CO)(η2- C6F6)H 2 is more likely than oxidative addition to give the rathe- nium(IV) intermediate Ru(NHC)(PPh3)(CO)(C6F5)FH 2. Kubas, G. J. Metal Dihydrogen and σ-Bond Complexes: Kuwer Academic: New York, 2001
    • 2. Kubas, G. J. Metal Dihydrogen and σ-Bond Complexes: Kuwer Academic: New York, 2001.
  • 116
    • 84891745110 scopus 로고    scopus 로고
    • Deuterium labelling studies indicate that the mechanism is not altogether this simple since reaction of Ru(lPr)(PPh3)2(CO)D 2 with 10 equiv of C6F6 in THF-d8 not only yields the expected C6F5D but also gives some C6F5H. The protio source appears to involve orthometallation of the PPh3 ligands. See ref 62
    • 3 ligands. See ref 62.
  • 117
    • 84891742312 scopus 로고    scopus 로고
    • An alternative catalytic pathway could involve the initial reaction of 15 with R3SiH rather than fluoroarene. Although no reaction was apparent when 15 was heated with 10 equiv of Et3SiH at 343 K in C6D6 the formation of both Ru(IPr)(PPh 3)2(CO)HD and Et3SiH was seen at room temperature within 5 min of mixing when 15 was treated with Et 3SiD. Thus, reaction of 15 does occur with Si-H bonds at room temperature, although the formation of a RuH2 rather than a Ru(SiR3)H product implies that any initial reaction with silane would only serve to generate the catalytic intermediate I
    • 3)H product implies that any initial reaction with silane would only serve to generate the catalytic intermediate I.
  • 118
    • 84891736629 scopus 로고    scopus 로고
    • Measurement of a kinetic isotope effect usingRu(lPr)(PPh 3)2(CO)D2 was thwarted by D/H exchange. While the dideuteride can be prepared by simply placing Ru(IPr)(PPh3) 2(CO)H2 under 1 atm of D2, we observed that efforts to maximize the level of D-incorporation by continually replenishing the D2 atmosphere and leaving the reaction for longer led to broadening of the 31P NMR signals, suggestive of H/D exchange into the ortfto-phenvl positions of the PPh3 ligands. Thus a sample of Ru(IPr)(PPh3) 2(CO)D2 (ca. 78% RuD2) was prepared from a single cycle of D, Ru(IPr)(PPh3)2(CO)H2, isolated, and then heated at 322 K for 1.5 h and followed by 1H and 31P NMR; we observed clear H/D exchange into the ortfto-phenyl protons leaving a mixture of the RuD2, RuHD, and RuH2 species. As this scrambling occurs
    • 2 would be exchanged before any K1E could be determined.
  • 119
    • 84891747287 scopus 로고    scopus 로고
    • See refs 50 and 51
    • See refs 50 and 51.
  • 122
    • 0034835662 scopus 로고    scopus 로고
    • 4) complexes were prepared relatively recently bv Hughes and co-workers, (a) Hughes, R. P.; Williamson, A.; Sommer, R. D.; Rheingold, A. L. J. Am. Chem. Soc. 2001, 123, 7443- 7444.
    • 4) complexes were prepared relatively recently bv Hughes and co-workers, (a) Hughes, R. P.; Williamson, A.; Sommer, R. D.; Rheingold, A. L. J. Am. Chem. Soc. 2001, 123, 7443- 7444.
  • 126
    • 84891740432 scopus 로고    scopus 로고
    • Coordinated or trapped fluorobenzynes have also been described in the following cases
    • Coordinated or trapped fluorobenzynes have also been described in the following cases:
  • 127
    • 84891747453 scopus 로고    scopus 로고
    • Reference 9
    • (a) Reference 9.
  • 136
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    • Sheldrick, G. M. Acta Crystalhgr. 1990, 46-47B, A46. Sheldrick, G. M. SHELXL-97, a computer program for crystal structure refine- ment, University of Gottingen, 1997.
    • Sheldrick, G. M. Acta Crystalhgr. 1990, 46-47B, A46. Sheldrick, G. M. SHELXL-97, a computer program for crystal structure refine- ment, University of Gottingen, 1997.

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