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Volumn 130, Issue 46, 2008, Pages 15490-15498

Computational study of the reaction of C6F6 with [IrMe(PEt3)3]: Identification of a phosphine-assisted C-F activation pathway via a metallophosphorane intermediate

Author keywords

[No Author keywords available]

Indexed keywords

ACTIVATION ANALYSIS; CHEMICAL BONDS; DENSITY FUNCTIONAL THEORY; ETHYLENE; IRIDIUM; METHANE; PHOSPHORUS; PHOSPHORUS COMPOUNDS;

EID: 56449129482     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja804622j     Document Type: Article
Times cited : (75)

References (104)
  • 6
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    • Transition-Metal Mediated C-F Bond Activation
    • Crabtree, R. H, Mingos, D. M. P, Eds, Elsevier: Amsterdam
    • (a) Braun, T.; Perutz, R. N. Transition-Metal Mediated C-F Bond Activation. In Comprehensive Organometallic Chemistry III; Crabtree, R. H., ; Mingos, D. M. P., Eds.; Elsevier: Amsterdam, 2006.
    • (2006) Comprehensive Organometallic Chemistry III
    • Braun, T.1    Perutz, R.N.2
  • 70
    • 0000381941 scopus 로고
    • For reviews of metallophosphorane chemistry see
    • (a) For reviews of metallophosphorane chemistry see: Dillon, K. B. Chem. Rev. 1994, 94, 1441.
    • (1994) Chem. Rev , vol.94 , pp. 1441
    • Dillon, K.B.1
  • 72
    • 0001649021 scopus 로고    scopus 로고
    • Other examples: Vierling, P.; Riess, J. G. Organometallics 1986, 5, 2543, and references therein.
    • (c) Other examples: Vierling, P.; Riess, J. G. Organometallics 1986, 5, 2543, and references therein.
  • 75
    • 56449098492 scopus 로고    scopus 로고
    • Gaussian, Inc, Wallingford CT
    • (a) Frisch, M. J.; et al. Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford CT, 2004.
    • (2004) Gaussian 03, revision , Issue.C.02
    • Frisch, M.J.1
  • 86
    • 56449085737 scopus 로고    scopus 로고
    • 6 was also tested and also found to be a high-energy process (ΔE = +150.1 kcal/mol in the gas phase, dropping to 101.8 kcal/mol in benzene).
    • 6 was also tested and also found to be a high-energy process (ΔE = +150.1 kcal/mol in the gas phase, dropping to 101.8 kcal/mol in benzene).
  • 87
    • 56449104006 scopus 로고    scopus 로고
    • 6 substitution to form trans-7′ (E = +31.3 kcal/mol). However, C-F activation in cis-7′ then has a barrier of 4.1 kcal/mol, whereas C-F activation in trans-7′ is effectively barrierless. Overall C-F activation is therefore easier via trans-7′ Details of the pathway via cis-7′ are in the Supporting Information.
    • 6 substitution to form trans-7′ (E = +31.3 kcal/mol). However, C-F activation in cis-7′ then has a barrier of 4.1 kcal/mol, whereas C-F activation in trans-7′ is effectively barrierless. Overall C-F activation is therefore easier via trans-7′ Details of the pathway via cis-7′ are in the Supporting Information.
  • 88
    • 56449106924 scopus 로고    scopus 로고
    • C-H activation of benzene via a phosphine-assisted C-H activation process was found to be extremely unfavorable, the metallophosphorane intermediate formed, Ir(PH3)2(Me)(Ph)PH3Et, having a prohibitively high energy of +56.1 kcal/mol
    • 3Et)], having a prohibitively high energy of +56.1 kcal/mol.
  • 89
    • 56449092653 scopus 로고    scopus 로고
    • An additional feature of the experimental selectivity was that C-H activation (but not C-F activation) was seen at 80°C. Our calculations for 1,3,5-C6F3H3 via Pathway 2b reproduce this preference with C-H activation (ΔG ‡, 27.2 kcal/mol) being far more accessible than C-F activation ΔG‡, 37.9 kcal/mol, It may be that at higher temperatures phosphine ligand dissociation becomes possible and so makes oxidative addition via Pathway 2b accessible
    • ‡ = +37.9 kcal/mol). It may be that at higher temperatures phosphine ligand dissociation becomes possible and so makes oxidative addition via Pathway 2b accessible.
  • 92
    • 56449097016 scopus 로고    scopus 로고
    • Calculations were attempted on the full species 1, but difficulties were encountered with locating true minima due to the large number of soft modes corresponding to ethyl group rotations.
    • Calculations were attempted on the full species 1, but difficulties were encountered with locating true minima due to the large number of soft modes corresponding to ethyl group rotations.
  • 93
    • 56449117374 scopus 로고    scopus 로고
    • 3) model was the presence of a second intermediate (E =-0.1 kcal/mol) between the normal precomplex 2′ (E =-4.6 kcal/mol) and the C-F activation transition state. However, the transition state linking these two pre-complexes is low in energy (E = + 0.1 kcal/mol), and so the overall barrier still corresponds to the C-F activation step.
    • 3) model was the presence of a second intermediate (E =-0.1 kcal/mol) between the normal precomplex 2′ (E =-4.6 kcal/mol) and the C-F activation transition state. However, the transition state linking these two pre-complexes is low in energy (E = + 0.1 kcal/mol), and so the overall barrier still corresponds to the C-F activation step.
  • 94
    • 0000097544 scopus 로고    scopus 로고
    • We also computed the energetics for Pathways 2a and 2b starting from the model species 1′(PMe3, All attempts to locate a transition state analogous to TS (2′-6′) for direct oxidative addition failed and led instead to the much more stable phosphine-assisted transition state at, 10.4 kcal/mol. For Pathway 2b dissociation of the PMe 2Et ligand from 1′(PMe3, 28.7 kcal/mol) is in fact significantly easier than PH2Et dissociation from 1′, 37.4 kcal/mol, This stabilisation of about 9 kcal/mol is retained in the subsequent C6F6 adduct (E, 22.5 kcal/mol) and the C-F activation transition state (E, 22.5 kcal/mol) derived from 1′(PMe3, Changing from 1′ to 1′(PMe3) therefore affects the energy of phosphine dissociation but not of the actual C-F oxidative addition step, which is effectively
    • 3] cyclometalation comparison with experiment gives a clear indication that the entropic contribution associated with phosphine loss is overestimated. (a) Tulip, T. H.; Thorn, D. L. J. Am. Chem. Soc. 1981, 103, 2448.
  • 96
    • 56449108372 scopus 로고    scopus 로고
    • This feature is retained with 1′(PMe3, even though the increased steric bulk of the PMe3 ligands causes the F(ortho)•••P contacts to increase to about 2.95 Å. The fact that, when this pattern is absent, F1 transfers onto PH3 rather than PH2Et does reflect the make-up of our model system; however, this result is entirely consistent with the build-up of negative charge on F1 in the transition state (see below, and the movement of this nucleophilic species towards the less electron-rich (non-alkyl) phosphine
    • 2Et does reflect the make-up of our model system; however, this result is entirely consistent with the build-up of negative charge on F1 in the transition state (see below), and the movement of this nucleophilic species towards the less electron-rich (non-alkyl) phosphine.
  • 102
    • 56449105109 scopus 로고    scopus 로고
    • The largest increase in negative charge was usually about 0.03e and was located at an ortho carbon site
    • The largest increase in negative charge was usually about 0.03e and was located at an ortho carbon site.
  • 104
    • 56449124771 scopus 로고    scopus 로고
    • 36c
    • 36c


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