Intramolecular activation of aromatic C–H bonds at tantalum(V) metal centers: evaluating cyclometallation ‘resistant’ and ‘immune’ aryloxide ligation[hair space]

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Jonathan S. Vilardo, Mark A. Lockwood, Linda G. Hanson, Janet R. Clark, Bernardeta C. Parkin, Phillip E. Fanwick and Ian P. Rothwell


Abstract

The trichloride compounds [Ta(OC6HPh2-2,6-R2-3,5)Cl3] (1: R = H a, Ph b, Me c, Pri d or But e) have been obtained by treating [Ta2Cl10] with the corresponding 3,5-disubstituted-2,6-diphenylphenols Ia–Ie. The solid-state structures of 1c and 1d show a square-pyramidal structure with an axial aryloxide ligand. The reaction of 1 with LiCH2SiMe3 (3 equivalents) led to the isolation of the tris(alkyls) [Ta(OC6HPh2-2,6-R2-3,5)2 (CH2SiMe3)3] (4a–4d) except in the case of the 3,5-di-tert-butyl derivative 1e which generated the alkylidene compound [Ta(OC6H3Ph2-2,6-But-3,5) 2([double bond, length as m-dash]CHSiMe3)(CH2SiMe3 )] 6e. The alkylidenes 6a–6d can be produced by photolysis of the corresponding tris(alkyls) 4a–4d. The alkylidenes 6a–6d undergo intramolecular cyclometallation of the aryloxide ligand (addition of an aromatic C–H bond to the tantalum alkylidene) at a rate which is extremely dependent on the meta substituents on the phenoxide nucleus. Kinetic studies show that conversion of 6a–6d into monometallated 7a–7d is first order with the phenyl, methyl and isopropyl substituents slowing the ring closure down by factors of 20, 90 and 360 respectively. The tert-butyl substituent completely shuts down cyclometallation of the adjacent phenyl ring. It is argued that bulky substituents inhibit rotation of the ortho-phenyl ring into a conformation necessary for C–H bond activation. Structural analysis of the torsion angles between ortho-phenyl and phenoxy rings has been carried out. The use of 1H NMR chemical shifts has been demonstrated to be a valuable tool to probe the average conformations adopted in solution.


References

  1. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, Wiley-Interscience, New York, 5th edn., 1988 Search PubMed.
  2. Activation and Functionalization of Alkanes, ed. C. Hill, John Wiley and Sons, New York, 1989 Search PubMed; Selective Hydrocarbon Activation, eds. J. A. Davis, P. L. Watson, J. F. Liebman and A. Greenberg, VCH Publishers, Toledo, OH, 1989 Search PubMed; A. E. Shilov, Activation of Saturated Hydrocarbons by Transition Metal Complexes, Reidel, Boston, 1984 Search PubMed.
  3. I. P. Rothwell, Acc. Chem. Res., 1988, 21, 153 CrossRef CAS.
  4. D. Rabinovich, R. Zelman and G. Parkin, J. Am. Chem. Soc., 1990, 112, 9632 CrossRef CAS; 1992, 114, 4611.
  5. J. S. Yu, L. Felter, M. C. Potyen, J. R. Clark, V. M. Visciglio, P. E. Fanwick and I. P. Rothwell, Organometallics, 1996, 15, 4443 CrossRef CAS.
  6. G. D. Smith, V. M. Visciglio, P. E. Fanwick and I. P. Rothwell, Organometallics, 1992, 11, 1064 CrossRef CAS.
  7. (a) R. W. Chesnut, G. J. Gayatry, J. S. Yu, P. E. Fanwick and I. P. Rothwell, Organometallics, 1991, 10, 321 CrossRef CAS; (b) F. Lefebvre, M. Leconte, S. Pagano, A. Mutch and J.-M. Basset, Polyhedron, 1995, 14, 3209 CrossRef CAS.
  8. (a) M. A. Lockwood, P. E. Fanwick, O. Eisenstein and I. P. Rothwell, J. Am. Chem. Soc., 1996, 118, 2762 CrossRef CAS; (b) M. A. Lockwood, P. E. Fanwick and I. P. Rothwell, Polyhedron, 1995, 14, 3363 CrossRef CAS.
  9. D. H. R. Barton, D. M. X. Donnelly, P. J. Guiry and J. H. Reibenspies, J. Chem. Soc., Chem. Commun., 1990, 1110 RSC; D. H. R. Barton, N. Y. Bhatnagar, J.-C. Blazejewski, B. Charpiot, J.-P. Finet, D. J. Lester, W. B. Motherwell, M. T. B. Papoula and S. P. Stanforth, J. Chem. Soc., Perkin Trans. 1, 1985, 2657 RSC.
  10. R. R. Schrock, Polyhedron, 1995, 14, 3177 CrossRef CAS.
  11. L. R. Chamberlain, I. P. Rothwell, K. Folting and J. C. Huffman, J. Chem. Soc., Dalton Trans., 1987, 155 RSC; L. R. Chamberlain and I. P. Rothwell, J. Chem. Soc., Dalton Trans., 1987, 163 RSC.
  12. L. R. Chamberlain, I. P. Rothwell and J. C. Huffman, Inorg. Chem., 1984, 23, 2575 CrossRef CAS.
  13. M. A. Lockwood, M. C. Potyen, B. D. Steffey, P. E. Fanwick and I. P. Rothwell, Polyhedron, 1995, 14, 3293 CrossRef CAS.
  14. J. R. Clark, A. L. Pulvirenti, P. E. Fanwick, M. Sigalis, O. Eisenstein and I. P. Rothwell, Inorg. Chem., in the press Search PubMed.
  15. R. W. Chesnut, L. D. Durfee, P. E. Fanwick, I. P. Rothwell, K. Folting and J. C. Huffman, Polyhedron, 1987, 6, 2019 CrossRef CAS.
  16. M. Perrin, K. Bekkouch and A. Thozet, Acta Crystallogr., Sect. C, 1987, 43, 2357 CrossRef.
  17. K. Nakatsu, H. Yoshioka, K. Kunimoto, T. Kingasa and S. Ueji, Acta Crystallogr., Sect. B, 1978, 34, 980 CrossRef.
  18. M. Oki and H. Iwamura, J. Am. Chem. Soc., 1967, 89, 576 CrossRef CAS; F. H. Allen, J. A. K. Howard, V. J. Hoy, G. R. Desiraju, D. S. Reddy and C. C. Wilson, J. Am. Chem. Soc., 1996, 118, 4081 CrossRef CAS and refs. therein.
  19. M. Brookhart and M. L. H. Green, J. Organomet. Chem., 1983, 250, 395 CrossRef CAS; M. Brookhart, M. L. H. Green and L. L. Wong, Prog. Inorg. Chem., 1988, 36, 1 CAS.
  20. R. R. Schrock, R. T. DePue, J. Feldman, K. B. Yap, D. C. Yang, W. M. Davis, L. Y. Park, M. DiMare, M. Schofield, J. Anhaus, E. Walborsky, E. Evitt, C. Kruger and P. Betz, Organometallics, 1990, 9, 2262 CrossRef CAS.
  21. I. P. Rothwell, in Homogeneous Alkane Activation, ed. C. G. Hill, Wiley, New York, 1989, pp. 151–195 Search PubMed.
  22. C. McDade, J. C. Green and J. E. Bercaw, Organometallics, 1982, 1, 1629 CrossRef CAS; A. R. Bulls, W. P. Schaefer, M. Serfas and J. E. Bercaw, Organometallics, 1987, 6, 1219 CrossRef CAS; L. R. Chamberlain, I. P. Rothwell and J. C. Huffmann, J. Am. Chem. Soc., 1986, 108, 1502 CrossRef CAS; J.-L. Couturier, C. Paillet, M. Leconte, J. M. Basset and K. Weiss, Angew. Chem., Int. Ed. Engl., 1992, 31, 628 CrossRef; K. C. Wallace, A. H. Liu, J. C. Dewan and R. R. Schrock, J. Am. Chem. Soc., 1988, 110, 4964 CrossRef CAS; J. A. van Doorn, H. van der Heijden and A. G. Orpen, Organometallics, 1994, 13, 4271 CrossRef CAS.
  23. H. van der Heijden and B. J. Hessen, J. Chem. Soc., Chem. Commun., 1995, 145 RSC; M. P. Coles, V. C. Gibson, W. Clegg, M. R. J. Elsegood and P. A. Porrelli, J. Chem. Soc., Chem. Commun., 1995, 145 RSC.
  24. C. P. Schaller, C. C. Cummins and P. T. Wolczanski, J. Am. Chem. Soc., 1996, 118, 591 CrossRef CAS.
  25. P. Yates and J. R. Hyre, J. Org. Chem., 1962, 27, 4101 CAS; A. S. Hay and R. F. Clark, Macromolecules, 1970, 3, 533 CrossRef CAS; H. Yang and A. S. Hay, Synthesis, 1992, 467 CrossRef CAS; D. E. Dana and A. S. Hay, Synthesis, 1982, 164 CrossRef CAS.
  26. D. H. Grayson and M. J. R. Tuite, J. Chem. Soc., Perkin Trans. 1, 1986, 2137 RSC.
  27. A. Galan, A. J. Sutherland, P. Ballester and J. Rebek jun., Tetrahedron Lett., 1994, 35, 5359 CrossRef CAS.
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