The conformational analysis of phosphine ligands in organometallic complexes. Part 2. Triphenylphosphine coordinated to achiral and prochiral octahedral metal centres ¹

Abstract

The novel concept of nadir energy planes has been used to illuminate the principles governing the preferred orientation of rings A–C in PPh₃ 1, coordinated to achiral octahedral metal complexes of the type [M(PPh₃)L_1–5] 2a–d, and prochiral octahedral metal complexes of the type [M(η⁵-C₅H₅)(PPh₃)L₂] 3, and [M(η⁶-C₆H₆)(PPh₃)L₂] 4. An achiral arrangement of complex-bound 1 (reminiscent of the transition state for the one-ring flip stereoisomerisation process) orients all three ring apices proximal to three of the four orthogonal nadir energy planes associated with an octahedral metal centre. From this achiral arrangement, the favoured, degenerate conformations of complex-bound 1 may be subsequently derived by applying the following principles (in descending order of priority), (i) superimpose the vertical ring A of the achiral conformer onto the least encumbered nadir plane, (ii) allowring B to tilt onto the least encumbered nadir plane orthogonal to the vertical ring A, and (iii) tilt ring B in a manner which orients the flatter ring C beneath the smallest ligand. These principles are wholly consistent with 60 X-ray crystal structures, and detailed conformational analyses. The phenomenon of PPh₃ ligand tilting, consistent with intramolecular steric strain, is characterised.

References

1. Part 1. J. F. Costello Part and S. G. Davies, J. Chem. Soc., Perkin Trans. 2, 1998, 1683.
2. For example, see E. L. Eliel, S. H. Wilen and L. N. Mander, Stereochemistry of Organic Compounds, Wiley Interscience, 1994, ch. 10–11.
3. Comprehensive Organometallic Chemistry II, Ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, New York, 1995.
4. Part 3. Triphenylphosphine coordinated to stereogenic octahedral metal centres, J. F. Costello and S. G. Davies, in preparation.
5. H. Brunner, B. Hammer, C. Kruger, K. Angermund and I. Bernal, Organometallics, 1985, 4, 1063.
6. B. J. Dunne, R. B. Morris and A. G. Orpen, J. Chem. Soc., Dalton Trans., 1991, 653; S. E. Garner and A. G. Orpen, J. Chem. Soc., Dalton Trans., 1993, 533.
7. D. A. V. Morton and A. G. Orpen, J. Chem. Soc., Dalton Trans., 1992, 641.
8. K. Chandrasekar and H. B. Bürgi, J. Am. Chem. Soc., 1983, 105, 7081; L. Nørskov-Lauritzen and H. B. Bürgi, J. Comput. Chem., 1985, 6, 216.
9. For studies upon P(C₆H₄Me-o)₃ coordinated to octahedral metal centres, see J. A. S. Howell, M. G. Palin, P. McArdle, D. Cunningham, Z. Goldschmidt, H. E. Gottlieb and D. Hezroni-Langerman, Inorg. Chem., 1991, 30, 4685; 1993, 32, 3493; Organometallics, 1993, 12, 1694; J. A. S. Howell, P. C. Yates, M. G. Palin, P. McArdle, D. Cunningham, Z. Goldschmidt, H. E. Gottlieb and D. Hezroni-Langerman, J. Chem. Soc., Dalton Trans., 1993, 2775.
10. For an interesting example see F. P. Fanizzi, M. Lanfranchi, G. Natile and A. Tiripicchio, Inorg. Chem., 1994, 33, 3331.
11. Equivalent to the transition state for the (a)zero-, (b)one- and (c)three-ring flip stereoisomerisation process. See, R. J. Kurland, I. I. Schuster and A. K. Colter, J. Am. Chem. Soc., 1965, 87, 2279; K. Mislow, Acc. Chem. Res., 1976, 9, 26; D. Gust and K. Mislow, J. Am. Chem. Soc., 1973, 95, 7157; P. Finocchiaro, D. Gust and K. Mislow, J. Am. Chem. Soc., 1973, 95, 1535; P. Finocchiaro, D. Gust and K. Mislow, J. Am. Chem. Soc., 1973, 95, 8172; M. R. Kates, J. D. Andose, P. Finocchiaro, D. Gust and K. Mislow, J. Am. Chem. Soc., 1975, 97, 1772.
12. R. S. Cahn, C. Ingold and V. Prelog, Angew. Chem., Int. Ed. Engl., 1966, 5, 385.
13. S. G. Davies, A. E. Derome and J. P. McNally, J. Am. Chem. Soc., 1991, 113, 2854; S. C. Case-Green, J. F. Costello, S. G. Davies, N. Heaton, C. J. R. Hedgecock, V. M. Humphreys, M. R. Metzler and J. C. Prime, J. Chem. Soc., Perkin Trans. 1, 1994, 933; S. J. Cook, J. F. Costello, S. G. Davies and H. T. Kruk, J. Chem. Soc., Perkin Trans. 1, 1994, 2369; J. F. Costello, S. G. Davies, R. M. Highcock, M. E. C. Polywka, M. W. Poulter, T. Richardson and G. G. Roberts, J. Chem. Soc., Dalton Trans., 1997, 105.
14. Molecular modelling calculations were carried out using the Chem-X package, distributed by Chemical Design Ltd., Oxford Molecular Group, The Medawar Centre, Oxford Science Park, Oxford, UK OX4 4GA.
15. M. S. Davies, G. W. Allen, M. J. Aroney, T. W. Hambley and R. K. Pierens, J. Mol. Struct., 1994, 326, 81.
16. F. A. Cotton, D. J. Darensbourg and W. H. Ilsley, Inorg. Chem., 1981, 20, 578; F. A. Cotton, D. J. Darensbourg and B. W. S. Kolthammer, Inorg. Chem., 1981, 20, 4440; A. Martin and A. G. Orpen, J. Am. Chem. Soc., 1996, 118, 1470.
17. M. J. Aroney, I. E. Buys, M. S. Davies and T. W. Hambley, J. Chem. Soc., Dalton Trans., 1994, 2827; K. J. Lee and T. L. Brown, Inorg. Chem., 1992, 31, 289; J. Polowin, S. C. Mackie and M. C. Baird, Organometallics, 1992, 11, 3724.
18. Originally, the conformational analysis of such transition metal complexes was based upon a pseudo-tetrahedral geometry. This led to the formulation of erroneous analyses and predictions, which were inconsistent with experimental data. For further detailed discussions, see: J. I. Seeman and S. G. Davies, J. Chem. Soc., Chem. Commun., 1984, 1019; J. Am. Chem. Soc., 1985, 107, 6522; A. D. Cameron, M. C. Baird, J. I. Seeman and S. G. Davies, J. Chem. Soc., Dalton Trans., 1985, 2691; S. G. Davies, I. M. Dordor-Hedgecock, K. H. Sutton and M. Whittaker, J. Am. Chem. Soc., 1987, 109, 5711.
19. P. M. Maitlis, Chem. Soc. Rev., 1981, 10, 1.
20. F. H. Allen and O. Kennard, Chemical Design Automation News, 1993, 8, 31.
21. G. Del Re, E. Gavuzzo, E. Giglio, F. Lelj, F. Mazza and V. Zappia, Acta Crystallogr., Sect. B, 1977, 33, 3289.