EPR study of electron transfer and group transfer in organoplatinum(II) and (IV) compounds †

Abstract

Chelate complexes between the 1,4-diazabuta-1,3-diene ligands RN[double bond, length half m-dash]CH–CH[double bond, length half m-dash]NR = R–DAB (R = alkyl, aryl) and the organoplatinum fragments PtMe₂, PtMe₄ and PtMes₂ (Mes = mesityl) can be reversibly reduced to paramagnetic compounds, formulated as platinum(II) or (IV) species bound by radical anion ligands (R-DAB^˙–). EPR studies in fluid and frozen solution support this assignment; however, the metal contribution to the singly occupied MO is higher for the paramagnetic Pt^II species than for the Pt^IV systems. Comparison with related radical complexes of the main group and transition element series reveals that even the organoplatinum(IV) compounds exhibit a relatively high degree of ligand-to-metal spin transfer as evident from small ¹H(CH) and large ¹⁴N and ¹⁹⁵Pt EPR hyperfine coupling constants. The tetramethylplatinum(IV) complexes are photoreactive; a platinum-containing primary dissociation product from platinum–carbon σ bond homolysis has been detected by EPR spectroscopy using Bu^t-NO as a spin trap reagent during irradiation. Group transfer reactivity has also been noted for radical anions where the conversion [(R-DAB)PtMe₂]^˙– → [(R-DAB)PtMe₄]^˙– could be monitored by EPR spectroscopy.

References

1. (a) N. Farrell in Transition Metal Complexes as Drugs and Chemotherapeutic Agents, ed. B. R. James and R. Ugo, Reidel-Kluwer, Dordrecht, The Netherlands, 1989, p. 46; (b) M. J. Bloemink and J. Reedijk, in Metal Ions in Biological Systems, vol. 32, ed. H. Sigel and A. Sigel, Marcel Dekker, Inc., New York, 1996, p. 641; (c) W. I. Sundquist and S. J. Lippard, Coord. Chem. Rev., 1990, 100, 293.
2. (a) S. S. Stahl, J. A. Labinger and J. E. Bercaw, J. Am. Chem. Soc., 1996, 118, 5961; (b) M. W. Holtcamp, J. A. Labinger and J. E. Bercaw, J. Am. Chem. Soc., 1997, 119, 848.
3. (a) V. M. Miskowski and V. H. Houlding, Inorg. Chem., 1989, 28, 1529; (b) C.-M. Che, L.-Y. He, C.-K. Poon and C. W. Mak, Inorg. Chem., 1989, 28, 3081; (c) J. Biedermann, G. Gliemann, U. Klement, K.-J. Range and M. Zabel, Inorg. Chem., 1990, 29, 1884; (d) J. Biedermann, G. Gliemann, U. Klement, K.-J. Range and M. Zabel, Inorg. Chim. Acta, 1990, 169, 63; (e) H. Kunkely and A. Vogler, J. Am. Chem. Soc., 1990, 112, 5625; (f) V. M. Miskowski and V. H. Houlding, Inorg. Chem., 1991, 30, 4446; (g) L. Chassot and A. von Zelewsky, Helv. Chim. Acta, 1986, 69, 1855; (h) V. M. Miskowski, V. H. Houlding, C. M. Che and Y. Wang, Inorg. Chem., 1993, 32, 2518; (i) V. H. Houlding and V. M. Miskowski, Coord. Chem. Rev., 1991, 111, 145; (j) C. Cornioley-Deuschel and A. von Zelewsky, Inorg. Chem., 1987, 26, 3354; (k) A. von Zelewsky, P. Belser, P. Hayoz, R. Dux, X. Husa, A. Suckling and H. Stoeckli-Evans, Coord. Chem. Rev., 1994, 75; (l) C.-W. Chan, L.-K. Cheng and C.-M. Che, Coord. Chem. Rev., 1994, 32, 87; (m) S. D. Cummings and R. Eisenberg, J. Am. Chem. Soc., 1996, 118, 1949; (n) C. S. Peyratout, T. K. Aldridge, D. K. Crites and D. R. McMillin, Inorg. Chem., 1995, 34, 4484; (o) W. B. Connick, L. M. Henling, R. E. Marsh and H. B. Gray, Inorg. Chem., 1996, 35, 6261.
4. (a) P. S. Braterman, J.-I. Song, C. Vogler and W. Kaim, Inorg. Chem., 1992, 31, 222; (b) C. Vogler, B. Schwederski, A. Klein and W. Kaim, J. Organomet. Chem., 1992, 436, 367; (c) A. Klein, H.-D. Hausen and W. Kaim, J. Organomet. Chem., 1992, 440, 207; (d) P. S. Braterman, J.-I. Song, F. M. Wimmer, S. Wimmer, W. Kaim, A. Klein and R. D. Peacock, Inorg. Chem., 1992, 31, 5084; (e) S. Hasenzahl, H.-D. Hausen and W. Kaim, Chem. Eur. J., 1995, 1, 95; (f) W. Kaim and A. Klein, Organometallics, 1995, 14, 1176; (g) A. Klein, W. Kaim, E. Waldhör and H.-D. Hausen, J. Chem. Soc., Perkin Trans. 2, 1995, 2121; (h) R. J. Klinger, R. J. Huffman and J. K. Kochi, J. Am. Chem. Soc., 1982, 104, 2147; (i) S. A. MacGregor, E. McInnes, R. J. Sorbie and L. J. Yellowlees, in Molecular Electrochemistry of Inorganic, Bioinorganic and Organometallic Compounds, ed. A. J. L. Pombeiro and J. A. McCleverty, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1993, p. 503; (j) D. Collison, F. E. Mabbs, E. J. L. McInnes, K. J. Taylor, A. J. Welch and L. J. Yellowlees, J. Chem. Soc., Dalton Trans., 1996, 329; (k) M. G. Hill, J. A. Bailey, V. M. Miskowski and H. B. Gray, Inorg. Chem., 1996, 35, 4585; (l) E. J. L. McInnes, A. J. Welchand and L. J. Yellowlees, J. Chem. Soc., Chem. Commun., 1996, 2393; (m) A. Klein, W. Kaim, J. Fiedler and S. Zalis, Inorg. Chim. Acta, in the press.
5. (a) G. van Koten and K. Vrieze, Adv. Organomet. Chem., 1982, 21, 151; (b) K. Vrieze and G. van Koten, Inorg. Chim. Acta, 1985, 100, 79.
6. H. tom Dieck, K.-D. Franz and F. Hohmann, Chem. Ber., 1975, 108, 163.
7. S. Hasenzahl, A. Klein, W. Kaim, H. Stoll, S. Zalis and J. Fiedler, submitted to Organometallics.
8. L. Deng, P. Margl and T. Ziegler, J. Am. Chem. Soc., 1997, 119, 1094.
9. (a) W. Kaim and A. Schulz, Angew. Chem., 1984, 96, 611; Angew. Chem., Int. Ed. Engl., 1984, 23, 615; (b) A. Schulz and W. Kaim, Chem. Ber., 1989, 122, 1863; (c) A. Lichtblau, W. Kaim, A. Schulz and T. Stahl, J. Chem. Soc., Perkin Trans. 2, 1992, 1497.
10. J. D. Scott and R. J. Puddephatt, Organometallics, 1983, 2, 1643.
11. (a) W. Kaim, Top. Curr. Chem., 1994, 169, 231; (b) S. Hasenzahl, W. Kaim and T. Stahl, Inorg. Chim. Acta, 1994, 225, 23.
12. (a) G. G. Janzen, Acc. Chem. Res., 1971, 4, 31; (b) C. A. Evans, Aldrichim. Acta, 1979, 12, 23.
13. J. D. Scott and R. J. Puddephatt, Organometallics, 1986, 5, 1538.
14. (a) H. tom Dieck and I. W. Renk, Chem. Ber., 1971, 104, 92; (b) H. tom Dieck, M. Svoboda and T. Greiser, Z. Naturforsch., Teil B, 1981, 36, 823.
15. C. Eaborn, K. Kundu and A. Pidcock, J. Chem. Soc., Dalton Trans., 1981, 933.
16. W. Kaim, S. Ernst and V. Kasack, J. Am. Chem. Soc., 1990, 112, 173.
17. N. G. Connelly and W. E. Geiger, Chem. Rev., 1996, 96, 877.
18. W. Kaim, Coord. Chem. Rev., 1987, 76, 187 and literature cited.
19. B. A. Goodman and J. B. Raynor, Adv. Inorg. Chem. Radiochem., 1970, 13, 135.
20. M. Symons, Electron Spin Resonance Spectroscopy, Van Nostrand Reinhold Comp., New York, 1978.
21. M. Kaupp, H. Stoll, H. Preuss, W. Kaim, T. Stahl, G. van Koten, E. Wissing, W. J. J. Smeets and A. L. Spek, J. Am. Chem. Soc., 1991, 113, 5606.
22. G. van Koten, J. T. B. H. Jastrzebski and K. Vrieze, J. Organomet. Chem., 1983, 250, 46.
23. P. Clopath and A. v. Zelewsky, Helv. Chim. Acta, 1972, 55, 52.
24. R. R. Andrea, W. G. J. de Lange, T. van der Graf, M. Rijkhoff, D. J. Stufkens and A. Oskam, Organometallics, 1988, 7, 1100.
25. K. D. Franz, H. tom Dieck, U. Krynitz and I. W. Renk, J. Organomet. Chem., 1974, 64, 361.
26. E. Wissing, S. van der Linden, E. Rijnberg, J. Boersma, W. J. J. Smeets, A. L. Spek and G. van Koten, Organometallics, 1994, 12, 2602.
27. (a) C. G. Howard, G. S. Girolami, G. Wilkinson, M. Thornton-Pett and M. B. Hursthouse, J. Chem. Soc., Chem. Commun., 1983, 1163; (b) K.-H. Thiele, H. Windisch, H. Schumann and G. Kociok-Köhn, Z. Anorg. Allg. Chem., 1994, 620, 523.
28. W. Kaim, T. Roth, B. Olbrich-Deussner, R. Gross-Lannert, J. Jordanov and E. K. H. Roth, J. Am. Chem. Soc., 1992, 114, 5693.
29. S. Ernst, S. Kohlmann and W. Kaim, J. Organomet. Chem., 1988, 354, 177.