Oxo-bridged binuclear molybdenum nitrosyl halides: structural and redox studies, mixed-valence behaviour, and characterisation of mononuclear hydroxo precursors

Abstract

The binuclear µ-oxo compounds [{Mo(NO)[HB(dmpz)₃]X}₂(µ-O)] (dmpz = 3,5-dimethylpyrazol-1-yl; X = I or Cl) have been prepared. These can occur as enantiomers, one of which (X = I) has been characterised previously, and a single-crystal X-ray diffraction study of the other enantiomer (X = I) established that the molecule has a slightly asymmetric Mo–O–Mo link. The binuclear complexes undergo two one-electron reductions (E_f¹ and E_f²) and one one-electron oxidation, established by cyclic voltammetry, the separation between E_f¹ and E_f² being ca. 1000 mV indicating that there is extremely strong interaction between the metal-containing redox centres. The EPR, IR and electronic spectra of the reduced monoanionic species [{Mo(NO)[HB(dmpz)₃]Cl}₂(µ-O)] ^- (S = ½) are consistent with valence-trapped (Class I) behaviour which is unusual in compounds with such short bridges. Formation of [{Mo(NO)[HB(dmpz)₃]X}₂(µ-O)] involves prior generation of [Mo(NO){HB(dmpz)₃}X(OH)] (X = Cl or I) by hydrolysis of [Mo(NO){HB(dmpz)₃}X₂] and reaction of the monohydroxide with [Mo(NO){HB(dmpz)₃}X₂]. The compound [Mo(NO){HB(dmpz)₃}(OH)₂] is also formed by reaction of [Mo(NO){HB(dmpz)₃}I₂] with water in solution and on contact with silica gel in dichloromethane. Its structure has been determined crystallographically, and it can be dehydrated on silica gel into [{Mo(NO)[HB(dmpz)₃](µ-O)}₂] which appears to contain a symmetrical {Mo(µ-O)₂Mo} bridging system.

References

1. N. J. Al Obaidi, S. S. Salam, P. D. Beer, C. D. Bush, T. A. Hamor, F. S. McQuillan, C. J. Jones and J. A. McCleverty, Inorg. Chem., 1992, 31, 263.
2. B. J. Coe, J.-D. Foulon, T. A. Hamor, C. J. Jones, J. A. McCleverty, D. Bloor, G. H. Cross and T. L. Axon, J. Chem. Soc., Dalton Trans., 1994, 3427; B. J. Coe, T. A. Hamor, C. J. Jones, J. A. McCleverty, D. Bloor, G. H. Cross and T. L. Axon, J. Chem. Soc., Dalton Trans., 1995, 673.
3. A. J. Amoroso, J. P. Maher, J. A. McCleverty and M. D. Ward, J. Chem. Soc., Chem. Commun., 1994, 1273.
4. H. Adams, N. A. Bailey, G. Denti, J. A. McCleverty, J. M. A. Smith and A. Wlodarczyk, J. Chem. Soc., Dalton Trans., 1983, 2287.
5. Nomenclature of Inorganic Chemistry, Recommendations 1990, ed. G. J. Leigh, Blackwell Scientific Publications, Oxford, 1990, p. 168.
6. S. L. W. McWhinnie, S. M. Charsley, C. J. Jones, J. A. McCleverty and L. J. Yellowlees, J. Chem. Soc., Dalton Trans., 1993, 413.
7. S. M. Charsley, C. J. Jones, J. A. McCleverty, B. D. Neaves, S. J. Reynolds and G. Denti, J. Chem. Soc.., Dalton Trans., 1988, 293; 1988, 301; N. J. Al Obaidi, S. L. W. McWhinnie, T. A. Hamor, C. J. Jones and J. A. McCleverty, J. Chem. Soc., Dalton Trans., 1992, 3299; A. Das, J. P. Maher, J. A. McCleverty, J. A. Navas and M. D. Ward, J. Chem. Soc., Dalton Trans., 1993, 681; A. Das, J. C. Jeffery, J. P. Maher, J. A. McCleverty, E. Schatz, M. D. Ward and G. Wollermann, Inorg. Chem., 1993, 32, 2145; J. P. Maher, J. A. McCleverty, M. D. Ward and A. Wlodarczyk, J. Chem. Soc., Dalton, Trans., 1994, 143.
8. J. A. McCleverty, D. Seddon, N. A. Bailey and N. W. Walker, J. Chem. Soc., Dalton Trans., 1976, 898.
9. A. S. Drane and J. A. McCleverty, Polyhedron, 1983, 2, 53; S. J. Reynolds, C. F. Smith, C. J. Jones, J. A. McCleverty, D. C. Bower and J. L. Templeton, Inorg. Synth., 1985, 23, 4; B. J. Coe, Ph.D. Thesis, The University of Birmingham, 1991.
10. J. A. Darr, S. R. Drake, M. B. Hursthouse and K. M. Abdul Malik, Inorg. Chem., 1993, 32, 5704.
11. N. P. C. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158; adapted for FAST geometry by A. Karaulov, University of Wales, Cardiff, 1991.
12. G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
13. G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Refinement, University of Göttingen, 1993.
14. J. A. McCleverty, A. E. Rae, I. Wolochowicz, N. A. Bailey and J. M. A. Smith, J. Chem. Soc., Dalton Trans., 1982, 951; A. Wlodarczyk, A. J. Edwards and J. A. McCleverty, Polyhedron, 1988, 7, 103.
15. A. Wlodarczyk, S. S. Kurek, J. A. McCleverty, S. Coles, M. H. B. Hursthouse and K. M. Abdul Malik, unpublished work.
16. C. J. Jones, J. A. McCleverty, B. D. Neaves, S. J. Reynolds, H. Adams, N. A. Bailey and G. Denti, J. Chem. Soc., Dalton Trans., 1986, 733; N. Al Obaidi, M. Chaudhury, D. Clague, C. J. Jones, J. C. Pearson, J. A. McCleverty and S. S. Salam, J. Chem. Soc., Dalton Trans., 1987, 1733.
17. J. A. Thomas, Ph.D. Thesis, University of Birmingham, 1993; A. Wlodarczyk, G. A. Doyle, J. P. Maher, J. A. McCleverty and M. D. Ward, Chem. Commun., 1997, 769; J. A. Thomas, A. Wlodarczyk, C. J. Jones, J. P. Maher, J. A. McCleverty and M. D. Ward, unpublished work.
18. J. A. McCleverty, J. A. Navas and M. D. Ward, J. Chem. Soc., Dalton Trans., 1994, 2415.
19. M. P. Robin and P. Day, Adv. Inorg. Chem. Radiochem., 1967, 10, 247.
20. J. H. Enemark and R. D. Feltham, Coord. Chem. Rev., 1974, 13, 339.
21. C. J. Jones, J. A. McCleverty, B. D. Neaves, S. J. Reynolds, H. Adams, N. A. Bailey and G. Denti, J. Chem. Soc., Dalton Trans., 1986, 733.
22. J. A. Baumann and T. J. Meyer, Inorg. Chem., 1980, 19, 345.
23. R. C. Cook, J. P. Maher, J. A. McCleverty and M. D. Ward, Polyhedron, 1993, 12, 2111.
24. A. Wlodarczyk, J. P. Maher, J. A. McCleverty and M. D. Ward, J. Chem. Soc., Chem. Commun., 1995, 2397; J. Chem. Soc., Dalton Trans., in the press.