Anion dependent deprotection of a thioether group in Schiff base NS₂ ligands results in new mononuclear and dinuclear thiolato nickel complexes

Abstract

The synthesis and characterisation of three Schiff base compounds of nickel with NS₂ donor groups is described as part of our research in structural modelling of nickel hydrogenase enzymes. 2-Aminothiophenol and 2-tert-butylthiobenzaldehyde reacted in ethanol to form a benzothiazolidine derivative, which is isolated as a yellow solid. The benzothiazolidine ring opens upon reaction with nickel acetate in ethanol to form a mononuclear complex, [Ni(^tBuL¹)₂], 1, which crystallises in the monoclinic space group P 2₁/n with cell dimensions, a = 14.665(4), b = 14.800(7), c = 14.923(6) Å, β = 94.45(3)°. Compound 1 is mononuclear with a cis N₂S₂ chromophore, which is square planar, but slightly distorted towards tetrahedral, and which shows weak interactions with two hydrogens of the ligands (Ni–H distances of 2.52 and 2.58 Å). These C–H  · · ·  Ni interactions are retained in solution as reflected in the ¹H NMR spectra of 1. With other nickel salts, the same benzothiazolidine ligand reacts in ethanol to form dinuclear species [Ni(L¹)]₂ 2, after loss of the protecting tertiary butyl group. Complex 2 crystallises in the monoclinic space group P 2₁/c with cell dimensions, a = 11.753(3), b = 11.977(3), c = 20.275(4) Å, β = 123.67(1)°. An analogous ligand, synthesised from 2-aminoethanethiol and 2-tert-butylthiobenzaldehyde, was not isolated, but was used in a template reaction with nickel salts in ethanol to form the dinuclear compound [Ni(L²)]₂ 3. Complex 3 crystallises in the monoclinic space group P 2₁/c with cell dimensions a = 15.049(4), b = 10.554(2), c = 12.921(4) Å, β = 108.68(2)°. Compounds 2 and 3 are dinuclear, in a ‘butterfly’ shape, with bridging thiolates. The nickel ions in these two dinuclear complexes are in a NS₃ chromophore with a square planar geometry.

References

1. M. W. W. Adams, L. E. Mortenson and J. S. Chen, Biochim. Biophys. Acta, 1980, 594, 105.
2. E. G. Graf and R. K. Thauer, FEBS Lett., 1981, 136, 165; M. W. W. Adams and L. E. Mortenson, J. Biol. Chem., 1984, 259, 7045; E. C. Hatchikian, N. Fourget, V. M. Fernandez, R. Williams and R. Cammack, Eur. J. Biochem., 1992, 209, 357.
3. R. K. Thauer, A. R. Klein and G. C. Hartmann, Chem. Rev., 1996, 96, 3031.
4. A. Volbeda, M.-H. Charon, C. Piras, E. C. Hatchikian, M. Frey and J. C. Fontecilla-Camps, Nature (London), 1995, 373, 580; A. Volbeda, E. Garcin, C. Piras, A. L. deLacey, V. M. Fernandez, E. C. Hatchikian, M. Frey and J. C. Fontecilla-Camps, J. Am. Chem. Soc., 1996, 118, 12989.
5. R. P. Happe, W. Roseboom, A. J. Pierik, S. P. J. Albracht and K. A. Bagley, Nature (London), 1997, 385, 126.
6. J. C. Fontecilla-Camps, J. Bioinorg. Chem., 1996, 1, 91; M. A. Halcrow and G. Christou, Chem. Rev., 1994, 94, 2421.
7. R. K. Henderson, E. Bouwman, J. Reedijk and A. K. Powell, Acta Crystallogr., Sect. C, 1996, 52, 2696; W. J. J. Smeets, A. L. Spek, R. K. Henderson, E. Bouwman and J. Reedijk, Acta Crystallogr., Sect. C, 1997, 53, 1564.
8. V. E. Kaasjager, R. K. Henderson, E. Bouwman, M. Lutz, A. L. Spek and J. Reedijk, Angew. Chem., Int. Ed., 1998, 37, 1668.
9. O. Meth-Cohn and B. Tarnowski, Synthesis, 1978, 58.
10. G. M. Sheldrick, SHELXTL (version 5.03) Siemens Analytical X-ray Instruments Inc., Madison, WI, 1993.
11. P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, S. García-Granda, R. O. Gould, J. M. M. Smits and C. Smykalla, The DIRDIF 92 program system, Technical Report of the Crystallography Laboratory, University of Nijmegen, 1992.
12. G. M. Sheldrick, SHELXS 96, Program for crystal structure solution, University of Göttingen, 1996.
13. A. L. Spek, Acta Crystallogr., Sect. A, 1990, 34, C34.
14. G. M. Sheldrick, SHELXL93, Program for crystal structure refinement, University of Göttingen, 1993.
15. L. F. Lindoy and S. E. Livingstone, Inorg. Chem., 1968, 7, 1149; L. F. Lindoy, D. H. Busch and V. Goedken, J. Chem. Soc., Chem. Commun., 1972, 683; T. Kawamoto, H. Huma and Y. Kushi, Chem. Commun., 1996, 2121; A. Müller, K. U. Johannes, W. Plass, H. Bögge, E. Krahn and K. Schneider, Z. Anorg. Allg. Chem., 1996, 622, 1765.
16. W. Yao, O. Eisenstein and R. H. Crabtree, Inorg. Chim. Acta, 1997, 254, 105.
17. H. Frydendahl, H. Toftlund, J. Becher, J. C. Dutton, K. S. Murray, L. F. Taylor, O. P. Anderson and E. R. T. Tiekink, Inorg. Chem., 1995, 34, 4467.
18. A. D. Watson, C. P. Rao, J. R. Dorfman and R. H. Holm, Inorg. Chem., 1985, 24, 2820.
19. G. J. Colpas, M. Kumar, R. O. Day and M. J. Maroney, Inorg. Chem., 1990, 29, 4779.
20. B. S. Snyder, C. P. Rao and R. H. Holm, Aust. J. Chem., 1986, 39, 936; J. R. Nicholson, G. Christou, J. C. Huffman and K. Folting, Polyhedron, 1987, 6, 863.
21. S. B. Choudhury and A. Chakravorty, Inorg. Chem., 1992, 31, 1055.
22. D. J. Baker, D. C. Goodall and D. S. Moss, Chem. Commun., 1969, 325; G. A. Barclay, E. M. McPartlin and N. C. Stephenson, Acta Crystallogr., Sect. B, 1969, 25, 1262; S. B. Choudhury, M. A. Pressler, S. A. Mirza, R. O. Day and M. J. Maroney, Inorg. Chem., 1994, 33, 4831.
23. H.-J. Krüger and R. H. Holm, Inorg. Chem., 1989, 28, 1148; S. A. Mirza, M. A. Pressler, M. Kumar, R. O. Day and M. J. Maroney, Inorg. Chem., 1993, 32, 977; R. Hahn, A. Nakamura, K. Tanaka and Y. Nakayama, Inorg. Chem., 1995, 34, 6562.