Synthesis and structural characterization of [Tp^But₂]GaS: a terminal gallium sulfido complex in a system for which the indium counterpart is a tetrasulfido derivative, [Tp^But₂]In(η²-S₄)

Abstract

The synthesis of the terminal gallium sulfido complex [Tp^But₂]GaS via the reaction of monovalent [Tp^But₂]Ga with elemental sulfur provides a striking contrast with the formation of the tetrasulfido derivative [Tp^But₂]In(η²-S₄) in the indium system; such an observation provides a strong indication that gallium exhibits a greater tendency to partake in multiple bonding than does indium.

References

1. M. C. Kuchta and G. Parkin, Coord. Chem. Rev., in the press.
2. M. C. Kuchta and G. Parkin, Inorg. Chem., 1997, 36, 2492.
3. M. C. Kuchta and G. Parkin, J. Am. Chem. Soc., 1995, 117, 12 651.
4. M. C. Kuchta and G. Parkin, Main Group Chem., 1996, 1, 291.
5. G. Parkin, Prog. Inorg. Chem., 1998, 47, 1.
6. A notable difference in their chemistry, however, is the greater tendency of indium to form subvalent derivatives. See, F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, Wiley, New York, 5th edn., 1988.
7. M. C. Kuchta, J. B. Bonanno and G. Parkin, J. Am. Chem. Soc., 1996, 118, 10 914.
8. Pentane (ca.10 mL) was added to a mixture of [Tp^But₂]Ga (0.300 g, 0.48 mmol) and sulfur (0.030 g, 0.94 mmol) which was stirred overnight at room temperature. The mixture was filtered and the residue was extracted into toluene (ca. 10 mL). The volatile components were removed from the toluene extract under reduced pressure and the solid obtained was washed with pentane (2 × 10 mL) and dried in vacuo giving [Tp^But₂]GaS as a white solid (0.065 g, 21% based upon [Tp^But₂]Ga)(Found: C, 58.5 H, 8.4; N, 11.4. Calc. for C₃₃H₅₈N₆BGaS: C, 60.8; H, 9.0; N, 12.9%). IR data: 2644m cm^–1[ν(B–H)]. ¹H NMR (C₆D₆): δ 1.19 [s, 27 H, 3C(CH₃)₃], 1.85 [s, 27 H, 3C(CH₃)₃], 6.00 [s, 3 H, 3CH](B–H not observed). ¹³C NMR (C₆D₆): δ 30.5 [q, ¹J_C–H= 126, 3C(CH₃)₃], 31.1 [q, ¹J_C-H= 126, 3C(CH₃)₃], 32.7 [s, 3C(CH₃)₃], 33.3 [s, 3C(CH₃)₃], 103.5 [d, ¹J_C–H= 175 Hz, 3CH], 159.7 [s, 3CC(CH₃)₃], 167.9 [s, 3CC(CH₃)₃].
9. ¹H NMR spectroscopy indicates that [Tp^But₂] GaS is stable in the presence of excess sulfur and furnishes no evidence for the formation of [Tp^But₂]Ga(η²-S₄).
10. [Tp^But₂]GaS: C₃₃H₅₈BGaN₆S, M= 651.44, triclinic, P1̄(no. 2), a= 10.870(2), b= 13.210(3), c= 13.308(3)Å, α= 95.29(1), β= 100.37(1), γ= 92.67(1)°, U= 1867.7(6)ų, Z= 2, µ= 0.822 mm^–1, T= 293 K, R1 = 0.1021 for 4780 reflections. CCDC reference number 186/1037.
11. The [Ga≈S] interaction may be considered to be a composite of the resonance structures [G⁺–S^–], [G=S] and [G^–≡S⁺]. Of these, it is likely that the polar form [G⁺–S^–] provides an important contribution, in which case the multiple bond is best viewed as being composed of both covalent, and ionic interactions, i.e. a semipolar double bond. See, L. Pauling, The Nature of the Chemical Bond, Cornell University Press, Ithaca, 3rd edn., 1960, p. 9.
12. The range of Ga–S bond lengths is 2.17–2.55 Å. CSD Version 5.14, 3 D Search and Research Using the Cambridge Structural Database, F. H. Allen and O. Kennard, Chem. Des. Artomat. News, 1993, 8, pp. 1 and 31–37..
13. For recent reviews which include singly bonded chalcogenolate complexes of the Group 13 elements, see, J. P. Oliver, J. Organomet. Chem., 1995, 500, 269; J. Arnold, Prog. Inorg. Chem., 1995, 43, 353.
14. For further comparisons, the Ga≈Se, and Ga≈Te bond lengths in [Tp^But₂]GaSe and [Tp^But₂]GaTe and 2.214(1) and 2.422(1)Å, respectively. The increments in M≈E bond lengths are comparable to the values predicted by the double bond covalent radii of E: S (0.94), Se (1.07) and Te (1.27 Å). See ref. 2 and L. Pauling, The Nature of the Chemical Bond, Cornell University Press, Ithaca, 3rd edn., 1960.
15. For example, [Tp^But₂] GaS does not react with PMe₃ at 80 °C. Furthermore, since the reverse reaction, i.e. sulfido transfer from R₃PS to [Tp^But₂]Ga, does not occur at tem peratures up to 120 °C, it is evident that there is an inaccessible kinetic barrier for sulfido transfer in this system such that it is not possible to infer relative Ga≈S versus P≈S bond energies. In contrast, selenido transfer between R₃PSe and [Tp^But₂]Ga is facile and equilibrium studies have demonstrated that the Ga≈Se interaction in [Tp^But₂]GaSe is ca. 7 kcal mol^–1(cal = 4.184 J) stronger than the P≈Se bond in Et₃PSe (see ref. 2)..
16. This reaction likewise does not yield spectroscopically identifiable quantities of [Tp^But₂]In(S_x)(x= 1–3).
17. Other complexes containing the [In(η²-S₄)] moiety are for example See, for example, P. P. Paul, T. B. Rauchfuss and S. R. Wilson, J. Am. Chem. Soc., 1993, 115, 3316; S. Dhingra and M. G. Kanatzidis, Polyhedron, 1991, 10, 1069; S. S. Dhingra and M. G. Kanatzidis, Inorg. Chem., 1993, 32, 3300; D. L. Reger and P. S. Coan, Inorg. Chem., 1995, 34, 6226; W. Bubenheim and U. Müller, Z. Anorg. Allg. Chem., 1994, 620, 1607.
18. N. Tokitoh, T. Matsumoto, H. Ichida and R. Okazaki, Tetrahedron Lett., 1991, 32, 6877.
19. Tbt = 2,4,6-[(Me₃Si)₂CH]₃C₆H₂, Tip = 2,4,6-Prⁱ₃C₆H₂, Mes = 2,4,6-Me₃C₆H₂.
20. Another noteworthy example of the formation of M≈E multiple versus single bonds is provided by the observation that {η²-[(C₉H₆N)(Me₃Si)CH]}₂SnSe exists as a terminal selenido complex, whereas [{(C₉H₆N)(Me₃Si)CH}₂Sn(µ-S)]₂ is a sulfido-bridged dimer; however, the supporting ligands adopt different co-ordination modes in these particular examples. See, W.-P. Leung, W.-H. Kwok, L. T. C. Law, Z.-Y. Zhou and T. C. W. Mak, Chem. Commun., 1996, 505.