The reactivity of Me3SiNMe2 towards AsF5 and BF3

2184

I. C. TORNIEPORT~-OE~ING~

Fig. 1. Temperature-dependent

and T. M. KLAPiiTKE*

‘H NMR spectrum of a mixture of 2,3 and 4 in SOz solution.

m, br (3). The temperature-dependent NMR spectrum of the CFCl 3 sample did not show any change in the range - 50 to + 60°C.

AsFs [eq. (I)] seems to be even more thermodyna~~lly favourable (AH = - 1.3 kcal mol- ‘, Scheme 1) and AsF,, Me,NF and Me&F are the only products which have been identified.

RESULTS AND DISCUSSION

l+AsF,--+

Although the adduct formation between 1 and AsF, should be exothermic,3 the oxidation of 1 by

AsF5(g)

As(g)

+

+

Ie3Si-Nfie2(9)

5 F(Q)

-

Me,SiF+Me2NF+AsF,

(1)

In contrast to AsF,, BF3 does not represent a strong oxidizing agent and therefore we investigated

He 2 NF(g)

+

14e3S1F(s)

+

AsF3(9)

I

I

Scheme 1. Energy cycle to estimate the heat of reaction (1). (a) B.E.(As”-F) = 97.1,9 (b) B.E.(Si-N) = 79.7, ‘O(c)B.E.(As”‘-F) = 116.5, ‘O(d) B.E.(Si-F) = 142.8, lo (e) B.E.(N-F) 3 74.2, calibrated on B.E.(N-F, NF,) = 66.5” and B.E.(N--F, NF,).= 70.3” (al1 values in kcal mol-’ ; cal = 4.184 J).

2186

I. C. TORNIEPDRTH-OETTING*

Table 1. Concentrations of 2,3 and 4 in a sealed NMR tube in SO2 solution at various temperatures and pressures, starting from an equimolar mixture of l(0.6 mmol) and BF,

T (“C)

p/bar (psi)

2

c (mol dm- 3, 3

4

+60 +20 -10 -30 -50

12.0 (168) 3.3 (46) 1.0 (14) 0.4 (5.6) 0.3 (4.2)

0.13 0.22 0.23 0.20 0.08

0.24 0.11 0.12 0.12 0.17

0.00 0.16 0.15 0.17 0.19

represents the major product, while the concentration of 4 decreased to almost zero. This behaviour can be explained by the exothermic dimerization of 2 yielding 3l’ and the weak but still exothermic adduct formation between 2 and SO* (yielding 4). Therefore, at high temperatures 2 should be favoured rather than 3. However, the SO,-containing NMR tube was sealed and the increasing pressure (cf. Fig. 1) strongly favours the formation of the dimer. REFERENCES 1. I. C. Tomieporth-Oetting, T. M. Klapiitke, T. S. Cameron, J. Valkonen, P. Rademacher and K. Kowski, J. Chem. Sot., Dalton Trans. 1992, 537.

and T. M. KLAPijTKE* U. Behrens, T. M. 2. I. C. Tomieporth-Oetting, Klapiitke and P. S. White, J. Chem. Sot., Dalton Trans. in press. and T. M. Klapiitke, 3. I. C. Tornieporth-Oetting Chem. Ber. 1992, 125,407. 4. I. C. Tomieporth-Oetting, T. M. Klapiitke and P. S. White, to be submitted. 5. K. Beeker, J. J. Lagowski and K. Niedenzu, Gmelin, Handbuch der Anorganischen Chemie, Vol. 22, p. 111. Borverbindungen, F.R.G. (1975). 6. E. A. Ebsworth and H. J. Emeltus, J. Chem. Sot. 1958,215O. 7. S. Sujisbi and S. Witz, J. Am. Chem. Sot. 1957, 79, 2447. 8. P. K. Gowik and T. M. Klapotke, J. Organomet. Chem. 1989,368,35. 9. J. E. Huheey, Anorganische Chemie. Walter de Gruyter, Berlin, New York (1988) appendix. 10. D. A. Johnson, Some Thermodynamic Aspects of Inorganic Chemistry, p. 202. Cambridge University Press, Cambridge (1982). 11. H. Niith and H. Vahrenkamp, Chem. Ber. 1967,100, 3353. 12. A. J. Banister and N. N. Greenwood, J. Chem. Sot. 1965, 1534. 13. R. G. Parr and R. G. Pearson, J. Am. Chem. Sot. 1983,105,7512. 14. R. G. Pearson, Znorg. Chem. 1988,27,734. 15. R. Minkwitz, W. Molsbeck and H. Preut, Z. Naturforsch. 1989,44b, 1581. 16. R. A. Wiesboeck and J. K. Ruff, Znorg. Chem. 1966, 5, 1629. 17. R. Schmutzler, J. Chem. Sot. 1964,455l.