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Direct Synthesis and Reactions of Bromo(pentafluorophenyl)silanes.

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It is here seen that chloro(chloroformy1)sulfane reacts only
monofunctionally. Attempts to replace also the CI atom of
the chloroformyl group by the trifluoromethyl group failed.
This accords with findings by Zumnch and KiihIersJ in which
ClCOSCl was attacked by thiols only at the S-bonded CI
atom.
Compounds ( I ) and (2) are water-clear, mobile liquids
which are stable in absence of moisture (see Table).
Received: March 9, 1970; revised: March 25, 1970 [Z 208 IE]
German version: Angew. Chem. 82, 484 (1970)
[*I Prof. Dr. Dr. A. Haas, Dr. H. Reinke, and
Dip1.-Chem. J. Sommerhoff
Lehrstuhl fur Anorganische Chemie 11 der Universitat
463 Bochum, Postfach 2148 (Germany)
[**I Part 3 of Chemistry of F-C-S Compounds. - Part 2: [2].
[l] B. H . Tattershall and G. H . Cady, J. inorg. nuclear Chem.
29, 2819 (1967).
121 See A . Haas and D . Y . Oh, Chem. Ber. 102, 77 (1969).
131 Philips HPK Type 57203 B/OO, 125 W.
141 A . Haas and W . Klug, Chem. Ber. 101, 2617 (1968).
[5] G . Zumach and E . Kiihle, Angew. Chem. 82, 63 (1970);
Angew. Chem. internat. Edit. 9, 54 (1970).
Direct Synthesis and Reactions of
Bromo(pentafluoropheny1)silanes 111
By Manfred Weidenbruch and Nezam Wessal[*l
Halo(pentafluorophenyI)silanes, which are of interest for the
preparation of novel polysiloxanes, cannot be obtained by
reaction of silicon tetrahalides with (pentafluoropheny1)magnesium bromide o r -lithium because, even with a large
excess of the Six4 components, only tetrakis(pentafluor0pheny1)silane is formed [21. We have now found that a direct
synthetic process [31 affords them easily and with a selectivity
that is remarkable for perhalogenated compounds.
For instance, brornopentafluorobenzene reacts (optimum
temperature: 600 "C) with a catalyst composed of silicon
(85%) and copper (15%) t o give 60% of dibromobisbentafluoropheny1)silane ( I ) , b.p. 110 'C10.6 torr, and 30% of tribromo(pentafluoropheny1)silane (2), b.p. 205-208 "C, together with a little bromotris(pentafluorophenyl)silane, m.p.
83 "C:
Conversion of C6FsBr amounts to 10-30%, which indicates
the advisability of a recycling technique in which the unused
CsFsBr, b.p. 136 "C, is continuously distilled off fractionally
from the less volatile products and returned to the heated
catalyst. Decafluorobiphenyl (3), m.p. 68 'C, b.p. 188 OC, is
the only by-product formed in detectable amounts; the
proportion of (3) formed depends on the copper content of
the catalyst and produces difficulties if it exceeds 20%. On
pure copper C6FsBr gives (3) quantitatively at 600 'C.
Chloropentafluorobenzene reacts analogously, giving chloro@entafmorophenyl)silanes, though the conversion is, as expected, lower because of the greater bond energy of R-CI
than of R-Br. Hexafluorobenzene does not react with the
Si/Cu catalyst up t o 600 OC.
Applicability of compounds ( I ) and (2) to synthesis of
further pentafluorophenyl-substituted silanes and polysiloxanes is indicated by the annexed chart of some reactions
of ( I ) :
Heating ( I ) or (2) with antimony trifluoride leads to the
fluorosilanes (41, b.p. 207 OC, and C6F5SiF3, b.p. 102 "C,
respectively, which, like bromosilanes, react spontaneously
with water. Hydrolysis of ( I ) and similarly of ( 4 ) proceeds
via the stable silanediol (51, m.p. 12@-122"C,
which condenses at the melting point to give the resinous polysiloxane
( 6 ) ,m.p. > 170 "C. On prolonged heating or o n storage, ( 6 )
changes, without alteration in composition, to a silicone
that is very resistant both thermally and chemically and has
celluloid-like properties, melting at > 350 'C.
Received: March 28, 1970
[Z 211 IEl
German version: Angew. Chem. 82, 483 (1970)
[ * ] Dr. M . Weidenbruch and Dipl.-Chem. N. Wessal
Institut fur Anorganische Chemie und Elektrochemie
der Technischen Hochschule
51 Aachen, Templergraben 55 (Germany)
[l] Pentafluorophenyl Compounds, Part 3. - Part 2: M ,
Schmeisser, N . Wessal, and M . Weidenbruch, Chem. Ber. 101.
1897 (1968).
[2] L. A . Wall, R . E. Donadio, and W. J . Pummer, J. Amer.
chem. SOC.82, 4846 (1960).
[3] For a review, see V . Baiant, J . Joklik, and J . Rathousk9,
Angew. Chern. 80, 133 (1968); Angew. Chem. internat. Edit.
7, 112 (1968).
C O N F E R E N C E REPORTS
Synthesis of Pteridine 8-Ribosides
By Wolfgang Pf?eiderer[*l
The synthesis ofpteridine 8-ribosides ( I ) , the structural analogs
of the purine nucleosides (21, has been the focal point of our
investigations in the field of pteridines for more than twelve
years.
Previous investigations o n the glycosidation of 7-oxo-7,8dihydropteridines by the heavy-metal salt method have shown
that 7-0 glycosides are always formed and no N-8 glycosides [I]. The analogous behavior of the 2-oxodihydroquinoxalines 121 and of 2-pyrazinone [31 helped to clarify the complex nature of the reaction and showed that the observed
selectivity in the direct glycosidation of the pteridine system
Angew. Chem. internat. Edit. f Vol. 9 (1970) No. 6
under such conditions is determined primarily by two factors
steric hindrance and the particular electronic features of the
pyrazine system - both of which oppose a n O + N transglycosidation.
467
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