Evidence for the Synthesis of a "Stable" a-Bonded Xenon-Carbon Compound: Bis(trifluoromethy1)xenon
Sir:
A target of prime interest since the pioneering work of Bartlett in xenon chemistry' has been the synthesis of a compound in which carbon is sigma
bonded to xenon. Such a species is a definite possibility in view of the recent synthesis of FXeN(SO2F)2* and evidence from ion cyclotron resonance
experiments which estimate the strength of a xenon-carbon
bond to be in the range of 43 +/- 8 kcal/mol for Xe(CH3)+ The less stable species FXeCF3 has also been proposed as a reaction intermediate.
Previously in our laboratory we have developed a general synthesis for trifluoromethyl organometallic compounds employing reactions of plasma
generated radicals with metal halide
C2F6 - > 2CF3.
X = I, Br, CI
nCF3. + MX -> M(CF3), + 1/2X2
Considering the fact that xenon-fluorine bond strengths in XeF2 are on the order of 3 1 kcal/mol, i.e. weaker than many of the halogen-metal bonds
which have been broken in previous syntheses, synthesis of a xenon-carbon compound in this manner was thought to be a reasonable possibility. Crucial
factors for the success of such a synthesis are ( I ) that the electronic rearrangement lifetime of the radical FXe. be long with respect to the
collision frequency with an excess of trifluoromethyl radicals and (2) that, once formed in the free radical process, the molecular species Xe(CF3)z
be stable cnough to withstand collision and condensation.
By this synthetic method we were able to obtain a volatile, waxy, white solid which has a half-life of -30 min when contained in a Kel-F
container at room temperature. It has a much longer half-life (-2 weeks) at liquid nitrogen temperatures and decomposition is catalyzed by oxygen,
glass, and moisture. This new compound, believed to be Xe(CF3)2, sublimes under vacuum with a vapor pressure significantly greater than that of XeF2
and has very different physical properties. Thermal decomposition in the solid state while contained in a Kel-F tube gives xenon difluoride
and at least six (GLC evidence) fluorocarbon
products, presumably by a difluorocarbene elimination mechanism:
20 o c
Xe(CF3)2 - XeF2 + C,F,,
The XeF2 produced appears as a highly crystalline solid on the Kel-F tube in contrast to the original waxy solid and the fluorocarbon layer separates
over a 30-min period. Decomposition in the gas phase produces xenon and fluorocarbons including The synthetic procedure is identical with that
reported previously5 except that the entire plasma system is constructed of Teflon and other vacuum components are stainless steel and Kel-F.
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