Perfluorovinyl–metal derivatives: a new one-pot synthesis
Kulbinder K. Banger, Alan K. Brisdon* and Arti Gupta
Department of Chemistry, University of Manchester Institute of Science and Technology, PO Box 88, Manchester, UK M60 1QD
The one-pot reaction of the CFC replacement
1,1,1,2-tetrafluoroethane (CF3CFH2, HFC-134a) with 2
equiv. of butyllithium in diethyl ether at 278 °C followed by
the addition of main-group or transition-metal halides
results in good yields of the corresponding metal–
perfluorovinyl compounds of high purity.
being worked up using existing routes.5 Extraction of the
organic phases followed by drying and evaporation of the
organic solvents results in the generation of the perfluorovinyl
metal compound in good yield (typically > 90%, based on the
metal complex).
An analogous reaction using a 1:1 ratio of mercury(ii)
chloride to perfluorovinyllithium reagent generates the mono-
substituted complex. NMR studies suggest that a very small
amount of bis(perfluorovinyl)mercury is also present (typically
< 5%) in the crude product. The relatively high volatility of
fluorine-containing compounds coupled with their thermally
robust nature means that further purification of the products, if
necessary, may often be achieved by distillation or sublimation.
For example sublimation of the crude product from the 1:1
reaction at 100 °C (20 mmHg) results in an air-stable, white
solid which is analytically pure ClHg(CFNCF2) 3.
Having confirmed that this route may be used successfully to
synthesise known perfluorovinyl complexes in high yield the
extent of its utility as a general method of introducing the
–CFNCF2 moiety into a wide range of substrates was investi-
gated by reaction with a variety of early- and late-transition
metal coordination complexes and organometallic compounds.
All reactions were carried out in a similar manner to that
described above. Confirmation of the identity of the materials
synthesised as perfluorovinyl metal complexes was obtained by
elemental analysis and spectroscopic measurements.† In all
cases 19F NMR spectra clearly demonstrated three sets of
doublets of doublets with the anticipated satellite structure due
to coupling with spin-active metal nuclei being evident where
appropriate. A summary of these reactions is presented in
Fig. 1.
The stability of these complexes is variable, with the majority
of these complexes being thermally stable, although decom-
position does occur in the presence of water or on extended
contact with glassware, however the pentacarbonyl manganese
perfluorovinyl complex decomposes rapidly under aqueous
conditions.
Although fluorine is capable of replacing hydrogen in many
organic systems usually without major structural changes the
number of examples of organometallic complexes containing
perfluorinated ligands is very much more limited than for the
comparable perprotio analogues.1 Of the examples that do exist
in the literature many of the smaller fluorine-containing organic
fragments are derived from bromofluorocarbons (BFCs) or
chlorofluorocarbons (CFCs). However starting materials like
these are currently being phased out under international and
national agreements, such as the Montreal Protocol, due to their
deleterious effect on the ozone layer. A case in point is the
synthesis of perfluorovinyl (CF2NCF–) derivatives which have
previously used bromotrifluoroethene as the starting material.
This pyrophoric compound is no longer commercially produced
which will ultimately result in it being unavailable for pure
research applications and thus this route will become obsolete.
Very recent work2 has focused on the use of one of the
hydrofluorocarbon replacements for CFCs, 1,1,1,2-tetrafluoro-
ethane (CF3CFH2, HFC-134a) as an alternative perfluorovinyl
source for organic synthesis.
In view of the recent resurgence in interest in the chemistry of
organofluorine compounds and in particular their coordination
to metal centres to induce C–F bond activation3 we report the
‘one-pot’ synthesis of metal perfluorovinyl compounds using
HFC-134a as a perfluorovinyl source. The addition of 2 equiv.
of n-butyllithium to a diethyl ether solution of HFC-134a at
278 °C results in the double deprotonation and elimination of
1 equiv. of lithium fluoride from HFC-134a to generate the
CF2NCF2Li+ reagent 1 in good yields. Compound 1 generated
in this way is stable in solution for up to 24 h at this temperature
but decomposes rapidly as the temperature is increased above
245 °C. The formation of metal perfluorovinyl complexes is
readily achieved by adding concentrated cold diethyl ether or
thf solutions of metal halides to the lithium reagent. This
immediately results in reaction and the formation of an off-
white precipitate of the lithium halide. Multinuclear NMR
studies were found to be a convenient method to monitor the
progress of these reactions and to determine the degree of
perfluorovinyl substitution, prior to work-up procedures. Sam-
ples withdrawn from the organic phase of the reaction of
CF2NCF2Li+ and HgCl2 in a 2:1 ratio were transferred to NMR
tubes and allowed to warm to room temperature. 19F NMR
spectra show replacement of the complex multiplet signals due
to HFC-134a at d 264.9 and 2226.5 by three sets of doublets
of doublets typical of the AMX pattern previously observed for
perfluorovinyl metal complexes4 each with associated mercury
satellite structure. The extent of substitution of the product may
also be conveniently determined by NMR, in this case from the
199Hg NMR spectra which exhibit a triplet of triplets of triplets
so confirming unequivocally the product as [Hg(CFNCF2)2]2 2.
This compound was isolated as a clear liquid after allowing the
reaction mixture to slowly warm to room temperature before
Me3Sn(CF=CF2)
HgCl(CF=CF2)
cis-[Pt(PPh3)2(CF=CF2)2]
Me3SnCl
0.5 equiv.
HgCl2
cis-[Pt(PPh3)2Cl2]
0.5 equiv. HgCl2
BuLi
CF2CF–Li+
Hg(CF=CF)2
CH2FCF3
Et2O, –78 °C
cis-[Pt(PBu3)2Cl2]
[Fe(η-C5H5)(CO)2I]
[Mn(CO)5Br]
cis-[Pt(PBu3)2(CF=CF2)Cl]
[Fe(η-C5H5)(CO)2(CF=CF2)]
[Mn(CO)5(CF=CF2)]
Fig. 1 Reactions of perfluorovinyllithium, derived from CF3CH2F, with a
variety of metal halides
Chem. Commun., 1997
139
Banger, Kulbinder K.
