Preparation and Functionalization of a Range of Main-Group Trifluoropropynyl Organometallic Compounds: The Application of Metalloid-Directed Carbolithiation to the Selective Synthesis of Novel Fluorocarbon Fragments

Article abstract of DOI:10.1021/om034146t

The reaction of 1,1,1,3,3-pentafluoropropane (CF₃CH ₂CF₂H, HFC-245fa) with 3 equiv of n-butyllithium at -10 °C leads to the generation of trifluoropropynyllithium in excellent yields. This reagent reacts readily with a range of group 14 electrophiles R _4-n-EX_n (R = Ph, Et; E = C, Si, Ge, Sn, Pb; X = Cl, Br) to yield the organometalloid trifluoropropynyl compounds R _4-nE(C≡CCF₃)_n. Three of these compounds, Ph₃EC≡CCF₃ (E = C, Si, Ge), have been crystallographically characterized, representing the first such study of these materials. The silane Ph₃SiC≡CCF₃ has been derivatized by reaction with LiAlH₄ and a range of organolithium reagents (RLi, R = n-Bu, Ph, t-Bu) to afford a new series of β-CF ₃-substituted vinylsilanes of the type Ph₃SiCH=C(CF ₃)R, with predominantly E geometry at the double bond. In the cases R = n-Bu, t-Bu, and Ph, these materials have been crystallographically characterized. Additionally, a remarkably facile cyclization pathway for Ph ₃Si≡CCF₃, initiated by t-BuLi, that yields the respective gem-difluorocyclopropene has been explored and is described in detail, along with its extension to a number of other systems.

Full text of DOI:10.1021/om034146t

5534
Organometallics 2003, 22, 5534-5542
P r ep a r a tion a n d F u n ction a liza tion of a Ra n ge of
Ma in -Gr ou p Tr iflu or op r op yn yl Or ga n om eta llic
Com p ou n d s: Th e Ap p lica tion of Meta lloid -Dir ected
Ca r bolith ia tion to th e Selective Syn th esis of Novel
F lu or oca r bon F r a gm en ts
Alan K. Brisdon,* Ian R. Crossley, Robin G. Pritchard, Ghazala Sadiq, and
J ohn E. Warren
Department of Chemistry, UMIST, P.O. Box 88, Manchester M60 1QD, U.K.
Received September 1, 2003
The reaction of 1,1,1,3,3-pentafluoropropane (CF3CH2CF2H, HFC-245fa) with 3 equiv of
n-butyllithium at -10 °C leads to the generation of trifluoropropynyllithium in excellent
yields. This reagent reacts readily with a range of group 14 electrophiles R4-nEXn (R ) Ph,
Et; E ) C, Si, Ge, Sn, Pb; X ) Cl, Br) to yield the organometalloid trifluoropropynyl
compounds R4-nE(CtCCF3)n. Three of these compounds, Ph3ECtCCF3 (E ) C, Si, Ge), have
been crystallographically characterized, representing the first such study of these materials.
The silane Ph3SiCtCCF3 has been derivatized by reaction with LiAlH4 and a range of
organolithium reagents (RLi, R ) n-Bu, Ph, t-Bu) to afford a new series of â-CF3-substituted
vinylsilanes of the type Ph3SiCHdC(CF3)R, with predominantly E geometry at the double
bond. In the cases R ) n-Bu, t-Bu, and Ph, these materials have been crystallographically
characterized. Additionally, a remarkably facile cyclization pathway for Ph3SiCtCCF3,
initiated by t-BuLi, that yields the respective gem-difluorocyclopropene has been explored
and is described in detail, along with its extension to a number of other systems.
In tr od u ction
compounds (-CtCCF3) can be similarly obtained, via
the respective lithium reagent, generated under mild
conditions from the commercially available hydrofluo-
rocarbon 245fa (1,1,1,3,3-pentafluoropropane, CF3CH2-
CF2H).5 This constitutes the most convenient synthetic
route yet developed for these materials, previous work
having utilized gaseous reagents and much lower
temperatures.6-9 Indeed, these materials are now more
readily available than ever before, potentially even on
an industrial scale.
Despite the unique biological and physical properties
imparted by the CF3 group, and the obvious versatility
of alkynes as building blocks for more functional mol-
ecules, trifluoropropynyl compounds have received rela-
tively little study to date. Where these materials have
been explored, work has been largely restricted to
organic derivatives,10 despite the existence of a signifi-
cant, though small, range of organometallic systems. In
particular, it is noted that while a number of silicon and
The importance of fluorinated compounds is becoming
paramount, particularly with regard to their pharma-
ceutical, agrochemical, and materials applications.1,2
Consequently, the identification of new synthetic routes
to such materials and subsequent exploration of their
reactivity continue to be areas of intense research. In
particular, the growing need for methods of selectively
introducing small, fluorinated functions is an area of
great current interest,3 which has led to a strong
impetus for the development and study of organome-
tallic systems, given the extensive applications of their
hydrocarbon counterparts.
We have been exploring organometallic trifluorovinyl
compounds, derived from readily available hydrofluo-
rocarbon precursors,4 to this end. More recently, we
have reported for the first time that trifluoropropynyl
* Corresponding author. E-mail: alan.brisdon@umist.ac.uk.
(1) See for example: Filler, R.; Kobayashi, Y. Biomedical Aspects
of Fluorine Chemistry; Kodasha/Elsevier: New York, 1982. Banks, R.
E. Organofluorine Chemicals and Their Industrial Applications; Ellis
Horwood Ltd.: Chichester, 1979. Kirk, K. L.; Filler, R. In Biomedical
Frontiers of Fluorine Chemistry; Symp. Ser. 639, American Chemical
Society: Washington, DC, 1996; pp 1-24.
(2) See for example: Banks, R. E. Organofluorine Chemistry:
Principles and Commercial Applications; Plenum Press: New York,
1994. Banks, R. E. Fluorine Chemistry at the Millennium: Fascinated
by Fluorine; Elsevier Science Ltd: Amsterdam, 2000; and references
therein.
(3) See for example: Gross, U.; Rudiger, S. In Houben Weyl; Baasner,
B., Hagemann, H., Tatlow J . C., Eds.; Thieme: Stuttgart, 2000; Vol.
E10a, pp 18-26.
(4) Banger, K. K.; Brisdon, A. K.; Gupta, A. J . Chem. Soc., Chem.
Commun. 1996, 139.
(5) Brisdon, A. K.; Crossley, I. R. Chem. Commun. 2002, 2420.
(6) Drakesmith, F. G.; Stewart, O. J .; Tarrant, P. J . Org. Chem.
1968, 33, 280.
(7) (a) Hemne, A. L.; Nager, M. J . Am. Chem. Soc. 1952, 74, 650.
(b) Bruce, M. L.; Harbourne, D. A.; Waugh, F.; Stone, F. G. A. J . Chem.
Soc. (A) 1968, 356.
(8) (a) Bunch, J . E.; Bumgardner, C. L. J . Fluorine Chem. 1987, 36,
313. (b) Yoneda, N.; Matsuoka, S.; Miyaura, N.; Fukuhara, T.; Suzuki,
A. Bull. Chem. Soc. J pn. 1990, 63, 3124.
(9) (a) Yamazaki, T.; Mizutani, K.; Kitazume, T. J . Org. Chem. 1995,
60, 6046. (b) Katritzky, A. R.; Qi, M.; Wells, A. P. J . Fluorine Chem.
1996, 80, 145.
(10) For example: Tajammal, S.; Tipping, A. E. J . Fluorine Chem.
1990, 47, 45. Barlow, M. G.; Tajammal, S.; Tipping, A. E. J . Fluorine
Chem. 1993, 63, 139. Barlow, M. G.; Suliman, N. N. E.; Tipping, A. E.
J . Fluorine Chem. 1995, 70, 109, and references therein.
10.1021/om034146t CCC: $25.00 © 2003 American Chemical Society
Publication on Web 11/25/2003

Trifluoropropynyl Organometallic Compounds
Organometallics, Vol. 22, No. 26, 2003 5535
Sch em e 1. F or m a tion of
Tr iflu or op r op yn yllith iu m fr om HF C-245fa a n d
n -Bu Lia
germanium derivatives have been prepared previously
(RnE(CtCCF3)4-n, R ) H/D, n ) 3; R ) Me, n ) 1-3;
R ) Et, n ) 3),6,11 their obvious potential as precursors
to more functional organo-transfer reagents seems
overlooked, few reports having described conversion of
the trifluoropropynyl unit to more elaborate function-
alities.11a,d,12
With this in mind, we have undertaken to prepare
and investigate a range of novel group 14 trifluoropro-
pynyl organometalloids, with a view to developing
functional building blocks. Herein, we detail the syn-
thesis of the parent trifluoropropynyls, and report for
the first time the structural facets of these materials.
We also describe subsequent investigation of the poten-
tial for selective reduction and carbolithiation at the
triple bond, as a means of generating â-CF3-substituted
alkenic systems. Moreover, we expand upon our recently
communicated discovery of a remarkable cyclization
pathway for these materials.13
a
Conditions: diethyl ether, -10 °C.
intermediate. Attempts to intercept the intermediate,
by generating it in the presence of an electrophile, were
unsuccessful, the noncoordinating bases necessary for
this experiment proving ineffective in initiating the
reaction.
Resu lts a n d Discu ssion
Additional information was obtained by quenching the
HFC/n-BuLi mixture with D2O at progressive stages of
mixing, which revealed in every case the presence of a
predominant concentration of 1, as determined by the
characteristic position of the alkynic CF3 resonance in
the 19F NMR spectrum. An appreciable amount of
unreacted HFC-245fa (δF -64.3 (m), -116.8 (m)) was
also consistently observed.
Syn th esis a n d Ch a r a cter iza tion of Tr iflu or op r o-
p yn yl Com p ou n d s. Under the conditions outlined, 1
reacts readily with a range of electrophilic centers to
afford the respective trifluoropropynyl compounds, typi-
cally in good to excellent yields. In our initial com-
munication, we reported that upon the addition of the
electrophile, the mixture should be allowed to warm to
ambient temperature over approximately 12 h. How-
ever, we have since discovered that if the mixture is held
at or below 0 °C over that period, thus extending the
lifetime of 1, yields can be increased by up to 20%. In
this way, the organic trifluoropropynyl 2, group 14
organometalloids 3-6, and organometallic analogues
7-9 (Table 1) have now been prepared and isolated as
air- and moisture-stable solids or liquids. Compounds
2, 3, and 7 can be prepared in analytically pure form,
while purification of all materials is conveniently ef-
fected by chromatography on silica, eluting with 1:1
dichloromethane/hexane, or by distillation.
In each case, the presence of the trifluoropropynyl
moiety is supported by the observation of a singlet
resonance in the 19F NMR spectrum in the region of -50
ppm (with respect to CFCl3), characteristic of an alkynic
CF3 function. With the exception of compounds 2 and
6, this resonance displays satellites due to coupling to
the low-abundance, spin-active group 14 centers (3-5
29Si, I ) 1/2, 4.67%; 7,8 119Sn, I ) 1/2, 8.59%; 9 207Pb, I )
1/2, 22.1%), the small magnitudes of these coupling
constants being consistent with considerable separation
of the metalloid and fluorine nuclei. Additional confir-
mation of the trifluoropropynyl unit is obtained by 13C
NMR spectroscopy, the CF3 group being clearly resolved
as a quartet resonance in the region 120-110 ppm (J CF
250-280 Hz). Two further quartet resonances are
observed in the range 100-70 ppm, corresponding to
Gen er a t ion of Tr iflu or op r op yn yllit h iu m fr om
HF C-245fa . The addition of 3 equiv of n-butyllithium
to an ethereal solution of HFC-245fa (1,1,1,3,3-pen-
tafluoropropane, CF3CH2CF2H) at -10 °C results in
formation of the trifluoropropynyllithium reagent
CF3CtC-Li+ (1) in high yields. We have found 1 to be
stable under these conditions for extended periods of
up to 24 h, after which time slow decomposition to
lithium fluoride and intractable organic material be-
comes significant. The stability is only marginally
affected on raising the temperature to 0 °C; however
above this temperature the onset of decomposition is
visibly more rapid, darkening of the initially deep-
orange solution to black occurring within minutes.
Nonetheless, decomposition has, thus far, proven to be
a nonviolent process, though exothermic.
The generation of 1 is presumed to occur via the
process outlined in Scheme 1. Thus, in the presence of
n-BuLi, HFC-245fa is deprotonated, with subsequent
elimination of lithium fluoride, to afford 1,3,3,3-tet-
rafluoropropene, which undergoes a second deprotona-
tion-elimination step to generate 3,3,3-trifluoropropyne
in situ. Subsequent deprotonation to afford 1 is, as
might be anticipated, rapid, this being apparent from
the near quantitative generation of 1 from HFC-245fa,
despite the volatility of 3,3,3-trifluoropropyne (bp -48
°C). Indeed, the rate-determining step would seem to
be initial deprotonation of the HFC, with successive
steps being considerably more facile, and this is sup-
ported by several investigations. Notably, when the
HFC and n-BuLi are present in equimolar amounts,
subsequent addition of an electrophile traps only the
trifluoropropynyl moiety, with no evidence of the alkenyl
(11) (a) Cullen, W. R.; Leeder, W. R. Inorg. Chem. 1966, 5, 1004. (b)
Anderson, D. W. W.; Cradock, S.; Ebsworth, E. A. V.; Green, A. R.;
Rankin, D. W. H. J . Organomet. Chem. 1984, 271, 235. (c) Bogoradov-
skii, E. T.; Zavgorodnii, V. S.; Polozov, B. V.; Petrov, A. A. J . Gen. Chem.
USSR 1982, 52, 399. (d) Cullen, W. R.; Waldman, M. C. Inorg. Nucl.
Chem. Lett. 1969, 6, 205. (e) Cullen, W. R.; Waldman, M. C. J . Fluorine
Chem. 1971, 1, 41. (f) Pant, B. C.; Sacher, R. E. Inorg. Nucl. Chem.
Lett. 1969, 5, 549.
(12) Cullen, W. R.; Waldman, M. C. Inorg. Nucl. Chem. Lett. 1968,
4, 205.
(13) Brisdon, A. K.; Crossley, I. R.; Flower, K. R.; Pritchard, R. G.;
Warren, J . E. Angew. Chem., Int. Ed. 2003, 42, 2399.

5536 Organometallics, Vol. 22, No. 26, 2003
Ta ble 1. Selected Sp ectr oscop ic Da ta for Gr ou p 14 Tr iflu or op r op yn yl Com p ou n d s
Brisdon et al.
δF (J EF/Hz)
δC (J CF/Hz)
ν
C≡C/cm-1
Ph3CCtCCF3 (2)
Ph3SiCtCCF3 (3)
Ph2Si(CtCCF3)2 (4)
Et3SiCtCCF3 (5)
Ph3GeCtCCF3 (6)
Ph3SnCtCCF3 (7)
Bu3SnCtCCF3 (8)
Ph3PbCtCCF3 (9)
-50.0
114.8 (q, 256.9, CF3), 93.9 (q, 6.7, CtCCF3), 72.6 (q, 52.2, CtCCF3)
113.3 (q, 258.7, CF3), 93.8 (q, 51.6, CtCCF3), 90.3 (q, 5.8, CtCCF3)
112.3 (q, 259.0, CF3), 94.1 (q, 52.0, CtCCF3), 85.9 (q, 5.7, CtCCF3)
112.0 (q, 258.8, CF3), 92.3 (q, 51.2, CtCCF3), 88.8 (q, 5.8, CtCCF3)
111.1 (q, 258.0, CF3), 90.6 (q, 51.2, CtCCF3), 88.8 (q, 6.0, CtCCF3)
111.5 (q, 260.0, CF3), 94.5 (q, 50.0, CtCCF3), 91.8 (q, 6.0, CtCCF3)
111.7 (q, 257.2, CF3), 94.7 (q, 6.0, CtCCF3), 93.5 (q, 50.0, CtCCF3)
111.5 (q, 257.9, CF3), 104.3 (q, 7.3, CtCCF3), 94.2 (q, 50.0, CtCCF3)
2256
2204
2210
2200
2200
2183
2175
2169
-50.4 (3.0)
-52.2 (unres.)
-51.1 (4.0)
-51.0
-50.8 (12.0)
-50.4 (11.7)
-50.0 (7.9)
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for P h 3ECtCCF 3 (E ) C 2, Si 3, Ge 6) w ith
Estim a ted Sta n d a r d Devia tion s in P a r en th eses
Ph3CCtCCF3 Ph3SiCtCCF3 Ph3GeCtCCF3
(2)
(3)
(6)
E1′-C1
C1-C2
C2-C3
C3-F1
C3-F2
C3-F3
1.475(2)
1.186(3)
1.444(3)
1.314(2)
1.325(3)
1.324(3)
1.860(3)
1.190(4)
1.469(4)
1.323(3)
1.323(3)
1.323(3)
1.933(3)
1.186(4)
1.466(4)
1.318(3)
1.318(3)
1.318(3)
E1′-C1-C2
C1-C2-C3
C2-C3-F1
C2-C3-F2
C2-C3-F3
F1-C3-F2
F2-C3-F3
F3-C3-F1
179.32(17)
178.6(2)
180.0(3)
180.0(4)
112.1(2)
112.1(2)
112.1(2)
106.7(2)
106.7(2)
106.7(2)
180.0(3)
180.0(4)
112.5(2)
112.5(2)
112.5(2)
106.3(2)
106.3(2)
106.3(2)
113.21(17)
112.42(17)
112.05(17)
106.77(17)
104.99(18)
106.85(17)
F igu r e 1. View of the molecular structure of Ph3GeCt
CCF3 (6) with thermal ellipsoids set at the 30% probability
level. The numbering scheme of the trifluoropropynyl
function is directly transposable to the structures of 2 and
3.
the centers R (J CF 5-10 Hz) and â (J CF 50-55 Hz) to
the metalloid. The alkyne function is also apparent from
a strong infrared absorption around 2200 cm-1, the
frequency of which decreases upon descending the
group, consistent with the increased mass of the met-
alloid fragment. In all cases, satisfactory microanalytical
data were obtained.
For the phenyl-substituted derivatives 2, 3, and 6,
additional information was acquired from single-crystal
X-ray diffraction studies. In each case, the anticipated
pseudotetrahedral geometry about the group 14 atom
was observed, as illustrated in Figure 1. Selected bond
distances and angles for these compounds are sum-
marized in Table 2. It is noteworthy that these consti-
tute the first crystallographic study of any main group
trifluoropropynyl compounds; indeed, only one σ-triflu-
oropropynyl has been so characterized previously,
namely, In(CtCCF3)3(THF)2.14 In common with this
indane, the internal geometries of the group 14 systems
are largely as anticipated, the CtC and C-CF3 dis-
tances being typical of CsptCsp [1.183 Å] and Csp-
Csp3 [1.466 Å],15 respectively, with near perfect linearity
of the alkyne function. Similarly, the C-F distances are
typical of Csp3-F [1.322 Å]15 and are consistent with
those of other, crystallographically characterized, alkyne-
bound CF3 moieties recorded in the Cambridge Crystal-
lographic Database. It is noteworthy that the E-C1
F igu r e 2. Packing diagram of Ph3CCtCCF3 (2) projected
along the c direction.
distances for 3 and 6 exhibit no appreciable shortening
to indicate delocalization of the π-system to the metal-
loid d orbitals. This supports the earlier assertion that
the decreasing frequency of the alkyne stretch on
descending the group reflects the increased mass of the
element E.
The extended structure of 2 is remarkable (Figure 2)
and differs from those of 3 and 6, the individual
molecules aligning in single file along the c direction,
with adjacent files stacking head-to-tail. The resulting
sheets in the ac plane stack in a manner that maximizes
congregation of the fluorinated functions into domains,
(14) Schumann, H.; Seuss, T. D.; J ust, O.; Weimann, R.; Hemlin,
H.; Go¨rlitz, F. H. J . Organomet. Chem. 1994, 479, 171.
(15) Lide, R. Handbook of Chemistry and Physics, 76th ed.; CRC
Press: New York, 1995.

Trifluoropropynyl Organometallic Compounds
Organometallics, Vol. 22, No. 26, 2003 5537
a
Sch em e 2. Ca r bolith ia tion of P h 3SiCtCCF 3
which propagate through the crystal in the c direction.
In contrast, the extended structures of 3 and 6 exhibit
less well-defined 3-D order. In all three cases there is a
notable absence of any, classically, short intermolecular
interactions, the structures apparently being deter-
mined by an extensive network of weak H‚‚‚F interac-
tions lying in the range 2.70-2.80 Å, which are just
beyond the sum of the van der Waals radii [2.67 Å].16
Der iva tiza tion of th e Tr iflu or op r op yn yls. Among
the most versatile aspects of alkyne reactivity are their
interactions with strongly nucleophilic species, resulting
in either reduction or carbolithiation of the triple bond.
In this way, a wealth of alkene derivatives can be
prepared, often with remarkable levels of stereocon-
trol.17 Notwithstanding, few reports describe the ap-
plication of these methods to trifluoropropynyl systems,
a fact that contributes significantly to the dearth of
reagents for introducing â-CF3-substituted vinylic func-
tions. Indeed, only a handful of silanes of the type R3-
SiCHdC(CF3)R′ have been reported, typically where
R ) Me and R′ ) -(CH2)3Ph, -Ph, -OCH2Cy, -OCH2-
Ph, -OCy, -N(C2H4)2O, -NEt(CH2Ph), or -S-n-hexyl.18
In all cases, the silanes were obtained by olefination of
the respective carbonyl compound, (CF3)RCdO, with
CpTi(SiMe3)3. One further example (R′ ) H) was
obtained by the Ru/Rh-catalyzed addition of Me3SiH to
3,3,3-trifluoromethylpropene, the product arising in
admixture with Me3SiCH2CH2CF3.19 It is noteworthy
that for all of the above materials, a trans arrangement
of the CF3 and Me3Si groups is observed.
Given that trifluoropropynyl compounds are now
more readily available than ever before, it would seem
appropriate that they begin to serve as precursors to
these potentially useful vinylic systems. With this in
mind, and in view of the utility of silanes as organo-
transfer reagents,20 and in fluoro/hydro-desilylation
chemistry,21 the chemistry of the silicon derivatives was
investigated further.
Ster eosp ecific Red u ction by LiAlH4. It has been
previously documented that, upon extended reflux with
LiAlH4 (THF/diglyme, 150 °C, 5 h), alkynes such as Et3-
SiCtCCH3 undergo stereospecific reduction to afford
the respective trans-alkenes.22 Given the enhanced
electrophilicity imparted to trifluoropropynyl analogues
by the CF3 function, milder conditions were sought to
effect a similar transformation of 5. Thus, 5 was treated,
in THF, with a slight excess of LiAlH4 and the mixture
brought to reflux for 4 h. Upon completion, the reaction
mixture was hydrolyzed and extracted into ether,
evaporation of the solvent affording a small amount of
colorless oil.
a
Conditions: (i) Et2O, -60 °C, (ii) RLi, 6 h, (iii) rt, (iv)
MeOH/hexane.
The 19F NMR spectrum indicated consumption of 5, the
singlet resonance at δF -51.1 having been replaced by
a doublet of doublets at δF -66.8 (J FH 5.2, 2.0 Hz),
characteristic of an alkenic CF3 function. This was
verified by observation of the corresponding alkenic
proton resonances at 6.6 and 6.1 ppm, with a mutual
1H-1H coupling constant of 18 Hz suggesting a trans
arrangement, thus identifying 10 as E-Et3SiCHd
CHCF3. However, 10 constitutes a minor component of
the mixture and is not readily separated from the bulk,
which apparently results from defluorination of the
substrate. Moreover, the crude mass yield was poor
(<20%), presumably due to loss of the volatile substrate
during the reaction and/or workup.
In view of these difficulties, further investigations
were restricted to the more robust, and considerably less
volatile, silane 3 (Ph3SiCtCCF3). A comparable reaction
again resulted in defluorination of the substrate, along-
side formation of small amounts of the alkene E-Ph3-
SiCHdCH(CF3) (11); hence less harsh conditions were
explored. It was thus determined that the reduction is
best effected when 3 and LiAlH4 are mixed at -60 °C
in THF, then stirred together while warming to ambient
temperature, over no more than 3 h. In this way, 11 is
obtained as the major product, in admixture with small
amounts of the Z isomer (E:Z 97:3 by 19F NMR), but no
evidence of defluorinated material. Formation of the Z
isomer is completely inhibited if the reaction is con-
ducted entirely at -60 °C; however, under these condi-
tions less than 10% of 11 is isolated.
Ca r bolith ia tion of th e Tr iflu or op r op yn yl Com -
p ou n d s. The interaction of 3 with a range of organo-
lithium reagents has also been explored (Scheme 2).
Thus, it was found that when RLi (R ) n-Bu, Ph) were
added to ethereal solutions of 3 at -60 °C, then stirred
together while warming to ambient temperature, non-
aqueous workup afforded isomeric mixtures of the
respective alkenes Ph3SiCHdC(CF3)R. As with the
dihydroalkenes 10 and 11, the 19F NMR spectra each
exhibit two vinylic CF3 resonances (R ) n-Bu δF -63.9
and -67.4 ppm; Ph δF -59.8 and -67.5 ppm), the lower
frequency of which was assigned, by comparison to 10
and 11, as E-Ph3SiCHdCHR (R ) n-Bu 12, Ph 13).
Indeed, as with the dihydroalkenes, when the reaction
is conducted entirely at low temperature (-60 °C), the
single isomers 12 and 13 are obtained, neither of which
exhibit NOE interactions between the R group and
alkenic protons, and both of which have been crystal-
lographically characterized with the E geometry (vide
infra). In contrast, when the reaction with n-BuLi is
preformed at ambient temperature, an appreciable
amount of the Z isomer is obtained, which clearly
exhibits a NOE interaction with the proximate butyl-
CH2 unit.
The presence of the alkene Et3SiCHdCHCF3 (10) was
confirmed by multinuclear (19F, 1H) NMR spectroscopy.
(16) Bondi, A. J . Phys. Chem. 1964, 68, 441.
(17) See for example: (a) Oestreich, M.; Fro¨hlich, R.; Hoppe, D.
Tetrahedron Lett. 1998, 39, 1745. (b) Oestreich, M.; Fro¨hlich, R.; Hoppe,
D. J . Org. Chem. 1999, 64, 8616, and references therein.
(18) Be´gue´, J .-P.; Rock, M. H. J . Organomet. Chem. 1995, 489, C7.
(19) Ojima, I.; Fuchikami, T.; Yatabe, M. J . Organomet. Chem. 1984,
260, 335.
(20) See for example: (a) Li, G. L.; Chen, Y. H.; Missert, J . R.;
Rungta, A.; Dougherty, T. J .; Grossman, Z. D.; Pandey, R. K. J . Chem.
Soc., Perkin Trans. 1 1999, 1785. (b) Xue, L.; Lu, S. D.; Pedersen, Q.;
Liu, R. M.; Narske, D. J .; Burton, J . Org. Chem. 1997, 62, 1064.
(21) See for example: (a) Dickson, R. S.; Kirsch, H. P. Aust. J . Chem.
1972, 25, 1815. (b) Greedy, B.; Gouverneur, V. Chem. Commun. 2001,
233.
Cr ysta llogr a p h ic Ch a r a cter iza tion of E-P h 3Si-
CHdC(CF 3)R. The solid-state structures of 12 and 13
(22) Magoon, E. F.; Slaugh, L. H. Tetrahedron 1967, 21, 4509

5538 Organometallics, Vol. 22, No. 26, 2003
Brisdon et al.
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for P h 3SiCHdC(CF 3)P h (13) w ith Estim a ted
Sta n d a r d Devia tion s in P a r en th eses
Si1-C1
C1-H1
C1-C2
C2-C3
C2-C4
C4-C5
C4-C9
1.8814(14)
0.983(19)
1.3324(19)
1.508(2)
1.491(2)
1.387(2)
C5-C6
C6-C7
C7-C8
C8-C9
C3-F1
C3-F2
C3-F3
1.393(3)
1.378(3)
1.380(3)
1.383(3)
1.336(2)
1.330(2)
1.337(2)
1.395(2)
Si1-C1-C2
Si1-C1-H1
C1-C2-C3
C1-C2-C4
C3-C2-C4
133.19(13)
112.1(9)
119.46(14)
126.18(14)
114.36(12)
C2-C1-H1
C2-C3-F1
C2-C3-F2
C2-C3-F3
114.6(9)
111.96(14)
114.38(12)
112.35(14)
[1.503 Å], respectively, though a slight foreshortening
of C2-C4 is apparent in 13, presumably due to partial
overlap of the alkenic and aromatic π-systems. All C-F
distances are close to idealized values [1.322 Å].15
F igu r e 3. View of the molecular structure of Ph3SiCHd
C(CF3)n-Bu (12) with thermal ellipsoids set at the 30%
probability level.
In common with 14, however, the internal geometries
of 12 and 13 are subject to notable distortion, due to
the cis arrangement of sterically demanding substitu-
ents. Thus, the angles Si1-C1-C2 and C1-C2-C4 are
“opened-out” relative to ideality, while Si1-C1-H1
are contracted. These effects are, however, somewhat
less severe than for 14 [ Si1-C1-C2 139.37(18)°;
C1-C2-C4 127.4(2)°], the n-Bu and Ph substituents
adopting conformations that minimize unfavorable in-
teractions with the triphenylsilyl fragment. Thus, in 12
[ Si1-C1-C2 129.13(16)°; C1-C2-C4 125.54(18)°]
the n-Bu group bends away from silicon, while in 13
[ Si1-C1-C2 133.19(13)°; C1-C2-C4 126.18(14)°]
the phenyl unit staggers the alkene π-system with a
torsion of 64°, an orientation enforced by a significant,
intramolecular π-stacking interaction with the ring
C10-C15 [d(Cg-Cg) 3.8772(9) Å, 18.82°]. Conse-
quently, the close approach of alkenic proton and
eclipsing fluorine atom previously noted of 14 [d(H‚‚‚F)
2.13(2) Å] is somewhat diminished in both cases [d(H‚‚‚F)
12 2.35(2) Å; 13 2.266(16) Å].
F igu r e 4. View of the molecular structure of E-Ph3SiCHd
C(CF3)Ph (13) with thermal ellipsoids set at the 30%
probability level.
Ca r bolith ia tion w ith t-Bu Li. When 3 is treated
with t-BuLi at -60 °C, as described above, three distinct
species are observed in the 19F NMR spectrum, char-
acterized by two alkenic resonances [δF -56.7 (∼2.5%)
and -60.7 (>95%)] and one further signal at appreciably
lower frequency [δF -103.1 (∼2.5%), vide infra]. The
corresponding proton resonances for the major product
are clearly identified (δH 6.9, CRH; 1.06 C(CH3)3) and
exhibit a discernible NOE interaction, which previously
led us to assign this material as Z-Ph3SiCHdC(CF3)t-
Bu.13 This contrasts the more recently explored reac-
tions with n-BuLi and PhLi, though it was again the E
isomer (14) that was crystallographically characterized.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for P h 3SiCHdC(CF 3)n -Bu (12) w ith Estim a ted
Sta n d a r d Devia tion s in P a r en th eses
Si1-C1
C1-H1
C1-C2
C2-C3
C2-C4
C4-C5
1.876(2)
0.98(2)
1.331(3)
1.501(3)
1.507(3)
1.531(3)
C5-C6
C6-C7
C3-F1
C3-F2
C3-F3
1.526(3)
1.501(3)
1.344(2)
1.340(2)
1.341(2)
Si1-C1-C2
Si1-C1-H1
C1-C2-C3
C1-C2-C4
C3-C2-C4
129.13(16)
113.0(12)
119.69(18)
125.54(18)
114.75(17)
C2-C1-H1
C2-C3-F1
C2-C3-F2
C2-C3-F3
117.3(12)
111.72(17)
113.86(18)
113.15(17)
In light of the more recent results, carbolithiation
with t-BuLi has now been reexamined. Fortuitously, in
one instance, upon mixing 3 and t-BuLi at ambient
temperature, the anticipated 19F NMR resonances at
103.1 (52%) and -60.7 (19%) ppm were accompanied
by a significant proportion of the previously trace
component observed at -56.7 ppm (29%). This finally
allowed unequivocal assignment of the corresponding
proton resonances [δH 6.7 (1H), 1.1 (9H)], which were
found to exhibit a strong NOE interaction. Significantly,
the original NOESY cross-peak was again observed,
though with a considerably lower intensity; this would
are illustrated in Figures 3 and 4, respectively, with
selected geometric parameters summarized in Tables
3 and 4. Along with the structure of E-Ph3SiCHd
C(CF3)t-Bu (14), which we have previously reported,13
these are the first examples of â-CF3-substituted vinylic
compounds to be crystallographically characterized. As
with the parent alkyne, the anticipated pseudotetrahe-
dral geometry is adopted about silicon, and the internal
distances of the vinylic unit are largely typical. Indeed,
the CRdCâ and Câ-Cγ distances compare well with the
average values for Csp2dCsp2 [1.326 Å] and Csp2-Csp3

Trifluoropropynyl Organometallic Compounds
Organometallics, Vol. 22, No. 26, 2003 5539
Sch em e 3. Cycliza tion of Gr ou p 14
Tr iflu or op r op yn yls, In itia ted by Ad d ition of
ter t-Bu tlylith iu m a
than 1 h at 50 °C. However, with less than 5% of 14
present, apparently infinite solution stability is ob-
served, samples remaining unchanged after several
weeks at 70 °C. Moreover, while defluorination had been
previously accelerated by the presence of an electrophile
(e.g., Ph3SiCl, Ph3CCl), no such effect is now observed.
Interestingly, such instability toward defluorination
has been previously reported for gem-difluorocyclopro-
penes, such as PhCdC(CF2)H, and the somewhat more
a
Conditions: (i) THF reflux, 20 h, (ii) rt, hexane.
stable PhCdC(CF2)I, both of which decompose in this
manner upon prolonged exposure to air at room tem-
perature.25 Moreover, a range of such materials, notably
suggest that relative concentrations had previously
biased the data. The bulk product from the low-tem-
perature reaction of 3 and t-BuLi is thus reassigned as
E-Ph3SiCHdC(CF3)t-Bu (14).
CH3(CH2)5CdC(CF2)H and PhCdC(CF2)Ph, are report-
edly moisture sensitive and hydrolyze rapidly to the
respective cyclopropenones.26 That 15 is indefinitely
stable in the absence of solvent, and even in solution
when in a pure state, is thus a significant feature.
Moreover, the extended exposure of 15, as solution, to
water affords no indication of hydrolysis.
Cycliza tion of Tr iflu or op r op yn yls via ter t-Bu -
tyllith iu m Ca r bolith ia tion . The carbolithiation of 3
with t-BuLi routinely affords, in addition to E and Z
alkenes, a species exhibiting a singlet 19F NMR reso-
nance at -103.1 ppm (15), characteristic of a gem-
difluorocyclopropenyl compound.23 This component be-
comes increasingly important as the reaction temperature
is increased, such that at ambient temperature it
typically constitutes up to 80% of the product mixture,
which also contains 14 (∼20%) and a trace of the Z
isomer. While 15 cannot be separated from the mixture
either chromatographically, due to limited stability upon
the column, or by recrystallization, its identity has been
Mech a n istic Con sid er a tion s. The formation of
exclusively E-Ph3SiCHdC(CF3)R at low temperature
would seem largely consistent with reaction proceeding
under kinetic control, a classical nucleophilic mecha-
nism resulting in anti addition of the organolithium
reagent. Indeed, evidence in support of this has been
obtained by the addition of tetramethylethylenediamine
(TMEDA) under these conditions, resulting, for n-BuLi
and Ph, in the exclusive generation of 12 and 13,
respectively. Surprisingly, in the case of t-BuLi, this
results in an approximately equimolar mixture of 14
and Z-Ph3SiCHdC(CF3)t-Bu, which had previously
seemed consistent with the preferential formation of
Z-Ph3SiCHdC(CF3)t-Bu under these conditions, the
product mixture being presumed to reflect inhibition of
a precursor lithium-alkyne π-complex.13 However, the
data do, in fact, support the preferential formation of
14 at low temperature, there being precedent for the
apparently anomalous behavior of t-BuLi in the pres-
ence of TMEDA. Indeed, the reactions of RLi/TMEDA
(R ) n-Bu, Et, Ph) with diphenylacetylene have been
reported to proceed with exclusively anti addition, the
exception being where R ) t-Bu, in which case a mixture
of syn (80%) and anti (20%) products was obtained.27
This was presumed to illustrate thermodynamic prefer-
ence, driven by the greater steric footprint of t-Bu.
Competition between kinetic and thermodynamic
control is similarly consistent with the enhanced gen-
eration of Z-Ph3SiCHdC(CF3)R observed at higher
reaction temperatures. Indeed, ab initio studies of the
trimethylsilyl analogues E/ Z-Me3SiCHdC(CF3)t-Bu at
the B3LYP/6-311+G* level suggest a slight thermody-
namic preference for the Z isomer of 19.5 kJ mol-1 (4.66
kcal mol-1). However, the necessity for preassociation
of the alkyne and organolithium reagent, to effect syn
addition, renders formation of the Z isomer inherently
slow, relative to anti addition; thus the E isomer still
predominates.
unequivocally established as Ph3SiCdC(CF2)t-Bu on the
basis of 13C NMR spectroscopic studies, which reveal
the presence of three quaternary centers, each one
appearing as a triplet resonance. The CF2 unit is clearly
observed at δC 108.2 (J CF 271 Hz), with CR (δC 124.6,
J CF 13.1 Hz) and Câ (δC 157.9, J CF 8.3 Hz) resonating
at higher frequency; characteristic resonances for the
Ph3Si and t-Bu functions are also clearly resolved.
Moreover, as we have previously communicated,13 15
preferentially crystallizes when a dichloromethane/
hexane solution is allowed to evaporate slowly; thus its
solid-state structure has been determined and found to
be consistent with the spectroscopic data.
While 15 cannot be prepared in complete isolation of
14, it has proven possible to maximize the proportion
of cyclization by operating at elevated temperatures, for
extended periods. Thus, when 3 and t-BuLi are held at
THF reflux for 20 h (Scheme 3), 15 accounts for over
95% of the isolated products, with yields in excess of
80% after purification, eluting from a short column with
1:1 DCM/hexane affording 15 as an air/moisture-stable
yellow solid. This methodology thus holds considerable
advantage over more traditional difluorocyclopropene
syntheses, based upon heavy-metal difluorocarbene
sources, which have been recently reviewed.24
Significantly, the reduced proportion of 14 in samples
obtained via these conditions has a considerable effect
upon the solution stability of 15. Indeed, it has been
observed that when mixtures containing over 15% of 14
are left in solution over a period of days, complete
defluorination of 15 results. This process has been noted
in a range of solvents, and the lifetime of 15 is temper-
ature dependent, ranging from 7 days at 20 °C to less
The remarkably facile cyclization observed with t-
BuLi at ambient and elevated temperature is presum-
(25) Xu, W.; Chen, Q.-Y. J . Org. Chem. 2002, 67, 9421.
(26) Bessard, Y.; Schlosser, M. Tetrahedron 1991, 47, 7323.
(27) Mulvaney, J . E.; Newton, D. J . J . Org. Chem. 1969, 34, 1936.
(23) Eujen, R.; Hoge, B. J . Organomet. Chem. 1995, 503, C51.
(24) Dolbier, W. R., J r.; Battiste, M. A. Chem. Rev. 2003, 103, 1071.

5540 Organometallics, Vol. 22, No. 26, 2003
Brisdon et al.
ably driven by the thermodynamically favorable elimi-
nation of LiF from the lithio-alkene intermediate
E-Ph3SiC(Li)dC(CF3)t-Bu (16). Indeed, this is supported
by the fact that, while carbolithiation at -60 °C affords
exclusively E-Ph3SiCHdC(CF3)t-Bu, allowing the reac-
tion to attain ambient temperature prior to workup
results in formation of an appreciable amount of the
cyclized product.
elimination of LiF from the carbolithiation product. The
susceptibility of a given trifluoropropynyl toward this
process would seem to be conveniently modeled by
consideration of the respective E-R3ECHdC(CF3)t-Bu
system, a syn H‚‚‚F contact of e2.12 Å indicating a likely
cyclization candidate. This affords the potential of more
widespread applicability for this methodology than has
yet been elucidated.
This mechanism is presumably enabled by the se-
verely distorted geometry imposed in accommodating
the cis arrangement of sterically demanding substitu-
ents. As noted previously (vide supra), the protonated
alkene 14 exhibits an extremely short H‚‚‚F contact
[2.13(2) Å] in the solid state, which would seem to
support the likelihood of an appreciable Li‚‚‚F interac-
tion within 16, thus predisposing it to LiF elimination.
In contrast, the somewhat longer H‚‚‚F distances ob-
served in 12 [2.35(2) Å] and 13 [2.266(16) Å] offer some
insight into the reluctance of these systems to undergo
cyclization and support the notion of a sterically driven
mechanism. Indeed, these data also concur with earlier
DFT studies, at the B3LYP/6-311+G* level, of E-Me3-
SiCHdC(CF3)t-Bu [d(H‚‚‚F) 2.119 Å] and E-Me3SiCHd
C(CF3)H [d(H‚‚‚F) 2.407 Å], which led us to a similar
conclusion.13 Significantly, it would appear that the
E-alkenes represent valuable models by which to assess
the potential for cyclization of a given substrate, thus
availing the possibility of theoretical screening. How-
ever, current data do not yet allow for determination of
the limiting H‚‚‚F separation for cyclization.
Exp er im en ta l Section
Gen er a l Meth od s. Reactions were carried out under
anaerobic conditions in flame-dried glassware, with moisture-
sensitive reagents being handled under an argon atmosphere
in a drybox (Belle Technologies, UK). Diethyl ether and THF
were dried over sodium wire for ca. 1 day prior to use. The
compounds CF3CH2CF2H (Honeywell), n-BuLi (2.5 M in hex-
ane), t-BuLi (1.5 M in pentane) (Acros), PhLi (1.8 M in ether/
pentane), Ph3CCl, Ph3GeBr, Bu3SnCl (Aldrich), Et3SiCl, Ph2-
SiCl2, Ph3SiCl, Ph3SnCl, LiAlH4, TMEDA (Lancaster), and
methanol (BDH) were used as supplied after spectroscopic
verification of purity. All NMR spectra were recorded of CDCl3
solutions on Bruker DPX200 (19F, 188.310 MHz, referenced
to external CFCl3) or DPX400 (1H, NOESY, 400.4 MHz; 13C,
Dept-135, 100.555 MHz referenced to external SiMe4) spec-
trometers. All resonances are reported using the high-
frequency positive convention. Infrared spectra were recorded
of chloroform solutions or neat liquids, between KBr plates
on a Nicolet Nexus FTIR spectrometer. Elemental analyses
were performed by the departmental microanalytical service.
P r ep a r a tion of P h 3CCtCCF 3 (2). Typically, a stirred
ethereal solution (200 cm3) of HFC-245fa (1.8 cm3, 17.73 mmol)
was treated, under N2, with n-BuLi (21.0 cm3, 52.50 mmol),
at -10 °C. After 15 min, Ph3CCl (3.264 g, 11.71 mmol) in ether
(40 cm3) was added, while maintaining -10 °C. Then the
mixture was held at 0 °C and stirred overnight. The reaction
was allowed to attain ambient temperature, then hexane (160
cm3) was added to precipitate the inorganics; the settled
mixture was filtered through Celite and the filtrate concen-
trated in vacuo. Purification on a silica column, eluting with
50:50 DCM/hexane, afforded 2 as a pale brown solid. Yield:
2.431 g, 62%. Mp: 150 °C. Anal. Calcd for C22H15F3: C, 78.6;
H, 4.5; F, 16.9. Found: C, 78.8; H, 4.3; F, 16.6. 13C NMR: δ
135.4 [CH, s], 131.6 [C, s], 131.1 [CH, s], 128.8 [CH, s], see
Table 1. 1H NMR: δ 7.7-7.4 (m). IR: νmax/cm-1 2256 (CtC
str.), 1276, 1145 (C-F str.).
Verification of a sterically driven process, as opposed
to one mediated by silicon d orbitals, arises from the
efficiency by which the trityl-trifluoropropynyl 2 can be
similarly cyclized to Ph3CCdC(CF2)t-Bu, which accounts
for 90% of the isolated products. However, the required
level of steric bulk to initiate cyclization remains
unclear, the ab initio studies suggesting substituents
smaller than Ph3Si- might prove equally effective.
Indeed, analytical scale investigations reveal that Et3-
SiCtCCF3 (5) reacts readily with t-BuLi to afford over
80% of the respective cyclopropene, which was identified
by a combination of 19F and 13C NMR spectroscopy. We
continue to explore an increasing range of substrates.
P h 3SiCtCCF 3 (3). HFC-245fa (2.16 cm3, 21.28 mmol),
n-BuLi (25.5 cm3, 63.75 mmol), Ph3SiCl (4.150 g, 14.07 mmol)
were used. 3 was obtained as a pale yellow solid. Yield: 4.520
g, 90%. Mp: 110 °C. Anal. Calcd for C21H15F3Si: C, 71.6; H,
4.3; F, 16.2. Found: C, 71.9; H, 4.5; F, 16.0. 13C NMR: δ 135.4
[CH, s], 131.6 [C, s], 131.1 [CH, s], 128.8 [CH, s], see Table 1.
1H NMR: δ 7.7-7.4 (m). IR: νmax/cm-1 2204 (CtC str.), 1245,
1151 (C-F str.).
Con clu sion s
Hydrofluorocarbon 245fa serves as an effective source
of the trifluoropropynyl moiety for the development of
metalloid-based systems, the first homologous series of
which has been prepared and fully characterized. For
the first time, the single-crystal X-ray structures of a
series of these compounds have been determined, and
these constitute the first series of σ-trifluoropropynyl
derivatives to be so characterized. The trifluoropropynyl
silane Ph3SiCtCCF3 has proven to be readily converted
into a range of â-CF3 vinyl derivatives, through its low-
temperature reactions with nucleophiles; the products
of these reactions constitute the first â-CF3 vinylic
systems to be crystallographically characterized. More-
over, trifluoropropynyl compounds of the type R3ECt
CCF3 (E ) C, Si) constitute convenient precursors to
the versatile gem-difluorocyclopropenyl compounds, which
can be generated under mild conditions, via a sterically
assisted process initiated by t-BuLi, and driven by
P h 2Si(CtCCF 3)2 (4). HFC-245fa (1.80 cm3, 17.73 mmol),
n-BuLi (21.0 cm3, 52.50 mmol), and Ph2SiCl2 (1.20 cm3, 5.71
mmol) were used. Crude product was distilled at 124 °C/9
mmHg. Yield: 1.460 g, 69%. Anal. Calcd for C18H10F6Si: C,
58.7; H, 2.7; F, 30.9. Found: C, 58.4; H, 2.4; F, 30.6. 13C NMR:
δ 135.4 [CH, s], 132.3 [CH, s], 129.2 [CH, s], 127.5 [C, s], see
Table 1. 1H NMR: δ 7.7-7.4 (m). IR: νmax/cm-1 2210 (CtC
str.), 1241, 1149 (C-F str.).
Et3SiCtCCF 3 (5). HFC-245fa (1.50 cm3, 14.77 mmol),
n-BuLi (17.4 cm3, 43.50 mmol), and Et3SiCl (1.60 cm3, 9.54
mmol) were used. Crude product was distilled at 30 °C/10
mmHg. Yield: 1.006 g, 51%. 13C NMR: δ 6.1 [CH3, s, J SiC 31.8
1
Hz], 3.9 [CH2, s, J SiC 57.0 Hz], see Table 1. H NMR: δ 1.0 (t,
J HH 8 Hz) 0.7 (q, J HH 8 Hz). IR: νmax/cm-1 2200 (CtC str.),
1253, 1143 (C-F str.).
P h 3GeCtCCF 3 (6). HFC-245fa (0.55 cm3, 5.42 mmol),
n-BuLi (6.25 cm3, 15.63 mmol), and Ph3GeBr (1.006 g, 2.62

Trifluoropropynyl Organometallic Compounds
Organometallics, Vol. 22, No. 26, 2003 5541
Ta ble 5. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for P h 3CCtCCF 3 (2), P h 3SiCtCCF 3 (3), P h 3GeCtCCF 3 (6),
E-P h 3SiCHdC(CF 3)n -Bu (12), a n d E-P h 3SiCHdC(CF 3)P h (13)
2
3
6
12
13
formula
mol wt
cryst syst
space group
cryst dimens, mm
habit
C
22H15F3
C21H15F3Si
352.42
cubic
Pa3h (No. 205)
0.15 × 0.13 × 0.08
prism
C21H15F3Ge
396.92
cubic
Pa3h (No. 205)
0.15 × 0.13 × 0.08
prism
C25H25F3Si
410.54
triclinic
P1h (No. 2)
0.20 × 0.20 × 0.10
plate
C27H21F3Si
430.53
triclinic
P1h (No. 2)
0.15 × 0.25 × 0.25
prism
336.34
monoclinic
C2/c (No. 15)
0.07 × 0.10 × 0.25
plate
color
a, Å
b, Å
c, Å
colorless
19.1078(7)
10.6047(4)
18.0521(8)
90
106.251(2)
90
3511.8(2)
8
1.272
0.095
2.22 to 27.44
9814, 3922
colorless
15.1654(7)
15.1654(7)
15.1654(7)
90
colorless
15.2629(7)
15.2629(7)
15.2629(7)
90
colorless
colorless
10.2298(4)
10.2607(4)
12.3244(6)
93.092(2)
105.670(2)
116.434(2)
1092.33(8)
2
1.248
0.141
1.75 to 24.91
10 774, 3777
9.2663(2)
11.1733(2)
12.7350(3)
105.3040(10)
98.6910(10)
114.0070(10)
1110.63(4)
2
1.287
0.142
2.50 to 27.50
22 312, 5044
R, deg
â, deg
90
90
90
90
γ, deg
V, Å3
3487.9(3)
8
1.342
0.164
3.00 to 26.33
21 893, 1188
3555.6(2)
8
1.483
1.752
2.98 to 28.69
19 041, 1213
Z
D
calc, g cm-3
µ mm-1
θ range, deg
no. of data collected,
unique reflns
no. of params refined
F(000)
286
1392
0.0539
0.1483
0.295, -0.241
96
1456
0.0584
0.0963
0.186, -0.177
96
1600
0.0344
0.0784
0.355, -0.355
362
432
0.0403
0.0970
0.223, -0.247
364
448
0.0374
0.0929
0.250, -0.250
R1 (I > 2σ(I))a
wR2 (all data)b
max. and min./e Å-3
R1 ) ∑||Fo| - |Fc||/∑|Fo |. wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]1/2
.
a
b
2
mmol) were used. 6 was obtained as a pale yellow solid.
Yield: 0.968 g, 93%. Mp: 108 °C. Anal. Calcd for C21H15F3Ge:
C, 63.5; H, 3.8; F, 14.8. Found: C, 63.8; H, 3.6; F, 14.4. 13C
NMR: δ 133.4 [CH, s], 131.6 [C, s], 129.2 [CH, s], 127.7
[CH, s], see Table 1. 1H NMR: δ 7.7-7.4 (m). IR: νmax/cm-1
2200 (CtC str.), 1247, 1149 (C-F str.).
filtered solution was concentrated in vacuo and purified on a
silica column eluting with 50:50 DCM/hexane to afford 12 as
a pale yellow solid. Yield: 0.694 g, 69%. Anal. Calcd for
C21H17F3Si: C, 71.2; H, 4.8; F, 16.1. Found: C, 72.0; H, 6.1; F,
16.7. 19F NMR: δ -66.8 (dd, J HF 5.8, 1.5 Hz). 13C NMR: δ
134.9 [CH, s], 131.1 [C, s], 129.2 [CH, s], 127.2 [CH, s], 136.3
[CRH, m], 134.3 [CH, q, J CF 5.0 Hz Câ], 121.1 [C, q, J CF 271.2
P h 3Sn CtCCF 3 (7). HFC-245fa (1.30 cm3, 12.81 mmol),
n-BuLi (14.6 cm3, 36.50 mmol), and Ph3SnCl (3.154 g, 8.18
mmol) were used. 7 was obtained as a pale yellow solid.
Yield: 3.186 g, 88%. Mp: 90 °C. Anal. Calcd for C21H15F3Sn:
C, 57.0; H, 3.4; F, 12.8. Found: C, 57.1; H, 3.6; F, 12.6. 13C
NMR: δ 135.6 [CH, s, J SnC 44 Hz], 133.6 [C, s], 129.2 [CH, s,
1
Hz, CF3]. H NMR: δ 7.2 (dq, J HH 18.6, J HF 1.5 Hz), 6.1 (dq,
J HH 18.6, J HF 5.8 Hz). IR: νmax/cm-1 1280, 1130 (C-F str.).
Syn th esis of E-P h 3SiCHdC(CF 3)R (R ) n -Bu ) (12). To
an ethereal solution (15 cm3) of 3 (0.503 g, 1.43 mmol), held
at -60 °C, was added dropwise n-BuLi (1.0 cm3, 2.5 mmol);
then the mixture was stirred for 5 h, before being quenched
by addition of methanol (∼3 cm3). Having attained ambient
temperature, hexane was added to precipitate the inorganic
salts, and the mixture filtered through Celite. Concentration
in vacuo afforded the crude product as an oil, which was
purified by passing down a short silica column (50:50 DCM/
hexane), affording analytically pure 13 as an off-white mate-
rial. Yield: 0.382 g, 65%. Anal. Calcd for C25H25F3Si: C, 72.2;
H, 6.2; F, 13.9. Found: C, 73.4; H, 6.4; F, 13.5. 19F NMR: δ
-67.4 (d, J HF 1.3 Hz). 13C NMR: δ 136.2 [CH, s], 134.1 [C, s],
130.3 [CH, s], 128.5 [CH, s], 149.5 [C, q, J CF 27.6 Hz, Câ], 127.9
[CH, q, J CF 4.0 Hz CR], 123.8 [C, q, J CF 276.8 Hz, CF3], 31.8
[CH2, s, CγH2n-Pr], 31.2 [CH2, s, CγH2CH2Et], 23.1 [CH2, s,
CγH2CH2CH2Me], 13.9 [CH3, s]. 1H NMR: δ 6.8 (q, J HF 1.3 Hz),
J
SnC 12.5 Hz], 128.1 [CH, s, J SnC 61 Hz], see Table 1. 1H NMR:
δ 7.7-7.4 (m). IR: νmax/cm-1 2184 (CtC str.), 1244, 1175 (C-F
str.).
Bu 3Sn CtCCF 3 (8). HFC-245fa (1.60 cm3, 15.76 mmol),
n-BuLi (18.6 cm3, 46.50 mmol), and Bu3SnCl (2.20 cm3, 8.11
mmol) were used. Crude product was distilled at 113 °C/15
mmHg. Yield: 1.976 g, 63%. Anal. Calcd for C15H27F3Sn: C,
47.0; H, 7.1; F, 14.9. Found: C, 47.1; H, 7.1; F, 14.7. 13C
NMR: δ 29.0 [CH2, s, J SnC 24 Hz], 27.3 [CH2, s, J SnC 60 Hz],
13.9 [CH3, s, J SnC 2.5 Hz], 11.7 [CH2, s, J SnC 377 Hz], see Table
1. 1H NMR: δ 1.6 (m, 2H), 1.4 (m, 2H), 1.1 (m, 2H), 0.9 (m,
3H). IR: νmax/cm-1 2175 (CtC str.), 1243, 1139 (C-F str.).
P h 3P bCtCCF 3 (9). HFC-245fa (0.22 cm3, 2.17 mmol),
n-BuLi (2.5 cm3, 6.25 mmol), and Ph3PbCl (0.498 g, 1.05 mmol)
were used. 9 was obtained as a beige solid. Yield: 0.212 g,
38%. Mp: 94 °C. Anal. Calcd for C21H15F3Pb: C, 47.5; H, 2.8;
F, 10.7. Found: C, 47.1; H, 3.0; F, 9.5. 13C NMR: δ 147.2
[C, s, J PbC 661.5 Hz], 135.9 [CH, s, J PbC 84.0 Hz], 129.1 [CH, s,
J PbC 104.0 Hz], 128.6 [CH, s, J PbC 23.2 Hz], see Table 1. 1H
NMR: δ 7.7-7.3 (m). IR: νmax/cm-1 2169 (CtC str.), 1241,
1141 (C-F str.).
Syn th esis of E-P h 3SiCHdCHCF 3 (11). To a suspension
of LiAlH4 (0.113 g, 2.98 mmol) in THF (10 cm3) cooled to -60
°C was added dropwise a THF solution (5 cm3) of 3 (1.001 g,
2.84 mmol). After complete addition, the mixture was allowed
to attain ambient temperature while stirring over 2.5 h. The
reaction was quenched at -30 °C by addition of 5 cm3 H2O,
then allowed to reattain ambient temperature and extracted
with diethyl ether (2 × 10 cm3). The organics were combined,
washed with water (2 × 10 cm3), and dried over MgSO4. The
2.1 (m, 2H), 1.1 (m, 2H), 0.7 (m, 2H), 0.6 (m, 3H). IR: νmax
/
cm-1 1589 (CdC str.), 1168, 1118 (C-F str.).
(R ) P h ) (13). Ph3SiCtCCF3 (3) (0.503 g, 1.43 mmol) and
PhLi (1.0 cm3, 1.80 mmol) were used at -30 °C for 5 h. The
product was isolated as an off-white solid. Yield: 0.397 g, 65%.
Anal. Calcd for C27H21F3Si: C, 75.3; H, 4.9; F, 13.2. Found:
C, 75.5; H, 4.9; F, 13.2. 19F NMR: δ -67.5 (br m). 13C NMR:
δ 135.8 [CH, s, Ph3Si], 133.3 [C, s, Ph3Si], 129.7 [CH, s, Ph3-
Si], 127.9 [CH, s, Ph3Si]; 148.2 [C, q, J CF 29.9 Hz, Câ], 131.1
[CH, q, J CF 3.4 Hz CR], 122.6 [C, q, J CF 276.0 Hz, CF3], 129.3
1
[CH, s, Ph], 128.4 [CH, s, Ph], 127.6 [CH, s, Ph]. H NMR: δ
7.4-7.1 (m), 6.9 (br m). IR: νmax/cm-1 1494 (CdC str.), 1249,
1172 (C-F str.).
(R ) t-Bu ) (14). Ph3SiCtCCF3 (3) (0.503 g, 1.43 mmol) and
t-BuLi (1.1 cm3, 1.65 mmol) were used at -60 °C for 5 h. The
product was isolated as an off-white solid. Yield: 0.480 g, 82%.

5542 Organometallics, Vol. 22, No. 26, 2003
Brisdon et al.
Mp: 89 °C. Anal. Calcd for C25H25F3Si: C, 73.2; H, 6.1; F, 13.9.
Found: C, 73.4; H, 6.1; F, 13.5. 19F NMR δ -60.7 [d, J HF 1.5
Hz]. 13C NMR: δ 134.7 [CH, s], 134.1 [C, s], 128.6 [CH, s],
127.0 [CH, s], 155.7 [C, q, J CF 23.7 Hz, Câ], 126.2 [CH, q, J CF
4.8 Hz, CR], 123.2 [C, q, J CF 279 Hz, CF3], 35.3 [C, s CMe3],
29.7 [CH3, s, C(CH3)3]. 1H NMR: δ 7.7-7.4 (m), 6.9 [q, J HF 1.5
Hz. 1H] 1.06 [s, 9H]. IR: νmax/cm-1 1429 (CdC str.), 1251, 1157
(C-F str.).
summarized in Table 5. Molecular representations shown in
the figures were generated using ORTEP 3 for Windows.29
Ab In itio Ca lcu la tion s. Calculations were performed with
the Gaussian 98 package, Revision A.7,30 running on a Sun
Enterprise HPC 4500 workstation. Geometries were optimized
at the B3LYP/6-311+G* level and characterized as minima
by frequency calculations. Thermally corrected free energies
were calculated at 298 K and used comparatively without
further scaling.
P r ep a r a tion of P h 3SiCdC(CF 2)t-Bu (15). In a typical
reaction, a THF solution (15 cm3) of 3 (0.501 g, 1.42 mmol)
was warmed to 40 °C, prior to the dropwise addition of t-BuLi
(1.1 cm3, 1.65 mmol); the mixture was then brought to reflux
for 20 h. The cooled mixture was then quenched by addition
of methanol (∼3 cm3). Then hexane (50 cm3) was added to
precipitate the inorganic salts. Filtration through Celite and
concentration in vacuo afforded the crude product, which was
purified by passing down a short silica column (50:50 DCM/
hexane), resulting in a yellow solid. Yield: 0.470 g, 85%. Anal.
Calcd for C25H24F2Si: C, 76.9; H, 6.2; F, 9.7. Found: C, 76.5;
H, 6.1; F, 10.0. 19F NMR: δ -103.1 [s]. 13C NMR: δ 134.6 [CH,
s], 130.9 [C, s], 129.3 [CH, s], 127.2 [CH, s], 157.9 [C, t, J CF
8.3 Hz, Câ], 124.6 [C, t, J CF 13.1 Hz, CR], 108.2 [C, t, J CF 271
Ack n ow led gm en t. We thank the Engineering and
Physical Sciences Research Council (EPSRC) and UMIST
for financial support, and Honeywell Specialty Chemi-
cals for donation of HFC-245fa. We acknowledge the
EPSRC for support of the UMIST NMR (GR/L52246)
and FT/IR Raman (GR/M30135) facilities, for a Research
Equipment Initiative grant for X-ray equipment, and
also for access to the Chemical Database Service at
Daresbury. We also thank Dr. K. R. Flower for useful
discussion.
Su p p or tin g In for m a tion Ava ila ble: For the single-
crystal structure determinations, tables of crystal data and
structure refinement, atomic coordinates, anisotropic displace-
ment parameters, bond lengths, and bond angles and an X-ray
crystallographic file, in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
1
Hz, CF2], 29.7 [C, s, CMe3], 27.4 [CH3, s, C(CH3)3]. H NMR:
δ 7.7-7.4 (m), 1.1 [s, 9H]. IR: νmax/cm-1 1729 (CdC str.), 1261,
1149 (C-F str.).
X-r a y Cr ysta llogr a p h y. Single crystals of compounds 2,
3, 6, 12, and 13 were obtained by slow evaporation of the
solvents from dichloromethane/hexane solutions. Diffraction
data were recorded on a Nonius κ-CCD 4-circle diffractometer
using graphite-monochromated Mo KR radiation (λ ) 0.71073
Å). Data collections were performed at 150(2) K in all cases.
The data for all structures were solved by direct methods and
subjected to full-matrix least-squares refinement on F2 using
the SHELX-9728 program. Structures were corrected for
absorption by the multiscan method using the SORTAV
program. All non-hydrogen atoms were refined with anisotro-
pic thermal parameters. For compounds 2-5 the aromatic
hydrogen atoms were included in idealized positions and
refined isotropically, while in all other cases hydrogen atoms
were located. Data collection and refinement parameters are
OM034146T
(29) ORTEP 3 for Windows. Farrugia, L. J . J . Appl. Crystallogr.
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Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
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B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
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