Spectroscopic and structural assignment of the absolute stereochemistry in a series of 1,2-difluorovinyl organometalloids. The first crystallographic characterization and structural series of group 14 fluorovinyl compounds

Article abstract of DOI:10.1021/ic025593o

The group 14 trifluorovinyl compounds Ph₃ECF=CF₂ (E = Ge, Sn, Pb) have been prepared in high yield by the low-temperature reaction of the triphenylelement halide with trifluorovinyllithium, generated from tetrafluoroethane (CF₃CH₂F, HFC-134a) and 2 equiv of n-butyllithium. The X-ray crystal structures of these materials have been obtained, so affording the first structural series for such species. Subsequent reaction of Ph₃GeCF=CF₂ with LiAlH₄ and a range of organolithium reagents has led to preparation of the 1,2-difluorovinylgermanes Ph₃GeCF= CFR (R = H, Me, n-Bu, t-Bu, Ph). Multinuclear NMR spectroscopic and X-ray crystallographic studies of these compounds have been undertaken and have shown unequivocally the exclusive trans-geometry of the 1,2-difluorovinyl moiety.

Full text of DOI:10.1021/ic025593o

Inorg. Chem. 2002, 41, 4748−4755
Spectroscopic and Structural Assignment of the Absolute
Stereochemistry in a Series of 1,2-Difluorovinyl Organometalloids. The
First Crystallographic Characterization and Structural Series of Group
14 Fluorovinyl Compounds
Alan K. Brisdon,* Ian R. Crossley, Robin G. Pritchard, and John E. Warren
Department of Chemistry, UMIST, P.O. Box 88, Manchester M60 1QD, U.K.
Received March 14, 2002
The group 14 trifluorovinyl compounds Ph3ECFdCF (E ) Ge, Sn, Pb) have been prepared in high yield by the
2
low-temperature reaction of the triphenylelement halide with trifluorovinyllithium, generated from tetrafluoroethane
(CF CH F, HFC-134a) and 2 equiv of n-butyllithium. The X-ray crystal structures of these materials have been
3
2
obtained, so affording the first structural series for such species. Subsequent reaction of Ph3GeCFdCF with
2
LiAlH and a range of organolithium reagents has led to preparation of the 1,2-difluorovinylgermanes Ph3GeCFd
4
CFR (R ) H, Me, n-Bu, t-Bu, Ph). Multinuclear NMR spectroscopic and X-ray crystallographic studies of these
compounds have been undertaken and have shown unequivocally the exclusive trans-geometry of the 1,2-difluorovinyl
moiety.
Introduction
the trifluorovinyl (CFdCF2) derivatives, among the first
examples of which were tin- and silicon-based species,
prepared from trifluorovinyl Grignard reagents3 derived from
halofluoroalkenes.4 These systems have been the subject of
considerable interest for their potential utility as transfer and
cross-coupling reagents.5
Increasingly, attention has turned to the use of these
species as precursors for 1,2-difluorovinyl reagents, an area
first explored by Seyferth. Thus, it was observed that
trifluorovinylsilanes interact with a range of nucleophiles,
via an addition-elimination mechanism, to afford predomi-
nantly a single 1,2-difluorovinylsilane species, which was
assigned as the trans isomer on the basis of 19F NMR
studies.6 Efforts to duplicate this reactivity with stannane-
based systems were unsuccessful, metathesis instead being
observed. However, such tin-based species have been
prepared by Burton et al., by effecting the transformation of
In recent years, there has been a surge of interest in the
chemistry of fluorinated compounds, in particular those with
potential pharmaceutical, agrochemical, and materials ap-
plications.1,2 Typically, a fluorinated group is employed as
an isosteric replacement for a key functionality, so imparting
electronic diversity, yet minimal perturbation of the molec-
ular geometry. Thus, it is possible to prepare compounds
with unique physical and chemical properties and biological
interactions, on the basis of well-understood structure-
reactivity relationships.
A consequence of this has been a renewed interest in the
chemistry of fluorocarbon-containing organometallic com-
pounds, driven by their potential to serve as convenient,
selective reagents for introducing small fluorocarbon moi-
eties. One such class of compounds, of current interest, is
* To whom correspondence should be addressed. E-mail: alan.brisdon@
umist.ac.uk.
(3) (a) Sterlin, R. N.; Li, W.-K.; Knunyants, I. L. IzV. Akad. Nauk. SSSR,
Otd. Khim. Nauk. 1959, 1506. (b) Kaesz, H. D.; Stafford, S. L.; Stone,
F. G. A. J. Am. Chem. Soc. 1959, 81, 6336.
(4) Park, J. D.; Seffl, R. J.; Lacher, J. R. J. Am. Chem. Soc. 1956, 78, 59.
(5) (a) Sorokina, R. S.; Rybakova, L. F.; Kalinovskii, I. O.; Chernoplekova,
V. A.; Baletskaya, I. P. J. Org. Chem. USSR 1982, 18, 2180. (b)
Sorokina, R. S.; Rybakova, L. F.; Kalinovskii, I. O.; Baletskaya, I. P.
Bull. Acad. Sci. USSR, DiV. Chem. Sci. 1985, 34, 1506. (c) Farina,
V.; Baker, S. R.; Benigni, D. A.; Hauck, S. I.; Sapina, C., Jr. J. Org.
Chem. 1990, 55, 5833.
(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; ACS Symposium Series; 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
(6) (a) Seyferth, D.; Wada, T.; Raab, G. Tetrahedron Lett. 1960, 20. (b)
Seyferth, D.; Wada, T. Inorg. Chem. 1962, 1, 78.
4748 Inorganic Chemistry, Vol. 41, No. 18, 2002
10.1021/ic025593o CCC: $22.00 © 2002 American Chemical Society
Published on Web 08/06/2002

Structure of 1,2-DifluoroWinyl Organometalloids
Technologies, U.K.). Diethyl ether and THF were dried over sodium
wire for ca. 1 day prior to use. The compounds CF3CH2F (Ineos
Fluor), n-BuLi (2.5 M in hexane), MeLi (1.6 M in ether), PhLi (2
M in ether/pentane), t-BuLi (1.7 M in pentane) (Acros), Ph3GeBr
(Aldrich), Ph3SnCl, LiAlH4 (Lancaster), and methanol (BDH) were
used as supplied. Fluorine NMR spectra of CDCl3 solutions were
recorded on a Bruker DPX200 spectrometer at 188.310 MHz and
referenced to external CFCl3. Carbon and proton NMR spectra were
recorded on a Bruker DPX400 spectrometer at 100.555 and 400.4
MHz, respectively, as solutions in CDCl3 and referenced to external
SiMe4. All resonances are reported using the high-frequency positive
convention. Infrared spectra were recorded as mineral oil mulls or
neat liquids between KBr plates on Nicolet PC-5 or Nexus FTIR
spectrometers. Elemental analyses were performed by the depart-
mental microanalytical service.
Preparation of Ph3GeCFdCF2 (2). To a three-necked round-
bottomed flask, equipped with nitrogen inlet/outlet and magnetic
stirrer, maintained at -78 °C, were added diethyl ether (150 cm3)
and CF3CH2F (1.09 g, 10.67 mmol). BuLi (8.5 cm3, 21.25 mmol)
was added slowly at such a rate as to maintain the low temperature.
The mixture was left to stir for 2 h, to ensure complete generation
of trifluorovinyllithium 1. After this time, Ph3GeBr (1.995 g, 5.20
mmol) dissolved in ether (50 cm3) was added dropwise, and the
reaction was left to stir overnight. Subsequently, the mixture was
allowed to warm to room temperature and then worked up by
addition of hexane (150 cm3) to precipitate the inorganic salts. After
filtration through a sinter, the filtrate was concentrated by rotary
evaporation to afford the crude product. Purification by column
chromatography on silica, with a 1:1 dichloromethane/hexane
eluent, yielded 1.426 g, 71% of the pure product, as a yellow solid.
Mp 79 °C. Anal. Calcd for C20H15F3Ge: C, 62.4; H, 3.9; F, 14.8.
Found: C, 62.2; H, 4.0; F, 15.0. For δF, see Table 2. δH 7.9-7.4
(m, C6H5). δC 161.5 (C, ddd, JCF 310, 277, 36 Hz, CF2), 135.4
(CH), 132.8 (C), 130.4 (CH), 129.0 (CH). νmax/cm-1 2000-1780
(Ar overtones), 1722.7 (CdC str), 1284.8, 1186.8, 1020.5 (CsF
str), 738.9, 696.4 (CsF def).
Preparation of Ph3SnCFdCF2 (3). In a similar procedure to
that given in the preceding paragraph, an ethereal solution of Ph3-
SnCl (1.9 g, 4.64 mmol) was added to 1.05 equiv of 1, generated
in situ from 0.5 cm3 (5.93 mmol) of HFC-134a and 3.9 cm3 (9.75
mmol) of n-BuLi. Workup yielded 1.800 g, 86% of the pure, yellow
product. Mp 73 °C. Anal. Calcd for C20H15F3Sn: C, 55.7; H, 3.5;
F, 13.2. Found: C, 57.0; H, 3.7; F, 12.9. For δF, see Table 2. δH
7.7-7.5 (m, C6H5). δC 160.9 (C, ddd, JCF 316, 269, 33 Hz, CF2),
137.4 (CH), 135.3 (C), 130.3 (CH), 129.4 (CH). νmax/cm-1 1970-
1740 (Ar overtones), 1712.5 (CdC str), 1272.8, 1107.0, 1076.1
(CsF str).
Preparation of Ph3PbCFdCF2 (4). Analogously, Ph3PbCl
(0.995 g, 2.1 mmol) was introduced to an ethereal solution of 2
equiv of 1, prepared from 0.4 cm3 (4.74 mmol) of HFC-134a and
3.4 cm3 (8.5 mmol) of n-BuLi. The pure product was obtained on
workup as a beige-colored solid, 0.842 g, 77%. Mp 67-9 °C. Anal.
Calcd for C20H15F3Pb: C, 46.2; H, 2.9; F, 10.9. Found: C, 46.5;
H, 2.9; F, 10.7. For δF, see Table 2. δH 7.8-7.5 (m, C6H5). δC
160.9 (C, ddd, JCF 318, 265, 29 Hz, CF2), 143.0 (C, ddd, JCF 315,
90, 9 Hz, CF), 146.7 (C, JPbC 651 Hz), 136.2 (CH, JPbC 77 Hz),
128.9 (CH, JPbC 97 Hz), 129.4 (CH, JPbC 28 Hz). νmax/cm-1 2000-
1780 (Ar overtones), 1711.1 (CdC str), 1263.7, 1113.1, 983.7 (Cs
F str), 726.4, 694.5 (CsF def).
a trifluorovinylsilane and subsequently using this as a transfer
reagent for the fluorocarbon moiety to a tin center.7
Comparison with the chemistry of group 14 vinyl com-
pounds would suggest that germanium and lead trifluoro-
vinyls should exhibit analogous reactivity to silicon and tin
derivatives, respectively. However, these systems have been
little explored. Only five trifluorovinylgermane compounds
have been reported, namely Ge(CFdCF2)4,8,9 Me2Ge(CFd
CF2)2,9 Me3GeCFdCF2,9,10 Et3GeCFdCF2, and Ph3GeCFd
CF2,11 all in low to moderate yield, while there is a single
report of a trifluorovinyllead compound, namely Pb(CFd
CF2)4.8 There is just one report of the reactivity of such
species, namely the reaction of Me3GeCFdCF2 with tin
hydrides to yield predominantly cis-(1,2-difluorovinyl)-
trimethylgermane, in addition to smaller amounts of the trans
and gem isomers and a range of dimeric species.10
With the progressive international phase-out of halofluoro-
carbons, because of their deleterious effect upon atmospheric
ozone levels, the availability of precursors for trifluorovinyl
Grignard, and lithium, reagents has been severely restricted,
thus necessitating the development of alternative routes. To
this end, it has recently been shown that trifluorovinyllithium
(1) can be obtained in high yield through the low-temperature
reaction of the commercially available CFC-replacement CF3-
CH2F (HFC-134a) with 2 equiv of butyllithium,12 and that
1 may be subsequently used to prepare trifluorovinyl-
containing species in high yields, in a one-pot procedure.13
We have thus prepared a range of systems and have obtained
the first structural characterizations of any trifluorovinyl
derivatives.14 In continuation of this work, we have now
turned our attention to the group 14 systems, for which no
structural data are currently available. Here, we report the
synthesis and structural characterization of the compounds
Ph3ECFdCF2 (E ) Ge, Sn, Pb). Moreover, in view of a
recent report where the assignment of fluorovinyl geometry
cannot be unambiguously made on the basis of the conven-
tional order of 19F NMR coupling constants,15 we have
undertaken to characterize thoroughly a range of 1,2-difluoro-
vinyls, derived from the trifluorovinylgermane, by a com-
bination of spectroscopic and crystallographic means.
Experimental Section
General Methods. Reactions were carried out under anaerobic
conditions in flame-dried glassware, with moisture-sensitive re-
agents being handled under an argon atmosphere in a drybox (Belle
(7) (a) Fontana, S. A.; Davis, C. R.; He, Y.-B.; Burton, D. J. Tetrahedron
1996, 52, 37. (b) Xue, L.; Lu, L.; Pedersen, S. D.; Liu, Q.; Narake, R.
M.; Burton, D. J. J. Org. Chem. 1997, 62, 1064.
(8) Sterlin, R. N.; Dubov, S. S.; Li, W.-K.; Vakhomchik, L. P.; Knunyants,
I. L. Zh. Vses. Khim. OVa. im. D. I. MendeleeVa 1961, 6, 110; Chem.
Abs. 1961, 55, 15336e.
(9) Coyle, T. D.; Stafford, S. L.; Stone, F. G. A. Spectrochim. Acta 1961,
17, 968.
(10) Akhtar, M.; Clark, H. C. Can. J. Chem. 1968, 46, 2165.
(11) Seyferth, D.; Wada, T.; Maciel, G. E. Inorg. Chem. 1962, 1, 232.
(12) Burdon, J.; Coe, P. L.; Haslock, I. B.; Powell, R. L. J. Chem. Soc.,
Chem. Commun. 1996, 49.
(13) Banger, K. K.; Brisdon, A. K.; Gupta, A. J. Chem. Soc., Chem.
Commun. 1996, 139.
(14) See for example: (a) Banger, K. K.; Brisdon, A. K.; Brain, P. T.;
Parsons, S.; Rankin, D. W. H.; Robertson, H. E.; Smart, B. A.; Buhl,
M. Inorg. Chem. 1999, 38, 5894. (b) Barnes, N. A.; Brisdon, A. K.;
Ellis, M. J.; Pritchard, R. G. J. Fluorine Chem. 2001, 112, 35.
(15) Kvicala, J. Proceedings of the 16th International Fluorine Conference,
Durham, UK, July 16-21, 2000, pp B17. Kvicala, J.; Hrabal, R.;
Czernek, J.; Bartozova, I.; Paleta, O.; Pelter, A. J. Fluorine Chem.
2002, 113, 211.
Inorganic Chemistry, Vol. 41, No. 18, 2002 4749

Brisdon et al.
Synthesis of Ph3GeCFdCFH (5). Synthesis was based upon
literature methods.7a A three-necked flask, equipped with N2 inlet/
outlet and magnetic stirrer, was charged with LiAlH4 (0.075 g, 1.98
mmol) suspended in 15 cm3 of dry THF. The suspension was cooled
to -30 °C and a solution of 2 (0.323 g, 0.8 mmol) in 10 cm3 of
THF added cautiously. The reaction was allowed to warm to room
temperature and stirred for 6 h. Excess LiAlH4 was quenched by
the cautious addition, at -20 °C, of degassed water (40 cm3). The
mixture was extracted with diethyl ether (3 × 40 cm3), and the
organics were combined and dried over MgSO4. Filtration and
removal of the solvent in vacuo afforded the product as a pale
yellow solid. Yield: 0.196 g, 64%. Mp 80 °C. Anal. Calcd for
C20H16F2Ge: C, 65.5; H, 4.4; F, 10.4. Found: C, 63.9; H, 5.2; F,
8.7. δF -169.7 (dd, JFF 131 Hz, JFH 78 Hz, trans-CFdCFH),
-172.4 (dd, JFF 131 Hz, JFH 10 Hz, trans-CFdCFH). δH 7.9 (1H,
dd, JFH 78, 10 Hz), 7.6 (6H, m), 7.5 (9H, m). δC 158.4 (C, dd, JCF
280, 58 Hz, CFdCFH), 152.2 (CH, dd, JCF 241, 50 Hz, CFdCFH),
134.0 (CH), 132.1 (C), 128.7 (CH), 127.4 (CH). νmax/cm-1 2000-
1780 (Ar overtones), 1649.4 (CdC str), 1147.8, 1026.3 (CsF str),
734.9, 696.4 (CsF def).
Synthesis of Ph3GeCFdCFPh (9). Analogous treatment of 2
(0.3 g, 0.78 mmol) with PhLi (1.2 cm3, 2.4 mmol) and subsequent
workup led to isolation of the compound as a pale brown solid.
Yield: 0.297 g, 86%. Mp 122 °C. Anal. Calcd for C26H20F2Ge:
C, 70.5; H, 4.6; F, 8.6. Found: C, 70.4; H, 4.7; F, 8.3. For δF, see
Table 5. δH 7.8-7.4 (m, C6H5). δC 159.5 (C, dd, JCF 226, 30 Hz,
CFdCFPh), 156.5 (C, dd, JCF 289, 80 Hz, CFdCFPh), 135.6 (CH),
134.2 (C), 130.1 (CH), 128.9 (CH), 129.9 (C, dd, JCF 27, 3 Hz,
i-C6H5), 129.8 (CH, d, JCF 2.5 Hz, p-C6H5), 129.2 (CH, d, JCF 3.5
Hz, m-C6H5), 126.2 (CH, dd, JCF 10, 7.5 Hz, o-C6H5). νmax/cm-1
2000-1800 (Ar overtones), 1637.8 (CdC str), 1122.5, 1074.5 (Cs
F str), 735, 696.4 (CsF def).
Synthesis of Ph3GeCFdCFOMe (10). Under the anaerobic
conditions outlined previously, germane 2 (0.215 g, 0.56 mmol)
was treated with sodium methoxide (0.63 g, 11.66 mmol), freshly
prepared from metallic sodium and analytical grade methanol, as a
solution in methanol (2 cm3). After 12 h, the reaction mixture was
worked-up with hexane. The product was recrystallized from
dichloromethane and obtained as a pale yellow solid. Yield: 0.143
g, 64%. Mp 76 °C. Anal. Calcd for C21H18F2GeO: C, 63.5; H,
4.6; F, 9.6. Found: C, 63.7; H, 4.9; F, 9.2. For δF, -118.1 (d, JFF
122 Hz, CFdCFOMe), -187.77 (d, JFF 122 Hz, CFdCFOMe).
δH 7.7-7.4 (15H, m, C6H5), 3.9 (3H, OCH3). δC 163.4 (C, dd, JCF
245, 31 Hz), 135.5 (CH), 134.2 (C), 130.0 (CH), 128.8 (CH), 59.4
(CH3, dd, JCF 4, 3 Hz).
X-ray Crystallography. Single crystals of compounds 2-5, 8,
and 9 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-mono-
chromated 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-9716 program. Structures were
corrected for absorption by the multiscan method using the
SORTAV program. All non-hydrogen atoms were refined with
anisotropic 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 summarized in Table
1. Molecular representations shown in the figures were generated
using ORTEP 3 for Windows.17
Synthesis of Ph3GeCFdCFMe (6). A three-necked round-
bottomed flask, equipped with N2 inlet/outlet, magnetic stirrer, and
a rubber septum, was charged with 0.3 g (0.78 mmol) of 2 in diethyl
ether (20 cm3), and the temperature was held at -78 °C during the
addition of MeLi (2.5 cm3, 4.00 mmol). The mixture was left to
stir and warm slowly to room temperature over 6 h, after which
time workup was effected by addition of hexane (80 cm3), followed
by filtration and solvent removal in vacuo. The product was
obtained as a pale yellow solid. Yield: 0.230 g, 77%. Mp 74.5 °C.
Anal. Calcd for C21H18F2Ge: C, 66.2; H, 4.8; F, 9.9. Found: C,
66.5; H, 4.9; F, 9.7. For δF, see Table 5. δH 7.6-7.4 (15H, m,
C6H5); see also Table 5. δC 162.5 (C, dd, JCF 236.6, 39.5 Hz, CFd
CFMe), 153.2 (C, dd, JCF 274.3, 77.3 Hz, CFdCFMe), 135.6 (CH),
134.4 (C), 130.0 (CH), 128.8 (CH), 13.5 (CH3, dd, JCF 26.5, 2.5
Hz, Me). νmax/cm-1 2000-1800 (Ar overtones), 1684.1 (CdC str),
1184.4, 999.3 (CsF str), 734.9, 696.3 (CsF def).
Synthesis of Ph3GeCFdCFn-Bu (7). In an analogous manner
to that described previously, 0.3 g (0.78 mmol) of 2 was treated
with 2 equiv of n-BuLi (0.6 cm3, 1.50 mmol). Workup afforded
the product as a pale yellow, viscous liquid. Yield: 0.293 g, 89%.
Anal. Calcd for C24H24F2Ge: C, 68.1; H, 5.7; F, 9.0. Found: C,
68.3; H, 5.9; F, 8.7. For δF, see Table 5. δH 7.7-7.4 (15H, m,
C6H5); see also Table 5. δC 165.9 (C, dd, JCF 239.5, 38.6 Hz, CFd
CFn-Bu), 152.8 (C, dd, JCF 274.3, 78.2 Hz, CFdCFn-Bu), 135.5
(CH), 134.5 (C), 130.0 (CH), 128.8 (CH), 28.6 (CH2, s, CH2CH2-
Et), 26.9 (CH2, dd, JCF 25, 1 Hz, CFdCFCH2Pr), 22.5 (CH2, s,
CH2CH2CH2Me), 14.2 (CH3, s, Me). νmax/cm-1 3071.1, 3051.8 (CH2
str), 2259.2-2872.4 (CH3 str), 2000-1800 (Ar overtones), 1676.4
(CdC str), 1431.4 (CsH def), 1093.8, 999.3 (CsF str), 735, 698.3
(CsF def).
Results and Discussion
Synthesis and Spectroscopic Characterization of Group
14 Trifluorovinyls. The reaction of trifluorovinyllithium (1),
prepared from CF3CH2F (HFC-134a), in cold diethyl ether
solution, with the group 14 precursors Ph3EX (E ) Ge, Sn,
Pb; X ) Cl, Br) yields the respective trifluorovinyl com-
pounds Ph3E(CFdCF2) (E ) Ge 2, Sn 3, Pb 4) as stable
materials. It is noteworthy that, while 3 is readily generated
from a 1:1 equivalence of the halide and trifluorovinyl-
lithium, 2 and 4 require a 2-fold excess of 1 to maximize
conversion. Moreover, while 3 and 4 are prepared in
analytically pure form, the germane forms in admixture with
other, unidentified species. Notwithstanding, this product is
readily purified by column chromatography on silica gel,
using a 1:1 dichloromethane/hexane eluent, to yield over 70%
of the desired material.
Synthesis of Ph3GeCFdCFt-Bu (8). Using a method similar
to that described previously, germane 2 (0.3 g, 0.78 mmol) was
treated with 2.1 equiv (1.1 cm3, 1.65 mmol) of t-BuLi. Workup
afforded the product as a beige solid. Yield: 0.306 g, 93%. Mp 88
°C. Anal. Calcd for C24H24F2Ge: C, 68.1; H, 5.7; F, 9.0. Found:
C, 68.4; H, 5.9; F, 8.7. For δF, see Table 5. δH 7.6-7.4 (15H, m,
C6H5); see also Table 5. δC 167.6 (C, dd, JCF 238.5, 31 Hz, CFd
CFt-Bu), 150.7 (C, dd, JCF 280, 91 Hz, CFdCFt-Bu), 134.0 (CH),
133.2 (C), 128.4 (CH), 127.3 (CH), 34.7 (C, dd, 24, 2.5 Hz, CMe3),
24.5 (CH3, dd, JCF 5, 3.6 Hz). νmax/cm-1 2880 (CH3 str), 2000-
1800 (Ar overtones), 1660 (CdC str), 1091.9, 1010 (CsF str), 735,
698.9 (CsF def).
(16) Sheldrick, G. M. SHELX-97; Institut fur Anorganische Chemie der
Universitat Gottingen: Gottingen, Germany, 1998.
(17) ORTEP 3 for Windows: Farrugia, L. J. J. Appl. Crystallogr. 1997,
30, 565.
4750 Inorganic Chemistry, Vol. 41, No. 18, 2002

Structure of 1,2-DifluoroWinyl Organometalloids
Table 1. Crystal Data and Structure Refinement for Ph3GeCFdCF2 (2), Ph3SnCFdCF2 (3), Ph3PbCFdCF2 (4), Ph3GeCFdCFH (5), Ph3GeCFdCFt-Bu
(8), and Ph3GeCFdCFPh (9)
2
3
4
5
8
9
formula
mol wt
cryst syst
space group
cryst dimens, mm3
habit
C20H15F3Ge
384.91
triclinic
P1h (No. 2)
0.4 × 0.3 × 0.3
prism
C20H15F3Sn
431.01
triclinic
P1h (No. 2)
0.2 × 0.1 × 0.1
prism
C20H15F3Pb
519.51
monoclinic
P21/c (No. 14)
0.25 × 0.22 × 0.2
prism
C20H16F2Ge
366.92
monoclinic
Cc (No. 9)
0.25 × 0.15 × 0.03
plate
C24H24F2Ge
423.02
monoclinic
P21/c (No. 14)
0.25 × 0.25 × 0.1
prism
C26H20F2Ge
443.01
monoclinic
P21 (No. 4)
0.3 × 0.2 × 0.2
prism
color
a, Å
b, Å
c, Å
colorless
10.087(2)
10.338(5)
18.704(9)
103.05(4)
95.43(3)
108.91(2)
1767.4(12)
4
1.447
1.759
1.14-24.99
6534, 6147
colorless
9.6807(6)
9.9819(8)
18.2114(14)
90.020(4)
85.893(4)
87.843(3)
1754.0(2)
4
1.632
1.483
2.11-27.45
10924, 7203
colorless
9.6770(5)
10.0367(7)
18.2499(10)
90
94.492(2)
90
1767.78(18)
4
1.952
9.570
3.02-29.11
11516, 4288
colorless
10.2386(6)
29.170(3)
7.3196(6)
90
129.109(4)
90
1696.3(2)
4
1.437
1.821
2.88-24.98
2206, 2206
colorless
11.4276(2)
11.4998(2)
32.0449(5)
90
93.7970(10)
90
4201.94
colorless
7.5395(3)
11.4621(6)
12.2168(6)
90
99.400(2)
90
1041.58(9)
2
1.413
1.497
3.82-27.43
7146, 4543
R, deg
â, deg
γ, deg
V, Å3
Z
D
8
calcd, g cm-3
1.337
1.480
2.55-27.46
24763, 9427
µ mm-1
θ range/deg
no. data collected,
unique reflns
params refined
F(000)
479
776
0.0648
0.1716
0.523, -0.371
452
848
0.087
0.2460
6.496, -1.879
217
976
0.0631
0.1717
2.088, -2.884
213
744
0.0426
0.1075
0.460, -0.511
679
1744
0.0448
0.1111
0.743, -0.432
342
452
0.0284
0.0656
0.602, -0.432
R1a (I > 2σ(I))
wR2b (all data)
max and min/e‚Å-3
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]1/2
.
2
2
2
Table 2. 19F NMR Assignments for Ph3ECFdCF2 (E ) Ge 2, Sn 3,
Pb 4)
cmpd
δ(19F)
J/Hz
Ph3GeCFdCF2 (2)
-86.2
-114.5
-190.9
-85.4
-118.9
-192.6
-88.5
-121.7
-184.2
65 (Fa, Fb), 31 (Fa, Fc)
118 (Fb, Fc), 65 (Fa, Fb)
119 (Fb, Fc), 31 (Fa, Fc)
70 (Fa, Fb), 34 (Fa, Fc), JSnF 23
117 (Fb, Fc), 70 (Fa, Fb), JSnF 26
117 (Fb, Fc), 35 (Fa, Fc), JSnF 184
78 (Fa, Fb), 41 (Fa, Fc), JPbF 18
114 (Fb, Fc), 78 (Fa, Fb), JPbF 32
114 (Fb, Fc), 41 (Fa, Fc), JPbF 187
Ph3SnCFdCF2 (3)
Ph3PbCFdCF2 (4)
and Fc, respectively. In the cases of compounds 3 and 4,
each resonance additionally exhibits satellite structure due
to coupling to the low-abundance, spin-active metalloid
1
1
isotopes (3 119Sn, I ) /2, 8.59%; 4 207Pb I ) /2, 22.1%).
This coupling is observed most readily to the geminal
fluorine center, the smallest interaction being observed for
Fa. Full assignments are presented in Table 2.
The 13C NMR spectra of 2-4 exhibit characteristic
aromatic resonances, due to the phenyl rings, in the region
125-150 ppm, with satellite coupling also being observed
for 3 and 4. A further resonance is observed at ca. 160 ppm
for all three compounds and appears as a doublet of doublet
of doublets. This is assigned as the â-CF2-carbon of the
trifluorovinyl moiety, on the basis of two large (ca. 300 Hz)
C-F coupling constants and one smaller coupling (ca. 30
Hz) to the R-fluorine. For compound 4, a signal due to the
R-carbon is observed at 143 ppm, resonating, as expected,
at lower frequency, and appearing as a doublet of doublet
Figure 1. (a) 19F NMR spectrum of Ph3GeCFdCF2 (2). (b) Labeling
scheme adopted for trifluorovinyl compounds.
In each case, the presence of a trifluorovinyl moiety is
evident from the 19F NMR spectra, a doublet of doublets
being observed for each of the three inequivalent fluorine
environments, in distinct regions, typical of an AMX spin
system (Figure 1a). The assignment of individual resonances
is based upon the unique chemical shift position of nucleus
Fc (Figure 1b) and the typically observed trends in the
magnitude of 19F-19F coupling constants for alkenic systems,
specifically that Jtrans > Jgem > Jcis. Thus, resonances in the
region of -85, -118, and -190 ppm are assigned to Fa, Fb,
1
of doublets, with a single large JCF coupling constant. The
equivalent signal for compounds 2 and 3 cannot be fully
resolved because it is coincident with the aromatic reso-
nances.
Structural Analysis of Group 14 Trifluorovinyl Com-
pounds. The molecular structures of compounds 2-4 each
Inorganic Chemistry, Vol. 41, No. 18, 2002 4751

Brisdon et al.
[e.g., Hg(CFdCF2)2 1.312(6) Å,14a PhP(CFdCF2)2 1.318(4)
Å,23 [(Ph3P)Au(CFdCF2)] 1.297(14) Å24]; however, they are
comparable to those found in the 1-chloro-2,2-difluorovinyl
derivatives HgCl(CCldCF2) [1.23(5) Å] and trans-[Pd(CCld
CF2)2(PBu3)2] [1.26(2) Å].24
It has previously been suggested that the shorter CdC
distance [1.3130(3) Å] observed for C2H4 in the solid-state19
compared with that found in the gas-phase [1.3384(10) Å]25
is due to librational effects. This too may account for the
apparent short CdC distances observed for compounds 2-4.
However, detailed analysis of the structural data suggests
that the trifluorovinyl moiety has a tendency to exhibit an
oscillation about an axis which passes through the metal and
a terminal fluorine, approximately bisecting the CdC bond.
This would foreshorten the CdC bond, but because of the
complex nature of the oscillation, it is difficult to make a
reliable estimate of this effect.
Figure 2. View of the molecular structure of Ph3GeCFdCF2 (2), with
thermal ellipsoids set at the 30% probability level. The molecular geometry
is comparable to that found for Ph3SnCFdCF2 (3) and Ph3PbCFdCF2 (4),
and the illustrated numbering scheme is directly transposable.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Ph3ECFdCF2 (E ) Ge 2, Sn 3, Pb 4) with Estimated Standard
Deviations in Parentheses
We have previously noted significant variation of the
internal CsF distances of the trifluorovinyl moiety, a trend
that is again evident in compounds 2-4. The R-CF distance
has consistently proven to be the longest, a fact also reported
for perfluoroalkyl systems and taken as evidence for R-CF
activation. This is reflected in compounds 2-4, which exhibit
largely comparable R-CF distances, these being the longest
yet observed for coordinated fluorovinyl systems [cf., Hg-
(CFdCF2)2 1.362(6) Å,14a PhP(CFdCF2)2 1.353(3) Å,23
[(Ph3P)Au(CFdCF2)] 1.350(11) Å24], but consistent with
those reported for fluoroethylene.20 The lengthening of the
R-CF bond in metal bound fluoroalkyl systems is ac-
companied by a concomitant increase in the strength of the
MsCR bond. However, while the SnsC1 distance of 3
[2.149(8) Å] is shorter than that of triphenylvinyltin [2.17-
(4) Å],21 neither this, nor the EsC1 distances of 2 or 4 are
significantly short. Variation in the two â-CF distances is
also observed in each molecule, though this is small in both
3 and 4. Significantly, in all three molecules, it is the CsF
linkage cis to the metalloid (C2sF2) that is the shortest.
Such consistency has not previously been observed, though
it is perhaps significant that the current work represents the
first structurally characterized series of trifluorovinyl homo-
logues.
In the extended structures, the trifluorovinyl compounds
2-4 each align in infinite stacks and exhibit a tendency for
aggregation of the fluorinated moieties in domains running
through the crystal lattice. Individual molecules tend to stack
in “head-to-tail” fashion, constrained by H‚‚‚F interactions
between the fluorovinyl moieties and aromatic hydrogen
atoms of adjacent molecules [3 d(F2‚‚‚H11) 2.45 Å; 4 d(F2‚‚‚
H5) 2.48 Å]. These contacts are notably shorter than the sum
of the atomic contact radii [2.67 Å].26 Additional packing
forces arise from intermolecular π-H interactions which
Ph3GeCFdCF2 (2) Ph3SnCFdCF2 (3) Ph3PbCFdCF2 (4)
E1-C1
C1-C2
C1-F1
C2-F2
C2-F3
1.969(6)
1.230(8)
1.383(7)
1.298(8)
1.345(7)
2.149(8)
2.234(13)
1.21(2)
1.372(17)
1.314(18)
1.365(16)
1.259(12)
1.373(10)
1.339(11)
1.345(10)
F1-C1-E1
F1-C1-C2
F2-C2-C1
F2-C2-F3
F3-C2-C1
114.6(4)
112.1(6)
121.7(6)
111.0(6)
127.2(7)
118.5(5)
115.2(8)
122.8(8)
108.4(8)
128.7(9)
117.5(11)
115.9(13)
123.7(14)
107.2(14)
129.1(15)
exhibit the anticipated pseudotetrahedral geometry about the
metalloid, as illustrated in Figure 2. For compounds 2 and
3, the asymmetric unit comprises two such molecules, one
of which displays some disorder in the fluorovinyl moiety.
In contrast, the asymmetric unit of 4 contains a single
molecule. Selected bond distances and angles for the three
structures are presented in Table 3.
In common with our previous work in this area, we note
that for each of 2-4 the CdC distance is shorter than that
for a typical vinyllic C(sp2)dC(sp2) bond [1.299 Å]18 and
the CdC distances found in C2H4 [1.3142(3) Å]19 and C2F4
[1.311(3) Å].20 Nonetheless, such distances are not without
precedence; for stannane 3, the observed distance [1.259-
(12) Å] is comparable to that reported for triphenylvinyltin
[1.27(7) Å].21 Indeed, even shorter CdC distances have been
reported for other tin-vinyl species, for example, 1.158-
(10) Å as observed in SnCl2(CHdCH2)2(bipy).22 Unfortu-
nately, for compounds 2 and 4, direct comparison with vinyl
analogues is impossible, no structural data being available
for the latter. Comparison with data for other trifluorovinyl-
containing inorganic systems shows that the CdC distances
are considerably shorter than has been previously observed
(18) Lide, R. Handbook of Chemistry and Physics, 76th ed.; CRC Press:
New York, 1995.
(19) Van Nes, G. J. H.; Vos, A. Acta Crystallogr. 1979, B35, 2593.
(20) Dixon, D. A.; Fukunaga, T.; Smart, B. E. J. Am. Chem. Soc. 1986,
108, 1585. Carlos, J. L.; Karl, R. R.; Bauer, S. H. J. Chem. Soc.,
Faraday Trans. 2 1974, 177.
(21) Theobald, F.; Trimaille, B. J. Organomet. Chem. 1984, 267, 143.
(22) Buntine, M. A.; Hall, V. J.; Kosovel, F. J.; Tiekink, R. T. J. Phys.
Chem. A 1998, 102, 2472.
(23) Banger, K. K.; Banham, R. P.; Brisdon, A. K.; Cross, W. I.; Damant,
G.; Parsons, S.; Pritchard, R. G.; Sousa-Pedrares, A. J. Chem. Soc.,
Dalton Trans. 1999, 427.
(24) Barnes, N. A.; Brisdon, A. K.; Cross, W. I.; Fay, J. G.; Greenall, J.
A.; Pritchard, R. G.; Sherrington, J. J. Organomet. Chem. 2000, 616,
96.
(25) Duncan, J. L. Mol. Phys. 1974, 28, 1177.
(26) Bondi, A. J. Phys. Chem. 1964, 68, 441.
4752 Inorganic Chemistry, Vol. 41, No. 18, 2002

Structure of 1,2-DifluoroWinyl Organometalloids
range between d(H-Cg) 2.8 and 2.9 Å and align essentially
orthogonal to the ring plane (5.15-5.74 °).
Reactivity of Group 14 Trifluorovinyls. Investigation of
the reactivity of group 14 trifluorovinyls toward nucleophiles
has previously been confined to derivatives of silicon,
typically Et3SiCFdCF26,7 and the products identified on the
basis of NMR spectroscopy. However, there is no structural
confirmation of these conclusions. It thus seemed logical,
in seeking to characterize these systems structurally, to
exploit the crystalline nature of Ph3SiCFdCF2. However, in
our hands, preparation of the triphenylsilane proved inef-
fectual, it being formed along with Ph3SiF and other products,
in yields of ca. 10% according to 19F NMR studies. We note
that this is consistent with reports of its preparation from
tetrafluoroethylene and triphenylsilyllithium, which resulted
in only 18% yield.27 In contrast, we have prepared the solid
germane 2 in high yield and purity. Given the common
reactivity traits shared by vinylsilanes and -germanes,28 the
reactions of this compound were studied in detail, confirming
an analogous reactivity to the trifluorovinylsilanes. Similarly,
our study of stannane 3 concurred with previous reports,6
revealing no reactivity toward LiAlH4 and a propensity for
metathesis with organolithium reagents. It is noteworthy that
plumbane 4 also undergoes metathesis with organolithiums,
as it does with LiAlH4, a fact that is attributed to the
decreasing E-C bond strength upon descending group 14.
Synthesis of Ph3Ge(CFdCFH) (5). The reaction of
trifluorovinyltriphenylgermane, 2, with an excess of LiAlH4
resulted in the isolation of 5 as a pale yellow solid in high
yield. In the 19F NMR spectrum of 5, the characteristic
trifluorovinyl signals were replaced by two mutually coupling
(JFF ) 131 Hz) doublet of doublet resonances at -169.7 and
-172.4 ppm. The large magnitude of the mutual 19F-19F
coupling would seem consistent with assignment of the trans,
or Z, isomer. This is supported by the presence of a high
frequency (7.9 ppm) doublet of doublets in the proton NMR
spectrum, which exhibits one large (78 Hz), typically geminal
19F-1H coupling and one smaller (10 Hz) cis interaction,
concurring with related work by Clark et al.10 On this basis,
the higher frequency 19F resonance is assigned to the fluorine
nucleus geminal to the proton.
Figure 3. View of the molecular structure of Ph3GeCFdCFH (5); thermal
ellipsoids are set at the 30% probability level.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
Ph3GeCFdCFH (5) with Estimated Standard Deviations in Parentheses
Ge-C1
C1-C2
C1-F1
1.958(9)
1.275(13)
1.388(9)
C2-F2
C2-H2
1.345(11)
1.16(11)
F1-C1-Ge
F1-C1-C2
F2-C2-C1
114.5(6)
114.3(8)
120.8(9)
F2-C2-H2
H2-C2-C1
103(5)
135(5)
center. The combined spectroscopic data therefore allow
unequivocal assignment of compound 5 as trans-Ph3GeCFd
CFH.
Further, inseparable, species are evident, at trace levels,
in the 19F and 1H NMR spectra. These are identified on the
basis of data reported elsewhere10 as the cis and geminal
monosubstitution products and cis-Ph3GeCHdCFH. It is
noteworthy that, when extended reaction times are employed,
the cis-1,2-dihydrofluorovinylgermane predominates, char-
acterized in the 19F NMR by a doublet of doublets at -91.4
ppm (JHF 92.2, 64.9 Hz), with corresponding proton reso-
nances at 7.3 (JHF 92, 5.6 Hz) and 5.5 (JHF 65, 5.6 Hz) ppm.
After 12 h, this is the sole isolable product, albeit in an
impure state.
Ultimately, confirmation of the geometry of 5 was obtained
by X-ray diffraction studies. The asymmetric unit contains
a single molecule that exhibits a pseudotetrahedral arrange-
ment about the germanium center and a trans configuration
across the double bond of the fluorovinyl moiety, as shown
in Figure 3 (selected bond lengths and angles are summarized
in Table 4). The molecule exhibits a short CdC distance
[1.275(13) Å, vide supra], which is comparable to that in
the parent germane 2 and, significantly, to that reported for
cis-[(CO)5Mn(CFdCFH)] [1.28 Å], the only previous ex-
ample of a structurally characterized 1,2-difluorovinyl com-
pound.29 In common with most recent reports,23,24 the R-CF
bond distance is the longer [1.388(9) Å cf. 1.345(11) Å
â-CF], though this contrasts with the case of cis-[(CO)5Mn-
(CFdCFH)] where both distances are comparable [1.46 Å
R-CF, 1.50 Å â-CF]. It is noteworthy that in 5 a lengthening
of the â-CF distance [d(C2sF2) 1.345(11) Å] is observed,
relative to trifluorovinylgermane 2 [1.298(8) Å]. This is
presumably due to partial rehybridization at the â-carbon
upon replacing fluorine with hydrogen, resulting in reduced
It has recently been reported that for 19F-19F coupling in
a range of fluorolithioolefins, the magnitude of Jgem often
exceeds that of Jtrans,15 contrasting with the conventional view
that Jtrans > Jgem > Jcis. Though generally considered an
anomaly arising from the low temperatures necessitated by
these studies, such alternative interpretation is not precluded
by previous work in respect to 1,2-difluorovinyl systems.
However, here we report additional information obtained
from 13C NMR spectroscopy, where both fluorovinyl carbons
are clearly observed, each exhibiting one large (>200 Hz)
and one small (<60 Hz) 13C-19F coupling constant. Thus,
the fluorine atoms must each reside on a different carbon
(27) Yakubovich, A. Y.; Sergeev, A. P.; Belyaeva, I. N. Dokl. Chem. 1965,
161, 399.
(28) (a) Seyferth, D. Prog. Inorg. Chem. 1962, 3, 129. (b) Cason, L. F.;
Brooks, H. G. J. Am. Chem. Soc. 1962, 74, 4582. (c) J. Org. Chem.
1954, 19, 1278.
(29) Einstein, F. W. B.; Luth, H.; Trotter, J. J. Chem. Soc. A 1967, 89.
Inorganic Chemistry, Vol. 41, No. 18, 2002 4753

Brisdon et al.
Figure 5. View of the molecular structure of Ph3GeCFdCFPh (9) with
Figure 4. View of the molecular structure of Ph3GeCFdCFt-Bu (8) with
thermal ellipsoids set at the 30% probability level. The atom numbering
scheme is shown for one molecule; for the second molecule, 30 is added to
each atom label.
thermal ellipsoids drawn at the 30% probability level.
Table 6. Selected Bond Distances (Å) and Angles (deg) for
Ph3GeCFdCFt-Bu (8) with Estimated Standard Deviations in
Parentheses
1
Table 5. 19F and H NMR Data for the Vinyl Group of Compounds
Ge1-C1
C1-C2
C1-F1
C2-F2
C2-C3
1.963(3)
1.304(4)
1.363(3)
1.364(3)
1.517(4)
Ge31-C31
C31-C32
C31-F31
C32-F32
C32-C33
1.959(3)
1.306(5)
1.379(4)
1.371(4)
1.515(5)
Ph3GeCFdCFR (R ) Me 6, Bu 7, t-Bu 8, and Ph 9)
cmpd
δ (J/Hz)
Ph3GeCFdCFMe (6)
δF -134.5 (dq, 128, 17); -165.4 (dq, 128, 6)
δ
H 2.2 (dd, 17.5, 6.5)
Ph3GeCFdCFn-Bu (7)
δF -141.8 (dt, 128, 23); -166.1 (dt, 127, 6)
F1-C1-Ge1
F1-C1-C2
F2-C2-C1
F2-C2-C3
C1-C2-C3
113.46(19)
117.8(3)
112.9(3)
111.5(2)
135.5(3)
F31-C31-Ge31
F31-C31-C32
F32-C32-C31
F32-C32-C33
C31-C32-C33
114.4(2)
118.6(3)
113.4(3)
111.1(3)
135.4(4)
δ
H 2.6 (ddt, 23, 6.4, 6.4); 1.7-1.5 (m);
1.5-1.4 (m); 1.1-0.9 (m)
Ph3GeCFdCFt-Bu (8)
Ph3GeCFdCFPh (9)
δF -143.9 (d, 126); -164.0 (dm, 127, 2)
δ
H 1.3 (dd, 2.2, 1.7)
δF -148.7 (d, 126); -156.3 (d, 126)
Table 7. Selected Bond Distances (Å) and Angles (deg) for
Ph3GeCFdCFPh (9) with Estimated Standard Deviations in Parentheses
s character of the CsF bonding orbital. Carbon NMR data
support this interpretation because the 1JCF coupling constant
is reduced in 5 compared with that observed in 2.
Ge1-C1
C1-C2
C1-F1
C2-F2
C2-C3
C3-C4
1.962(2)
1.319(4)
1.367(3)
1.367(3)
1.463(4)
1.400(4)
C4-C5
C5-C6
C6-C7
C7-C8
C8-C3
1.384(4)
1.380(5)
1.385(5)
1.386(4)
1.397(4)
In the extended structure, molecules of 5 align in stacks
along the c cell dimension, with a single molecular orienta-
tion. Adjacent stacks demonstrate aggregation of the fluo-
rocarbon moieties and intermolecular hydrogen fluorine
interactions to aromatic [d(F1‚‚‚H12) 2.57 Å] and vinyllic
[d(F1‚‚‚H2) 2.60(8) Å] protons of adjacent molecules.
Reaction of Ph3GeCFdCF2 (2) with Organolithium
Reagents. Treatment of germane 2 with an excess of
organolithium reagents resulted, after workup, in compounds
Ph3GeCFdCFR (R ) Me, 6; n-Bu, 7; t-Bu, 8; Ph 9) in high
yields. In each case, the 19F NMR spectrum of the product
consists of two multiplet resonances in the region -135 to
-165 ppm, with one large (JFF > 120 Hz) mutual doublet
F1-C1-Ge1
F1-C1-C2
F2-C2-C1
116.22(19)
117.8(2)
112.9(2)
F2-C2-C3
C1-C2-C3
C4-C3-C8
113.5(2)
133.6(2)
119.0(3)
bonding between the alkyl/aryl moiety and vinyllic fluorine
atoms. Thus, in 8, C4 is coplanar with the fluorovinyl group
with interactions between F1 and H4b and H4c (dav 2.50
Å), augmented by F2‚‚‚H5 and F2‚‚‚H6 interactions [dav 2.51
Å]. Analogous interactions are observed in the phenyl
substituted fluorovinyl 9 [d(F1‚‚‚H4) 2.29(3) Å; d(F2‚‚‚H8)
2.37(4) Å]. Additionally, there is evidence for conjugation
of the aromatic and vinyllic π-systems. The CdC distance
[1.319(4) Å] is notably longer than that of the parent germane
2 [1.230(8) Å] although this may be anticipated because of
the reduced motion of the fluorovinyl moiety. More signifi-
cantly, this distance is also longer than that found in the other
1,2-difluorovinyls [5 1.275(13) Å; 8 1.304(4) Å], and this
is accompanied by a short C2sC3 bond [1.463(4) Å], as
compared to the alkyl substituted system 8 [1.517(4) Å] and
a typical C(sp2)-C(ar) bond [1.488 Å].18
Synthesis of Ph3GeCFdCFOMe (10). In an analogous
manner to its reaction with organolithium reagents, germane
2 was treated with an excess of methanolic sodium meth-
oxide. After workup, a pale yellow solid was isolated, the
19F NMR spectrum of which indicates predominantly a single
species, again the trans-difluorovinylgermane, which exhibits
two doublet resonances at -118 and -187.8 ppm, with a
1
coupling. Additionally, for compounds 6-8, H-19F cou-
pling to the alkyl moiety is also observed, this being reflected
1
in the H NMR data (Table 5).
Structural Characterization of Ph3GeCFdCFt-Bu (8)
and Ph3GeCFdCFPh (9). Crystals of 8 and 9 were obtained
by the slow evaporation of mixed solvent (dichloromethane
and hexane) solutions. The asymmetric unit of 8 contains
two unique molecules, the molecular geometry of one is
shown in Figure 4 with selected bond distances and angles
summarized in Table 6. For the most part, there is little
variation between the two molecules except that one exhibits
no significant variation in CsF distances, in contrast to the
parent germane 2 and difluorovinyl 5. A similar trait is
observed in 9, which comprises a single molecule in the
asymmetric unit (Figure 5 and Table 7). In both materials,
there is evidence of extensive intramolecular hydrogen
4754 Inorganic Chemistry, Vol. 41, No. 18, 2002

Structure of 1,2-DifluoroWinyl Organometalloids
mutual coupling of 122 Hz. A single vinyllic carbon
Acknowledgment. We thank the Engineering and Physi-
cal Sciences Research Council (EPSRC) and UMIST for
financial support and Ineos Fluor and ICI Klea for donation
of HFC-134a. We acknowledge the EPSRC for support of
the UMIST NMR (GR/L52246) and FTIR Raman (GR/
M30135) facilities, a Research Equipment Initiative grant
for X-ray equipment, and also for access to the Chemical
Database Service at Daresbury.
resonance could be resolved, having one 1JCF (264.6 Hz) and
2
one JCF (31 Hz) CsF coupling constant.
Conclusion
The crystal structures of a series of trifluorovinyl group
14 compounds and their derivatives are reported. This is the
first time such data have been obtained, and they show
unequivocally that the interaction of a trifluorovinylgermane
with nucleophiles leads to stereospecific replacement of the
fluorine atom trans to germanium, in support of multinuclear
NMR spectroscopic studies. Verification of the similarity in
reactivity displayed by trifluorovinylsilicon and -germanium
compounds mitigates the conclusion that these data are
equally supportive of previous work on the stereospecific
derivatization of trifluorovinylsilanes.
Supporting Information Available: For the single-crystal
structure determinations, tables of crystal data and structure
refinement, atomic coordinates, anisotropic displacement param-
eters, bond lengths, bond angles, packing diagrams, and an X-ray
crystallographic file, in CIF format. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC025593O
Inorganic Chemistry, Vol. 41, No. 18, 2002 4755