Syntheses, spectroscopy, and redox properties of fluoro-carbyne and derived fluoro-vinylidene complexes of rhenium and of analogous chloro complexes

Article abstract of DOI:10.1021/om970397o

The fluoro- or chloro-carbyne complexes trans-[ReX(≡CCH₂R)(dppe)₂][BF₄] (X = F (1), R = H (1a), Bu^t (1b), CO₂Me (1c), CO₂Et (1d), Ph (1e), or C₆H₄Me-4 (1f); X = Cl (2), R = H (2a), Bu^t (2b), CO₂Me (2c), CO₂Et (2d), Ph (2e), or C₆H₄Me-4 (2f); dppe = Ph₂PCH₂CH₂-PPh₂) have been prepared by a single-pot reaction, in THF and under sunlight, of the appropriate 1-alkyne (HC≡CR) with trans-[ReCl(N₂)(dppe)₂] and [NH₄][BF₄] in the presence or in the absence, respectively, of Tl[BF₄]. With the exception of the less acidic tertbutylcarbyne complexes (1b and 2b), these complexes are deprotonated by [Bu₄N]OH to give the corresponding vinylidene complexes trans-[ReX(=C=CHR)(dppe)₂] (X = F (3) or Cl (4)) which, by treatment with HBF₄, regenerate the carbyne complexes. This route is more convenient for the synthesis of the chloro-carbyne complexes 2 from the vinylidenes 4, the latter being then prepared upon reaction of the dinitrogen complex with HC≡CR in toluene under sunlight. The electrochemical behavior of complexes 1-4 has been investigated by cyclic voltammetry and controlled potential electrolysis in aprotic media and at a Pt electrode. These complexes undergo single-electron reversible oxidations at half-wave oxidation potentials in the range from 1.39 to 1.48 (1, 2) and -0.35 to 0.25 (3, 4) V vs SCE. The corresponding electrochemical P_L and E_L ligand parameters have been estimated for the carbyne (P_L = 0.21-0.24 V, E_L ca. 1.2 V vs NHE) and the vinylidene (P_L = -0.27 to -0.13 V, E_L = 0.50-0.62 V vs NHE) ligands and discussed in terms of redox potential-structure relationships. The former ligands behave as remarkably strong π-electron acceptors and undergo cathodically induced C-H bond cleavage to give the corresponding vinylidenes. Both the carbyne and the vinylidene ligands are effectively stabilized by the trans-fluoride ligand, although it presents, relative to chloride, a slightly stronger destabilizing effect on the HOMO in these complexes.

Full text of DOI:10.1021/om970397o

Organometallics 1997, 16, 4469-4478
4469
Syn th eses, Sp ectr oscop y, a n d Red ox P r op er ties of
F lu or o-Ca r byn e a n d Der ived F lu or o-Vin ylid en e
Com p lexes of Rh en iu m a n d of An a logou s Ch lor o
Com p lexes
S´ılvia S. P. R. Almeida and Armando J . L. Pombeiro*
Centro de Quı´mica Estrutural, Complexo I, Instituto Superior Te´cnico, Av. Rovisco Pais,
1096 Lisboa Codex, Portugal
Received May 13, 1997X
The fluoro- or chloro-carbyne complexes trans-[ReX(≡CCH2R)(dppe)2][BF4] (X ) F (1),
R ) H (1a ), But (1b), CO2Me (1c), CO2Et (1d ), Ph (1e), or C6H4Me-4 (1f); X ) Cl (2), R ) H
(2a ), But (2b), CO2Me (2c), CO2Et (2d ), Ph (2e), or C6H4Me-4 (2f); dppe ) Ph2PCH2CH2-
PPh2) have been prepared by a single-pot reaction, in THF and under sunlight, of the
appropriate 1-alkyne (HC≡CR) with trans-[ReCl(N2)(dppe)2] and [NH4][BF4] in the presence
or in the absence, respectively, of Tl[BF4]. With the exception of the less acidic tert-
butylcarbyne complexes (1b and 2b), these complexes are deprotonated by [Bu4N]OH to
give the corresponding vinylidene complexes trans-[ReX(dCdCHR)(dppe)2] (X ) F (3) or Cl
(4)) which, by treatment with HBF4, regenerate the carbyne complexes. This route is more
convenient for the synthesis of the chloro-carbyne complexes 2 from the vinylidenes 4, the
latter being then prepared upon reaction of the dinitrogen complex with HC≡CR in toluene
under sunlight. The electrochemical behavior of complexes 1-4 has been investigated by
cyclic voltammetry and controlled potential electrolysis in aprotic media and at a Pt electrode.
These complexes undergo single-electron reversible oxidations at half-wave oxidation
potentials in the range from 1.39 to 1.48 (1, 2) and -0.35 to 0.25 (3, 4) V vs SCE. The
corresponding electrochemical PL and EL ligand parameters have been estimated for the
carbyne (PL ) 0.21-0.24 V, EL ca. 1.2 V vs NHE) and the vinylidene (PL ) -0.27 to -0.13
V, EL ) 0.50-0.62 V vs NHE) ligands and discussed in terms of redox potential-structure
relationships. The former ligands behave as remarkably strong π-electron acceptors and
undergo cathodically induced C-H bond cleavage to give the corresponding vinylidenes. Both
the carbyne and the vinylidene ligands are effectively stabilized by the trans-fluoride ligand,
although it presents, relative to chloride, a slightly stronger destabilizing effect on the HOMO
in these complexes.
In tr od u ction
and often the presence of an anionic strong electron
donor ligand, such as chloride (bromide or iodide) or
alkoxyde, helps the stabilization of the metal-carbon
triple bond. However, in contrast with the developed
chemistry of organotransition-metal complexes with
such halide ligands, that of the fluoro complexes still
remains relatively unexplored,8 especially for low-
valent metal centers. Particularly in carbyne chemis-
try, fluoride is an almost unknown ligand,9-11 and
its carbyne complexes are usually obtained10,11 in low
yields. Moreover, attempts to prepare fluorocarbyne
complexes analogous to other halocarbyne compounds
have failed.12
Since the discovery1 of the first carbyne (alkylidyne)
metal complexes nearly 25 years ago, the field has
developed enormously and a few books and extensive
reviews have appeared.2,3 However, in comparison with
the group 6 transition metals (Mo or W), carbyne
complexes of rhenium (in particular with phosphine
coligands4,5) are still in a limited number. They com-
monly involve a relatively electron-poor rhenium site
and/or cyclopentadienyl-type or carbonyl coligands6,7
X Abstract published in Advance ACS Abstracts, August 15, 1997.
(1) Fischer, E. O.; Kreis, G.; Kreiter, C. G.; Mu¨ler, J .; Huttner, G.;
Lorenz, H. Angew. Chem., Int. Ed. Engl. 1973, 12, 564.
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NATO ASI Series; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 1993. (b) Fischer, H.; Hofmann, P.; Kreissl, F. R.; Schrock,
R. R.; Schubert, U.; Weiss, K. Carbyne Complexes; VCH Publishers:
Weinheim, Germany, 1988.
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Richards, R. L. J . Chem. Soc., Dalton Trans. 1981, 1629. (b) Pombeiro,
A. J . L.; Hughes, D. L.; Pickett, C. J .; Richards, R. L. J . Chem. Soc.,
Chem. Commun. 1986, 246. (c) Carvalho, M. F. N. N.; Pombeiro, A. J .
L.; Bakalbassis, E. G.; Tsipis, C. A. J . Organomet. Chem. 1989, 371,
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Rheingold, A. L. Organometallics 1990, 9, 1562.
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Chem., Int. Ed. Engl. 1976, 15, 616.
S0276-7333(97)00397-X CCC: $14.00 © 1997 American Chemical Society

4470 Organometallics, Vol. 16, No. 20, 1997
Almeida and Pombeiro
In the present study and within our interest13 on the
activation of unsaturated small molecules by electron-
rich metal centers, we have succeeded in preparing a
series of fluoro-carbyne complexes of rhenium, trans-
[ReF(≡CCH2R)(dppe)2][BF4] (R ) H(1a ), But (1b),CO2-
Me (1c),CO2Et (1d ), Ph (1e), or C6H4Me-4 (1f)), in which
the [BF4]- anion behaved as the metal fluorinating
agent. The carbyne ligands in 1 were generated from
the activation of 1-alkynes (HC≡CR) toward a 1,2-
hydrogen shift to give vinylidenes (CdCHR) which
undergo â-protonation, a known route for such spe-
cies.1,2,14 In contrast with the usual synthetic pathways
for carbyne complexes, which occur in a stepwise man-
ner, complexes 1 are prepared in a convenient single-
pot synthesis from the reaction of trans-[ReCl(N2)-
(dppe)2] with the appropriate 1-alkyne, in the presence
of a chloride abstractor, Tl[BF4], and suitable proton
([NH4]+) and fluoride ([BF4]-) sources, in sunlight.
Deprotonation of carbyne complexes 1 leads to the
corresponding fluoro-vinylidene complexes trans-[ReF-
(dCdCHR)(dppe)2] (3). The analogous chloro-carbyne
and chloro-vinylidene complexes trans-[ReCl(≡C-
CH2R)(dppe)2][BF4] (2) and trans-[ReCl(dCdCHR)-
(dppe)2] (4), respectively, have also been prepared either
in a similar manner, without using Tl+, or more
adequately via the prior formation of 4 from the above
dinitrogen compound (a process that we have previously
applied15 but now have substantially improved), fol-
lowed by proton addition to give 2.
terms of defining the electron-donor/acceptor properties
of those ligands17a and of their promising redox-induced
chemistry, we have also investigated the electrochemical
behavior of those rhenium carbyne and vinylidene
complexes, which is also described in detail.
Some preliminary results have already been briefly
reported by us,28 including the crystal structure of 1b,28a
a complex that was then obtained fortuitously in an
extremely low yield as a side product. We now describe
in detail the systematic and extended study that devel-
oped since this report. However, the investigation of
the detailed mechanisms of the formation of the carbyne
complexes 1 and 2 is the subject of a subsequent
publication.
Resu lts a n d Discu ssion
F lu or o-Ca r byn e a n d F lu or o-Vin ylid en e Com -
p lexes. The fluoro-carbyne complexes trans-[ReF-
(≡C-CH2R)(dppe)2][BF4] (R ) H (1a ), But (1b), CO2Me
(1c), CO2Et (1d ), Ph (1e), or C6H4Me-4 (1f)) (isolated
as white or pale yellow solids in ca. 60-40% yields) are
obtained by treatment of a THF solution of the dinitro-
gen complex trans-[ReCl(N2)(dppe)2] with the appropri-
ate 1-alkyne (HC≡CR) in the presence of Tl[BF4] and
[NH4][BF4] in sunlight under argon (eq 1). The simplest
Moreover, since very few studies of the redox proper-
ties of carbyne or carbene complexes have been re-
ported,16-27 in spite of their expected significance in
(13) (a) Pombeiro, A. J . L.; Richards, R. L. Coord. Chem. Rev. 1990,
104, 13. (b) Pombeiro, A. J . L. Inorg. Chim. Acta 1992, 198, 179. (c)
Pombeiro, A. J . L. In Transition Metal Carbyne Complexes; Kreissl, F.
R., Ed.; NATO ASI Series; Kluwer Academic Publishers: Dordrecht,
The Netherlands, 1993; pp 105-121. (d) Pombeiro, A. J . L. New J .
Chem. 1994, 18, 163.
(14) Bruce, M. I. Chem. Rev. 1991, 91, 197.
(15) Pombeiro, A. J . L.; Almeida, S. S. P. R.; Silva, M. F. C. G.;
J effrey, J . C.; Richards, R. L. J . Chem. Soc., Dalton Trans. 1989,
2381.
(16) Molecular Electrochemistry of Inorganic, Bioinorganic and
Organometallic Compounds; Pombeiro, A. J . L., McCleverty, J . A. Eds.;
NATO ASI Series; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 1993.
(17) (a) Facchin, G.; Mozzon, M.; Michelin, R. A.; Ribeiro, M. T. A.;
Pombeiro, A. J . L. J . Chem. Soc., Dalton Trans. 1992, 2827. (b) Bertani,
R.; Mozzon, M.; Michelin, R. A.; Castilho, T. J .; Pombeiro, A. J . L. J .
Organomet. Chem. 1992, 431, 117. (c) Wang Y.; Pombeiro, A. J . L.;
Michelin, R. A.; Mozzon, M.; Bertani, R. Bull. Pol. Acad. Sci. 1994,
42, 307. (d) Belluco, U.; Bertani, R.; Michelin, R. A.; Mozzon, M.;
Guedes da Silva, M. F. C.; Frau´sto da Silva, J . J . R.; Pombeiro, A. J .
L.; Yu, W. Inorg. Chim. Acta 1995, 235, 397.
(18) Lemos, M. A. N. D. A.; Guedes da Silva, M. F. C.; Pombeiro, A.
J . L. Inorg. Chim. Acta 1994, 226, 9.
member (1a ) of the series is derived similarly from
HC≡CSiMe3, although in a modest yield (ca. 15%) and
with concomitant desilylation (eq 2). These complexes,
as well as all the other complexes discussed in this
study, have been characterized (see Experimental Sec-
tion) by IR and NMR spectroscopies, elemental analysis,
and electrochemical methods.
Their preparative reactions are of a considerable
complexity, involving five reagents and a number of
steps which are combined in a convenient single-pot
process, starting from readily available starting materi-
(19) Connelly, N. G. In Molecular Electrochemistry of Inorganic, Bio-
inorganic and Organometallic Compounds; Pombeiro, A. J . L., Mc-
Cleverty, J . A., Eds.; NATO ASI Series; Kluwer Academic Publishers:
Dordrecht, The Netherlands, 1993; pp 317-329.
(20) Lloyd, M. K.; McCleverty, J . A.; Connor, J . A.; Hall, M. B.;
Hillier, I. H.; J ones, E. M.; McEwen, G. K. J . Chem. Soc., Dalton. Trans.
1973, 1743.
(21) (a) Fischer, E. O.; Schluge, M.; Besenhard, J . O. Angew. Chem.,
Int. Ed. Engl. 1976, 15, 683. (b) Fischer, E. O.; Gammel, F. J .;
Besenhard, J . O.; Frank, A.; Neugebauer, D. J . Organomet. Chem.
1980, 191, 261.
(22) Rieke, R. D.; Kojima, H.; O¨ fele, K. Angew Chem., Int. Ed. Engl.
1980, 19, 538.
(23) Fischer, E. O.; Wittmann, D.; Himmerlreich, D.; Neugebauer,
D. Angew. Chem., Int. Ed. Engl. 1982, 21, 444.
(24) Krusic, P. J .; Klabunde, U.; Casey, C. P.; Block, T. F. J . Am.
Chem. Soc. 1976, 98, 2015.
(25) Casey, C. P.; Albin, L. D.; Seaman, M. C.; Evans, D. H. J .
Organomet. Chem. 1978, 155 , C37.
(26) Battioni, J .-P.; Lexa, D.; Mansuy, D.; Save´ant, J .-M. J . Am.
Chem. Soc. 1983, 105, 207.
(27) Lange, M.; Mansuy, D. Tetrahedron Lett. 1981, 22, 2561.
(28) (a) Pombeiro, A. J . L.; Hills, A.; Hughes, D. L.; Richards, R. L.
J . Organomet. Chem. 1988, 352, C5. (b) Almeida, S. S. P. R.; Frau´sto
da Silva, J . J . R.; Pombeiro, A. J . L. J . Organomet. Chem. 1993, 450
C7. (c) Lemos, M. A. N. D. A.; Pombeiro, A. J . L. J . Organomet. Chem.
1988, 356, C79.

Fluoro-Carbyne and Fluoro-Vinylidene Complexes
Organometallics, Vol. 16, No. 20, 1997 4471
als to lead to very rare examples of fluoro-carbyne
complexes. The formation of the carbyne ligands should
occur through the corresponding vinylidene intermedi-
ate species derived from the replacement of N2 (which
is assisted by light in agreement with some simplified
π-MO schemes29) by the alkyne (although no alkyne
complex was isolated), followed by a 1,2-hydrogen
migration, as known to occur at related d6 metal
centers.9,14,15,30 This type of behavior has been rational-
ized in terms of repulsive electronic interactions9,30
and by extended-Hu¨ckel calculations.31 The vinylidene
ligand in our system is susceptible to â-protonation to
give the corresponding carbyne product, as known for
related cases,9-11,32-35 and the detailed mechanism of
such a protonation will be reported in a subsequent
paper.
that, 2.418(9) Å,15 for this vinylidene compound, in
accord with the expected weaker π-electron release to
the phosphine ligands from the metal center in the
former complex.
The fluoro-carbyne complexes 1c, 1d and 1f undergo
deprotonation by a base, [NBu4]OH, in CH2Cl2 to give
(eq 3) the corresponding neutral fluoro-vinylidene
compounds trans-[ReF(dCdCHR)(dppe)2] 3c (R ) CO2-
Me), 3d (R ) CO2Et), and 3f (R ) C6H4Me-4) which
have been isolated as yellow or rose solids in ca. 60-
50% yields. Complex 3a (R ) H), although not isolated,
The formation of complexes 1 also involves Cl/F
exchange. The metal fluorination is unusual,8 particu-
larly in low-valent transition metal complexes due, inter
alia, to the expected unfavorable combination of a soft
acid (the metal center) with a hard base (fluoride).
However, in our system this reaction occurs even in the
absence of a deliberately added fluoride source. Nev-
ertheless, the ability of [BF4]- to fluorinate related
metal centers has been observed8,10,11,36 in a few cases.
The preparation of the fluoro-carbyne trans-[WF-
(≡CCH2Ph)(CO)2(dppe)] has been reported9 in a high
yield, but it occurs by free F- addition from [NEt4]F to
the five-coordinate carbyne complex [W(≡CCH2Ph)-
(CO)2(dppe)2][BF4].
has been generated in the same way and detected in
situ electrochemically (see below). However, 1b, which
has a weaker acid character in view of the electron-
donor ability of the But group, is not deprotonated even
under refluxing solvent conditions. The deprotonation
reaction (eq 3) of the fluoro-carbyne complexes can be
reversed on treatment of the fluoro-vinylidene products
by acid (HBF4), which readily regenerates the corre-
sponding carbyne compounds (eq 4).
The X-ray crystal structure of 1b, which we have
previously obtained accidentally in a very low yield and
as a contaminant of the analogous chloro-carbyne
complex upon treatment of trans-[ReCl(dCdCHBut)-
(dppe)2] with HBF4, has already been reported28a and
will not be discussed here apart from the relevant
metal-ligand bonds. The rhenium-carbyne carbon
distance, 1.772(7) Å, is only slighty longer than that
expected (1.75-1.72 Å) for a RetC(sp) triple bond5a,37
and is much shorter than that quoted15 for the rhe-
nium-vinylidene carbon (RedC) distance, 2.046(8) Å,
in trans-[ReCl(dCdCHPh)(dppe)2]. The average Re-P
distance in 1b, 2.455(2) Å, is significantly longer than
In complexes 1 and 3 the presence of the fluoride
trans to the carbyne or vinylidene is unambiguously
shown by the expected quintet (2J FP ) 34-44 Hz) and
doublet (with identical coupling constant) resonances
observed in the 19F (δ -316 to -329 ppm relative to
CFCl3) and 31P{1H} (δ -110 to -116 ppm relative to
P(OMe)3) NMR spectra (CD2Cl2), respectively. In the
13C NMR spectra, the carbyne- or vinylidene-carbon
resonance occurs as a low-field multiplet (δ ca. 291-
267 or 298-291 ppm relative to SiMe4, respectively)
whose quintet structure (2J CP ) 11 Hz) is resolved for
1d . Moreover, the CsCH2R or CdCHR resonances
are the expected triplet (J CH ) 127-129 Hz, δ 52-65)
or doublet (J CH ) 156 Hz, δ 97.4 for 3d ), respectively.
In the 13C{1H} NMR spectra, the resonance (δ ca.
32-33) of the dppe methylene carbons is a quintet,
due to virtual coupling to the four phosphorus nuclei
(J CP ) ca. 10-12 Hz), which, in the proton-coupled
spectra, splits to a triplet (J CH ) ca. 135 Hz) of quintets.
In the 1H NMR spectra, the CsCH2R or CdCHR
resonance is an unresolved multiplet usually at a
considerable higher field (δ 0.5-2.4) than the broad
multiplet resonances of the dppe methylene protons (δ
2.5-3.9).
The IR spectra of complexes 3 have strong bands in
the ca. 1610-1480 cm-1 range which are assigned to
ν(CdC) of the vinylidene ligand or to ν(CO) in the
methyl- or ethyl-propiolate derivatives 3c and 3d for
which the two detected bands conceivably result15,38
from coupling of those vibrations.
Ch lor o-Ca r byn e a n d Ch lor o-Vin ylid en e Com -
p lexes. The chloro-carbyne complexes trans-[ReCl-
(≡C-CH2R)(dppe)2][BF4] 2 can be obtained as pale
yellow solids (eqs 5 and 6, with isolated yields up to ca.
(29) (a) Pombeiro, A. J . L. In New Trends in the Chemistry of
Nitrogen Fixation; Chatt, J ., Caˆmara Pina, L. M., Richards, R. L., Eds.;
Academic Press: London, 1980; pp 153-197. (b) Chatt, J .; Leigh, G.
J .; Pickett, C. J .; Pombeiro, A. J . L.; Richards, R. L. Nouv. J . Chim.
1978, 2, 541.
(30) (a) Templeton, J . L.; Winston, P. B.; Ward, B. C. J . Am. Chem.
Soc. 1981, 103, 7713. (b) Tatsumi, K.; Hoffmann, R.; Templeton, J . L.
Inorg. Chem. 1982, 21, 466. (c) Birdwhistell, K. R.; Burgmayer, S. J .
N.; Templeton, J . L. J . Am. Chem. Soc. 1983, 105, 7789.
(31) Silvestre, J .; Hoffmann, R. Helv. Chim. Acta 1985, 68, 1416.
(32) (a) Beevor, R. G.; Green, M.; Orpen, A. G.; Williams, I. D. J .
Chem. Soc., Chem. Commun. 1983, 673. (b) Beevor, R. G.; Green, M.;
Orpen, A. G.; Williams, I. D. J . Chem. Soc., Dalton Trans. 1987, 1319.
(c) Mayr, A.; Scharfer, K. C.; Huang, E. Y. J . Am. Chem. Soc. 1984,
106, 1517. (d) Nickias, P. N.; Selegue, J . P.; Young, B. A. Organome-
tallics 1988, 7, 2248.
(33) Carvalho, M. F. N. N.; Henderson, R. A.; Pombeiro, A. J . L.;
Richards, R. L. J . Chem. Soc., Chem. Commun. 1989, 1796.
(34) (a) Pombeiro, A. J . L.; Hughes, D. L.; Richards, R. L.; Silvestre,
J .; Hoffmann, R. J . Chem. Soc., Chem. Commun. 1986, 1125. (b)
Henderson, R. A.; Pombeiro, A. J . L.; Richards, R. L.; Wang, Y. J .
Organomet. Chem. 1993, 447, C11.
(35) (a) Pombeiro, A. J . L.; Hughes, D. L.; Richards, R. L. J . Chem.
Soc., Chem. Commun. 1988, 1052. (b) Frau´sto da Silva, J . J . R.; Guedes
da Silva, M. F. C.; Henderson, R. A.; Pombeiro, A. J . L.; Richards, R.
L. J . Organomet. Chem. 1993, 461, 141.
(36) Silva, M. F. C. G.; Pombeiro, A. J . L.; Hills, A.; Hughes, D. L.;
Richards, R. L. J . Organomet. Chem. 1991, 403, C1.
(37) Edwards, D. S.; Biondi, C. V.; Ziller, J . W.; Churchill, M. R.;
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(38) Bruce, M. I.; Wallis, R. C. Aust. J . Chem. 1979, 32, 1471.

4472 Organometallics, Vol. 16, No. 20, 1997
Almeida and Pombeiro
75% or ca. 15%, respectively) in a manner similar to
that described above for the synthesis of the fluoro
analogues 1 (eqs 1 and 2), without requiring the use of
the chloride ligand abstractor. However, a cleaner and
In the 13C NMR spectra, the carbyne or vinylidene
carbon resonance, CsCH2R or CdCHR, respectively, is
observed as a low-field multiplet (δ ca. 297-259) which,
in some of the cases, is resolved into a quintet (2J CP ca.
8.5-12.5 Hz). By comparing the homologous complexes
in the various families, one observes that replacement
of the chloride ligand by fluoride results in a downfield
shift for both the vinylidene and carbyne carbon reso-
nances: fluoro-vinylidenes (δ ca. 298-291) > chloro-
vinylidenes (δ ca. 297-285) > fluoro-carbynes (δ ca.
291-267) > chloro-carbynes (δ ca. 280-259). In the
1H NMR spectra, the CsCH2R and CdCHR resonances
are detected at relatively high fields (δ ca. 0-2.2),
usually resolved into a quintet (4J HP ca. 3-5 Hz). The
trans geometry of all of these complexes and the ab-
sence of any fluoride ligand are unambiguously con-
firmed by the singlet resonance observed in their
31P{1H} NMR spectra. The X-ray structure of the
phenylvinylidene complex 4e has been described previ-
ously15 and will not be discussed further herein (see also
above).
higher-yield route (typically above 80% yield) for 2
consists of treatment of the corresponding vinylidene
complexes trans-[ReCl(dCdCHR)(dppe)2] 4 (in CH2Cl2
or in THF) with acid, commonly HBF4 (eq 7), although
a weaker acid such as [NH4][BF4] or an alkyl derivative,
e.g., [NHEt3][BPh4], can also be used.
Red ox P r op er ties. The cyclic voltammograms of
NCMe solutions of the complexes, at a Pt electrode (see
Experimental Section), display a single-electron revers-
ox
ible anodic wave at oxidation potentials (E1/2 vs SCE,
Table 1) in the ranges ca. 1.5-1.4 (chloro-carbynes 2)
g ca. 1.4 (fluoro-carbynes 1) >> ca. 0.3 to -0.2 (chloro-
vinylidenes 4) > 0.1 to -0.4 (fluoro-vinylidenes 3). In
the case of 3 and 4, a second anodic wave, with only a
partial reversible character, is detected at a much
higher potential (in the range of 0.9-1.5 V).
The first anodic processes (eqs 12 and 13) should
involve the formal Re(n) f Re(n + 1) single-electron
oxidations, similar to the observed Re(+1) f Re(+2)
oxidation for related isocyanide39 or nitrile40 complexes,
to form the relatively stable (in the time scale of the
cyclic voltammetry experiment) paramagnetic car-
byne and vinylidene complexes trans-[ReX(≡C-CH2R)-
(dppe)2]2+ (1+ (X ) F) or 2+ (X ) Cl)) and trans-[ReX-
(dCdCHR)(dppe)2]+ (3+ (X ) F) or 4+ (X ) Cl)). This
Inversely, complexes 2, with the exception of the less
acidic tert-butyl derivative 2b, are susceptible to depro-
tonation by base, [NBu4]OH, to regenerate the corre-
sponding chloro-vinylidene complexes 4, isolated as red
solids (eq 8). However, the latter complexes are more
directly prepared from the reaction of trans-[ReCl(N2)-
(dppe)2], in toluene, with the appropriate 1-alkyne (ca.
4 equiv) under argon and in sunlight for ca. 0.5-3 h
(depending on the light intensity) (eq 9) following an
improvement of the procedure we reported previously15
in which the reaction proceeded slowly (ca. 4 to 6 days)
in refluxing THF or in toluene under tungsten-fila-
ment bulb irradiation, even in the presence of a much
higher excess of the alkyne (15-30-fold molar excess).
A chloro-vinylidene complex, e.g., 4e or 4d , can be
converted into the corresponding fluoro-vinylidene
(3e) or fluoro-carbyne (1e or 1d ) complex by reac-
tion (ca. 1 h) in THF and under sunlight with Tl[BF4]
in the absence or in the presence, respectively, of
[NH4][BF4] (eqs 10 and 11), suggesting that in the
above-mentioned single-pot synthesis of 1, replace-
ment of the chloride ligand by fluoride can occur at an
earlier stage than the protonation of the vinylidene
intermediate.
indicates a strong stabilization of both the carbyne and
vinylidene ligands by the fluoro- and the chloro-
(39) Pombeiro, A. J . L.; Pickett, C. J .; Richards, R. L. J . Organomet.
Chem. 1982, 224, 285.
(40) Guedes da Silva, M. F. C.; Frau´sto da Silva, J . J . R.; Pombeiro,
A. J . L. J . Chem. Soc., Dalton Trans. 1994, 3299.

Fluoro-Carbyne and Fluoro-Vinylidene Complexes
Organometallics, Vol. 16, No. 20, 1997 4473
Ta ble 1. Cyclic Volta m m etr ic Da ta a for
tr a n s-[ReX(≡C-CH2R)(d p p e)2][BF 4] 1 (X ) F ) a n d 2
(X ) Cl) a n d tr a n s-[ReX(dCdCHR)(d p p e)2] 3 (X )
F ) a n d 4 (X ) Cl)
IE1/2
E
1/2
ox
II
ox
complex
R
1a
1b
1c
1d
1f
2a
2b
2c
2d
2e
2f
3a
3c
3d
3f
4a
4b
4c
4d
4e
4f
H
1.39
1.39
1.44
1.41
1.42
1.39
1.41
1.48
1.48
But
CO2Me
CO2Et
C6H4Me-4
H
But
CO2Me
CO2Et
Ph
F igu r e 1. Cathodic cyclic voltammogram of a 0.92 mmol
dm-3 solution of trans-[ReF(≡CCH2CO2Et)(dppe)2][BF4] 1d
in 0.2 mol dm-3 [NBu4][BF4]/NCMe, Pt-wire electrode (scan
rate ) 200 mV s-1; potential in V vs SCE). The anodic wave
is due to the corresponding cathodically-derived vinylidene
complex.
1.45
C6H4Me-4
H
1.44
-0.30b
0.06
1.37
1.53
1.44
1.42
1.38
CO2Me
CO2Et
C6H4Me-4
H
0.09
-0.35b
-0.02b
-0.24
0.24b
0.25
We have previously detected18 the cathodically-
induced dehydrogenation of trans-[ReCl(CNH2)(dppe)2]+
to form trans-[ReCl(CNH)(dppe)2], via reduction of
liberated H+ from the former complex (which, in solu-
tion, partially dissociates to the isocyanide compound)
with the resulting shift of this H+ dissociation equilib-
rium. However, in the case of the carbyne complexes 1
and 2, proton dissociation has not been detected to any
extent in the electrolyte medium, and therefore, the
cathodically-induced deprotonation should result from
a genuine reduction of the complex. Since the LUMO
is expected to be π-antibonding between the metal and
carbon and mainly localized at the carbyne carbon in a
cationic complex41,42 (which accounts for the well-
documented frontier-orbital-controlled nucleophilic ad-
dition to carbyne ligands, in particular at Re com-
plexes),43 the reduction of the complex is expected to
lead to a decrease in the metal-carbon bond order and
to a significant localization of the electron at the carbyne
carbon; pairing this unpaired electron could then occur
via the homolytic cleavage of a C-H bond (the hydrogen
atom acceptor has not been identified) with formation
of the vinylidene product:
Butc
CO2Me
CO2Et
Phd
1.48
1.41
-0.18
-0.21
0.96e
0.85e
C6H4Me-4d
Values in volts ((0.02) vs SCE, measured in 0.2 mol dm-3
a
[NBu4][BF4]/NCMe, unless stated for THF, at a Pt-wire electrode,
by using the [Fe(η5-C5H5)2]0/+ redox couple (E1/2 ) 0.42 V vs
ox
SCE in NCMe or 0.54 V vs SCE in THF) as an internal standard;
b
for conversion into V vs NHE, simply add 0.245 V. Measured
for the complex generated in situ by deprotonation of the corre-
sponding carbyne complex upon addition of [NBu4]OH to its
electrolytic solution. c In THF due to its instability in NCMe.
In THF due to its low solubility in NCMe. e Irreversible wave
d
(IIEp/2).
rhenium centers. The much higher oxidation potential
of the carbyne complexes 1 and 2 in comparison with
that of the vinylidene compounds 3 and 4 reflects the
much greater stabilization of the HOMO in the former
relative to the latter complexes.
Complexes 1 and 2 are also reversibly oxidized at a
substantially more anodic potential than that observed
ox
(Ep/2 ca. 0.9 V)18,28c for the chemically irreversible
anodic wave of trans-[ReCl(CNH2)(dppe)2][BF4] in which
the aminocarbyne ligand undergoes proton loss upon
oxidation. Hence, the carbyne ligands CCH2R present
a stronger net electron-acceptor ability than the ami-
nocarbyne CNH2 and are stable toward anodically-
induced deprotonation.
Interestingly, the fluoro complexes (either the carbyne
or the vinylidene ones) exhibit oxidation potentials at
slightly lower values than the corresponding chloro
compounds (Table 1), suggesting that the HOMO is less
stabilized in energy for the former complexes. Although
this could conceivably account, in part, for the rarity
(see above) of fluoro-carbyne and fluoro-carbene com-
plexes in comparison with chloro complexes, our syn-
thetic studies indicate that the former can also be
readily obtained.
Electr och em ica l Liga n d (P L a n d EL) P a r a m eter s
for th e Ca r byn e a n d Vin ylid en e Liga n d s. Electro-
chemical quantifications of the relative electron-donor/
acceptor abilities of ligands based on the redox potential
values of their complexes have already been proposed,
in particular by C. J . Pickett et al.44 and A. B. P.
Lever,45,46 and the values of the defined electrochemical
parameters have been quoted for a wide variety of
ligands. However, very little information is still avail-
able for carbyne or carbene ligands,16,17,28c but this work
Although neither the carbyne nor the vinylidene
complexes exhibit, by cyclic voltammetry, any clear
cathodic wave at a potential distinctly above the solvent/
electrolyte discharge, when we cathodically scan the
potential down to this level, in the case of a carbyne
complex solution, the carbyne ligand undergoes dehy-
drogenation, as a result of electron-transfer, to form the
corresponding vinylidene complex which is detected
during the subsequent anodic sweep by its characteristic
reversible anodic wave (Figure 1) (eq 14).
(41) Bakalbassis, E. G.; Tsipis, C. A.; Pombeiro, A. J . L. J . Orga-
nomet. Chem. 1991, 408, 181.
(42) (a) Kostic, N. M.; Fenske, R. F. J . Am. Chem. Soc. 1981, 103,
4677; Organometallics 1982, 1, 489. (b) Hoffmann, P. In Carbyne Com-
plexes; Fischer, H., Hofmann, P., Kreissl, F. R., Schrock, R. R., Schu-
bert, U., Weiss, K., Eds.; VCH Publishers: Weinheim, Germany, 1988.
(43) Boag, N. M.; Kaez, H. D. In Comprehensive Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon
Press, Oxford, 1982; Vol. 4, p 161.
(44) Chatt, J .; Kan, C. T.; Leigh, G. J .; Pickett, C. J .; Stanley, D. R.
J . Chem. Soc., Dalton Trans. 1980, 2032.
(45) Lever, A. B. P. Inorg. Chem. 1990, 29, 1271.
(46) Lever, A. B. P. Inorg. Chem. 1991, 30, 1980.

4474 Organometallics, Vol. 16, No. 20, 1997
Almeida and Pombeiro
experimentally observed45 (for a considerable number
of ligands but not for CO) between EL and PL, one can
estimate the EL (Table 2) by knowing PL. The vi-
nylidene EL values, thus estimated (0.50-0.62 V vs
NHE), are much lower than that (0.99)45 for CO but
significantly higher than those known for organonitriles
(0.37-0.49 V vs NHE),45 indicating that vinylidenes are
stronger net-electron donors than CO but weaker than
organonitriles. Application of eq 17 to the carbyne
ligands leads to EL values of ca. 1.2 V vs NHE (upon
correction48 due to their strong π-electron acceptor
character), which are the highest ones so far reported.
Ta ble 2. Estim a ted P L a n d EL Liga n d P a r a m eter s
for Ca r byn e a n d Vin ylid en e Liga n d s (L)
L
PL (V)a
EL (V vs NHE)b
CCH3
0.21
0.21
0.24
0.24
0.23
ca. 1.2
ca. 1.2
ca. 1.2
ca. 1.2
ca. 1.2
ca. 1.2
0.56
0.50
0.62
0.62
0.52
CCH2But
CCH2CO2Me
CCH2CO2Et
CCH2Ph
CCH2C6H4Me-4
CdCH2
0.22
-0.21
-0.27
-0.13
-0.13
-0.25
-0.26
CdCHBut
CdCHCO2Me
CdCHCO2Et
CdCHPh
CdCHC6H4Me-4
0.51
PL ) 1.17EL - 0.86
(17)
a
Estimated using expression 15,44 applied to the {ReCl(dppe)2}
site (Es ) 0.68 V, â ) 3.4 V)39 and to complexes 2 and 4 (see text).
Application of eq 16 to our complexes presents serious
difficulties. For the carbyne complexes, not knowing the
IM and SM values for the metal redox couple prevents
the use of such an expression. This difficulty should
not arise for the vinylidene complexes (for the Re(+1/
+2) redox couple, SM ) 0.76 and IM ) -0.95 V vs
NHE),46 but eq 16 needs correction to be valid for
potentials below ca. 0.2 V vs NHE (corresponding to ∑EL
values below ca. 1.6 V vs NHE).46 In our vinylidene
complexes 3 and 4, only those with the stronger electron
accepting ester groups have an oxidation potential value
well above that restriction and the EL values for the
ester-vinylidenes (average 0.66 or 0.68 V vs NHE for
CdCHCO2Me or CdCHCO2Et), estimated by applica-
tion of this equation (knowing45 the EL values for the
other coligands), are in agreement with that (0.62 V)
obtained from eq 17; however, for the other vinylidene
complexes, the EL values estimated from eq 16 are in
high disagreement with those obtained by using eq 17.
Peculiarities of the Re(+1/+2) redox systems have
been recognized by Lever46 who, in terms of the two
available sets of data well-separated in complex redox
potentials (above ca. 0.2 and at ca. -1.0 V vs NHE),
postulated that either two distinct linear relationships
(an “upper” and, although with highly scattered points,
a “lower” one) of the type of eq 16 but with different SM
and IM values or a curved relationship between the
redox potential and ∑EL (Figure 2, dotted lines) occurs.
In such a plot, the points which represent the first
oxidation of our vinylidene complexes 4, with the
exception of those with ester substituents, are situated
below the upper line (Figure 2). This observation
supports the hypothesis of a curved relationship, al-
though it shoud be confirmed by studying other Re(+1/
+2) systems with lower oxidation potentials. In con-
trast, the plot for the second oxidation potential of 4,
i.e., for the oxidation potential of 4+ (Figure 2), does not
deviate much from the straight line presented by
Lever46 for other Re(+3/+2) systems (extrapolated to
higher redox potentials).
Estimated by using expression 1745 plus, in the case of the
b
carbynes, a proposed48 correction of ca. 0.25 V.
provides an opportunity to gain insight into the elec-
tronic properties of these types of ligands.
For several series of closed-shell octahedral-type
complexes [MsL], a linear relationship (eq 15) has been
E1/2ox[MsL] ) Es + âPL
(15)
observed44 between their redox potential and the elec-
tronic properties of the ligand L and its binding metal
center {Ms}, expressed by the PL ligand parameter, the
electron-richness (Es, that is the redox potential of the
carbonyl complex [Ms(CO)]) and polarizability (â) of the
metal center. The PL parameter is considered44 as a
measure of the net electron σ-donor minus π-acceptor
ability of the ligand (L): the lower is this character, the
higher the oxidation potential of the complex [MsL] and
thus (eq 15) the higher PL.
Knowing39 Es (0.68 V) and â (3.4) for our trans-{ReCl-
(dppe)2} center and the measured values of the oxidation
potential of its carbyne and vinylidene complexes 2 and
4, we have estimated the PL parameter for these ligands
(Table 2) which, together with related ones, can be
ordered as follows according to their net-electron ac-
ceptance (the PL ranges being indicated in parenthe-
ses): carbynes (CCH2R, 0.21-0.24 V) > aminocarbyne
(CNH2, ca. 0.1V)28c > CO (0) > isocyanides (CNR, -0.10
to -0.18 V)47 g vinylidenes (CdCHR, -0.13 to -0.27
V) >> aminocarbenes or other related heterosubstituted
carbenes (-0.6 to -0.8 V).17a The carbynes behave as
very strong π-electron acceptors, even more effective
than carbonyl although not as strong as NO+ (PL ) 1.40
V).44
Another ligand electrochemical parameter (EL) has
been proposed45 for which the empirical linear correla-
tion (eq 16) was shown to be followed by many redox
couples. The redox potential of the complex (E) is
E ) S ( E ) + I
M
(16)
∑
M
L
(48) The direct application of eq 17 to the carbyne ligands in our
complexes would give EL values (0.91-0.94 V vs NHE range) which
are lower than that for CO, in disagreement with the fact that the
carbyne complexes have oxidation potentials (1.39-1.48 V range)
(Table 1) higher than that of the carbonyl analogue (0.68 V); moreover,
the proposed EL value for CO (0.99 V vs NHE)45 is significantly higher
than that (0.74 V vs NHE, since PL ) 0 V for CO) obtained from the
expression, appearing to be invalid for ligands (like carbynes and CO)
that are strong π-acceptors, accounting for the recognized45 need to
introduce positive corrections to EL for ligands with an extensive
π-stabilizing influence on the energy of the HOMO. If the EL values
for the carbynes given by expression 17 would need a correction similar
to that of CO (0.25 V, see above), they would lie in the 1.16-1.19 V vs
NHE range.
expressed in volts vs the normal hydrogen electrode
(NHE), ∑EL is the sum of the EL values for all the
ligands (additive effects),whereas SM and IM depend
upon the metal and redox couple, the spin state, and
stereochemistry.45 Values of EL have been proposed for
a wide variety of ligands45 but not for carbynes or
carbenes. However, from the linear relationship (eq 17)
(47) Carvalho, M. F. N. N.; Pombeiro, A. J . L. J . Chem. Soc., Dalton
Trans. 1989, 1209.

Fluoro-Carbyne and Fluoro-Vinylidene Complexes
Organometallics, Vol. 16, No. 20, 1997 4475
Electrochemical methods were also shown to be suc-
cessfully applicable to the activation of the carbyne
ligands toward C-H bond cleavage, which is induced
cathodically to generate the corresponding vinylidene
species, as well as to the investigation of the electron-
donor/acceptor properties of the carbyne and vinylidene
ligands, the former being shown to behave as rather
strong net electron acceptors. The electrochemical PL
and EL ligand parameters have been estimated and
corroborate a curved relationship between the oxidation
potential and ∑EL comprising the vinylidene ligands,
which is interpreted on the basis of the low ability of
the electron-rich Re(I)-halide center to buffer changes
in the energy of the HOMO. The fluoride ligand, in
comparison with chloride, has a slightly stronger de-
stabilizing effect on the HOMO, which, however, does
not avoid the ready formation of stable fluoro-carbyne
and -vinylidene complexes even with the electron-rich
metal centers of this study. Hence, the still rather
limited number of transition metal fluoro complexes
with multiple metal-carbon bonds is expected to expand
in the future.
In addition, these studies can also be of some biologi-
cal importance since vinylidene complexes are recog-
nized intermediates in some enzymatic processes (e.g.,
in the matabolism of some chlorinated hydrocarbons)49
and they can be postulated, with carbyne species of the
type we have obtained, as conceivable intermediates13a
in the reduction of 1-alkynes by nitrogenases.
F igu r e 2. Plot of the first (() and the second (9) oxidation
ox
II
ox
potentials (IE1/2 and
E
(V vs NHE), respectively) vs
1/2
∑EL(V vs NHE) for the vinylidene complexes trans-[ReCl-
(dCdCHR)(dppe)2], 4 (R ) H (4a ), But (4b), CO2Me (4c),
CO2Et (4d ), Ph (4e), or C6H4Me-4 (4f)). The dotted lines
correspond to the relationships previously proposed by
Lever (Figure 2 in ref 46) for other Re(+2/+1) or Re(+3/
+2) redox systems.
Exp er im en ta l Section
All reactions were carried out using standard inert gas flow
or high-vacuum techniques. The complex trans-[ReCl(N2)-
(dppe)2] was prepared by a published method;40 the acid
[Et2OH][BF4], the alcoholic solution of [NBu4]OH, and the
1-alkynes (HC≡CR) were used as purchased from Aldrich (R
) But, CO2Me, CO2Et, Ph, or C6H4Me-4) or Fluorochem (R )
SiMe3). The solvents were purified and dried by standard
methods and freshly distilled under dinitrogen. The IR spectra
were recorded on a Perkin-Elmer 683 spectrophotometer and
NMR spectra (run in CD2Cl2 unless stated otherwise) on a
Varian Unity 300 spectrometer. 1H, 31P, 19F, and 13C chemical
shifts (δ) are reported in ppm relative to TMS, P(OMe)3, CFCl3,
and TMS, respectively. In the 13C NMR data, assignments
and coupling constants common to the 13C{1H} NMR spectra
are not repeated. Abbreviations: s ) singlet; d ) doublet; t
) triplet; q )quartet; qnt ) quintet; m ) complex multiplet;
br ) broad; tqnt ) triplet of quintets; dm ) doublet of
multiplets; tm ) triplet of multiplets; qt ) quartet of triplets;
o, m, or p ) the ortho-, meta- or para-phenyl proton, respec-
tively; sh ) shoulder.
The electrochemical experiments were carried out either on
an EG & G PAR 173 potentiostat/galvanostat and an EG & G
PARC 175 Universal programmer or on an HI-TEK DT 2101
potentiostat/galvanostat and an HI-TEK PP RI waveform
generator. Cyclic voltammetry was undertaken in a two-
compartment three-electrode cell, at a platinum wire or disc
or a vitreous carbon working electrode, probed by a Luggin
capillary connected to a silver-wire pseudo-reference electrode;
a platinum or tungsten auxiliary electrode was employed.
Controlled-potential electrolyses were carried out in a three-
electrode H-type cell with platinum-gauze working and counter
electrodes in compartments separated by a glass frit; a Luggin
capillary, probing the working electrode, was connected to a
The above curved correlation indicates that for our
electron-rich vinylidene-rhenium(+1) complexes with
the stronger electron donor ligands, the energy of the
redox orbital is more sensitive to a change of the elec-
tronic properties of the ligands (reflecting a change in
∑EL) than in the case of other less electron-rich rhenium
centers. This supports the finding,39,44 on the basis of
the Pickett formalism, that in a series of related com-
plexes, an increase of the electron-rich character of the
metal site (Es) is accompanied by an increase of its pol-
arizability (â), the energy of the HOMO thus becoming
less buffered with respect to a ligand change. Hence,
the influence of a ligand on the energy of the redox orbi-
tal of a complex is a delicate function of the properties
not only of the ligand but also of the metal center,
including the effect of the other coligands, a situation
which can invalidate the hypothesis of the additive effect
of ligands on the redox potential of the complexes.
Con clu sion s
Series of fluoro-carbyne and fluoro-vinylidene com-
plexes (apart from the related chloro species), which are
interconvertible by acid-base reactions or upon electron
transfer, have been prepared by activation of 1-alkynes
by the electron-rich {ReCl(dppe)2} center, in the former
case through a convenient single-plot synthesis. The
[BF4]- ion behaves as a ready metal fluorinating agent,
and fluoride is shown to have a good stabilizing effect
on the trans-carbyne or -vinylidene ligand, even in the
corresponding oxidized complexes generated anodically.
(49) Bruce, M. I.; Swincer, A. G. Adv. Organomet. Chem. 1983, 22,
59.
(50) Chatt, J .; Dilworth, J . R.; Leigh, G. J . J . Chem. Soc., Dalton
Trans. 1973, 612.

4476 Organometallics, Vol. 16, No. 20, 1997
Almeida and Pombeiro
silver wire pseudo-reference electrode. The first anodic wave
in the cyclic voltammograms of the complexes has ∆Ep of ca.
100 mV, ip (anodic)/ip (cathodic) close to one, and the current-
function ipC-1v-1/2 (C ) concentration, v ) scan rate) without
appreciable variation in the 50-1000 mV s-1 scan rate range,
thus following the usual criteria for a single-electron rever-
sible process. Controlled potential electrolysis at this anodic
wave corresponds to the consumption of 1 F/mol, confirming
the involvement of a single-electron process. The oxidation
potentials of the complexes were measured by cyclic voltam-
metry in 0.2 mol dm-3 [NBu4][BF4]/NCMe or THF, and the
redox potential are quoted relative to the SCE (saturated
calomel electrode) by using the [Fe(η5-C5H5)2]0/+ couple (0.42
or 0.54 V vs SCE in 0.2 mol dm-3 [NBu4][BF4]/NCMe or THF,
respectively, as an internal reference). To convert to the NHE
(normal hydrogen electrode), this reference redox couple, in
NCMe or THF, is considered45 to lie at 0.665 or 0.785 V vs
NHE respectively; hence, the values of the oxidation potentials
of the complexes relative to NHE were estimated by adding
0.245 V to the corresponding ones quoted relative to SCE.
P r ep a r a tion of tr a n s-[ReF (≡C-CH2R)(d p p e)2][BF 4] 1a
(R ) H), 1b (R ) Bu t), 1c (R ) CO2Me), 1d (R )CO2Et), 1e
(R ) P h ), or 1f (R ) C6H4Me-4). These fluoro-carbyne
complexes have been prepared in a single-pot synthesis by
treating a THF solution of trans-[ReCl(N2)(dppe)2] with the
appropriate 1-alkyne and [NH4][BF4] in the presence of Tl-
[BF4], under sunlight, in an argon atmosphere. They are also
formed, eventually, in lower yields and as side products in the
syntheses of the chloro-carbyne complexes 2 described below.
Complex 1a was obtained from HC≡CSiMe3 which underwent
desilylation.
As a typical example, the synthesis of trans-[ReF(≡C-CH2-
CO2Me)(dppe)2][BF4], 1c, can be described as follows: A THF
solution (250 cm3) of trans-[ReCl(N2)(dppe)2] (0.30 g, 0.29
mmol), under argon, was treated with Tl[BF4] (0.13 g, 0.43
mmol), [NH4][BF4] (0.15 g, 1.4 mmol), and HC≡CCO2Me (0.096
cm3, 1.2 mmol), and the system was left stirring in sunlight
for 0.5 h. The solution was then taken to dyness in vacuo.
Extraction with CH2Cl2 (5 cm3) followed by filtration and
addition of diethyl ether led to the precipitation of 1c as a
white solid, which was filtered off, washed with diethyl ether,
and dried in vacuo. Further crops could be obtained from the
mother liquor upon concentration and addition of diethyl ether
(ca. 60% yield).
6.0 Hz, 2H, CO2CH2CH3), 3.00 (m, br, 4H, CH2-dppe), 2.65
(m, br, 4H, CH2-dppe), 1.67 (s, 2H, CCH2CO2Et), 0.89 (t, J )
2
6.0 Hz, 3H, CO2CH2CH3). 31P{1H} (CDCl3): δ -114.3 (d, J PF
2
) 43 Hz). 19F NMR: δ -318.5 (qnt, J PF ) 42 Hz). 13C{1H}
2
NMR (CDCl3): δ 290.50 (qnt, J CP ) 11 Hz, CCH2CO2Et),
163.45 (s, CO2Et), 134.3-128.1 (m, Ph-dppe), 61.42 (s, COCH2-
CH3), 53.68 (s, CCH2CO2Et), 32.37 (qnt, virtual J CP ) 9.2 Hz,
CH2-dppe), 13.64 (s, COCH2CH3). 13C NMR (CDCl3): δ 290.50
(qnt), 163.45 (s), ca. 134-128 (m), 61.42 (t, J CH ) 146.5 Hz),
53.68 (t, J CH ) 129 Hz), 32.37 (tm, J CH ) 134.9 Hz), 13.64 (q,
J CH ) 123.3 Hz). Anal. Calcd for BC57F5H55O2P4Re‚1.8CH2-
Cl2: C, 58.2; H, 4.8. Found: C, 58.2; H, 5.3.
1e: Yellow, ca. 20% (not analytically pure). 1H NMR
(CDCl3): δ 8.1-6.5 (m, 43H, Ph-dppe + CCH2Ph (m, p)), 5.68
(d, J ) 5.5 Hz, 2H, CCH2Ph (o)), 3.1-2.6 (m, br, 8H, CH2-
dppe), 1.25 (m, 2H, CCH2Ph). 31P{1H} (CDCl3): δ -114.2 (d,
2
2J PF ) 43 Hz) . 19F NMR (CDCl3): δ -322.1 (qnt, J PF
)
43 Hz).
1f: Pale yellow, ca. 40% yield. 1H NMR: δ 7.50-6.80 (m,
40H, Ph-dppe), 6.51(d, J ) 6.0 Hz, 2H, C6H4Me), 5.64 (d, J )
6.0 Hz, 2H, C6H4Me), 2.65 (m, 8H, CH2-dppe), 2.42 (s, br, 2H,
CCH2C6H4Me), 2.10 (s, 3H, C6H4CH3). 31P{1H} NMR:
δ
-112.8 (d, J PF ) 43 Hz). 19F NMR: δ -321.4 (qnt, J PF ) 42
Hz). 13C{1H} NMR: δ 279.60 (m, CCH2C6H4Me), 135.0-127.1
(m, Ph-dppe), 55.84 (s, br, CCH2C6H4Me), 32.46 (qnt, virtual
J CP ) 10 Hz, CH2-dppe), 20.62 (s, C6H4CH3). 13C NMR: δ
279.60 (m), ca. 135-127 (m), 55.84 (t, br, J CH ) 127 Hz), 32.46
(tqnt, J CH ) 132.4 Hz), 20.62 (q, J CH ) 112.3 Hz).
2
2
P r ep a r a tion of tr a n s-[ReF (dCdCHR)(d p p e)2] 3c (R )
CO2Me), 3d (R ) CO2Et), or 3f (R ) C6H4Me-4). These
fluoro-vinylidene complexes have been prepared by the depro-
tonation reaction, in CH2Cl2 and under dinitrogen, of the
corresponding fluoro-carbyne compounds 1c, 1d , or 1f by
[NBu4]OH in alcoholic solution (base added in a ca. stoichio-
metric amount). However, the less acidic carbyne 1b did not
appear to undergo deprotonation even under refluxing solvent
conditions.
As
a typical example, the preparation of trans-[ReF-
(dCdCHCO2Et)(dppe)2], 3d , was carried out as follows:
a
CH2Cl2 solution (15 cm3) of trans-[ReF(≡C-CH2CO2Et)(dppe)2]-
[BF4] (0.12 g, 0.10 mmol) was treated with a 0.1 M solution of
[NBu4]OH in methanol (1.1 cm3, 0.13 mmol). Addition of
diethyl ether followed by concentration of the solution led
to the precipitation of complex 3d as a yellow solid, which
was filtered off, washed with diethyl ether, and dried in
vacuo. Further crops were obtained from the mother liquor
upon concentration and addition of diethyl ether (ca. 60%
yield).
1a : Pale yellow, ca. 15% yield. 1H NMR (CDCl3): δ 7.6-
6.9 (m, 40H, Ph-dppe), 2.9-2.5 (m, 8H, CH2-dppe), 0.49 (s,
br, 3H, CCH3). 31P{1H} NMR (CDCl3): δ -112.2 (d, 2J PF ) 39
2
Hz). 19F NMR (CDCl3): δ -324.3 (qnt, J PF ) 39 Hz). Anal.
Calcd for BC54F5H51P4Re‚0.5CH2Cl2: C, 56.5; H, 4.5. Found:
C, 56.5; H, 4.7.
3c: Yellow, ca. 50% yield. IR (KBr pellet, cm-1): 1610, 1480
(νCO and νCdC).1H NMR (CDCl3): δ 7.43-6.98 (m, 40 H, Ph-
dppe), 3.10 (s, br, 3H, CO2CH3), 2.90 (m, br, 4H, CH2-dppe),
2.54 (m, br, 4H, CH2-dppe), 1.28 (m, br, 1H, CCHCO2Me).
1b: White, ca. 55% yield. 1H NMR: δ 7.58-7.19 (m, 40 H,
Ph-dppe), 3.87 (m, br, 4H, CH2-dppe), 3.07 (m, br, 4H, CH2-
dppe), 1.69 (s, 2H, CCH2But), 0.01 (s, 9H, CCH2But). 31P{1H}
2
31P{1H} NMR (CDCl3): δ -109.9 (d, J PF ) 34 Hz). 19F NMR
2
NMR: δ -116.3 (d, J PF ) 44 Hz). 19F NMR: δ -324.3 (qnt,
(CDCl3): δ -328.6 (m, br). 13C{1H} NMR (CDCl3): δ 298.20
(m, CCHCO2Me), 168.27 (s, CO2Me), 138.0-127.0 (m, Ph-
dppe), 97.7 (m, br, CCHCO2Me), 53.40 (s, CO2CH3), 32.80 (qnt,
virtual J CP ) 12.2 Hz, CH2-dppe). 13C NMR (CDCl3): δ 298.20
(m), 186.27 (s), ca. 138-127 (m, br), 53.40 (m), 32.80 (tqnt,
J CH ) 132.8 Hz). Anal. Calcd for C56FH52O2P4Re‚2CH2Cl2:
C, 59.8; H, 4.7. Found: C, 59.0; H, 4.8.
2J PF ) 44 Hz). 13C{1H} NMR: δ 135.9-128.7 (m, Ph-dppe),
4
65.28 (qnt, J CP ) 10 Hz, CCH2But), 33.06 (qnt, virtual J CP
)
10 Hz, CH2-dppe), 31.85 (s, C(CH3)3), 30.05 (s, C(CH3)3). Anal.
Calcd for BC58F5H57P4Re: C, 59.4; H, 5.1. Found: C, 59.6; H,
5.6.
1c: White, ca. 60% yield. IR (KBr pellet, cm-1): 1726 (νCO).
1H NMR (CDCl3): 7.39-6.98 (m, 40H, Ph-dppe), 2.95 (s, 3H,
CO2CH3), 3.1-2.9 (m, br, 4H, CH2-dppe), 2.8-2.6 (m, br, 4H,
CH2-dppe), 1.85 (s, br, 2H, CCH2CO2Me).31P{1H} NMR
3d : Yellow, ca. 60% yield. IR (KBr pellet, cm-1): 1610, 1485
(νCO and νCdC). 1H NMR: δ 7.33-7.02 (m, 40 H, Ph-dppe),
3.75 (m, 2H, CH2CH3), 2.82 (m, br, 4H, CH2-dppe), 2.47 (m,
br, 4H, CH2-dppe), 1.4-0.6 (m, 4H, CCHCO2CH2CH3). 31P-
2
(CDCl3): δ -114.1 (d, J PF ) 43 Hz). 19F NMR (CDCl3): δ
2
-316.3 (qnt, J PF ) 42 Hz). 13C{1H} NMR (CDCl3): δ 266.53
2
{1H} NMR: δ -109.8 (d, J PF ) 34 Hz). 19F NMR: δ -325.5
(m, CCH2CO2Me), 163.55 (s, CO2Me), 134.3-127.9 (m, Ph-
dppe), 52.20 (s, CCH2CO2Me), 51.93 (s, CO2CH3), 32.26
(qnt, virtual J CP ) 10 Hz, CH2-dppe). Anal. Calcd for
BC56F5H53O2P4Re‚2CH2Cl2: C, 57.1; H, 4.7. Found: C, 56.9;
H, 4.9.
2
(qnt, J PF ) 34 Hz). 13C{1H} NMR: δ 290.80 (m, CCHCO2-
Et), 168.15 (s, CO2Et), 137.6-127.5 (m, Ph-dppe), 97.40 (m,
CCHCO2Et), 58.72 (s, CO2CH2CH3), 32.00 (s, CH2-dppe), 15.24
(s, CO2CH2CH3). 13C NMR: δ 290.80 (m), 168.15 (s), ca. 138-
127 (m), 97.40 (dm, J CH ) 156.3), 58.72 (t, J CH ) 144.5 Hz),
32.00 (t, J CH ) 133.4 Hz), 15.24 (q, J CH ) 126.5 Hz). Anal.
1d : White, ca. 55% yield. IR (KBr pellet, cm-1): 1470 (νCO).
1H NMR (CDCl3): δ 7.29-6.50 (m, 40H, Ph-dppe), 3.47 (q,

Fluoro-Carbyne and Fluoro-Vinylidene Complexes
Organometallics, Vol. 16, No. 20, 1997 4477
Calcd for C57FH54O2P4 Re‚2CH2Cl2: C, 60.1; H, 4.8. Found:
C, 60.0; H, 5.2.
(R ) P h ), or 2f (R ) C6H4Me-4). These chloro-carbyne
complexes can be prepared (i) by treatment of a solution (in
CH2Cl2 or in THF) of the appropriate chloro-vinylidene
precursor trans-[ReCl(dCdCHR)(dppe)2] 4 with acid (HBF4,
[NH4][BF4], or an alkylammonium salt such as [NHEt3] [BPh4])
or (ii) in a single-pot synthesis (although in a lower yield) from
trans-[ReCl(N2)(dppe)2] by treating a THF solution of this
complex with the appropriate 1-alkyne (RC≡CH) and [NH4]-
[BF4], under sunlight, in an argon atmosphere. Complex 2a
was obtained, via route (ii), from HC≡CSiMe3 which under-
went desilylation. As a typical example, let us consider the
preparation of trans-[ReCl(≡CCH2Ph)(dppe)2][BF4] 2e: Route
(i). To a stirred CH2Cl2 solution (25 cm3) of trans-[ReCl-
(dCdCHPh)(dppe)2], 4e (0.36 g, 0.32 mmol), under dinitro-
gen, was added dropwise a diluted solution of [Et2OH][BF4]
in diethyl ether (0.32 mmol of acid, i.e., 0.50 cm3 of a 1:11
diluted solution of the commercially available 54% concen-
trated acid solution). Concentration of the solution was
followed by slow addition of diethyl ether until the formation
of a fine white powder, which was filtered off. Further addition
of diethyl ether to the filtered solution and/or cooling to ca. 0
°C led to precipitation of complex 2e as a pale yellow crystal-
line solid, which was filtered off, washed with a solutioon of
diethyl ether/dichloromethane (3:1), and dried in vacuo. Fur-
ther crops were obtained from the mother liquor upon con-
centration and addition of diethyl ether (ca. 70% yield). The
use of an excess (3:1) of [Et2OH][BF4], as well as of an
ammonium salt (the reaction was then carried out in THF)
instead of this acid, resulted in the formation of the same
complex.
Route (ii). A THF solution (250 cm3) of trans-[ReCl(N2)-
(dppe)2] (0.20 g, 0.19 mmol), under argon, was treated with
[NH4][BF4] (0.10 g, 0.96 mmol) and HC≡CPh (0.084 cm3, 0.77
mmol), and the system was left stirring in the sunlight for ca.
1 h and then overnight. The solvent was removed in vacuo
nearly to dryness, CH2Cl2 (2 cm3) added, and the solution
filtered. Diethyl ether was added until a white powder started
to be formed. It was filtered off, and complex 2e precipitated
from the filtered solution as a crystalline solid. It was isolated
by filtration, washed with diethyl ether, and dried in vacuo.
It could by recrystallized from CH2Cl2/diethyl ether. Further
crops could be obtained from the mother liquor by a similar
precipitation procedure (ca. 60% total yield).
3f: Rose, ca. 45% yield: IR (KBr pellet, cm-1): 1520 (νCdC).
1H NMR (CDCl3): δ 7.58-6.94 (m, 40 H, Ph-dppe), 6.79 (d, J
) 6.6Hz, 2H, C6H4Me), 5.90 (d, J ) 6.6Hz, 2H, C6H4Me), 3.2-
2.3 (m, 8H, CH2-dppe), 2.00 (s, 3H, C6H4CH3), 1.25 (m, br,
2
1H, CCHC6H4Me). 31P{1H} NMR (CDCl3): δ -114.2 (d, J PF
2
) 40 Hz). 19F NMR (CDCl3): δ -318.8 (qnt, J PF ) 42 Hz).
Anal. Calcd for
Found: C, 58.7; H, 5.0.
C61FH56P4Re‚2CH2Cl2: C 58.8; H, 4.7.
P r ep a r a tion of tr a n s-[ReCl(dCdCHR)(d p p e)2] 4b (R
) Bu t), 4c (R ) CO2Me), 4d (R ) CO2Et), 4e (R ) P h ) or
4f (R ) C6H4Me-4). With the exception of 4f, which was
prepared for the first time in this work, the other chloro-
vinylidene complexes 4b,c-e have previously15 been obtained
from the slow reaction (for ca. 4 to 6 days) of trans-[ReCl(N2)-
(dppe)2] with the appropriate 1-alkyne (present in a 15-30-
fold molar excess) in refluxing THF or under tungsten-filament
bulb irradiation. We now report an improved synthetic
method by exposure of the reaction solution to sunlight, a
procedure that drastically reduces the reaction time to ca.
0.5-3 h (depending on the light intensity), even in the presence
of a signicantly lower excess of the alkyne (4-fold stoichiometric
excess, relative to the dinitrogen complex) than that required
by the previous method (see above).
This general and new procedure consists of the preparation
of a solution in toluene or THF (although with lower yields
than when using toluene) of trans-[ReCl(N2)(dppe)2] and the
appropriate 1-alkyne (4-fold stoichiometric excess), which is
stirred under argon and in sunlight for ca. 0.5-3 h; the
corresponding vinylidene product 4 precipitates out of the
solution upon concentration and addition of pentane or diethyl
ether, respectively. As a typical example, the detailed proce-
dure for the novel complex trans-[ReCl(dCdCHC6H4Me-4)-
(dppe)2], 4f, is given as follows: the alkyne HC≡CC6H4Me-4
(0.145 cm3, 1.15 mmol) was added to a solution of trans-[ReCl-
(N2)(dppe)2] (0.30 g, 0.29 mmol) in toluene (300 cm3), prepared
under argon, which was then stirred in sunlight. Its color
turned from yellow to red, and after ca. 1 h no further changes
were observed. The red solution (after ca. 2 h from the
beginning) was concentrated in vacuo until a yellowish powder
appeared which was filtered off. Upon further concentration
in vacuo of the filtered solution and addition of pentane,
complex 4f precipitated as a red crystalline solid, which was
filtered off, washed with pentane and dried in vacuo; further
crops could be obtained from the mother liquor upon further
concentration, addition of pentane, and/or cooling to ca. 0 °C
(ca. 85% yield). Identical procedures were applied for the
preparation of the other chloro-vinylidene complexes 4 and
shorter reaction times could be used (ca. 0.5-1 h for 4b, 4c,
or 4d ).
Complexes 4, with the exception of 4b, can also be prepared,
although in a much less convenient and indirect way, upon
deprotonation of the corresponding chloro-carbynes 2 (see
below) by [NBu4]OH, following a procedure identical to that
described above for the analogous fluoro-vinylidene complexes
3; however, the less acidic carbyne 2b does not undergo such
a deprotonation reaction.
4f: Red, ca. 85% yield. IR (KBr pellet, cm-1): 1550, 1570
(sh) (νCdC). 1H NMR: δ 7.45-6.94 (m, 40H, Ph-dppe), 6.38
(d, J ) 7.5 Hz, 2H, C6H4Me), 5.68 (d, J ) 7.5 Hz, 2H, C6H4-
Me), 2.71 (m, br, 4H, CH2-dppe), 2.53 (m, br, 4H, CH2-dppe),
2.31 (s, 3H, C6H4CH3), 0.72 (m, br, 1H, CCHC6H4Me). 31P-
{1H} NMR: δ -126.4 (s).13C{1H} NMR: δ 295.30 (s, CCHC6H4-
Me), 137.6-123.6 (m, Ph-dppe, C6H4Me), 108.46 (s, CCHC6H4-
Me), 31.89 (qnt, virtual J CP ) 11.3 Hz, CH2-dppe), 21.48 (s,
C6H4CH3). 13C NMR: δ 295.30 (s), ca. 138-123 (m), 108.46
(d, J CH ) 148.2 Hz), 31.89 (tm, J CH ) 126.7 Hz), 21.48 (q, J CH
) 124.7 Hz). Anal. Calcd for C61ClH56P4Re: C, 64.8; H, 5.0.
Found: C, 64.9; H, 5.3.
2a : Pale yellow, ca. 15% yield. 1H NMR (CDCl3): δ 7.65-
6.90 (m, 40H, Ph-dppe), 3.05-2.60 (m, br, 8H, CH2-dppe),
4
0.45 (qt, J HP ) 3.5Hz, 3H, CCH3). 31P{1H} NMR (CDCl3): δ
-118.2(s). 13C{1H} NMR (CDCl3): δ 273.60 (m, CCH3), 135.1-
127.4 (m, Ph-dppe), 36.30 (s, CCH3), 31.20 (qnt, virtual J CP
) 10.9 Hz, CH2-dppe). 13C NMR (CDCl3): δ 273.60 (m), ca.
135-127 (m), 36.30 (q, J CH ) 130.6 Hz), 31.20 (tqnt, J CH
)
130.6 Hz). Anal. Calcd for BC54ClF4H51P4Re‚0.5CH2Cl2: C,
55.7; H, 4.4. Found: C, 55.7; H, 4.5.
2b: White, ca. 65% yield. 1H NMR: δ 7.65-6.80 (m, 40H,
4
Ph-dppe), 3.2-2.4 (m, br, 8H, CH2-dppe), 0.88 (qnt, br, J HP
) 4.0 Hz, 2H, CCH2But), 0.05 (s, 9H, CCH2But). 31P{1H}
NMR: δ -114.6 (s). 13C{1H} NMR: δ 280.21 (qnt, 2J CP ) 10.5
Hz, CCH2But), 134.0-128.3 (m, Ph-dppe), 64.89 (s, CCH2But),
32.13 (s, C(CH3)3), 31.45 (qnt, virtual J CP ) 10.6 Hz, CH2-
dppe), 30.00 (s, C(CH3)3). 13C NMR: δ 280.21 (qnt), ca. 134-
128 (m), 64.89 (t, J CH ) 125.9 Hz), 32.13 (s), 31.45 (tm,
J CH ) 133.3 Hz), 30.00 (q, J CH ) 126.0 Hz). Anal. Calcd for
BC58ClP4H57P4Re‚0.5CH2Cl2: C, 57.1; H, 4.9. Found: C, 57.1;
H, 5.1.
2c: Pale yellow, ca. 95% yield. IR (KBr pellet, cm-1): 1740
(νCO). 1H NMR: δ 7.45-7.06 (m, 40H, Ph-dppe), 3.02 (s, 3H,
4
CO2CH3), 2.89 (m, br, 8H, CH2-dppe), 1.62 (qnt, br, J HP
)
3.5 Hz, CCH2CO2Me). 31P{1H} NMR: δ -117.2 (s). 13C{1H}
NMR: δ 259.78 (qnt, J CP ) 8.5 Hz, CCH2CO2Me), 162.70 (s,
2
CO2Me), 135.7-127.2 (m, Ph-dppe), 54.18 (s, CCH2CO2Me),
52.65 (s, CO2CH3), 31.00 (qnt, virtual J CP ) 10.9 Hz, CH2-
dppe). 13C NMR: δ 259.78 (qnt), 162.70 (s), ca. 136-127 (m),
54.18 (t, J CH ) 129.3 Hz), 52.65 (q, J CH ) 148.5 Hz), 31.00
P r ep a r a tion of tr a n s-[ReCl(≡C-CH2R)(d p p e)2] 2a (R
) H), 2b (R ) Bu t), 2c (R ) CO2Me), 2d (R ) CO2Et), 2e

4478 Organometallics, Vol. 16, No. 20, 1997
Almeida and Pombeiro
(tqnt, J CH ) 135.9 Hz). Anal. Calcd for BC56ClF4H53O2P4-
Re‚0.25 CH2Cl2: C, 55.8; H, 4.2. Found: C, 55.9; H, 4.6.
Anal. Calcd for BC60ClF4H55P4Re: C, 59.6; H, 4.6. Found: C,
59.3; H, 4.6.
2f: Pale yellow, ca. 75% yield. 1H NMR: δ 7.50-7.00 (m,
40H, Ph-dppe), 6.87 (d, J ) 7.5 Hz, 2H, C6H4Me), 5.92 (d, J
) 7.5 Hz, 2H, C6H4Me), 2.90 (m, br, 4H, CH2-dppe), 2.60 (m,
2d : Pale yellow, ca. 75% yield. IR (KBr pellet, cm-1): 1750
(νCO).1H NMR: δ 7.44-7.09 (m, 40H, Ph-dppe), 3.44 (q, J )
6.9 Hz, 2H, CO2CH2CH3), 2.88 (m, br, 8H, CH2-dppe), 1.60
4
4
br, 4H, CH2-dppe), 2.26 (s, 3H, C6H4CH3), 2.14 (qnt, br, J HP
(qnt, br, J HP ) 2.9 Hz, 2H, CCH2CO2Et), 0.94 (t, J ) 6.9 Hz,
) 3.4 Hz, 2H, CCH2C6H4Me). 31P{1H} NMR: δ -115.8 (s).
3H, CO2CH2CH3). 31P{1H} NMR: δ -117.0 (s). 13C{1H}
NMR: δ 260.03 (s, CCH2CO2Et), 162.33 (s, CO2Et), 135.2-
127.2 (m, Ph-dppe), 62.22 (s, CO2CH2CH3), 54.44 (s, CCH2-
CO2Et), 31.00 (qnt, virtual J CP ) 10.0 Hz, CH2-dppe), 13.74
(s, CO2CH2CH3). 13C NMR: δ 260.03 (m), 162.33 (s), ca. 135-
127 (m), 62.22 (t, J CH ) 148.4 Hz), 54.44 (t, J CH ) 130.9 Hz),
31.00 (tqnt, J CH ) 136.7 Hz), 13.74 (q, J CH ) 126.8 Hz). Anal.
Calcd for BC57ClF4H55O2P4Re‚0.75CH2Cl2: C, 54.7; H, 4.7.
Found: C, 54.6; H, 4.7.
13C{1H} NMR: δ 270.54 (m, CCH2C6H4Me), 134.5-127.5 (m,
Ph-dppe), 56.52 (s, CCH2C6H4Me), 31.03 (qnt, virtual J CP
)
12.2 Hz, CH2-dppe), 21.03 (s, C6H4CH3). 13C NMR: δ 270.54
(m), ca. 135-127 (m), 56.52 (t, J CH ) 129.2 Hz), 31.03 (tqnt,
3
J CH ) 132.0 Hz), 21.03 (qt, J CH ) 126.5 Hz, J CH ) 4.5 Hz).
Anal. Calcd for BC61ClF4H57P4Re‚3/2CH2Cl2: C, 55.6; H, 4.3.
Found: C, 55.5; H, 4.
Ack n ow led gm en t. This work has been partially
supported by J NICT, the PRAXIS XXI Programme
(Portugal), and the EC Network ERBCHRXCT 940501.
We also thank Dr. R. L. Richards (Nitrogen Fixation
Laboratory, J ohn-Innes Centre, U.K.) and Prof. A. B.
P. Lever (York University, North York, Canada) for
stimulating discussions.
2e: Pale yellow, ca. 70% yield. 1H NMR: δ 7.60-6.95 (m,
43H, Ph-dppe + CCH2Ph (m, p)), 6.07 (d, J ) 5.5 Hz, 2H,
4
CCH2Ph (o)), 3.2-2.4 (m, br, 8H, CH2-dppe), 2.23 (qnt, J HP
) 3.5 Hz, CCH2Ph). 31P{1H} NMR: δ -114.0 (s). 13C{1H}
2
NMR: δ 269.89 (qnt, J CP ) 12.4 Hz, CCH2Ph), 134.0-127.9
(m, Ph-dppe), 56.75 (s, CCH2Ph), 31.00 (qnt, virtual J CP
)
11.0 Hz, CH2-dppe). 13C NMR: δ 269.89 (qnt), ca. 134-127
(m), 56.75 (t, J CH ) 128.5 Hz), 31.00 (tqnt, J CH ) 130.7 Hz).
OM970397O