Nucleophilic vinylic substitution with transition metal carbonyl anions - A rare case of a halophilic reaction mechanism. Formation of halo(acyl)rhenate complexes and X-ray structure of cis-[CF2=CF(CO)Re(CO)4Br]Na

Article abstract of DOI:10.1016/S0022-328X(03)00531-X

Reactions of polyfluorinated alkenyl halides Z-(CF₃) ₃CCF=6;CFHal (Hal=Cl,I-Cl, Hal=Br, I-Br) and CF₂=CFBr (II-Br) with [CpFe(CO)₂]K (FpK) and [Re(CO)₅]Na proceed through the initial attack of metal carbonyl anion on halogen. Reaction with FpK gives minor amounts of σ-alkenyl complexes Z-R_fCF=CFFe(CO)₂Cp (I-Fe, II-Fe) (3-30%), but primarily leads to dimer [CpFe(CO)₂] ₂. Reaction with [Re(CO)₅]Na produces anionic halo(acyl)rhenates cis-[Z-R_fCF=CF(CO)Re(CO)₄Hal]Na (V-Cl, V-Br, VI) (70-90%) which were isolated, and halo(acyl)rhenate VI (R_f=F) was characterized by X-ray structure analysis. Halo(acyl)rhenates result from the attack of the intermediate carbanion [R_fCF=CF]^- on the carbonyl ligand of Re(CO) ₅Hal. The involvement of [R_fCF=CF]^- is demonstrated by their trapping with t-BuOH or CH-acid, which gives the protodehalogenated alkenes I-H and II-H, and suppresses the nucleophilic substitution reaction leading to I-Fe, II-Fe or V-Cl. Arguments against a radical/SET mechanism for the substitution reaction are also advanced.

Full text of DOI:10.1016/S0022-328X(03)00531-X

Journal of Organometallic Chemistry 681 (2003) 59Á69
/
www.elsevier.com/locate/jorganchem
Nucleophilic vinylic substitution with transition metal carbonyl
anions*a rare case of a halophilic reaction mechanism
Formation of halo(acyl)rhenate complexes and X-ray structure of cis-
CF(CO)Re(CO)4Br]Na
/
[CF2Ä
/
P.K. Sazonov a, G.A. Artamkina a, V.N. Khrustalev b, M.Yu. Antipin b,
I.P. Beletskaya a,*
a Chemistry Department, Moscow State University, Leninskie Gory 1, GSP-2, Moscow 119992, Russia
b A.N. Nesmeyanov Institute of Organoelement Compounds (INEOS), Russian Academy of Sciences, Vavilov Street 28, Moscow 119991, Russia
Received 23 April 2003; received in revised form 23 May 2003; accepted 23 May 2003
Abstract
Reactions of polyfluorinated alkenyl halides Z-(CF3)3CCFÄ
[CpFe(CO)2]K (FpK) and [Re(CO)5]Na proceed through the initial attack of metal carbonyl anion on halogen. Reaction with FpK
gives minor amounts of s-alkenyl complexes Z-RfCFÄCFFe(CO)2Cp (I-Fe, II-Fe) (3Á30%), but primarily leads to dimer
[CpFe(CO)2]2. Reaction with [Re(CO)5]Na produces anionic halo(acyl)rhenates cis-[Z-RfCFÄCF(CO)Re(CO)4Hal]Na (V-Cl, V-
Br, VI) (70Á90%) which were isolated, and halo(acyl)rhenate VI (Rf ꢀF) was characterized by X-ray structure analysis.
Halo(acyl)rhenates result from the attack of the intermediate carbanion [RfCFÄ
CF]ꢁ on the carbonyl ligand of Re(CO)5Hal. The
involvement of [RfCFÄ
CF]ꢁ is demonstrated by their trapping with t-BuOH or CH-acid, which gives the protodehalogenated
/
CFHal (Halꢀ
/
Cl, I-Cl, Halꢀ
/
Br, I-Br) and CF2Ä/CFBr (II-Br) with
/
/
/
/
/
/
/
alkenes I-H and II-H, and suppresses the nucleophilic substitution reaction leading to I-Fe, II-Fe or V-Cl. Arguments against a
radical/SET mechanism for the substitution reaction are also advanced.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Carbonylmetallates; HalogenÁmetal exchange; Polyfluorinated alkenyl halides; Rhenium acyl anions; SNV reactions
/
1. Introduction
unusual halophilic mechanism (Scheme 1) operates in
nucleophilic aromatic substitution reaction of metal
carbonyl anions with halopentafluorobenzenes [5,6].
Nucleophilic substitution with metal carbonyl anions
is the most straightforward method of forming transi-
The evidence of halogenÁmetal exchange (HME) on
/
tion metalÃcarbon s-bond(s). Only aliphatic nucleophi-
/
the first reaction step was obtained via trapping of
[C6F5]-carbanion intermediate with certain CH- or OH-
acids: in the presence of t-BuOH or PhCH(Et)CN
formation of nucleophilic substitution (NS) products
was suppressed completely, and pentafluorobenzene and
related products were formed (Scheme 2).
lic substitution with metal carbonyl anions was studied
in some detail, the operation of both SN2 [1] and SET
reaction mechanisms being demonstrated [2]. The sub-
stitution mechanisms at sp2-carbon atom in aromatic
and vinylic systems were not studied with these anions
prior to our publications [3,4]. Having embarked upon
such an investigation, we have recently shown that an
And though the reactions of [CpFe(CO)2]ꢁ anion and
[M(CO)5]ꢁ (Mꢀ
/
Re, Mn) anions with halopentafluor-
* Corresponding author. Tel./fax: ꢂ7-095-939-3618.
E-mail address: beletska@org.chem.msu.ru (I.P. Beletskaya).
/
Scheme 1.
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00531-X

60
P.K. Sazonov et al. / Journal of Organometallic Chemistry 681 (2003) 59Á69
/
Scheme 2.
obenzenes give absolutely different types of products,
the s-aryl iron complexes (a) and the manganese and
rhenium halo(acyl)metallate adducts (b) respectively
(Scheme 2), they all follow the same two-step halophilic
mechanism. The intermediate metal carbonyl halide
behaves as an ambident electrophile and can be attacked
by the aryl carbanion not only at the metal center but
also at the carbonyl ligand. In the latter case, the
intermediates simply ‘‘collapse’’ preserving their identity
in the halo(acyl)metallate products, this being probably
the best proof of the halophilic mechanism.
Despite the notorious mechanistic diversity of nucleo-
philic vinylic substitution [7], the halophilic mechanism
(Scheme 1) still lacks experimental confirmation. Sub-
stitution pathway via attack on halogen is accepted for
acetylenic systems [8,9]. By contrast, in vinylic systems
halophilic processes are usually associated with un-
wanted halophilic reduction of the alkenyl halides [10].
The only, yet notable exceptions are the substitution
reactions with [R3Sn]ꢁ [11] and [R2P]ꢁ [12] anions in
alkenyl bromides, for which the halophilic mechanism
was suggested. However, no attempt was made to prove
it experimentally. In this paper, we are going to show
that the reactions of metal carbonyl anions with certain
vinylic substrates follow this halophilic pathway.
2. Results and discussion
2.1. Reaction of polyfluoroalkenyl halides with
[CpFe(CO)2]K (FpK)
The reactions were carried out at ꢁ50 8C in THF
/
with a slight excess of alkenyl halide and even at that
low temperature were almost instantaneous1 as can be
judged by the rapid color change from orange-red of the
starting anion to deep cherry of metal carbonyl dimer,
Fp2. Indeed, the Fp2 dimer was the principal product in
these reactions, its yield varying from 60 to 100% (Table
1). Surprisingly, no products corresponding to the
alkenyl halide reduction (dehalogenation) were detected,
which at present has no satisfactory explanation.
The s-alkenyl iron complexes (I-Fe and II-Fe), which
are the products of NS of halogen (Cl, Br), were formed
in minor quantities. Their yields varied from trace with
I-Cl to modest with alkenyl bromides (entries 1Á3,
/
Table 1, Scheme 3). Traces of iron carbonyl bromide
FpBr (entries 2 and 3) were also found among the
reaction products.
Next we carried out the same reactions in the presence
of proton donors, PhCH(Et)CN (estimated pKaꢀ
/
21)
and t-butyl alcohol (pKa]20), that had proved their
/
The alkenyl halides suitable for our task should be
good positive halogen atom donors (their hydrogen
analogs should be strong CH-acids). At the same time
the double bond in these substrates should be as little
activated towards nucleophilic attack as possible, to
efficiency previously in our study of halophilic reactions
with halopentafluorobenzenes.2 With the added proton
donor no NS products with Fpꢁ anion were formed
(entries 4,5 and 7), or, in case of II-Br and CH-acid, the
yield of II-Fe decreased from 30 to 5% (entry 6). Instead
avoid competition from the additionÁelimination route.
/
the hydrodehalogenated alkenes (I-H and II-H) (in 28Á
/
Polyfluorinated alkenyl halides without strong EWG
groups in b-position to halogen, such as (Z)-1-chloro-
(bromo)-1,2,4,4,4-pentafluoro-3,3-bis(trifluoromethyl)-
1-butenes (I-Cl and I-Br) and bromotrifluoroethylene
(II-Br), appeared to be the suitable models. Further-
more, our own preliminary results, when [CpFe(CO)2]ꢁ
anion substituted bromine in bromotrifluoroethylene
[4], already suggested the halophilic substitution me-
chanism.
1
At ꢁ
/
90 8C the reaction with Z-(CF3)3CCFÄCFCl still takes no
/
more than several minutes.
2
The choice of proton donors for anion trapping is of particular
importance, as their pKa should fit into relatively narrow pKa interval
between that of FpH (pKaꢀ
values of 2094 and 27 cited for CF2Ä
lower and upper limits for polyfluorinated alkenes without a-EWG
substituents).
/19.2 [13]) and parent alkenyl hydride (pKa
/
/CFH [14] may be considered as

P.K. Sazonov et al. / Journal of Organometallic Chemistry 681 (2003) 59Á
/69
61
Scheme 3.
50% yield) were produced, together with such com-
pounds as III and IV (Schemes 4 and 5). All these
compounds were identified by their characteristic pat-
terns in 1H- and 19F-NMR spectra of reaction solutions
(Table 2), and (I-H) also by chromato-mass spectrum.
2.2. Reaction of polyfluoroalkenyl halides with
[Re(CO)5]Na
The reactions were carried out at room temperature
with a slight excess of alkenyl halide. In marked contrast
to the reactions with FpK, no s-alkenyl rhenium
complexes were detected in these reactions. Nucleophilic
substitution of halogen with [Re(CO)5]Na (Cl or Br, but
not F) gave anionic halo(acyl)rhenates (Scheme 6), as
was clearly demonstrated by IR, 13C- (Table 3) and 19F-
NMR spectra (Table 2) of the reaction mixtures. Minor
amounts of Re(CO)5Br (5Á10%) were also detected in
/
the case of alkenyl bromides. Reactions with
[Re(CO)5]Na, which is much less nucleophilic than
FpK [1], allowed us to compare the reactivity of alkenyl
halides. The reaction of I-Cl took about 1 h to complete,
while the reactions of both alkenyl bromides I-Br and II-
Br were completed in less then 4 min (first NMR
spectrum recorded) at room temperature.
Halo(acyl)rhenates V-Cl, V-Br and VI were isolated
in the form of crystalline complexes with 18-crown-6
and dioxane. Addition of dioxane (5%, v/v) to the
diethyl ether solution of halo(acyl)rhenate containing
18-crown-6 caused immediate crystallization of the
complex. The complexes gave satisfactory element
analysis and were characterized by solution IR spectra.
All bands in metal CÅ/O frequencies region, and
especially the lowest frequency band, corresponding to
the nas of two equatorial CO groups (B2 mode), were
shifted to lower frequencies, compared to spectra of the
same halo(acyl)rhenates without 18-crown-6 (Table 3).
Surprisingly, n(CÄO) of acyl group, which is usually
supposed to be the coordination site of the cation in
metal acyl anions, exhibited small or no shift in the
presence of 18-crown-6. This raises the question about
the site and mode of coordination of sodium in
halo(acyl)rhenates; however, it lies beyond the scope
of the present work.
The structure of halo(acyl)rhenate salt VI was con-
firmed by single crystal X-ray diffraction analysis of its

62
P.K. Sazonov et al. / Journal of Organometallic Chemistry 681 (2003) 59Á69
/
Scheme 4.
position to bromine. The cis-geometry has always been
assumed for the previously described halo(acyl)rhenate
anions [R(CO)Re(CO)4Hal]ꢁ [15,16], though they were
obtained only as intermediates in solutions and were
never isolated. The same geometry with cis-arrangement
of non-carbonyl ligands is found in various Re(CO)4X2
complexes, a large number of them structurally char-
acterized by now, including several acyl anions [17]. The
bond lengths and angles in VI are in the range expected
from the previous data. No direct contacts between the
Scheme 5.
cationic and anionic parts of the complex (VI×
/
18-crown-
6×dioxane) are observed, which may be described as a
/
complex of a ‘‘naked’’ acyl anion. The sodium cations
are bound in a polymeric chain with bridging dioxane
molecules, which together with six donor oxygen atoms
of the crown ether form around sodium a completely
saturated coordination sphere of eight donor centers
(Fig. 2).
Scheme 6.
complex with 18-crown-6 containing one molecule of
dioxane. The structure of the complex is shown in Fig. 1.
The acyl anion VI has an expected geometry of a
distorted octahedron, with acyl group occupying a cis-
The effect of proton donors on the formation
halo(acyl)rhenate salts (V-Cl, V-Br, VI) was examined
Table 2
19F-NMR spectral data (THF, 23 8C)
Compound
X
dF, ppm (n JFÃH, Hz)
n JFÃF, Hz
F1
F2
CF3
JF ÃF JCF ÃF JCF ÃF
3
4
5
1
2
1
3 3
2
/
/
/
Formula A
I-Cl
Cl
Br
ꢁ
/
149.23 d m
143.02 d m
149.5 d m
ꢁ
/
99.80 d m
ꢁ
/
62.44 dd
62.44 dd
62.51 dd
62.63 dd
62.04 dd
62.07 dd
62.00 dd
136
144
131
133
136
134
135
12.0
12.2
13.6
11.9
12.2
12.6
12.5
16.2
15.5
18.0
15.5
18.0
17.6
17.0
I-Br
I-Fe
ꢁ
/
ꢁ
/
97.87 d m
ꢁ
/
Fe(CO)2Cp
H
ꢁ
/
ꢁ
/
75.6 d m
154.51 dd m (2JHÃF
131.5 d m
ꢁ
/
I-H
III
ꢁ
/
170.06 dd m (3JHÃF
150.4 d m
ꢀ/
9)
ꢁ
/
ꢀ/
72)
ꢁ
/
C(Et)(Ph)CN
[CORe(CO)4Cl]Na
[CORe(CO)4Br]Na
ꢁ/
ꢁ/
ꢁ
/
V-Cl
V-Br
ꢁ
/
166.22 d m
ꢁ
/
129.41 d m
ꢁ
/
ꢁ
/
166.09 d m
ꢁ
/
128.62 d m
ꢁ/
3
2
3
F1
F2
F3
JF ÃF JF ÃF
JF ÃF
1
2
1
3
2
3
/
/
/
Formula B
II-Br
II-Fe
II-H
Br
Fe(CO)2Cp
H
ꢁ
/
116.21 dd
ꢁ
/
144.15 dd
ꢁ
/
96.08 dd
123
115
73
53
41
ꢁ
/
130.5 dd
126.2 ddd (3JHÃF
106.5 dd
ꢁ
/
136.8 dd
204.2 ddd (2JHÃF
161.0 dd
ꢁ
/
84.4 dd
100.5 ddd (3JHÃF
101.5 dd
102
86
ꢁ
/
ꢀ
/
4.5)
3)
ꢁ
/
ꢀ
/
71)
ꢁ
/
ꢀ
/
13) 118
33
33.5
VI
VIII
[CORe(CO)4Br]Na
CHPh2
ꢁ/
ꢁ/
ꢁ/
108.6 24.1
141
ꢁ
/
107.72 d
ꢁ
/
130.93 d
Á/
(Yꢀ
/
Br)
Á/
Á/
Formula C
IV
IX
t-BuO
CHPh2
ꢁ/
76.66 ddd (3JHÃF
ꢀ/
ꢁ
ꢁ/
/
155.30 d t (2JHÃF
150.13 d t (2JHÃF
ꢀ
/
48)
46)
ꢁ/
77.82 ddd (3JHÃF
ꢀ/
6) 14
141
18 263
15
ꢁ
/
102.68 dd
ꢀ/
ꢁ
/
107.43 dt
Â
/
Â18
/

P.K. Sazonov et al. / Journal of Organometallic Chemistry 681 (2003) 59Á
/69
63
Table 3
IR and 13C-NMR spectra of rhenium carbonyl complexes (THF, r.t.)
Compound
IR spectrum a, n, cmꢁ1 (o, ꢃ
/
10ꢁ3
)
13C-NMR spectrum, dC, ppm (JCÃF, Hz)
CÄ CÅ
nCÄO
nCÅO
/O
/O
[Re(CO)5]Na
Re2(CO)10
Re(CO)5Cl
Re(CO)5Br
1840s, 1875vs, 1918s
219.43 br
192.5 br (4C), 183.2 br (1C)
1977 (3.6), 2017 (18), 2076 (5.0)
1988 (1.8), 2047 (6.7), 2160 (0.08)
1991 (2.2), 2047 (8), 2158 (0.2)
1936 s, 1996 vs, 2101 m
Á/
Á/
[Z-(CF3)3CCFÄ
(V-Cl)
/CF(CO)Re(CO)4Cl]Na
1592 m
258.47 d 190.66 s (1C), 190.13 t (2C, J :
/
3),
(Jꢀ42) 187.48 d (1C, J :5)
/
/
V-Cl×
[Z-(CF3)3CCFÄ
(V-Br)
V-Br×18-crown-6
[CF2Ä
CF(CO)Re(CO)4Br]Na c (VI)
/
18-crown-6
1592 m
1593 m
1920 s, 1991 vs, 2095 m
1936 s, 1997 vs, 2100 m
Á
/
Á
/
b
/CF(CO)Re(CO)4Br]Na
189.52 s, 189.45 d (J :
187.09 d (1C, J :6)
Á/
/
3.5) (3C),
/
/
1590 m
1556 m
1921 s, 1992 vs, 2095 m
1933 s, 1993 vs, 2097 m
Á/
/
258.77 d 190.03 s (1C), 189.96 d (2C, Jꢀ
(Jꢀ47) 187.98 d (1C, Jꢀ8.5)
Á/
/
4.5),
/
/
VI×
/
18-crown-6 d
[t-BuO(CO)Re(CO)4Cl]Na (VII)
1560 m 1918 s, 1977 sh, 1992 vs, 2093 m
1605 br, m (0.5) 1930 (3), 1986 (4), 2094 (0.4)
Á/
207.90 s
191.77 s, 191.68 s (3C), 188.20 s (1C)
a
lcell
ꢀ
/
0.02 cm, range: 1600Á .
/
2300 cmꢁ1
b
c
Out of the recorded spectral range.
nCÄC: 1722 cmꢁ1 (s).
nCÄC: 1727 cmꢁ1 (s).
d
Fig. 1. The general view of the compound VI×
atom with occupancies 0.4 are not shown. Selected bond distances (A) and angles (8): Re(1)Ã
1.968(9); Re(1)ÃBr(1), 2.500(2); C(5)ÃRe(1)ÃC(3), 92.3(3); C(5)ÃRe(1)ÃC(4), 175.1(3); C(5)ÃRe(1)Ã
/
18-crown-6×dioxane (40% probability ellipsoids); the positions of disordered carbonyl group and Br
/
˚
/
C(5), 2.231(9); Re(1)Ã
/
C(4), 1.984(9); Re(1)ÃC(3),
/
/
/
/
/
/
/
/
Br(1), 89.0(2).
in the reaction of [Re(CO)5]Na with I-Cl. In the presence
of t-butyl alcohol (10 equivalents), only 6% V-Cl was
formed and I-H (30%) was the only other fluoroalkene-
derived product (Scheme 7). Characteristic bands of a
different halo(acyl)rhenate anion (corresponding to :
/
30% yield) were also observed in the IR spectrum of the
reaction mixture. We suppose that these bands belong to
cis-[t-BuO(CO)Re(CO)4Cl]Na (VII). And indeed they
coincided with the IR spectrum of halo(acyl)rhenate VII
obtained independently from t-BuONa and Re(CO)5Cl
(Table 3).
Fig. 2. View of the polymeric chain formed by Na cations and dioxane
molecules in the crystal structure of VI×18-crown-6×dioxane.
/
/

64
P.K. Sazonov et al. / Journal of Organometallic Chemistry 681 (2003) 59Á69
/
Scheme 7.
Scheme 8.
In the reaction of I-Cl with [Re(CO)5]Na, besides
donor, [t-BuO]ꢁ or [PhC(Et)CN]ꢁ, with the starting
alkenyl halide produces such compounds as III and IV
(Scheme 9). Interestingly, the fate of [t-BuO]ꢁ is
different in the case of [Re(CO)5]Na. The alkoxide [t-
BuO]ꢁ is trapped by Re(CO)5Cl to give halo(acyl)rhe-
nate VII, indicating that Re(CO)5Cl is much more
electrophilic than FpHal, or the starting alkenyl halide.3
It is worth noting that halo(acyl)rhenates V-Cl, V-Br,
VI and s-alkenyl iron complexes I-Fe and II-Fe are not
protodemetallated with alcohols and could not be the
source of I-H or II-H under our reaction conditions.
halo(acyl)rhenate V-Cl up to 25% Re2(CO)10 is formed.
Interestingly, carrying out this reaction in the presence
of tertiary phosphine PEt3 (2.5 equivalents) allows one
to avoid the formation of Re2(CO)10, leading to almost
quantitative yield of V-Cl (90%).
2.3. Reaction of bromotrifluoroethylene (II-Br) with
[Ph2CCN]ꢁ carbanion
To demonstrate that the choice between the halophilic
and ‘‘normal’’ (additionÁ
chanisms also depends on the nucleophile, we have
carried out the reaction of CF2ÄCFBr with a soft
carbanion nucleophile (Scheme 8). In marked contrast
to its reactions with metal carbonyl anions (Schemes 3
and 6), vinylic fluorine (trans to bromine) was sub-
stituted in a highly selective manner with the sodium salt
of a,a?-diphenylacetonitrile. The reaction was carried
out in the presence of a large excess (10 equivalents) of
/
elimination) substitution me-
Reaction with CF2Ä
/
CFBr provides us with another
argument in favor of the halophilic (but also SET)
reaction mechanism, the so-called intramolecular vicinal
‘‘element effect’’. Only bromine is substituted by both
carbonylates (Schemes 3 and 6). If the reaction followed
/
the additionÁ
elimination mechanism4 normal for vinylic
/
NS (Scheme 10) the fluorine from CF2 group would be
substituted, as it happens in the reaction with
[Ph2CCN]ꢁ carbanion (Scheme 8) or other common
nucleophiles (RSꢁ, ROꢁ, amines) [20]. The intermole-
cular ‘‘element effect’’ observed in the reaction of
[Re(CO)5]Na with alkenyl halides (I-Br more active
than I-Cl, see Section 2.2) also shows that CÃ
breaking takes place on the rate-limiting stage of
reaction and is not consistent with the additionÁ
anion trap, Ph2CHCN (pKaꢀ
trifluorovinyl carbanion should it be formed as inter-
CFH was not detected in the reaction
/18), to protonate the
mediate. Yet CF2Ä
/
mixture by 19F-NMR. In addition to the signals of
nucleophilic substitution product VIII (80% yield, iso-
lated in 70% yield), a characteristic pattern correspond-
ing to RCF2CFHX adduct (15% yield according to the
integral intensity) was also observed in 19F-NMR
spectrum. It seems reasonable to suppose that it is
/Hal bond
/
elimination mechanism [7,10,20], but agrees well with
the proposed HME pathway (Scheme 1).
Arguments against the SET pathway will be discussed
in detail later, in connection with the halo(acyl)rhenate
complexes. Here, we will only point to the complete
retention of Z/E configuration of the starting alkenyl
halide (I-Cl, I-Br) both in NS and reduction (I-H)
IX*
to CF2Ä
/
the product of nucleophilic addition of Ph2CHCN
CFBr.
/
2.4. The halophilic mechanism: supporting arguments
All of the NS reactions discussed in this paper, both
with iron and rhenium carbonylates, have one very
important feature in common: NS is suppressed by
proton donors. Thus, the intermediacy of alkenyl
carbanion species is clearly indicated. Their protona-
tion, or we may call it ‘‘trapping’’, by t-BuOH or CH-
acid gives the protodehalogenated alkenes I-H or II-H,
while the reaction of the conjugated base of the proton
3
We are not going to discuss it here, but as it was mentioned
previously [6] the halophilic mechanism does not necessarily involve
free carbanion and metal carbonyl halide intermediates. They may be
bound together in an at-complex [R-Hal-M(CO)n ]ꢁ [18,9], which
transforms to NS products via intramolecular rearrangement. In the
protonation reaction, such at-complexes may give the same products,
I-H and II-H, as the free carbanions [19].
4
With the rate-limiting addition step.

P.K. Sazonov et al. / Journal of Organometallic Chemistry 681 (2003) 59Á
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65
Scheme 9.
Scheme 10.
products. When the reaction of the same substrates I-Cl
and I-Br with FpK was carried out under ‘‘electro-
chemical activation’’ conditions, and the cathode reduc-
tion of the alkenyl halide produced the corresponding
radicals, both Z and E isomers of the product I-Fe were
formed [21].
However, the halophilic mechanism reveals itself most
vividly in the reactions with [Re(CO)5]Na, when halo(a-
cyl)rhenates V-Cl, V-Br and VI are formed. In contrast
to s-vinyl complexes, or other possible products of
reactions that may follow the HME step, halo(acyl)rhe-
nates are formed by a simple recombination reaction
(Scheme 11) and contain structurally intact fragments of
alkenyl carbanion and Re(CO)5Hal. This fact allows one
to regard formation of halo(acyl)rhenate as an ‘‘auto-
trapping’’ of both HME intermediates and the most
impressive proof of the halophilic character of these
reactions.
would have given ‘‘normal’’ nucleophilic substitution
products, the s-alkenyl metal complexes in case of
carbonylates. One may argue that the initially formed
s-alkenyl Re(CO)5 complex could undergo migratory
insertion of CÅ
/O ligand induced by NaHal giving
halo(acyl)rhenate products. This alternative can be
easily rejected, since s-alkenyl M(CO)5 complexes
(MꢀRe, Mn) are known to be stable under our
/
reaction conditions [22,23] and, more importantly,
NaCl or NaBr are not soluble in THF. Moreover,
lithium bromide (LiBr) failed to induce Me group
migration in Re(CO)5Me [15], and this migration would
be much more facile than the migration of polyfluor-
oalkenyl EWG group.
On the other hand, the nucleophilic addition to CO
ligand is very well documented for various classes of
metal carbonyls, including metal carbonyl halides, in
which the sight of nucleophilic attack is often not the
metal atom but the CO ligand. The addition of MeLi to
Obviously, halo(acyl)rhenates cannot be formed by
additionÁelimination reaction (Scheme 10), which
/
rhenium
carbonyl
halides
Re(CO)5Hal
and
Scheme 11.

66
P.K. Sazonov et al. / Journal of Organometallic Chemistry 681 (2003) 59Á
/69
Scheme 12.
Re(CO)4PPh3Br giving halo(acyl)rhenate complexes has
been reported [15,16]. If halo(acyl)rhenates V-Cl, V-Br
and VI are formed through the same carbanion addition
pathway, and we see no alternative, the alkenyl carban-
ion and Re(CO)5Hal intermediates have to be generated
on the preceding reaction stage, and this first stage has
to be HME (Scheme 11).
towards carbanions than Re(CO)5Hal.5 On the other
hand, the rate constants for the reactions of
Re(CO)5Hal with [Re(CO)5]ꢁ and FpHal with [Fp]ꢁ
have been measured and are of the same order of
magnitude [26]. As a result, a large part of FpHal will be
consumed in a very fast [26,27] competing reaction with
FpK giving Fp2 (Scheme 12).
An alternative of a radical or a radical chain
mechanism for halo(acyl)rhenates formation does not
seem feasible at all. While the addition to CO group of a
metal carbonyl is typical for nucleophilic agents, it
would be quite an unusual reaction for the free radicals.
A much more likely reaction pathway for alkenyl
radicals would be the hydrogen atom abstraction from
the solvent, THF, giving I-H or II-H. Yet only small
amounts of I-H or II-H are formed in the absence of
proton donors. Furthermore, almost quantitative for-
mation of halo(acyl)rhenate V-Cl in the presence of PEt3
shows that there are no rhenium-centered radical
intermediates in this reaction. The CO ligand substitu-
tion in metal carbonyl radicals with phosphines is an
Alkenyl bromides I-Br and II-Br give higher yields of
NS products in the reaction with FpK than the alkenyl
chloride I-Cl (entries 1Á3, Table 1). The simplest though
/
not necessarily the only explanation is that a higher
steady-state concentration of the HME intermediates is
generated in the reaction with the more reactive
substrates (I-Br and II-Br), which increases the produc-
tion rate of NS product quadratically (Â
][FpHal]), while the increase in Fp2 production rate is
only first order in FpHal (ÂkFp [FpK][FpHal]).
/
kNS[Vinꢁ][F-
/
2
extremely fast reaction (k2Â
107 l molꢁ1 sꢁ1) [24],
which makes it a sort of mechanistic probe for such
radical intermediates [25].
/
3. Conclusions
Attack on halogen has turned out to be the most
favorable pathway for the reactions of metal carbonyl
anions, FpK and [Re(CO)5]Na, with polyfluorinated
alkenyl halides I-Cl, I-Br and II-Br. The interaction
between metal carbonyl halide and alkenyl carbanion
intermediates on the second reaction stage gives two
types of substitution products, different for iron and
rhenium. ‘‘Ordinary’’ s-alkenyl complexes are formed
with the iron carbonylate (Scheme 12); the rhenium
carbonyl halides reveal their ambident character and are
attacked by the alkenyl carbanion at the CO ligand
leading to halo(s-acyl)rhenate anions (Scheme 11). This
halophilic pathway of vinylic substitution may indeed be
of rare occurrence and require a super-halophilic
reagent such as metal carbonyl anion. Even soft
carbanions ([Ph2CN]ꢁ), which are considered especially
reactive halophiles [28], react with II-Br via ‘‘common’’
2.5. Comments on the reactions with FpK
One cannot but admit that in the case of FpK the
evidence available in support of the halophilic mechan-
ism is not as conclusive as in the reactions with
[Re(CO)5]Na. While the trapping of alkenyl carbanions
leaves little doubt as to their involvement in the NS
reaction, we have no direct proof for the other HME
intermediate*the FpHal. The presence of FpBr in the
/
reaction mixtures (entries 2,3 and 5, Table 1) certainly is
a point in favor of the proposed scheme, but cannot
serve as its final proof. Besides, it is not clear why FpCl
is not found among the reaction products, neither with
alkenyl chloride I-Cl nor with the aryl chlorides studied
earlier [5,6]. Nevertheless, the halophilic mechanism
remains the best possible interpretation for the observed
FpK chemistry (Scheme 12).
additionÁ
/
elimination mechanism (Scheme 10).
The relatively low yield of s-alkenyl Fp complexes I-
Fe and II-Fe in these reactions poses another problem,
especially in comparison to much higher yields of
halo(acyl)rhenates V-Cl, V-Br and VI. Reasonably, the
presence of a donor Cp ligand makes FpHal less reactive
5
The same may be presupposed from the higher n(CÅO) frequencies
observed for Re(CO)5Hal (Table 3) than for FpHal (Â
/
2005, 2045
cmꢁ1).

P.K. Sazonov et al. / Journal of Organometallic Chemistry 681 (2003) 59Á
/69
67
4. Experimental
4.1. Reaction of alkenyl halides with FpK
Preparation of metal carbonyl anion salts and their
reactions with alkenyl halides were carried out in ‘‘all-
fused’’ glassware using vacuum-line techniques. Less air-
sensitive materials, such as the reaction products, were
handled under argon atmosphere, when necessary.
THF, diethyl ether and dioxane were vacuum-trans-
ferred from sodium benzophenone ketyl.
Bromotrifluoroethylene was a gift from Dr. U.V.
Zeifman (INEOS, RAS, Moscow). The syntheses of I-Cl
and I-Br are described elsewhere [29]. Volatile reagents
and NMR standards were dried over the appropriate
drying agent (I-Cl, I-Br, II-Br, PEt3, C6H5CF3,
In a typical experiment, Â
halide was mixed (breaking the thin-walled glass sphere)
with Â
2 ml of FpK solution (0.06 mol lꢁ1) pre-cooled
in a cold bath (ꢁ50 8C). Immediately the solution
became darker, turning from orange-red of FpK to
dark cherry of Fp2. After 10Á15 min the reaction
/
0.15 mmol of alkenyl
/
/
/
mixture was allowed to reach r.t. and part of it was
filtered through Celite into NMR sample tube.
To isolate the volatile product I-H the preparative
experiment was carried out in diglyme instead of THF.
FpK was obtained from 197 mg Fp2 and 0.15 ml NaK2.8
in 10 ml THF, which was replaced with 1.5 ml diglyme,
and the PhCH(Et)CN ‘‘anion trap’’ (295 mg) was added.
C6H5F*
/
over sodium mirror, t-BuOH*over t-
/
The reaction mixture was cooled to ꢁ
/
50 8C and 290 mg
BuOK) and deoxygenated by several freeze-pump-
thaw cycles. Small portions required for a single
experiment were vacuum-transferred into thin-walled
glass spheres, which were sealed off. Portions of alkene
II-Br, a gas at room temperature (r.t.) (b.p.: 3 8C), were
prepared in a similar manner, except that they were
of alkene I-Cl was added. After 15 min at ꢁ
/
50 8C the
reaction mixture was allowed to reach r.t. The volatile
fraction (135 mg) was evaporated at r.t. and collected in
a cold trap. According to NMR and chromato-mass
spectra, it contained 35% of the starting I-Cl, 55% I-H,
small amounts of diglyme and THF. E-(?F3)3CCFÄ
CFH (I-H): 1?-NMR (acetone-d6, d, ppm): 8.188 dd
(JHÃF 71.6, 9.1 Hz). MS, m/z: 283 [Mꢂ
H]ꢂ (22%),
282 Mꢂ (87%), 263 [MꢁF]ꢂ (60%), 243 [Mꢁ
HF, ꢁ
/
measured out by vapor pressure (20Á
with THF and kept frozen in liquid nitrogen. FpK was
obtained quantitatively (95Á98%) by reductive cleavage
of the dimer Fp2 with excess of NaK2.8 alloy (0.10Á0.15
/300 Torr), diluted
ꢀ
/
/
/
/
/
/
F]ꢂ (19%), 213 (67%), 194 (86%), 181 (36%), 175 (94%).
The rest of the reaction mixture was evaporated in
vacuo at 80 8C, removing diglyme and the major part of
PhCH(Et)CN (part of III could have been lost at this
stage), and separated by column chromatography on
/
ml per 1 mmol of dimer) [30]. [Re(CO)5]Na was
prepared by the reduction of Re2(CO)10 with 0.5%
NaHg (30Á50% excess) and purified by the low-tem-
/
perature crystallization from THF [31].
NMR spectroscopy (1H and 19F) was used as a
primary tool for the analysis of reaction solutions,
allowing us to determine the yields of all the reaction
products, including volatile or unstable compounds. 1H-
NMR (400 MHz), 19F-NMR (376.3 MHz) and 13C-
NMR (100.57 MHz) spectra were obtained on a Varian
silica gel (60/200). The fist fraction eluted with hexaneÁ
/
Et2O (30:1) contained III (26 mg), which was purified by
plate chromatography on Silufol UV-254. E-
1
(?F3)3CCFÄ
tone-d6, d, ppm): 7.45Á
1H), 2.35 m (CH2, 1H), 1.091 t (CH3, JHÃH
3H). MS, m/z: 425 Mꢂ(65%), 397 [MꢁC2H4]ꢂ (92%),
356 (39%), 328 (100%), 177 (52%).
/CFC(C6H5)(C2H5)CN (III): ?-NMR (ace-
/
7.60 m (C6H5, 5H), 2.53 m (CH2,
3
ꢀ7.2 Hz,
/
/
VXR-400 spectrometer at r.t. C6H5F (dF ꢁ
/
112.75 ppm)
and PhCF3 (dF 61.96 ppm) were used as
ꢁ
/
internal standards both for fluorine chemical shift
reference and determination of the product yields,
which were calculated from the relative integral intensity
of the signals of the products and the signal of
internal standard. The signals in the spectra of
reaction solutions were referenced to the individual
components by comparison to the spectra of the isolated
compounds or with the literature data. Compounds I-
Fe, I-Re [32], II-Fe [23] and II-H have been described
previously and were identified spectroscopically without
isolation.
IR spectra of reaction mixtures and isolated products
were recorded using UR-20 spectrophotometer. Mass
spectra were recorded on an MS-890 spectrometer, with
electron impact ionization, 70 eV ionizing energy, the
direct inlet method, with a source temperature of
150 8C.
4.2. Reaction of alkenyl halides with [Re(CO)5]Na
Typically Â
mol lꢁ1) was mixed with all additives (if necessary) and
then with Â0.25 mmol of alkenyl halide at r.t. The
/
0.7 ml of [Re(CO)5]Na solution (Â
/0.3
/
reaction solution was immediately decanted into NMR
sample, which was sealed off, and the reaction progress
was monitored by 19F-NMR spectroscopy at r.t. Ha-
lo(acyl)rhenate
cis-[Z-(CF3)3CCFÄ
/
CF(CO)R-
e(CO)4Cl]Na (V-Cl) was isolated from the reaction
mixture obtained from 100 mg I-Cl and [Re(CO)5]Na
(1.25 ml of 0.34 mol lꢁ1 solution). The yellow solution
was filtered through Celite, THF was removed in vacuo,
and the residue was dissolved in 3 ml Et2O. The addition
of an excess of 18-crown-6 (Â
dioxane resulted in an immediate precipitation of yellow
crystals of the complex V-Cl×18-crown-6×2 dioxane (220
/150 mg) and 0.2 ml
/
/

68
P.K. Sazonov et al. / Journal of Organometallic Chemistry 681 (2003) 59Á69
/
mg). Calc. for C31H40ClF11NaO15Re: C, 33.66; H, 3.64.
Found: C, 33.52; H, 3.54%. The complex itself is highly
soluble in diethyl ether, but its solubility drops down
sharply in the presence of dioxane. The crystalline
(100%), 165 [C13H9]ꢂ (20%), 151 (20%), 77 [C6H5]ꢂ
(25%).
4.4. X-ray crystallographic data
complex of cis-[Z-(CF3)3CCFÄ
/
CF(CO)Re(CO)4Br]Na
(V-Br) with 18-crown-6 and two molecules of dioxane
(185 mg) was prepared similarly from I-Br (126 mg) and
[Re(CO)5]Na (1 ml of 0.34 mol lꢁ1 solution). Calc. for
C31H40BrF11NaO15Re: C, 32.36; H, 3.50; F, 18.16.
Found: C, 32.10; H, 3.66; F, 17.99%. Similarly, from
II-Br (200 mg) and 0.85 mmol [Re(CO)5]Na (not
crystallized; prepared from 326 mg Re2(CO)10 and 0.8
The crystal of complex VI with 18-crown-6 and
dioxane (C23H32BrF3NaO13Re, Mꢀ
/
862.59) is mono-
12.5403(18)
clinic, space group P21/n, at Tꢀ110 K; aꢀ
/
/
˚
˚
˚
A, bꢀ
Vꢀ
F(0 0 0)ꢀ
Total of 26 167 reflections were measured on a Bruker
SMART CCD 1000 diffractometer (l(MoÁKa), gra-
phite monochromator, v-scans, umax 278) and cor-
/
21.308(3) A, cꢀ
/
13.938(2) A, bꢀ
4, Dcalc
4.781 mmꢁ1
/
112.661(4)8,
3
/
3436.8(9) A , Zꢀ
/
ꢀ ,
1.667 Mg mꢁ3
/
˚
/
1688, mꢀ
/
.
ml 0.5% NaHg in 8 ml THF; estimated yield :
[30,31]) was obtained the orange-yellow complex (VI)
cis-[CF2ÄCF(CO)Re(CO)4Br]Na×18-crown-6×dioxane
/
85%
/
ꢀ
/
/
/
/
rected for Lorentz and polarization effects and for
absorption [33]. The structure was determined by direct
methods and refined by full-matrix least-squares tech-
nique with anisotropic thermal parameters for non-
hydrogen atoms. The positions of one carbonyl group
and Br atom are statistically disordered with occupan-
cies 0.6:0.4. The position of carbonyl group with
occupancy 0.4 was refined isotropically. The hydrogen
atoms were placed in calculated positions and refined in
riding model with fixed thermal parameters. The final
(450 mg). Calc. for C23H32BrF3NaO13Re: C, 32.03; H,
3.74; Br, 9.26; F, 6.61. Found: C, 32.40; H, 3.82; Br,
10.08; F, 5.93%. Crystalline complexes of halo(acyl)rhe-
nates with dioxane and 18-crown-6 are thermally stable
at r.t. and can be handled in the open air for short
periods of time (hours), but are oxidized being exposed
to air for several weeks. Crystals of VI×
dioxane suitable for X-ray diffraction were grown by
solvent diffusion in Et2OÁdioxane system.
/
18-crown-6×
/
/
cis-[t-BuO(CO)Re(CO)4Cl]Na (VII) was obtained
with the purpose of identifying its bands in the IR
spectra of reaction solutions. The solution of t-BuONa
(25 mg) in 2 ml THF was added to Re(CO)5Cl (95 mg)
dissolved in 5 ml THF. The product was characterized
in solution by IR and 13C-NMR spectra.
divergence factors were R1ꢀ
/
0.0675 for 4515 indepen-
0.1863 for all
dent reflections with I ꢀ2s(I) and wR2ꢀ
/
/
7421 independent reflections. All calculations were
carried out by use of the SHELXTL PLUS (PC Version
5.0) program [34].
Similarly for the purpose of identification t-
BuOCF2CFHBr (IV) was obtained by the reaction of
II-Br (0.74 mmol in 0.15 ml THF) with an excess of t-
BuOH in the presence of t-BuOK (12.7 mg) in THF (2
ml) at r.t. and characterized by 19F-NMR.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Center, CCDC No. 194840 for VI×
dioxane. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union
/
18-crown-6×
/
4.3. Reaction of CF2Ä
/
CFBr with [Ph2CCN]ꢁ carbanion
Road, Cambridge CB2 1EZ, UK (Fax: ꢂ44-1223-
336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
/
4.3.1. Reaction of II-Br with [Ph2CCN]Na: the isolation
of Ph2C(CN)CFÄCFBr (VIII)
/
Ph2CHCN (112 mg) dissolved in 2 ml THF was
treated with excess of NaH. When vigorous liberation of
gas ceased the bright yellow solution was filtered and II-
Br (0.8 mmol) was added by vacuum transfer. After 30
min at r.t. the solution became colorless and a crimson
colored gel formed. Reaction mixture was placed on a
Acknowledgements
This work was supported by the Russian Foundation
for Basic Research (Project Nos.: 00-15-97406; 00-03-
32807) and by the program ‘‘The State support of the
integration of High School with Fundamental Science’’
(Project AO115).
column with silica gel and eluted with petroleum etherÁ
/
CH2Cl2 mixture, gradually increasing the solvent ratio
from 5:1 to 1:2. The fraction corresponding to the first
colorless band was collected yielding 135 mg
Ph2C(CN)CFÄ
/
CFBr (VIII). Calc. for C16H10BrF2N:
C, 57.51; H, 3.02; N, 4.19. Found: C, 57.54; H, 3.08;
N, 4.47%. MS, m/z (relative to 79Br): 333 [M]ꢂ (1%),
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/
Br]ꢂ (55%), 234 [Mꢁ
/
Br, ꢁ
/
F]ꢂ (40%), 177
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/
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/
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