Transmetalation of Pentafluorophenylmercury Derivatives with Organylmagnesium Bromides

Article abstract of DOI:10.1134/S1070363219070090

The reactions of pentafluorophenylmercury derivatives with organomagnesium compounds have been studied. The interaction of pentafluorophenylmercury chloride with RMgBr (R = Et, Ph) has afforded diphenyl- and diethylmercury or phenylmercury chloride, besides the expected product (C₆F₅HgR). The results have been explained by the transmetalation of C₆F₅HgR with the Grignard reagent, followed by the reaction of the resulting C₆F₅MgX (X = Br, C₆F₅) with pentafluorophenylmercury chloride. Transmetalation of (C₆F₅)₂Hg with organylmagnesium bromides has led to the formation of C₆F₅MgX and R₂Hg.

Full text of DOI:10.1134/S1070363219070090

ISSN 1070-3632, Russian Journal of General Chemistry, 2019, Vol. 89, No. 7, pp. 1406–1408. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Obshchei Khimii, 2019, Vol. 89, No. 7, pp. 1047–1050.
Transmetalation of Pentafluorophenylmercury Derivatives
with Organylmagnesium Bromides
V. V. Bardina*
a N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences,
ul. Akademika Lavrentieva 9, Novosibirsk, 630090 Russia
*e-mail: bardin@nioch.nsc.ru
Received November 1, 2018; revised November 14, 2018; accepted June 4, 2019
Abstract—The reactions of pentafluorophenylmercury derivatives with organomagnesium compounds have been
studied. The interaction of pentafluorophenylmercury chloride with RMgBr (R = Et, Ph) has afforded diphenyl-
and diethylmercury or phenylmercury chloride, besides the expected product (C6F5HgR). The results have been
explained by the transmetalation of C6F5HgR with the Grignard reagent, followed by the reaction of the resulting
C6F5MgX (X = Br, C6F5) with pentafluorophenylmercury chloride. Transmetalation of (C6F5)2Hg with organyl-
magnesium bromides has led to the formation of C6F5MgX and R2Hg.
Keywords: transmetalation, bis(pentafluorophenyl)mercury, diethylmercury, diphenylmercury, ethylmagnesium
bromide, phenylmagnesium bromide
DOI: 10.1134/S1070363219070090
One of the approaches to the synthesis of asym-
metrical organyl mercury derivatives R1HgR2 is a halogen
(X) substitution in the R1HgX derivatives under the ac-
tion of a nucleophile R2MgX. For example, the interac-
tion of isobutylmercury chloride with RMgBr (R = Alk,
CH=CH2, C≡CH, Ph, C6Cl5) [1] has afforded a series
of asymmetrical derivatives (CH3)2CHCH2HgR (yield
50–80%) and the R1HgR2 compounds (R1, R2 = Alk,
Ar). The latter ones have been prepared via two ways:
the reactions of R1MgBr with R2HgBr or R1HgBr with
R2MgBr [2]. Polyfluorinated aromatic derivatives of
mercury ArFHgR have been prepared by the reaction of
RHgX (R = Me, Et, Ph) with nucleophiles ArFM (ArF =
C6F5, 2,3,4,5-C6F4H; M = Li, MgX) [3–6]. This method
is not advantageous due to low nucleophilicity of ArFM
and their thermal instability.
by the reaction of pentafluorophenylmercury chloride 1
with organomagnesium compounds. The reaction with
EtMgBr, besides the expected pentafluorophenyl(ethyl)-
mercury 2a, unexpectedly led to the formation of a mixture
of di(pentafluorophenyl)mercury 3, diethylmercury 4a,
and pentafluorobenzene 5 (Scheme 1). A similar mixture
was obtained in the reaction of compound 1 with PhMgBr.
The increase in the reaction duration from 3 to 19 h
(R = Et) did not lead to the conversion of pentafluoro-
phenyl(ethyl)mercury 2a into compounds 3 and 4a, which
ruled out the formation of the latter via symmetrization
of the arylalkylmercury 2a. Likely, transmetalation of
C6F5HgR occurred under the action of the Grignard
reagent with the formation of C6F5MgX, which was not
observed in the case of the above-mentioned arylmercury
derivatives [1, 2].
In this study, we attempted an alternative approach to
the synthesis of mercury derivativesArFHgR exemplified
Indeed, the interaction of C6F5HgEt with EtMgBr led to
the formation of pentafluorophenylmagnesium bromide 6,
Scheme 1.
Et2OTHF
22oC, 3 h
C6F5HgCl + EtMgBr
C6F5HgEt + (C6F5)2Hg + C6F5H + Et2Hg
1
2a
5
4a
3
Et2OTHF
22oC, 5 h
C6F5HgCl + PhMgBr
C6F5HgPh + (C6F5)2Hg + PhHgCl
2b
1
3
4b
1406

TRANSMETALATION OF PENTAFLUOROPHENYLMERCURY DERIVATIVES
1407
Scheme 2.
Et2O
H2O
C6F5MgBr + (C6F5)2Mg + R2Hg
C6F5HgR + RMgBr
5 + 4a, 4b
22oC, 3 h
6
4a, 4b
7
2a, 2b
R = Et (a), Ph (b).
Scheme 3.
Et2O
H2O
C6F5MgBr + (C6F5)2Mg + C6F5HgR + R2Hg
4a, 4b
2 + 5
(C6F5)2Hg + RMgBr
22oC, 3 h
6
2a, 2b
7
3
R = Et (a), Ph (b).
bis(pentafluorophenyl)magnesium 7, and diethylmercury
(Scheme 2). Similarly, the reaction of C6F5HgPh with
PhMgBr gave compounds 6, 7, and diphenylmercury 4b
(19F and 199Hg NMR). Hydrolysis of the reaction mixture
led to conversion of products 6 and 7 into pentafluoro-
benzene (Scheme 2).
EXPERIMENTAL
(C6F5)2Hg, C6F5HgPh [3], C6F5HgCl, and C6F5HgEt
[6] were synthesized by the known procedures. The yield
of the fluorinated products was determined by 19F NMR
spectroscopy with internal reference C6F6 or C6H5F. The
yield of the organomercury products was determined
by the 199Hg NMR spectroscopy by comparison of the
intensity of the considered signal with that of pentaf-
luorophenylmercury compound, the content of which
was determined from the 19F NMR spectroscopy. The
NMR data for compounds 6 and 7 [7], 5 [8, 9] (19F), and
4a–4c [10] (199Hg) coincided with the reference ones. The
operations were performed under dry argon atmosphere.
Interestingly, the treatment of an equimolar mix-
ture of compounds 2a and 2b with 1.3 eq. of
EtMgBr in ether resulted in complete conversion of
C6F5HgPh, while the amount of C6F5HgEt remain-
ing unchanged (19F NMR). That fact evidenced
significant effect of the substituent R in the starting
C6F5HgR on the transmetalation rate. Nevertheless,
di(pentafluorophenyl)mercury, as compounds 2a, 2b,
underwent to transmetalation under the action of RMgBr.
The reaction occurred within 3 h and led to the formation
of magnesium derivatives 6 and 7 as well as the corre-
sponding organomercury compounds 2a, 4a and 2b, 4b
(Scheme 3).
NMR spectra were recorded using BrukerAvance 300
(19F, 282.40 MHz) andAvance 600 (199Hg, 107.51 MHz)
instruments.
Reaction of pentafluorophenylmercury 1 with
RMgBr. a. R = Et. 0.54 M. solution of EtMgBr in
diethyl ether (1.0 mL, 0.54 mmol) was added to a
stirred solution of compound 1 (175 mg, 0.43 mmol)
in 2.5 mL of THF. The obtained solution was kept
at 22°C during 5 h. A mixture of compounds 2a
(0.19 mmol), 3 (0.16 mmol), diethylmercury (0.14 mmol),
and pentafluorobenzene (0.04 mmol) was obtained (19F
and 199Hg NMR data).
More comprehensive analysis of the reasons for the
difference in the reactivity of perfluorinated organomer-
cury compounds towards the Grignard reagents from
that of the non-fluorinated analogs demands additional
experiments involving polyfluorinated derivatives of
alkenyl- and alkynylmercury.
In summary, in contrast to the known method of
preparation of asymmetrical mercury compoundsArHgR
and their fluorinated analogs ArFHgR from ArM (ArFM)
and RHgX, the alternative approach based on the inter-
action of organomagnesium nucleophiles RMgBr with
pentafluorophenylmercury derivatives gave a mixture
of symmetrical and asymmetrical products C6F5HgR,
(C6F5)2Hg, and R2Hg (R = Alk, Ar). The reaction in-
volved perfluoromagnesium compounds formed via
transmetalation of perfluoroarylmercury compounds with
the Grignard reagents.
b. R = Ph. The reaction was performed similarly using
182 mg (0.45 mmol) of compound 1 in 1 mL of THF and
0.51 M. solution of PhMgBr in diethyl ether (1.0 mL,
0.51 mmol); reaction duration 3 h.Amixture of compounds
2b (0.31 mmol), 3 (0.09 mmol), and 4c (0.10 mmol)
was obtained (19F and 199Hg NMR data).
Reaction of pentafluorophenyl(ethyl)mercury 2a
with EtMgBr. 0.54 M. solution of EtMgBr in diethyl
ether (1.2 mL, 0.64 mmol) was added to a stirred solu-
tion of compound 2a (225 mg, 0.56 mmol) in 2 mL of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 7 2019

1408
BARDIN
diethyl ether. The obtained solution was kept at 22°C
during 5 h. A mixture of compounds 2a (0.09 mmol), 6
(0.34 mmol), 7 (0.10 mmol), and 4а (0.40 mmol) was
obtained (19F and 199Hg NMR data). 1 mL of 5% HCl
was added to the obtained solution, the organic phase
was separated and dried over MgSO4. The solution con-
tained C6F5HgEt (0.09 mmol) and C6F5H (0.33 mmol)
(19F NMR data).
b. R = Ph. The reaction was performed similarly us-
ing a solution of 144 mg (0.27 mmol) of compound 3 in
1 mL of diethyl ether and 0.51 M. solution of PhMgBr
in diethyl ether (1.0 mL, 0.51 mmol); reaction dura-
tion 3 h. A mixture of compounds 2b (0.14 mmol), 6
(0.20 mmol), 7 (0.06 mmol), and 4b (0.09 mmol) was
obtained. Upon keeping the mixture during 48 h and
hydrolysis, the products contained compounds 2b
(0.14 mmol) and 5 (0.27 mmol) (19F NMR data). The
presence of compound 4a was not verified.
Reaction of pentafluorophenyl(phenyl)mercury 2b
with PhMgBr. 0.51 M. solution of PhMgBr in diethyl
ether (1 mL, 0.51 mmol) was added to a stirred solution of
compound 2b (213 mg, 0.47 mmol) in 1.5 mL of diethyl
ether. The obtained solution was kept at 22°C during 3 h.
Amixture of compounds 2b (0.18 mmol), 6 (0.19 mmol),
7 (0.09 mmol), and 4b (0.52 mmol) was obtained (19F
and 199Hg NMR data). 1 mL of 5% HCl was added to the
obtained solution, the organic phase was separated and
dried over MgSO4. The solution contained C6F5HgPh
(0.16 mmol) and C6F5H (0.28 mmol) (19F NMR data).
Author acknowledges the Multi-Access Chemical
Research Center of Siberian Branch of RussianAcademy
of Sciences for spectral measurements.
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
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