Novel sterically hindered ferrocenyl-phosphonium salt

Article abstract of DOI:10.1080/10426507.2019.1630406

New sterically hindered ferrocenyl containing phosphonium salt was synthesized in two steps starting from ferrocene. To avoid halogen contamination di-tert-butylferrocenylphosphine was quaternized with methyl bis(trifluoromethanesulfonyl)imide directly. Obtained phosphonium salt was characterized with several physical methods.

Full text of DOI:10.1080/10426507.2019.1630406

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: https://www.tandfonline.com/loi/gpss20
Novel sterically hindered ferrocenyl-phosphonium
salt
Liliya Kadyrgulova, Vadim Ermolaev, Leysan Gilmanova & Vasiliy Miluykov
To cite this article: Liliya Kadyrgulova, Vadim Ermolaev, Leysan Gilmanova & Vasiliy Miluykov
(2019): Novel sterically hindered ferrocenyl-phosphonium salt, Phosphorus, Sulfur, and Silicon and
the Related Elements, DOI: 10.1080/10426507.2019.1630406
To link to this article: https://doi.org/10.1080/10426507.2019.1630406
Published online: 17 Jun 2019.
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PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
https://doi.org/10.1080/10426507.2019.1630406
Novel sterically hindered ferrocenyl-phosphonium salt
Liliya Kadyrgulova, Vadim Ermolaev, Leysan Gilmanova, and Vasiliy Miluykov
Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center, Russian Academy of Sciences, Kazan, Russian Federation
ABSTRACT
ARTICLE HISTORY
Received 20 May 2019
Accepted 7 June 2019
New sterically hindered ferrocenyl containing phosphonium salt was synthesized in two steps
starting from ferrocene. To avoid halogen contamination di-tert-butylferrocenylphosphine was
quaternized with methyl bis(trifluoromethanesulfonyl)imide directly. Obtained phosphonium salt
was characterized with several physical methods.
KEYWORDS
Phosphonium salt; steric
hindrance; bis(trifluorome-
thanesulfonyl)imide-anion;
NTf2; ferrocene
GRAPHICAL ABSTRACT
Introduction
formation of dilithiated compounds and to obtain single
monolithium ferrocene, the reaction has been carried out in
diethyl ether (Scheme 2).
An addition of tert-butyllithium to a solution of ferrocene
and t-BuOK[13] in diethyl ether results in a color change of
the solution from brown to orange, indicating that the Fc-H
was lithiated. Subsequent slow dropwise addition of di(tert-
butyl)chlorophosphine 1 leads to the precipitation of orange
di(tert-butyl)ferrocenylphosphine 3.
The desired salt was obtained by direct alkylation with
MeNTf2 in one step. Initial imide 4 was synthesized accord-
ing to known method.[9] (Scheme 3) Iodomethane was
added to obtained in situ RTIL [Ag(MeCN)4]2[Ag(NTf2)3] at
ꢀ78 ꢁC and left stirring overnight at room temperature.
At the next step imide 4 was added to phosphine 3 dis-
solved in toluene (Scheme 4).
Sterically hindered phosphonium salts became an important
sub-class of ionic liquids over the past decade, an integral
part of these industrially relevant solvents.[1,2] Thus phos-
phonium salts as well as their functionalized analogs have
found application as Pd nanocatalyst stabilizers[3] in
Suzuki[4] and Sonogashira[5] cross-coupling reactions.[6]
Moreover it was found that structure and texture of bulky
phosphonium salt allow to apply it as a binder for paste
electrodes to study redox properties of insoluble com-
pounds.[7,8] The synthesis and physicochemical properties
especially redox activity of phosphonium salts containing
ferrocenyl fragment are a very intriguing assignment.[9,10] In
present work synthesis of ferrocene containing salt utilized
direct quaternization reaction with MeNTf2 was discussed.
Since imide is less active than methyl iodide, the reaction
mixture was stirred at 50 ꢁC for 12 hours. Unreacted phos-
phine was washed sequentially with petroleum ether and
Et2O. Solvents residue was removed in vacuo. Resulting
product was obtained as ocher crystalline powder.
Results and discussion
Results and discussion
In 31P NMR spectrum of compound 5 (Figure S1), one
signal is observed at 49.04 ppm, in the same region as the
Di(tert-butyl)ferrocenylphosphine has been prepared by the
most common way, namely the Fc lithiation with tert-butyl-
lithium and subsequent reaction with di(tert-butyl)chloro-
phosphine 1.[11]
The starting substrate di(tert-butyl)chlorophosphine has
been obtained by the reaction of an excess of tert-butylmag-
nesium chloride with phosphorus trichloride followed by
separation of the product from the reaction mixture by dis-
tillation under reduced pressure (Scheme 1).[12]
1
signal of bulky phosphonium salts appears.[14] In H NMR
spectrum of compound 5 (Figure S2), the protons of tert-
butyl group appear as a doublet at 1.48 ppm. The protons of
the methyl group form a doublet at 2.30 ppm. The signal of
protons in the unsubstituted cyclopentadienyl ring of ferro-
cene is present as a five-proton singlet at 4.44 ppm and two
multiplets with an intensity of two protons, corresponding
to the signals of the monosubstituted cyclopentadienyl
Lithiation with tert-butyllithium usually results in a
mixture of mono- and 1,1-dilithidated derivatives. To avoid fragment of ferrocene are exist at 4.67 and at 4.83 ppm.
CONTACT Vadim Ermolaev
ermolaev@iopc.ru
Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center, Russian Academy of
Sciences, Arbuzov str., 8, 420088, Kazan, Russian Federation.
ß 2019 Taylor & Francis Group, LLC

2
L. KADYRGULOVA ET AL.
Scheme 1. Preparation of di(tert-butyl)chlorophosphine.
Scheme 4. Synthesis of di-tert-butyl(ferrocenyl)methylphosphonium bis(trifluor-
omethanesulfonyl)imide 5.
purification. Mass Electrospray ionization mass spectrometry
(ESI-MS) was performedon the AmazonX mass spectrometer
(Bruker Daltonik GmbH, Bremen, Germany). The measure-
ments were carried out in the positive/negative ion detection
mode in the m/z range from 100 to 1000. The voltage on
the capillary was 140 V. Data was processed using the
DataAnalysis 4.0 program (Bruker Daltonik GmbH,
Bremen, Germany).
Scheme 2. Preparation of di(tert-butyl)ferrocenylphosphine 3.
The procedure for the synthesis of di(tert-butyl)ferroce-
nylphosphine (3) In a two-necked Schlenk vessel equipped
with a magnetic stirrer, ferrocene (10.3 mol, 1.923 g) and t-
BuOK (1.55 mmol, 0.173 g) were placed, the mixture was
dissolved in 150 ml diethyl ether. The solution was cooled
down to ꢀ78 ꢁC. A solution of t-BuLi (10.3 mmol) was
added over 10-15 minutes. Stirring of the reaction mixture
was carried out at ꢀ70ꢁ C. for 1 hour. An orange precipitate
of di(tert-butyl) ferrocenylphosphine was formed. Next the
reaction mixture was brought to 0 ꢁC and t-Bu2PCl
(5.15 mmol, 0.98 ml) was added dropwise. After the comple-
tion of the reagent adding, the cooling bath was removed,
the reaction mixture was allowed to reach room tempera-
ture. After Et2O was removed in vacuum, the residual was
dissolved in 200 ml of the petroleum ether and filtered
through short silica column. The solvent removal results in
the dark-brown solid 2.431 g (71%). 31P NMR (162 MHz) d,
ppm: 28.5 (s).
Scheme 3. Synthesis of methyl bis(trifluoromethanesulfonyl)imide 4.
Electrospray ionization mass-spectrometry (ESI-MS) of
phosphonium salt 5 was performed (Figure S3). The spec-
trum clearly revealed the peaks of cationic part and bis(tri-
fluoromethanesulfonyl)imide anion.
The phosphonium salt 5 melts at ꢂ146 ꢁC with sequential
decomposition that could be clearly observed from TG-DSC
data (Figure S4) as well as from direct melting point meas-
urement. Despite the presence of NTf2-anion, compound 5
has a high melting point due to the compact structure of
the cation.
The procedure for the synthesis of methyl bis(trifluoro-
methanesulfonyl)imide (4) 2.41 g silver nitrate (14.2 mmol,
1.11 eq.) in 4 ml acetonitrile and added to 4.09 g lithium
bis(trifluoromethanesulfonyl)imide (14.2 mmol, 1.11 eq.) in
4 ml acetonitrile. The reaction mixture was stirred for 2 h at
room temperature. The formation of white precipitate was
observed. The solvent was removed in vacuo. The in situ
generated [Ag(MeCN)4]2[Ag(NTf2)3] was cooled down to
ꢀ78 ꢁC and 1.82 g methyl iodide (12.8 mmol, 1.0 eq.) was
added. The reaction mixture was stirred within 12 h at room
temperature. The crude product was purified by vacuum
distillation. Yield 2.38 g (63%) B.p. ¼ 78-80 ꢁC/200 mm Hg.
The procedure for the synthesis of di-tert-butyl(ferroce-
nyl)methylphosphonium bis(trifluoromethanesulfonyl)i-
mide (5) 0.69 g methyl bis(trifluoromethanesulfonyl)imide
(2.32 mmol) was added to 0.731 g di(tert-butyl)ferrocenyl-
phosphine (2.2 mmol) dissolved in 10 ml toluene. The reac-
tion mixture was stirred at 50ꢁ‘ for 12 h. The crude
product was washed with 20 ml petroleum ether twice and
with 20 ml diethyl ether twice. The precipitate was filtered
and the solvent residues was removed in vacuo. Yield
Conclusions
We have successfully synthesized new di-tert-butyl(ferro-
cenyl)-methylphosphonium bis(trifluoro-methanesulfonyl)i-
mide from phosphine and MeNTf2 directly. Obtained
compound was characterized by NMR, TG-DSC, ESI-MS.
Experimental
All the work related to the preparation of the starting sub-
strates, the synthesis and the workup of products, was car-
ried out in an inert atmosphere using standard Schlenk
apparatus. All solvents and purchased reagents were absolute
by the appropriate methods, mainly by distillation in an
inert atmosphere. NMR spectra were recorded with multi-
nuclear spectrometer Bruker AVANCE-400 (400.1 MHz
(1H), 100.6 MHz (13C) and 162.0 MHz (31P)). Chemical
shifts are given in parts per million relative to SiMe4 (1H,
internal solvent) and 85% H3PO4 (31P, external). Thermo
gravimetric analysis was performed on the NETZSCH STA
449F3 with a heating rate 10 K per minute up to 400 ꢁC in
an argon atmosphere. Melting points was measured with
Stuart SMP30 (Stuart, Cole-Parmer, UK). t-BuLi (“1.6 M sol-
1
1.100 g (76%). M.p. ¼ 146 ꢁC. H NMR (400 MHz, CDCl3),
d, ppm: 1.48 (d, 18H,3JPH ¼ 15.66 Hz, P(C(CH3)3)2), 2.30
ution”) (by Sigma Aldrich) were used without a preliminary (d, 3H,2JPH ¼ 11.74 Hz, P-CH3), 4.44 (s, 5H, HCp), 4.67 (s,

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
3
2H, HCp), 4.83 (s, 2H, HCp). 31P NMR (162 MHz, CDCl3), d,
ppm: 49.04 (s). ESI-MS m/z 345.2 (Mþ - H), 279.8 (M-).
Phosphonium Ionic Liquids: Synthesis and Application.
Phosphorus, Sulfur, Silicon Relat. Elem. 2015, 190, 899–901.
DOI: 10.1080/10426507.2014.993759.
[7] Khrizanforov, M. N.; Arkhipova, D. M.; Shekurov, R. P.;
Gerasimova, T. P.; Ermolaev, V. V.; Islamov, D. R.; Miluykov,
V. A.; Kataeva, O. N.; Khrizanforova, V. V.; Sinyashin, O. G.;
Budnikova, Y. H. Novel Paste Electrodes Based on
Phosphonium Salt Room Temperature Ionic Liquids for
Studying the Redox Properties of Insoluble Compounds//. J.
Solid State Electrochem. 2015, 19, 2883–2890. DOI: 10.1007/
s10008-015-2901-0.
Funding
The authors are grateful to the Assigned Spectral-Analytical Center of
FRC Kazan Scientific Center of RAS for technical assistance
in research.
[8] Khrizanforov, M. N.; Shekurov, R. P.; Ermolaev, V. V.;
Arkhipova, D. M.; Miluykov, V. A.; Kataeva, O. N.;
Khrizanforova, V. V.; Budnikova, Y. H. Novel Phosphonium
Salt for Paste Electrode to Study the Redox Properties of
Insoluble Compounds. Phosphorus, Sulfur, Silicon Relat. Elem.
2016, 191, 1611–1612. DOI: 10.1080/10426507.2016.1217215.
[9] Ku€bler, P.; Sundermeyer, J. Ferrocenyl-Phosphonium Ionic
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