1,1′-Diphenyl-bis-germatrane with persistent radical cation

Article abstract of DOI:10.1016/j.mencom.2020.09.004

Bis-phenyl derivative of a novel family of bis-metallatranes, 1,1′-diphenyl-bis-germatrane, was synthesized and characterized. One-electron oxidation of this compound is electrochemically and chemically reversible providing a persistent radical cation.

Full text of DOI:10.1016/j.mencom.2020.09.004

Mendeleev
Communications
Mendeleev Commun., 2020, 30, 567–568
1,1'-Diphenyl-bis-germatrane with persistent radical cation
Vitalijs Romanovs,*a Daria M. Vakhrusheva,b,c Irina V. Krylova,b Badma N. Mankaev,d
Anna Ya. Kozmenkova,b Mikhail A. Syroeshkin,*b Mikhail P. Egorovb and Viatcheslav V. Jouikov*e
a Latvian Institute of Organic Synthesis, LV-1006 Riga, Latvia. E-mail: vitalijs.romanovs@inbox.lv
b N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow,
Russian Federation. E-mail: syroeshkin@ioc.ac.ru
c Higher Chemical College of the Russian Academy of Sciences, D. I. Mendeleev University of Chemical
Technology of Russia, 125047 Moscow, Russian Federation
d Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation
e University of Rennes, 35042 Rennes, France. E-mail: vjouikov@univ-rennes1.fr
DOI: 10.1016/j.mencom.2020.09.004
O
O
NꢄCꢅꢂCꢅ2Oꢅꢃ2ꢆꢁ
EtOꢅ
NEtꢁ
PhꢀeClꢁ
PhꢀeꢂOEtꢃꢁ
Ph ꢀe
N
ꢀe Ph
O
Bis-phenyl derivative of a novel family of bis-metallatranes,
1,1'-diphenyl-bis-germatrane, was synthesized and
characterized. One-electron oxidation of this compound is
electrochemically and chemically reversible providing a
persistent radical cation.
O
O
O
ꢇ000 ꢇ200 ꢇꢈ00 ꢇꢉ00 ꢇꢊ00 2000
EꢋmV vs. AgꢋAgCl
Keywords: organogermanium compounds, metallatranes, redox properties, radical cations, cyclic voltammetry, actuator systems.
EtOH
NEt3
N[CH(CH2OH)2]3
Germatranes, cage compounds with trigonal bipyramid
coordination of Ge and an intramolecular 3c–4e bonding, are
known for half a century.1 Redox reactions of metallatranes and
the products of their one-electron oxidation, radical cations,
attract attention for surface modification, spin writing and as
possible actuator systems.2,3 With this, redox-related
experimental and theoretical properties of germatranes are
contradictory,3 so correct description of the type and localization
of HOMO in such systems requires a special attention.4,5 In view
of development of hyperbonded systems beyond 3c–4e and the
perspectives of their applications, germatranes and recently
prepared bis-germatranes5 are of an acute interest from both
theoretical and experimental points of view; stabilizing their
radical cations being another special issue. In this preliminary
report, we present synthesis of 1,1'-diphenyl-bis-germatrane and
generation of its persistent radical cation.
PhGeCl3
PhGe(OEt)3
2
3
+
O
O
O
O
–e–
e–
Ph Ge
Ge
Ph Ge
O
Ge
Ph
N
Ph
N
O
O
O
O
O
O
O
+
1
1
Scheme 1
Redox properties of bis-germatrane 1 were assessed using
cyclic voltammetry at a glassy carbon (GC) disc electrode in a
0.1 m Bu4NPF6/MeCN solution. The voltammograms recorded
at the scan rates from 0.05 to 1 V s–1 (Figure 2) demonstrated a
reversible one-electron oxidation leading to formation of radical
ꢄaꢆ
The title compound was synthesized by ethoxylation of
(trichloro)phenylgermane 1 followed by reaction of thus formed
(triethoxy)phenylgermane with tris(1,3-dihydroxyprop-2-yl)amine
(Scheme 1, for the preparation of the polyol amine see ref. 6).†
ꢃ00
ꢂ0
ꢁ0
ꢀ0
20
0
The obtained 1,1'-diphenyl-bis-germatrane
1
was
characterized by several instrumental techniques (for details, see
Online Supplementary Materials). In particular, Figure 1 shows
the polyisotopic HRMS (ESI-MS) spectrum with a specific
isotope cluster for compounds containing two germanium atoms.
ꢇ2ꢁ
ꢇ2ꢂ
ꢇꢈ0
ꢇꢈ2
mꢉz
ꢇꢈꢀ
ꢇꢈꢁ
ꢇꢈꢂ
ꢇꢀ0
ꢄbꢆ
ꢃ00
†
Triethylamine (0.43 g, 4.3 mmol) and EtOH (0.14 g, 4.3 mmol) were
ꢂ0
ꢁ0
ꢀ0
20
0
added to a solution of PhGeCl3 (0.30 g, 1.16 mmol) in light petroleum
(10 ml) at 0 °C. The mixture was stirred at 0 °C for 30 min, and then at
40–45 °C for 2 h. After cooling to room temperature, Et3N·HCl was
filtered off and washed with light petroleum. Tris(1,3-dihydroxyprop-2-
yl)amine (0.14 g, 0.58 mmol) in MeOH (5 ml) was added to the combined
filtrate at 0 °C; the mixture was stirred for 30 min and then at room
temperature for 8 h. The solvent was evaporated to a half, the solution
was cooled to 0 °C, and the precipitated 1,1'-diphenyl-bis-germatrane 1
was filtered off as amorphous white solid (yield, 0.14 g, 45%).
ꢇ2ꢁ
ꢇ2ꢂ
ꢇꢈ0
ꢇꢈ2
mꢉz
ꢇꢈꢀ
ꢇꢈꢁ
ꢇꢈꢂ
ꢇꢀ0
Figure 1 HRMS (ESI-MS) spectrum of 1,1'-diphenyl-bis-germatrane 1
(the molecular ion formation upon H+-ionization): (a) experimental and
(b) calculated.
© 2020 Mendeleev Communications. Published by ELSEVIER B.V.
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
– 567 –

Mendeleev Commun., 2020, 30, 567–568
for bis-germatrane 1 might reflect similar intramolecular
5
4
interactions, supposedly corresponding to a 5c–6e system,
though a more detailed analysis is complicated by the absence of
Ep of phenyl germatrane so far. Nevertheless, some estimation
can be done using the Epox of phenyl silatrane, which is reported
to be the same as that of 3-thienyl silatrane and approximately
100 mV more positive than Ep of methyl silatrane.9 By analogy,
from Ep of 3-thienyl and methyl germatranes (1.65 and 1.5 V,
respectively), the Ep of phenyl germatrane is expected to be
about 1.6–1.65 V. The Ep’s of other aryl germatranes also
conform this value.3 In this rough estimation, Ep of the new bis-
germatrane 1 is slightly lower than expected. Furthermore, Ep of
2-(3-bromothienyl)-bis-germatrane (1.975 V vs. SCE, ref. 5) is
also slightly lower (applying –0.31 V reference electrode
conversion) than that of its germatrane analogue (1.705 vs.
Ag/AgNO3, ref. 3). With a substituent-located HOMO in these
compounds, the formal electron-donor effect of bis-atrane cage
appears stronger than that of a simple atrane, albeit an opposite
trend would be expected supposing the participation of N lone
pair in two N®Ge dative interactions in bis-germatranes. Further
work on structural characterization and electronic properties of
this new class of carcass systems and of their radical cations is
forthcoming.
3
2
ꢁ0 µA
1
ꢀ000 ꢀ200 ꢀꢁ00 ꢀꢂ00 ꢀꢃ00 2000
EꢄmV vs. AgꢄAgCl
Figure 2 Cyclic voltammograms of 3×10–3
germatrane 1 at a GC disc electrode (1.7 mm) in 0.1 m Bu4NPF6 /MeCN at
scan rates of (1) 0.05, (2) 0.1, (3) 0.2, (4) 0.5 and (5) 1.0 V s–1. Temperature
298 K.
m
1,1'-diphenyl-bis-
cation 1 + (see Scheme 1). Within the given scan rate range, the
·
behaviour of this reversible one-electron system is comparable
to that of a standard ferrocene solution under the same conditions,
showing similar forward and reverse peak currents with the 1:1
ratio. Extrapolating Ep’s to zero peak currents allows one to
estimate the formal potential of this bis-germatrane 1 as
E0’ = 1.506 V. The separation of anodic and cathodic peak
potentials is DEp = 0.063 V, which is very close to 0.059 V, a
theoretical value for electrochemically reversible reactions.‡,7–9
The data on electrooxidation of phenylgermanium derivatives
are quite scarce, but from few electrochemical studies on phenyl
mono-germane derivatives, their chemically irreversible
oxidation occurs at 1.16–1.24 V vs. Fc+/Fc10 (ca 1.4 V vs.
Ag/AgCl). On the other hand, chemically reversible oxidation at
E1/2 = 0.88 V§ vs. Ag/AgCl6 was reported for the precursor of
bis-germatrane, tris(1,3-dihydroxyisopropyl)amine. Reversibility
of oxidation of the bis-germatrane can then be considered as an
argument that the center of electron withdrawal (HOMO) in this
molecule does not locate on the Ph substituent but is rather bis-
atrane nitrogen-located. Consequently, the resulting radical
cation center is sterically protected inside the bis-atrane cage
providing the remarkable stability to the whole system.
Russian co-authors acknowledge the support by the Russian
Science Foundation (grant no. 18-73-10180). V. R. and V. J. are
grateful for the support from European Regional Development
Fund ERDF – Latvia (no. 1.1.1.2/VIAA/3/19/577).
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2020.09.004.
References
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‡
It is worth noting that the increase in the value of DEp with potential
sweep rate fully correlates with uncompensated resistance that was
evaluated from the cyclic voltammograms recorded for a ferrocene
solution under similar conditions in the same range of potential sweep
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§
Apparently, there is confusion between E1/2 and Ep/2 in ref. 6; allowing
57 mV for Ep – Ep/2 separation (ref. 7), one comes up with 0.94 V vs.
Ag/AgCl.
Received: 30th April 2020; Com. 20/6211
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