Electrochemistry and catalytic properties of amphiphilic Vitamin B12 derivatives in nonaqueous media

Article abstract of DOI:10.1039/c6dt00355a

The reduction pathway of cobalester (CN)Cble, an amphiphilic vitamin Bf₁₂ derivative, was investigated in organic solvents under electrochemical conditions and compared with mono- and dicyanocobyrinates. The redox characteristics were determined using cyclic voltammetry and spectroelectrochemical methods. The presence of a nucleotide moiety in B₁₂-derivative impedes the in situ formation of dicyano-species thus facilitating the (CN)Co(iii) to Co(i) reduction. The (CN)Cble shows stepwise reduction to Co(i) via (CN)Co(ii). The reduction of (CN)Co(ii)/Co(i) was found to depend on cyanide-solvent exchange equilibrium with weakly coordinating solvents and bulky peripheral chains promoting intact (CN)Co(ii) species existence. The studied complexes were also utilized as catalysts in bulk electrolysis of benzyl bromide affording bibenzyl in very good yield. The Royal Society of Chemistry.

Full text of DOI:10.1039/c6dt00355a

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DOI: 10.1039/C6DT00355A
Journal Name
ARTICLE
Electrochemistry and Catalytic Properties of Amphiphilic Vitamin
B12 Derivatives in Nonaqueous Media
M. Giedyk,a H. Shimakoshi,b* K. Goliszewska,a D. Gryko,a* and Y. Hisaedab*
Received 00th January 20xx,
Accepted 00th January 20xx
Reduction pathway of cobalester (CN)Cble, an amphiphilic vitamin B12 derivative, was investigated in organic solvents
under electrochemical conditions and compared with mono- and dicyanocobyrinates. Redox characteristics were
determined using cyclic voltammetry and spectroelectrochemical methods. The presence of nucleotide moiety in
B12-derivative impedes the in situ formation of dicyano- species thus faciliating the (CN)Co(III) to Co(I) reduction. The
(CN)Cble shows stepwise reduction to Co(I) via (CN)Co(II). Reduction of (CN)Co(II)/Co(I) was found to depend on cyanide-
solvent exchange equilibrium with weakly coordinating solvents to form (solvent)Co(II) and bulky peripheral chains
promoting intact (CN)Co(II) species existence. Studied complexes were also utilized as catalysts in bulk electrolysis of
benzyl bromide affording bibenzyl in very good yield.
DOI: 10.1039/x0xx00000x
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continuously expanding, now including such processes as
dehalogenation, addition to double bonds, ring expansion, C-H
functionalization etc.
Catalytic properties of vitamin B12 derivatives rely on redox
chemistry of the central cobalt cation with the reduction of
Co(III) to active Co(II) or Co(I) forms being critical.10 Therefore,
the understanding of their electrochemistry comes across as
an essential element for rational design and successful
application of B12-catalyzed reactions.
Introduction
Vitamin B12 (cyanocobalamin
1) is a highly functionalised
organometalic complex comprising corrin ring with the central
cobalt cation and peripheral amide chains as shown in Figure
1.1,2 As a cofactor for B12-dependent enzymes it plays an
important role in normal functioning of mammalian
organisms.3–5 Inspired by the nature, scientists successfully
employed cyanocobalamin (1) and its derivatives as catalysts in
Even though natural, nontoxic, and stable cyanocobalamin (1)
organic synthesis, due to their ability to form and selectively
may appear as an ideal catalyst, it suffers from low solubility in
synthetically useful organic solvents such as DCM, MeCN, THF
etc. Hence, modification of its structure are commonly
performed giving access to more lipophilic derivatives.11 For
example, the synthesis and utilization of heptamethyl
cleave Co-C bonds.6–9 The scope of B12-catalyzed reactions is
cobyrinates (e.g. monocyanocobyrinate
3) has been well
established.12–17 An alternative approach was recently
reported by Gryko et al. who synthesized cobalester ((CN)Cble,
2
) - a derivative possessing six ester groups on the periphery of
the corrin ring with the nucleotide fragment intact that
displays good solubility both in aquous and in organic media.18
A direct comparison of derivatives with and without the
nucleotide loop became thereby possible.
Whereas redox characteristics of cobyrinate derivatives in
organic solvents were extensively studied by Murakami and
Hisaeda,19–21 no suitable data are available for cobalester (
2).
We wondered whether the nucleotide fragment influences the
redox behavior and catalytic activity of cobalamin derivatives
in organic solvents, preferred in organic synthesis.
Figure 1. Structures and abbreviations of vitamin B12 derivatives.
a.Institute of Organic Chemistry Polish Academy of Science, Kasprzaka 44/52, 01-
224 Warsaw, (Poland), e-mail: dorota.gryko@icho.edu.pl, homepage:
http://ww2.icho.edu.pl/gryko_group.
Herein, we present redox characteristics of cobalester (2) with
regard to factors influencing the reduction of Co(III) to
catalytically active Co(II) and Co(I) species and demonstrate its
application as a catalyst in potential-controlled electrolysis of
benzyl bromide.
b.Department of Chemistry and Biochemistry, Graduate School of Engineering,
Kyushu University, Fukuoka, 819-0395 (Japan), E-mail:
shimakoshi@mail.cstm.kyushu-u.ac.jp, yhisatcm@mail.cstm.kyushu-u.ac.jp
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: details of mechanistic
-
studies, and spectroscopic data of (CN)Cble (
2
), [(CN)Cby]+ClO4
(
3
) and hexa(n-
butyl)cobalamin (12). See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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cobyrinates
3
and
4
for which Co(III)/Co(II) and Co(II)/Co(I)
Results and discussion
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DOI: 10.1039/C6DT00355A
redox couples are well separated (Figure 2C and 2D). This
indicates an efficient formation of Co(I) species of cobalester
(2) at less negative potentials comparing to cobyrinate
derivatives having the cyanide ligand.
Subsequently, we evaluated if and how the presence of an
excess of cyanide anion influence redox properties of
cobalester
(2). A series of measurements were performed,
proving that the two-electron reduction peak shifts towards
the cathodic side (Ered = -1.2 V vs. Ag-AgCl) with total current
remaining the same (Figure 2B) with the addition of cyanide
ion. Supposedly, this was caused by the formation of base-off
(CN)2Co(III) form with electron rich cobalt centre which is more
difficult to reduce. A similar observation has already been
described for cyanocobalamin (1
).22
Electronic spectra of vitamin B12 derivatives in organic solvents
Subsequently, cyanocobalester was examined using
(2)
controlled-potential electronic spectroscopy. The spectrum
recorded after 15 min of electrolysis at -1.0 V vs. Ag-AgCl
revealed the presence of expected Co(I) species with
absorption maximum at 390 nm, which was accompanied by a
by-product exhibiting maximum absorption at 370 and 580 nm
– wavelengths that are characteristic for (CN)2Co(III) species
(Figure 3A).
Figure 2. Cyclic voltamograms of 1.0 mM MeCN solutions of: A) cyanocobalester (2),
B) cyanocobalester (2) with addition of Bu4N+CN- (5 eq.), C) monocyanocobyrinate (3)
and D) dicyanocobyrinate and E) cobalt(II) cobyrinate; (4); All solutions contained 0.1
-
M
Bu4N+ClO4 and measurements were carried out at room temperature under a
nitrogen atmosphere using GC working electrode and Pt counter electrode; sweep
rate: 0.1 V/s.
Cyclic voltammetry of vitamin B12 derivatives in organic solvents
In order to understand the influence of the nucleotide
fragment on cobalesters (2) redox behaviour in organic
solvents, a series of cyclic voltammograms was recorded. The
use of glassy carbon working electrode proved superior over
Pt, allowing for the reproducible observation of spectra in a
broad range of potentials with clear detection of reduction and
Figure 3. Electronic spectra of 0.33 mM solution in MeCN of: A) (CN)Cble (2) (red),
(CN)Cble (2) subjected to 15 min electrolysis at -1.0 V vs. Ag-AgCl (purple) and fully
oxidation peaks. Spectrum of cobalester (2) in MeCN displayed
apparent one quasi-reversible reduction peak (Ered) at ca. -0.9
V vs. Ag-AgCl which corresponds to two-step reduction of
reduced (CN)Cble (2) (green, 15 min electrolysis at -1.4
V vs. Ag-AgCl); B)
-
[(CN)Cby]+ClO4 (3) subjected to 15 min reduction at -1.0 V vs. Ag-AgCl; All solutions
-
contained 0.1
M
Bu4N+ClO4 and measurements were carried out at room
complex
2, leading to Co(I) species via (CN)Co(II) species
temperature under a nitrogen atmosphere using carbon grid ITO working electrode
and Pt counter electrode.
(Figure 2A). Such redox behaviour is in agreement with that
observed by Lexa and Savéant for cyanocobalamin in water
and DMSO,22,23 but is distinctively different from heptamethyl
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The absorption bands did not disappear upon prolonging the
time of electrolysis, but once the potential was lowered to -1.4
V vs. Ag-AgCl, a mixture quantitatively transformed into final
Co(I) form. Such a behaviour proves in situ formation of
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DOI: 10.1039/C6DT00355A
(CN)2Co(III) complex from cyanocobalester
released during the electrolysis of . The (CN)2Co(III) complex
(2)
and CN-
2
was reduced to Co(I) complex at -1.4 V vs. Ag-AgCl (Figure 3A).
The working hypothesis was confirmed by superimposing the
spectrum of the mixture with the one recorded for solution of
[(CN)2Cble]- (prepared by mixing cyanocobalester with 5 eq. of
Bu4N+CN-) (see SI). Formation of cobalt(III) dicyano-complex
was also observed when monocyanocobyrinate
3 was
subjected to electrolysis at -1.0 V vs. Ag-AgCl (Figure 3B). In
this case the presence of (CN)2Co(III) complex was even more
pronounced as it was dominating over Co(I) species. The
difference in the amount of (CN)2Co(III) formation was also
detectable by cyclic voltammetry. No formation of
dicyanocobalester was observed in
time scale of the measurement, while the spectrum of
cobyrinate having no nucleotide fragment showed a reduction
peak at ca. -1.2 V vs. Ag-AgCl (Figure 2C), revealing the
presence of (CN)2Co(III) complex
2 (Figure 2A) within the
3
4
.
Mechanistic aspects of the reduction process
Figure 4 Cyclic voltamograms of 1.0 mM solutions of: A) cyanocobalester (2) in THF
and B) hexabutylcobalamin (12) in MeCN; All solutions contained 0.1
M
-
Bu4N+ClO4 and measurements were carried out at room temperature under a
nitrogen atmosphere using GC working electrode and Pt counter electrode; sweep
rate: 0.1 V/s.
than the one for cobalester
2
(KIII
< KIIICby). This stays in
Cble
agreement with reports by Zelder, who studied cyanide
complexation by cobalamin and cobinamide derivatives.24,25
After identification of dicyano-compounds
4 and 8 as
important intermediates in the reduction pathways, the
attention was focused on the mechanism of Co(I) species
formation. Murakami et al. proposed (CN)Co(II) complex
an intermediate formed in the first step upon monocyano
cobyrinate
reduction in DMF.20 This in turn supposedly
9 as
3
undergoes further reduction to Co(I) species 11 at ca. -1.4 V vs.
Ag-AgCl. While this is consistent with our observations for
monocyano cobyrinate
) did not reveal such a negatively located signal in CV.
Therefore, an exchange of the cyanide anion coordinating
(CN)Co(II) for a solvent molecule was considered (Scheme 1).
In the first step of the reduction (at ca. -0.9 V and -0.4 V vs. Ag-
AgCl for compounds and respectively), (CN)Co(II) species
and were formed. Additionally to direct reduction at -1.4 V
vs. Ag-AgCl, they could also undergo axial ligand exchange to
yield (solvent)Co(II) complexes and 10, which are readily
reduced at more positive potentials. This stays in contrast to
what was proposed for cyanocobalamin ( ) in protic solvents,
3 in MeCN, the spectrum of cobalester
(2
5
Scheme 1 Proposed mechanism for reduction of: A) cobalester (2) and B)
monocyanocobyrinate (3). a vs. Ag-AgCl.
2
3
5
9
Results presented above clearly demonstrate the existence of
(CN)Co(III)/(CN)2Co(III) equilibrium during the reduction of
6
compounds
2 and 3 (Scheme 1), with the cyanide binding
1
equilibrium constant for monocyano cobyrinate
3 much higher
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On our quest to understand the catalytic activity of vitamin B12
View Article Online
DOI: 10.1039/C6DT00355A
derivatives in nonaqueous environment we examined redox
Scheme 2 Interactions of solvent molecules with (CN)Co(II) complex 5.
where no (CN)Co(II) intermediate was considered in the
absence of purposely added cyanide.23 Furthermore, as it is
generally accepted that benzimidazole moiety in vitamin B12
possesses stronger electron donating abilities than MeCN, the
Scheme 3 Cobalester-catalyzed generation of benzyl radical via intermediate Co-
C species 13 and 14. a vs. Ag-AgCl.
mechanism involving base-on Co(II) form
7 would require
more negative potentials. On the other hand, the equilibrium
of Co(II)base-on/Co(II)base-off should not favour base-on form
in MeCN as it does in water. This allowed us to exclude the
pathway involving base-on Co(II) complex as less favoured.
behaviour of cobalester (
We have previously reported that cobalester (
2
) in the presence of benzyl bromide.
) catalyzes
2
dimerization of various benzyl bromides in the microwave-
assisted reaction yielding substituted bibenzyl derivatives in
high yields.18 A control measurement of benzyl bromide
solution revealed a direct reduction peak at negative potential
(Ered = -1.9 V vs. Ag-AgCl) (Figure 5A). The addition of
To further confirm the existence of (CN)Co(II) intermediate
and a key role of axial ligand exchange in the generation of
Co(I) species , reaction environment was modified in a
5
7
following manner (Figure 4). Firstly, cyclic voltamogram was
recorded using THF as a solvent. Contrary to the experiment in
MeCN, a second reduction peak appeared at ca. -1.4 V vs. Ag-
cobalester (2) (10 mol%) shifted the signal towards anodic side
by ca. 0.5 V marking a catalytic current (Figure 5B). Moreover,
when the scan was reversed at -0.95 V vs. Ag-AgCl, no
reversible wave was observed (see SI). This implies that once
AgCl, indicating direct reduction of cyano- form
complex . Such a behavior is consistent with our mechanistic
hypothesis, as weaker coordination abilities (compared to
MeCN) towards transition metals, results in lower KII
value
5 to Co(I)
7
Co(I) species
7 is generated, it rapidly reacts with the
Cble
electrophile forming complex 13 with cobalt-carbon bond. The
presence of plateau between -0.9 and -1.0 V vs. Ag-AgCl
indicated stability of complex 13 in this range of spectrum.
Further negative sweeping of potential might cause reduction
of complex 13 to anion radical 14 that decomposed forming
and affords stabilization of (CN)Co(II) complex
5
in the
experimental
hexabutylcobalamin
conditions
(Scheme
2).
Secondly,
(
12) was synthesized by Bu4N+CN--
catalyzed aminolysis of cobalester (2) and examined using
cyclic voltammetry. Due to changes at the periphery of the
corrin ring, we expected cyanide ligand exchange to be
altered. Indeed, a peak assigned to direct (CN)Co(II)/Co(I)
reduction was observed (Figure 4B), thus supporting our
proposed mechanism in Scheme 1.
benzyl radical and regenerating the active form of catalyst
(Scheme 3).
7
Controlled-potential electrolysis of benzyl bromide
The controlled-potential electrolysis of benzyl bromide in the
presence of (CN)Cble ( ) gave bibenzyl (Table 1). ESI MS
2
Redox behaviour of amphiphilic vitamin B12 in the presence
of benzyl bromide
analysis of the reaction mixture revealed the presence of Co-
benzyl intermediate 13 (see SI).
Table 1 Optimisation of catalytic reactiona
Entry
1
Working electrode
Pt
Potentialb [V]
Yieldc [%]
-1.1
-1.1
-1.1
-1.1
-1.0
-1.1
69
76
13
71
67
13
2
carbon-felt
carbon-felt
carbon-felt
carbon-felt
carbon-felt
3d
4e
5
6f
a
contolled-potential electrolyses were carried out in MeCN under N2
Figure 5. Cyclic voltamogram of MeCN solutions of: A) benzyl bromide (10
mM) and B) cyanocobalester 2 (1.0 mM) in the presence of BnBr (10 mM);
atmosphere at rt in divided cell system with Zn counter-electrode. Initial
-
All solutions contained 0.1 M Bu4N+ClO4 and measurements were carried
out at room temperature under a nitrogen atmosphere using GC working
electrode and Pt counter electrode; sweep rate: 0.1 V/s.
4 | J. Name., 2012, 00, 1-3
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concentration in working-electrode compartment: BnBr: 0.25 M, (CN)Cble
2:
understanding of factors that influence the gVeineweArartitciloe nOnlionef
active Co(I) will soon result in develDoOpmI: 1e0n.1t03o9/fC6nDeTw003B5152A-
catalyzed organic reactions.
-
b
1.25 mM, Bu4N+ClO4 : 0.2 M; vs. Ag-AgCl; c The quantity of the product is the
d
average of at least two repeated experiments from GC-MS results; Reaction
performed in THF; e 0.125 M solution of benzyl bromide was used; f no catalyst.
The use of carbon felt as a working electrode proved superior
over Pt, which was consistent with the conditions of cyclic
voltammetry measurements (compare entries 1 and 2). Among
potentials examined, -1.1 V vs. Ag-AgCl was optimal giving the
yield of 76% (entry 2). As expected, the use of THF as a solvent
(entry 3) led to a dramatic decrease
Experimental
Materials
All solvents and chemicals were of reagent grade and used
without further purification. Dry MeCN, THF and N,N-
dimethylformamide (DMF) were purchased from Wako
in yield, due to impeded generation of active Co(I) species 7.
Lowering the concentration of the starting material only
slightly affected the yield (entry 4). As for applied potential, -
1.0 V vs. Ag-AgCl still allowed for efficient reaction to occur
(entry 5), however, no further decrease was possible (data not
shown). Background reaction without the addition of the
catalyst gave desired product in low yield (entry 6).
-
Chemicals. Tetra(n-butyl)ammonium perchlorate (n-Bu4N+ClO4
) was purchased from Sigma Aldrich. Cyanocobalester
2,
monocyanocobytinate
3 and dicyanocobyrinate 4 were
synthesized according to reported procedures.12,18,26
Next we examined cobyrinate–derived complexes
3 and 4 as
General analysis and measurements
catalysts in bulk electrolysis (Table 2). Surprisingly, changing
-
the catalyst to [(CN)Cby]+ClO4
(3) did not affect the reaction
outcome (compare entries 1 and 2). This stays in contrast to
the efficiency of Co(I) form generation which was proven to be
higher for catalyst 2. Furthermore, the use of (CN)2Cby (4)
afforded the product in comparable yield, suggesting a shift in
Co(I) formation equilibria which is caused by irreversible
The electronic absorption spectra were measured using a
Hitachi U-3000 spectrophotometer and a 10-mm cell.
Cyclic voltammograms were obtained using a BAS ALS-630C
electrochemical analyzer. The gas chromatography-mass
spectra (GC-MS) were obtained using a Shimadzu GCMS-
QP5050 equipped with a J&W Scientific DB-1 column (length:
reaction of Co(I) species
7 with benzyl bromide. Moreover,
once the active Co(I) complex is formed, it recoveres in the
catalytic cycle, masking initial differences.
30 m; ID: 0.25 mm, film: 0.25 m) and helium as the carrier
gas. For the measurement, the injector and detector
temperatures were 250 ⁰C, the oven temperature was initially
held at 40 ⁰C for 4 min, then increased to 240 ⁰C at the rate of
10 ⁰C/min. The ESI-MS was measured by an JMS-T100LC
AccuTOF from JEOL.
Table 2 Comparison of B12 derivatives as catalystsa
Entry
Catalyst
Conversionb [%]
Yieldb [%]
1
2
3
(CN)Cble (
2
)
95
88
86
76
76
64
-
[(CN)Cby]+ClO4
(3)
The spectroelectrochemical measurements for
2 and 3 were
(CN)2Cby (4)
a
carried out in MeCN containing of 0.1 M n-Bu4N+ClO4- under N2
with a BAS SEC2000 spectrometer equipped with carbon-grid
ITO glass as a working electrode, Pt wire as an counter
electrode, and Ag/AgCl electrode (3M NaCl aq.) as reference.
contolled-potential electrolyses were carried out at -1.1 V vs. Ag-AgCl in MeCN
under N2 atmosphere at rt in divided cell system with carbon-felt working
electrode and Zn counter-electrode. Initial concentration in working-electrode
-
compartment: BnBr: 0.25 M, catalyst: 1.25 mM, Bu4N+ClO4 : 0.2 M; b The quantity
of the product is the average of at least two repeated experiments from GC-MS
results.
Cyclic voltammetry
Conclusions
A cylindrical three-electrode cell was used that was equipped
with a glassy carbon working electrode, a 25 mm platinum
wire as the counter electrode and an Ag/AgCl (3.0 M NaCl)
electrode as the reference electrode. The scan rate for a
typical experiment was 100 mV s-1. The dry solution of the
In conclusions, for the first time, the reduction pathway for
cobalester
(2
)
was determined in aprotic solvents and
and . The
compared with mono- and dicyanocobyrinates
3
4
reaction mechanism involves axial cyanide exchange which
depends on coordination abilities of a solvent, as well as the
steric hindrance around the cobalt centre. Furthermore, it was
found that the reduction process is influenced by the affinity
of cobalt cation to cyanide, which results in formation of stable
-
vitamin B12 derivatives (1.0x10-3 M) and n-Bu4N+ClO4 (1.0x10-1
M) were deaerated by N2 gas bubbling before the
measurements, and the cyclic voltammetry was carried out
under an N2 gas atmosphere at room temperature. The E1/2
value of the ferrocene-ferrocenium (Fc/Fc+) was 0.56 V vs.
Ag/AgCl with this setup.
base-off dicyano- species
4 and 8. The latter feature, however,
does not determine the outcome of Co(I)-catalyzed bulk
electrolysis of benzyl bromide, as the irreversible formation of
Co-benzyl complex facilitate the reduction process.
Our findings provide a new insight into B12 derivatives redox
chemistry in organic, aprotic environment. We expect that the
Catalytic benzyl bromide dimerization reaction under
electrochemical conditions
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Controlled-potential electrolyses were carried out in dry MeCN
at -1.1 V vs. Ag/AgCl under an N2 atmosphere in a divided
electrolysis cell separated with polypropylene membrane.
Cathodic compartment was equipped with a Pt mesh or
carbon felt working electrode, Ag/AgCl (3M NaCl aq.)
reference electrode and a stirring bar. Anodic compartment
was equipped with a sacrificial Zn-plate electrode. The applied
potential between the working and reference electrodes in the
electrolysis was maintained constant with a Hokuto Denko HA
BF-501A potentiostat, and the electrical quantity was also
recorded on it. For a typical reaction, a MeCN solution of the
vitamin B12 derivative (1.25x10-3 M), BnBr (2.5x10-1 M),
Acknowledgements
The authors acknowledge the generous support from the
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DOI: 10.1039/C6DT00355A
National
Science
Centre:
grant
OPUS
no.
a
2012/07/B/ST5/02016, ETIUDA 2014/12/T/ST5/00113,
Grant-in-Aid for Scientific Research (C) (No.26410122) from
the Japan Society for the Promotion of Science (JSPS) and a
Grant-in-Aid for Scientific Research on Innovative Areas
“Stimuli-responsive Chemical Species for Creation of
Functional Molecules” (No. l5H00952) from the Ministry of
Education, Culture, Sports, Science and Technology (MEXT) of
Japan.
-
n-Bu4N+ClO4 (2.0x10-1 M) was deaerated by N2 and subjected
to electrolysis for 2 h at room temperature. Solution from both
compartments were then mixed together, passed through
silica pad and analyzed by GC-MS with biphenyl as the internal
standard.
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A sealed pressure tube was charged with cyanocobalester (2,
15 mg, 1.0x10-2 mmol), Bu4N+CN- (17 mg, 6x10-2 mmol), dry
MeOH (0.1 mL) n-butylamine (0.5 mL) and diethyl
cyanophosphonate (30 µL, 2.0x10-1 mmol). The reaction was
stirred for 4 days at 55 ⁰C. It was then diluted with CH2Cl2 and
washed with 10% HCl, water and saturated NaHCO3. Organic
phase was dried over Na2SO4, filtred and concentrated in
vacuo. The crude product was purified using reverse phase
(C18) column chromatography (gradually from 50 to 75%
MeOH in water) and subsequent chromatography on silica
(gradually from 0 to 10% MeOH in toluene). Recrystalization
from CH2Cl2/hexane gave a red solid (8 mg; 47%). HRMS ESI
(m/z) calcd for C87H136N14O14PCoNa2 [M+2Na]2+ 1736.92145,
found 868.4607. UV/Vis (DMSO): λmax (ε [l.mol-1.cm-1]) = 547
(8.65x103), 516 (7.59x103), 361 (2.56x104), 325 (8.75x103), 278
(1.67x104), 262 (1.66x104) Anal. calcd. for C87H136CoN14O14P +
CH2Cl2: C 59.48, H 7.83, N 11.04; found: C 59.50, H 7.83, N
10.40. 1H NMR (500 MHz, CD3OD): δ = 7.25 (s, 1H), 7.11 (s, 1H),
6.55 (s, 1H), 6.26 (d, J = 3.1 Hz, 1H), 6.03 (s, 1H), 4.70–4.63 (m,
7
8
9
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1H), 4.57–4.51 (m, 1H), 4.37-4.28 (m, 1H), 4.19 (t, J = 3.5 Hz, 17 Y. Hisaeda, T. Nishioka, Y. Inoue, K. Asada and T. Hayashi, Coord.
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1H), 4.12–4.05 (m, 2H), 3.92–3.88 (m, 1H), 3.76-3.72 (m, 1H),
3.68 (d, J = 14.0 Hz, 1H), 3.63 (s, 1H), 3.49 (q, J = 5.2 Hz, 1H),
3.28–3.07 (m, 10H), 3.02–2.91 (m, 2H), 2.87–2.80 (m, 2H),
2.66–2.44 (m, 11H), 2.42–2.32 (m, 4H), 2.28–2.24 (m, 6H),
18 M. Giedyk, S. N. Fedosov and D. Gryko, Chem. Commun., 2014,
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19 Y. Murakami, Y. Hisaeda, A. Kajihara and T. Ohno, Bull. Chem.
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2.18–2.08 (m, 2H), 2.05–1.93 (m, 3H), 1.91–1.84 (m, 4H), 1.77– 20 Y. Murakami, Y. Hisaeda, T. Ozaki and Y. Matsuda, Chem. Lett.,
1988, 469.
1.67 (m, 2H), 1.57–1.15 (m, 42H), 1.14-1.05 (m, 2H), 0.97–0.86
(m, 18H), 0.42 (s, 3H) ppm. 13C NMR (125 MHz, CD3OD): δ =
181.5, 180.2, 177.6, 175.6, 174.6, 174.4, 174.0, 173.6, 172.7,
172.5, 171.6, 167.2, 166.5, 143.4, 138.3, 135.4, 133.8, 131.5,
21 H. Shimakoshi, M. Tokunaga and Y. Hisaeda, Dalt. Trans., 2004,
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22 D. Lexa, J. M. Savéant and J. Zickler, J. Am. Chem. Soc., 1980,
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130.7, 117.9, 112.5, 109.0, 105.0, 95.6, 87.9, 86.5, 83.7, 76.2, 23 D. Lexa and J. M. Savéant, Acc. Chem. Res., 1983, 16, 235.
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25 F. H. Zelder, Inorg. Chem., 2008, 47, 1264.
26 L. Werthemann, ETH Zurich, 1968.
75.4, 73.7, 73.6, 71.5, 70.7, 62.7, 60.3, 57.8, 57.6, 55.0, 52.9,
46.85, 46.82, 45.2, 43.7, 40.6, 40.5, 40.4, 40.32, 40.28, 40.1,
36.9, 35.8, 33.6, 33.5, 33.0, 32.9, 32.7, 32.56, 32.55, 32.50,
32.4, 32.3, 30.7, 29.8, 27.7, 27.5, 23.7, 21.3, 21.24, 21.22,
21.17, 21.15, 21.1, 20.9, 20.43, 20.39, 20.3, 20.20, 20.17, 19.9,
17.6, 17.1, 16.3, 16.0, 14.10, 14.09, 14.08, 14.02 ppm.
6 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C6DT00355A