Heteroleptic cobalt(iii) acetylacetonato complexes with N-heterocyclic carbine-donating scorpionate ligands: Synthesis, structural characterization and catalysis

Article abstract of DOI:10.1039/c8dt04469d

Exposure of O₂ to a reaction mixture containing bis(acac)cobalt(ii), a facially capping tris(N-heterocyclic carbene)borate ligand and 1-methylimidazole yields a heteroleptic cobalt(iii) complex with acac, 1-methylimidazole and tris(NHC)borate ligands. meta-Chloroperbenzoic acid is efficiently activated by this heteroleptic complex to catalytically oxidize cyclohexane at ambient temperature.

Full text of DOI:10.1039/c8dt04469d

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DOI: 10.1039/C8DT04469D
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COMMUNICATION
Heteroleptic cobalt(III) acetylacetonato complexes with N-
heterocyclic carbine-donating scorpionate ligands: synthesis,
structural characterization and catalysis†
Received 00th January 20xx,
Accepted 00th January 20xx
Toshiki Nishiura, a Asako Takabatake, a Mariko Okutsu, a Jun Nakazawa a and Shiro Hikichi *a
DOI: 10.1039/x0xx00000x
www.rsc.org/
Exposure of O2 to a reaction mixture containing bis(acac)cobalt(II), iron and manganese complexes with planar tetradentate
a facially capping tris(N-heterocyclic carbene)borate ligand and 1- pyridine- or phenoxide-containing bis(NHC) ligands.4(a)-(c) No
methylimidazole yields a heteroleptic cobalt(III) complex with cobalt-NHC complex has been applied to oxidation catalysts so
acac, 1-methylimidazole and tris(NHC)borate ligands. meta- far, although a few cobalt-dioxygen adducts with NHC ligands
Chloroperbenzoic acid is efficiently activated by this heteroleptic have been reported.5
complex to catalytically oxidize cyclohexane at ambient
temperature.
Metal complexes designed with hindered [XB(RIm)3]−
ligands, where R = tert-butyl and mesityl, have been explored
extensively because the space restriction induced by the bulky
R substituents can stabilize the coordinatively unsaturated
metal centers of the complexes. Conversely, related less-
hindered ligands have received less attention. Hitherto, there
are multiple reports detailing the structural characterizations
and reactivity of tetra-coordinated cobalt(II) and cobalt(III)
species supported by the hindered [PhB(RIm)3]− ligand,6–9
whereas, to the best of our knowledge, there is only one
report detailing the structural characterization of a hexa-
coordinated cobalt(III) complex possessing the less-hindered
N-heterocyclic carbene (NHC) transition metal complexes have
received significant attention because the strong -electron-
donating nature of NHCs influences the degree of metal-based
reactivity.1 To date, various metallocomplex catalysts
comprising NHC ligands have been explored. Particularly, NHC-
containing chelating ligands have been employed extensively
in the design of stable catalysts arising from the chelate
effect.2 Tris(1-R-imidazol-2-ylidene)borates ([XB(RIm)3]−; X = H
or Ph, R denotes the substituent group at the first position on
the imidazole), which have recently been classified into a new
generation of scorpionate ligands, are unique NHC-containing
chelators. These ligands are promising for applications in
oxidation reaction catalysts on the basis of the characteristics
of their complexes. First, upon coordination, these facially-
capping tridentate ligands offer cis-orientated vacant sites for
binding reactants. Second, the intramolecular charge
separation created by the negatively charged borate with
respect to cationic metal centers stabilizes complexes of high
valent metals. The three strong -donors of these NHC ligands
render metal centers relatively susceptible to oxidation.3
Hitherto, however, [XB(RIm)3]− ligands have not been designed
into oxidation catalysts, although several metal complexes
comprising NHC ligands other than [XB(RIm)3]− are known to
be active in the catalytic oxidation of organic compounds.4
Catalytic oxygenations of hydrocarbons, such as arene
hydroxylation and olefin epoxidation, have been achieved by
imidazole-based
ligand,
hydrotris(1-ethyl-imidazol-2-
ylidene)borate ([HB(EtIm)3]−)10. Our previous study revealed
that highly-hindered scorpionate ligand complexes are not
suitable as oxidation catalysts due to inaccessibility of
substrates and/or intramolecular oxidation of substituent
groups of the ligand.11 Herein, the synthesis, structural
characterization and alkane oxidation catalytic performance of
cobalt
complexes
comprising
tris(1-methylimidazol-2-
ylidene)phenylborate, [PhB(MeIm)3]−, that possesses less-
hindered methyl groups surrounding the metal center of the
resulting complexes, [CoIII([PhB(MeIm)3])(acac)(MeImH)](OTf)
(1[OTf]) and [CoIII([PhB(MeIm)3])2](OTf) (2[OTf]), are
investigated.
a. Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa
University, Yokohama 221-8686, Japan. E-mail: hikichi@kanagawa-u.ac.jp
†Electronic Supplementary Information (ESI) available: Experimental details, IR, 1H
NMR, electrospray ionization (ESI)-MS and UV-vis spectra, time course of catalytic
reactions. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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CoII(acac)2
signals suggested that the lower symmetric struVciteuwrAerticolefO1nli(nae
pseudo mirror symmetric structure consisting two equatorial
DOI: 10.1039/C8DT04469D
1) [PhB(MeIm)3]- (1eq.), under Ar
[PhB(MeIm)3]- (2eq.), under Air
and one axial MeIm in [PhB(MeIm)3]− and neutral MeImH)
and partial dissociation of the neutral MeImH ligand from 1
giving the mixture of cobalt(III) complexes. Recrystallization of
the brown species yielded pale brown crystals of 1[OTf] and X-
ray crystallographic analysis revealed the molecular structure
of 1 as the desired heteroleptic cobalt complex possessing a
3-capping [PhB(MeIm)3]− ligand and a bidentate acac ligand
(Fig. 1 (a)). The sixth coordination site is occupied by the 1-
methylimidazole nitrogen donor. The Co-C bond lengths in 1
are calculated to be 1.908(2), 1.922(2) and 1.943(2) Å—close
to the Co-C bond lengths of cobalt(III) complexes possessing
related ligands. The Co-C bond lengths of previously reported
pseudo-tetrahedral cobalt complexes comprising the bulky
[PhB(RIm)3]− ligand are reported to be between 2.01 and 2.13
Å for cobalt(II) species (Co-Cl,6 Co-Me,6 Co-amido,7 Co-azido8
and Co-OH9) and 1.89–1.99 Å for cobalt(III) complexes (imido,7
hydroxo9 and oxo9 complexes). The distorted square-pyramidal
di(azido) cobalt(III) complex of [PhB(tBuIm)3]− has Co-C bond
lengths between 1.89 and 2.01 Å.8 Additionally, the Co-C bond
2) MeImH (1eq.), under O2 or Air
+
+
N
N
N
N
N
N
O
III
N
N
B
III
Co
N
O
B
B
Co
N
N
N
N
N
N
N
N
N
N
N
1
2
Scheme
1
Synthesis of cobalt(III) complexes with
[PhB(MeIm)3]−.
The less-hindered [PhB(MeIm)3]− ligand typically forms
hexa-coordinated homoleptic
[Mn([PhB(MeIm)3])2]n−2
complexes (n = oxidation number of M); complexes of this
general formula containing Mn(IV),12 Mn(III),13 Ru(III) and
Os(III)14 have been structurally characterized. However, only
two heteroleptic [M([PhB(MeIm)3])Lx]y complexes, where L, x,
and y denote ligands other than [PhB(MeIm)3]−, the number of
L ligands, and the charge of the resulting complex (depending
lengths
of
the
homoleptic
cobalt(III)
complex
[CoIII(HB(EtIm)3)2]+ are in the range of 1.943–1.959 Å.9
Furthermore, free OTf− exists as a counter anion in the crystal
lattice of 1. Therefore, the charge of the cobalt center in 1 is
assigned as +3, as predicted from the diamagnetic nature.
Notably, related scorpionate ligand complexes comprising
on the charges of
L and x), respectively, have been
characterized by spectroscopic methods.12,15 A tricarbonyl
complex of d6 manganese(I), [MnI([PhB(MeIm)3])(CO)3], has
been characterized by 1H NMR and IR spectra, although its
molecular structure has not been determined by X-ray
crystallography.12 In this work, the synthesis of a cobalt
heteroleptic complex was studied. For this purpose, CoII(acac)2
was employed as a starting compound because the slow ligand
exchanging behavior of acac, compared with other ligands,
allows isolation of the desired heteroleptic complex, formed
via the substitution of one acac ligand with [PhB(MeIm)3]−
chelated to the cobalt center. The reaction of CoII(acac)2 with
an equivalent of the deprotonated [PhB(MeIm)3]− ligand—
generated in situ by treatment of [PhB(MeImH)3](OTf)2 with
three equivalents of lithium diisopropylamide (LDA) under
Ar—yielded an air-sensitive green species. Although the
isolation and characterization of the green species were not
successful, exposure of the green species solution to O2 (or air)
resulted in the formation of a brown species 1 (Scheme 1). It is
noteworthy that 1 forms in low yield (~10%) even when 1-
methylimidazole (MeImH) is not added; this trapped MeImH
presumably forms via degradation of either [PhB(MeIm)3]− or
[PhB(MeImH)3](OTf)2. The yield of 1 increases to 45% when
one equivalent of MeImH is added. The electrospray
ionization-mass spectrometry (ESI-MS) spectra obtained from
the brown species displayed ion peaks ascribed to
[Co([PhB(MeIm)3])(acac)]+. Also, the cold-spray ionization mass
spectra (CSI-MS; ionized at ambient temperature) exhibited
ion peaks attributed to the same acac complex and its MeImH
adduct 1 (Fig. S2). The IR spectrum exhibited bands at 1580
and 1513 cm−1 attributed to the C=O and C=C stretching
vibrations of acac, respectively.16,17 1H NMR signals appeared
across the 0–10 ppm region supporting that the isolated
brown species is a diamagnetic compound. The multiple
cobalt(II) with acac, [CoII(Tp*)(acac)(NCMe)] (3; Tp*
hydrotris(3,5-dimethylpyrazol-1-yl)borate) and
[CoII(ToM)(acac)] (4; ToM
tris(4,4-dimethyloxazol-2-
=
=
yl)phenylborate), are inert toward O2 and the formation of the
corresponding cobalt(III)-acac complexes have, to the best of
our knowledge, never been observed.17 Hence, the observed
differences in the oxidizing behaviors of the cobalt centers
indicate that the electron-donating ability of [PhB(MeIm)3]− is
higher than the Tp* and ToM ligands.
A homoleptic complex 2[OTf] could also be synthesized by
the reaction of CoII(acac)2 and two equivalents of
1
[PhB(MeIm)3]− under air (Scheme 1). A diamagnetic H NMR
spectrum of 2[OTf] exhibited only
a single set of
imidazolylidene signals indicating C3 symmetric arrangement
of [PhB(MeIm)3]−. X-ray analysis of almost colorless 2[OTf]
crystals revealed
a pseudo-octahedral cobalt(III) center
supported by two 3-[PhB(MeIm)3] ligands (Fig. 1 (b)). The Co-
C bond lengths of 2[OTf] are calculated to be 1.932(2),
1.946(2) and 1.952(2) Å (for molecule 1) and 1.931(2),
1.946(2) and 1.951(2)
Å
(for the crystallographically
independent molecule 2 in the same lattice). An average Co-C
length in 2[OTf] (1.94 Å) is ca 0.02 Å longer than that in 1[OTf].
2 | J. Name., 2012, 00, 1-3
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Cl
O
O
O
H
View Article Online
O
DOI: 10.1039/C8DT04469D
Cl
Cat. (Cobalt compounds ;2 mol)
K
L
A
+
+
+
Oxidant (mCPBA ; 2.0 mmol)
Solvent (CH2Cl2 3 mL + MeCN 1 mL)
Ar, 298 K or 308 K
15 mmol
Scheme 2 Conditions of catalytic reactions.
Table 1 Oxidation of cyclohexane with meta-chloroperbenzoic
acid (mCPBA) at 25 °C a.
A /
(K + L)
0.9
Products / mol
Cat.
TON b
A
3.9
K
L
Cl
3.6
Blank
4.1
0.2
−
1
2
3
4
704.7
18.0
146.3
80.7
11.7
43.8
82.4
0.3
3.6
37.9
32.5
56.7
4.7
14.2
36.3
46.2
543.8
23.3
127.6
453.9
585.3
4.3
1.5
3.1
3.4
547.0 124.4
Fig.
1
Molecular
structures
(1),
of:
and
(a)
(b)
CoII(acac)2 674.5 192.5
3.0
[CoIII([PhB(MeIm)3])(acac)(MeImH)]+
a Reaction time: 3 h.
TON = {cyclohexanol (A) + chlorocyclohexane (Cl) + 2 
{cyclohexanone (K) + ε-caprolactone (L)}} / cobalt compound.
[CoIII([PhB(MeIm)3])2]+ (2). Thermal ellipsoids are set at 30%
probability. All hydrogen atoms and trifluoromethanesulfonate
counter anions for 1 and 2 are omitted for clarity.
b
As noted above, the catalytic performance of the
heteroleptic complex 1 was observed to be efficient, whereas
the corresponding performance of the homoleptic complex 2
was almost inactive at 25 °C. The change in the UV-vis spectra
during the reaction of mCPBA with 1 or 2, without any
substrate, at the same temperature supported the difference
of the catalytic performance. Addition of excess mCPBA (ca. 10
equivalents) to a solution of 1 (dissolved in a 3:1 v:v mixture of
CH2Cl2:MeCN) resulted in initially increasing the absorbance at
370 nm, but the intensity of this absorption band eventually
decreased (Fig. S15). In contrast, addition of mCPBA to the
homoleptic complex 2 under same condition led to increase
the absorbance at 395 nm and this band remained intact on
reaching the saturation of the spectral changing (Fig. S16).
Although structures of the formed species are unclear at this
moment, the thermal stabilities of the initially formed putative
cobalt-mCPBA complexes are different and that is consistent
with the catalytic performances. The lability of the MeImH
and/or acac ligands likely facile permit mCPBA access to the
cobalt center of 1, and following activation of the cobalt-
binding mCPBA seems to occur at ambient temperature. Even
the homoleptic cobalt(III) complex 2 reacted with mCPBA at 25
°C to form something stable species. The pseudo-tetrahedral
cobalt(II)-chlorido complexes possessing the hindered tert-
butyl and mesityl-substituted ligands, [CoII([PhB(RIm)3])Cl],
react with HCl under ambient conditions, to form the carbene
donor protonated complex [CoII(Cl)2([PhB(RIm)2(RImH)])].6
Therefore, protonation of one carbene donor of [PhB(MeIm)3]−
in 2 would allow to access of mCPBA to the cobalt center.
Further work is necessary to definitively explain the
differences in activity of pre-catalysts 1 and 2.
There are reports of cobalt compounds, including those
comprising scorpionate ligand complexes 3,
4
and
[CoII(ToM)(OAc)], that demonstrate activity toward the catalytic
oxidation of alkanes with meta-chloroperbenzoic acid
(mCPBA).17–23 Hence, the catalytic performance of the
synthesized cationic cobalt(III) complexes 1 and 2 toward the
oxidation of cyclohexane with mCPBA was examined under
the condition shown in Scheme 2 and their efficiencies
compared with 3 and 4. The catalytic performance of
Co(acac)2—the precursor to 1–4—was examined as the
control. At a reaction temperature of 25 °C, the order of
alcohol yields was: 1 > CoII(acac)2 > 4 >> 3 >> 2 (Table 1).
Although the total turnover numbers (TON; estimated based
on the oxidizing equivalents of the products) of 1 is observed
to be lower than that of CoII(acac)2, the alcohol selectivity
(A/(K + L)) of 1 is enhanced by a factor of 1.3 relative that of
CoII(acac)2. The initial turnover frequency (TOF, 369 h−1) of 1 is
observed to be higher than that of the cobalt(II)-acetato
complex
chelated
to
tris(2-pyridylmethyl)amine,
[CoII(OAc)(TPA)]+ (300 h−1), which is known to be an efficient
hydroxylation catalyst.19 Although the catalytic reaction in the
presence of 1 reached saturation after 3 h, the addition of
additional mCPBA (2 mmol) promoted the catalytic reaction to
re-start without negatively impacting the oxidant utilization
efficiency (ca. 53%; see Fig. S13). These observations suggest
that the integrity of the catalyst structure (derived from 1) was
retained even in the presence of a large excess amount of the
acidic mCPBA. Furthermore, the moderate oxidant utilization
efficiency observed together with the moderate alcohol
selectivity indicates that a putative reaction intermediate, such
as metal-oxyl (Mn+‒O∙) or oxo (M(n+1)+=O) species formed via O-
When increasing the reaction temperature to 35 °C, the
O
homolyses of the corresponding metal-acylperoxo
complex,24 may possess strong radical characteristics,
concomitant to the non-productive consumption of mCPBA.
homoleptic complex
2 also exhibited catalytic activity.
Appearance of the catalytic activity of 2 was supported by
changing the UV-vis spectra of the reaction of 2 with mCPBA.
The stable intermediate formed at 25 °C changed to another
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species immediately at 35 °C (Fig. S16). The order of alcohol the Brønsted-acidic oxidant, will expand the use of
View Article Online
25
yields was 1 > 2 > 4 > 3 > CoII(acac)2. The initial TOF of the most tris(carbene)borate complexes to other catalyst designs.
DOI: 10.1039/C8DT04469D
active complex 1 reached ~1050 h−1, although the catalytic
reaction was terminated at 30 min and the oxidant utilization This research was funded by CREST, JST (JPMJCR16P1) and
efficiency was 53%. When subjected to the same reaction Kanagawa University (ordinary budget: 411).
conditions, an N4-donating ligand-supported cobalt complex,
[CoII(OAc)(LtBu)]+ where LtBu denotes N,N-bis(2-pyridylmethyl)- There are no conflicts to declare.
N-[(1-R-1H-1,2,3-triazol-4-yl)methyl]amine
(Fig.
S17),
demonstrated higher oxidant utilization efficiency (83 %) and
comparable alcohol selectivity (A/(K + L) = 5.4), however, the
initial TOF (950 h−1) was observed to be lower when compared
with 1.20 The initial TOF of 2 was ~50% of that of 1, although
the final oxidant utilization efficiency was similar to that of 1.
The significantly higher TOF of 1 is considered to be attributed
to the [PhB(MeIm)3]− ligand having excellent electron-donating
properties compared with other ligands, including N4-donating
pyridylamines.19–21 The catalytic reaction mediated by
CoII(acac)2 at 35 °C was terminated after 30 min with an
oxidant utilization efficiency of 40%. When increasing the
reaction temperature to 35 °C, the catalyst derived from
Co(acac)2 was not sufficiently stable. Conversely, the
scorpionate ligands [PhB(MeIm)3]−, Tp* and ToM appear to
significantly enhance the thermal stabilities of their
homogeneous cobalt catalysts relative that derived from
CoII(acac)2.
Notes and references
1. (a) N-Heterocyclic Carbenes: From Laboratory Curiosities to
Efficient Synthetic Tools: Edition 2 (RSC Catalysis Series No.27),
ed. S. Diez-Gonzalez, The Royal Society of Chemistry, London,
2017; (b) N-Heterocyclic Carbenes in Transition Metal Catalysis
and Organocatalysis (Catalysis by Metal Complexes, vol.32), ed.
C. S. J. Cazin, Springer Science+Business Media, Berlin, 2011; (c)
N-Heterocyclic Carbenes in Transition Metal Catalysis (Topics in
Organometallic Chemistry, vol.21), ed. F. Glorius, Springer-
Verlag, Berlin, Heidelberg, 2007.
2. V. Charraa, P. de Frémonta and P. Braunsteina, Coord. Chem.
Rev., 2017, 341, 53-176.
3. (a) C. Santini, M. Marinelli and M. Pellei, Eur. J. Inorg. Chem.
2016, 2312-2331; (b) A. Nasr, A. Winkler and M. Tamm, Coord.
Chem. Rev., 2016, 316, 68-124; (c) J. M. Smith, Comments.
Inorg. Chem., 2008, 29, 189-233; (d) J. Cheng, L. Wang, P. Wang
and L. Deng, Chem. Rev., 2018, 118, 9930-9987.
4. (a) A. Raba, M. Cokoja, W. A. Herrmann and F. E. Kühn, Chem.
Commun., 2014, 50, 11454-11457; (b) J. W. Kück, A. Raba, I. I.
E. Markovits, M. Cokoja and F. E. Kühn, ChemCatChem, 2014, 6,
1882-1886; (c) T. Yagyu, K. Yano,T. Kimata and K. Jitsukawa,
Organometallics, 2009, 28, 2342-2344; (d) M. J. Schultz, S. S.
Hamilton, D. R. Jensen and M. S. Sigman, J. Org. Chem., 2005,
70, 3343-3352; (e) F. Hanasaka, K. Fujita and R. Yamaguchi,
Organometallics, 2004, 23, 1490-1492; (f) M. Poyatos, J. A.
Mata, E. Falomir, R. H. Crabtree and E. Peris, Organometallics,
2003, 22, 1110.
5. (a) X. Hu, I. Castro-Rodriguez and K. Meyer, J. Am. Chem. Soc.,
2004, 126, 13464-13473; (b) A. A. Danopoulos, J. A. Wright, W.
B. Motherwell and S. Ellwood, Organometallics, 2004, 23,
4807-4810; (c) S. Dürr, B. Zarzycki, D. Ertler, I. Ivanović-
Burmazović and U. Radius, Organometallics, 2012, 31, 1730-
1742.
Table 2 Catalytic reactions at 35 °C.
A /
(K+L)
Reaction
Products / mol
Cat.
TON a
time / min
A
K
L
Cl
Blank
1
2
3 b
4 b
CoII(acac)2
a
180
30
60
180
60
30
69.4
731.7
675.0 116.7
587.2 104.1
653.9 149.3
473.3 130.2
0.5
88.8
2.1
3.8
−
26.6
5.8
4.2
3.8
3.6
3.2
36.6
43.1
52.4
32.8
17.2
70.0
57.0
36.2
47.9
24.8
526.0
525.8
468.1
533.0
396.4
b
TON = {cyclohexanol (A) + chlorocyclohexane (Cl) + 2 
{cyclohexanone (K) + ε-caprolactone (L)}} / cobalt compound.
b From ref. 17.
6. R. E. Cowley, R. P. Bontchev, E. N. Duesler and J. M. Smith,
Inorg. Chem., 2006, 45, 9771-9779.
7. R. E. Cowley, R. P. Bontchev, J. Sorrell, O. Sarracino, Y. Feng, H.
Wang and J. M. Smith, J. Am. Chem. Soc., 2007, 129, 2424-
2425.
8. J. J. Scepaniak, C. G. Margarit, R. P. Bontchev and J. M. Smith,
Acta Cryst., 2013, C69, 968-971.
9. M. K. Goetz, E. A. Hill, A. S. Filatov and J. S. Anderson, J. Am.
Chem. Soc., 2018, 140, 13176−13180.
10. R. Fränkel, U. Kernbach, M. B. Christianopoulou, U. Plaia, M.
Suter, W. Ponikwar, H. Nöth, C. Moinet and W. P. Fehlhammer.
J. Organomet. Chem., 2001, 617-618, 530-545.
11. S. Hikichi, K. Hanaue, T. Fujimura, H. Okuda and J. Nakazawa,
Dalton Trans., 2013, 42, 3346-3356.
12. A. P. Forshaw, R. P. Bontchev and J. M. Smith, Inorg. Chem.,
2007, 46, 3792-3794.
13. (a) A. P. Forshaw, J. M. Smith, A. Ozarowski, J. Krzystek, D.
Smimov, S. A. Zvyagin, T. D. Harris, H. I. Karunadasa, J. M.
Zadrozny, A. Schnegg, K. Holldack, T. A. Jackson, A. Alamiri, D.
M. Barnes and J. Telser, Inorg. Chem., 2013, 52, 144-159; (b) H.
E. Colmer, C. G. Margarit, J. M. Smith, T. A. Jackson and J.
Telser, Eur. J. Inorg. Chem., 2016, 2413-2423.
In summary, the synthesis of a heteroleptic cobalt(III)
tris(carbene)borate complex with a low degree of hindrance,
via aerobic oxidation of a cobalt(II) species, was successful. To
the best of our knowledge, 1[OTf] is the first heteroleptic
complex of the less hindered [PhB(MeIm)3]− to be
characterized by X-ray crystallography. This heteroleptic
complex was observed to be an efficient catalyst for the
oxidation of alkanes with mCPBA, even at ambient
temperatures. The homoleptic cobalt(III) bis([PhB(MeIm)3])
complex also exhibited catalytic activity at elevated
temperatures, but was inert at ambient temperatures. Both
the formation of the cobalt(III) species by the oxidation of the
cobalt(II) precursors, and the high catalytic performance of the
[PhB(MeIm)3]− ligand-containing complexes were attributed to
the higher electron-donating ability of the carbene donors
compared with the nitrogen donors of the related scorpionate
ligands, Tp* and ToM. Additionally, the catalytic data
presented, relating to the oxidation reaction in the presence of
14. F. Che, G.-F. Wang, Y.-Z. Li, X.-T. Chen and Z.-L. Xue, Inorg,
Chem. Commun., 2012, 21, 88-91.
4 | J. Name., 2012, 00, 1-3
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Journal Name
COMMUNICATION
15. I. Nieto, R. P. Bontchev, A. Ozarowski, D. Smirnov, J. Krzystek, J.
Telser and J. M. Smith, Inorg. Chim. Acta, 2009, 362, 4449-
4460.
View Article Online
DOI: 10.1039/C8DT04469D
16. (a) S. Pasko, L. G. Hubert-Pfalzgraf, A. Abrutis and J.
Vaissermann, Polyhedron, 2004, 23, 735-741; (b) H. Lee, C. H.
Lee., I. S. Oh, and I. M. Lee, Bull. Korean Chem. Soc., 2010, 31,
891-894; (c) M. Cortijo, C. Viala, T. Reynaldo, L. Favereau, I.
Fabing, M. S. Hooper, J. Autschbach, N. R. Ramond, J. Crassous
and J. Bonvoisin, Inorg. Chem., 2017, 56, 4555-4567.
17. T. Nishiura, T. Uramoto, Y. Takiyama, J. Nakazawa and S.
Hikichi., Molecules, 2018, 23, 1466.
18. R. R. Reinig, D. Mukherjee, Z. B. Weinstein, W. Xie, T. Albright,
B. Baird, T. S. Gray, A. Ellern, G. J. Miller, A. H. Winter, S. L.
Bud’ko and A. D. Sadow, Eur. J. Inorg. Chem. 2016, 2486-2494.
19. T. Nagataki, Y. Tachi and S. Itoh, Chem. Commun., 2006, 4016-
4018.
20. (a) J. Nakazawa, A. Yata, T. Hori, T. D. P. Stack, Y. Naruta and S.
Hikichi, Chem. Lett., 2013, 42, 1197-1199; (b) J. Nakazawa, Y.
Doi and S. Hikichi, Mol. Catal., 2017, 443, 14–24.
21. E. Tordin, M. List, U. Monkowius, S. Schindler and G. Knör,
Inorg. Chim. Acta, 2013, 402, 90-96.
22. (a) W. Nam, I. Kim, Y. Kim and C. Kim, Chem. Commun., 2001,
14, 1262-1263; (b) W. Nam, J. Y. Ryu,; I. Kim and C. Kim,
Tetrahedron Lett., 2002, 43, 5487-5490.
23. G. B. Shul’pin, D. A. Loginov, L. S. Shul’pina, N. S. Ikonnikov, V.
O. Idrisov, M. M. Vinogradov, S. N. Osipov, Y. V. Nelyubina and
P. M. Tyubaeva, Molecules, 2016, 21, 1593.
24. Acylperoxo complexes of nickel(II) formed during alkane
oxidation reaction have been characterized; ref. 11 and
follows; J. Nakazawa, S. Terada, M. Yamada and S. Hikichi, J.
Am. Chem. Soc., 2013, 135, 6010-6013.
25. (a) C. Tubaro, A. Biffis, E. Scattolin and M. Basato, Tetrahedron,
2008, 64, 4187-4195; (b) A. Biffis, C. Tubaro, E. Scattolin, M.
Basato, G. Papini, C. Santini, E. Alvarezc and S. Conejeroc,
Dalton Trans., 2009, 7223-7229.
This journal is © The Royal Society of Chemistry 20xx
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A table of contents entry
A first structure-determined heteroleptic cobalt(III) complex with the less
hindered tris(carbene)borate works as a catalyst precursor for alkane oxidation.
N
C
Cl
B
O
N
C
OO
H
Co
N
O
O
H
C
+
1