Molecular structure and spectroscopic properties of [Co(Me 2dtc)2{(Ph2PO)2BF2}] (Me2dtc = N,N-dimethyldithiocarbamate)

Article abstract of DOI:10.1016/j.ica.2013.10.028

Oxidation of a blue ethanolic mixture containing Co(BF₄) ₂·6H₂O and PClPh₂ by tetramethylthiuram disulfide afforded a red-colored complex having a cis-[Co^III(Me ₂dtc)₂(P)₂] environment (Me₂dtc ^- = N,N-dimethyldithiocarbamate), although the yield was relatively low. Single-crystal X-ray crystallography revealed that the product was [Co(Me₂dtc)₂{(Ph₂PO)₂BF ₂}] (1), where bis(diphenylphosphinito)difluoroborate was probably formed by hydrolysis of PClPh₂ followed by reaction with BF ₄^- in ethanol. The same complex was also prepared by hydrolysis of cis-[Co(Me₂dtc)₂(PHPh₂) ₂]BF₄ in a mixture of acetonitrile, methanol and water. The molecular structure and spectroscopic properties of complex 1 were compared with those of the corresponding Ph₂POMe complex, cis-[Co(Me ₂dtc)₂(Ph₂POMe)₂]BF₄.

Full text of DOI:10.1016/j.ica.2013.10.028

Inorganica Chimica Acta 410 (2014) 122–125
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Inorganica Chimica Acta
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Molecular structure and spectroscopic properties of [Co(Me2dtc)2
{(Ph2PO)2BF2}] (Me2dtc = N,N-dimethyldithiocarbamate)
a
a
Kyohei Sakano a, Syohei Yamaguchi a, Takayoshi Suzuki a, , Yukinari Sunatsuki , Masaaki Kojima ,
⇑
Kazuo Kashiwabara b
a Department of Chemistry, Faculty of Science, Okayama University, Tsushima-naka 3-1-1, Okayama 700-8530, Japan
b Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Nagoya 464-8602, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 June 2013
Received in revised form 29 October 2013
Accepted 30 October 2013
Available online 7 November 2013
Oxidation of a blue ethanolic mixture containing Co(BF4)2Á6H2O and PClPh2 by tetramethylthiuram
disulfide afforded a red-colored complex having a cis-[CoIII(Me2dtc)2(P)2] environment (Me2dtcÀ = N,N-
dimethyldithiocarbamate), although the yield was relatively low. Single-crystal X-ray crystallography
revealed that the product was [Co(Me2dtc)2{(Ph2PO)2BF2}] (1), where bis(diphenylphosphinito)difluor-
oborate was probably formed by hydrolysis of PClPh2 followed by reaction with BF4À in ethanol. The same
complex was also prepared by hydrolysis of cis-[Co(Me2dtc)2(PHPh2)2]BF4 in a mixture of acetonitrile,
methanol and water. The molecular structure and spectroscopic properties of complex 1 were compared
with those of the corresponding Ph2POMe complex, cis-[Co(Me2dtc)2(Ph2POMe)2]BF4.
Keywords:
(Phosphinito)borate
Chlorodiphenylphosphine
Cobalt(III)
Ó 2013 Elsevier B.V. All rights reserved.
Dithiocarbamate
Crystal structure
1. Introduction
characterization of complex 1 in comparison with those of the cor-
responding Ph2POMe complex, as well as the formation of
bis(diphenylphosphinito)difluoroborate anion.
N,N-Dimethyldithiocarbamate (Me2dtcÀ) [1] is a versatile auxil-
iary ligand for syntheses of cobalt(III) complexes containing vari-
ous P-donor ligands (P), [Co(Me2dtc)2(P)2]+, owing to its steric
2. Experimental
compactness and
r- and p-electron donating properties which
make the CoIII center softer for better bonding with soft P-donors
[2]. In previous studies, we have succeeded in synthesizing and
characterizing such complexes bearing a number of monodentate
and bidentate P-donor ligands [2–8]. Particularly interesting
examples are the complexes with diphenylphosphine (PHPh2),
cis- and trans-[Co(Me2dtc)2(PHPh2)2]BF4 [3], because Werner-type
cobalt(III) coordination compounds with PHPh2 are limited [9],
2.1. Materials
Chlorodiphenylphosphine (PClPh2), tetramethylthiuram disul-
fide (Me2NC(S)S–SC(S)NMe2) and other chemicals and solvents
were commercially available, and they were used as received.
The complexes, trans-[Co(Me2dtc)2(PPh3)2]BF4 [4] and cis-[Co(Me2-
dtc)2(PHPh2)2]BF4 [3], were prepared by the methods reported
previously.
presumably due to a very weak
we have attempted to prepare analogous complexes with chlorodi-
phenylphosphine (PClPh2) having a much weaker -donicity and a
r-donicity of PHPh2. In this study,
r
2.2. Preparation of [Co(Me2dtc)2{(Ph2PO)2BF2}] (1)
larger steric demand than PHPh2 [10]. To our best knowledge the
only one precedent example of cobalt(III) compound with PClPh2
g
5–C5H5À) [11].
2.2.1. Method A
is [CpCo{S2C2(CN)2}(PClPh2)] (Cp =
Under a dinitrogen atmosphere PClPh2 (1.21 g, 5.48 mmol) was
added dropwise to an ethanol solution (60 cm3) of Co(BF4)2Á6H2O
(0.793 g , 2.33 mmol), and the mixture was refluxed for 24 h. After
cooling the mixture in an ice bath, a solution of tetramethylthiu-
ram disulfide (0.503 g, 2.09 mmol) in a mixture of dichlorometh-
ane and ethanol (1:1, 30 cm3) was added dropwise for 2 h. The
resulting green precipitate of [Co(Me2dtc)3] was filtered off, and
the filtrate was concentrated under reduced pressure, affording a
A similar reaction with PClPh2 to that for cis-[Co(Me2dtc)2
(PHPh2)2]BF4, however, gave an unexpected bis(diphenylphosphi-
nito)difluoroborate complex, [Co(Me2dtc)2{(Ph2PO)2BF2}] (1). Here,
we describe the molecular and crystal structure and spectroscopic
⇑
Corresponding author. Tel./fax: +81 862517900.
E-mail address: suzuki@okayama-u.ac.jp (T. Suzuki).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.10.028

K. Sakano et al. / Inorganica Chimica Acta 410 (2014) 122–125
123
greenish oily residue. The residue was dissolved in a minimum
2.4. X-ray crystallographic study
amount of methanol, and the solution was subjected to column
chromatography using Sephadex LH-20 resin. A red band was
eluted with methanol, and the eluate was evaporated at room tem-
perature and ambient pressure to give a red precipitate. The pre-
cipitate was collected by filtration and recrystallized from
methanol by vapor diffusion of diethyl ether, depositing red block
crystals. Yield: 54.6 mg (3.5%). Anal. Calc. for C30H32BCoF2N2O2P2-
S4: C, 48.01; H, 4.30; N, 3.73. Found: C, 47.30; H, 4.05; N, 3.61%.
1H NMR (CDCl3, 400 MHz, 22 °C): d 2.47 (s, N–CH3, 6H), 2.80 (s,
N–CH3, 6H), 7.12 (t, Ph, J = 7.3 Hz, 4H), 7.21 (t, Ph, J = 7.3 Hz, 2H),
7.40–7.48 (m, Ph, 6H), 7.67–7.71 (m, Ph, 4H), 8.00–8.07 (m, Ph,
The X-ray diffraction data of 1 were obtained at À85(2) °C on a
Rigaku R-axis rapid imaging plate detector with a graphite-mono-
chromated Mo Ka radiation (k = 0.71073 Å). A suitable crystal was
mounted with a cryoloop and flash-cooled by cold nitrogen stream.
Data were processed by the Process-Auto program package [12],
and absorption corrections were applied by the numerical integra-
tion method from crystal shape [13]. The structure was solved by
the direct method using SIR2004 [14], and refined on F2 (with all
independent reflections) using SHELXL97 program [15]. All non-H
atoms were refined anisotropically. Hydrogen atoms were intro-
duced at the positions calculated theoretically and treated with
riding models. All calculations were carried out using CRYSTALSTRUC-
TURE software package [16].
4H). IR (KBr disc): m , m .
(B–F) 1096 cmÀ1 (P–O) 1005 cmÀ1
2.2.2. Method B
Crystal data are collected in Table 1.
To an acetonitrile solution (3 cm3) of cis-[Co(Me2dtc)2
(PHPh2)2]BF4 (49.5 mg, 0.065 mmol) was added a methanol solu-
tion (1 cm3) of LiBF4 (12.2 mg, 0.13 mmol) and an aqueous NaOH
solution (5.9 mg, 0.15 mmol, 1 cm3). The mixture was stirred in
the dark for 24 h at room temperature, and the resulting green pre-
cipitate was filtered off. The brown filtrate was evaporated under
reduced pressure, and the resulting oily residue was extracted with
dichloromethane. The filtered extract was concentrated to ca.
2 cm3 by flow of dry nitrogen, and the red brown concentrate
was subjected to column chromatography using Sephadex LH-20
resin. A major red band and a minor green band were eluted with
methanol. The major red eluate was evaporated to dryness under
reduced pressure, and the resulting crude product was recrystal-
lized from dichloromethane/methanol by slow evaporation of the
solvents at room temperature, depositing red block crystals. Yield:
7.8 mg (16%).
3. Results and discussion
3.1. Preparation and structural characterization of cobalt(III) complex
According to the synthetic methods for trans- and cis-[Co(Me2-
dtc)2(PHPh2)2]BF4 [3], we have tried to prepare the analogous
PClPh2 complexes. Firstly, the ligand substitution of PClPh2 for
PPh3 in trans-[Co(Me2dtc)2(PPh3)2]BF4 was attempted, likewise to
the preparation of trans-[Co(Me2dtc)2(PHPh2)2]BF4. However, the
reaction gave a complicated mixture of products, and no complex
could be isolated from the mixture except for [Co(Me2dtc)3] and
trans-[Co(Me2dtc)2(PPh3)2]BF4. Then, we examined an oxidative
addition of tetramethylthiuram disulfide to a mixture of cobalt(II)
tetrafluoroborate and PClPh2. In the case of PHPh2 this method
gave the cis-isomer of [Co(Me2dtc)2(PHPh2)2]BF4. When PClPh2
was added to a pale pink solution of Co(BF4)2Á6H2O in ethanol,
the color of reaction mixture immediately turned to blue, unlike
for PHPh2 which afforded a reddish brown solution. To this mixture
was added a solution of tetramethylthiuram disulfide in a mixture
of dichloromethane and ethanol. This reaction also gave a compli-
cated mixture of products, and the main product was green
[Co(Me2dtc)3]. After removal of [Co(Me2dtc)3] by washing with
diethyl ether, the residue was subjected to column chromatogra-
phy (Sephadex LH-20), and a red band was collected by elution
with methanol. From the eluate red crystals of 1 were obtained.
Although the yield of 1 was only a few percent, it was reproducible
in several experiments.
2.3. Measurements
Infrared spectra were measured on a JASCO FTIR-001 spectro-
photometer using KBr disc method. UV–Vis absorption spectra
were recorded on a JASCO V-550 spectrophotometer at room tem-
perature. Proton and phosphorus-31 NMR spectra were acquired
on a Varian 400-MR spectrometer at 22 °C. The 1H NMR chemical
shifts were referenced to the residual 1H NMR signals of the deu-
terated solvents and are reported versus TMS. The 31P NMR chem-
ical shifts were referenced to the external 85% H3PO4.
The molecular and crystal structure of 1 was determined by X-
ray crystallography. It was found that compound 1 crystallized in a
triclinic space group P1 with Z = 4. There are two crystallographi-
Table 1
Crystallographic data for compound 1.
ꢀ
Chemical formula
Formula weight
T (K)
Crystal color and shape
Size of specimen (mm)
Crystal system
Space group
C30H32BCoF2N2O2P2S4
750.50
188(2)
cally independent complex molecules in the asymmetric unit,
and both molecules are similar in structure, as shown in Fig. 1.
It was revealed that these complexes contain an anionic
Ph2POBF2OPPh2À ligand, which forms a six-membered chelate ring.
The chelate ring in molecule 1 (with Co1) has a skew conformation,
while that in molecule 2 (with Co2) has a distorted envelope con-
formation. Regardless, the chelate bite angles are very similar to
each other: 93.44(4)° versus 93.21(4)°. The average P–O, O–B and
red, block
0.20 Â 0.20 Â 0.20
triclinic
ꢀ
P1
Z
4
a (Å)
b (Å)
c (Å)
13.7205(7)
14.4337(8)
17.7699(8)
105.946(2)
90.256(2)
91.363(2)
3380.8(3)
1.474
0.892
0.081
0.065
0.190
B–F bond lengths in
1 are 1.574(6), 1.46(1) and 1.38(1) Å,
respectively. These bond lengths Àare comparable to those of the
a
(°)
b (°)
previously reported R2POBF2OPR2 complexes [17–19].
c
(°)
The above-mentioned P–O bonds (average 1.574(6) Å) are
shorter than those of cis-[Co(Me2dtc)2(Ph2POMe)2]BF4 (average
1.604(4) Å), which has the same coordination environment with
monodentate phosphinite (Ph2POMe) [2]. The Co–P bond lengths
in 1 are in the range of 2.222(1)–2.234(1) Å (average 2.227(2) Å),
which are also a little shorter than those in cis-[Co(Me2dtc)2
(Ph2POMe)2]BF4 (average 2.245 Å). These bond shortenings are
U (Å3)
Dcalc (Mg mÀ3
l
)
(Mo K
a
) (mmÀ1
)
Rint
R1 (F2: Fo2 > 2
r
(Fo2))
wR2 (F2: all data)
Goodness-of-fit (GOF) on F2
1.073

124
K. Sakano et al. / Inorganica Chimica Acta 410 (2014) 122–125
Fig. 1. ORTEPs (50% probability level, H-atoms omitted for clarity) of two crystallographically independent molecules of [Co(Me2dtc)2{(Ph2PO)2BF2}] (1).
probably caused by the anionic nature, as well as the chelate effect,
of bidentate Ph2POBF2OPPh2 ligand.
structure obtained by X-ray analysis (Fig. 1) is maintained in
solution.
À
The Co–S bonds in 1 showed a significant difference between
the chemically non-equivalent bonds. The Co–S bonds trans to P
donor (average 2.304(2) Å) was apparently longer than the mutu-
ally trans Co–S bonds (average 2.260(2) Å), indicating a strong trans
influence of Ph2POBF2OPPh2À. This extent of elongation by the
bis(phosphinito)borate (ꢀ0.04 Å) is much larger than that by Ph2-
POMe (ꢀ0.02 Å) [2].
Fig. 2 compares the visible absorption spectrum of complex 1
with that of cis-[Co(Me2dtc)2(Ph2POMe)2]BF4. The first and the sec-
ond d–d transition bands of 1 are observed at 19600 cmÀ1
(e (e
= 822 MÀ1 cmÀ1) and 24300 cmÀ1 = 3350 MÀ1 cmÀ1), respec-
tively, which are relatively blue-shifted from those of cis-[Co(Me2-
dtc)2(Ph2POMe)2]BF4 (18330 and 23200 cmÀ1). This indicates that
À
the ligand-field strength of anionic (Ph2PO)2BF2 is moderately
stronger than that of a neutral Ph2POMe, being consistent with
the above-mentioned difference in their Co–P bond lengths.
3.2. 1H NMR and visible absorption spectra
In the 1H NMR spectrum of 1 in CDCl3 two resonances for
N–CH3 were observed at d 2.47 and 2.80, corresponding to the
molecular C2 symmetry of complex 1. Also, the spectral patterns
for the phenyl protons were consistent with the proposed
molecular C2 symmetry. Thus, it is concluded that the molecular
3.3. Formation of (Ph2PO)2BF2 and its cobalt(III) complex
À
In this study the formation of bis(diphenylphosphinito)difluo-
roborate anion, Ph2POBF2OPPh2À, from chlorodiphenylphosphine
was observed [20,21]. In the first place of this conversion, PClPh2
would presumably be hydrolyzed in wet ethanol to give Ph2P(O)H.
The 31P{1H} NMR spectrum of PClPh2 in CDCl3 gave a single reso-
nance at d 82.33 (Fig. 3a); however, a CD3OD solution of PClPh2
gave a completely different spectrum, as shown in Fig. 3b. The
main resonance at d 24.33 was a characteristic triplet with
JP–D = 76 Hz. A commercially available diphenylphosphine oxide,
Ph2P(O)H, gave a singlet 31P{1H} NMR signal at d 22.11 in CDCl3
(Fig. 3c), but in CD3OD the phosphine oxide showed a triplet
(d 24.17, JP–D = 75 Hz; Fig. 3d) due probably to a H/D exchange on
P atom. These experiments suggested that PClPh2 was easily
hydrolyzed to give Ph2P(O)D in CD3OD. In wet ethanol a similar
hydrolysis would take place to give a diphenylphosphine oxide
and a chloride anion, the latter of which seemed to be responsible
for a blue color of a mixture of Co(BF4)2Á6H2O and PClPh2 in etha-
nol. Duncan et al. suggested the same hydrolysis of PClPh2 in the
preparation of rhodium(III) and iridium(III) complexes bearing a
hydrogen-bonded Ph2PO–HÁ Á ÁOPPh2 ligand [20,21].
The most annoying result in this study is a very low yield of the
(Ph2PO)2BF2 complex, 1. We have also attempted to prepare
complex 1 using Ph2P(O)H, instead of PClPh2, but the yield was
not improved. In solution diphenylphosphine oxide exists as
an equilibrium mixture with its valence tautomer of
diphenyl(hydroxyl)phosphine, Ph2P(OH), which acts as a P-donor
ligand to a soft metal ion [18,19], but cobalt(II) ion can not be a
suitable Lewis acid for formation of its Ph2P(OH) complex.
Thus, little formation of a precursor for complex 1, that is
cis-[Co(Me2dtc)2(Ph2POH)2]+ or [Co(Me2dtc)2(Ph2PO–HÁ Á ÁOPPh2)],
in the oxidation products from an ethanolic reaction mixture of
Fig. 2. Absorption spectra of [Co(Me2dtc)2{(Ph2PO)2BF2}] (blue solid line) and cis-
[Co(Me2dtc)2(Ph2POMe)2]BF4 (red broken line) in visible region (in acetonitrile at
room temperature). (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)

K. Sakano et al. / Inorganica Chimica Acta 410 (2014) 122–125
125
Fig. 3. 31P{1H} NMR spectra (22 °C, 162 MHz) of (a) PClPh2 in CDCl3, (b) PClPh2 in CD3OD, (c) Ph2P(O)H in CDCl3, and (d) Ph2P(O)H in CD3OD.
Co(BF4)2, PClPh2 {or Ph2P(O)H} and tetramethylthiuram disulfide
would be responsible for the low yield of complex 1. Once a
bis(Ph2POH) complex or a hydrogen-bonded Ph2PO–HÁ Á ÁOPPh2
complex was formed, conversion to the correspÀonding (Ph2PO)2-
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.ica.2013.10.028.
À
BF2 complex by a reaction with BF3ÁEt2O or BF4 anion was well
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