Synthesis, reactivity and complexation studies of N,S exo- heterodisubstituted o-carborane ligands. Carborane as a platform to produce the uncommon bidentate chelating (pyridine)N-C-C-C-S(H) motif

Article abstract of DOI:10.1039/b715362g

The synthesis of N,S-heterodisubstituted 1-(2′-pyridyl)-2-SR-1,2- closo-C₂B₁₀H₁₀ compounds (R = Et, 2; R = ⁱPr, 3) has been accomplished starting from 1-(2′-pyridyl)-1,2- closo-C₂B₁₀H₁₁ (1), and their partial deboronation reaction leading to the structurally chiral [7-(2′-pyridyl)- 8-SR-7,8-nido-C₂B₉H₁₀]^- derivatives (R = Et, [4]^-; R = ⁱPr, [5]^-) has been studied. Capillary electrophoresis combined with the chiral selector α-cyclodextrin has permitted the separation of the electrophoretically pure racemic [7-(2′-pyridyl)-8-SR-7,8-nido-C₂B ₉H₁₁]^- ions into two peaks each one corresponding to the interaction of one enantiomer with the α- cyclodextrin. The N,S-heterodisubstituted o-carborane containing a mercapto group, 1-(2′-pyridyl)-2-SH-1,2-closo-C₂B₁₀H ₁₀, 1, is one of the two examples of a rigid bidentate chelating (pyridine)N-C-C-C-S(H) motif having been structurally fully characterized. To study the potential of such a binding site, 1 has been tested as a ligand with metal ions requiring different coordination numbers, two (Au⁺) and four (Pd²⁺ and Rh⁺). The crystal structures of the Pd(ii) and Au(i) complexes are reported. For the Pd(ii) complex, 1 acts as a bidentate ligand whereas for Au(i), 1 acts as a monodentate ligand through the thiolate. The Royal Society of Chemistry.

Full text of DOI:10.1039/b715362g

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www.rsc.org/dalton | Dalton Transactions
Synthesis, reactivity and complexation studies of N,S exo-heterodisubstituted
o-carborane ligands. Carborane as a platform to produce the uncommon
bidentate chelating (pyridine)N-C-C-C-S(H) motif†‡§
F. Teixidor,a A. Laromaine,a R. Kiveka¨s,b R. Sillanpa¨a¨,c C. Vin˜as,*a R. Vespalecd and H. Hora´kova´d
Received 5th October 2007, Accepted 14th November 2007
First published as an Advance Article on the web 6th December 2007
DOI: 10.1039/b715362g
The synthesis of N,S-heterodisubstituted 1-(2ꢀ-pyridyl)-2-SR-1,2-closo-C2B10H10 compounds (R = Et, 2;
i
R = Pr, 3) has been accomplished starting from 1-(2ꢀ-pyridyl)-1,2-closo-C2B10H11 (1), and their partial
deboronation reaction leading to the structurally chiral [7-(2ꢀ-pyridyl)-8-SR-7,8-nido-C2B9H10]−
i
derivatives (R = Et, [4]−; R = Pr, [5]−) has been studied. Capillary electrophoresis combined with the
chiral selector a-cyclodextrin has permitted the separation of the electrophoretically pure racemic
[7-(2ꢀ-pyridyl)-8-SR-7,8-nido-C2B9H11]− ions into two peaks each one corresponding to the interaction
of one enantiomer with the a-cyclodextrin. The N,S-heterodisubstituted o-carborane containing a
mercapto group, 1-(2ꢀ-pyridyl)-2-SH-1,2-closo-C2B10H10, 1, is one of the two examples of a rigid
bidentate chelating (pyridine)N-C-C-C-S(H) motif having been structurally fully characterized. To
study the potential of such a binding site, 1 has been tested as a ligand with metal ions requiring
different coordination numbers, two (Au+) and four (Pd2+ and Rh+). The crystal structures of the Pd(II)
and Au(I) complexes are reported. For the Pd(II) complex, 1 acts as a bidentate ligand whereas for
Au(I), 1 acts as a monodentate ligand through the thiolate.
heterodisubstituted 1-PR2-2-SR-1,2-closo-C2B10H10 compounds.9
Recently, the synthesis, partial deboronation and crystal structures
Introduction
of 1-(2ꢀ-pyridyl)-1,2-closo-C2B10H11 and [7-(2ꢀ-pyridyl)-7,8-nido-
C2B9H11]− have been reported.10 The first full characterization
of an o-carborane containing a mercapto group, 1-(2ꢀ-pyridyl)-
2-SH-1,2-closo-C2B10H10, 1, has been recently communicated.11
Compound 1 represents a potential ligand for metal complexation
acting as a bidentate chelating N,S-ligand. There are only two
molecules reported with the bidentate chelating (pyridine)N-C-C-
C-S(H) moiety whose crystal structures have been determined.
One corresponds to 1 shown in Fig. 1C, and the second to the
thiofenchone derivative shown in Fig. 1A.12 Of notice is that
whereas 1 crystallizes as such, the thiofenchone derivative requires
protonation with HCl. In what concerns metal complexes of the
bidentate chelating (pyridine)N-C-C-C-S(H) motif, only one metal
Derivatives of o-carborane 1-R-1,2-closo-C2B10H11 bearing a
nitrogen-containing substituent R attached to the cage carbon
atom (Cc), have attracted attention as potential medicinal agents
for use in boron neutron capture therapy (BNCT) and as
potentially-chelating carboranyl ligand precursors.1
Cyclodextrins are chiral selectors of first choice in chromatogra-
phy and electrophoresis.2 a-Cyclodextrin and its derivatives proved
to be powerful selectors in chiral liquid chromatography separa-
tions and preparations of zwitterionic boron cluster compounds.3
Surprisingly, a-cyclodextrin has been shown to be an effective
chiral selector for a set of randomly chosen boron cluster anions
if capillary electrophoresis was the separation technique.4
Our group has been concerned with the synthesis of dithio-
ether 1,2-(SR)2-1,2-closo-C2B10H10,5 monothioether 1-SR-2-Rꢀ-
1,2-closo-C2B10H10,6 diphosphino 1,2-(PR)2-1,2-closo-C2B10H10,7
monophosphino 1-PR2-2-Rꢀ-1,2-closo-C2B10H10
and S,P-
8,7d
aInstitut de Cie`ncia de Materials de Barcelona, Campus U.A.B, 08193,
Bellaterra, Spain
bDepartment of Chemistry, P.O. Box 55, FIN-00014. University of Helsinki,
Finland
cDepartment of Chemistry. University of Jyva¨skyla¨, FIN-40531, Finland
dInstitute of Analytical Chemistry, Czech Academy of Sciences, Veverˇ´ı 97,
611 42, Brno, Czech Republic
† It is a pleasure for the authors to dedicate this paper to Prof. Dr. Ken
Wade on the occasion of his 75th birthday, in recognition of his outstanding
contribution to the fields of borane clusters and organometallic chemistry.
‡ CCDC reference numbers 663535–663537. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b715362g
§ Electronic supplementary information (ESI) available: UV spectra of
compounds [NMe4][4], [NMe4][5], [NMe4][9]–[NMe4][12]. Chiral separa-
tion of [NMe4][5], [NMe4][9]–[NMe4][11]. See DOI: 10.1039/b715362g
Fig. 1 Examples of bidentate chelating (pyridine)N-C-C-C-S(H) ligands:
B and C rigid and A and D non-rigid.
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(Ru) complex of a geometrically similar chelating coordination site
to that of 1 (see ligand B in Fig. 1) has been published.13 The lack
of information on these bidentate chelating (pyridine)N-C-C-C-
S(H) ligands was even more pronounced when the restriction of
rigidity on the moiety linking the pyridine and the –S(H) group
was removed. This led to ligands with no double bonds between
the two denticities of the ligand. For such a situation only one
crystal structure of a Ni complex with the bulky ligand shown in
Fig. 1D has been described.14
[1-(2ꢀ-pyridyl)-2-S-1,2-closo-C2B10H10]− thiolate ligand with metal
complexes.
Compounds 2 and 3 have been characterized by elemental
analyses, IR and NMR techniques. The IR spectra show typical
m(B–H) absorptions at frequencies above 2550 cm−1, characteristic
1
for 1,2-closo-C2B10H10 derivatives.15 The 11B{ H}-NMR of 2 and
3 present spectral data in the typical −2.0 to −10.5 ppm range
for a closo-C2B10 cluster. This is even more compressed than the
spectral range observed for 1-SR-1,2-closo-C2B10H11 and 1-PPh2–2-
SR-1,2-closo-C2B10H10 compounds that appear in the range 0 to
−10.5 and −1 to −13 ppm, respectively. The nature of the R alkyl
This paper describes the synthesis of N,S-heterodisubstituted 1-
(2ꢀ-pyridyl)-2-SR-1,2-closo-C2B10H10 (R= Et, 2; iPr, 3) compounds
and their partial degradation which leads to the racemic anionic
1
group does not greatly influence the 11B{ H}-NMR spectrum. In
i
[7-(2ꢀ-pyridyl)-8-SR-7,8-nido-C2B9H10]− (R = Et, [4]−; Pr, [5]−)
this way a 1 : 1 : 2 : 2 : 4 pattern for 2 and 1 : 1 : 2 : 6 pattern for 3
are observed as was expected for Cc non-equivalently substituted
carborane. The resonances of intensity 4 and 6 shall be attributed
to the coincidental overlap of two and three resonances of intensity
two, respectively.
derivatives. Capillary electrophoresis with cyclodextrin in addition
to instrumental techniques has been used to separate and identify
these racemic mixtures. The absence of metal complexes with
bidentate chelating (pyridine)N-C-C-C-S(H) ligands motivated us
to start preliminary coordination studies on 1 with Pd(II), Au(I),
and Rh(I) cations. Thus complexes 6–8 with Pd(II), Au(I) and
Rh(I) are reported along with the crystal structures of the Pd(II)
and Au(I) complexes. The few existing examples of complexes
with the bidentate chelating (pyridine)N-C-C-C-S(H) ligands do
not permit one to draw many conclusions on the influence of the
carborane cage in such a chelating motif but their complexes may
help to fill this important void.
2
Partial deboronation of 1-(2ꢀ-pyridyl)-2-SR-1,2-closo-
i
C2B10H10 (R = Et, Pr). Partial deboronation or the formal
removal of a B+ from 1-(2ꢀ-pyridyl)-2-SR-1,2-closo-C2B10H10 (R =
Et, 2; iPr, 3) derivatives to yield the corresponding anionic species
[7-(2ꢀ-pyridyl)-8-SEt-7,8-nido-C2B9H10]− [4]− and [7-(2ꢀ-pyridyl)-
8-SiPr-7,8-nido-C2B9H10]− [5]− was readily accomplished using
KOH in ethanol (see Scheme 1B).16 These species were isolated as
the tetramethylammonium salts in analytically stoichiometric but
not in isomeric purity (see Fig. 2). This is explained by considering
that two equivalent boron atoms exist in 1-(2ꢀ-pyridyl)-2-SR-1,2-
closo-C2B10H10 that are susceptible to the deboronation process.
These are the boron atoms adjacent to both cluster carbon atoms.
Upon nucleophilic attack to remove only one boron in the cluster,
it is expected that the anion generated will be obtained as a
Results and discussion
Reactivity of 1-(2ꢀ-pyridyl)-2-SH-1,2-closo-C2B10H10
1
Synthesis and characterization of 1-(2ꢀ-pyridyl)-2-SR-1,2-
closo-C2B10H10 (R = Et, iPr) species. Starting from 1 the synthe-
sis of closo-Cc-heterodisubstituted 1-(2ꢀ-pyridyl)-2-SR-1,2-closo-
C2B10H10 (R = Et, 2, Pr, 3) compounds has been accomplished
i
after deprotonation with KOH in ethanol followed by alkylation
with the appropriate alkyl bromide in 81 and 88% yield respec-
tively (see Scheme 1A). These compounds contain two possible
coordinating sites, Cc-C–N and Cc-SR, in the same carborane
cluster. This is the first time that bidentate ligands with these
functional groups have been reported and is the result of advances
in the development of easy routes to alkylate the mercapto group in
carborane chemistry. The existence of one available Cc-pyridyl unit
in 1-(2ꢀ-pyridyl)-1,2-closo-C2B10H11 has allowed the introduction
of a second and different functional group. These ligands add to
the 1,2-(SR)2–1,2-closo-C2B10H10,5 1,2-(PR2)2–1,2-closo-C2B10H10
7
9b
and 1-PPh2–2-SR-1,2-closo-C2B10H10 series and open the way
to study the reactivity of chelating S,N-heterodisubstituted
Fig. 2 Formation of a racemic mixture of the [7-(2ꢀ-pyridyl)-8-SR-
7,8-nido-C2B9H10]− anions upon deboronation of 1-(2ꢀ-pyridyl)-2-SR-1,2-
closo-C2B10H10.
Scheme
1
A, synthetic pathway to N,S closo-heterodisubstituted
o-carborane derivatives. B, their partial degradation.
346 | Dalton Trans., 2008, 345–354
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racemic mixture. The heterodisubstituted closo compounds show
a similar reactivity towards nucleophilic attack by EtO− as that
reported for 1-SR-1,2-closo-C2B10H11 compounds. The existence
of the pyridyl group does not alter the stability of the Cc–S bond
towards EtO−.
The nido species have been characterized by elemental analyses,
MALDI-TOF-MS, IR and NMR techniques. Both [4]− and [5]−,
show strong IR m(B–H) resonances near 2520 cm−1, in agreement
1
with a nido [C2B9]− cluster.15 The 11B{ H}-NMR resonances for
[4]− and [5]− appear in the range −8 to −36 ppm with patterns 2 :
1 : 1 : 2 : 1 : 1 : 1 and 2 : 1 : 2 : 1 : 1: 1 : 1, respectively, in agreement
with an asymmetric nido [C2B9H10]− cluster. The H{ B} NMR
spectra of [4]− and [5]− shows the resonances that correspond to
the Et- and iPr-groups and the three common ones: i) resonances
between 8.37 and 7.00 ppm corresponding to the pyridyl group, ii)
resonances between 2.51–0.24 ppm corresponding to the hydrogen
atoms bonded to boron and iii) a resonance at high field −2.05 ppm
characteristic of the B–H–B hydrogen bridge.
1
11
Fig. 3 The structure of the anion [5]− in [NMe4][5]. Displacement
ellipsoids are drawn at 30% probability level. Hydrogen atoms are omitted
for clarity.
The anionic nido compounds were also analyzed by MALDI-
TOF-MS analysis. As an example, the highestpeakfor [5]− displays
a signal with isotopic distribution centred at m/z 284.4 corre-
ꢀ
i
˚
the Cc–Cpyridyl distance 1.510(3) A in [NMe4][7-(2 -pyridyl)-8-S Pr-
7,8-nido-C2B9H10], is appreciably smaller than the Cc–P distance
i
9b
˚
of 1.855(3) A in [NMe4][7-PPh2–8-S Pr-7,8-nido-C2B9H10]. The
packing of the anions and cations does not show any abnormal
features: the cation has six anion neighbours and the anion has six
cation ones. Both heteroatoms form very weak H-bonds with CH
1
sponding to the expected anionic fragment 12C10 H2111B914N32S and
two peaks at 238.3 and 208.3. The experimental peak position
and isotopic distribution match the theoretical calculations that
correspond to the molecular peak and the -iPr and -SiPr cleavage
products respectively.
˚
hydrogens. The shortest N · · · H distance is 2.68 A.
Spectral study of [NMe4][4] and [NMe4][5]
Crystal structure of
[NMe4][7-(2ꢀ-pyridyl)-8-SiPr-7,8-nido-C2B9H10]
UV electrospectrophotometry is a simple accessible detection tech-
nique for anionic boron clusters.10b To optimize the photometric
detection, UV spectra of the anions [4]−, [5]− and several reported
thioether and pyridyl derivatives, [7-Rꢀ-8-SR-7,8-nido-C2B9H10]−
(Rꢀ = H, R = Et, [9]−; Rꢀ = R = Ph, [10]−; Rꢀ = Me, R =
Ph, [11]− and [NMe4][7-(2ꢀ-pyridyl)-7,8-nido-C2B9H11]; [12]−, were
measured before running electrophoretic experiments in order
to determine the influence of the exo-substituents (Table 2).
The investigated anions have low molar extinction coefficients
at wavelengths between 200 and 210 nm that can be used for
detection. The weakest UV-light absorption was for the species
[9]− and monotonously decreased up to 235 nm. The phenyl group
bonded to Cc extend the light absorption to higher wavelengths
and provoked formation of absorption maxima above 200 nm.
The pyridine ring shifts the absorption cut-off to slightly higher
wavelengths than the phenyl and thiophenyl groups.
Crystallization by slow evaporation of [NMe4][5] in acetone
at a controlled temperature (4 ◦C), afforded air and moisture
insensitive yellow single crystals suitable for X-ray analysis. The
ORTEP plot of the structure of the anion [5]− is presented in
˚
Fig. 3 and selected bond lengths (A), angles and torsion angles
(◦) for [5]− in Table 1. Although it has different substituents on
the cluster carbon atoms, the molecular structure of [NMe4][5] is
similar to that of [NMe4][7-PPh2–8-SiPr-7,8-nido-C2B9H10].9b The
S–Cc and Cc–Cc bond lengths are comparable in both compounds
despite large differences in the Cc-substituents. In this regard,
◦
◦
˚
Table 1 Selected bond lengths (A), angles ( ) and torsion angles ( )
of [NMe4][5]
S–C8
S–C19
C7–C8
C7–C13
C8–S–C19
C8–C7–C13
C8–C7–C13–N14
1.786(3)
1.834(3)
1.603(3)
1.510(3)
103.05(12)
118.0(2)
97.9(3)
C7–B11
C8–B9
B9–B10
B10–B11
S–C8–C7
1.613(4)
1.648(4)
1.832(5)
1.802(4)
118.51(18)
Capillary electrophoresis
The simplest variant of the technique, capillary electrophoresis in
free solution, is dominant in electrophoretic methods developed
Table 2 Light absorption characteristics of studied monothioethers of the type [7-R-8-SRꢀ-7,8-nido-C2B9H10]−
Compound
UV cut-off/nm
k200/nm
e200/L mol−1 cm−1
k1/nm
e1/L mol−1 cm−1
k2/nm
e2/L mol−1 cm−1
[4]−
317
317
268
308
308
400
200
200
200
200
200
204
1.31 × 104
1.07 × 104
6.68 × 103
4.06 × 104
1.84 × 104
5.99 × 103
209
211
—
260
258
263
1.26 × 104
1.03 × 104
—
260
259
—
—
—
4.18 × 103
3.00 × 103
—
[5]−
[9]−
[10]−
[11]−
[12]−
6.68 × 103
1.05 × 104
2.87 × 103
—
—
339
2.95 × 103
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Table 3 Influence of the a-cyclodextrin concentration on the difference
in migration speed of atropoisomers of investigated chiral anions, Dl, in
the background electrolyte obtained by mixing of aqueous buffer, which
was prepared by adjusting 14.4 mmol L−1 methylsulfonic acid to pH 7.3
with TRIS, and methanol in 7 : 3 (v/v) ratio
for both achiral and chiral analysis of charged organic compounds
of low molecular mass.2 Application of capillary electrophoresis
to the analysis of electrophoretically charged cluster species has
been reported.4 In this work capillary zone electrophoresis was
used with the aim of determining the chemical purity and chirality
of the anions [4]−, [5]−, [9]−–[12]−.
a-Cyclodextrin concentration/mmol L−1
Compound
0.3
1.6
3.0
6.0
9.0
14.0
18.0
Chemical purity
a
a
[4]−
0.07
0.09
1.40
0
0.13
0.19
0.22
0.23
0.20
a
a
a
[5]−
0.23
0.25
The background electrolyte at pH 7.3 (see Experimental section)
was selected to check the chemical purity of these monothioether
anions. Electrophoretic analysis revealed that all the anions are
electrophoretically pure.
[9]−
0.12
1.61
0
0.06
a
a
a
a
a
[10]−
[11]−
0.07
0.09
0.07
0.09
0.08
0.08
0.05
a
a
0
a Not measured.
Chirality
Separation of a racemic compound or ion, which is electrophore-
tically pure, into two peaks by action of a chiral selector is
evidence for its chirality.17,2 The tetramethylammonium salts of the
investigated racemic boron cluster anions are practically insoluble
in water but they easily dissolve in polar organic solvents like
methanol, ethanol, acetonitrile or acetone, which, however, do
not dissolve native cyclodextrins. Water–organic solvents must be
thereforeusedforchiralseparations. Theorganicconstituentofthe
background electrolyte (BGE) dissolves boron cluster anions and
adjusts the strength of their interaction with the cavity of the used
cyclodextrin, which is excessively strong in aqueous solution. The
chirality of the anionic species was verified by using a-cyclodextrin
as the chiral selector.
A voltage of −20 kV was applied to the polyacrylamide
coated fused silica capillary18 of a 53 cm separation length. BGE
containing a-cyclodextrin was prepared daily by dissolution of the
proper amount from the stock aqueous TRIS buffer adjusted with
methylsulfonic acid at pH 7.3. After dissolving a-cyclodextrin, the
buffer was mixed with methanol in 7 : 3 (v/v) ratio.
Chiral discrimination of any compound with a proper chiral
selector depends on the chiral selector concentration in the
background electrolyte and passes through a maximum.2b A wide
range of a-cyclodextrin concentrations had to be used for the
generation of a measurable separation selectivity for these ions.
The influence of the a-cyclodextrin concentration on the difference
of migration speed of atropoisomers of the investigated chiral
anions separated with a-cyclodextrin, Dl, was therefore measured
up to an 18 mmol L−1 concentration of a-cyclodextrin. This
concentration approaches the solubility limit of a-cyclodetrin in
the water–methanol 7 : 3 (v/v) mixture. Measurable Dl values
evidence electrophoretic separation of the studied compounds into
two zones with clearly developed maxima. In Fig. 4 the separation
of [4]− into its enantiomers is shown. For chiral separations of
other investigated anions see ESI.§ Table 3 shows that chirality
was safely evidenced for any stable compound using more than
one a-cyclodextrin concentration.
Fig. 4 Chiral separation of [4]− in BGE containing 11 mmol L−1 of
a-cyclodextrin. The BGE was prepared by mixing aqueous methylsulfonic
acid–TRIS buffer of pH 7.3 with methanol 7 : 3 (v/v) ratio. The difference
in mobilities of the atropoisomers of [4]−, Dl, was 0.25 mobility units when
a voltage of −20 kV was applied on the polyacrylamide coated fused silica
capillary of 75 lm inner diameter and 53 cm separation length.
to deboronation of the closo cluster producing an 11-vertex
monoanionic nido species.9a A nucleophilic attack by ethanol at
the more positive boron atoms, either B(3) or B(6), takes place
producing a mononegative chelating ligand as a result of removal
of one boron atom. Therefore special care, avoiding possible
nucleophiles, needs to be taken in attempting the synthesis of
transition metal complexes in which the closo C2B10 fragment is
retained. Preserving the closo nature of the cluster is not a simple
task19c,g,20 but [1-(2ꢀ-pyridyl)-2-S-1,2-closo-C2B10H10]− offered a
unique chance to study a S−/pyridine 6-membered chelating
bidentate ligand. To this aim coordination was addressed towards
transition metals Pd(II), Au(I) and Rh(I) that demand different
coordinating sites.
Diethyl ether was the solvent of choice to avoid competing
reactions caused by nucleophiles. The requirement for the absence
of any nucleophile was even applied in the purification process.
These restrictions were applied in the synthesis of [PdCl(1-(2ꢀ-
pyridyl)-2-S-1,2-closo-C2B10H10)(PPh3)] (6); [Au (1-(2ꢀ-pyridyl)-2-
S-1,2-closo-C2B10H10)(PPh3)] (7) and [Rh(1-(2ꢀ-pyridyl)-2-S-1,2-
closo-C2B10H10)(PPh3)2] (8). The syntheses of these complexes was
achieved by reacting [RhCl(PPh3)3], [PdCl2(PPh3)2], [AuClPPh3]
with the “in situ” prepared [1-(2ꢀ-pyridyl)-2-S-1,2-closo-C2B10H10]−
in diethyl ether (Scheme 2).
3
Metal complexation studies of 1-(2ꢀ-pyridyl)-2-SH-1,2-closo-
C2B10H10. The chelating properties of 1,2-(PR2)2–1,2-closo-
C2B10H10,7d,10,19 1,2-(SR)2–1,2-closo-C2B10H10, 1-PPh2–2-SR-1,2-
closo-C2B10H10 and 1-PPh2–2-SR-1,2-closo-C2B10H109a have already
been studied. As we have demonstrated earlier19g,20 the reaction
of exo-heterodisubstituted carborane derivatives with transition
metal complexes, [MCl(PPh3)n] in methanol or ethanol, leads
The IR spectra of 6–8 show m(B–H) resonances near 2560 cm−1
that agree with a retention of the closo structure in the complexes.
The 11B-NMR spectrum in the range −1.9 to −13.3 ppm points
348 | Dalton Trans., 2008, 345–354
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Fig. 5 Molecular structure of 6. Displacement ellipsoids are drawn at
30% probability level. Hydrogen atoms are omitted for clarity.
Scheme
2
Complexation reaction between the “in situ” prepared
[1-(2ꢀ-pyridyl)-2-S-1,2-closo-C2B10H10]− ligand with transition metals that
demand different coordinating sites.
to the same conclusion, with a pattern 2 : 2 : 2 : 2 : 2 for 6, 1 : 4 : 5
for 7 and 1 : 1 : 2 : 2 : 2 : 2 for 8.
Unambiguous determination of the molecular structures of
6 and 7, was possible after good crystals of these complexes
were obtained from acetone–n-hexane and acetone–chloroform,
respectively. Perspective views of the complex units are presented
in Fig. 5 and 6, and selected bond distances and angles are gathered
in Tables 4 and 5. The X-ray analyses of 6 and 7 confirmed the
closo nature of the resulting palladium and gold complexes but
with a different coordination behavior of the ligand originated
by the different coordination requirements of the metals. In 6 the
carborane cage is co-ordinated bidentately through the N and
S atoms to the Pd(II) ion thus forming a 6-membered C3NPdS
chelate ring. In 6, the Cl atom and the PPh3 group in cis positions
complete the distorted square-planar coordination around the
metal. In 7, the ligand is monodentately coordinated through
Fig. 6 Molecular structure of 7. Displacement ellipsoids are drawn at
30% probability level. Hydrogen atoms are omitted for clarity.
the S atom (S is a softer Lewis base than NPyr) to Au(I) with
no participation of the pyridyl group in the coordination. Nearly
linear coordination of Au(I) is completed by the P atom of the
PPh3 group.
◦
◦
˚
Table 4 Selected bond lengths (A), angles ( ) and torsion angles ( ) for 6
Pd–Cl
Pd–S
Pd–P
Pd–N14
Cl–Pd–S
S–Pd–N14
P–Pd–N14
Pd–S–C2
C2–C1–C13–N14
2.3339(8)
2.3041(8)
2.2314(9)
2.143(3)
S–C2
C1–C2
C1–C13
1.778(3)
1.703(4)
1.516(5)
Comparison of the conformation of the carborane ligand in
6 and 7 with the free (1-(2ꢀ-pyridyl)-2-SH-1,2-C2B10H10) ligand
reveals noticeable differences in the orientation of the pyridyl
group. For the free ligand the N–Cpyr–Cc–Cc torsion angle is
96.4(2)◦.11 Monodentate coordination of the ligand in 7 does
not change the angle very much (N–Cpyr–Cc–Cc = −78.2(5)◦),
but in 6, bidentate coordination of the ligand to Pd (II) changes
the orientation of the pyridyl group markedly (N–Cpyr–Cc–Cc =
−44.1(4)◦). In addition, minor differences in the Cc–Cc distances
can be seen between the free ligand and complexes 6 and 7. The
175.44(3)
Pd–N14–C13
C2–C1–C13
S–C2–C1
129.3(2)
117.8(3)
120.1(2)
87.23(7)
175.31(7)
98.32(10)
−44.1(4)
◦
◦
˚
Table 5 Selected bond lengths (A) and angles ( ) and torsion angles ( )
for 7
˚
Cc–Cc distance of 1.730(3) A in the free ligand is comparable with
˚
the distance of 1.725(6) A in 7, but in the bidentately coordinated
Au–S
Au–P
S–C2
S–Au–P
Au–S–C2
C2–C1–C13–N14
2.3052(10)
2.2616(10)
1.774(4)
174.86(4)
108.48(14)
C1–C2
C1–C13
1.725(6)
1.501(6)
˚
ligand of 6 the distance is shortened to 1.703(4) A.
The crystal packing of the neutral complex units in 6 and 7 is
controlled by very weak van der Waals contacts. In both complexes
there are only weak charges on the heteroatoms and on the other
hand the compounds contain very weakly acidic H-atoms.
C2–C1–C13
S–C2–C1
119.5(3)
121.3(3)
−78.2(5)
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1
1
11B-NMR (96.3 MHz), 13C{ H}-NMR (75.0 MHz) and 31P{ H}-
Conclusions
NMR (121.5 MHz) spectra were recorded on a Bruker ARX 300
The synthesis of closo and nido Cc heterodisubstituted 1-(2ꢀ-
pyridyl)-2-SR-1,2-C2B10H10 (R = Et, iPr) and [7-(2ꢀ-pyridyl)-8-SR-
spectrometer. Chemical shift values for 1H-NMR, 13C{ H}-NMR,
1
11B-NMR and 31P{ H}-NMR were referenced relative to external
1
7,8-nido-C2B9H10]− (R = Et, Pr) derivatives has been conducted
i
SiMe4, BF3·OEt2 and 85% H3PO4 respectively. Chemical shifts are
reported in units of parts per million, and all coupling constants
are reported in Hz.
starting from 1-(2ꢀ-pyridyl)-1,2-closo-C2B10H11 (1). They contain
the Cc–C5H4N and Cc–S groups in the same carborane cluster. An-
alytical separation of the racemic mixture has been accomplished
using capillary electrophoresis assisted with a-cyclodextrin. Two
well defined bands have been observed due to the non-equal
interaction of the two enantiomers with a-cyclodextrin. The het-
erodisubstituted 1-(2ꢀ-pyridyl)-2-SH-1,2-closo-C2B10H10 ligand is
able to coordinate to metals producing pure samples of complexes
with closo cluster retention by using dry non-nucleophilic solvents
to perform the reaction. The two coordinating moieties Cc–C5H4N
and Cc–S are non-equivalent, as has been demonstrated upon
reaction with Au(I), where the Cc–S moiety is the only one reactive.
With metals requiring a higher coordination number than two,
such as Pd(II) and Rh(I), both the Cc–C5H4N and Cc–S moieties
coordinate to the metal. The Pd(II) complex is one of only two
structurally characterized complexes of the bidentated chelating
(pyridine)N-C-C-C-S(H) rigid motif.
Spectra of [NMe4][7-(2ꢀ-pyridyl)-8-SEt-7,8-nido-C2B9H10],
[NMe4][4];
[NMe4][7-(2ꢀ-pyridyl)-8-SiPr-7,8-nido-C2B9H10],
[NMe4][5]; [NMe4][8-SEt-7,8-nido-C2B9H10], [NMe4][9]; [NMe4][7-
Ph-8-SPh-7,8-nido-C2B9H10], [NMe4][10]; [NMe4][7-Me-8-SPh-
7,8-nido-C2B9H10], [NMe4][11] were measured using the double-
beam UV-VIS spectrophotometer UNICAM UV 500 (Thermo
Spectronic, Cambridge, UK) equipped with a fused quartz
cuvette of 1 cm optical path length and with the Vision 3.5
software (Unicam Limited, Cambridge, UK). The latter contains
routines for automatic correction of the light absorption of the
used solvent. Acetonitrile was utilized for dissolution of milligram
quantities of solid tetramethylammonium salts of [4]−, [5]−, [9]−-
[11]− to 1 mmol L−1 concentration. These primary solutions were
further diluted with acetonitrile by the trial-and-error method to
concentrations at which the tetramethylammonium dissolved salts
of [4]−, [5]−, [9]−-[11]− exhibited the highest absorbances close to
1 AU. The UV spectrum [NMe4][7-(2ꢀ-pyridyl)-7,8-nido-C2B9H11],
[NMe4][12] was measured in the radially illuminated fused silica
capillary of inner diameter 75 lm placed in the spectrophotometer
JASCO 875 specified below. Software for this spectrophotometer
supply optical spectra of the dissolved species after correction for
the solvent. The concentration of [NMe4][12] in acetonitrile was
1 × 10−3 mol L−1. The spectra of the tetramethylammonium salts
of anions [4]−, [5]−, [9]−–[12]− are given as ESI.§
Experimental
Materials
1-Pyridyl-2-SH-1,2-closo-carborane was synthesized according to
the literature.11 A 1.6 M solution of n-butyllithium in n-hexane
was used as purchased. [8-SEt-7,8-nido-C2B9H10]−, [9]−; [7-Ph-8-
SPh-7,8-nido-C2B9H10]−, [10]−; [7-Me-8-SPh-7,8-nido-C2B9H10]−,
[11]−; [NMe4][7-(2ꢀ-pyridyl)-7,8-nido-C2B9H11], [12]− were syn-
thesized according to reported methods.21,10b [RhCl(PPh3)3],22
[PdCl2(PPh3)2],23 [AuClPPh3]24 were synthesized as described else-
where. All organic compounds and inorganic salts were analytical
reagent grade and were used as received. The solvents for the
synthesis were reagent grade. All reactions were carried out under
a dinitrogen atmosphere using standard Schlenk techniques.
Mesityloxide, a-cyclodextrin, acetonitrile and methanol were
from Sigma-Aldrich, the solvents being of HPLC grade. Mesity-
loxide, which migrates through the capillary with the speed of
electroosmotic flow due to the absence of its own charge, served
as the electroosmosis marker. It was a constituent of injected
samples in experiments utilizing the uncoated capillary. Methylsul-
fonic acid, of 99% purity, was from Fluka. Tris(hydroxymethyl)-
aminomethane (TRIS) of analytical grade purity was from
Lachema. All other chemicals were of analytical grade purity.
Distilled and boiled water was used for the preparation of the water
solutions. The spectra are mean values from three subsequent
measurements corrected for the background UV-light absorption
of the used acetonitrile.
The main parts of the laboratory electrophoretic set-up were
the switchable high voltage power supply Spellman CZE 1000 R
(Plainview, NY, USA) and the UV-VIS spectrophotometer JASCO
875 (Tokyo, Japan). The spectrophotometer constructed for liquid
chromatography was adapted for experiments with fused silica
capillaries whose outer wall was thermostated by circulating liquid
with precision better than 0.1 ◦C. Joule heat input into the
separation capillary up to 0.2 W at the applied −20 kV driving
voltage guaranteed a very low difference between the temperature
of the outer capillary wall thermostated to 25 ◦C and the
temperature in the capillary centre. The electrode compartments
and paths for filling the compartments, for injecting samples
and for flushing of the separation capillary were drilled in a
polyetheretherketon (PEEK) block (DSM Engineering Plastic
Products, Tielt, Belgium).4 The polyacrylamide coated18 fused
silica capillary of 75 lm inner diameter, 53 cm separation length
and 64.5 cm total length, free of electroosmotic flow, was used for
the experiments. 0.8 mm of the capillary radially illuminated by the
UV light of 200 nm worked as the photometric detection cell. Stock
aqueous buffer was prepared from 14.4 mmol L−1 methylsulfonic
acid adjusted to pH 7.3 with solid TRIS; approximately 1 mol L−1
TRIS solution was used in the last step of the pH adjustment.
Injected samples were prepared from known milligram amounts
of solid tetramethylammonium salts dissolved in a few drops of
acetonitrile and then diluted to concentrations close to 1 mmol L−1
using the 1 : 1 : 2 (v/v/v) mixture of water with aqueous stock
buffer and acetonitrile. Concentrations of measured compounds
are given in spectra (see ESI§). Background electrolyte was
Instrumentation
Microanalyses were performed on a Carlo Erba EA1108 micro-
analyzer. The mass spectra were recorded in the negative ion
mode using a Bruker Biflex MALDI-TOF-MS [N2 laser; kexc
337 nm (0.5 ns pulses); voltage ion source 20.00 kV (Uis1) and
17.50 kV (Uis2)]. IR spectra were obtained as KBr pellets on a
Nicolet 710-FT spectrophotometer. The 1H-NMR (300.0 MHz),
350 | Dalton Trans., 2008, 345–354
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1
prepared by mixing the stock aqueous buffer with methanol in a 7 :
3 (v/v) ratio. The CSW 1.7 (Data Apex, Prague, Czech Republic)
data station served for the measurement of migration times of
detected zones and for calculation of peak characteristics common
in chromatography. Migration times were converted to mobilites
given in 10−9 m2 V−1 s−1 units using the definition equation given
elsewhere.2
3H). 11B-NMR (CD3COCD3): d −2.0 (d, JBH = 196, 1B), −2.9
(d, 1JBH = 144, 1B), −7.6 (d, 1JBH = 172, 2B), −9.1 (2B), −9.8 (d,
1JBH = 132, 4B). 13C{ H}-NMR (CD3COCD3): d 148.8 (s, C2pyr),
1
148.1 (s, C6pyr), 139.1 (s, C4pyr), 125.5 (s, C3pyr), 124.9 (s, C5pyr), 87.51
(s, Cc–Py), 85.2 (s, Cc–SEt), 30.0 (s, CCH2), 11.9 (s, CCH3).
Synthesis of 1-(2ꢀ-pyridyl)-2-SiPr-1,2-closo-C2B10H10 (3)
In the same manner as for compound 2, to a solution of KOH
(6 mg, 0.11 mmol) in deoxygenated ethanol (5 ml), was added (1-
(2ꢀ-pyridyl)-2-SH-1,2-closo-C2B10H10) (28 mg, 0.11 mmol). After
stirring for 1 h at room temperature the solvent was evaporated
and the residue redissolved in dry THF (5 ml). Bromoisopropyl
(0.02 ml, 0.22 mmol) was added and the mixture was refluxed
for 2 h. All volatiles were evaporated under vacuum, and the
residue was treated with diethyl ether (10 ml) and water (10 ml),
the organic layer was separated and washed with KOH (3 ×
10 ml, 0.5 M), dried over anhydrous MgSO4 and evaporated under
vacuum resulting a yellow oil. Yield: 29 mg (81%). Anal. calcd for
C10H21B9NS: N, 4.92; C, 42.20; H, 7.44; S, 11.27. Found: N, 4.64;
C, 42.2; H, 7.70; S, 10.91%. IR: m/cm−1 2932 (Caryl–H/Calkyl–H);
2577 (B–H); 2352, 2361 (S–R); 1464, 1434 (C–N); 1081, 1012 (C–
Synthesis of 1-(2ꢀ-pyridyl)-1,2-closo-C2B10H11 (1)
This compound synthesis was first reported by Wade et al.10a,25 The
synthetic procedure described here is different to the one reported.
A total of 0.747 g (6 mmol) of decaborane and 1.56 ml of
dimethylaniline dissolved in 20 ml of toluene was refluxed for 2 h
under nitrogen. After cooling, 0.41 ml (4 mmol) of ethynylpiridine,
was added and the reaction mixture was heated under reflux for
18 h more. The solvents were removed under vacuum, and the
residue was treated with 5 ml of methanol for 30 min under stirring.
Upon evaporation of the solvent, the product was treated with
◦
petroleum ether (boiling range = 35–70 C). The insoluble solid
was sublimed and the petroleum ether was evaporated to dryness
to afford in total 0.36 g (1.6 mmol) of 1 (40%). Anal. calcd for
C7H15B10N: N, 6.33; C, 37.99; H, 6.83; S, 11.4; Found: N, 6.08; C,
11
N–C). 1H{ B}-NMR (CDCl3): d 8.65 (d, 3JHH = 4.5, Cpyr–H, 1H),
4
38.57; H, 6.82%. IR: m/cm−1 3067 (Caryl–H); 2958, 2924, 2854 (Caryl
–
7.75 (m, Cpyr–H, 2H), 7.39 (ddd, 3JHH = 5.3, JHH = 1.8, Cpyr–H,
1H), 3.25 (h, 3JHH = 6.9, CH, 1H), 2.95 (s, B–H, 2H), 2.57 (s, B–H,
=
H); 2643, 2631, 2605, 2590, 2567 (B–H); 1574 (C N); 1464, 1434
11
3
(C–N); 1019, 1011 (C–N–C). 1H{ B}-NMR (CD3COCD3): d 8.51
2H), 2.47 (s, B–H, 4H), 2.27 (s, B–H, 2H), 1.12 (d, JHH = 6.9,
1
(d, 3JHH = 4.4, Cpyr–H6, 1H), 7.92 (td, 3JHH = 7.8, 4J(H,H) = 1.6
CH3, 6H). 11B-NMR (CDCl3): d −2.4 (d, JBH = 156, 1B), −3.6
1
1
1
Cpyr–H4, 1H), 7.71 (d, 3JHH = 7.8, Cpyr–H3, 1H), 7.51 (ddd, 3JHH
=
(d, JBH = 138, 1B), −8.5 (d, JBH = 159, 2B), −10.4 (d, JBH
=
7.8, 4JHH = 4.4, 5JHH = 0.6, Cpyr–H5, 1H), 5.42 (s, Cc–H, 1H), 2.49
126, 6B). 13C{ H}-NMR (CDCl3): d 149.1 (s, Cpyr), 136.9 (s, Cpyr),
126.1 (s, Cpyr), 124.7 (s, Cpyr), 121.5 (s, Cpyr), 87.5 (s, Cc–pyr), 85.7
(s, Cc–SiPr), 42.6 (s, S–CH), 23.8 (s, CH–CH3).
1
(s, B–H), 2.35 (s, B–H), 2.27 (s, B–H). 11B-NMR (CD3COCD3): d
−2.7 (d, 1JBH = 152, 1B), −3.5 (d, 1JBH = 150, 1B), −7.9 (d, 1JBH
=
=
153, 2B), −9.8 (d, 2B), −10.5 (d, 1JBH = 167, 2B), −12.4 (d, 1JBH
1
158, 2B). 13C{ H}-NMR (CDCl3): d 148.8 (s, C2pyr), 152.0 (s, C2pyr),
150.6 (s, C6pyr), 139.6 (s, C4pyr), 126.4 (s, C3pyr), 123.1 (s, C5pyr), 77.6
(s, Cc–Py), 59.6 (s, Cc–H).
Synthesis of [NMe4][7-(2ꢀ-pyridyl)-8-SEt-7,8-nido-C2B9H10],
[NMe4][4]
To a Schlenk flask containing a solution of KOH (70 mg, 1.2 mmol)
in deoxygenated ethanol (5 ml), was added 1-(2ꢀ-pyridyl)-2-SEt-
1,2-closo-C2B10H10 (71 mg, 0.25 mmol). The mixture was refluxed
for 3 h, cooled to room temperature and the solvent evaporated.
The residue was dissolved in water (2 ml) and treated with a
solution of tetramethylammonium chloride. The white solid was
filtered off and washed with water and diethyl ether. Yield: 61 mg,
0.17 mmol (70%). Anal. calcd for C13H31B9N2S: N, 8.13; C, 45.29;
H, 9.06; S, 9.30. Found: N, 8.01; C, 45.41; H,9.17, S, 9.51%. IR:
Synthesis of 1-(2ꢀ-pyridyl)-2-SEt-1,2-closo-C2B10H10 (2)
To a two necked round bottom flask (50 ml), containing a solution
of KOH (25 mg, 0.45 mmol) in deoxygenated ethanol (10 ml),
was added (1-(2ꢀ-pyridyl)-2-SH-1,2-closo-C2B10H10) (115 mg,
0.45 mmol). After stirring for 1 h at room temperature the solvent
was evaporated and the residue redissolved in dry THF (10 ml).
Bromoethane (0.013 ml, 0.90 mmol) was added and the mixture
was refluxed for 2 h. All volatiles were evaporated under vacuum,
and the residue was treated with diethyl ether (10 ml) and water
10 ml, the organic layer was separated and washed with KOH
(3 × 10 ml, 0.5 M), dried over anhydrous MgSO4 and evaporated
under vacuum resulting a yellow solid. Yield: 112 mg (88%). Anal.
calcd for C9H19B10NS: N, 4.97; C, 38.41; H, 6.8; S, 11.4; Found: N,
m/cm−1 2937 (Caryl–H); 2534 (B–H), 2362, (S–R); 1472 (C–N); 1026
11
(C–N–C). 1H-{ B}NMR (CD3COCD3): d 8.37 (d, 3JHH = 4, Cpyr
–
=
H, 1H), 7.48 (t, 3JHH = 8, 4JHH = 2, Cpyr–H, 1H), 7.26 (d, 3JHH
3
4
8, Cpyr–H, 1H), 7.00 (t, JHH = 6, JHH = 2, Cpyr–H, 1H), 3.44 (s,
N(CH3)4, 12H), 2.92 (q, 3JHH = 7.5, CH2–CH3, 1H), 2.65 (q, 3JHH
=
7.5, CH2–CH3, 1H), 2.47 (s, B–H, 1H), 2.23 (s, B–H, 1H), 2.20 (s,
B–H, 1H), 1.73 (s, B–H, 2H), 1.48 (s, B–H, 1H), 1.38 (s, B–H, 1H),
0.83 (t, 3JHH = 7.5, CH2–CH3, 3H), 0.73 (s, B–H, 1H), 0.24 (s, B–
H, 1H), −2.05 (s, BHB, 1H). 11B-NMR (CD3COCD3): d −7.1 (d,
1JBH = 138, 2B), −12.1 (d, 1JBH = 158, 1B), −15.9 (d, 1JBH = 142,
3B), −18.48 (d, 1JBH = 145, 1B), −32.6 (dd, 1JBH = 132, 1JBH = 29,
4.95; C, 38.20; H, 6.50; S, 11.15%. IR: m/cm−1 2965, 2924 (Caryl
–
=
H/Calkyl–H); 2569 (B–H); 2364, 2338 (S–R); 1584 (C N); 1463,
1433 (C–N); 1081, 1014 (C–N–C); 811 (CH3); 774, 740 (Caryl–H).
11
1H{ B}-NMR (CD3COCD3): d 8.67 (d, 3JHH = 4.7, Cpyr–H6, 1H),
3
4
5
7.95 (ddd, JHH = 7.6, J(H,H) = 7.7, JHH = 1.5, Cpyr–H4, 1H),
7.89 (ddd, 3JHH = 7.7, 4JHH = 4.7, Cpyr–H5, 1H), 7.5 (ddd, 3JHH
=
B(10)), −35.1 (d, 1JBH = 138, B(1)). 13C{ H}-NMR (CD3COCD3):
1
7.2, 4JHH = 4.6, 5JHH = 0.6, Cpyr–H3, 1H), 2.77 (q, 3JHH = 7.5, S–
CH2CH3, 2H), 3.00 (s, B–H, 1H), 2.53 (s, B–H, 1H), 2.45 (s, B–H,
4H), 2.37 (s, B–H, 2H), 2.22 (s, B–H, 2H), 0.90 (t, 3JHH = 7.5, CH3,
d 155.9 (s, Cpy), 147.4 (s, Cpyr), 135.2 (s, C4pyr), 125.2 (s, C3pyr), 120.4
(s, C5pyr), 62.7 (s, Cc), 55.1 (s, N(CH3)4), 22.2 (s, CH2), 13.4 (s, CH3).
MALDI-TOF-MS: 270.36 (47.5%, M), 208.27 (100%, M − SEt).
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Synthesis of [NMe4][7-(2ꢀ-pyridyl)-8-SiPr-7,8-nido-C2B9H10],
[NMe4][5]
(78 mg, 0.16 mmol) was added and stirred during 2 h at RT. A
brown solid was generated and filtered off and not identified. To
the organic fraction was added hexane (2 ml) and a pale brown
solid precipitated that was washed with hexane. Yield: 112 mg
(62%). Anal. calcd for C25H29B10AuNSP + 0.1C6H14: N, 1.86;
C, 41.66; H, 4.46; S, 4.52. Found: N, 1.86; C, 41.73; H, 4.03,
To a Schlenk flask containing a solution of KOH (11 mg,
0.20 mmol) in deoxygenated ethanol (5 ml), was added 1-
(2ꢀ-pyridyl)-2-SiPr-1,2-closo-C2B10H10 (12 mg, 0.04 mmol). The
mixture was refluxed for 3 h, cooled to room temperature and
evaporated. The residue was dissolved in water (2 ml) and treated
with a solution of tetramethylammonium chloride. The white solid
was filtered off and washed with water and diethyl ether. Yield:
9 mg, 0.025 mmol, (64%). Anal. calcd for C14H33B9N2S: N, 7.83;
C, 47.00; H, 9.02, S, 8.96. Found: N, 7.65; C, 47.12; H 9.14, S,
8.80%. IR: m/cm−1 3035, 2970, 2922, 2866 (Caryl–H); 2528 (B–H),
S, 3.95%. IR: m/cm−1 3052 (Caryl–H); 2597, 2578, 2561 (B–H),
1
=
2363 (S–R); 1583 (C N); 1434, 1101, 752, 690, 540 (PPh3). H-
11
3
{ B}-NMR (CDCl3): d 8.40 (d, JHH = 3, Cpyr–H6, 1H), 7.73 (d,
3JHH = 8, Cpyr–H3, 1H), 7.59 (t, JHH = 8, Cpyr–H4, 1H), 7.42
3
(m, PPh3, 15H), 7.19 (m, Cpyr–H, 1H), 3.49 (s, B–H, 2H), 2.88
(s, B–H, 2H), 2.45 (s, B–H, 3H), 2.22 (s, B–H, 3H). 11B-NMR
1
1
(CDCl3): d −1.9 (d, JBH = 152, 1B), −5.9 (d, JBH = 134, 4B),
1
11
=
1587 (C N); 1481, 1471 (Calkyl). H-{ B}NMR (CD3COCD3): d
−9.6 (d, JBH = 153, 5B). 13C{ H}-NMR (CDCl3): d 150.34 (s,
1
1
3
3
4
8.37 (d, JHH = 4, Cpyr–H, 1H), 7.49 (td, JHH = 8, J(H,H)= 2,
1
Cpy), 149.11 (s, Cpyr), 136.50 (s, Cpyr), 134.13 (d, JCP = 14, CPh),
3
3
Cpyr–H, 1H), 7.31 (d, JHH = 8, Cpyr–H, 1H), 7.01 (td, JHH = 6,
131.90 (s, CPh), 129.31 (d, 1JCP = 11, CPh), 128.61 (s, CPh), 126.22
4JHH = 2, Cpyr–H, 1H), 3.44 (s, N(CH3)4, 12H), 3.07 (h, JHH
=
3
(s, Cpyr), 124.20 (s, Cpyr), 88.95 (s, Cc), 86.52 (s, Cc). 31P{ H}-NMR
1
7, CH, 1H), 2.51 (s, B–H, 1H), 2.28 (s, B–H, 1H), 1.65 (s, B–H,
(CDCl3): d 38.13 (s, PPh3). MALDI-TOF-MS: 251.25 (100%,
M − AuPPh3).
1H), 1.50 (s, B–H, 1H), 1.29 (s, B–H, 1H), 1.03 (d, 3JHH = 7, CH–
3
CH3, 3H), 0.85 (d, JHH = 7, CH–CH3, 3H), 0.75 (s, B–H, 1H),
0.24 (s, B–H, 1H), −2.04 (s, BHB, 1H). 11B-NMR (CD3COCD3):
d −8.3 (d, 1JBH = 137, 2B), −13.4 (d, 1JBH = 154, 1B), −15.7 (d,
Synthesis of [Rh(1-(2ꢀ-pyridyl)-2-S-1,2-closo-C2B10H10)(PPh3)2] (8)
1JBH = 152, 1B), −17.7 (d, JBH = 131, 2B), −18.8 (d, JBH
=
1
1
The procedure was as for6 taking 1-(2ꢀ-pyridyl)-1,2-closo-C2B10H11
(37 mg, 0.16 mmol) in dry diethyl ether (4 ml), n-BuLi (0.1 ml,
0.16 mmol) and S powder (5 mg, 0.16 mmol). [RhCl(PPh3)3]
(152 mg, 0.16 mmol) was added and stirred during 20 h at RT. The
solution was concentrated and after the addition of hexane, a
brown solid precipitated that did not contain boron. The solution
was taken to dryness and a brown solid was obtained. Yield: 54 mg
(50%). Anal. calcd for C43H44B10NSRhP2: N, 1.59; C, 58.70; H,
5.04; S, 3.64. Found: N, 1.70; C, 58.66; H, 5.33, S, 3.73%. IR:
m/cm−1 3059, 2962 (Caryl–H); 2569 (B–H), 1435, 1118, 692, 542
1
1
162,1B), −33.6 (d, JBH = 169, 1B), −36.0 (d, JBH = 141, 1B).
13C{ H}-NMR (CD3COCD3): d 161.2 (s,C2py), 147.4 (s, C6pyr),
1
134.4 (s, C4pyr), 125.9 (s, C3pyr), 120.3 (s, C5pyr), 69.8 (s, Cc), 55.1
(s, N(CH3)4), 38.7 (s, CH), 24.4 (s, CH3), 23.1 (s, CH3). MALDI-
i
TOF-MS: 284.4 (100%, M), 238.3 (75.4%, M − Pr), 208.3 (55.2%,
M − SiPr).
Synthesis of [PdCl(1-(2ꢀ-pyridyl)-2-S-1,2-closo-C2B10H10)(PPh3)]
(6)
To a Schlenk flask containing a solution of 1-(2ꢀ-pyridyl)-1,2-
closo-C2B10H11 (41 mg, 0.18 mmol) in dried diethyl ether (5 ml),
was added n-BuLi (0.12 ml, 0.18 mmol) at 0 ◦C. Stirring was
maintained for 30 min at room temperature. S powder was added
(6 mg, 0.18 mmol) at 0 ◦C during 10 min. Stirring was maintained
for 30 min at 0 ◦C and 30 min at RT. [PdCl2(PPh3)2] (129 mg,
0.18 mmol) was added and stirred during 1 h at RT. A brown solid,
that does not contain boron, precipitated. The orange solution was
filtered and taken to dryness. Yield: 97 mg (80%). Anal. calcd for
C25H29B10NSClPPd: N, 2.13; C, 45.74; H, 4.45; S, 4.88. Found:
11
(PPh3). 1H-{ B}-NMR (CDCl3): d 8.39 (d, 3JHH = 4, Cpyr–H, 1H),
7.74–7.1 (m, 30H), 2.46 (s, B–H, 1H), 2.33 (s, B–H, 8H), 2.25 (s,
1
B–H, 1H). 11B-NMR (CDCl3): d −2.5 (d, JBH = 147, 1B), −3.1
1
1
1
(d, JBH = 151, 1B), −7.6 (d, JBH = 151, 2B), −9.9 (d, JBH
=
1
1
129, 2B), −10.6 (d, JBH = 182, 2B), −12.5 (d, JBH = 160, 2B).
13C{ H}-NMR (CDCl3): d 148.7 (s, Cpy), 137.4 (s, Cpyr), 132.9 (s,
1
Cpyr), 131.6 (s, CPh), 128.6 (s, CPh), 124.3 (s, Cpyr), 121.4 (s, Cpyr).
1
31P{ H}-NMR (CDCl3): d 42.0 (br s, PPh3).
N, 2.03; C, 45.88; H, 4.56, S, 5.01%. IR: m/cm−1 2930 (Caryl
–
X-Ray crystallography
H); 2607, 2592, 2567 (B–H), 1433, 1101, 1018, 690, 515 (PPh3).
Single-crystal data collections for [NMe4][5], 6 and 7 were
performed at −100 ◦C with an Enraf Nonius KappaCCD diffrac-
tometer using graphite monochromatized Mo-Karadiation. Crys-
tallographic parameters for [NMe4][5], 6 and 7 are gathered in
Table 6.
The structures were solved by direct methods and refined
on F2 using the SHELX97 program.26 For each compound,
non-hydrogen atoms were refined with anisotropic displacement
parameters. For [NMe4][5], the hydrogen atoms were treated
as riding atoms using the SHELX97 default parameters or
positional parameters of the atoms were refined, while for 6 and
7, all hydrogen atoms were treated as riding atoms using the
SHELX97 default parameters. [NMe4][5] crystallizes in a non-
centrosymmetric space group, and the absolute configuration of
[NMe4][5] was determined by refinement of the Flack x parameter.
11
1H-{ B}-NMR (CDCl3): d 8.41 (s, Cpyr–H, 1H), 7.71–7.32 (m,
1
18H), 2.48–2.23 (m, B–H). 11B-NMR (CDCl3): d 0.4 (d, JBH
=
1
1
158, 1B), −0.3 (d, JBH = 158, 1B), −4.8 (d, JBH = 140, 2B),
1
1
−7.0 (d, JBH = 123, 2B), −7.8 (d, JBH = 191, 2B), −9.6 (d,
1JBH = 174, 2B). 13C{ H}-NMR (CDCl3): d 150.9 (s, Cpyr), 148.7
1
1
(s, Cpyr), 137.4 (s, Cpyr), 132.2 (d, J(C,P) = 11, CPPh3), 131.6 (s,
1
CPPh3), 128.5 (d, J(C,P) = 12.4, CPPh3), 124.3 (s, Cpyr), 121.5 (s,
Cpyr), 75.3 (s, Cc), 65.9 (s, Cc). 31P{ H}-NMR (CDCl3): d 44.7
1
(s, PPh3).
Synthesis of [Au(1-(2ꢀ-pyridyl)-2-S-1,2-closo-C2B10H10)(PPh3)] (7)
The process was as for 6 taking 1-(2ꢀ-pyridyl)-1,2-closo-C2B10H11
(37 mg, 0.16 mmol), dry diethyl ether (4 ml), n-BuLi (0.1 ml,
0.16 mmol) at 0 ◦C and S powder (5 mg, 0.16 mmol). [AuClPPh3]
352 | Dalton Trans., 2008, 345–354
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Table 6 Crystallographic data and refinement parameters of [NMe4][5], 6 and 7 at −100 ◦
C
[NMe4][5]
6
7
Formula
C14H33B9N2S
358.77
C25H29B10ClNPPdS
656.50
Triclinic
C25H29AuB10NPS
711.59
Mr/g mol−1
Crystal system
Crystal habit, color
Space group
Orthorhombic
Prism, colourless
P212121 (no. 19)
9.0020(9)
14.9136(14)
15.8719(15)
90
90
90
2130.8(4)
4
0.71073
1.118
Monoclinic
Plate, colourless
P21/n (no. 14)
12.8012(2)
13.3513(4)
17.1365(5)
90
103.541(2)
90
2847.43(13)
4
Block, yellow
¯
P1 (no. 2)
˚
a/A
9.3314(4)
11.9503(6)
15.2810(4)
104.695(2)
98.904(2)
111.702(2)
1471.71(10)
2
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
V/V3
Z
˚
k/A
0.71073
1.482
0.866
0.71073
1.660
5.315
qcalcd/g cm−3
l/mm−1
0.152
Rint
0.300
4147/0/254
1.027
0.0478
0.1156
0.0426
4805/0/361
1.027
0.0316
0.0650
0.0665
5260/0/353
1.019
0.0285
0.0547
Data/restraints/parameters
Goodness-of-fita on F2
Rb [I > 2r(I)]
c
Rw [I > 2r(I)]
Flack parameter x
0.08(9)
—
—
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
a S = [ (w(Fo − Fc2)2]/(n − p)1/2
.
b R = ꢁFo| − |Fcꢁ/ |Fo|. c Rw = [ w(|Fo2| − |Fc2|)2/ w|Fo2|2]1/2
.
6 F. Teixidor, C. Vin˜as, J. Casabo´, A. M. Romerosa, J. Rius and C.
Miravitlles, Organometallics, 1994, 13, 914.
Acknowledgements
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Kabachnik, Izv. Akad. Nauk SSSR, Ser. Khim., 1973, 2369; (c) R.
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10 (a) E. S. Alekseyeva, A. S. Batsanov, L. A. Boyd, M. A. Fox, T. G.
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The authors are grateful to the MCyT for financial sup-
port (project MAT06–05339 and CTQ2006–26257-E/PPQ) and
Generalitat de Catalunya for 2005/SGR/00709.
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