1,3-Dipolar cycloaddition of nitrones to a nitrile functionality in closo -decaborate clusters: A novel reactivity mode for the borylated C≡N group

Article abstract of DOI:10.1021/om200993f

The Z-configured nitrones ^-O⁺N(Me)=C(H)C ₆H₄R²-p (R² = OMe (2a), Me (2b), NO₂ (2c)) react with the nitrile functionality of the closo-decaborate clusters [Buⁿ₄N][B₁₀H ₉(NCR¹)] (R¹ = Me (1a), Et (1b), Bu^t (1c), Ph (1d)) in CHCl₃ solution under mild conditions (20-25 °C, 16-18 h) to afford the products of cycloaddition: viz., the borylated 2,3-dihydro-1,2,4-oxadiazoles [Buⁿ₄N][B₁₀H ₉{N^a=CR¹ON(Me)C^bH(C ₆H₄R²-p)}]^(a-b) (3a-l). This reaction represents the first example of boron-mediated 1,3-dipolar cycloaddition of allyl anion type dipoles, i.e. nitrones, to the nitrile group. Alteration of the lipophilic [Buⁿ₄N]⁺ counterion with the hydrophilic Na⁺ via the metathetical reaction with NaBPh₄ in 3a,b,e,f allows the modification of their hydrophilic-lipophilic properties and, consequently, solubility. Compounds 3a-j and 5a-d were characterized by high-resolution ESI-MS, IR, and ¹H, ¹³C{¹H}, and ¹¹B{¹H} NMR spectroscopy. The structures of 3a,e,f were determined by single-crystal X-ray diffraction.

Full text of DOI:10.1021/om200993f

Article
pubs.acs.org/Organometallics
1
,3-Dipolar Cycloaddition of Nitrones to a Nitrile Functionality in
closo-Decaborate Clusters: A Novel Reactivity Mode for the Borylated
CN Group
†
∥
,†
‡
†
§
†
Aleksey L. Mindich, Nadezhda A. Bokach,* Fedor M. Dolgushin, Matti Haukka, Leonid A. Lisitsyn,
∥
∥
Andrey P. Zhdanov, Konstantin Yu. Zhizhin, Serguei A. Miltsov, Nikolay T. Kuznetsov,
,
†,⊥
and Vadim Yu. Kukushkin*
†Department of Chemistry, Saint-Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof, Russian Federation
‡A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova str. 28, 119991 Moscow,
Russian Federation
§
Department of Chemistry, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland
∥
N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky Pr., 119991 Moscow,
Russian Federation
⊥
Institute of Macromolecular Compounds, Russian Academy of Sciences, V.O. Bolshoi Pr. 31, 199004 Saint-Petersburg, Russian
Federation
*
S Supporting Information
−
+
2
ABSTRACT: The Z-configured nitrones O N(Me)C(H)C H R -
6
4
2
p (R = OMe (2a), Me (2b), NO (2c)) react with the nitrile
functionality of the closo-decaborate clusters [Bu N][B H (NCR )]
R = Me (1a), Et (1b), Bu (1c), Ph (1d)) in CHCl solution under
2
n
1
4
10
9
1
t
(
3
mild conditions (20−25 °C, 16−18 h) to afford the products of
cycloaddition: viz., the borylated 2,3-dihydro-1,2,4-oxadiazoles
n
a
1
b
2
(a−b)
[
Bu N][B H {N CR ON(Me)C H(C H R -p)}]
(3a−l).
4
10
9
6
4
This reaction represents the first example of boron-mediated 1,3-
dipolar cycloaddition of allyl anion type dipoles, i.e. nitrones, to the
nitrile group. Alteration of the lipophilic [Bu N] counterion with the
n
4
+
+
hydrophilic Na via the metathetical reaction with NaBPh in 3a,b,e,f
4
allows the modification of their hydrophilic−lipophilic properties and,
1
13
1
consequently, solubility. Compounds 3a−j and 5a−d were characterized by high-resolution ESI-MS, IR, and H, C{ H}, and
11
1
B{ H} NMR spectroscopy. The structures of 3a,e,f were determined by single-crystal X-ray diffraction.
1
1−20
n general, nitrilesalthough they represent attractive
cycles
and, to a lesser degree, with the DCA of
and relevant allyl anion type dipoles (e.g.,
21−23
I
starting materials for generation of various nitrogen
nitrones
24
25
26
heterocyclesexhibit moderate dipolarophilicity, and this
oxazoline N-oxides, imidazoline N-oxides, and nitronates )
and also nitrile oxides
represent dipoles of the propargyl−allenyl anion type.
2
7,28
hampers the application of RCN species in cycloaddition
that, as is the case for azides,
(
CA) reactions. The reactivity of the nitrile functionality can be
enhanced either by an electron-withdrawing substituent at the
C atom or by affecting the nitrile group through the N atom
In view of our general interest in reactions of substrates
activated by binding to a Lewis acid and, in particular, those
with the CN bond (for reviews see refs 1−3, and for recent
works see refs 29−34), we decided to attempt DCA of the most
common representatives of allyl anion type dipoles, i.e.
nitrones, to borylated nitrilium derivatives having a relatively
strong B−N bond, i.e. nitrilium hydroborates. The latter
category of species has been scarcely investigated, although data
for various nitrilium-substituted boron clusters gradually
emerged in the literature indicating a high reactivity of the
(
i.e., protonation, alkylation, or coordination to the metal). The
group of methods associated with the N atom includes
alkylation (followed by cycloaddition to thus generated
nitrilium salts) and coordination to a transition-metal center
(
and cycloaddition to these ligated nitrile substrates); these two
1
−3
approaches were considered in our reviews on the subject.
1
,3-Dipolar cycloaddition (DCA) to highly reactive nitrilium
+
salts [RNCR′] has been studied for such dipoles as
4
−8
9
10
azides,
nitrile oxides, and heterocyclic nitrones. In recent
CN group. These examples include facile addition of H O (a
2
years, growing attention has been paid to metal-mediated DCA
3
to RCN, and these works are greatly associated with the
Received: October 16, 2011
Published: February 7, 2012
nitrile−azide interactions accomplishing tetrazole hetero-
©
2012 American Chemical Society
1716
dx.doi.org/10.1021/om200993f | Organometallics 2012, 31, 1716−1724

Organometallics
Article
35−37
R′OH (b),38−40 and amines (c)
38,39,41
and f, Scheme 1),
nitrilium derivatives of borohydride
to
and carborane-
dihydro-1,2,4-oxadiazoles linked via the N−B bond to closo-
decaborate clusters.
35,38,40
RESULTS AND DISCUSSION
■1
Scheme 1. Reactivity Modes of the Nitrilium-Substituted
Cage Boron Compounds
,3-Dipolar Cycloaddition. For this study we addressed
n
1
1
the four closo-decaborates [Bu N][B H (NCR )] (R = Me
4
10
9
t
(
1a), Et (1b), Bu (1c), Ph (1d)) and three acyclic nitrones in
−
+
2
2
the Z form, i.e., O N(Me)C(H)C H R -p (R = OMe (2a),
6
4
Me (2b), NO (2c)). The reaction between the nitrilium
2
n
4
1
substituents in the clusters [Bu N][B H (NCR )] and the
10
9
nitrones (in all possible combinations) proceeds in CHCl3
solution under mild conditions (20−25 °C, 16−18 h) to afford
cycloaddition products 3a−l (ca. 100% NMR yield; 39−69%
isolated yield after column chromatography; the products
slowly decompose on SiO and the chromatography should be
2
performed rapidly) (Scheme 2, route a).
Our experiments suggest that the CN group in the boron
clusters is strongly activated toward DCA of nitrones as
compared to the CN group in the conventional alkyl- and
3
6,39
49
II
21
(
ate)
clusters as well as the hydrogenation of cobalt
arylnitriles and even in (RCN)Pt moieties. Under similar
1
nitrilium bis(1,2-dicarbollide) with Me S·BH (d) and the
reaction with hydrazine (e) in EtOH.
In the context of the current work, it is important to stress
that no single example of the cycloaddition to the CN group
bound to the B atom at any of the boron clusters has been
reported to date, although BF -catalyzed DCAs are rather
common in organic chemistry (see, e.g., refs 42−48).
experimental conditions, no reaction was observed (by H
2
3
39
NMR) between the relevant free nitriles RCN and the nitrones,
indicating that CA is boron-mediated. Moreover, no CA
reaction of the most reactive nitrone 2a was observed under
similar reaction conditions (20−25 °C, CDCl ) at prolonged
3
times (24 h), even in the case of nitriles bearing strong acceptor
3
substituents: viz., CHCl CN, EtO CCH CN, MeC(O)CN, m-
2
2
2
49
NO C H CN, and o-BrC H CN. As noticed previously, CA
2
6
4
6
4
The main goals of this work were at least 2-fold. First, we
anticipated to determine the possibility of DCA of nitrones to
the nitrile functionality in nitrilium closo-decaborates and to
compare the reactivity of these CN dipolarophiles with that
of uncomplexed and metal-bound RCN species. Second, we
intended to synthesize various anionic closo-decaborate clusters
featuring 2,3-dihydro-1,2,4-oxadiazoles and to obtain, via
alteration of the counterion, their water-soluble forms for
further biological investigations. We now report on an
extension of the DCA reaction of nitrones to completely
different dipolarophiles bearing the CN group, i.e., nitrilium
borates, that allow the generation of a novel family of 2,3-
of acyclic nitrones to free alkylnitriles does not occur even at
elevated temperatures and only the rather electron-deficient
−
+
PhCN reacts with the acyclic nitrone (Z)- O N(Me)C(H)
Ar under harsh conditions (10 days at 110 °C) to give 2-
methyl-3,5-diphenyl-2,3-dihydro-1,2,4-oxadiazole in moderate
49
(
57%) yield.
2
The character of the substituent R has a moderate effect on
CA rate in spite of the considerable difference in electronic
effects of the OMe, Me, and NO substituents (σpara(OMe) =
2
50
−0.27, σ (Me) = −0.17, σ (NO ) = 0.78 ) in the nitrones.
Thus, competitive DCA of nitrones 2a/2b and 2b/2c to the
nitrilium group of 1a in a molar ratio 1:1:0.3 by means of H
para
para
2
1
Scheme 2. Generation and Transformations of the Borylated 2,3-Dihydro-1,2,4-oxadiazoles
1
717
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Organometallics
Article
1
NMR monitoring demonstrates the following relative reaction
The specific feature of the H NMR spectra of 3a−j and 5a−
d is the presence of a singlet at 5.53−5.89 ppm from the N−
rate constants: k :k :k ≈ 23:13:1. This dependence indicates
1a
1b 1c
1
3
1
negative ρ values, and it supports attribution of this reaction to
C(5)H−N group. The most characteristic signal in the C{ H}
NMR of 3a−j and 5a−d is the C(1)N resonance that falls in
type I (normal electron demand) of CA in the Sustmann
5
1
11
1
classification, where HOMOnitrone−LUMOnitrile interactions
the interval 166.4−177.4 ppm. The B{ H} NMR confirmed
the closo-decaborate structure of 3a−j. Two singlets assigned to
apical boron atoms were observed in the range from +1.12 to
−2.56 ppm, a weak singlet of the substituted boron atom
appeared from −11.22 to −13.31 ppm, and multiple signals
determine the occurrence of the reaction.
It is worth mentioning that the character of the substituent
1
R plays a dramatic role in the stability of 3a−j. Thus, the closo-
1
decaborate cluster ions with R = Me, Et (3a,b,e,f,i,j) are stable
in the solid state and in chloroform or methanol solutions,
were observed corresponding to other equatorial atoms
1
t
35,40 11
whereas the species with R = Ph (3d,h) and especially with Bu
(
between −23.13 and −28.28 ppm.
B NMR spectra
t
2
3c,g) (probably due to steric repulsion of the bulky Bu group)
demonstrate that the borate cluster has only one substituted B
atom; therefore, DCA does not lead to alterations of the borate
unit.
decompose at room temperature. Thus, the appearance of
1
foreign signals in the H NMR spectra was found upon keeping
3
c,d,g,h in the solid state for 3 days or after 12 h in an undried
The single-crystal X-ray diffraction study conducted for 3a,e
(Figures S1 and S2 in the Supporting Information) and 3f
(Figure 1) indicates the presence of two independent ionic
1
CDCl solution. Compounds 3k,l were detected by H NMR
and IR spectroscopy and HRESI -MS but not isolated as pure
3
−
solids because of their instability. In the case of 3c, an
equimolar mixture of nitrone 2a and amide 4a (amides similar
to 4a are known and the X-ray data indicate the double bond
3
5
1
between the NC atoms ) was detected by both H NMR
±
and HRESI -MS; 2a and 4a are formed upon the hydrolytic
cleavage of the heterocyclic moiety (Scheme, 2, route b). We
also found that 3a−j are unstable toward hydrolysis under both
acidic (1 M AcOH/CDCl ) and alkaline (1 M NaOH/
3
CD OD) conditions: i.e., they decompose for 2 h, giving a
3
broad mixture of as yet unidentified products (at least five new
spots on TLC were detected along with the disappearance of
the starting species). The instability most probably relates to
the oxadiazole ring, insofar as we did not observe any changes
in the closo-borate cluster at room temperature for 2−6 h,
which is in agreement with literature data on the stability of
3
5,40
these clusters.
Cation Metathesis. Compounds 5a−d were obtained in
Figure 1. ORTEP view of 3f with the atomic numbering scheme.
Thermal ellipsoids are drawn at the 30% probability level; the cation is
omitted for clarity.
the metathetical reaction between 3a,b,e,f and NaBPh in
4
methanol/acetonitrile solution (Scheme 2, route c). Sodium
salts 5a−d were isolated as pale yellow solids after separation of
n
+
n
parts. In the cation, the alkyl chains of [Bu N] are always in
4
the solid [Bu N]BPh followed by evaporation of the solvent
4
4
anti or gauche conformations and all bond lengths are close to
and crystallization of the resulted oily residues in a desiccator
70% yields after crystallization). These species exhibit rather
52
those reported in the literature. The anionic parts of 3a,e,f
consist of a substituted 2,3-dihydro-1,2,4-oxadiazole ring bound
to a boron cluster via the N(1) atom. In the clusters, the B−B
bond distances and angles are typical for 2-substituted
The bond lengths
N(1)−B(2) are equal, within 3σ, to those in the starting
nitrilium closo-decaborate. The geometrical parameters of the
,3-dihydro-1,2,4-oxadiazole rings in 3a,e,f are the same, within
σ, as those in the previously described (2,3-dihydro-1,2,4-
and also those in the known
examples of structurally characterized uncomplexed 2,3-
(
good solubility in water (>20 mg per 1 mL).
Characterization of the closo-Decaborate Clusters
Featuring 2,3-Dihydro-1,2,4-oxadiazoles. All isolated
35,53
±
nonahydro-closo-decaborate clusters.
species were characterized by HRESI mass spectrometry,
ICP-MS (% B for the six most stable species 3a,b,e,f,i,j), IR and
53
1
13
1
11
1
H and C{ H} NMR (3a−j, 5a−d), and B{ H} NMR (3a−
2
j) spectroscopy and also by X-ray diffraction (for 3a,e,f). All
physicochemical data are in agreement with the proposed
formulas.
3
21,22
oxadiazole)Pt complexes
−
In the ESI mass spectra of 3a−j, the most intense signals are
54−56
−
−
dihydro-1,2,4-oxadiazoles.
had normal values (Table 1).
All other bonds and angles
due to [A] (where A is the anionic borylated heterocycle) or,
n
−
+
in some instances, [2A + Bu N] , while the ESI mass spectra
exhibit signals from [Bu N] or [2Bu N + A] . In the ESI
mass spectra of 5a−d, only signals of [A] were detected and
no signals from [Bu N] were observed in ESI -MS. In the IR
4
n
4
+
n
4
+
−
Final Remarks. The results from this work could be
considered from at least three perspectives. First, we observed
that the nitrilium group bound to a closo-decaborate moiety
exhibits dipolarophilicity so significant that DCA of rather
inactive acyclic nitrones in the Z form proceeds efficiently
under mild conditions. The competitive reactivity study
indicates that the observed reaction belongs to type I (normal
electron demand) of CA in the Sustmann classification, where
HOMOnitrone−LUMO interactions determine the occur-
rence of DCA. However, on the basis of previous theoretical
−
n
4
+
+
spectra of 3a−j and 5a−d, strong bands due to ν(B−H) and
ν(CN) stretching vibrations were found in the ranges of
−
1
2
450−2510 and 1590−1650 cm , respectively. No ν(CN)
−1
35
bands at ca. 2300 cm , specific for the starting materials,
51
were detected. The IR spectra of 3a−j exhibit strong bands for
−1
ν(C−H) in the range 2870−2970 cm , in contrast to the
spectra of 5a−d, where only weak signals were observed in this
region.
nitrile
57
calculations conducted for boron-mediated CA to nitriles and
1
718
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Organometallics
Article
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
closo-decaborate cluster unit behaves as a sufficiently stable,
small, and hydrophilic functional group that imparts an aqueous
solubility to the heterocycles. Consequently, water-soluble
sodium salts (e.g., 5a−d) seem to be logical candidates for
biological tests and work in this direction is underway in our
group. On the other hand, boron-containing species and, in
particular, various polyhedral boranes have attracted special
attention as potential agents in boron neutron capture cancer
3
a,e,f
3
a
3e
3f
O(1)−C(1)
1.336(2)
1.503(2)
1.284(2)
1.493(2)
1.546(3)
1.470(2)
1.486(2)
1.484(3)
1.338(2)
1.492(2)
1.289(2)
1.482(2)
1.545(2)
1.471(3)
1.485(2)
1.473(3)
1.3368(16)
1.4934(15)
1.2907(17)
1.4861(16)
1.5438(18)
1.471(3)
O(1)−N(2)
N(1)−C(1)
N(1)−C(5)
N(1)−B(2)
N(2)−C(4)
N(2)−C(5)
C(1)−C(2)
C(2)−C(3)
69
therapy. The growing role of polyhedral boron hydrides in
radionuclide diagnostics and drug design, including anti-AIDS
1.4852(17)
1.4805(19)
1.532(2)
69
agents, should also be noted.
EXPERIMENTAL SECTION
■
C(1)−O(1)−N(2)
C(1)−N(1)−C(5)
C(1)−N(1)−B(2)
C(5)−N(1)−B(2)
C(4)−N(2)−C(5)
C(4)−N(2)−O(1)
C(5)−N(2)−O(1)
N(1)−C(1)−O(1)
N(1)−C(1)−C(2)
O(1)−C(1)−C(2)
106.38(14)
108.09(16)
129.09(16)
122.70(15)
110.77(15)
103.59(14)
102.02(13)
114.97(17)
128.68(18)
116.34(17)
106.91(13)
108.25(15)
128.83(16)
122.79(14)
110.86(15)
103.74(14)
102.34(13)
114.57(17)
128.97(18)
116.46(16)
106.52(10)
107.74(11)
129.01(11)
123.22(10)
110.42(11)
103.40(10)
101.89(9)
Instrumentation and Materials. N-Methylhydroxylamine hydro-
2
2
2
chloride (Aldrich), p-R C H CHO (R = Me, NO , Aldrich; R =
6
4
2
OMe, Lancaster), and solvents were obtained from commercial
70
37
sources and used as received. closo-Decaborate clusters 1a and 1d
were prepared in accord with the published methods, while the
syntheses and characterization of 1b,c are described later in this
section. Nitrones 2a−c were synthesized by condensation of the
corresponding aldehyde and N-methylhydroxylamine via the known
114.73(12)
128.76(13)
116.41(12)
1
0
protocols.
Elemental analysis for boron was performed by the FSUE IREA
Center (Moscow) on a iCAP 6300 Duo ICP spectrometer using In as
an internal standard. Infrared spectra were recorded on a Shimadzu
also considering the coherent theoretical data on metal-
1
13
1
11
1
FTIR 8400S instrument in KBr pellets. H, C{ H}, and B{ H}
NMR spectra were measured on a Bruker-DPX 300 spectrometer at
ambient temperature (BF ·Et O was used as the external standard for
58
mediated DCAs, it is anticipated that the cycloaddition
could exhibit an asynchronous character.
3
2
11
1
Second, the observed reaction represents the first example of
boron-mediated DCA of allyl anion type dipoles, i.e. nitrones, to
the nitrile functionality. Note that several boron-catalyzed
B{ H} NMR). Electrospray ionization mass spectra were obtained
on a Bruker micrOTOF spectrometer equipped with an electrospray
ionization (ESI) source, and MeOH was used as the solvent. The
instrument was operated both at positive and negative ion modes
using a m/z range of 50−3000. The capillary voltage of the ion source
DCAs to nitrile species were reported and all these examples
−
(
viz., F B-catalyzed CAs of N , organic azides, or nitrile oxides
3
3
+
−
59−66
was set at −4500 V (ESI -MS) or 3500 V (ESI -MS) and the capillary
exit at ±30 V. In the isotopic pattern, the most abundant peak is
to RCN species
) are restricted exclusively to CA of
propargyl−allenyl type dipoles.
̈
reported. Melting points were determined in a capillary on a Buchi 530
In this context, it is of interest to compare the reaction
conditions for various boron-mediated DCAs. Thus, in the case
of the propargyl−allenyl type dipoles, CA of sodium azide or
melting point apparatus. TLC was carried out on Al plates precoated
with a layer of silica gel Merck 60 F254. For column chromatography
silica gel 60 F254, 0.063−0.200 mm (Merck), was used.
6
4,65
organic azides to substituted arylacetonitriles
and to
X-ray Crystal Structure Determinations. Crystals of 3a,e,f were
obtained by a slow evaporation of the solvent from methanol solution
of 3a or acetonitrile solutions of 3e,f. Single-crystal X-ray diffraction
experiments were carried out with a Bruker Kappa Apex II Duo
65
perfluoro- or perchloroalkylnitriles takes place only with
prolonged heating at 100−150 °C. Furthermore, CAs of the
+
−
nitrile oxides ArCN O to RCN were conducted under
7
1
5
9,60
60,61
diffractometer (for 3a) and a Bruker SMART 1000 CCD
72
reflux conditions for 0.5−2 h in the case R = alkyl,
aryl
diffractometer (for 3e,f) using Mo Kα radiation (λ = 0.710 73 Å).
or at room temperature for much more reactive malononitrile
A multiscan absorption correction based on equivalent reflections
5
9,62,63
derivatives.
In contrast to all these examples, the nitrile
73
(
SADABS) was applied to the data. The structures were solved by
functionality in the closo-decaborate clusters exhibits enhanced
reactivity in the DCA of nitrones (CAs were completed over
direct methods and refined by the full-matrix least-squares technique
2
against F with anisotropic temperature factors for all non-hydrogen
7
4
1
6−18 h at 20−25 °C) similar to that found earlier for CA of
atoms using the SHELXTL program package. In 3e,f, the hydrogen
atoms of the boron cage were located from difference Fourier maps
and involved in refinement in isotropic approximation. The rest of the
hydrogen atoms in 3e,f, as well as all hydrogen atoms in 3a, were
positioned geometrically and constrained to ride on their parent
atoms, with C−H = 0.95−1.00 Å, B−H = 1.12 Å, and Uiso = 1.2−
nitrones to nitrile ligands bound to such exceptionally powerful
IV
66
activators as Pt centers. Moreover, in DCA with nitrones,
the reactivity of the borylated CN group is quite comparable to
that observed for the DCA of nitrones to highly reactive N-alkyl
2
2
nitrilium salts.
1
.5[U (parent atom)]. The crystallographic details are summarized in
eq
Third, the products originating from DCA, viz., closo-
decaborate clusters featuring 2,3-dihydro-1,2,4-oxadiazoles
Table S1 (Supporting Information).
Competitive Reactivity Study. Compound 1a (0.17 mmol) was
added to a solution of nitrones 2a (0.51 mmol) and 2b (0.50 mmol)
3
a−j, have a dual interest. On one hand, 2,3-dihydro-1,2,4-
oxadiazoles represent a class of little explored heterocycles
whose chemistry was elaborated only in the past decade upon
developing the metal-mediated synthetic approaches to these
(or 2b (0.54 mmol) and 2c (0.45 mmol)) in CDCl (0.5 mL) in an
3
NMR tube. After 1 h at 25 °C no signals of compound 1a were
1
observed in the H NMR spectra. The k
/k
value was evaluated using
1
2
3
integral intensities of the reaction products according to the formula
species. It is worth mentioning thatother than two reports
II
on the antitumor activity of (2,3-dihydro-1,2,4-oxadiazole)Pt
6
7,68
k
S(1)
S(2)
1
complexes
the biological/medicinal properties of these
=
·a
k
heterocycles have not been unexplored. We believe that the
2
1
719
dx.doi.org/10.1021/om200993f | Organometallics 2012, 31, 1716−1724

Organometallics
Article
where S(1) and S(2) are integral intensities of signals of C H OCH
3
6
4
and C H CH -p groups in 3a,e, correspondingly, or NCHN signals in
6
4
3
3
e,i and a is the initial ratio (2a:2b and 2b:2c) of the starting nitrones.
Synthetic Work. Synthesis of 1b,c. Nitrilium borates were
70
n
prepared by a modified literature method. [Bu N][B H ]
(
4
5.00 g, 0.014 mol) was dissolved in RCN (30 mL; R = Et
10 11
t
(
1b), Bu (1c)), and the solution was heated to 75 °C for 1.5 h.
Then the solvent was evaporated under vacuum at 40 °C to
furnish a solid residue that was crystallized under CH CN and
3
NCH ), 1.27 (t, 3H, J = 7 Hz, CCH CH ), 1.61−1.48 (m, 8H), 1.47−
3
2
3
−2
n
4
13
1
dried at 60 °C/10 mm Hg on a Kugelrohr apparatus.
1
.33 (m, 8H), 0.96 (t, J = 7 Hz, 12H) (NBu ). C{ H} NMR (75.49
−1
1
b: yield 5.37 g (93%). IR spectrum in Nujol, selected bands, cm :
MHz, CDCl ): δ 173.0 (CN), 160.6 (ipso to MeO), 128.9 (meta to
3
1
2
2
1
482 s ν(B−H), 2331 s ν(CN). H NMR (300.13 MHz, CDCl ): δ
3
MeO), 128.0 (para to MeO), 114.1 (ortho to MeO), 91.6 (NCN),
59.0 (NCH Pr), 55.7 (OCH ), 47.1 (NCH ), 24.5 (NCH CH Et),
.82 (q, 2H, NCH CH ), 1.12 (t, 3H, NCH CH ), 3.13 (t, 8H), 1.60−
2
3
2
3
2
3
3
2
2
n
4
13
1
.47 (m, 8H), 1.46−1.30 (m, 8H), 0.95 (t, 12H) (NBu ). C{ H}
20.1 (N(CH ) CH Me), 20.0 (CCH CH ), 14.2 (N(CH ) CH ), 9.9
2 2 2 2 3 2 3 3
NMR (75.49 MHz, CDCl ): δ 117.4, 58.4, 24.3, 23.0, 19.3, 14.3, 12.8.
11
1
1
3
(CCH CH ). B{ H} NMR (96.32 MHz, CDCl ): 0.60 (B ), −2.07
2
3
3
1
1
1
10
1
2
B{ H} NMR (96.32 MHz, CDCl ): 1.0 (B ), −1.9 (B ), −20.5 (B ),
25.4 (B , B , B , B ), −28.1 (B , B , B ). High-resolution ESI -MS:
10 2 4 7 8 3 5 6 9
3
(B ), −13.09 (B ), −24.36 (B , B , B ), −28.28 (B , B , B , B ). High-
3
5
6
9
4
7
8
−
+
n
+
−
resolution ESI -MS: m/z 823.8813 [A + 2Bu N] (823.8542 calcd),
4
−
n
−
n
+
−
m/z 172.2625 [A] (172.2604 calcd), 586.9877 [2A + NBu ]
242.2927 [Bu N] (242.2843 calcd). High-resolution ESI -MS: m/z
4
4
−
n
−
(
586.9852 calcd).
3
39.2875 [A] (339.2846 calcd), 920.8578 [2A + Bu N] (920.8541
4
−
1
1
c: yield 5.16 g (84%). IR spectrum in Nujol, selected bands, cm :
calcd). Mp: 123−125 °C dec.
1
2
533 s, 2471 s ν(B−H), 2348 s ν(CN). H NMR (300.13 MHz,
CDCl ): δ 1.37 (s, 9H, NCC(CH ) ), 3.13 (t, 8H), 1.60−1.47 (m,
8
3
3
3
n
4
13
1
H), 1.46−1.30 (m, 8H), 0.95 (t, 12H) (NBu ). C{ H} NMR
(
75.49 MHz, CDCl ): δ 115.4, 58.0, 30.6, 28.6, 23.0, 19.3, 12.6.
3
1
1
1
10
1
2
B{ H} NMR (96.32 MHz, CDCl ): 1.1 (B ), −1.9 (B ), −20.4 (B ),
3
3
5
6
9
4
7
8
−
−
25.3 (B , B , B , B ), −27.4 (B , B , B ). High-resolution ESI -MS:
− n −
m/z 200.2656 [A] (200.3136 calcd), 643.0985 [2A + NBu ]
4
(
643.0917 calcd).
Boron-Mediated Cycloaddition of the Nitrones. The reaction
−
1
between each of the nitrones (2a−c; 0.14 mmol) and each of the
nitrilium derivatives (1a−d; 0.14 mmol) was performed in a
chloroform (3 mL) solution at room temperature, and its
completeness was monitored by TLC. After 16−18 h the product of
the cycloaddition was separated from the reaction mixture by column
chromatography on silica gel (eluent is 10/1 v/v chloroform/acetone).
Evaporation of the solvent (at 20−25 °C) from the first fraction gave
an oily product that was crystallized under a layer of diethyl ether at
room temperature to furnish solid 3a−j.
3
c: yield 51 mg (60%). IR spectrum in KBr, selected bands, cm :
1
2
505 s, 2463 s ν(B−H), 1610 s ν(CN). H NMR (300.13 MHz,
CDCl ): δ 7.17 (d, 2H, J = 9 Hz, meta to MeO), 6.87 (d, 2H, J = 9 Hz,
3
ortho to MeO), 5.88 (s, 1H, NCHN), 3.81 (s, 3H, OCH ), 2.81 (s,
3
3
8
H, NCH ), 1.71−1.50 (m, 17H, NCH CH Et and C(CH ) ), 3.16 (t,
3
2
2
3 3
n 13 1
H), 1.49−1.36 (m, 8H), 0.99 (t, J = 7 Hz, 12H) (NBu ). C{ H}
4
NMR (75.49 MHz, CDCl ): δ 177.4 (CN), 160.3 (ipso to MeO),
3
1
9
28.9 (meta to MeO), 128.2 (para to MeO), 114.1 (ortho to MeO),
3.1 (NCN), 59.0 (NCH Pr), 55.7 (OCH ), 46.0 (NCH ), 35.4
2
3
3
(
(
C(CH ) ), 27.7 (C(CH ) ), 24.4 (NCH CH Et), 20.1 (N-
3 3 3 3 2 2
11
1
CH ) CH Me), 14.2 (N(CH ) CH ). B{ H} NMR (96.32 MHz,
2
2
2
2
3
3
1
10
2
4
7
8
CDCl ): 0.40 (B ), −0.97 (B ), −11.27 (B ), −24.93 (B , B , B ),
−
2
3
3
5
6
9
+
27.94 (B , B , B , B ). High-resolution ESI -MS: m/z 851.9152 [A +
n
4
+
n
4
+
Bu N] (851.8855 calcd), 242.2948 [Bu N] (242.2843 calcd).
−
−
High-resolution ESI -MS: m/z 367.3124 [A] (367.3159 calcd). Mp:
8
5−87 °C, dec.
3
a: yield 51 mg (64%). Anal. Found: B, 18.75. Calcd for
C H N B O : B, 19.10. IR spectrum in KBr, selected bands,
2
7
59
3
10
2
−
1
1
cm : 2505 s, 2463 s ν(B−H), 1647 s ν(CN). H NMR (300.13
MHz, CDCl ): δ 7.26 (d, 2H, J = 9 Hz, meta to MeO), 6.83 (d, 2H, J
3
=
9 Hz, ortho to MeO), 5.53 (s, 1H, NCHN), 3.77 (s, 3H, OCH3),
2
8
.79 (s, 3H, NCH ), 2.63 (s, 3H, CCH ), 3.13 (t, 8H), 1.60−1.47 (m,
3
3
n
13
1
H), 1.46−1.30 (m, 8H), 0.95 (t, J = 7 Hz, 12H) (NBu ). C{ H}
4
−
1
NMR (75.49 MHz, CDCl ): δ 169.7 (CN), 160.6 (ipso to MeO),
3d: yield 57 mg (65%). IR spectrum in KBr, selected bands, cm :
3
1
1
9
29.0 (meta to MeO), 127.8 (para to MeO), 114.1 (ortho to MeO),
2505 s, 2463 s ν(B−H), 1647 s ν(CN). H NMR (300.13 MHz,
1.8 (NCN), 58.9 (NCH Pr), 55.7 (OCH ), 47.2 (NCH ), 24.4
CDCl ): δ 8.06 (d, J = 7 Hz, 2H, ortho in Ph), 7.60 (t, 1H, J = 7 Hz,
2
3
3
3
(
NCH CH Et), 20.1 (N(CH ) CH Me), 14.2 (N(CH ) CH ), 13.1
2 2 2 2 2 2 3 3
para in Ph), 7.50−7.37 (m, 4H, meta to MeO and meta in Ph), 6.91
(d, 2H, J = 9 Hz, ortho to MeO), 5.83 (s, 1H, NCHN), 3.82 (s, 3H,
OCH ), 2.92 (s, 3H, NCH ), 3.11 (t, 8H), 1.60−1.47 (m, 8H), 1.46−
11
1
1
10
(
−
CCH3). B{ H} NMR (96.32 MHz, CDCl ): 0.69 (B ), −2.35 (B ),
3
2
4
7
8
3
5
6
9
13.03 (B ), −24.12 (B , B , B ), −28.13 (B , B , B , B ). High-
+ n +
3
3
resolution ESI -MS: m/z 242.2846 [Bu N] (242.2843 calcd). High-
n
13
1
4
1
.30 (m, 8H), 0.94 (t, J = 7 Hz, 12H) (NBu ). C{ H} NMR (75.49
−
−
4
resolution ESI -MS: m/z 325.2728 [A] (325.2690 calcd), 892.8264
MHz, CDCl ): δ 167.0 (CN), 160.7 (ipso to MeO), 135.1, 132.5,
n
+
3
[
2A + Bu N] (892.8228 calcd). Mp: 125−128 °C dec.
4
1
5
29.0 128.5, 128.8, 127.6, 114.1 (Ar), 92.4 (NCN), 59.0 (NCH Pr),
2
3
b: yield 56 mg (69%). Anal. Found: B, 18.32. Calcd for
5.7 (OCH ), 46.8 (NCH ), 24.4 (NCH CH Et), 20.1 (N-
3
3
2
2
C H N B O : B, 18.64. IR spectrum in KBr, selected bands,
2
8
61
3
10
2
11
1
−
1
1
(CH ) CH Me), 14.2 (N(CH ) CH ). B{ H} NMR (96.32 MHz,
CDCl ): 0.38 (B ), −1.88 (B ), −11.52 (B ), −23.75 (B , B , B ),
−27.89 (B , B , B , B ). High-resolution ESI -MS: m/z 871.8863 [A +
2Bu N] (871.8541 calcd), 242.2991 [Bu N] (242.2843 calcd).
cm : 2508 s, 2466 s, 2442 s ν(B−H), 1641 s ν(CN). H NMR
2
2
2
2
10
3
3
1
2
4
7
8
(
300.13 MHz, CDCl ): δ 7.25 (d, 2H, J = 9 Hz, meta to MeO), 6.84
3
3
3
5
6
9
+
(
d, 2H, J = 9 Hz, ortho to MeO), 5.54 (s, 1H, NCHN), 3.77 (s, 3H,
n
4
+
n
4
+
OCH ), 3.26−3.05 (m, 10H, NCH Pr and CCH CH ), 2.77 (s, 3H,
3
2
2
3
1
720
dx.doi.org/10.1021/om200993f | Organometallics 2012, 31, 1716−1724

Organometallics
Article
−
−
4
7
8
3
5
6
9
−
High-resolution ESI -MS: m/z 387.2891 [A] (387.2846 calcd). Mp:
3−75 °C dec.
(B , B , B ), −27.87 (B , B , B , B ). High-resolution ESI -MS: m/z
−
7
351.3259 [A] (351.3210 calcd). Mp: 118−120 °C dec.
−
1
3
e: yield 51 mg (66%). Anal. Found: B, 19.71. Calcd for
3h: yield 35 mg (52%). IR spectrum in KBr, selected bands, cm :
−1
1
C H N B O: B, 19.66. IR spectrum in KBr, selected bands, cm :
2472 s ν(B−H), 1622 s ν(CN). H NMR (300.13 MHz, CDCl ): δ
2
7
59
3
10
3
1
2
506 s, 2463 s ν(B−H), 1647 s ν(CN). H NMR (300.13 MHz,
8.09 (d, 2H, J = 7 Hz, ortho in Ph), 7.63−7.42 (m, 5H, meta and para
in Ph and meta to Me), 7.21 (d, 2H, J = 8 Hz, ortho to Me) 5.88 (s,
1H, NCHN), 2.95 (s, 3H, NCH ), 2.37 (s, 3H, CH C H ), 3.12 (t,
CDCl ): δ 7.23 (d, 2H, J = 8 Hz, meta to Me), 7.13 (d, 2H, J = 8 Hz,
3
ortho to Me) 5.56 (s, 1H, NCHN), 2.80 (s, 3H, NCH ), 2.65 (s, 3H,
3
3
3
6
4
CCH ), 2.31 (s, 3H, CH C H ), 3.15 (t, 8H), 1.68−1.51 (m, 8H),
8H), 1.68−1.48 (m, 8H), 1.47−1.35 (m, 8H), 0.97 (t, J = 7 Hz, 12H)
3
3
6
4
n
13
1
n 13 1
1
.50−1.30 (m, 8H), 0.97 (t, J = 7 Hz, 12H) (NBu ). C{ H} NMR
(NBu ). C{ H} NMR (75.49 MHz, CDCl ): δ 166.4 (CN),
141.7, 135.0, 133.5, 131.4, 129.7, 128.3, 127.5, 126.2 (Ar), 92.5
4
4
3
(
(
75.49 MHz, CDCl ): δ 169.9 (CN), 139.4, 132.8, 129.4, 127.4
3
Ar), 91.1 (NCN), 59.0 (NCH Pr), 47.3 (NCH ), 24.5
(NCN), 59.0 (NCH Pr), 47.7 (NCH ), 24.5 (NCH CH Et), 21.8
2
3
2
3
2
2
1
1
1
(
(
1
−
(
NCH CH Et), 21.7 (C H CH ), 20.1 (N(CH ) CH Me), 14.2
(C H CH ), 20.1 (N(CH ) CH Me), 14.2 (N(CH ) CH ). B{ H}
2
2
6
4
3
2
2
2
6 4 3 2 2 2 2 3 3
11
1
1
10
2
N(CH ) CH ), 13.1 (CCH ). B{ H} NMR (96.32 MHz, CDCl ):
NMR (96.32 MHz, CDCl ): 1.00 (B ), −1.64 (B ), −11.42 (B ),
4 7 8 3 5 6 9
2
3
3
3
3
3
1
10
2
4
7
8
.12 (B ), −2.56 (B ), −13.26 (B ), −23.90, −25.38 (B , B , B ),
28.14 (B , B , B , B ). High-resolution ESI -MS: m/z 309.2767 [A]
−23.35, −24.38 (B , B , B ), −27.87 (B , B , B , B ). High-resolution
3
5
6
9
−
−
− −
ESI -MS: m/z 371.2937 [A] (371.2897 calcd). Mp: 69−70 °C dec.
309.2741 calcd). Mp: 119−120 °C dec.
3
i: yield 55 mg (68%). Anal. Found: B, 18.48. Calcd for
3
f: yield 44 mg (64%). Anal. Found: B, 19.07. Calcd for
C H N B O : B, 18.61. IR spectrum in KBr, selected bands,
2
7
59
3
10
2
−1
−
1
C H N B O: B, 19.17. IR spectrum in KBr, selected bands, cm :
2
8
61
3
10
cm : 2501 s, 2464 s, ν(B−H), 1644 s ν(CN), 1521, 1346 ν(NO ).
2
1
1
2
508 s, 2466 s ν(B−H), 1643 s ν(CN). H NMR (300.13 MHz,
H NMR (300.13 MHz, CDCl ): δ 8.18 (d, 2H, J = 9 Hz, ortho to
3
CDCl ): δ 7.19 (d, 2H, J = 8 Hz, meta to Me), 7.10 (d, 2H, J = 8 Hz,
3
NO ), 7.63 (d, 2H, J = 9 Hz, meta to NO ), 5.69 (s, 1H, NCHN), 2.87
2
2
ortho to Me) 5.54 (s, 1H, NCHN), 3.16−3.08 (m, 10H, NCH Pr and
CCH CH ), 2.77 (s, 3H, NCH ), 2.29 (s, 3H, CH C H ), 1.27 (t, 3H,
J = 7 Hz, CCH CH ), 1.60−1.42 (m, 8H), 1.42−1.33 (m, 8H), 0.99
t, J = 7 Hz, 12H) (NBu ). C{ H} NMR (75.49 MHz, CDCl ): δ
2
(s, 3H, NCH ), 2.68 (s, 3H, CCH ), 3.14 (t, 8H), 1.63−1.50 (m, 8H),
3
3
n
13
1
2
3
3
3
6
4
1.48−1.35 (m, 8H), 0.96 (t, J = 7 Hz, 12H) (NBu ). C{ H} NMR
4
2
3
(75.49 MHz, CDCl ): δ 170.9 (CN), 148.7, 142.5 (ipso and para to
3
n
13
1
(
1
(
(
(
(
4
3
NO ), 129.1 (meta to NO ), 123.8 (ortho to NO ), 90.1 (NCN), 59.1
2
2
2
72.9 (CN), 139.1, 133.0, 129.1, 127.0 (Ar), 91.5 (NCN), 58.7
(
NCH Pr), 47.5 (NCH ), 24.4 (NCH CH Et), 20.1 (N-
(CH ) CH Me), 14.1 (N(CH ) CH ), 13.1 (CCH ). B{ H} NMR
2 3 2 2
NCH Pr), 46.9 (NCH ), 24.2 (NCH CH Et), 21.4 (C H CH ), 19.8
11
1
2 3 2 2 6 4 3
2 2 2 2 3 3 3
N(CH ) CH ), 19.7 (CCH CH ), 13.9 N(CH ) CH ), 9.6
1
10
2
2
3
3
2
3
2
3
3
(96.32 MHz, CDCl ): 0.69 (B ), −2.35 (B ), −13.03 (B ), −24.12
4 7 8 3 5 6 9 +
3
1
1
1
1
CCH CH ). B{ H} NMR (96.32 MHz, CDCl ): 1.00 (B ), −2.36
2
3
3
(B , B , B ), −28.13 (B , B , B , B ). High-resolution ESI -MS: m/z
10
2
4
7
8
3
5
6
B ), −13.31 (B ), −24.01, −25.44 (B , B , B ), −28.14 (B , B , B ,
n
+
−
2
3
42.2888 [Bu N] (242.2843 calcd). High-resolution ESI -MS: m/z
4
9
−
−
B ). High-resolution ESI -MS: m/z 323.2933 [A] (323.2897 calcd).
Mp: 124−125 °C dec.
−
40.2466 [A] (340.2435 calcd). Mp: 85−90 °C dec.
3
j: yield 45 mg (55%). Anal. Found: B, 18.01. Calcd for
−
1
3
g: yield 27 mg (39%). IR spectrum in KBr, selected bands, cm :
C H N B O : B, 18.17. IR spectrum in KBr, selected bands,
1
27 59
−1
3
10
2
2
525 s, 2477 s ν(B−H), 1597 s ν(CN). H NMR (300.13 MHz,
1
cm : 2473 s, ν(B−H), 1647 s ν(CN), 1521, 1346 ν(NO ). H
2
CDCl ): δ 7.12 (d, 2H, J = 8 Hz, meta to Me), 7.08 (d, 2H, J = 8 Hz,
3
NMR (300.13 MHz, CDCl ): δ 8.18 (d, 2H, J = 9 Hz, ortho to NO ),
3
2
ortho to Me) 5.89 (s, 1H, NCHN), 2.82 (s, 3H, NCH ), 2.34 (s, 3H,
3
7.61 (d, 2H, J = 9 Hz, meta to NO ), 5.70 (s, 1H, NCHN), 3.35−3.05
(m, 10H, NCH Pr and CCH CH ), 2.86 (s, 3H, NCH ), 1.29 (t, 3H, J
= 8 Hz, CCH CH ), 1.66−1.51 (m, 8H), 1.49−1.35 (m, 8H), 0.97 (t,
J = 7 Hz, 12H) (NBu ). C{ H} NMR (75.49 MHz, CDCl ): δ
4 3
2
CH C H ), 1.63−1.44 (m, 17H, NCH CH Et and C(CH ) ), 3.17 (t,
3
6
4
2
2
3
3
2
2
3
3
n
13
1
8
H), 1.43−1.30 (m, 8H), 0.94 (t, J = 7 Hz, 12H) (NBu ). C{ H}
4
2
3
n 13 1
NMR (75.49 MHz, CDCl ): δ 177.2 (CN), 138.7, 133.5, 129.2,
3
1
(
1
26.5 (Ar), 93.0 (NCN), 58.8 (NCH Pr), 45.8 (NCH ), 35.1
174.2 (CN), 148.6, 142.3 (ipso and para to NO ), 129.0 (meta to
2
3
2
C(CH ) ), 27.4 (C(CH ) ), 24.2 (NCH CH Et), 21.3 (C H CH ),
NO ), 123.8 (ortho to NO ), 90.8 (NCN), 59.1 (NCH Pr), 47.3
3
3
3
3
2
2
6
4
3
2
2
2
11
1
9.8 (N(CH ) CH Me), 13.9 (N(CH ) CH ). B{ H} NMR (96.32
MHz, CDCl ): 1.10 (B ), −0.84 (B ), −11.22 (B ), −23.13, −24.81
(NCH ), 24.4 (NCH CH Et), 20.0 (N(CH ) CH Me and
(CCH CH )), 14.1 (N(CH ) CH ), 9.8 (CCH CH ). B{ H}
2 3 2 3 3 2 3
2
2
2
2
3
3
3 2 2 2 2 2
1
10
2
11
1
3
1
721
dx.doi.org/10.1021/om200993f | Organometallics 2012, 31, 1716−1724

Organometallics
Article
1
10
2
−1
NMR (96.32 MHz, CDCl ): 0.60 (B ), −2.07 (B ), −13.09 (B ),
5b: yield 21 mg (72%). IR spectrum in KBr, selected bands, cm :
3
4
7
8
3
5
6
9
+
1
−
24.36 (B , B , B ), −28.28 (B , B , B , B ). High-resolution ESI -MS:
m/z 242.2945 [Bu N] (242.2843 calcd). High-resolution ESI -MS:
m/z 354.2650 [A] (354.2591 calcd) Mp: 68−70 °C dec.
2508 s, 2478 s, 2471 s, 2459 s ν(B−H), 1638 s ν(CN). H NMR
n
4
+
−
(300.13 MHz, CDCl
): δ 7.23 (d, 2H, J = 9 Hz, meta to MeO), 6.89
3
−
(d, 2H, J = 9 Hz, ortho to MeO), 5.59 (s, 1H, NCHN), 3.81 (s, 3H,
OCH ), 3.27−2.98 (m, 2H, CH CH ) 2.80 (s, 3H, NCH ), 1.29 (t,
H, J = 8 Hz, CH CH ). C{ H} NMR (75.49 MHz, CDCl ): δ 173.5
3
2
3
3
13
1
3
2
3
3
(
CN), 160.8 (ipso to MeO), 128.7 (meta to MeO), 128.1 (para to
MeO), 113.6 (ortho to MeO), 91.5 (NCN), 54.7 (OCH ), 45.9
3
−
(NCH ), 19.3 (CCH CH ), 9.0 (CCH CH ). High-resolution ESI -
3
2
3
2
3
−
MS: m/z 339.2902 [A] (339.2846 calcd).
3
k was not isolated as a pure solid because of its instability. IR
−1
1
spectrum in KBr, selected bands, cm : 1647 ν(CN). H NMR
(
300.13 MHz, CDCl , selected signals): δ 6.01 (s, NCHN). High-
3
−
−
resolution ESI -MS: m/z 382.2936 [A] (382.2905 calcd).
−
1
5
c: yield 18 mg (68%). IR spectrum in KBr, selected bands, cm :
1
2
(
508 s, 2478 s, 2471 s, 2459 s ν(B−H), 1638 s ν(CN). H NMR
300.13 MHz, CDCl ): δ 7.22−7.13 (2d, 4H, C H ), 5.61 (s, 1H,
3
6
4
NCHN), 2.81 (s, 3H, NCH ), 2.63 (s, 3H, CCH ), 2.35 (s, 3H,
3
3
13
1
C H CH ). C{ H} NMR (75.49 MHz, CDCl ): δ 170.8 (CN),
6
4
3
3
1
(
39.2, 133.1, 128.8, 127.2 (Ar), 91.8 (NCN), 46.1 (NCH ), 20.3
3
−
C H CH ), 11.6 (CCH ). High-resolution ESI -MS: m/z 309.2751
6
4
3
3
−
3
l was not isolated as a pure solid because of its instability. IR
[A] (309.2741 calcd).
−1
1
spectrum in KBr, selected bands, cm : 1644 ν(CN). H NMR
(
300.13 MHz, CDCl , selected signals): δ 5.98 (s, NCHN). High-
3
−
−
resolution ESI -MS: m/z 402.2613 [A] (402.2592 calcd).
Preparation of Water-Soluble Compounds 5a−d. A solution of
each of 3a,b,e,f (0.28 mmol) in a methanol/acetonitrile mixture (1.5
mL/0.5 mL) was added to a solution of sodium tetraphenylborate
(
0.28 mmol) in methanol (2 mL), whereupon the colorless precipitate
n
of [Bu N]BPh that formed was filtered off. The volume of the filtrate
4
4
was reduced to 1 mL at room temperature, and water (0.5 mL) was
added. The solid was separated by filtration, and the resulted solution
was dried under vacuum until the formation of a yellow oily residue
that was dried and crystallized in a desiccator over silica gel (in the
presence of a moisture indicator) as a light yellow solid.
−1
5
d: yield 21 mg (76%). IR spectrum in KBr, selected bands, cm :
1
2
(
508 s, 2478 s, 2471 s, 2459 s ν(B−H), 1638 s ν(CN). H NMR
300.13 MHz, CDCl ): δ 7.22−7.13 (2d, 4H, C H ), 5.61 (s, 1H,
3
6
4
NCHN), 3.29−2.99 (m, 2H, CH CH ), 2.80 (s, 3H, NCH ), 2.34 (s,
2
3
3
1
3
1
3
H, C H CH ), 1.30 (t, 3H, J = 8 Hz, CH CH ). C{ H} NMR
6 4 3 2 3
(
1
(
3
75.49 MHz, CDCl ): δ 173.7 (CN), 139.2, 133.1, 128.8, 127.2,
3
13.6 (Ar), 91.7 (NCN), 46.0 (NCH ), 20.3 (C H CH ), 19.3
3 6 4 3
−
CCH CH ), 8.9 (CCH CH ). High-resolution ESI -MS: m/z
2 3 2 3
−
23.2921 [A] (323.2897 calcd).
ASSOCIATED CONTENT
* Supporting Information
■
S
CIF files, Figures S1 and S2, and a table giving crystallographic
data, molecular structures, and details of the refinement for 3a,f.
This material is available free of charge via the Internet at
http://pubs.acs.org.
−
1
5
a: yield 20 mg (70%). IR spectrum in KBr, selected bands, cm :
1
2
(
(
508 s, 2478 s, 2471 s, 2459 s ν(B−H), 1638 s ν(CN). H NMR
300.13 MHz, CDCl ): δ 7.24 (d, 2H, J = 9 Hz, meta to MeO), 6.90
3
d, 2H, J = 9 Hz, ortho to MeO), 5.59 (s, 1H, NCHN), 3.81 (s, 3H,
OCH ), 2.81 (s, 3H, NCH ), 2.62 (s, 3H, CCH ). C{ H} NMR
13
1
3
3
3
(
(
(
75.49 MHz, CDCl ): δ 170.5 (CN), 160.8 (ipso to MeO), 128.7
AUTHOR INFORMATION
Corresponding Author
Fax: +7 812 4286939. Tel: +7 812 4286890. E-mail: bokach@
3
■
*
meta to MeO), 128.0 (para to MeO), 113.6 (ortho to MeO), 91.7
NCN), 54.8 (OCH ), 46.0 (NCH ), 11.6 (CCH ). High-resolution
3
3
3
−
−
ESI -MS: m/z 325.2662 [A] (325.2690 calcd).
nb17701.spb.edu (N.A.B.); kukushkin@vk2100.spb.edu
V.Y.K.).
(
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the Federal Targeted Program “Scientific and
Scientific-Pedagogical Personnel of the Innovative Russia in
■
2
009−2013” (Contract No. P1294 from 09/06/2010), Russian
Fund for Basic Research (Grant No. 11-03-00262). We
1
722
dx.doi.org/10.1021/om200993f | Organometallics 2012, 31, 1716−1724

Organometallics
Article
acknowledge Saint-Petersburg State University for a research
grant and the RAS Presidium Subprogram. A.L.M. expresses his
gratitude to the Government of Saint-Petersburg for a grant for
graduate and undergraduate students (2011). We are obliged to
the FSUE IREA Center (Moscow, Russia) sponsored by the
Federal Targeted Program “Research and Development in the
Priority Areas for the Development of Scientific and
Technological Complex of Russia for 2007−2012” (Contract
No. 16.552.11.7010 from 29/04/2011) for providing ICP-MS
analysis.
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