Reactions of diiminopyridine ligands with chalcogen halides

Article abstract of DOI:10.1021/ic202213x

The reactions of the chalcogen halides (Ch = S, Se, Te) with a series of diiminopyridine (DIMPY) ligands were explored. It was determined through these studies that varying both the substitution on the α-carbon and the chalcogen halide reagent afforded di

Full text of DOI:10.1021/ic202213x

Article
pubs.acs.org/IC
Reactions of Diiminopyridine Ligands with Chalcogen Halides
Caleb D. Martin and Paul J. Ragogna*
Department of Chemistry, The Chemistry Building, The University of Western Ontario, 1151 Richmond Street, London, Ontario,
Canada N6A 5B7
S
* Supporting Information
ABSTRACT: The reactions of the chalcogen halides (Ch = S, Se,
Te) with a series of diiminopyridine (DIMPY) ligands were
explored. It was determined through these studies that varying
both the substitution on the α-carbon and the chalcogen halide
reagent afforded different products. If methyl groups were present
on the α-carbon, reactivity was observed through the eneamine
tautomer to yield N,N′,C-bound neutral chalcogen complexes. In the cases where H and C6H5 groups were in the same position,
N,N′,N″-chelated chalcogen cations or dications were produced. Many of the reactions resulted in complex mixtures postulated to
occur by the release of halogen decomposing the product or, for reactions with the CH3 substituted ligand, uncontrollable
reactivity with the eneamine tautomer. This is the first report of reactions of sulfur and selenium halides with the ubiquitous
diiminopyridine ligands and only the second example for a tellurium halide.
using a methyl substituted DIMPY (2), which resulted in a
N,N′,C-bound tellurium complex (24), rather than the expected
N,N′,N″-bound species as observed in the DAB chemistry, once
again believed to occur through reaction with the enamine
tautomer (2′). In this context, we report a synthetic study of the
DIMPY ligand with the chalcogen halides varying the
substitution at the α-carbon within the ligand, while keeping
the groups on the imine nitrogens constant. The difference of a
hydrogen versus a methyl or phenyl group greatly influenced
the reaction outcome giving either neutral, monocationic, or
dicationic chalcogen centers. In some cases uncontrolled
halogenation occurred resulting in complex mixtures, indicating
that the reactivity of the group 16 halides with the
diiminopyridine ligands is not necessarily predictable.
INTRODUCTION
■
The use of α-diimine ligands (e.g., diazabutadiene, DAB;
diiminopyridine, DIMPY; Figure 1; 1−5) in transition metal
chemistry has opened a gateway to a plethora of new
discoveries, especially in catalysis.1 The main group chemistry
of these ligands is far less developed.2−12 The traditional
bonding motif for these Schiff bases has typically been via
chelation through the nitrogen centers in the multidentate
ligands. In virtually all cases, reports detailing the use of the 1,4-
diazabutadiene (DAB) ligand with group 13−15 halides
produce N,N′-bound species regardless of the substitution on
the backbone carbon atom.13−21 For the chalcogens it was
determined that, with varying the substitution on the backbone
carbon atom within the ligands, different products were
obtained.22−30 Hydrogen atoms, phenyl groups, or an
acenaphthene backbone led to the formation of N,N′-chelate
chalcogen complexes of TeCl2, TeBr4, SeCl2, SeBr2, and Ch2+
(Ch = S, Se, Te; Figure 2; 6−9) whereas a methyl group on the
α-carbon resulted in N,C-bound heterocycles (10−19), which
was postulated to occur by reaction with the enamine tautomer
of the ligand (4′ and 5′).25 The tellurium(IV) halides formed
heterocycles featuring an exocyclic imine, whereas when using
sulfur and selenium(II) halides exocyclic amines were observed.
Recent discoveries have indicated the DIMPY ligands have
the ability to stabilize low oxidation state main group centers
(e.g., In(I), As(I), P(I), S(II), Se(II), and Te(II)).4,8,31−33 Our
recent report of the first N,N′,N″-DIMPY chalcogen complexes
(Ch = S, Se, Te; 20−23), by the facile reaction of a chalcogen
bistriflate synthon and ligand 1, indicated that the tridentate
chelate imposed remarkable stability to the dicationic
complexes, differing greatly from other chalcogen(II) dications,
in particular the very unstable dicationic DAB complexes (7).31
Aside from these systems there has only been one report of a
reaction of this class of ligands with the chalcogen halides
reported by Cowley et al.28 The reaction described was TeCl4
EXPERIMENTAL SECTION
■
All manipulations were performed under an inert atmosphere in a
nitrogen filled MBraun Labmaster dp glovebox or using standard
Schlenk techniques. Sulfur dichloride, SeCl2, SeBr2, 1, 2, and 3 were
synthesized according to the literature procedures.2,33−37 The
SbPh3Cl2 generated from the production of SeCl2 could be easily
separated from the desired products in all cases by washing with Et2O.
Selenium tetrabromide, SeCl4, TeCl4, and TeBr4 were purchased from
Alfa Aesar and used as received. Dichloromethane, CH3CN, n-
pentane, THF, and Et2O were obtained from Caledon Laboratories
and dried using an MBraun Controlled Atmospheres Solvent
Purification System. The dried solvents were stored in Strauss flasks
under a N2 atmosphere, or over 4 Å molecular sieves in the glovebox
1
(3 Å for MeCN). Solvents used for H NMR spectroscopy (CD3CN
and CDCl3) were purchased from Sigma-Aldrich, and dried by storing
in the glovebox over 3 or 4 Å molecular sieves. Multinuclear NMR
data are listed in ppm, relative to Me4Si (13C and 1H), coupling
constants are in Hertz, and all NMR spectra were recorded on an
Received: October 12, 2011
Published: February 16, 2012
© 2012 American Chemical Society
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Figure 1. Structures of the diiminopyridine (DIMPY) and diazabutadiene (DAB) ligands and the corresponding enamine tautomers of the methyl
substituted derivatives (Dipp = 2,6-diisopropylphenyl; Cy = cyclohexyl).
Figure 2. Reaction products of chalcogen halides with DAB and DIMPY ligands (Dmp = 2,6-dimethylphenyl).
INOVA 400 MHz (1H = 399.76 MHz, 13C = 100.52 MHz)
spectrometer or INVOVA 600 MHz spectrometer. Single crystal X-
ray diffraction data were collected on a Nonius Kappa-CCD area
detector or a Bruker Apex II-CCD using Mo Kα radiation (λ = 0.710
73 Å). Crystals were selected under Paratone-N oil, mounted on nylon
loops or micromounts, and then immediately placed in a cold stream
of N2. Structures were solved and refined using SHELXTL.
CH3CN solution. Decomposition point: 130−132 °C. 1H NMR
3
(CD3CN, δ) 9.81 (s, 2H, α-CH), 9.09 (d, 2H, J = 7.8 Hz, m-H
pyridine), 8.99 (t, 1H, 3J = 7.8 Hz, p-H pyridine), 7.47 (t, 2H, 3J = 7.8
Hz, p-H C6H3), 7.39 (d, 4H, 3J = 7.8 Hz, m-H C6H3), 2.66 (sept, 4H,
3J = 6.0 Hz, CH(CH3)2), 1.22 (d, 12H, 3J = 6.0 Hz, CH(CH3)2), 1.17
(d, 12H, 3J = 5.4 Hz, CH(CH3)2). ESI-MS m/z 612 [M+], M =
C31H39N3SeBr.
Samples for FT-Raman spectroscopy were packed in capillary tubes
and flame-sealed. Data were collected using a Bruker RFS 100/S
spectrometer, with a resolution of 4 cm−1. FT-IR spectra were
collected on samples as KBr pellets using a Bruker Tensor 27
spectrometer, with a resolution of 4 cm−1. Decomposition points were
recorded in flame-sealed capillary tubes using a Gallenkamp variable
heater.
Synthesis of 27. A solution of 2 (0.100 g, 0.208 mmol in 3 mL of
THF) was added to a solution of TeBr4 (0.093 g, 0.208 mmol in 3 mL
of THF) and stirred for 4 h resulting in an orange solution. The
mixture was centrifuged and the solvent removed in vacuo from the
supernatant producing an orange powder. Yield: 0.109 g, 62%. Crystals
for X-ray diffraction studies were grown from vapor diffusion of n-
pentane into THF. Decomposition point: 171−173 °C. 1H NMR
3
(CDCl3, δ) 8.79 (d, 1H, 3J = 8.0 Hz, m-H pyridine), 8.46 (t, 1H, J =
Synthesis of 25. A solution of 1 (0.077 g, 0.170 mmol in 3 mL of
THF) was added to a freshly prepared solution of SeCl2 (0.341 mmol
in 6 mL of THF) and stirred for 5 min resulting in a red slurry.
Normal pentane (6 mL) was added resulting in the formation of more
solids. The supernatant was decanted, and the resulting solids were
washed with Et2O (3 × 5 mL). The red powder was dried in vacuo.
Yield: 0.110 g, 86%. Crystals suitable for X-ray diffraction studies were
grown by vapor diffusion of Et2O into a saturated CH3CN solution.
8.0 Hz, p-H pyridine), 8.25 (d, 1H, 3J = 7.6 Hz, m-H pyridine), 7.25−
7.17 (m, 6H, m, p-H C6H3), 4.57 (s, 2H, CH2), 2.97 (sept, 2H, 3J = 7.2
Hz, CH(CH3)2), 2.79 (sept, 2H, 3J = 7.2 Hz, CH(CH3)2), 2.37 (s, 3H,
CH3), 1.27 (overlapping doublets, 12H, CH(CH3)2), 1.13 (over-
lapping doublets, 12H, CH(CH3)2). 13C{1H} NMR (CDCl3, δ) 160.8,
146.2, 142.5, 141.4, 133.8, 133.6, 132.1, 131.6, 129.6, 127.2, 125.1,
28.4, 26.5, 23.4. 125Te{1H} NMR (CD2Cl2, δ) 1290.
1
Decomposition point: 180−182 °C. H NMR (CD3CN, δ) 9.78 (s,
Synthesis of 28. A solution of 2 (0.164 g, 0.342 mmol in 4 mL
THF) was added to a freshly prepared solution of SeCl2 (0.341 mmol
in 4 mL of THF) and stirred for 5 min generating a red solution.
Normal pentane (8 mL) was added to the mixture resulting in a red
precipitate. The supernatant was removed, the solids were washed with
Et2O (5 × 5 mL), and the red solids were dried in vacuo. Yield: 0.129
2H, α-CH), 9.07 (br, 2H, m-H pyridine), 8.96 (br, 1H, p-H pyridine),
3
3
7.46 (t, 2H, J = 7.6 Hz, p-H C6H3), 7.37 (d, 4H, J = 7.6 Hz, m-H
C6H3), 2.67 (br, 4H, CH(CH3)2), 1.19 (br, 24H, CH(CH3)2). ESI-MS
m/z 567 [M+]. HRMS found (calcd for C33H42N3Se1): [M+ − HCl]
560.2540 (560.2544).
1
Synthesis of 26. A solution of 1 (0.115 g, 0.253 mmol in 3 mL of
THF) was added to a freshly prepared solution of SeBr2 (0.507 mmol
in 6 mL of THF) and stirred for 5 min resulting in a deep red slurry.
Normal pentane (6 mL) was added resulting in the formation of more
solids. The supernatant was decanted and the red powder was dried in
vacuo. Yield: 0.196 g, 84%. Crystals suitable for X-ray diffraction
studies were grown by vapor diffusion of Et2O into a saturated
g, 58%. Decomposition point: 188−190 °C. H NMR (CDCl3, δ)
8.36−8.23 (m, 2H, m, p-H pyridine), 8.17 (s, 1H, CH), 8.02 (d, 1H, 3J
= 7.2 Hz, m-H pyridine), 7.58−7.56 (m, 1H, p-H C6H3), 7.30−7.16
(m, 5H, m, p-H C6H3), 4.44 (s, 1H, NH), 3.11 (sept, 2H, 3J = 6.8 Hz,
3
CH(CH3)2), 2.69 (sept, 2H, J = 6.8 Hz, CH(CH3)2), 2.37 (s, 3H,
CH3), 1.22 (d, 18H, 3J = 6.8 Hz, CH(CH3)2), 1.14 (d, 6H, 3J = 6.8 Hz,
CH(CH3)2).
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Scheme 1. Reaction of Selenium Dihalides with 1 To Produce 25 and 26
Scheme 2. Reactions of TeBr4 and SeCl2 with 2
Synthesis of 29. A solution of 3 (0.150 g, 0.247 mmol in 4 mL of
CH2Cl2) immediately generating a yellow solution. The solution was
stirred for 5 min, n-pentane added (9 mL) and the reaction vessel
stored at −35 °C overnight resulting in the formation of a large crop of
yellow crystals. The supernatant was decanted, and the crystals were
dried in vacuo. Yield: 95%, 0.166 g. Crystals suitable for X-ray
diffraction studies were grown by vapor diffusion of n-pentane into a
(d, 12H, 3J = 6.8 Hz, CH(CH3)2). HRMS found (calcd for
C43H47N3Se1): [M+ − HCl] 585.2905 (585.2935).
RESULTS AND DISCUSSION
Synthesis. The 1:1 stoichiometric reaction of a selenium
dihalide with the hydrogen substituted ligand (1) in THF
■
1
solution of 29 in chloroform. Decomposition point: 124−127 °C. H
3
Scheme 3. Reactions of SCl2 and SeCl2 with 3
NMR (CD3CN, δ) 9.47 (d, 2H, J = 8.4 Hz, m-H pyridine), 9.30 (t,
1H, 3J = 8.4 Hz, p-H pyridine), 7.83−7.81 (m, 2H, p-H C6H5), 7.72−
7.68 (m, 8H, o, m-H C6H5), 7.60 (t, 2H, 3J = 7.8 Hz, p-C6H3), 7.41 (d,
4H, 3J = 7.8 Hz, m-H C6H5), 2.87 (sept, 4H, 3J = 6.6 Hz, CH(CH3)2),
3
3
1.14 (d, 12H, J = 7.2 Hz, CH(CH3)2), 0.81 (d, 12H, J = 6.6 Hz,
CH(CH3)2). 13C{1H} NMR (CDCl3, δ) 160.8, 146.2, 142.5, 141.4,
133.8, 133.6, 132.1, 131.6, 129.6, 127.2, 125.1, 28.4, 26.5, 23.4. HRMS
found (calcd for C43H47N3S1): [M+] 637.3484 (637.3475).
Synthesis of 30. A solution of 3 (0.075 g, 0.124 mmol in 2 mL of
THF) was added to a freshly prepared solution of SeCl2 (3.72 mmol in
6 mL of THF) and stirred 5 min generating a red solution. Normal
pentane (10 mL) was added to the solution precipitating orange
material. The mixture was stored at −35 °C for 30 min and
centrifuged. The supernatant was decanted, and the solids were
washed with Et2O (2 × 6 mL). The solids were dried in vacuo giving
an orange powder. Yield: 0.090 g, 66%. X-ray quality crystals of 30
were obtained by vapor diffusion of n-pentane into a saturated CH2Cl2
1
solution. Decomposition point: 174−177 °C. H NMR (CD3CN, δ)
3
8.97−8.89 (m, 3H, m, p-H pyridine), 7.71 (t, 2H, J = 7.2 Hz, p-H
3
C6H5), 7.63−7.59 (m, 4H, m-H C6H5), 7.49 (d, 4H, J = 7.2 Hz, o-H
C6H5), 7.41 (t, 2H, 3J = 8.0 Hz, p-H C6H3), 7.28 (d, 4H, 3J = 8.0 Hz,
m-H C6H3), 2.72 (sept, 4H, 3J = 6.8 Hz, CH(CH3)2), 1.27 (d, 12H, 3J
= 6.8 Hz, CH(CH3)2), 0.96 (d, 12H, 3J = 6.4 Hz, CH(CH3)2). ESI-MS
m/z 685 [M+ − Cl], M = C43H47N3SeCl.
Synthesis of 31. A solution of 3 (0.075 g, 0.124 mmol in 2 mL of
THF) was added to a freshly prepared solution of SeBr2 (3.72 mmol in
6 mL of THF) and stirred 5 min resulting in a dark red solution. A red
precipitate was generated after adding n-pentane (10 mL) to the
mixture. The supernatant was removed, and the remaining solids were
washed with Et2O (2 × 6 mL). Yield: 68%, 0.125 g. Decomposition
point: 182−184 °C. 1H NMR (CD3CN, δ) 9.09−9.03 (m, 3H, m, p-H
pyridine), 7.73 (t, 2H, 3J = 7.2 Hz, p-H C6H5), 7.65−7.61 (m, 4H, m-
Figure 3. Solid-state structure of the cation in 25. Ellipsoids are drawn
to 50% probability; hydrogen atoms, anion, solvates, and isopropyl
groups are omitted for clarity.
immediately gives orange (X = Cl; 25) or red (X = Br; 26)
slurries. The products were precipitated from solution by the
addition of n-pentane to yield fine orange and red powders,
respectively. The supernatant was decanted, and the solids were
dried in vacuo. Redissolving a sample of the powders in CD3CN
3
3
H C6H5), 7.54 (d, 4H, J = 8.0 Hz, o-H C6H5), 7.45 (t, 2H, J = 8.0
Hz, p-H C6H3), 7.31 (d, 4H, 3J = 8.0 Hz, m-H C6H3), 2.73 (sept, 4H,
3J = 6.8 Hz, CH(CH3)2), 1.24 (d, 12H, 3J = 6.8 Hz, CH(CH3)2), 0.94
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displace a halide.26 The rationalization is that having the
additional donor on the DIMPY ligand requires a halide to
vacate a coordination site to form the preferential square planar
bonding arrangement about selenium.
Stirring a CH2Cl2 solution of 1 with solution of SCl2 in
1
CH2Cl2 resulted in no reaction as indicated by H NMR
spectroscopy. Reactions of the same ligand with the chalcogen
tetrahalides SeCl4, SeBr4, TeBr4, TeCl4 resulted in complex
mixtures, which were not further investigated. It has been
established in related work that the chalcogen halides are
susceptible to releasing X2 in the presence of strong Lewis
bases, subsequently degrading what is present in solution,
which includes the ligand.38−40
The reactions of the chalcogen halides with the methyl-
substituted ligand (2) were also examined. Literature precedent
indicated that TeCl4 reacts with 2 in THF to produce the
N,N′,C-bound complex (24) by reacting with the enamine
tautomer (2′) and ultimately eliminating HCl.8 Stirring TeBr4
with 2 in THF produced an orange solution with an orange
suspension over 4 h (Scheme 2). Filtering the solids and
removing the solvent from the supernatant gave an orange
powder, which was washed with Et2O. Redissolving a sample of
Figure 4. Solid-state structure of the cation in 26. Ellipsoids are drawn
to 50% probability; hydrogen atoms, anion, solvates, and isopropyl
groups are omitted for clarity.
and obtaining a 1H NMR spectrum revealed highly pure
products with a symmetric ligand framework; virtually identical
spectra were obtained for both the SeCl2 and SeBr2 reactions.
Downfield shifts were observed for the two protons on the α-
carbon atoms with respect to the free ligand but upfield in
comparison to the known dicationic complex (X = Cl, 25, δH =
9.78 ppm; X = Br, 26, δH = 9.74 ppm cf. 10.35 ppm).31,33
Crystals suitable for X-ray diffraction studies were grown by
vapor diffusion of Et2O into saturated CH3CN solutions and
revealed a [SeX]+ monocation sequestered by ligand 1 paired
with a [SeX3]− anion (dimerizes in the solid state to give
[Se2X6]2‑, Scheme 1). This was consistent with a 2:1
stoichiometric reaction between the selenium dihalde and
ligand.
1
the powder in CDCl3 and obtaining an H NMR spectrum
revealed a single product with a break in symmetry of the ligand
framework with two separate isopropyl resonances. It was also
apparent that one methyl group on the α-carbon was absent
indicating that the N,N,C-bound TeBr3 unit, analogous to the
TeCl3 complex observed by Cowley et al., was likely the
isolated product.28 A signal at δH = 4.57 ppm integrating to 2
was consistent with a methylene resonance, and a peak at δH =
2.37 ppm integrating to 3 accounts for the methyl group, both
of which are shifted downfield with respect to the free ligand (δ
= 2.28 ppm).37 The FT-IR spectrum lacked an N−H stretch,
consistent with the formation of an exocyclic imine. Crystals for
X-ray diffraction studies were grown from vapor diffusion of n-
pentane into THF confirming the identity of 27, the DIMPY
analogue of the TeBr3 DAB complexes 11 and 13 (Figure 2).
The reaction of SeCl2 with 2 in THF produced a dark red
solution. Normal pentane was added to precipitate the product,
and the solids were washed with Et2O. A red powder was
Upon removing the solvent in vacuo from the reaction
supernatant, the mass of the solids obtained corresponded to
half of the ligand used. Redissolving the powder in CDCl3 and
1
obtaining a H NMR spectrum indicated only the presence of
unreacted ligand. Given the 1:1 stoichiometric reaction only
resulted in ∼45% yield and a ratio of one ligand to two SeX2
moieties incorporated in the product, the stoichiometry of SeX2
was increased to two, where the yields then improved to over
85%. This demonstrates that regardless of the stiochiometry
only 25 and 26 were produced. This reactivity was different
from the SeX2 DAB complexes (7; Figure 2), which do not
1
obtained after drying in vacuo. The H NMR spectrum of the
redissolved solids in CDCl3 displayed a break in symmetry once
again, in addition to a reduction of the integration of the methyl
group to 3, consistent with binding of the ligand through one of
Table 1. Selected Bond Lengths (Å) and Angles (deg) for the N,N′,N″-DIMPY Complexes 25, 26, 29, 30 and the Previously
Reported Complexes 20−22
25
26
29
30
2031
2131
2231
Bond Lengths
Ch(1)−N(1)
Ch(1)−N(3/1A )
Ch(1)−N(2)
2.209(4)
2.056(4)
1.932(4)
1.276(6)
1.298(6)
2.6499(14)
2.087(9)
2.138(9)
1.932(9)
1.276(15)
1.290(15)
2.845(2)
1.883(4)
1.923(4)
1.727(4)
1.295(6)
1.279(5)
2.077(4)
2.103(4)
1.946(5)
1.275(7)
1.286(7)
2.6948(18)
1.9068(17)
1.9068(17)
1.719(3)
2.025(2)
2.025(2)
1.872(3)
1.275(3)
1.275(3)
2.243(4)
2.241(4)
2.098(3)
1.284(6)
1.284(7)
a
a
a
a
a
C(1)−N(1/1A )
1.280(3)
a
a
a
C(7/1A )−N(3/1A )
Ch(1)−X(1)
1.280(3)
Bond Angles
82.37(18)
N(1)−Ch(1)−N(2)
76.00(16)
78.56(15)
111.23(11)
94.17(11)
78.0(4)
76.8(4)
92.4(3)
109.7(3)
78.03(19)
76.85(18)
97.93(14)
106.94(14)
82.39(6)
78.79(6)
78.79(6)
72.77(15)
73.35(16)
a
a
a
N(2)−Ch(1)−N(3/1A )
N(1)−Ch(1)−X(1)
82.68(17)
82.39(6)
a
N(3/1A )−Ch(1)−X(1)
a
The dications in 20 and 21 lie on a site of symmetry with N(1) and N(3) being symmetry related.
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Table 2. X-ray Details for 25, 26, 27, 29, and 30
25
26
27
29
30
empirical formula
fw (g/mol)
cryst syst
space group
a (Å)
C37H45F6Cl4N6Se2
873.51
C37H39F6Br4N3Se2
1045.30
monoclinic
P21/c
C37H42Br3N3OTe
912.07
C45H49Cl8N3S
947.53
C86H94Cl6N6Se3
1661.25
monoclinic
P21/c
monoclinic
P21/c
monoclinic
P21/c
triclinic
P1
̅
11.413(2)
14.310(3)
26.554(7)
90
11.950(2)
14.476(3)
26.043(8)
90
10.592(2)
14.103(3)
26.737(7)
90
12.5843(19)
13.324(2)
16.054(2)
71.556(3)
72.774(3)
80.973(4)
2433.1(6)
2
12.7211
20.3795
17.9128
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
101.87(3)
90
103.39(3)
90
104.43(3)
90
95.894
90
4225.6(16)
4
4382.7(18)
4
3867.9(15)
4
4619.3(8)
2
Z
Dc (mg m−3
)
1.373
1.584
1.566
1.293
1.194
radiation, λ (Å)
0.710 73
150(2)
0.0604
0.710 73
150(2)
0.710 73
150(2)
0.0438
0.710 73
150(2)
0.710 73
150(2)
0.0652
0.1768
0.949
temp (K)
a
R1 [I > 2σI]
0.0924
0.0775
a
wR2 (F2)
0.1822
0.2812
0.1337
0.2031
a
GOF (S)
0.965
1.227
1.055
1.045
a
R1(F[I > 2(I)]) = ∑∥|Fo| − |Fc |∥/ ∑ |Fo|; wR2(F2 [all data]) = [w(Fo2 − Fc2)2]1/2; S(all data) = [w(Fo2 − Fc2)2/(n − p)]1/2 (n = no. of data; p =
no. of parameters varied; w = 1/[2(Fo ) + (aP)2 + bP] where P = (Fo + 2Fc2)/3 and a and b are constants suggested by the refinement program.
2
2
Figure 5. Solid-state structure of 27. Ellipsoids are drawn to 50%
probability; hydrogen atoms, solvate, and isopropyl groups are omitted
for clarity. Selected bond lengths (Å) and angles (deg): Te(1)−C(1)
2.133(4), Te(1)−N(2) 2.359(3), Te(1)−Br(2) 2.6323(7), Te(1)−
Figure 6. Solid-state structure of 29. Ellipsoids are drawn to 50%
probability; hydrogen atoms, solvate, and isopropyl groups are omitted
for clarity.
Br(3) 2.6562(8), Te(1)−Br(4) 2.6774(7), Te(1)−N(3) 2.793(3),
N(3)−C(8) 1.269(5), N(1)−C(2) 1.268(5), C(2)−C(1) 1.507(6).
C1−Te1−N2 77.84(14), C(1)−Te(1)−Br(2) 86.40(12), N(2)−
Te(1)−Br(2) 164.07(8), C(1)−Te(1)−Br(3) 84.59(14), N(2)−
In examing the reactivity of the other chalcogen halides with
Te(1)−Br(3) 83.56(9), Br(2)−Te(1)−Br(3) 97.42(2), C(1)−Te-
2, reactions with SeCl4, SeBr4, SeBr2, and SCl2 all produced
(1)−Br(4) 85.25(14), N(2)−Te(1)−Br(4) 82.36(9), Br(2)−Te(1)−
complex mixtures, likely resulting from the release of X2 giving
uncontrollable side reactions.
Br(4) 94.12(2), Br(3)−Te(1)−Br(4) 164.10(2).
In order to examine the effect of an aryl group at the α-
carbon, the reaction of SCl2 with 3 in CH2Cl2 was carried out,
resulting in the generation of an orange solution (Scheme 3).
Adding n-pentane to the solution and storing the reaction vial
at −35 °C produced a large crop of yellow crystals. Obtaining a
1H NMR spectrum of the dried crystals redissolved in CDCl3
displayed a single symmetric product. The protons on the 3 and
5 positions on the pyridine group were shifted downfield with
respect to free ligand (δH = 9.43 cf. δH = 7.53 ppm).2 Obtaining
a solid-state structure from crystals grown by vapor diffusion of
n-pentane into chloroform revealed a N,N′,N″-bound sulfur(II)
dication with two chloride counteranions (29), reminiscent of
the reaction of 1 with “S(OTf)2” (20; Figure 2).31 This was
surprising as the aryl substituted DAB ligands did not react at
all with SCl2 in the absence of TMSOTf, confirming the higher
the methyl carbon atoms. A new peak with respect to the free
ligand was observed at 8.16 ppm consistent with a single C−H
integrating to 1 rather than the CH2 group observed for 27.
Obtaining an FT-IR spectrum of the powder displayed a
diagnostic N−H stretch (broad peak at 3425 cm−1) supporting
the presence of an exocyclic amino group corresponding to the
1
singlet integrating to 1 at 4.44 ppm in the H NMR spectrum.
Although crystals of suitable quality for X-ray diffraction studies
could not be grown, the identity of the compound could be
assigned as the SeCl complex 28 bound to one of the carbon
atoms of the ligand based on the data and analogy to the DAB
chemistry.25 As with the DAB chemistry, Te forms a complex
with an exocyclic imine (10−13; Figure 2) whereas Se
produces an exocyclic amine (16−19).
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Inorganic Chemistry
Article
the cations are long [X = Cl, 2.6498(14) Å; X = Br, 2.845(2)
Å], which is attributed to the strong donation of the pyridine
nitrogen trans to the halide. The imine within the ligand
framework is retained [C−N = 1.276(6)−1.298(6) Å].
Upon examination of the solid-state structure of 2TeBr, the
tellurium center is best described as a distorted octahedron with
a stereochemically inactive lone pair (Figure 5). The electronic
configuration is viewed as AX6 with a distant nitrogen contact.
The Te−Br bond lengths are similar to the CH3DAB reaction
products [range 2.6323(7)−2.6774(7) Å, cf. 2.634(1)−
2.680(1) Å]. The N−Te bond distance for the pyridine
nitrogen is markedly shorter than that of the imine [2.359(3) Å,
cf. 2.793(3) Å] which retains its N−C double bond [1.268(5)
Å], and the exocyclic carbon−nitrogen bond is also character-
istic of an imine moiety [1.269(5) Å]. The carbon−tellurium
bond of 2.133(4) Å is consistent with a typical Te−C single
bond.28
Figure 7. Solid-state structure of 30. Ellipsoids are drawn to 50%
probability; hydrogen atoms, solvate, and isopropyl groups are omitted
for clarity.
The structure of the dicationic center in 29 is isostructural to
20 (Figure 2) as both are T-shaped consistent with an AX3E2
electron pair configuration (Figure 6). The S−N bond lengths
are almost identical [av S−Nimine 1.903 Å, cf. 1.9068(17) Å; S−
Npyridine 1.727(4) Å, cf. 1.719(3) Å].31 There are no detectable
S···Cl contacts between the cation and chloride anions within
the sum of the van der Waals radii (3.25 Å) indicative of a
dicationic species.41 On the basis of the similarities between 29
and 20, it is reasonable to believe a complex with 1 and SCl2
should be stable, but the observations indicate that 3 is more
reactive than 1 toward SCl2.
reactivity of DIMPY ligands in comparison to their DAB
counterparts.29,30
The 1:2 stoichiometric reactions of 3 with SeX2 in THF
produced brown (X = Br) and red (X = Cl) solutions. Adding
n-pentane to the mixture resulted in the precipitation of orange
(X = Cl; 30) and brown (X = Br; 31) powders. Redissolving a
1
sample of the powders in CDCl3 and obtaining a H NMR
spectrum revealed a new product; the most diagnostic features
were the downfield shifts of the pyridine protons. X-ray quality
crystals of 30 were obtained by vapor diffusion of n-pentane
into a saturated CH2Cl2 solution indicating the identity as two
The solid-state structure of 30 reveals a SeCl+ monocation as
observed in 25, and the bond lengths within the cation are
similar (Figure 7). The main difference in 30 lies with the
2‑
SeCl+ monocations paired with with a SeCl4 dianion. A
2‑
counteranion which is a SeCl4 dianion, a rare counteranion
with only two other solid-state structures reported in the
virtually identical proton NMR spectrum was obtained from
the SeBr2 reaction, supporting that the reaction product is the
analogous SeBr+ cation 31, although the exact nature of the
anion is not certain. Unfortunately, repeated attempts at
crystallization were unsuccessful, so a solid-state structure was
not obtained.
Further evidence that complexation of ligand 3 has occurred
are sharp resonances in the proton NMR spectra. The free
ligand undergoes restricted rotation on the NMR time scale
due to the presence of the bulky phenyl groups that results in
severe broadening of all signals except at elevated temperatures
(115 °C in DMSO-d6).2 However, the complexes formed with
SeX2 and SCl2 do not display hindered dynamics at ambient
temperature on the NMR time scale. This phenomenon has
also been observed in other complexes with phenyl substituted
DIMPY ligands.2−4 The corresponding reactions of SeCl4,
SeBr4, TeCl4, and TeBr4 all resulted in complex mixtures or
decomposition likely due to the concomitant release of
dihalogen.
CSD.42,43
CONCLUSION
■
By the reactions of chalcogen halides with diiminopyridine
ligands featuring H, Ph, or CH3 substitution on the α-carbon,
new sulfur, selenium, and tellurium complexes were isolated.
The methyl DIMPY derivative (2) reacted through a methyl
group to give N,N′,C-bound complexes with an exocyclic imine
(Ch = Te) or an exocyclic amine moiety (Ch = Se). The
reaction is believed to go through the enamine tautomer and
expel hydrohalide in the process similar to the related DAB
chemistry. The hydrogen DIMPY ligand (1) reacted with the
selenium dihalides in a 1:2 stoichiometry to afford the N,N′,N″-
chelated SeX+ monocationic complexes differing from the
neutral DAB SeX2 complexes. The phenyl substituted DIMPY
(3) proved to be more reactive than the H substituted
derivative to produce a dicationic sulfur complex with two
chloride counteranions. In the case of selenium, a four
2‑
X-ray Crystallography. The solid-state structures of 25
and 26 both revealed a selenium halide monocation
sequestered in the DIMPY chelate (Figures 3 and 4; see
Table 1 for selected bond lengths and angles and Table 2 for X-
ray details). The cationic selenium center is in a distorted
square planar geometry consistent with an AX4E2 electron pair
configuration. The Se−N bond lengths are slightly longer than
the dicationic analogues which can be accounted for by the
lesser degree of attraction from the ligand to the monocationic
center as well as the presence of the halide trans to the pyridine
coordinate monocationic complex with a SeX4 anion was
isolated. Selenium binds weakly to a halide in contrast to sulfur
as it can accommodate higher coordination numbers making a
square planar geometry. In many cases with chalcogen halide
starting materials in the +4 oxidation state undesireable
halogenation occurred.
ASSOCIATED CONTENT
■
S
* Supporting Information
2‑
−
nitrogen. The anion is a Se2X6 dianion (SeX3 dimer) shared
over two asymmetric units. The selenium halide bonds within
1H NMR spectra as well as FT-IR and FT-Raman data for all of
the reported compounds. Crystallographic information in CIF
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Inorganic Chemistry
Article
(23) Dutton, J. L.; Tuononen, H. M.; Jennings, M. C.; Ragogna, P. J.
J. Am. Chem. Soc. 2006, 128, 12624−12625.
format. This material is available free of charge via the Internet
at http://pubs.acs.org.
(24) Dutton, J. L.; Sutrisno, A.; Schurko, R. W.; Ragogna, P. J. Dalton
Trans. 2008, 3470−3477.
AUTHOR INFORMATION
■
(25) Dutton, J. L.; Martin, C. D.; Sgro, M. J.; Jones, N. D.; Ragogna,
P. J. Inorg. Chem. 2009, 48, 3239−3247.
Corresponding Author
(26) Dutton, J. L.; Farrar, G. J.; Sgro, M. J.; Battista, T. L.; Ragogna,
P. J. Chem.Eur. J. 2009, 15, 10263−10271.
*E-mail: pragogna@uwo.ca. Phone: 1-519-661-2111 ext 87048.
Fax: 1-519-661-3022
(27) Dutton, J. L.; Battista, T. L.; Sgro, M. J.; Ragogna, P. J. Chem.
Commun. 2010, 46, 1041−1043.
ACKNOWLEDGMENTS
(28) Reeske, G.; Cowley, A. H. Chem. Commun. 2006, 4856−4858.
(29) Martin, C. D.; Ragogna, P. J. Inorg. Chem. 2010, 49, 4324−4330.
(30) Martin, C. D.; Jennings, M. C.; Ferguson, M. J.; Ragogna, P. J.
Angew. Chem., Int. Ed. 2009, 48, 2210−2213.
■
The authors are very grateful to the Natural Sciences and
Engineering Research Council of Canada (NSERC), the
Canada Foundation for Innovation, Ontario Ministry of
Research and Innovation, and The University of Western
Ontario for generous financial support. We acknowledge P.
Break for inspiration.
(31) Martin, C. D.; Le, C. M.; Ragogna, P. J. J. Am. Chem. Soc. 2009,
131, 15126−15127.
(32) Martin, C. D.; Ragogna, P. J. Dalton Trans. 20111197611980.
(33) Britovsek, G. J. P.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.;
Maddox, P. J.; Mastroianni, S.; McTavish, S. J.; Redshaw, C.; Solan, G.
A.; Strmberg, S.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1999,
121, 8728−8740.
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