Group 15 pnictenium cations supported by a conjugated bithiophene backbone

Article abstract of DOI:10.1021/ic201983n

Thiophene based polymers and oligomers have attracted considerable attention because they can be functionalized to alter the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which enables the design of tunable light emitting materials. One area, which has been less explored, is the incorporation of low coordinate, low oxidation state main group elements into these systems. We have currently developed a novel π-conjugated ligand containing two contiguous thiophene rings in which we have demonstrated its ability to support both pnictogen cations and their metal complexes.

Full text of DOI:10.1021/ic201983n

Article
pubs.acs.org/IC
Group 15 Pnictenium Cations Supported by a Conjugated
Bithiophene Backbone
Jacquelyn T. Price, Melanie Lui, Nathan D. Jones, and Paul J. Ragogna*
Department of Chemistry, The University of London Ontario, 1151 Richmond St., London, Ontario N6A 5B7, Canada
S
* Supporting Information
ABSTRACT: Thiophene based polymers and oligomers have
attracted considerable attention because they can be
functionalized to alter the gap between the highest occupied
molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO), which enables the design of
tunable light emitting materials. One area, which has been less
explored, is the incorporation of low coordinate, low oxidation
state main group elements into these systems. We have
currently developed a novel π-conjugated ligand containing
two contiguous thiophene rings in which we have demon-
strated its ability to support both pnictogen cations and their
metal complexes.
INTRODUCTION
■
The current renaissance in p-block chemistry has borne witness
to some remarkable developments for main group elements,
with many of the breakthroughs centering on new structure,
bonding, and reactivity.1−7 An emerging tenet in this area of
research is to use these novel molecules and their unique
reactivity to bridge the gap into functional or applied chemical
processes. Excellent examples have surfaced in the past few
years including efforts in organic light-emitting devices
(OLEDs), catalysis, and small molecule activation.5−9 One of
the limitations to further expanding p-block chemistry into the
realm of the applied has been the challenge of developing novel
frameworks with which to support low coordinate and low
oxidation state main group element centers. New directions
could be realized by installing various functionalities onto these
supporting ligands and by taking advantage of the inherent
electronic influence as well as the chemical versatility of the
p-block elements. Combined, these can have a significant
impact on the resulting materials that are not always possible in
exclusively organic systems.7,10
Figure 1. Previously reported phosphenium cation with the triiodide
salt and the reported new pnictenium cations (1) reported in this
work.
and pnictenium cations were readily synthesized using
established dehydrohalogen coupling protocols between
diamine ligands and p-block halides in high yields, and a
platinum complex of both the phosphenium and arsenium
cation were prepared. These achievements represent a unique
opportunity to bring together the known and emerging
chemistry of low coordinate p-block cations, with the alluring
photophysical properties of thiophene based materials.
It has been well established that thiophene based materials
lend themselves to the design of tunable, light emitting
polymers and materials.11 Related efforts in this area by other
research groups have realized the synthesis of both a
polythiophene with orthogonal carbenes and a redox active
thiophene substituted diazabutadiene ligand for the construc-
tion of phosphenium cations.12−14 Although each development
is novel, a key drawback to the utility of these systems has been
the lack of a conjugated system between the thiophene rings
and the rest of the molecule. In this context, we have
undertaken an effort to model a wholly new ligand system
where two contiguous thiophene rings occupy the supporting
backbone (Figure1). The corresponding diaminochloropnictine
RESULTS AND DISCUSSION
■
Synthesis. Our entry into the new thiophene-based
systems (Scheme 1) rested on the known 2,2′-bithiophene-
3,3′-biscarboxaldehyde (1).15
Compound 2 was made by a condensation reaction between
a yellow ethanolic suspension of 1 with 2.1 stoichiometric
equivalents of p-anisidine. Upon addition of the amine, the
solution turned from yellow to black, and during the 4 h reflux
a yellow solid precipitated. The slurry was then cooled to room
Received: September 9, 2011
Published: November 17, 2011
© 2011 American Chemical Society
12810
dx.doi.org/10.1021/ic201983n|Inorg. Chem. 2011, 50, 12810−12817

Inorganic Chemistry
Article
a
diamine target (3) was carried out by the addition of
dimethylformamide (DMF) to solid NaCN and 2. The mixture
immediately became dark green, and was stirred at room
temperature for 2 days. The reaction mixture was diluted with
CH2Cl2 and washed with water. Removal of the volatiles and the
subsequent addition of MeOH caused precipitation of a bright
orange solid. A sample of the bulk material was redissolved for
1H NMR spectroscopy, which revealed the disappearance of the
aldimine proton and no significant change in the aryl groups,
indicating that the cyclization was likely successful. Single
crystals suitable for X-ray diffraction studies (Figure 2) were
grown from a solution of MeOH at room temperature
confirming the successful synthesis of 3, isolated in 86% yield.
A 3:1:1 stoichiometric reaction between N-methylmorpho-
line (NMM), PCl3, and 3 in tetrahydrofuran (THF) resulted in
an immediate color change from brown/orange to a bright
orange. The reaction was monitored by 31P{1H} NMR spectro-
scopy, which showed the reaction was complete after 4 days by
the disappearance of PCl3 (δp = 220 ppm), and the appearance
of a new peak (δp = 136 ppm) was tentatively assigned to the
chlorophosphine 4a. X-ray quality, orange crystals were grown
by CH2Cl2/pentane liquid diffusion at room temperature, and
subsequent X-ray diffraction analysis confirmed the production
Scheme 1. Synthesis of 3
a
(i) p-OMe-C6H4NH2, EtOH, reflux 4 h, 82%; (ii) NaCN, DMF, r.t.
48 h, 80%.
temperature, and the yellow solid was isolated by filtration. The
1H NMR spectrum of the redissolved yellow powder revealed
the disappearance of the aldehyde proton at δH = 9.85 ppm and
the appearance of a singlet at δH = 8.35 ppm consistent with an
imine, along with the protons corresponding to the p-MeOPh
group. Coupling of the diimine to form the corresponding
Figure 2. Solid-state structures of 3 to 6. Ellipsoids are drawn to 50% probability. Hydrogen atoms are removed except on the nitrogen atoms for
compound 3 for clarity. Compounds 3, 4a, and 5a, one of two formula units within the asymmetric unit is shown. Compounds 5−6, the triflate
anion has been removed for clarity. Compounds 6a and 6b, all but the ipso-C in the PPh3 has been removed for clarity.
12811
dx.doi.org/10.1021/ic201983n|Inorg. Chem. 2011, 50, 12810−12817

Inorganic Chemistry
Article
Scheme 2. Synthesis of 4a, 4b, and 4c, and the Subsequent Halide Abstraction Yielding 5a and 5b
Scheme 3. Synthesis of 5c
of the cyclic diaminochlorophosphine (4a), isolated in 83%
yield (Figure 2). The corresponding diaminochloroarsine, 4b
was synthesized using a similar procedure of a 3:1:1
stochiometric reaction between NMM, AsCl3, and 3 in THF,
and resulted in a slight color change from an orange to a red
solution. The reaction was complete after 4 days, denoted by the
proton shifts in the 1H NMR spectrum (Scheme 2). The
protons belonging to the thiophene ring shifted significantly
upfield 4b (δH = 7.04 and 6.20 ppm) compared to the proligand
3 (δH = 7.18 and 7.04 ppm). Whereas the resonances in the
phenyl rings were further split in compound 4b (δH = 7.48 and
6.98 ppm; Δδ = 0.50) compared to the free ligand, 3 (δH = 6.69
and 6.62 ppm; Δδ = 0.07). Another indication that the desired
chloroarsine was synthesized was the disappearance of the NH
Crystals suitable for X-ray diffraction studies were obtained by
vapor diffusion of pentane into a CH2Cl2 solution of 5a,
confirming the production of the title compound, which was
isolated in 90% yield (Figure 2). To convert 4b to the cor-
responding arsenium cation, 5b, one stoichiometric equivalent
of Me3SiOTf was added in CH2Cl2 (Scheme 2). The solution
remained red in color; however after 15 min of stirring an
orange solid began to precipitate from the reaction mixture. To
this mixture 5 mL of Et2O was added, and the supernatant was
decanted off leaving an orange solid, which was dried in vacuo.
The Fluorine-19 NMR spectrum revealed an ionic triflate, and
in the 1H NMR spectrum, both signals belonging to thiophene
and phenyl rings were shifted downfield by 0.1 ppm. Crystals
suitable for X-ray diffraction studies were obtained by vapor
diffusion of Et2O into CH2Cl2 solution of 5b, confirming the
synthesis of the desired product in 93% yield (Figure 2).
The corresponding stibenium cation could not be isolated,
1
peak in the H NMR spectrum (δH = 5.63). X-ray quality,
orange crystals were grown by CH2Cl2/pentane liquid diffusion
at room temperature, and subsequent X-ray analysis confirmed
the production of 4b isolated in 54% yield (Figure 2). The 3:1:1
stoichiometric reaction between NMM, SbCl3, and 3 resulted
in no reaction so the reaction mixture was heated to 50 °C
for 48 h, and 3 stoichiometric equivalents Et3N were added.
Upon completion of the reaction as detected by proton NMR
spectroscopy, X-ray quality, red crystals were grown from
CH2Cl2/Et2O liquid diffusion at room temperature confirming
the synthesis of the diaminochlorostibine (Figure 2).
1
and only decomposition products were observed by H NMR
spectroscopy when halide-abstracting agents TMS-OTf or
GaCl3 were added to a CH2Cl2 solution of the diamino-
chlorostibine; however, the stibenium cation could be trapped
using a Lewis base. To a CH2Cl2 solution of chlorostibine (4c),
2 stoichiometric equivalents of PMe3 and 1 stoichiometic
equivalent of Me3SiOTf were added (Scheme 3). A yellow solid
precipitated from the orange solution after 15 min of stirring,
and the orange solution was decanted off. The yellow solid was
isolated in 37% yield. Upon examination of the yellow solid by
31P NMR spectroscopy a peak at −1.2 ppm was observed along
with ionic triflate at δF = 78.7 indicating the target product was
likely synthesized. A doublet in the 1H NMR spectrum at 1.55 ppm
corresponding to the methyl groups on the PMe3 was also
observed providing further evidence that the desired product
was isolated. Single crystals were grown by vapor diffusion of
Et2O into a CH2Cl2 solution of the product, and single X-ray
quality crystals were obtained confirming the target compound
(Figure 2).
To convert 4a to the corresponding phosphenium cation,
(5a) two stoichiometric equivalents of trimethylsilyltrifluoro-
methanesulfonate (Me3SiOTf) were added to 4a in CH2Cl2.
The solution immediately turned from orange to red, and after
a few minutes a yellow solid precipitated from the reaction
mixture. The red liquid was decanted and the yellow powder
dried in vacuo. A phosphorus-31 NMR spectrum of the
redissolved yellow solid revealed a singlet at δP = 191 ppm and
ionic triflate was detected in 19F{1H} NMR spectrum (δF
=
−78.5 ppm cf. [Bu4N]OTf δF = −78.7 ppm);16 thus the solid
was assigned as the triflate salt of the phosphenium cation (5a).
12812
dx.doi.org/10.1021/ic201983n|Inorg. Chem. 2011, 50, 12810−12817

Inorganic Chemistry
Article
Scheme 4. Synthesis of Pnictogenium Metal Complexes
The ability to readily modify the pnictogenium framework is
important for the successful manipulation of the photophysical
and electronic properties of the thiophene system; metalation
strategies are often useful in this regard.17 This was probed by
the addition of a CH2Cl2 solution of Pt(PPh3)4 to a CH2Cl2
solution of 5a (both yellow), causing an immediate color change
to deep red. The reaction mixture was concentrated in vacuo to
a red oil. Diethylether was added to precipitate a bright orange
powder. A 31P{1H} spectrum of the redissolved solid revealed an
upfield doublet and a downfield triplet, each with corresponding
195Pt satellites, in an approximate 2:1 integration ratio that were
assigned to two PPh3 and one phosphenium ligand, respectively
(δP = 47 ppm, 1JPt−P = 2358 Hz, 2JPP = 490 Hz; δP = 249 ppm,
the solvent composition from acetonitrile to ether in about
10 vol % increments, there was no dramatic shift in the UV−vis
absorption; however, the absorption coefficient decreased as
a
Table 1. Optical Properties of Compounds 2−6
compound
λabs nm (εmax L mol−1 cm−1
)
λem (nm)
ϕFL
2
273 (3.5 × 104)
333 (3.3 × 104)
279 (2.7 × 104)
266 (3.1 × 104)
373 (7.1 × 103)
271 (3.1 × 104)
383 (1.3 × 103)
252 (4.8 × 105)
276 (4.6 × 105)
372 (8.0 × 104)
465 (4.0 × 104)
258 (2.5 × 104)
377 (8.2 × 103)
256 (5.6 × 104)
282 (2.9 × 104)
423 (3.9 × 103)
279 (6.6 × 104)
386 (1.2 × 104)
259 (5.9 × 104)
394 (1.3 × 104)
466 (9.5 × 103)
276 (3.2 × 104)
576 (2.7 × 104)
3
450
400
0.011
0.023
4a
4b
4c
2
1JPtP = 2326 Hz, JPP = 490 Hz). Single crystals were grown by
450
400
0.011
0.019
vapor diffusion of pentane into a CH2Cl2 solution of the
product, and subsequent X-ray diffraction studies revealed the
coordinatively unsaturated Pt(0) phosphenium complex (6a)
isolated in 77% yield (Figure 2). The reactivity of 5b was also
explored by the addition of 1 equiv of Pt(PPh3)4 in CH2Cl2
causing an immediate color change from red to dark purple
(Scheme 4). The reaction mixture was concentrated in vacuo to
give a purple oil, to which 3 mL of Et2O was added precipitating
a purple solid. A 31P{1H} NMR spectrum of the purple powder
displayed a single peak at δp = 41.8 ppm with 195Pt satilites
(1JPt−P = 3579.6 Hz) and the disappearence of the Pt precursor
at δp = 23.0 ppm. Upon examination of the 1H NMR spectrum,
again the protons on the thiophene backbone are very
diagnostic and have shifted upfield from δH = 6.28 in 5b, to
δH = 6.01 ppm in the metal complex 6b. Single crystals were
grown by vapor diffusion of Et2O into a CH2Cl2 solution of the
product, and X-ray diffraction studies revealed the Pt(0)
arsenium complex, 6b (Figure 2; 90%).
5a
5b
5c
6a
450
0.010
6b
a
Fluorescence quantum yields measured in CH2Cl2 solution using
9,10 diphenylanthracene (ϕFL = 0.90 in CH2Cl2) as a standard, excited
at 260 nm.18
Photophysical properties. The photophysical properties
of compounds 3−6b were examined by UV−vis and
fluorescence spectroscopy (Table 1). In comparison to the
ligand 3 (λabs = 279, λem = 450), upon the addition of the
pnictogen center, phosphorus (4a, λabs = 266, 373 nm), arsenic
(4b, λabs = 271, 373), and antimony (4c, λabs = 252, 276, 372,
465), the absorption was blue-shifted to shortened wavelengths
with antimony having an absorption maxima at the highest
energy. Absorption maxima for the pnictenium cations are
shifted to a higher energy as the charge is increased on the five
membered ring; phosphorus (5a, λabs = 258, 377), arsenic (5b,
λabs = 256, 282) however the base stabilized stibenium cation,
the λabs was shifted to a lower energy (5c, λabs =279, 386).
Although as one goes down group 15, both the maximum
absorption wavelength and the maximum absorption emission
wavelengths of these compounds were similar in dichloro-
methane solutions. This suggests that the substitution did not
cause significant changes in the conjugation of the molecular
structure, and the photophysical properties are dominated by
the bithiophene backbone. The solvatochromatic effects of the
pnictenium compounds were investigated, and upon changing
the vol % of ether increased. The quantum yields were
calculated against diphenylanthracene, which were low, ranging
from 0.01% to 0.02%.18
X-ray Crystallography. Compounds 3−6b have been
characterized by single X-ray diffraction studies. Views of the
solid state structures are shown in Figure 2, and refinement
details can be found in Table 2. Key bond lengths and angles
are summarized in Table 3.
An examination of the solid-state structures of compounds
3−6b revealed that the metrical parameters for the C2N2 ring
were all consistent with two C−N single bonds (1.388−1.415 Å
cf. 1.420 Å (ave.) in the free ligand) and a C−C double bond
(1.386−1.399 Å cf. 1.382 Å (ave.) in 3). The C−N bonds are
slightly shortened upon coordination to pnictogen, and the
C−C double bond in the backbone remained the same as in the
free ligand (3).
Compound 4a is isostructural with 4b and 4c, and all feature
long E(1)−Cl(1) bonds and are all pyramidal at the pnictogen
center. Upon examination of the pnictogen halogen linkage the
12813
dx.doi.org/10.1021/ic201983n|Inorg. Chem. 2011, 50, 12810−12817

Inorganic Chemistry
Article
bond length increases down the group from 2.2123(9) Å for
compound 4a, 2.3296(5) for 4b, and 2.5129(6) for 4c,
corresponding to the increase in size of the central element.
The pnictogen atom is pyramidal which is expected from a
three coordinate pnictogen center with a lone pair; however,
the Cl(1)−Pn(1)−N(1) angle decreases as one goes down the
group from 4a (Σang = 102.81(7)°), 4b (Σang = 100.85(5)) to
4c (Σang = 92.70(6)) because of the decrease in hybridization at
the pnictogen.
Upon examination compound 5a (5b is isostructural) the
thiophene−P(1) portion deviates from planarity only by 0.0348 Å.
The p-MeOPh rings are twisted out of the plane by 96.0(7)°
and are almost perpendicular to the plane of the bithiophene
backbone. In general, the metrical parameters of the
phosphenium cation (5a) are comparable to those reported for
other NHP systems. Upon formation of the arsenium cation
there is a contraction in the C−N bond from 1.405(2) Å for
compound 4b to C(11)−N(2) 1.369(6) Å and C(12)−N(1)
1.372(6) Å. This contraction was also observed in the P−N
bond, P(1)−N(1) 1.683(2) Å; P(1)−N(2) 1.6942(19) Å for
compound 4a and P(1)−N(1) 1.649(5) Å; P(1)−N(2)
1.655(5) Å for 5a. The structural changes that were observed
with the formation of the trimethyphosphine stabilized stibenium
cation 5c from 4c are summarized in Table 3. There is a slight
increase in the Sb−N bond lengths (Sb−N(1) = 2.057(2) Å,
Sb−N(2) = 2.053 Å), and is slightly longer than previously
reported examples of N-heterocyclic stibenium cations.19,20 The
Sb−P bond is elongated at 2.6171(11) Å and is outside the sum
of the covalen radii (cf. 2.50 Å)21 and is in line with other values
reported for P→Sb bonding modes.22,23 Figure 3 shows the
crystal structure and packing motifs of compound 5b forming an
extended network of zigzag chains. When viewed down the c-axis
the molecules are π-stacked in a head to tail cation conformation
orientated in a perpendicular fashion with the pnictogenium
center in one cation directed toward the centroid of the
bithiophene unit on an adjacent cation. They are packed in
four nonequivalent stacks that are nearly vertical to each other
(ca. 75.49°) because of the occurrence of As···π intermolecular
contacts with an interplanar distance of 6.18 Å. This packing
motif is most likely attributed to the existence of C−H···π and
As···π interactions and is not observed in any of the other
pnictogen complexes. These interactions are similar to those
reported between three coordinate As(III) centers and
arenes24−26 and other arsenium cations.27
The Pt complex 6a is trigonal planar at the metal (Σ ang
=
360.00°). The geometry at the phosphenium P-atom is almost
trigonal planar (Σang = 356.87°). The N(1)−P(1)−N(2) plane
of the phosphenium makes a torsion angle of 78.9(2)° with the
coordination plane of the metal likely because of the bulky
nature of the triphenylphosphine ligands. The Pt−NHP bond
P(1)−Pt(1) (2.1157(12) Å) is shorter than the Pt(1)−
P(2) (2.3315(13) Å) and Pt(1)−P(3) bonds (2.2935(12) Å)
suggesting strong backbonding from the Pt to the phosphe-
nium similar to that observed in related phosphenium→Pt
complexes (cf. 2.116(3) Å; 2.107(3) Å).28,29 Upon examination
of the solid state structure of 6a, it consists of a central Pt
center with two triphenylphosphine ligands. In contrast to 6a,
compound 6b is pyramidal at the pnictenium center and has a
coordination geometry (Σang = 307.24) consistent with a
nonbonding lone pair still present on the arsenium and can be
described as primarly M → L bonding.30 Progressing down
group 15 from P to As, the bonding changes from the filled sp2
hybrid orbital on phosphorus interacting with the empty
12814
dx.doi.org/10.1021/ic201983n|Inorg. Chem. 2011, 50, 12810−12817

Inorganic Chemistry
Article
Table 3. Selected Bond Lengths [Å] and Angles [deg] for Compounds 3−6
compound bond
3
4a
4b
4c
5a
5b
5c
6a
6b
N(1)−C(12)
N(2)−C(11)
C(11)−C(12)
Pn(1)−X(1)
N(1)−Pn(1)
N(2)−Pn(1)
Pn(1)−Pt(1)
N(1)−Pn(1)−N(2)
N(1)−Pn(1)−X(1)
N(2)−Pn(1)−X(1)
N(1)−Pn(1)−Pt(1)
N(2)−Pn(1)−Pt(1)
1.404(4)
1.434(4)
1.379(4)
N/A
1.413(3)
1.415(3)
1.399(3)
2.2123(9)
1.683(2)
1.6942(19)
N/A
1.405(2)
1.406(2)
1.395(2)
2.3296(5)
1.8224(13)
1.8255(13)
N/A
1.406(3)
1.396(3)
1.412(3)
2.5129(6)
2.0203(19)
2.0091(18)
N/A
1.396(8)
1.388(8)
1.396(7)
N/A
1.372(6)
1.369(6)
1.408(6)
N/A
1.417(4)
1.423(4)
1.391(4)
2.6171(11)
2.057(2)
2.053(3)
N/A
1.401(6)
1.395(5)
1.386(6)
N/A
1.394
1.388(7)
1.408(7)
N/A
N/A
1.649(5)
1.655(5)
N/A
1.790(4)
1.798(4)
N/A
1.660(4)
1.666(4)
2.1157(12)
90.90(18)
N/A
1.835(4)
1.825(5)
2.4462(7)
84.5(2)
N/A
N/A
N/A
N/A
89.79(10)
102.81(7)
100.40(7)
N/A
85.72(6)
100.85(5)
101.12(5)
N/A
79.67(7)
92.70(6)
95.81(6)
N/A
91.3(3)
N/A
85.89(17)
N/A
81.52(10)
89.17(8)
89.69(8)
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
134.49(14)
131.48(14)
107.78(14)
114.98(15)
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Figure 3. Crystal packing of 5b.
d-orbitals on Pt0, and metal backbonding to the empty p orbital
on phosphorus leading to a coplanar arrangement. However for
As, only the metal is donating into the empty p orbital on As
leading to a pyramidal geometry. This bonding is similar to the
heavy N-heterocyclic plumbylenes observed by Hahn. The
metal (Pt0 or Pd0) acts as a d-electron donor to the empty p
orbital on PbII, and the lone pair of electrons on Pb, located in
the sp2 hybrid orbital, do not participate in bonding to the
metal center. By going down group 14 in synthesizing the
heavier group 14 NHC metal complexes, the geometry at the
coordinating atom changes from coplanar to tetrahedral.31
Reagents were obtained from commercial sources. Phosphorus(III)
chloride was distilled prior to use while all other reagents were used
without purification. CDCl3 was dried over calcium hydride. Solvents
were dried and deoxygenated by using an MBraun controlled-
atmosphere solvent purification system and stored in Straus flasks
under N2 atmosphere or over 4 Å molecular sieves in the glovebox. All
NMR spectra were recorded on a Varian INOVA 400 MHz
spectrometer (1H = 399.76 MHz, 13C = 100.52 MHz, 19F = 376.15 MHz,
31P = 161.85 MHz). All 31P{1H} NMR spectra were recorded relative
to an external standard (85% H3PO4, δ 0.00). X-ray diffraction data
were collected on a Nonius Kappa-CCD area detector or Bruker
Kappa Apex II using Moκ radiation (λ = 0.71073 Å). Crystals were
selected under oil, mounted on glass fibers or scoops, and immediately
placed in a cold stream of N2. Structures were solved by direct
methods and refined using full matrix least-squares of F2. Hydrogen-
atom positions were calculated. UV−visible absorption spectra were
recorded over a range of 250−600 nm using a Varian Cary 300
spectrometer in CH2Cl2. Emission spectra were recorded on a
Fluorolog (QM-7/2005) instrument with a slit width of 0.5 nm in
CH2Cl2. High resolution mass spectrometry data were collected by
Mr. Doug Hairsine (UWO) using a Finnigan MAT 8400 instrument.
Synthesis of 2′,2-bithiophene,32 3,3′,5,5′-tetrabromo-2,2′-bithiophene,32
3,3′-dibromo-2,2′-bithiophene,32 and 2,2′-bithiophene-3,3′-biscarboxal-
dehyde15 were synthesized following literature procedures.
CONCLUSION
■
The successful synthesis of a new diamine ligand with a
conjugated fused bithiophene backbone was achieved and
subsequently converted to the diaminochloropnictine and
pnictenium cations. These complexes are the first examples of
pnictogens containing a conjugated bithiophene backbone and the
first example of a pnictogen containing a thiophene heterocycle
complexed to a transition metal. These new complexes did not
display any solvatochromic properties. Compounds 3, 4a, 4c, 5a,
and 5c did display fluorescence; however, the efficiencies were
low. This new ligand system opens the door to the preparation of
other p-block derivatives, which could have new electronic or
photophysical properties, and is a step toward narrowing the gap
between pure and applied chemistry.
Compound 2. A solution of 2,2′-bithiophene-3,3′-biscarboxalde-
hyde (1.50 g, 6.70 mmol) in EtOH (40 mL) was cooled to 0 °C and a
solution of p-anisidine (1.74 g, 14.1 mmol) in EtOH (10 mL) was
added dropwise. The reaction mixture was warmed to room
temperature and then heated to reflux for 4 h. The solvent was
concentrated, and the resulting yellow powder was collected by
filtration and washed with cold EtOH (3 × 5 mL). Yield: 86% (2.50 g,
EXPERIMENTAL SECTION
All manipulations were performed under N2 atmosphere using
standard Schlenk or glovebox techniques unless stated otherwise.
■
1
5.78 mmol); mp 148−149 °C (dec). H NMR (CDCl3): δ 8.38 (s,
2H, CH), 7.81 (d, 2H, aryl, 3JHH = 5.2), 7.45 (d, 2H, aryl, 3JHH = 5.2),
12815
dx.doi.org/10.1021/ic201983n|Inorg. Chem. 2011, 50, 12810−12817

Inorganic Chemistry
Article
3
3
7.08 (d, 4H, aryl, JHH = 8.8), 6.83 (d, 4H, aryl, JHH = 9.2), 3.78 (s,
6H, CH3). 13C{1H} NMR (CDCl3): δ 55.4, 114.3, 122.1, 127.0, 127.3,
136.2, 139.1, 144.6, 151.7, 158.4. FT-IR (relative intensities) ν =
533(14), 630(9), 715(11), 728(13), 781(7), 826(4), 1034(2),
1105(12), 1207(6), 1251(1), 1293(10), 1458(8), 1500(3), 1611(5),
2360(15) cm−1. FT- Raman (relative intensities) ν = 160(3), 679(12),
788(15), 968(13), 1166(7), 1209(4), 1247(14), 1295(11), 1355(8),
1392(9), 1462(5), 1501(6), 1592(1), 1624(2), 3101(15). HRMS:
C24H20N2O2S2 calcd (found) 432.0966 (432.0955).
3.88 (s, 6H, CH3). 13C{1H} NMR (CDCl3): 45.7, 55.5, 110.7, 114.7,
122.5, 128.0, 134.6, 136.5, 158.2. FT-IR (relative intensities) ν =
638(10), 704(8), 722(4), 814(11), 909(5), 942(14), 1030(6),
1102(12), 1178(8), 1241(2), 1274(7), 1349(3), 1450(9), 1503(1),
1601(15). FT- Raman (relative intensities) ν = 96.7(5), 173(11),
195(13), 227(4), 245(1), 676(8), 784(10), 1098(12), 1224(3),
1270(6), 1307(9), 1348(2), 1388(14), 1449(15), 1496(7).
Compound 5a. To a solution of 3 (0.10 g, 0.20 mmol) in CH2Cl2
(4 mL) the halide-abstracting agent Me3SiOTf (0.04 mL, 0.22 mmol)
was added dropwise. The solution was stirred for 10 min at room
temperature during which time a yellow solid precipitated from the
solution. The red solution was decanted off, and the remaining yellow
solid was dried in vacuo. The product was washed with Et2O (2 × 3
mL) and dried. Yield: 90% (0.11 g, 0.18 mmol); mp >300 (dec) °C.
Compound 3. A DMF (5 mL) solution of 2 (2.50 g, 5.78 mmol)
and sodium cyanide (0.28 g, 5.78 mmol) stirred at room temperature
for 48 h. To the reaction mixture 10 mL of CH2Cl2 was added and
washed with water (3 × 50 mL). The CH2Cl2 layer was then dried
with MgSO4 and concentrated. The product was then precipitated
with MeOH and isolated by filtration. The resulting orange powder
was washed with MeOH (3 × 5 mL). Yield: 80% (2.05 g, 4.62 mmol);
mp 173−175 °C (dec). 1H NMR (CD3CN): δ 7.39 (d, 2H, aryl,
3
1H NMR (CDCl3): δ 7.84 (d, 4H, aryl, JHH = 8.4), 7.36 (d, 2H, aryl,
3
3
3JHH = 5.2), 7.20 (d, 4H, aryl, JHH = 8.8), 6.41 (d, 2H, aryl, JHH
=
5.2), 3.97 (s, 6H, CH3). 13C{1H} NMR (pyridine-d5): δ54.3, 114.5
119.5 123.8, 125.2, 127.6, 127.8 128.2, 128.3 129.7, 159.4. 31P{1H}
NMR (CDCl3): 191.00. 19F {1H} NMR (CDCl3):δ −78.5. FT-IR
(relative intensities) ν = 527(13), 635(5), 649(11), 724(12), 740(9),
824(8), 1030(2), 1159(3), 1174(6), 1221(7), 1257(1), 1307(10),
1325(15), 1509(3), 1608(14) cm−1. FT-Raman (relative intensities)
ν = 633(9), 709(10), 736(12), 794(13), 1029(6), 1180(5), 1325(14),
1366(15), 1433(7), 1491(1), 1605(4), 1892(8), 2115(3), 2609(2),
3081(11) cm −1. HRMS: [C24H18N2O2PS2]+ calcd (found) 461.0547
(461.0538). Elemental Analysis (%) calc for C25H18F3N2O5PS3·
3J HH = 5.6), 7.10 (d, 2H, aryl, 3J HH = 5.6), 6.69 (d, 4H, aryl, 3J HH = 8.8),
3
6.62 (d, 4H, aryl, J
= 8.8), 6.28 (s, 2H, NH), 3.66 (s, 6H, CH3).
HH
13C{1H} NMR (CDCl3): δ 55.6, 114.6, 117.5, 123.5, 123.9, 128.84,
130.5, 134.5, 139.8, 153.7. FT-IR (relative intensities) ν = 653(9),
732(4), 806(6), 901(10), 1033(3), 1107(15), 1167(11), 1179(12),
1245(2), 1297(13), 1356(14), 1397(8), 1449(5), 1507(1), 3336(7)
cm−1. FT-Raman (relative intensities) ν = 1314(4), 1462(2), 1499(1),
1587(3), 2061(15), 2076(13), 2146(14), 2157(7), 2171(12),
2205(11), 2220(10), 2243(9), 2265(8), 2732(5), 3059(6). HRMS:
C24H22N2O2S2 432.0966 (432.0955).
C
0.25H0.5Cl0.5: C 48.00, H 2.95, N 4.43, S 15.23; found C 47.91, H
Compound 4a. A THF (5 mL) solution of 3 (0.30 g, 0.69 mmol)
and n-methylmorpholine (0.29 mL, 2.08 mmol) stirred for 10 min at
room temperature. PCl3 (0.06 mL, 0.69 mmol) was added to the
solution. The reaction then stirred for 4 days at room temperature.
The white precipitate was removed by centrifuge, and the resulting
orange solution was concentrated in vacuo yielding an orange solid.
3.03, N 4.43, S 15.39.
Compound 5b. To a solution of 4b (0.18 g, 0.33 mmol) in
CH2Cl2 (4 mL) the halide-abstracting agent Me3SiOTf (0.11 mL,
0.66 mmol) was added dropwise. The solution was stirred for 45 min
at room temperature during which time the solution turned red and a
dark yellow solid precipitated from the solution. The red solution was
decanted off, and the remaining yellow solid was dried in vacuo. The
product was washed with Et2O (2 × 3 mL) and dried. Yield: 93%
1
Yield: 83% (0.28 g, 0.57 mmol); mp 207−211 °C (dec). H NMR
(CDCl3): δ 7.62 (br. s, 4H, aryl), 7.16 (d, 2H, aryl, 3JHH = 6.0), 7.07 (d,
3
4H, aryl, 3JHH = 7.6), 6.28 (d, 2H, aryl, JHH = 5.2), 3.92 (s, 6H, CH3).
1
(0.20 g, 0.31 mmol); mp >300 (dec) °C. H NMR (CDCl3): δ 7.68
13C{1H} NMR (CDCl3): δ 55.5, 114.8, 120.9, 124.2, 125.2, 129.1,
129.4, 129.9, 130.0, 130.3, 159.9. 31P{1H} NMR (CDCl3): δ 136.53 FT-
IR (relative intensities) ν = 532(12), 724(2), 817(7), 918(10), 978(5),
1031(9), 1104(13), 1124(4), 1167(8), 1247(2), 1280(11), 1437(15),
1463(14), 1363(6), 1508(1) cm−1. FT-Raman (relative intensities) ν =
215(2), 384(3), 795(8), 1238(5), 1365(1), 1500(6), 2619(7), 3321(7)
cm−1. HRMS: [C22H18N2O2PS2]+ calcd (found) 461.0547 (461.0547).
Elemental Analysis (%) calc for C22H18N2O2PS2Cl: C 58.00, H 3.65, N
5.64; found C 57.86, H 3.70, N 5.44.
3
3
(d, 4H, aryl, JHH = 8.0), 7.27 (d, 2H, aryl, JHH = 8.0) δ 7.15 (d, 4H,
3
3
aryl, JHH = 8.4), 6.34 (d, 2H, aryl, JHH = 4.8), 3.94 (s, 6H, CH3).
13C{1H} NMR (CDCl3): δ55.7, 115.3, 116.3, 122.2, 124.9, 125.7,
128.9, 129.3, 135.1, 136.4, 161.4. 19F {1H} NMR (CDCl3):δ −78.2.
FT-IR (relative intensities) ν = 521 (8), 635 (4) 715 (10), 738 (7),
819 (5), 1029 (3), 1157 (5), 1173 (14), 1221 (15), 1256 (10), 1458
(13), 1508 (2), 1540 (11), 1606 (9), 3084 (12) cm−1. HRMS:
[C24H18N2O2AsS2]+ calcd (found) 505.0020 (505.0003). Elemental
Analysis (%) calc for C25H18AsClF3N2O5S3: C 45.88, H 2.77, N 4.28;
found C 45.72, H 2.49, N 4.12.
Compound 4b. A THF (40 mL) solution of 3 (1.0 g, 23 mmol)
and n-methylmorpholine (0.76 mL, 69 mmol) stirred for 10 min at
room temperature. AsCl3 (0.20 mL, 23 mmol) was added to the
solution. The reaction then stirred for 4 days at room temperature.
The white precipitate was removed by centrifuge, and the resulting red
solution was concentrated in vacuo yielding a red solid. Yield: 54%
(0.67 g, 12.4 mmol); mp 208.4−213.2 °C (dec). 1H NMR (CDCl3): δ
7.48(d, 4H, aryl, 3JHH = 8.8) 7.04 (d, 2H, aryl, 3JHH = 5.2), 6.98 (d, 4H,
Compound 5c. To an orange solution of 5c (0.1 g, 0.17 mmol) in
CH2Cl2 (3 mL) was added PMe3 (0.035 mL, 0.034 mmol) and
Me3SiOTf (0.031 mL, 0.17 mmol). The reaction mixture stirred at
room temperature for 1 h and was then concentrated. The CH2Cl2 was
decanted off leaving a yellow solid, which was washed (2 × 5 mL) with
pentane. Yield: 36% (0.135 g, 0.061 mmol); decomp. 223−225 (dec) °C.
1H NMR (CDCl3): δ 7.15 (m, 6H, aryl), 6.82 (d, 4H, aryl, JHH = 8.4),
3
3
3
3
aryl JHH = 8.8), 6.20 (d, 2H, aryl JHH = 5.6), 3.84 (s, 6H, CH3).
13C{1H} NMR (CDCl3): δ 55.5, 114.8, 121.5, 123.5, 126.0, 129.0,
129.8, 131.1, 132,2, 142,2, 159.6. FT-IR (relative intensities) ν =
485(15), 521(6), 642(5), 728(3), 812(10), 912(8), 945(12), 1028(4),
1116(13), 1244(1), 1277(11), 1363(7), 1455(14), 1505(2), 1602(9)
cm−1. HRMS: [C22H18N2O2As]+ calcd (found) 505.0026 (505.0029).
Elemental Analysis (%) calc for C22H18N2O2AsS2Cl: C 53.29, H 33.35,
N 5.18; found C 53.29, H 3.33, N 5.15.
6.68 (d, 2H, JHH = 5.4), 3.78 (s, 6H, CH3), 1.55 (d, 9H, CH3,
2JPH = 12) . 13C{1H} NMR (CD3CN): δ 9.5 (CP, 1JPC = 106.8), 55.1,
114.2, 123.0, 124.4, 125.6, 141.5, 137.8, 140.8, 156.4. 19F {1H} NMR
(CDCl3):δ −78.2. 31P{1H} NMR (CD3CN): δ −1.19. FT-IR (relative
intensities) ν = 510(6), 633(4), 704(14), 732(6), 810(13), 901(9),
956(8), 1024(3), 1109(12), 1161(7), 1237(1), 1291(5), 1386(10),
1453(15) cm−1. FT-Raman (relative intensities) v = 87(3), 194(10),
244(2), 674(12), 780(6), 1025(11), 1221(8), 1262(15), 1312(7),
Compound 4c. In a pressure tube a THF (30 mL) solution of 3
(1.0 g, 23 mmol) and NEt3 (0.96 mL, 0.0069 mmol) stirred for 10 min at
room temperature. A THF solution (5 mL) of SbCl3 (0.52 g, 0.0023 mmol)
was added to the solution. The reaction was then heated to 60 °C
for 48 h. The precipitate was removed by centrifuge, and the
resulting red solution was concentrated in vacuo yielding a red solid.
Yield: 95% (1.27 g, 21 mmol); decomp. 152 °C (dec). 1H NMR
1361(5), 1387(9), 1452(13), 1497(1), 1606(4), 2914(14) cm−1
.
Elemental Analysis (%) calc for C28H27F3N2O5PS3Sb·C0.5H1Cl1: C
41.75, H 3.44, N 3.42, S 11.73; found C41.48, H 3.61, N 3.47,
S 11.71.
Compound 6a. To a solution of 5a (0.015 g, 0.032 mmol) in
CH2Cl2 (2 mL) was added a CH2Cl2 (2 mL) solution of Pt(PPh3)4
(0.04 g, 0.032 mmol). The solution turned from yellow to red and was
stirred for 10 min at room temperature. The CH2Cl2 was removed in
vacuo, yielding a red oil. After triturating the red oil with Et2O (3 mL)
3
3
(CDCl3): δ 7.33 (d, 4H, aryl, JHH = 8.4), 7.03 (d, 2H, aryl, JHH
=
3
3
5.6), 6.96 (d, 4H, aryl, JHH = 8), 6.32 (d, 2H, aryl, JHH = 4.8),
12816
dx.doi.org/10.1021/ic201983n|Inorg. Chem. 2011, 50, 12810−12817

Inorganic Chemistry
Article
for 10 min an orange solid precipitated from solution. The Et2O was
decanted off and dried under reduced pressure. Yield: 77% (0.028 g,
(12) Powell, A. B.; Brown, J. R.; Vasudevan, K. V.; Cowley, A. H.
Dalton Trans. 2009, 2521−2527.
1
0.024 mmol); mp 146−148 °C (dec). H NMR (CDCl3): δ 7.29 (t,
(13) Powell, A. B.; Bielawski, C. W.; Cowley, A. H. J. Am. Chem. Soc.
2010, 132, 10184.
6H, aryl, 3JHH = 7.6), 7.21(d, 2H, 3JHH = 5.6), 7.10 (t, aryl, 12H, 3JHH
=
3
8), 6.91 (br. 15H, aryl), 6.82 (pseudo d, 2H, aryl, JHH = 8.8), 3.85
(s, 6H, CH3). 13C{1H} NMR (CDCl3): 55.8, 115.4, 120,6, 123.6,
125.9, 127.5, 127.6, 128.7, 128.8, 129.3, 130.9, 131.6, 133.4, 160.9.
(14) Powell, A. B.; Brown, J. R.; Vsudevan, K. V.; Cowley, A. H.
Dalton Trans. 2009, 2521−2527.
(15) Mitsumori, T.; Inoue, K.; Koga, I.; Iwamura, H. J. Am. Chem.
Soc. 1995, 117, 2467−2478.
1
31P{1H} NMR (CDCl3): 47.45 (2JPP = 490.8, JPPt = 2358), 249.5
1
(2JPP = 492.4, JPPt = 2326). 19F {1H} NMR (CDCl3): δ 78.41. FT-IR
(16) Boersma, A. D.; Goff, H. M. Inorg. Chem. 1982, 21, 581−586.
(17) Wolf, M. Adv. Mater. 2001, 13, 545−553.
(relative intensities) ν = 514(5), 528(2), 636(3), 693(3), 743(9),
922(11), 998(14), 1030(4), 1094(10), 1130(8), 1248(1), 1435(7),
1478(15), 1507(2), 1605(12) cm−1. FT- Raman (relative intensities)
ν = 174(6), 363(7), 999(3), 1027(12), 1096(14), 1131(2), 1236(3),
1375(1), 1494(11), 1321(15), 1585(5), 1887(8), 2112(13), 2560(10),
3057(9) cm−1.
(18) Zhang, X.; Chi, Z.; Yang, Z.; Chen, M.; Xu, B.; Zhou, L.; Wang,
C.; Zhang, Y.; Liu, S.; Xu, J. Opt. Mater. 2009, 32, 94−98.
(19) Spinney, H. A.; Korobkov, I.; DiLabio, G. A.; Yap, G. P. A.;
Richeson, D. S. Organometallics 2007, 26 (20), 4972−4982.
(20) Spinney, H. A.; Korobkov, I.; Richeson, D. S. Chem. Commun.
2007, No. 16, 1647−1649.
Compound 6b. To a solution of 5b (0.015 g, 0.032 mmol) in
CH2Cl2 (2 mL) was added a CH2Cl2 (2 mL) solution of Pt(PPh3)4
(0.04 g, 0.032 mmol). The solution turned from orange to purple and
was stirred for 10 min at room temperature. The CH2Cl2 was removed
in vacuo, yielding a purple oil. After triturating the purple oil with Et2O
(3 mL) for 10 min a purple solid precipitated from solution. The Et2O
was decanted off and dried under reduced pressure. Yield: 92% (0.035
(21) Blom, R.; Haaland, A. J. Mol. Struct. 1985, 128 (1−3), 21−27.
(22) Kilah, N. L.; Petrie, S.; Stranger, R.; Wielandt, J. W.; Willis, A.
C.; Wild, S. B. Organometallics 2007, 26 (25), 6106−6113.
(23) Wielandt, J. W.; Kilah, N. L.; Willis, A. C.; Wild, S. B. Chem.
Commun. 2006, No. 35, 3679−3680.
(24) Schmidbaur, H.; Bublak, W.; Huber, B.; Muller, G. Angew.
Chem., Int. Ed. 1987, 26, 234.
1
g, 0.029 mmol); decomp. 225(dec) °C. H NMR (CDCl3): 7.28 (m,
6H, aryl), 7.20 (m, 15H, aryl), 7.07 (m, 15H, aryl), 6.81 (d, 4H, aryl,
3JHH = 8.8), 5.97 (d, 2H, aryl, 3JHH = 5.6), 3.87 (s, 6H, CH3). 13C{1H}
NMR (CDCl3): δ 55.8, 114.5, 122.9, 123.9, 124.5, 128.5, 129.1, 131.3,
(25) Probst, T.; Steigelmann, O.; Riede, H.; Schmidbaur, H. Chem.
Ber. 1991, 124, 1089.
(26) Schmidbaur, H.; Nowak, R.; Steigelmann, O.; Muller, G. Chem.
Ber. 1990, 123, 1221.
(27) Spinney, H. A.; Korobkov, I.; DiLabio, G. A.; Yap, G. P. A.;
Richeson, D. Organometallics 2007, 26 (20), 4972−4982.
(28) Caputo, C. A.; Jennings, M. C.; Tuononen, H. M.; Jones, N. D.
Organometallics 2009, 28, 990−100.
1
134.6, 156.6. 31P{1H} NMR (CDCl3): 41.9 (t, JPPt = 5347.6). 19F
{1H} NMR (CDCl3):δ - 78.3. FT-IR (relative intensities) ν = 515(2),
538(10), 636(6), 695(4), 744(7), 1025(5), 1097(11), 1157(8),
1222(12), 1263(1), 1303(13), 1386(14), 1435(9), 1478(15), 1506(3).
ASSOCIATED CONTENT
(29) Hardman, N. J.; Abrams, M. B.; Pribisko, M. A.; Gilbert, T. M.;
Martin, R. L.; Kubas, G. J.; Baker, R. T. Angew. Chem., Int. Ed. 2004,
43, 1955−1958.
■
S
* Supporting Information
Spectroscopic data for compounds 3−6b. This material is
(30) Burck, S.; Daniels, J.; Gans-Elchler, T.; Gudat, D.; Nattinen, K.;
Nieger, M. ZAAC 2005, 631, 1403−1412.
available is free of charge via the Internet at http://pubs.acs.org.
(31) Heitmann, D.; Pape, T.; Hepp, A.; Muck-Lichtenfeld, C.;
̈
AUTHOR INFORMATION
Corresponding Author
*E-mail: pragogna@uwo.ca.
Grimme, S.; Hahn, F. E. J. Am. Chem. Soc. 2011, 133 (29), 11118−
■
11120.
(32) Letizia, J. A.; Salata, M. R.; Tribout, C. M.; Facchetti, A.; Ratner,
M. A.; Marks. J. Am. Chem. Soc. 2008, 130 (30), 9679−9694.
ACKNOWLEDGMENTS
■
We are grateful for the generous financial support of the
Natural Sciences and Engineering Research Council of Canada
(NSERC), The Canada Foundation for Innovation, and the
Ontario Ministry of Research and Innovation-Early Researcher
Award and UWO.
REFERENCES
■
(1) Chivers, T.; Konu, J. Comments Inorg. Chem. 2009, 30, 131−176.
(2) Prabusankar, G.; Gemel, C.; Parameswaran, P.; Flener, C.;
Frenking, G.; Fisher, R. A. Angew. Chem., Int. Ed. 2009, 48, 5526−
5529.
(3) Power, P. P. Chem. Rev. 1999, 99 (12), 3463−3503.
(4) Fisher, R. C.; Power, P. P. Chem. Rev. 2010, 110, 3877−3923.
(5) Holthausen, M. H.; Weigand, J. J. J. Am. Chem. Soc. 2009, 131,
14210−14211.
(6) Scheer, M.; Balazs, G.; Seitz, A. Chem. Rev. 2010, 110, 4236−
4256.
(7) Romero-Nieto, C.; Durben, S.; Kormos, I. M.; Baumgartner, T.
Adv. Funct. Mater. 2009, 19, 3625−3631.
(8) Chen, C.; Roland, F.; Kehr, G.; Erker, G. Chem. Commun. 2010,
46, 3580−3582.
(9) Stephen, D. W. Dalton Trans. 2009, 17, 3129−3136.
(10) Hill, N. J.; Vargus-Baca, I.; Cowley, A. H. Dalton Trans. 2009,
240−253.
(11) Perepichka, I., R.; Perepichka, D. F.; Meng, H.; Wudl, F. Adv.
Mater. 2005, 17, 2281−2305.
12817
dx.doi.org/10.1021/ic201983n|Inorg. Chem. 2011, 50, 12810−12817