Azadibenzophospholes: Functional building blocks with pronounced electron-acceptor character

Article abstract of DOI:10.1021/ic200951x

A series of azadibenzophospholes with varying location of the nitrogen center has been synthesized and comprehensively characterized. In the context of the study, suitably brominated phenylpyridine precursors were accessed via Suzuki-Miyaura cross-coupling for the first time. Despite being nonfluorescent, X-ray crystallographic studies of two azadibenzophosphole oxides revealed planar conjugated scaffolds with high degree of π-conjugation. The P-oxidized species were found to show desirable reversible reduction features that support promising electron-accepting properties of the materials. The presence of the nitrogen as well as phosphorus centers within the scaffold allowed for further functionalization with transition metals, as well as methyl groups that result in altered absorption and redox features for the materials. Subsequent bromination of the scaffold selectively occurred at the exocyclic P-phenyl group, as confirmed via X-ray crystallography. This halogenation allowed for further modification of the system via catalytic cross-coupling with pyridine.

Full text of DOI:10.1021/ic200951x

ARTICLE
pubs.acs.org/IC
Azadibenzophospholes: Functional Building Blocks with Pronounced
Electron-Acceptor Character
Stefan Durben and Thomas Baumgartner*
Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
S Supporting Information
b
ABSTRACT: A series of azadibenzophospholes with varying location of the
nitrogen center has been synthesized and comprehensively characterized. In the
context of the study, suitably brominated phenylpyridine precursors were
accessed via SuzukiꢀMiyaura cross-coupling for the first time. Despite being
nonfluorescent, X-ray crystallographic studies of two azadibenzophosphole
oxides revealed planar conjugated scaffolds with high degree of πꢀconjugation.
The P-oxidized species were found to show desirable reversible reduction
features that support promising electron-accepting properties of the materials.
The presence of the nitrogen as well as phosphorus centers within the scaffold
allowed for further functionalization with transition metals, as well as methyl
groups that result in altered absorption and redox features for the materials.
Subsequent bromination of the scaffold selectively occurred at the exocyclic
P-phenyl group, as confirmed via X-ray crystallography. This halogenation
allowed for further modification of the system via catalytic cross-coupling with pyridine.
’ INTRODUCTION
(in the all hydrocarbon analogues) to n-type character upon
introduction of electron-poor N-heterocycles.
Research in the field of π-conjugated organic materials has for
a long time been focused on the development and application of
p-type semiconductors such as oligoacenes,1 fused and nonfused
oligo- and polythiophenes,2,3 fluorenes4 and carbazoles.5 How-
ever, the necessity for accessing n-type materials with good
processability and electron-conducting features has recently been
recognized and thus led to an increased research effort in this
area.6,7 While the array of accessible p-type materials is large, the
number of suitable n-type materials is still limited to date. More-
over, the resulting devices often suffer from an imbalanced charge
carrier transport between holes and electrons, limiting the overall
performance.8 To harvest the full potential of molecular electro-
nics, n-type materials with high electron mobilities that are similar
to the hole mobilities of established p-type materials are therefore
sought after. An effective strategy toward the generation of n-type
or ambipolar semiconductors is the functionalization of hydro-
carbon scaffolds with fluorine-,9 cyano-,10 or phosphine oxide
substituents.11 Furthermore, replacement of CH-groups with
electron-withdrawing elements such as boron,12 or functional
groups, such as carbonyls,6a,10a or imines1e,6c,13 has been em-
ployed. Even incorporation of oxidized phosphorus centers into
the scaffold of conjugated materials has been identified to afford
desirable electron-accepting features.6b,14 All these modifications
usually result in stabilized lowest unoccupied molecular orbital
(LUMO) energy levels, providing materials that are easily redu-
cible. Many of these materials were also found to function as
electron conductors in a device setting. Nitrogen-containing
heteroacenes suchasI,13a,b II,13c and III6c (Chart 1) are interesting
species in this context, as they showcase the transition from p-type
Tetraazapentacene derivative I shows a low first reduction
potential (Ered = ꢀ0.79 V, vs Fc/Fcþ) and, in contrast to parent
pentacene, pronounced n-type behavior in OFET devices.13a,b The
pyrazinacenes IIa/b show low first reduction potentials Ered
(IIa: ꢀ0.24 V; IIb: ꢀ1.20 V, vs Fc/Fcþ), indicating their potential
foranapplicationaselectrontransport materials. Upon introduction
of the electron-donating methoxide substituent (IIb, R = OMe),
the reduction potential is significantly increased (ΔEred = ꢀ0.96 V),
but notably, still no oxidation is observed up to a potential of Eox =
1 V (vs Fc/Fcþ).13c The anthrazoline derivatives IIIa-d exhibit
reduction potentials comparable to IIb, ranging from Ered
=
ꢀ1.08 V to ꢀ1.15 V (vs Fc/Fcþ), only slightly depending on the
nature of the bridge “X”.6c Furthermore, phosphorus-based systems
such as dibenzophosphole oxide DBPO,15 the phosphine oxide
substituted examples IVa/b11j and V,11d and the fused phosphole
oxides VIa-c14c (Chart 1) have illustrated the applicability of
phosphorane moieties in the design of n-type materials. Com-
pounds IVa/b show reduction waves at Ered = ꢀ2.26 V (IVb)
and Ered = ꢀ2.36 V (IVa, vs Fc/Fcþ), respectively. OLEDs using
IVa/b as hole-blocking and electron-transport materials revealed
higher electron mobility for IVa, compared to IVb.11j Compound V
has been shown to function as a multifunctional material in
blue light emitting OLEDs. It simultaneously serves as emitter,
electron-transporting, and -injection material.11d The annelated
phosphole oxides VIa-c show consistently low reduction potentials
Received: May 6, 2011
Published: June 15, 2011
r
2011 American Chemical Society
6823
dx.doi.org/10.1021/ic200951x Inorg. Chem. 2011, 50, 6823–6836
|

Inorganic Chemistry
ARTICLE
Chart 1. Examples of N- and P-Containing Electron-Acceptor (n-Type) Organic Conjugated Materials
(Ered = ꢀ1.82 V (VIa); ꢀ1.62 V (VIb); ꢀ1.89 V (VIc)), indicating
potential for an application as electron-transport material.14c
In this work, we now report the combination of an electron-
poor, N-heterocyclic backbone and incorporation of a tunable
phosphole moiety to access novel functional electron-acceptor
building blocks. The chosen backbone geometry for this funda-
mental structureꢀproperty study is phenylpyridine, offering the
possibility to investigate the effect of the position of the imine
nitrogen on the materials properties. The combination of the
phenylpyridine backbone with the phosphole moiety was ex-
pected to have low-lying frontier orbital energy levels and offer
the possibility of further chemical functionalization and fine-
tuning of the electronic properties via chemical modification of
the phosphorus and the imine-nitrogen center, respectively.
crystallography can befoundinTable 1. Cyclic voltammetry analyseswere
performed on an Autolab PGSTAT302 instrument, with a polished glassy
carbon electrode as the working electrode, a Pt-wire as counter electrode,
and an Ag/AgCl/KCl3M reference electrode, using ferrocene/ferroce-
nium as internal standard. If not otherwise noted, cyclic voltammetry
experiments were performed in acetonitrile solution with tetrabutylam-
monium hexafluorophosphate (0.1 M) as supporting electrolyte. Theo-
retical calculations have been carried out at the B3LYP/6-31Gþ(d) level
by using the GAUSSIAN 03 suite of programs.18
3-Bromo-2-(2-bromophenyl)pyridine 9. 2,3-Dibromopyri-
dine 7 (1.00 g, 4.22 mmol) and 2-bromo-phenylboronic acid 8
(854 mg, 4.22 mmol) were dissolved in tetrahydrofuran (20 mL),
aqueous K2CO3 (1 M, 15 mL), 5 drops of aqueous KOH (10%) and
then degassed. Pd(PPh3)4 (244 mg, 0.21 mmol) was added and the
mixture refluxed for 72 h. After cooling, the phases were separated and
the aqueous phase extracted three times with chloroform. The combined
organic phases were dried over Na2SO4 and concentrated under
vacuum. The crude mixture was separated by column chromatography
(SiO2, hexanes/ethylacetate, 2:1, Rf = 0.38), giving 1.22 g (92%) of the
’ EXPERIMENTAL SECTION
General Procedures. Reactions were carried out in dry glassware
and under inert atmosphere of purified argon or nitrogen using Schlenk
techniques. Solvents were dried over appropriate drying agents and then
distilled or used directly from an MBraun solvent purification system.
Starting materials were purchased from Aldrich, Alfa Aesar, or Pressure
Chemical Co., and used as received. PhPCl2 was distilled prior to use.
[Pt(acac)(DMSO)Cl]16 and [Au(tht)Cl]17 were prepared by literature
methods. 1H NMR, 13C NMR, and 31P NMR spectra were recorded on
Bruker AC200, Bruker DMX-300, or Bruker Avance(-II, -III) 400
spectrometers. Chemical shifts δ were referenced to external 85%
H3PO4 (31P) or solvent signal (1H, 13C). Elemental analyses were
performed at the Department of Chemistry, University of Calgary, on a
Perkin-Elmer Model 2400 series II instrument. MALDI/TOF, EI, and
ESI mass spectra were recorded on a Bruker Daltonics AutoFlex III,
Finnigan SSQ 7000 or Agilent 6520 Q-TOF instrument, respectively. All
UV/vis experiments were recorded in dilute dichloromethane solution
on a UVꢀvisꢀNIR Cary 5000 spectrophotometer. X-ray crystallo-
graphic data was measured on a Nonius Kappa CCD diffractometer at
173 K. The structures were solved by direct methods and refined using
SHELX. After full-matrix least-squares refinement of the non-hydrogen
atoms with anisotropic thermal parameters, the hydrogen atoms were
placed in calculated positions using a riding model. Further details on the
1
title product 9 as colorless oil, which solidified overnight. H NMR
(CDCl3, 400 MHz): δ = 8.64 (dd, 1 H, 3J(H,H) = 4.7 Hz, 4J(H,H) = 1.5
3
4
Hz, 6-pyridine), 8.00 (dd, 1 H, J(H,H) = 8.1 Hz, J(H,H) = 1.5 Hz,
4-pyridine), 7.67 (dd, 1 H, 3J(H,H) = 8.1 Hz, 4J(H,H) = 1.0 Hz, Ph),
3
4
7.42 (td, 1 H, J(H,H) = 7.5 Hz, J(H,H) = 1.2 Hz, Ph), 7.35ꢀ7.27
(complex area, 2 H) 7.23 (dd, 1 H; 3J(H,H) = 8.1 Hz, 4J(H,H) = 4.7 Hz,
5-pyridine); 13C{1H} NMR (CDCl3, 100.6 MHz): δ = 158.5 (C), 147.8
(CH), 141.0 (C), 140.4 (CH), 132.7 (CH), 130.2 (CH), 130.0 (CH),
127.3 (CH), 124.1 (CH), 122.4 (CH), 121.3 (C) ppm; HRMS (EI,
70 eV): m/z calcd for C11H7Br2N: 312.8925 [Mþ]; found: 312.8933;
elemental analysis calcd (%) for C11H7Br2N: C 42.21, H 2.25, N 4.48;
found: C 42.32, H 2.39, N 4.44.
3-Bromo-4-(2-bromophenyl)pyridine 12. 3-Bromo-4-iodopyri-
dine 11 (1.50 g, 5.3 mmol) and 2-bromophenylboronic acid 8 (1.06 g, 5.3
mmol) were dissolved in tetrahydrofuran (35 mL), aqueous K2CO3
(1 M, 25 mL), 5 drops of aqueous KOH (10%), and degassed. Pd(PPh3)4
(306 mg, 0.27 mmol) was added, and the mixture refluxed for 72 h. After
cooling, the phases were separated, and the aqueous phase extracted with
chloroform. The combined organic phases were dried with Na2SO4 and
concentrated under vacuum. The crude mixture was separated by column
chromatography(SiO2, hexanes/ethylacetate, 4:1), giving 1.49 g (90%) of
6824
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
Table 1. Crystal Data and Structure Refinement for 1b, 4b, and 21
1b
4b
21
empirical formula
formula weight
temperature (K)
wavelength (Å)
crystal system
space group
a (Å)
C
17H12NOP
C17H12NOP
277.26
C17H11BrNOP
356.14
277.26
173(2)
173(2)
173(2)
0.71073
0.71073
0.71073
monoclinic
P21/c
monoclinic
P21/c
monoclinic
C2/c
11.3208(3)
8.4178(4)
16.3424(9)
119.650(8)
1353.49(15)
4
9.9305(7)
9.5391(4)
14.1372(9)
92.259(2)
1338.15(14)
4
26.4755(11)
8.7326(4)
13.7296(8)
115.3807(26)
2867.9(3)
8
b (Å)
c (Å)
β (deg)
volume (Å3)
Z
density, calcd (Mg/m3)
1.361
1.376
1.650
abs. coefficient (mmꢀ1
)
0.501
0.199
2.975
F(000)
576
576
1424
crystal size (mm3)
θ range (deg)
0.24 ꢁ 0.19 ꢁ 0.11
2.07ꢀ27.46
4654
0.12 ꢁ 0.08 ꢁ 0.03
2.58ꢀ27.48
4658
0.05 ꢁ 0.05 ꢁ 0.02
1.70ꢀ27.55
10809
reflections collected
independent reflections
data/restraints/parameters
GoF on F2
3064 [R(int) = 0.0228]
3064/0/193
1.217
2992 (R(int) = 0.0193)
2992/0/181
1.191
3282 (R(int) = 0.0879)
3282/0/190
1.105
final R indices [I > 2σ(I)]
R1 = 0.0506
wR2 = 0.1412
R1 = 0.0592
wR2 = 0.1586
R1 = 0.0485
wR2 = 0.1373
R1 = 0.0574
wR2 = 0.1591
R1 = 0.0595
wR2 = 0.1205
R1 = 0.0897
wR2 = 0.1375
R indices (all data)
the title product 12 as colorless oil, which solidified overnight. 1H NMR
(CDCl3, 400 MHz): δ = 8.82 (s, 1 H, 2-pyridine), 8.57 (d, 1 H, 3J(H,H) =
4.9 Hz, 6-pyridine), 7.78 (dd, 1 H, 3J(H,H) = 8.0 Hz, 4J(H,H) = 1.1 Hz,
Ph), 7.40 (td, 1 H, 3J(H,H) = 7.5 Hz, 4J(H,H) = 1.2 Hz, Ph), 7.30 (dt, 1 H;
3J(H,H) = 8.0 Hz, 4J(H,H) = 1.8Hz, Ph), 7.20ꢀ7.17 (complex area, 2 H);
13C{1H} NMR (CDCl3, 100.6 MHz): δ = 152.2 (CH), 149.4 (C), 148.1
(CH), 139.4 (C), 132.9 (CH), 130.2 (CH), 130.2 (CH), 127.4 (CH),
125.6 (CH), 122.2 (C), 122.0 (C) ppm; HRMS (EI, 70 eV): m/z calcd for
C11H7Br2N: 312.8925 [Mþ]; found: 312.8928; elemental analysis calcd
(%) for C11H7Br2N: C 42.21, H 2.25, N 4.48; found: C 42.57, H 2.22,
N 4.37.
3-(2-Bromophenyl)-2-chloropyridine 14. 2-Chloro-3-iodo-
pyridine 13 (1.00 g, 4.2 mmol), 2-bromophenylboronic acid 8 (844
mg, 4.2 mmol), and xantphos (122 mg, 0.21 mmol) were dissolved in
tetrahydrofuran (15 mL) and aqueous K2CO3 solution (1 M, 12 mL).
The biphasic mixture was degassed and subsequently Pd(PPh3)4 (243
mg, 0.21 mmol) was added. The solution was heated to reflux and stirred
for 72 h. After cooling, the phases were separated, and the aqueous phase
extracted with chloroform. The combined organic phases were dried
with MgSO4 and concentrated under vacuum. The crude mixture was
separated by column chromatography (SiO2, hexanes/ethylacetate,
4:1), giving 876 mg (78%) of the title product 14 (Rf = 0.32) as slightly
yellow oil. 1H NMR (CD2Cl2, 400 MHz): δ = 8.44 (dd, 1 H, 3J(H,H) =
4.8 Hz, 4J(H,H) = 2.0 Hz, 6-pyridine), 7.73 (ddd, 1 H, 3J(H,H) = 8.0 Hz,
4J(H,H) = 1.2 Hz, 5J(H,H) = 0.4 Hz, 6-Ph), 7.63 (dd, 1 H, 3J(H,H) = 7.5
Hz, 4J(H,H) = 2.0 Hz, 4-pyridine), 7.43 (td, 1 H, 3J(H,H) = 7.5 Hz, 4J(H,
H) = 1.2 Hz, Ph), 7.35 (dd, 1 H, 3J(H,H) = 7.5 Hz, 3J(H,H) = 4.8 Hz,
5-pyridine), 7.32 (dd, 1 H, 3J(H,H) = 15.5 Hz, 4J(H,H) = 1.8 Hz, Ph),
7.31 (ddd, 1 H, 3J(H,H) = 15.5 Hz, 4J(H,H) = 1.8 Hz, 5J(H,H) = 0.4 Hz,
3-Ph); 13C{1H} NMR (CD2Cl2, 100.6 MHz): δ = 150.7 (C), 149.8
(CH), 140.4 (CH), 139.1 (C), 136.9 (C), 133.3 (CH), 131.6 (CH),
130.7 (CH), 128.1 (CH), 123.9 (C), 122.9 (CH) ppm; HRMS (EI,
70 eV): m/z calcd for C11H7BrClN: 268.9430 [Mþ]; found: 268.9442.
2-Bromo-3-(2-bromophenyl)pyridine 15. 3-(2-Bromophenyl)-
2-chloropyridine 14 (840 mg, 3.13 mmol) was dissolved in PBr3 (10 mL,
∼106 mmol) and heated to 140 °C for 16 h. The volatiles were removed
and fresh PBr3 (10 mL, ∼106 mmol) was added, and the mixture heated
to 140 °C for another 24 h. The volatiles were removed under vacuum,
and the resulting mixture neutralized with aqueous Na2CO3 solution
(sat.). The aqueous phase was extracted three times with chloroform, the
combined organic phases dried over Na2SO4, and concentrated. The
crude mixture was separated by column chromatography (SiO2, hexanes/
ethylacetate, 2:1, Rf = 0.46), giving 836 mg(85%) ofthetitle product15as
colorless oil, which solidified overnight. 1H NMR (CD2Cl2, 400 MHz):
δ = 8.40 (dd, 1 H, 3J(H,H) = 4.8 Hz, 4J(H,H) = 2.0 Hz, 6-pyridine), 7.71
(ddd, 1 H, 3J(H,H) = 8.0 Hz, 4J(H,H) = 1.2 Hz, 5J(H,H) = 0.4 Hz, Ph),
7.58 (dd, 1 H, 3J(H,H) = 7.5 Hz, 4J(H,H) = 2.0Hz, 4-pyridine), 7.43 (td, 1
H, 3J(H,H) = 7.5 Hz, 4J(H,H) = 1.2 Hz, Ph), 7.38 (dd, 1 H, 3J(H,H) = 7.5
Hz, 3J(H,H) = 4.8 Hz, 5-pyridine), 7.31ꢀ7.27 (complex area, 2 H, Ph);
13C{1H} NMR (CD2Cl2, 100.6 MHz): δ = 150.0 (CH), 143.4 (C), 140.5
(C), 139.8 (CH), 139.7 (C), 133.3 (CH), 131.6(CH), 130.7 (CH), 128.1
(CH), 123.8 (C), 123.2 (CH) ppm; HRMS (EI, 70 eV): m/z calcd for
C11H7Br2N: 312.8925 [Mþ]; found: 312.8924; elemental analysis calcd
(%) for C11H7Br2N: C 42.21, H 2.25, N 4.48; found: C 42.27, H 2.18,
N 4.46.
1-Azadibenzophosphole 1a. 3-Bromo-2-(2-bromophenyl)pyridine
9 (313 mg, 1.0 mmol) was dissolved in dry diethyl ether (40 mL), and t-BuLi
(1.25 mL, 1.6 M in pentane) was added dropwise at ꢀ78 °C. The mixture
was stirred for 1 h at this temperature, phenyldichlorophosphane (181 mg,
1.0 mmol) was added, and subsequently quickly heated to room temperature
(rt). The yellow suspension was concentrated (15 mL), filtered over neutral
alumina, and washed with diethyl ether. The filtrate was concentrated, and the
6825
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
yellow crude product was washed twice with cold pentane (10 mL) and dried
to give 152 mg (58%) of the title product 1a as slightly yellow powder. 1H
NMR (CD2Cl2, 400 MHz): δ = 8.67 (dd, 1 H, 3J(H,P) = 4.8 Hz, 4J(H,H) =
1.7 Hz, 2-H), 8.29ꢀ8.32 (m, 1 H, 4-H), 8.01 (ddd, 1 H, 3J(H,H) = 7.6 Hz,
133.7 (d, J(C,P) = 2.0 Hz, CH), 133.5 (d, J(C,P) = 106.9 Hz, C), 132.7
(d, J(C,P) = 2.9 Hz, CH), 131.9 (d, J(C,P) = 11.1 Hz, CH), 131.0 (d,
J(C,P) = 11.1 Hz, CH), 130.2 (d, J(C,P) = 9.8 Hz, CH), 129.5 (d, J(C,
P) = 106.1 Hz, C), 129.0 (d, J(C,P) = 13.0 Hz, CH) 128.1 (d, J(C,P) =
103.7 Hz, C), 122.5 (d, J(C,P) = 9.7 Hz, CH), 115.8 (d, J(C,P) = 7.8 Hz,
CH) ppm; HRMS (EI, 70 eV): m/z calcd for C17H12NOP: 277.0657
[Mþ]; found: 277.0652; elemental analysis calcd (%) for C17H12NOP:
C 73.64, H 4.36, N 5.05; found: C 73.29, H 4.57, N 4.94.
4
4J(H,P) = 3.9 Hz, J(H,H) = 1.7 Hz, 3-H), 7.78ꢀ7.70 (m, 1 H, Ar),
7.60ꢀ7.54(m, 1H, Ar),7.50ꢀ7.44 (m, 1 H, Ar), 7.35ꢀ7.20(m, 6H,Phand
Ar); 31P{1H} NMR (CD2Cl2, 162.0 MHz): δ = ꢀ16.5; 13C{1H} NMR
(CD2Cl2, 100.6 MHz): δ = 161.5 (d, J(C,P) = 6.0 Hz, C), 150.5 (s, CH),
143.9 (d, J(C,P) =1.8Hz, C), 143.4(d,J(C,P) =4.0Hz, C),138.5(d,J(C,P)
= 20.1 Hz, CH), 137.5 (d, J(C,P) = 6.5 Hz, C), 135.5 (d, J(C,P) = 18.4 Hz,
C), 133.2(d, J(C,P) = 20.5 Hz, CH), 130.9 (d, J(C,P) = 21.6 Hz, CH), 130.2
(d, J(C,P) = 1.0 Hz, CH), 129.9 (d, J(C,P) = 7.7 Hz, CH), 129.7 (s, CH),
129.4 (d, J(C,P) = 7.8 Hz, CH), 123.5 (s, CH), 122.5 (d, J(C,P) = 5.7 Hz,
CH) ppm; HRMS (EI, 70 eV): m/z calcd for C17H12NP: 261.0707 [Mþ];
found: 261.0659; elemental analysis calcd (%) for C17H12NP: C 78.15, H
4.63, N 5.36; found: C 77.97, H 4.82, N 5.27.
1
NMR-Data for Phosphole 3a. H NMR (CD2Cl2, 400 MHz):
δ = 8.88 (ps. t, 1 H, J = 1.1 Hz, Py), 8.66 (d, 1 H, J = 5.2 Hz, Py),
8.05ꢀ7.99 (m, 1 H, Ar), 7.82ꢀ7.77 (m, 1 H, Ar), 7.77ꢀ7.72 (m, 1 H,
Ar), 7.56ꢀ7.49 (m, 1 H, Ar), 7.48ꢀ7.42 (m, 1 H, Ar), 7.31ꢀ7.19 (m,
5 H, Ph); 31P{1H} NMR (CD2Cl2, 400 MHz): δ = ꢀ12.3 ppm.
4-Azadibenzophosphole 4a. 2-Bromo-3-(2-bromophenyl)pyridine
15 (627 mg, 2.0 mmol) was dissolved in dry diethyl ether (85 mL) and t-BuLi
(2.50 mL, 1.6 M in pentane) was added dropwise at ꢀ78 °C. The mixture
was stirred for 1 h at this temperature, phenyldichlorophosphane (359 mg,
2.0 mmol) was added and subsequently quickly heated to rt. The yellow
suspension was concentrated (35 mL), filtered over neutral alumina, and
washed with diethyl ether. The filtrate was concentrated, and the yellow crude
product was washed twice with 20 mL of cold pentane and dried to give
361 mg (69%) of the title product 4a as slightly yellow powder. 1H NMR
(CD2Cl2,400MHz):δ=8.61(dd,1H,3J(H,H) =4.8Hz,4J(H,H) =1.5Hz,
3-H), 8.15 (ps. dt, 1 H, J=7.9Hz,J=1.6Hz,1-H),7.98(br. d,1H,J=7.8Hz,
Ar), 7.85ꢀ7.78 (m, 1 H, Ar), 7.58ꢀ7.51 (m, 1 H, Ar), 7.53ꢀ7.37 (m,
3 H, Ph and Ar), 7.34 (dd, 1 H, 3J(H,H) = 7.9 Hz, 3J(H,H) = 4.8 Hz, 2-H),
7.32ꢀ7.24 (m, 3 H, Ph); 31P{1H} NMR (CD2Cl2, 162.0 MHz): δ = ꢀ14.8;
13C{1H} NMR (CD2Cl2, 100.6 MHz): δ = 169.4 (d, J(C,P) = 12.1 Hz),
150.0 (d, J(C,P) = 11.3 Hz), 141.9 (s), 141.3 (d, J(C,P) = 3.5 Hz), 138.3
(d, J(C,P) = 9.1 Hz), 135.0 (d, J(C,P) = 19.3 Hz), 133.0 (d, J(C,P) =
19.0 Hz, C), 131.4 (d, J(C,P) = 21.4 Hz), 129.8 (br. s), 129.7 (s), 129.3 (d,
J(C,P) =7.4 Hz), 128.9 (d, J(C,P) = 7.4 Hz, CH), 128.6 (s), 123.1 (s), 122.6
(s) ppm; HRMS (EI, 70 eV): m/z calcd for C17H12NP: 261.0707 [Mþ];
found: 261.0714; elemental analysis calcd (%) for C17H12NP: C 78.15, H
4.63, N 5.36; found: C 78.45, H 4.83, N 5.27.
1-Azadibenzophosphole oxide 1b. 1-Azadibenzophosphole
1a (159 mg, 0.61 mmol) was dissolved in chloroform (20 mL) and
water (15 mL). H2O2 (30%, 1 mL) was added, and the mixture was
vigorously stirred for 2 h. The organic phase was separated, the aqueous
phase washed twice with chloroform, and the combined organic phases
dried over Na2SO4 and concentrated. The yellow solid was washed twice
with cold pentane (10 mL) and dried to give 160 mg (95%) of the title
1
product 1b as slightly yellow powder. H NMR (CD2Cl2, 400 MHz):
3
5
4
δ = 8.75 (ddd, 1 H, J(H,H) = 5.0 Hz, J(H,P) = 2.2 Hz, J(H,H) =
1.7 Hz, 2-H), 8.28ꢀ8.20 (m, 1 H, Ar), 7.99 (ddd, 1 H, 3J(H,P) = 9.1 Hz,
3J(H,H) = 7.5 Hz, J(H,H) = 1.7 Hz, 4-H), 7.78ꢀ7.68 (m, 2 H, Ph),
4
7.67ꢀ7.58 (m, 2 H, Ph and Ar), 7.58ꢀ7.50 (m, 2 H, Ph), 7.46ꢀ7.38 (m,
2 H, Ar), 7.30 (ddd, 1 H, 3J(H,H) = 7.5 Hz, 3J(H,H) = 5.0 Hz, 4J(H,P) =
3.2 Hz, 3-H); 31P{1H} NMR (CD2Cl2, 162.0 MHz): δ = 29.7; 13C{1H}
NMR (CD2Cl2, 100.6 MHz): δ = 160.4 (d, J(C,P) = 24.5 Hz, C), 154.4
(d, J(C,P) = 1.5 Hz, CH), 142.9 (d, J(C,P) = 16.0 Hz, C), 137.8 (d, J(C,
P) = 8.3 Hz, CH), 134.5 (d, J(C,P) = 104.2 Hz, C, ipso-Py), 134.3 (d,
J(C,P) = 2.3 Hz, CH), 133.0 (d, J(C,P) = 2.9 Hz, CH), 131.8 (d, J(C,
P) = 11.5 Hz, CH), 131.5 (d, J(C,P) = 11.0 Hz, CH), 131.0 (d, J(C,P) =
104.9 Hz, C, ipso-Ar), 129.9 (d, J(C,P) = 8.8 Hz, CH), 129.4 (d, J(C,
P) = 12.7 Hz, CH) 128.6 (d, J(C,P) = 106.1 Hz, C, ipso-Ar), 124.2
(d, J(C,P) = 8.3 Hz, CH), 123.0 (d, J(C,P) = 10.3 Hz, CH) ppm; HRMS
(EI, 70 eV): m/z calcd for C17H12NOP: 277.0657 [Mþ]; found:
277.0645; elemental analysis calcd (%) for C17H12NOP: C 73.64, H
4.36, N 5.05; found: C 73.22, H 4.49, N 5.04.
4-Azadibenzophosphole Oxide 4b. 4-Azadibenzophosphole
4a (189 mg, 0.72 mmol) was dissolved in chloroform (20 mL) and water
(15 mL). H2O2 (30%, 1 mL) was added, and the mixture was vigorously
stirred for 2 h. The organic phase was separated, the aqueous phase
washed twice with chloroform, and the combined organic phases dried
over Na2SO4 and concentrated. The yellow solid was washed twice with
cold pentane (10 mL) and dried to give 179 mg (89%) of the title product as
slightly yellow powder. 1H NMR (CD2Cl2, 400 MHz): δ = 8.65 (dd, 1 H,
3J(H,H) = 4.8 Hz, 4J(H,H) = 1.4 Hz, 3-H), 8.10 (ddd, 1 H, 3J(H,H) = 8.0
Hz, 3J(H,P) = 4.1 Hz, 4J(H,H) = 1.4 Hz, 1-H), 7.90ꢀ7.85 (m, 1 H, Ar),
7.81ꢀ7.75 (m, 1 H, Ar), 7.70ꢀ7.61 (m, 3 H, Ph and Ar), 7.57ꢀ7.47 (m, 2
H, Ph and Ar), 7.45 (ddd, 1 H, 3J(H,H) = 8.0 Hz, 3J(H,H) = 4.8 Hz, 5J(H,
P) = 1.1 Hz, 2-H), 7.44ꢀ7.38 (m, 2 H, Ph); 31P{1H} NMR (CD2Cl2, 162.0
MHz): δ = 25.1; 13C{1H} NMR (CD2Cl2, 100.6 MHz): δ = 158.1 (d, J(C,
P) = 132.3 Hz, C), 151.8 (d, J(C,P) = 17.0 Hz, CH), 139.9 (d, J(C,P) = 16.9
Hz, C), 137.5 (d, J(C,P) = 35.3 Hz, C), 134.3 (d, J(C,P) = 1.8 Hz, CH),
133.0 (d, J(C,P) = 2.9 Hz, CH), 131.9 (d, J(C,P) = 106.1 Hz, C), 131.7 (d,
J(C,P) = 10.8 Hz, CH), 130.8 (d, J(C,P) = 10.9 Hz, CH), 130.6 (d, J(C,P)
= 9.1 Hz, CH), 130.2 (d, J(C,P) = 101.2 Hz, C), 129.4 (d, J(C,P) = 12.6Hz,
CH), 128.9 (d, J(C,P) = 8.4 Hz, CH), 126.9 (d, J(C,P) = 2.7 Hz, CH),
122.6 (d, J(C,P) = 8.3 Hz, CH) ppm; elemental analysis calcd (%) for
C17H12NOP: C 73.64, H 4.36, N 5.05; found: C 73.69, H 4.48, N 4.93.
Pt-Complex 17. To a solution of 3-azadibenzophosphole oxide 3b
(62 mg, 0.22 mmol) in ethanol (5 mL), a solution of potassium
tetrachloroplatinate(II) (46 mg, 0.11 mmol) in water (5 mL) was added
at rt. The yellow solution was stirred for 18 h at 50 °C, during which a
white precipitate formed. After cooling, the white solid was filtered off,
washed with water and dried under vacuum to give 58 mg (62%) of the
3-Azadibenzophosphole Oxide 3b. 3-Bromo-4-(2-bromophe-
nyl)pyridine 12 (314 mg, 1.0 mmol) was dissolved in dry diethyl ether
(40 mL) and t-BuLi (1.25 mL, 1.6 M in pentane) was added dropwise at
ꢀ78 °C. The mixture was stirred for 1 h at this temperature, phenyldi-
chlorophosphane (184 mg, 1.0 mmol) was added and subsequently
quickly heated to rt. The yellow suspension was filtered over neutral
alumina and washed with degassed diethyl ether/dichloromethane
(1:1). The filtrate was concentrated, and the yellow crude product 3a
was taken up in chloroform (25 mL). To this water (15 mL) and H2O2
(30%, 1 mL) were added and the emulsion vigorously stirred for 2 h. The
organic phase was separated, the aqueous phase washed twice with
chloroform and the combined organic phases dried over Na2SO4 and
concentrated. The yellow solid was washed twice with cold pentane
(10 mL) and dried to give 192 mg (69%) of the title product 3b as
slightly yellow powder. 1H NMR (CDCl3, 400 MHz): δ = 8.91 (dd, 1 H,
3J(H,P) = 4.4 Hz, 5J(H,H) = 1.0 Hz, 4-H), 8.82 (dd, 1 H, 3J(H,H) = 5.2
Hz, 5J(H,P) = 2.4 Hz, 2-H), 7.92 (br. dd, 1 H, J(H,H) = 7.7 Hz, J(H,P) =
2.9 Hz, Ar), 7.82ꢀ7.75 (m, 1H, Ar), 7.72 (ddd, 1 H, 3J(H,H) = 5.2 Hz,
4J(H,P) = 2.3 Hz, 5J(H,H) = 1.0 Hz, 1-H), 7.70ꢀ7.62 (m, 3 H, o-Ph and
Ar), 7.59ꢀ7.51 (m, 2 H, p-Ph and Ar), 7.46ꢀ7.39 (m, 2 H, m-phenyl);
31P{1H} NMR (CDCl3, 162.0 MHz): δ = 34.0; 13C{1H} NMR (CDCl3,
100.6 MHz): δ = 154.2 (d, J(C,P) = 0.9 Hz, CH), 150.8 (d, J(C,P) = 10.6
Hz, CH), 149.5 (d, J(C,P) = 20.0 Hz, C), 139.3 (d, J(C,P) = 21.0 Hz, C),
1
title product 17. H NMR (CDCl3, 400 MHz): δ = 9.12 (d, 1 H,
6826
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
3J(HꢀP) = 5.8 Hz, 4-H), 9.05 (dd, 1 H, 3J(HꢀH) = 6.2 Hz, 5J(HꢀP) =
1.6 Hz, 2-H), 7.95 (dd, 1 H, J = 7.7 Hz, J = 2.9 Hz, Ar), 7.82 (dd, J = 7.3
Hz, J = 10.1 Hz, Ar), 7.73 (m, 1 H, Ar), 7.70ꢀ7.54 (m, 4 H, Ar and Ph),
7.50ꢀ7.41 (m, 1 H, m-Ph); 31P{1H} NMR (CDCl3, 162.0 MHz): δ =
32.1; 195Pt NMR (CDCl3, 86.0 MHz): δ = ꢀ312.2 ppm; The low
solubility in common organic solvents precluded 13C NMR spectros-
copy in solution; HRMS (ESI): m/z calcd for C34H24Cl2N2NaO2P2Pt:
843.02217 [Mþ þ Na]; found: 843.02419; elemental analysis calcd (%)
for C34H24Cl2N2O2P2Pt: C 49.77, H 2.82, N 3.18 ; found: C 48.78, H
2.73, N 3.10.
Scheme 1. Targeted Azadibenzophospholes and General
Synthetic Strategy toward Dithienophospholes
4-Azadibenzophosphole-methyltriflate Adduct 19. To a
solution of 4-azadibenzophosphole 4a (137 mg, 0.52 mmol) in dichloro-
methane (15 mL), a solution of MeOTf (86 mg, 0.52 mmol) in
dichloromethane (10 mL) was dropwise added at 0 °C. The volatiles
were removed, and the yellow powder washed three times with cold
pentane to give 201 mg (90%) of the title product 19 as yellow solid. 1H
NMR (CD2Cl2, 400 MHz): δ = 9.00 (dd, 1 H, 3J(H,H) = 5.8 Hz, 4J(H,
H) = 2.8 Hz, 3-H), 8.92 (br. d, 1 H, J = 8.1 Hz, 1-H), 8.22 (dd, 1 H, J = 7.9
Hz, Ar), 8.17ꢀ8.10 (m, 1 H, 2-H), 7.81ꢀ7.75 (m, 1 H, Ar), 7.73 (td, 1
H, 3J(H,H) = 7.6 Hz, 4J(H,H) = 1.2 Hz, Ar), 7.66ꢀ7.59 (m, 1 H, Ar)
7.55ꢀ7.48 (m, 1 H, Ph), 7.43ꢀ7.36 (m, 2 H, Ph), 7.35ꢀ7.27 (m, 2 H,
Ph), 4.32 (s, 3 H, CH3); 31P{1H} NMR (CD2Cl2, 162.0 MHz): δ =
ꢀ10.4; 13C{1H} NMR (CD2Cl2, 100.6 MHz): δ = 164.1 (d, J(C,P) =
18.4 Hz), 145.8 (s), 144.7 (d, J(C,P) = 4.5 Hz), 139.8 (d, J(C,P) = 1.2
Hz), 138.4 (s), 136.6 (s), 135.5 (d, J(C,P) = 22.7 Hz), 133.0 (d, J(C,P) =
1.4 Hz), 132.2 (d, J(C,P) = 8.8 Hz), 131.3 (s), 131.0 (d, J(C,P) = 23.8
Hz), 130.7 (d, J(C,P) = 9.5 Hz), 128.5 (d, J(C,P) = 1.1 Hz), 126.0
4J(HꢀH) = 1.4 Hz, 1-H), 7.88 (br. dd, 1 H, J = 7.7 Hz, J = 3.4 Hz, Ar),
7.82ꢀ7.62 (m, 4 H, Ar), 7.62ꢀ7.55 (m, 1 H, Ar), 7.55ꢀ7.49 (m, 1 H, Ar),
7.47 (ddd, 1 H, 3J(HꢀH) = 8.0 Hz, 3J(HꢀH) = 4.8 Hz, 5J(HꢀP) = 2.2 Hz,
2-H) 31P{1H} NMR (CD2Cl2, 162 MHz): δ = 23.6; 13C{1H} NMR
(CD2Cl2, 100.6 MHz): δ = 157.4 (d, 1J(CꢀP) = 133.7 Hz, C, ipso-Py),
152.0 (d, J(CꢀP) = 17.2 Hz, CH), 139.9 (d, J(CꢀP) = 17.3 Hz, C), 137.6
(d, J(CꢀP) = 36.1 Hz, C), 136.1 (d, J(CꢀP) = 2.7 Hz, CH), 134.7
(d, J(CꢀP) = 2.0 Hz, CH), 134.3 (d, J(CꢀP) = 11.7 Hz, CH), 133.0
(d, J(CꢀP) = 100.0 Hz, C, ipso-Ar), 131.2 (d, J(CꢀP) = 107.4 Hz, C, ipso-
Ar), 131.1 (d, J(CꢀP) = 12.5 Hz, CH), 131.0 (d, J(CꢀP) = 10.6 Hz, CH),
130.8 (d, J(CꢀP) = 9.2 Hz, CH), 130.4 (d, J(CꢀP) = 10.3 Hz, CH), 129.1
(d, J(CꢀP) = 8.6 Hz, CH), 127.2 (d, J(CꢀP) = 2.7 Hz, CH), 123.7 (d,
J(CꢀP) = 16.0 Hz, C), 122.7 (d, J(CꢀP) = 8.4 Hz, CH) ppm; HRMS (EI,
70 eV): m/z calcd for C17H11BrNOP: 354.9762 [Mþ]; found: 354.9757.
Pyridine-Coupled 4-Azadibenzophosphole 23. A degassed
solution of brominated 4-azadibenzophosphole 21 (68 mg, 0.19 mmol),
2-(tributylstannyl)pyridine 22 (105 mg, 0.29 mmol) and [Pd(PPh3)4]
(11 mg, 0.01 mmol) in toluene (5 mL) was refluxed for 48 h. After
cooling, chloroform (15 mL) and NH4Cl-solution (sat., 15 mL) was
added. The phases were separated, and the aqueous phase was extracted
with chloroform (3 ꢁ 10 mL). The organic phases were combined, dried
over Na2SO4, and concentrated. The orange greasy crude product was
separated by column chromatography (SiO2, chloroform/ethyl acetate,
1:1 þ 3% ethanol) to give 52 mg (76%) of the title product 23 as a
1
(d, J(C,P) = 15.2 Hz), 124.5 (s), 121.4 (q, J(CꢀF) = 320.8 Hz),
3
48.9 (d, J(C,P) = 10.0 Hz) ppm; elemental analysis calcd (%) for
C19H15F3NO3PS: C 53.65, H 3.55, N 3.29 ; found: C 53.88, H 3.50,
N 3.22.
4-Azadibenzophosphole-methyltriflate Adduct Gold Chlor-
ide Complex 20. To a solution of 4-azadibenzophosphole-methyltriflate
adduct 19 (190 mg, 0.45 mmol) in dichloromethane (20 mL), [Au(tht)Cl]
(160 mg, 0.5 mmol) was added, and the solution stirred for 16 h at rt. All
volatiles were removed under vacuum, and the crude product recrystallized
from hot ethanol to give 160 mg (54%) of the title product 20 as yellow
needles. 1H NMR (CD2Cl2, 400 MHz): δ = 9.13ꢀ9.01 (m, 2 H, Py), 8.36
(br. dd, 1 H, 3J(HꢀH) = 6.1 Hz, 3J(HꢀH) = 7.2 Hz, 2-H), 8.27 (dd, 1 H,
J = 7.9 Hz, J = 2.5 Hz, Ar), 7.94ꢀ7.81 (m, 2 H, Ar), 7.80ꢀ7.62 (complex
area, 4 H, Ar), 7.61ꢀ7.52 (m, 2 H, Ar), 4.45 (s, 3 H, CH3); 31P{1H} NMR
(CD2Cl2, 162.0 MHz): δ = 25.8; 13C{1H} NMR (CD2Cl2, 100.6 MHz):
δ= 150.5 (d, 1J(CꢀP) = 60.6 Hz, ipso-Py), 148.2 (s, Py), 144.3 (d, J(CꢀP) =
14.2 Hz, Py), 138.2 (d, J(CꢀP) = 4.0 Hz, Ar), 137.2 (d, J(CꢀP) = 6.7Hz,
Ar), 135.4 (d, J(CꢀP) = 16.8 Hz, Ar), 135.4 (d, J(CꢀP) = 2.8 Hz, Ar),
134.4 (d, J(CꢀP) = 2.0 Hz, Ar), 133.0 (d, J(CꢀP) = 13.1 Hz, Ar), 131.6
(s, Ar), 131.5 (d, J(CꢀP) = 23.8 Hz, Ar), 130.8 (d, J(CꢀP) = 13.4 Hz,
Ar), 129.8 (d, 1J(CꢀP) = 67.8, ipso-Ar), 124.8 (d, J(CꢀP) = 6.2 Hz, Ar),
120.6 (q, 1J(CꢀF) = 324.2 Hz, CF3), 119.0 (d, 1J(CꢀP) = 59.8 Hz, ipso-
Ar), 48.4 (d, 3J(CꢀP) = 7.8 Hz, CH3) ppm; elemental analysis calcd (%)
for C19H15F3NO3PSAuCl: C 34.69, H 2.30, N 2.13; found: C 35.01,
H 2.31, N 1.97.
1
colorless solid. H NMR (CD2Cl2, 400 MHz): δ = 8.66 (dd, 1 H,
4
3J(HꢀH) = 4.8 Hz, J(HꢀH) = 1.4 Hz, 3-H), 8.65ꢀ8.59 (m, 1 H,
6-Pyridyl), 8.36 (br. d, 1 H, J = 13.4 Hz, Ar), 8.25ꢀ8.16 (m, 1 H, Ar),
8.12 (ddd, 1 H, 3J(HꢀH) = 8.0 Hz, 4J(HꢀP) = 4.1 Hz, 3J(HꢀH) = 1.4
Hz, 1-H), 7.89 (br. dd, 1 H, J = 7.7 Hz, J = 3.3 Hz, Ar), 7.86ꢀ7.79 (m, 1
H, Ar), 7.79ꢀ7.64 (complex area, 3 H, Ar), 7.64ꢀ7.55 (m, 1 H, Ar),
7.55ꢀ7.48 (complex area, 2 H, Ar), 7.46 (ddd, 1 H, 3J(HꢀH) = 8.0 Hz,
3J(HꢀH) = 4.8 Hz, 5J(HꢀP) = 2.1 Hz, 2-H), 7.25 (ddd, 1 H, J = 6.5 Hz,
J = 4.8 Hz, J = 2.2 Hz, Ar); 31P{1H} NMR (CD2Cl2, 162 MHz): δ =
25.2; 13C{1H} NMR (CD2Cl2, 100.6 MHz): δ = 158.0 (d, J(CꢀP) =
132.6 Hz, C, ipso-Ar), 156.4 (s, C, 2-Pyridyl), 151.9 (d, J(CꢀP) = 17.1
Hz, CH, Ar), 150.3 (s, CH, Pyridyl), 140.7 (d, J(CꢀP) = 12.4 Hz, C, Ar),
139.9 (d, J(CꢀP) = 16.9 Hz, C, Ar), 137.6 (d, J(CꢀP) = 35.2 Hz, C, Ar),
137.4 (s, CH, Pyridyl), 134.4 (d, J(CꢀP) = 1.9 Hz, CH, Ar), 131.9 (d,
J(CꢀP) = 11.3 Hz, CH, Ar), 131.9 (d, J(CꢀP) = 106.3 Hz, C, ipso-Ar),
131.5 (d, J(CꢀP) = 2.8 Hz, CH, Ar), 130.9 (d, J(CꢀP) = 10.9 Hz, CH,
Ar), 130.7 (d, J(CꢀP) = 11.2 Hz, CH, Ar), 130.7 (d, J(CꢀP) = 103.1
Hz, C, ipso-Ar), 130.2 (d, J(CꢀP) = 11.2 Hz, CH, Ar), 129.8 (d, J(CꢀP) =
13.1 Hz, CH, Ar), 129.0 (d, J(CꢀP) = 8.5 Hz, CH, Ar) 127.0 (d, J(CꢀP) =
2.5 Hz, CH, Ar), 123.3 (s, CH, Pyridyl), 122.7 (d, J(CꢀP) = 8.2 Hz, CH,
Ar), 121.1 (s, CH, Pyridyl) ppm; HRMS (EI, 70 eV): m/z calcd for
C22H15N2OP: 354.0922 [Mþ]; found: 354.0914.
Brominated 4-Azadibenzophosphole 21. To a solution of
4-azadibenzophosphole oxide 4b (275 mg; 0.99 mmol) in trifluoroacetic
acid (25 mL) and sulfuric acid (conc., 2.5 mL), N-bromosuccinimide (282
mg, 1.58 mmol) was added in eight portions over 8 h at 0 °C, and the
mixture stirred overnight in the dark. The solution was then poured into ice
water and neutralized with NaHCO3 solution. The aqueous phase was
extracted three times with chloroform, the combined organic phases dried
over Na2SO4 and concentrated under vacuum. The crude mixture was
separated by column chromatography (SiO2, chloroform/ethyl acetate,
1:1) to give 113 mg (32%) of the product 21 as white powder. 1H NMR
(CD2Cl2, 400 MHz): δ = 8.67 (dd, 1 H, 3J(HꢀH) = 4.8 Hz, 4J(HꢀH) =
3
4
1.4 Hz, 3-H), 8.11 (ddd, 1 H, J(HꢀH) = 8.0 Hz, J(HꢀP) = 4.2 Hz,
6827
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
Scheme 2. Synthesis of the Dibrominated Phenylpyridine
Precursors 9, 12, and 15
phenylpyridines show similar absorption features with absorp-
tion maxima in the UV range of the optical spectrum (9: λmax
=
271 nm; 12: λmax = 269 nm; 15: λmax = 268 nm). The molar
absorptivity rises in the order 12 < 9 < 15, potentially because of
some planarization via BrꢀH (9, 12, 15) and/or BrꢀN (9)
interactions in solution, which seem to be increasing in strength
in the same order (9: εmax = 4080 L molꢀ1 cmꢀ1; 12: εmax = 3240
L molꢀ1 cmꢀ1; 15: εmax = 5290 L molꢀ1 cmꢀ1). Compounds 9
and 15 exhibit shoulders at 279 and 262 nm, respectively,
whereas in 12, only the low energy transition at 279 nm is
observed. The electrochemical properties (Table 2) of dibromo-
(phenylpyridine)s 9, 12, and 15 were studied by means of cyclic
voltammetry (CV) in acetonitrile solution with tetrabutylammo-
nium hexafluorophosphate ([NBu4][PF6]) as supporting elec-
trolyte, and Fc/Fcþ as internal reference (see Supporting
Information for details). All three compounds show irreversible
reductions at high potentials (9: Ered,peak = ꢀ2.75 V, ꢀ2.90 V;
12: Ered,peak = ꢀ2.72 V; 15: Ered,peak = ꢀ2.82 V) and two
irreversible oxidations (9: Eox,peak = 0.71 V, 0.94 V; 12: Eox,peak
=
0.78 V, 1.00 V; 15: Eox,peak = 0.75 V, 0.98 V). Compound 12
also exhibits an additional quasireversible reduction at Ered,1/2
ꢀ2.89 V, which overlaps with the irreversible reduction.
=
’ RESULTS AND DISCUSSION
2. Azadibenzophospholes and Azadibenzophosphole
Oxides. Syntheses and Structures. With the dibromo-
(phenylpyridine)s 9, 12, and 15 in hand, we then proceeded to
synthesize the corresponding azadibenzophospholes 1a, 3a, and
4a. The best results were observed with the use of t-BuLi as
metalating reagent, diethyl ether as solvent, ꢀ78 °C as tempera-
ture during the metalation reaction, and 1 h reaction time for
metalation. The synthesis of the azadibenzophospholes and
corresponding phosphole oxides 1a/b, 3a/b, and 4a/b is out-
lined in Scheme 3.
1. Phenylpyridine Starting Materials. Syntheses. Our tar-
geted synthetic approach toward the azadibenzophospholes 1ꢀ4
followed a strategy analogous to that toward the dithieno[3,2-
b:20,30-d]phosphole 619 and related systems20 that we have been
systematically investigating in recent years (Scheme 1).
Consequently, access to the corresponding dihalogenated phe-
nylpyridine precursors had to be verified first. The synthesis of
the starting material 9 for 1-azadibenzophosphole 1 proved to be
facile, starting from commercially available 2,3-dibromopyridine 7
(Scheme 2). Dibromopyridine 7 was cross-coupled to 2-bromo-
phenylboronic acid 8 to give 3-bromo-2-(2-bromophenyl)pyridine
9 in very good yield (92%) as colorless oil, which solidified
overnight. Consistent 1H and 13C NMR data as well as MS and
CHN analysis supported the successful formation of 9. The
preparation of the corresponding precursor for 2-azadibenzo-
phospholes 2 proved to be challenging and even after several
different synthetic attempts, the precursor could not be obtained.
By contrast, precursor 12 for the 3-azadibenzophospholes 3 was
obtained via a facile approach starting from commercially avail-
able 3-bromopyridine 10 (Scheme 2), which was converted to
3-bromo-4-iodopyridine 11 according to a known procedure.21
Subsequently, SuzukiꢀMiyaura coupling of 11 with boronic acid
8 gave 3-bromo-4-(2-bromophenyl)pyridine 12 in excellent yield
(90%). In addition to consistent NMR-, MS- and CHN-analysis,
the identity of 12 was confirmed by single crystal X-ray crystal-
lography (see Supporting Information). The synthesis of the
precursor for 4-azadibenzophospholes 4 was achieved using
2-chloro-3-iodopyridine 13, which was converted to the 3-(2-
bromophenyl)-2-chloropyridine 14 via the established Suzukiꢀ
Miyaura cross-coupling protocol (Scheme 2).22 Subsequent
treatment with neat tribromophosphane (PBr3) at elevated tem-
perature (140 °C) for 24 h yielded the 2-bromo-3-(2-bromo-
phenyl)pyridine 15 in good isolated yield (85%) as a colorless
solid and single crystals, suitable for X-ray crystallography (see
Supporting Information for details).
Note that all azadibenzophospholes exhibit an asymmetric
backbone structure, making the phosphorus atom a stereocenter.
Since the reaction conditions did not entail any stereospecific
reagents or additives, the products 1a,b, 3a,b and 4a,b were
obtained as racemic mixtures (vide infra). 1-Azadibenzophosp-
hole 1a and 4-azadibenzophosphole 4a were cleanly formed
under the reaction conditions, next to minor amounts of the
corresponding oxidized phosphole species 1b and 4b. The
trivalent species could, however, be isolated analytically pure as
slightly yellow powders in moderate yields after workup (1a:
58%; 4a: 69%). The phosphole oxides are formed in the presence
of traces of oxygen during workup and show significantly
increased polarity over their trivalent congeners because of the
generally very polar nature of the PdO bond. Since the back-
bones of the trivalent 1a and 4a exhibit only moderately polar
character overall, filtration over alumina with Et2O efficiently
separates the trivalent phospholes from the corresponding
oxides. In the case of 3-azadibenzophosphole 3a, however, the
position of the electronegative nitrogen atom evidently makes
the scaffold of the trivalent form considerably more polar, and the
difference in polarity between phosphole 3a and phosphole oxide
3b appears much less pronounced than in the other congeners.
Consequently, phosphole 3a and the corresponding oxide 3b
(∼10%) could not be separated by column chromatography, or
by crystallization from various solvents.
The successful formation of the phospholes 1a, 3a, and 4a was
supported by multinuclear NMR spectroscopy; 1H NMR
analysis indicated the expected additional signals for the P-phenyl
substituent. It is interesting to note that all resonances of the
P-phenyl group in compounds 1a and 3a fall together in one broad
Photophysics and Electrochemistry. The UV/vis spectra of
the dibromo(phenylpyridine)s 9, 12, and 15 (see Supporting
Information) were measured in dilute dichloromethane
(DCM) solution and are summarized in Table 2. All three
6828
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
Table 2. Photophysical and Electrochemical Data for 9, 12, and 15
Compd
λabsa [nm]
εmaxa [L molꢀ1 cmꢀ1
]
Ered,peakb [V]
Ered,1/2c [V]
Eox,peakd [V]
9
271
269
268
4080
3240
5290
ꢀ2.75/-2.90
ꢀ2.72
0.71/0.94
0.78/1.00
0.75/0.98
12
15
ꢀ2.89
ꢀ2.82
a UV/vis absorption maxima in CH2Cl2. b Irreversible reduction peak potentials vs Fc/Fcþ. c Quasireversible reduction half-step potential vs Fc/Fcþ.
d Irreversible oxidation peak potentials vs Fc/Fcþ.
Scheme 3. Synthesis of Azadibenzophospholes 1a, 3a, and 4a
and the Corresponding Oxides 1b, 3b, and 4b
multiplet (δ 1H = 7.35ꢀ7.20 ppm), while the resonances for the
P-phenyl substituent in 4-azadibenzophosphole 4a split into two
1
groups (δ H = 7.33ꢀ7.23 ppm [3 H] and 7.44ꢀ7.38 ppm
Figure 1. Molecular structure of 1b (left) and packing diagram (right)
in the solid state (50% probability level, H-atoms are omitted for clarity).
[2 H]), probably because of some through-space NꢀH interac-
tions of the o-hydrogens on the phenyl-ring with the nitrogen in
Selected bond lengths [Å] and angles [deg]: P1ꢀC1 1.804(2), P1ꢀC10
the backbone. Furthermore, the appearance of characteristic 31P
1.809(2), P1ꢀC20 1.799(2), P1ꢀO1 1.4850(16), N1ꢀC2 1.344(3),
NMR resonances indicated the presence of trivalent azadibenzo-
N1ꢀC3 1.341(3), C1ꢀC2 1.401(3), C3ꢀC4 1.386(4), C4ꢀC5
phosphole species (δ 31P = ꢀ16.5 (1a); ꢀ12.3 (3a); ꢀ14.8 (4a)
1.392(4), C1ꢀC5 1.385(3), C2ꢀC11 1.477(3), C10ꢀC11 1.397(3),
ppm). All 31P NMR signals are shifted upfield relative to dibenzo-
phosphole (δ 31P = ꢀ11.7 ppm)23 and downfield relative to
dithienophosphole 6 (E = lone pair; δ 31P = ꢀ21.5 ppm).19a,b
The oxidation to the corresponding phosphole oxides, according
to the established procedure,19a,b proceeded cleanly in excellent
isolated yields for 1b (95%) and 4b (89%). Phosphole oxide 3b was
cleanly obtained from 15 in 69% isolated yield over two steps. The
oxidation of the phosphorus centers resulted in significant downfield
shifts of the 31P NMR resonances (δ 31P = 29.7 (1b); 34.0 (3b);
25.1 (4b) ppm), comparable to that of dibenzophosphole oxide
DBPO (δ 31P = 31.4 ppm).24 In the case of 1b and 4b, the
successful formation was furthermore confirmed by single-crystal
X-ray crystallography (Figures 1 and 2; Table 1). For both
compounds, single-crystals could be obtained from a concentrated
ethanol solution upon evaporation of the solvent at room tempera-
ture. The structure of 1b showcases a planar backbone with only
small CꢀC bond-length alternation. Compound 1b exhibits endo-
and exocyclic PꢀC bonds of essentially equal length (1.799(2)ꢀ
1.809(2) Å), comparable to those observed in dibenzophos-
phole oxide DBPO (1.798(3)ꢀ1.801(3) Å).25 The PꢀO
distance in 1b (1.4850(16) Å) correlates well to the analogous
bond length in DBPO (1.475(2) Å). Similarly, the bond angles
around the phosphorus atom are in good agreement with
those observed in DBPO.25 In the packing motif, close π-stacking
interactions (3.35 Å) are observed between inversion-related pairs of
enantiomers.
C11ꢀC12 1.384(3), C12ꢀC13 1.386(4), C13ꢀC14 1.380(4),
C14ꢀC15 1.392(4), C10ꢀC15 1.385(3), C20ꢀC21 1.399(3),
C21ꢀC22 1.386(3), C22ꢀC23 1.382(4), C23ꢀC24 1.384(4),
C24ꢀC25 1.388(3), C20ꢀC25 1.393(3); C1ꢀP1ꢀC10 92.00(10),
C1ꢀP1ꢀC20 108.13(9), C10ꢀP1ꢀC20 107.13(10), C1ꢀP1ꢀO1
117.85(10), C10ꢀP1ꢀO1 116.90(10), C20ꢀP1ꢀO1 112.70(10).
those observed in dibenzophosphole oxide DBPO. The PꢀO
distance in 4-azadibenzophosphole 4b (1.4856(17) Å) as well as
the bond angles around the phosphorus center are in good
agreement with the corresponding bond lengths and angles in
DBPO.25 However, in the packing motif, some differences
between 1b and 4b can be observed. Compound 4b exhibits
somewhat weaker π-stacking interactions (3.44 Å) between
inversion-related pairs of enantiomers. Another difference in the
packing motif is seen in the overlap between the molecules. In
contrast to 1b, the overlap of the π-systems in 4b is significant,
involving almost the whole annelated ring system. However, no
close face-to-face interactions between the phenyl-substituents are
observed.
Photophysics and Electrochemistry of Azadibenzophospholes
and Oxides. In contrast to the dithienophosphole system, none
of the azadibenzophospholes and corresponding oxides shows
notable photoluminescence. The azadibenzophospholes 1a, 3a,
and 4a, in analogy to dibenzophosphole,15 were found to oxidize
readily in the presence of air (traces) plecluding meaningful UV/
vis-spectroscopical studies. The electrochemical properties were
determined via cyclic voltammetry, performed under inert gas
atmosphere (Table 3). However, significant reduction peaks
corresponding to the analogous oxides can be found in all
cyclic voltammograms for the azadibenzophospholes (see Sup-
porting Information). Compounds 1a and 4a show very similar
electrochemical characteristics with irreversible reductions at
Ered,1/2 = ꢀ2.69 V and ꢀ2.67 V, respectively. In the analyzed
The πꢀoverlap between the molecules is small; only C3, N1,
C12, and C13 of the respective molecules are in the overlapping
region. No close face-to-face interactions between the phenyl-
substituents are observed. Similar to the structure of 1b, com-
pound 4b features a planar backbone with little CꢀC bond-length
alternation, which is an expected result for 6π-electron N-hetero-
and carbocycles. Compound 4b also exhibits equally long endo-
and exocyclicPꢀC bonds (1.800(2)ꢀ1.809(2) Å), comparable to
6829
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
range, the 3-aza-isomer 3a only shows one quasireversible reduc-
tion at Ered,1/2 = ꢀ2.55 V. However, multiple irreversible oxida-
tions in the range between Eox,peak = 0.52 and 1.18 V are also
observed for all compounds (Table 3).
On the basis of our earlier studies,14f,20c we anticipated the
phosphole oxide series 1b, 3b, and 4b to be more interesting in
terms of their electron-accepting features than the above-men-
tioned trivalent phospholes 1a, 3a, and 4a. The photophysical
properties of the azadibenzophosphole oxides were determined
in dilute (c ∼ 10ꢀ5 M) dichloromethane solution, and the UV/
vis spectra are depicted in Figure 3. The three phosphole oxides
1b, 3b, and 4b show absorption maxima in a narrow range within
the UV-region of the optical spectrum (276ꢀ284 nm) with
absorption coefficients rising in the order 3b < 1b < 4b (Table 3).
The position of the nitrogen atom in the backbone does
influence the charge distribution and concomitantly the transi-
tion dipole moment within the molecule, resulting in the
observed molar absorptivities. It is interesting to see that DBPO
shows a significantly smaller absorption coefficient (by a factor of
14ꢀ18), probably because of the symmetry, leading to weaker,
forbidden electronic transitions.15 DBPO shows a red-shifted
absorption maximum (Δλ = 48ꢀ56 nm), but it should be noted
that the aza-congeners 1b, 3b, and 4b show weak to medium
intensity shoulders in the same range of the optical spectrum.
Compared to the dibromo(phenylpyridine)s 9, 12, and 15, the
absorption maxima are only red-shifted by ∼10 nm, the onset of
absorption, however, experiences a more significant bathochro-
mic shift (∼40 nm), indicating the increased size of the con-
jugated system by planarization of the backbone.
Figure 2. Molecular structure of 4b (left) and packing diagram (right)
in the solid state (50% probability level, H-atoms are omitted for clarity).
Selected bond lengths [Å] and angles [deg]: P1ꢀC1 1.809(2), P1ꢀC10
1.804(2), P1ꢀC20 1.800(2), P1ꢀO1 1.4856(17), N1ꢀC1 1.361(3),
N1ꢀC5 1.375(4), C1ꢀC2 1.398(3), C2ꢀC3 1.398(3), C3ꢀC4
1.387(4), C4ꢀC5 1.370(5), C2ꢀC11 1.479(3), C10ꢀC11 1.405(3),
C11ꢀC12 1.388(3), C12ꢀC13 1.383(4), C13ꢀC14 1.383(4),
C14ꢀC15 1.372(4), C10ꢀC15 1.360(3), C20ꢀC21 1.398(3),
C21ꢀC22 1.388(3), C22ꢀC23 1.393(3), C23ꢀC24 1.380(3),
C24ꢀC25 1.386(3), C20ꢀC25 1.391(3); C1ꢀP1ꢀC10 91.70(11),
C1ꢀP1ꢀC20 108.97(10), C10ꢀP1ꢀC20 107.08(10), C1ꢀP1ꢀO1
116.97(10), C10ꢀP1ꢀO1 117.96(10), C20ꢀP1ꢀO1 112.17(10).
The electrochemical features of the azadibenzophosphole
oxides were determined by cyclic voltammetry (Figure 4).
In contrast to the trivalent phospholes 1a, 3a, and 4a, the
corresponding oxides showed no significant oxidation waves in
the oxidative regime up to a potential of 1.05 V. Importantly,
reversible reduction waves are observed for all phosphole oxides.
The azadibenzophosphole oxides show half-step reduction po-
tentials at Ered,1/2 = ꢀ2.30 V (1b), ꢀ2.14 V (3b), and ꢀ2.27 V
(4b), respectively. These values are comparable to those of
IVa/b, indicating a potential application as electron-transporting
or hole-blocking material.11i The reduction potential of 3b is
lower than those of 1b and 4b, indicating that the 4-phenylpyr-
idine backbone stabilizes the LUMO more effectively than the
other scaffolds. As anticipated, the reduction potentials decrease
significantly upon oxidation (Table 3). Furthermore, it should
be noted that there is a clear transition from an irreversible (or
quasireversible) to a reversible reduction behavior upon oxida-
tion of the phospholes to the corresponding oxides. Since the
materials showed reversible one-electron reduction events,
Figure 3. UV/vis absorption spectra of 1b, 3b, and 4b in DCM
(c ∼ 10ꢀ5 M).
Table 3. Photophysical and Electrochemical Data for Azadibenzophospholes 1a, 3a, 4a, Corresponding Phosphole Oxides 1b, 3b,
4b and Dibenzophosphole Oxide DBPO15
λabsa [nm]
εmaxa [L molꢀ1 cmꢀ1
]
Ered,1/2 [V]
Eox,peake [V]
ELUMOf [eV]
kETg [cm sꢀ1
]
1a
ꢀ2.69b
ꢀ2.55c
ꢀ2.67b
ꢀ2.30d
ꢀ2.14d
ꢀ2.27d
ꢀ2.33d
0.52/0.75/1.08
0.68/1.18
ꢀ2.11
ꢀ2.25
ꢀ2.13
ꢀ2.50
ꢀ2.66
ꢀ2.53
ꢀ2.47
3a
4a
0.58/1.13
1b
284
276
280
332
13,000
11,330
14,900
800
7.04 ꢁ 10ꢀ4
1.61 ꢁ 10ꢀ3
6.45 ꢁ 10ꢀ4
3b
4b
DBPO
a UV/vis absorption maxima in CH2Cl2. b Irreversible reduction half step potentials vs Fc/Fcþ. c Quasireversible reduction half-step potential vs Fc/Fcþ.
d Reversible reduction half-step potential vs Fc/Fcþ. e Irreversible oxidation peak potentials vs Fc/Fcþ. f Calculated using the ferrocene HOMO level at
-(4.8 þ Ered,1/2) eV. g Calculated according to Nicholson.26
6830
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
Table 4. Calculated Energies for Selected Orbitals of the
Azadibenzophosphole (1aꢀ4a) and Azadibenzophosphole
Oxide (1bꢀ4b) Seriesa
1a
2a
3a
4a
1b
2b
3b
4b
ELUMO/eV ꢀ1.53 ꢀ1.60 ꢀ1.75 ꢀ1.56 ꢀ1.97 ꢀ2.16 ꢀ2.20 ꢀ2.00
EHOMO/eV ꢀ6.38 ꢀ6.44 ꢀ6.51 ꢀ6.37 ꢀ6.72 ꢀ6.80 ꢀ6.99 ꢀ6.71
EHOMO-1/eV ꢀ6.45 ꢀ6.61 ꢀ6.68 ꢀ6.41 ꢀ7.20 ꢀ7.28 ꢀ7.26 ꢀ7.02
EHOMO-2/eV ꢀ7.11 ꢀ7.11 ꢀ7.04 ꢀ7.01 ꢀ7.28 ꢀ7.36 ꢀ7.35 ꢀ7.23
a Calculated with Gaussian 03, Revision E.01; B3LYP/6-31Gþ(d) level
of theory.18
Figure 5. Frontier orbital diagrams for 1-aza-isomers 1a (left, E = lone
pair) and 1b (right, E = O).
Figure 4. Cyclic voltammograms of 1b (top), 3b (center), and 4b
(bottom) in acetonitrile solution, [NBu4][PF6] as supporting electro-
lyte, potential E referenced vs Fc/Fcþ.
electron transfer processes, well within the range of thiadiazole,
thiadiazole-oxide, and -dioxide fused phenanthrenes and pyrenes,
which have previously been reported by our group.7 Rapid
electronic processes are beneficial for an application in electronic
devices, since charge-transfer phenomena in organic electronics
are generally in the nano- to picosecond regime.27
Theoretical Calculations. To better understand the electronic
and photophysical characteristics, density functional theory
(DFT) calculations (B3LYP/6-31Gþ(d)) have been performed
on the azadibenzophospholes 1aꢀ4a and the corresponding
oxides 1bꢀ4b, to determine their frontier orbital energies
(Table 4).18 Since the orbital structures are similar within the
respective series, only selected orbitals (HOMO-2ꢀLUMO) for
1-azadibenzophosphole 1a and 1-azadibenzophosphole oxide 1b
assessed by the separation between anodic and cathodic peak
potentials, their electron transfer kinetics kET were evaluated
(Table 3).26 Cyclic voltammograms were measured at different
scan rates and kET extracted from the peak positions and heights.
1-Aza-isomer 1b and 4-aza-isomer 4b show similar kET values
(kET = 7.04 ꢁ 10ꢀ4 cm sꢀ1 (1b); 6.45 ꢁ 10ꢀ4 cm sꢀ1 (4b)),
whereas 3-azadibenzophosphole oxide 3b exhibits a slightly in-
creased value (kET = 1.61 ꢁ 10ꢀ3 cm sꢀ1), probably because of
the more polar backbone structure, resulting in higher mobility in
an electric field. Overall, the obtained kET values indicate fast
6831
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
Table 5. Calculated Electronic Transitions and Oscillator
Scheme 4. Reactivity of Azadibenzophospholes 1b, 3b, and
4b toward Pt(II)
Strengths f for Azadibenzophosphole Oxides 1b, 3b, and 4ba
1b
3b
4b
λ [nm] 303
0.030
305
304
f
0.010
0.004
transition HOMOꢀLUMO
HOMO-1ꢀLUMO HOMOꢀLUMO
λ [nm] 285
296
292
f
0.088
0.036
0.028
transition HOMO-2ꢀLUMO HOMOꢀLUMO HOMO-1ꢀLUMOþ1
λ [nm] 277
0.006
284
286
f
0.008
0.062
transition HOMOꢀLUMOþ1 HOMO-2ꢀLUMO HOMOꢀLUMOþ1
a TD-DFT calculations with Gaussian 03, Revision E.01; B3LYP/6-
31Gþ(d) level of theory.18
are depicted in Figure 5 (for additional orbital diagrams, see
Supporting Information). The LUMO and HOMO orbital
diagrams show a major contribution from the π-system of the
backbone for both 1-aza-isomer 1a and oxide 1b.
center after, for example, a preceding cross-coupling reaction,
generally requiring protection of the phosphorus to avoid
poisoning of the catalyst.19c The reduction of dithienophos-
pholes is accomplished via treatment with borane and subsequent
addition of triethylamine. In the case of the azadibenzophos-
pholes, this approach was anticipated to be not suitable, because
of the presence of the imine-nitrogen in the backbone, which
would readily coordinate to the borane. The approach investi-
gated for the reduction of the phosphole oxide moiety in this
study, involved the treatment of 1-aza-isomer 1b with trin-
butylphosphane.28 Compound 1b was dissolved in freshly de-
gassed benzene-D6 and an excess of phosphane added and
sonicated for 1 h at 60 °C. However, 31P NMR spectroscopy
did not provide the resonance corresponding to the reduced,
trivalent phosphole, suggesting that reduction cannot be
achieved according to the outlined procedure, potentially be-
cause of the electron-poor nature of the backbone, which could
strengthen the PꢀO bond.20b,c
For 1a, the highest occupied molecular orbital (HOMO) also
shows significant contribution from the phosphorus lone pair.
The HOMO-1 orbitals show contribution from the nitrogen lone
pair for both the phospholes and phosphole oxides. In the case of
1a, the HOMO-1 also shows some contribution from the
nitrogen lone pair, whereas in 1b, the π-system and the phenyl
substituents are major contributors. In contrast to 1b, the
HOMO-2 level in 1a still shows some nitrogen lone pair
character. In accordance with the electrochemical data, the
calculations clearly indicate that the oxidation of the phospholes
lead to significant stabilization of the LUMO energy levels (ΔE
∼ 0.4ꢀ0.5 eV). It is also interesting to note that the calculated
energies are very similar for the respective pairs 1a/4a, 2a/3a,
1b/4b, and 2b/3b. The electrochemical data confirm the simi-
larity for the sets 1a/4a and 1b/4b (Table 4), giving rise to the
assumption that 2-aza-isomer 2a,b (not obtained synthetically)
likely exhibits electrochemical properties comparable to the
3-aza-congener 3a,b. In addition to the orbital energy levels,
the electronic spectra for the synthetically accessible azadiben-
zophosphole oxides 1b, 3b, and 4b were modeled via TD-DFT
calculations (Table 5). The agreement between the calculated
and measured UV/vis spectra is fair; all calculated spectra show
onsets within 10ꢀ20 nm of the experimentally determined data,
resulting from HOMOꢀLUMO (1b, 4b) or HOMO-1ꢀLUMO
(3b) transitions. Other significant transitions are listed in Table 5
and include transitions from the HOMO-2ꢀHOMO orbitals to
the LUMO or LUMOþ1 energy levels, respectively. Although
the experimentally observed absorptivities are not matched very
well by the calculated data, it should be noted that the calculated
absorption coefficients agree better with experimental data in the
low-energy portion (275ꢀ350 nm) of the absorption spectra. In
the high-energy range of the spectra (240ꢀ270 nm); however,
the correlation between calculated and measured photophysical
data is poor.
Metal Coordination. The presence of a Lewis-basic nitrogen
center in the backbone of azadibenzophospholes gives rise to a
potential application for the materials as N-donor ligands in combina-
tion with transition metals. To explore the coordination behavior of
the azadibenzophosphole scaffold and the resulting effect of the
functionalization on the photophysical and electronic properties,
different Pt-species were reacted with the azadibenzophosphole
oxides. Since the 1-azadibenzophosphole oxide 1b incorporates a
backbone analogous to 2-phenylpyridine, cyclometalation was at-
tempted (Scheme 4). It has been shown that cyclometalation of
phenylpyridines with platinum gives rise to phosphorescence, tunable
in color via the electronic features of the chelate ligand.29
However, treatment of the 1-aza-isomer 1b with either
[Pt(acac)(DMSO)Cl], or K2PtCl4/acac (acac = acetylacetonate),
according to reported procedures,29a,b did not result in the
formation of the target complex 16. Only starting materials or
inseparable decomposition products could be observed under
varying conditions, respectively.
3. Chemical Modification of the Azadibenzophosphole
Scaffold. Attempted Reduction of 1-Azadibenzophosphole
Oxide 1b. As shown in previous work, phosphole oxides can
often be reduced to the corresponding trivalent species, which
presents an interesting way to functionalize the phosphorus
It should be noted that the reported procedures use non-
bridged phenylpyridines as starting materials, giving rise to the
assumption that the phenylpyridine-unit in 1b is an unsuitable
scaffold for cyclometalation. The lack of success in the synthesis
6832
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
of 16 can be rationalized by the distortion of the phenylpyridine
backbone because of the bridging phosphorus, widening the bite-
angle of the prospective ligand, thus providing an unfavorable
geometry for cyclometalation with platinum. Since the 3- and
4-aza-isomers 3b and 4b possess potentially accessible nitrogen
donor centers, the Pt-pyridine complexes 17 and 18 (Scheme 4)
were established as our next synthetic targets. The azadibenzo-
phosphole oxides 3b and 4b were dissolved in ethanol and
treated with K2PtCl4, dissolved in water at 50 °C. In the case of
the 3-aza-isomer 3b, a precipitate started to form after 15 min,
whereas no visible change was observed in the reaction with 4b,
even after stirring for 16 h at 50 °C. After workup, NMR
spectroscopy on crude product 18 revealed the presence of
starting material 4b only. The inaptness of 4b to act as a ligand
can be rationalized with its steric and electronic characteristics;
quite possibly, the environment around the nitrogen is sterically
too congested to accommodate a metal in its vicinity. In terms of
electronic properties, the nitrogen lone pair likely exhibits
reduced donor-capability because of the electron-withdrawing
effect of the oxidized phosphorus in ortho-position.
Scheme 5. Reactivity of 4a toward MeOTf and Au(tht)Cl
Reactivity Toward a Lewis-Acid and Subsequent Metal Coordi-
nation. Since the trivalent azadibenzophospholes incorporate two
Lewis-basic functionalities, that is, the nitrogen and the phosphorus
center, their relative basicity was investigated by treatment of
4-azadibenzophosphole 4a with 1 equiv of methyltriflate
(MeOTf), added in five increments. After each addition, a sample
was taken and a 31P NMR spectrum measured showing a clean
conversion of 4a (δ 31P = ꢀ14.8 ppm) to a single product (δ 31P =
ꢀ10.4 ppm) upon addition of 1 equiv of MeOTf (see Supporting
Information). Previous studies on the dithienophosphole36 and
related systems14f,20c have shown that the methylation of the
phosphorus center leads to a downfield shift of the 31P NMR
resonance by ∼34ꢀ43 ppm and the occurrence of a 1HNMRsignal
(doublet) with a characteristic coupling constant of ∼15 Hz. In the
case presented here, the difference in the 31P NMR resonance is
However, more success was observed in the synthesis of Pt-
complex 17, which was obtained in moderate yield (62%) as white
powder. The 31P NMR resonance of 17 (δ 31P = 32.1 ppm) is
shifted upfield by 1.9 ppm compared to that of starting material 3b
1
merely 4.5 ppm, and the H NMR signal corresponding to the
1
(δ 31P = 34.0 ppm). Furthermore, the H NMR shifts of the
methyl-group shows no coupling (singlet). These results clearly
support the methylation at the nitrogen, rather than the phosphorus
center (Scheme 5), indicating that the imine-fragment in the
backbone is significantly more Lewis-basic than the phosphorus
center.
hydrogen atoms adjacent to the nitrogen, showing a downfield
displacement by ∼0.2 ppm, as well as the occurrence of a 195Pt
NMR resonance (δ 195Pt = ꢀ312.2 ppm), indicated the successful
formation of complex 17. The 195Pt NMR resonance is shifted
significantly downfield compared to cis-[Pt(py)2Cl2] (δ 195Pt =
ꢀ2014 ppm), probably because of the electron-withdrawing
nature of the phosphole oxide-containing ligand.30 trans-[Pt-
(py)2Cl2] shows a 195Pt NMR resonance a δ 195Pt = ꢀ1964
ppm,30 allowing no clear assignment of the configuration of
complex 17. However, cis-configured Pt-complexes are commonly
formed under the applied reaction conditions.31 The electroche-
mical properties of 17 were probed via cyclic voltammetry (see
Supporting Information). The analysis revealed multiple irrever-
sible reduction events (Ered,peak = ꢀ1.80 V, ꢀ2.06 V, ꢀ2.22 V,
ꢀ2.58 V) probably because of sequential reduction of the ligands
and the metal center. Furthermore, an irreversible oxidation (Eox,
peak = ꢀ0.96 V) was observed, likely caused by oxidation of the
metal center.32 The photophysical properties of compound 17
were investigated by means of UV/vis spectroscopy (see Support-
ing Information). Very strong absorption bands in the UV range of
the optical spectrum were observed (λabs = 333 nm, ε333 = 148,700
This result is consistent with experimentally determined pKa
values for the conjugate acids of 1-methylphosphole (pKa = 0.5)37
and pyridine (pKa =5.2),38 indicating that pyridine is a stronger base
than phosphole. To investigate whether the phosphorus center is
still basic enough for further functionalization, the MeOTf-adduct
19 was subsequently treated with 1 equiv of [Au(tht)Cl] (tht =
tetrahydrothiophene; Scheme 5) to give gold-complex 20 as off-
white, crystalline solid in moderate isolated yield (54%). The
formation of 20 was indicated by a significant shift of the 31P
NMR resonance (δ 31P = 25.8 ppm), clearly showing that a reaction
occurred at the phosphorus center. The electrochemical properties
of 20 were investigated via cyclic voltammetry (see Supporting
Information). The analysis revealed two irreversible reduction
events (Ered,peak = ꢀ1.21 V, ꢀ2.28 V, vs Fc/Fcþ) likely because
of sequential reduction of the metal center and the ligand. Further-
more, an irreversible oxidation (Eox,peak = 0.13 V, vs Fc/Fcþ)
occurred after the first reductive sweep, indicating decomposition
of the complex under reductive conditions. The appearance of the
oxidative wave is the result of the oxidation of the decomposition
products formed during the reductive sweeps. The photophysical
properties of compound 20 were investigated by means of UV/vis
spectroscopy (see Supporting Information). Medium to strong
absorption bands in the UV range of the optical spectrum were
L molꢀ1 cmꢀ1; λabs = 287 nm, ε287 = 115,700 L molꢀ1 cmꢀ1
;
λabs = 255 nm, ε255 = 290,400 L molꢀ1 cmꢀ1), probablybecause of
electronic decoupling of the ligands into two independent chro-
mophores. Similar behavior with a significant increase of the molar
absorptivity has been observed for a dithienophosphole oxide-
capped, biphenyl bridged oligomer;33 however, the increase in the
extinction coefficient is much more substantial for 17, possibly
because of metal to ligand charge transfer (MLCT) nature of the
bands.34 The absorption wavelengths are in fair agreement
observed (λmax = 337 nm, ε337 = 4180 L molꢀ1 cmꢀ1; λshoulder
=
299 nm, ε299 = 19,720 L molꢀ1 cmꢀ1; λmax = 290 nm, ε299 = 21,440
L molꢀ1 cmꢀ1), that relate well to the absorption features seen in
the Pt-complex 17 and azadibenzophosphole oxide 4b. The increase
in molar absorptivity compared to 4b is likely also a result of the
MLCT nature of the bands.34
with those observed in cis-[Pt(py)2Cl2] (λabs = 310 nm, ε310
1800 L molꢀ1 cmꢀ1; λabs = 280 nm, ε280 = 6660 L molꢀ1 cmꢀ1
λabs = 238 nm, ε238 = 12,100 L molꢀ1 cmꢀ1 34 and azadibenzo-
=
;
)
Halogenation and Cross-Coupling. We were interested to see
whether it was possible to further functionalize the backbone of
the azadibenzophosphole scaffold by halogenation, which would
subsequently allow extension of the building blocks via cross-
phosphole oxide 3b (Figure 3), albeit with significantly higher
extinction coefficients for 17. The pronounced changes in the
absorption behavior upon metal complexation suggest a potential
use for 3b in the context of molecular sensors.35
6833
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
Scheme 6. Bromination and Subsequent Cross-Coupling of
4b
Figure 6. Molecular structure of 21 (left) and packing diagram (right)
in the solid state (50% probability level, H-atoms are omitted for clarity).
Selected bond lengths [Å] and angles [deg]: P2ꢀC1 1.813(5), P2ꢀC10
1.805(5), P2ꢀC20 1.800(5), P2ꢀO1 1.478(4), N1ꢀC1 1.340(6),
N1ꢀC5 1.362(7), C22ꢀBr1 1.904(5), C1ꢀC2 1.393(6), C2ꢀC3
1.393(7), C3ꢀC4 1.379(7), C4ꢀC5 1.385(7), C2ꢀC11 1.478(6),
C10ꢀC11 1.404(6), C11ꢀC12 1.395(6), C12ꢀC13 1.381(7),
C13ꢀC14 1.385(8), C14ꢀC15 1.386(7), C10ꢀC15 1.381(7),
C20ꢀC21 1.397(6), C21ꢀC22 1.378(7), C22ꢀC23 1.375(8),
C23ꢀC24 1.393(7), C24ꢀC25 1.387(6), C20ꢀC25 1.404(7);
C1ꢀP2ꢀC10 91.4(2), C1ꢀP2ꢀC20 106.2(2), C10ꢀP2ꢀC20
109.0(2), C1ꢀP2ꢀO1 117.9(2), C10ꢀP2ꢀO1 117.0(2),
C20ꢀP1ꢀO1 113.1(2).
coupling reactions with aromatic groups. Previous studies have
shown that extension of the conjugated scaffold leads to dramatically
altered photophysical and electronic properties, which allows tuning
of these features to a targeted application.19c,f,33 It should be noted
that substituted dibenzophosphole oxides are usually synthesized via
precursor routes, starting from suitably functionalized biphenyls that
are subsequently transformed into the phosphole derivatives.39
However, because of the difference of the backbone, we anticipated
that direct halogenation with N-bromosuccinimide (NBS) may be
possible for the azadibenzophospholes. Initially, standard condi-
tions, established for the bromination of dithienophosphole 6, were
applied.19c However, no conversion was observed after treatment of
4b with NBS in refluxing chloroform/acetic acid or DMF (rt or
100 °C). This result can be rationalized by the electron-poor nature
of the azadibenzophosphole oxide system, rendering it strongly
deactivated for electrophilic attack by the brominating agent.
According to a procedure for the bromination of deactivated
arenes,40 the bromination of 4b was then attempted with 1.6 equiv
of NBS in trifluoroacetic acid (TFA)/sulfuric acid in the dark
overnight. After workup, NMR spectroscopy indicated the
formation of several species, one of which could be isolated in
Subsequently, compound 21 was subjected to a proof-of-
principle Stille cross-coupling with commercially available 2-tri-
n-butylstannylpyridine 22 to investigate whether the brominated
4-aza-derivative could be further functionalized (Scheme 6). The
reaction proceeded cleanly, and the azadibenzophosphole-func-
tionalized phenylpyridine derivative 23 was obtained as white
solid in good isolated yield (76%). The successful formation of
23 was indicated by occurrence of the expected additional 1H and
13C NMR resonances as well as a downfield shift of the 31P NMR
resonance (δ 31P = 25.2 ppm), compared to starting material 21
(δ 31P = 23.6 ppm).
’ CONCLUSION
In conclusion, we have succeeded in synthesizing and character-
izing a series of novel azadibenzophospholes and -phosphole oxides
and their respective precursors. The azadibenzophosphole oxides in
particular, exhibit intriguing electrochemical properties, such as
reversible reduction potentials with fast electron-transfer rates,
comparable to established electron-transporting or hole-blocking
materials, making the new compounds promising materials for an
application in organic electronics. These results were supported by
DFT calculations. It has been shown that the position of the
nitrogen in the backbone has some influence on the electrochemical
and photophysical features, but significant impact of the coordina-
tion behavior toward transition metals. Pt(II)-coordination to an
extended 3-azadibenzophosphole oxide led to significantly increased
absorption features, when compared with established pyridine
complexes of Pt2þ, whereas the other isomers do not show any
utility as ligands, largely because of the results of the steric bulk or
distortion of the scaffold, respectively. The relative basicity of the
nitrogen to the trivalent phosphorus center in the scaffold has been
determined qualitatively and is in agreement to the expected trend
for pyridine and phosphole species. Finally, an interesting regio-
chemistry for bromination reactions has been observed, giving rise
to a potential incorporation of the electroactive azadibenzophosp-
hole scaffold as a pendant side chain into conjugated oligomers.
1
32% yield, and identified as monobrominated 21 by H NMR
spectroscopy (Scheme 6). To establish where the functionaliza-
tion specifically took place, the 13C NMR spectrum was
analyzed. The number of signals clearly proved that a desymme-
trization of the exocyclic phenyl-substituent occurred, meaning
that the bromination must have unexpectedly occurred at the
ortho- or meta-position of the phenyl ring. The formation of the
brominated species was accompanied by an upfield shift of
the 31P NMR resonance (δ 31P = 23.6 (21); cf. 4b: δ 31P = 25.1
ppm), but the site of the bromination (meta) was finally
unambiguously proven by single-crystal X-ray crystallography
(Figure 6; Table 1). The molecular structure of 21 in the solid
state corresponds well to the ones described above, exhibiting a
planar backbone with little bond length alternation.
All bond lengths and angles are in good agreement with the
structures for 1- and 4-aza-isomers 1b and 4b, as well as dibenzo-
analogue DBPO. The packing motif of 21 shows close π-stacking
interactions (3.37 Å) between the π-systems of pairs of enantiomers,
as seen previously. Furthermore, the structure exhibits face-to-face
interactions (3.60 Å) between the phenyl-groups.
6834
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
The feasibility of cross-coupling reactions of a brominated species
has been demonstrated and further investigation with regard to
the ligand properties of 23 as well as the incorporation of the
azadibenzophosphole-functionalized phenylpyridine 21 into
π-conjugated oligomers are currently underway and will be
reported in due course. The same is true for the verification of
the electron-transfer capability of the azadibenzophospholes 1b,
3b, and 4b in corresponding devices.
Leclerc, M. Acc. Chem. Res. 2008, 41, 1110–1119. (c) Boudreault, P.-L.
T.; Beauprꢀe, S.; Leclerc, M. Polym. Chem. 2010, 1, 127–136.
(6) (a) Usta, H.; Facchetti, A.; Marks, T. J. Org. Lett. 2008,
10, 1385–1388. (b) Ren, Y.; Dienes, Y.; Hettel, S.; Parvez, M.; Hoge,
B.; Baumgartner, T. Organometallics 2009, 28, 734–740. (c) Ahmed, E.;
Earmme, T.; Ren, G.; Jenekhe, S. A. Chem. Mater. 2010, 22, 5786–5796.
(7) (a) Linder, T.; Sutherland, T. C.; Baumgartner, T. Chem.—Eur.
J. 2010, 16, 7101–7105. (b) Linder, T.; Badiola, E.; Baumgartner, T.;
Sutherland, T. C. Org. Lett. 2010, 12, 4520–4523.
(8) (a) Newman, C. R.; Frisbie, C. D.; da Silva Filho, D. A.; Brꢀedas,
J.-L.; Ewbank, P. C.; Mann, K. R. Chem. Mater. 2004, 16, 4436–4451. (b)
Kappaun, S.; Slugovc, C.; List, E. J. W. Int. J. Mol. Sci. 2008,
9, 1527–1547.
’ ASSOCIATED CONTENT
S
Supporting Information. X-ray crystallographic data of
b
(9) (a) Bao, Z.; Lovinger, A. J.; Brown, J. J. Am. Chem. Soc. 1998,
120, 207–208. (b) Sakamoto, Y.; Suzuki, T.; Kobayashi, M.; Gao, Y.;
Fukai, Y.; Inoue, Y.; Sato, F.; Tokito, S. J. Am. Chem. Soc. 2004,
126, 8138–8140. (c) Swartz, C. R.; Parkin, S. R.; Bullock, J. E.; Anthony,
J. E.; Mayer, A. C.; Malliaras, G. G. Org. Lett. 2005, 7, 3163–3166.
(10) (a) Usta, H.; Risko, C.; Wang, Z.; Huang, H.; Deliomeroglu,
M. K.; Zhukhovitskiy, A.; Facchetti, A.; Marks, T. J. J. Am. Chem. Soc.
2009, 131, 5586–5608. (b) Jones, B. A.; Facchetti, A.; Wasielewski,
M. R.; Marks, T. J. Chem. Mater. 2007, 19, 2703–2705. (c) Andrew,
T. L.; Cox, J. R.; Swager, T. M. Org. Lett. 2011, 12, 5302–5305.
(11) (a) Hsu, F.-M.; Chien, C.-H.; Shih, P.-I.; Shu, C.-F. Chem.
Mater. 2009, 21, 1017–1022. (b) Jeon, S. O.; Yook, K. S.; Joo, C. W.; Lee,
J. Y. Adv. Funct. Mater. 2009, 19, 3644–3649. (c) Hsu, F.-M.; Chien,
C.-H.; Shu, C.-F.; Lai, C.-H.; Hsieh, C.-C.; Wang, K.-W.; Chou, P.-T.
Adv. Funct. Mater. 2009, 19, 2834–2843. (d) Chien, C.-H.; Chen, C.-K.;
Hsu, F.-M.; Shu, C.-F.; Chou, P.-T.; Lai, C.-H. Adv. Funct. Mater. 2009,
19, 560–566. (e) Tsuji, H.; Sato, K.; Sato, Y.; Nakamura, E. J. Mater.
Chem. 2009, 19, 3364–3366. (f) Chou, H.-H.; Cheng, C.-H. Adv. Mater.
2010, 22, 2468–2471. (g) Jeon, S. O.; Yook, K. S.; Joo, C. W.; Lee, J. Y.
Adv. Mater. 2010, 22, 1872–1876. (h) Koech, P. K.; Polikarpov, E.;
Rainbolt, J. E.; Cosimbescu, L.; Swensen, J. S.; Von Ruden, A. L.;
Padmaperuma, A. B. Org. Lett. 2010, 12, 5534–5537. (i) Von Ruden,
A. L.; Cosimbescu, L.; Polikarpov, E.; Koech, P. K.; Swensen, J. S.; Wang,
L.; Darsell, J. T.; Padmaperuma, A. B. Chem. Mater. 2010, 22,
5678–5686.
the dibromo(phenylpyridine)s 12 and 15; photophysics and
electrochemistry of the dibromo(phenylpyridine)s 9, 12, and
15; cyclic voltammograms of azadibenzophospholes 1a, 3a, and
4a; 31P NMR spectra of 4a before and after addition of MeOTf;
frontier orbital diagrams for compound 2a/b, 3a/b and 4a/b;
cyclic voltammograms and UVꢀvis absorption spectra of 17 and
20. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: thomas.baumgartner@ucalgary.ca.
’ ACKNOWLEDGMENT
Financial support by NSERC of Canada and the Canada
Foundation for Innovation (CFI) is gratefully acknowledged.
We also thank Alberta Ingenuity, now part of Alberta Innovates-
Technology Futures, for a graduate scholarship (S.D.) and a New
Faculty Award (T.B.). Thanks to Prof. T. Sutherland for his help
with the electrochemical studies, and Dr. T. Linder for helpful
discussions with regard to X-ray crystallography.
(12) (a) Wood, T. K.; Piers, W. E.; Keay, B. A.; Parvez, M. Angew.
Chem., Int. Ed. 2009, 48, 4009–4012. (b) Wood, T. K.; Piers, W. E.; Keay,
B. A.; Parvez, M. Chem.—Eur. J. 2010, 16, 12199–12206. (c) Chen, J.;
Kampf, J. W.; Ashe, A. J., III Organometallics 2008, 27, 3639–3641.
(13) (a) Miao, S.; Appleton, A. L.; Berger, N.; Barlow, S.; Marder,
S. R.; Hardcastle, K. I.; Bunz, U. H. F. Chem.—Eur. J. 2009,
15, 4990–4993. (b) Bunz, U. H. F. Chem.—Eur. J. 2009,
15, 6780–6789. (c) Lian, Z.; Tang, Q.; Xu, J.; Miao, Q. Adv. Mater.
2011, 23, 1535–1539. (d) Richards, G. J.; Hill, J. P.; Subbaiyan, N. K.;
D’Souza, F.; Karr, P. A.; Elsegood, M. R. J.; Teat, S. J.; Mori, T.; Ariga, K.
J. Org. Chem. 2009, 74, 8914–8923.
(14) (a) Fukazawa, A.; Hara, M.; Son, T.; Okamoto, E.-C.; Xu, C.;
Tamao, K.; Yamaguchi, S. Org. Lett. 2008, 10, 913–916. (b) Fukazawa, A.;
Ichihashi, Y.; Kosaka, Y.; Yamaguchi, S. Chem.—Asian J. 2009,
4, 1729–1740. (c) Saito, A.; Miyajima, T.; Nakashima, M.; Fukushima,
T.; Kaji, H.; Matano, Y.; Imahori, H. Chem.—Eur. J. 2009,
15, 10000–10004. (d) Miyajima, T.; Matano, Y.; Imahori, H. Eur. J.
Org. Chem. 2008, 255–259. (e) Matano, Y.; Miyajima, T.; Fukushima, T.;
Kaji, H.; Kimura, Y.; Imahori, H. Chem.—Eur. J. 2008, 14, 8102–8115. (f)
Dienes, Y.; Eggenstein, M.; Kꢀarpꢀati, T.; Sutherland, T. C.; Nyulꢀaszi, L.;
Baumgartner, T. Chem.—Eur. J. 2008, 14, 9878–9889.
(15) Su, H.-C.; Fadhel, O.; Yang, C.-J.; Cho, T.-Y.; Fave, C.; Hissler,
M.; Wu, C. C.; Rꢀeau, R. J. Am. Chem. Soc. 2006, 128, 983–995.
(16) (a) De Pascali, S. A.; Papadia, P.; Ciccarese, A.; Pacifico, C.;
Fanizzi, F. P. Eur. J. Inorg. Chem. 2005, 788–796. (b) Rochon, F. D.;
Bensimon, C.; Tessier, C. Inorg. Chim. Acta 2008, 361, 16–28.
(17) Usꢀon, R.; Laguna, A.; Laguna, M. Inorg. Synth. 1989, 26, 85–91.
(18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
’ REFERENCES
(1) (a) Anthony, J. E. Chem. Rev. 2006, 106, 5028–5048. (b)
Anthony, J. E. Angew. Chem., Int. Ed. 2008, 47, 452–483. (c) Subramanian,
S.; Park, S. K.; Parkin, S. R.; Podzorov, V.; Jackson, T. N.; Anthony, J. E.
J. Am. Chem. Soc. 2008, 130, 2706–2707. (d) Kim, D. H.; Lee, D. Y.; Lee,
H. S.; Lee, W. H.; Kim, Y. H.; Han, J. I.; Cho, K. Adv. Mater. 2007,
19, 678–682. (e) Tang, M. L.; Reichardt, A. D.; Miyaki, N.; Stoltenberg,
R. M.; Bao, Z. J. Am. Chem. Soc. 2008, 130, 6064–6065.
(2) (a) Perepichka, I. F.; Perepichka, D. F.; Meng, H.; Wudl, F. Adv.
Mater. 2005, 17, 2281–2305.(b) M€ullen, K.; Scherf, U. Organic Light
Emitting Devices; Wiley-VCH: Weinheim, 2006. (c) Veinot, J. G. C.;
Marks, T. J. Acc. Chem. Res. 2005, 38, 632–643.(d) Klauk, H. Organic
Electronics; Wiley-VCH: Weinheim, 2006.
(3) (a) Gao, P.; Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann,
V.; Baumgarten, M.; Pisula, W.; M€ullen, K. Adv. Mater. 2009, 21,
213–216. (b) Gao, P.; Feng, X.; Yang, X.; Enkelmann, V.; Baumgarten,
M.; M€ullen, K. J. Org. Chem. 2008, 73, 9207–9213. (c) Takimiya, K.;
Ebata, H.; Sakamoto, K.; Izawa, T.; Otsubo, T.; Kunugi, Y. J. Am. Chem.
Soc. 2006, 128, 12604–12605. (d) Ebata, H.; Izawa, T.; Miyazaki, E.;
Takimiya, K.; Ikeda, M.; Kuwabara, H.; Yui, T. J. Am. Chem. Soc. 2007,
129, 15732–15733. (e) Zhang, X.; Cot^e, A. P.; Matzger, A. J. J. Am.
Chem. Soc. 2005, 127, 10502–10503.
(4) (a) Jacob, J.; Sax, S.; Piok, T.; List, E. J. W.; Grimsdale, A. C.;
M€ullen, K. J. Am. Chem. Soc. 2004, 126, 6987–6995. (b) Zhou, Y.; Liu,
W.-J.; Ma, Y.; Wang, H.; Qi, L.; Cao, Y.; Wang, J.; Pei, J. J. Am. Chem. Soc.
2007, 129, 12386–12387.
(5) (a) Skotheim, T. A.; Reynolds, J. R. Handbook of Conducting
Polymers, 3rd ed.; CRC Press: Boca Raton, FL, 2006. (b) Blouin, N.;
6835
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836

Inorganic Chemistry
ARTICLE
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski,
V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.;
Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill,
P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian 03, Revision E.01; Gaussian Inc.: Wallingford, CT, 2007.
(19) (a) Baumgartner, T.; Neumann, T.; Wirges, B. Angew. Chem.,
Int. Ed. 2004, 43, 6197–6201. (b) Baumgartner, T.; Bergmans, W.;
Kꢀarpꢀati, T.; Neumann, T.; Nieger, M.; Nyulꢀaszi, L. Chem.—Eur. J. 2005,
11, 4687–4699. (c) Dienes, Y.; Durben, S.; Kꢀarpꢀati, T.; Neumann, T.;
Englert, U.; Nyulꢀaszi, L.; Baumgartner, T. Chem.—Eur. J. 2007,
(36) Durben, S.; Dienes, Y.; Baumgartner, T. Org. Lett. 2006,
8, 5893–5896.
(37) Quin, L. D.; Bryson, J. G.; Moreland, C. G. J. Am. Chem. Soc.
1969, 91, 3308–3316.
(38) Brown, H. C.; Mihm, X. J. Am. Chem. Soc. 1955, 77, 1723–1726.
(39) (a) Cornforth, J.; Cornforth, R. H.; Gray, R. T. J. Chem. Soc.,
Perkin Trans. I 1982, 2289–2297. (b) Cornforth, J.; Sierakowski, A. F.;
Wallace, T. W. J. Chem. Soc., Perkin Trans. I 1982, 2299–2315. (c)
Cornforth, J.; Ridley, D. D.; Sierakowski, A. F.; Uguen, D.; Wallace,
T. W.; Hitchcock, P. B. J. Chem. Soc., Perkin Trans. I 1982, 2317–2331.
(d) Cornforth, J.; Ridley, D. D.; Sierakowski, A. F.; Uguen, D.; Wallace,
T. W. J. Chem. Soc., Perkin Trans. I 1982, 2333–2339.
(40) Zhang, L. H.; Duan, J.; Xu, Y.; Dolbier, W. R., Jr. Tetrahedron
Lett. 1998, 39, 9621–9622.
ꢀ
13, 7487–7500. (d) Romero-Nieto, C.; Merino, S.; Rodriguez-Lꢀopez,
J.; Baumgartner, T. Chem.—Eur. J. 2009, 15, 4135–4145. (e) Dienes, Y.;
Englert, U.; Baumgartner, T. Z. Anorg. Allg. Chem. 2009, 635, 238–244.
(f) Romero-Nieto, C.; Durben, S.; Kormos, I. M.; Baumgartner, T. Adv.
Funct. Mater. 2009, 19, 3625–3631.
(20) (a) Ren, Y.; Linder, T.; Baumgartner, T. Can. J. Chem. 2009,
87, 1222–1229. (b) Ren, Y.; Baumgartner, T. Chem.—Asian J. 2010,
5, 1918–1929. (c) Ren, Y.; Baumgartner, T. J. Am. Chem. Soc. 2011,
133, 1328–1340.
(21) Baxter, P. N. W. Chem.—Eur. J. 2003, 9, 2531–2541.
(22) (a) Rao, Y. L.; Amarne, H.; Zhao, S. B.; McCormick, T. M.;
Martic, S.; Sun, Y.; Wang, R. Y.; Wang, S. J. Am. Chem. Soc. 2008,
130, 12898–12900. (b) Baik, C.; Hudson, Z. M.; Amarne, H.; Wang, S.
J. Am. Chem. Soc. 2009, 131, 14549–14559.
(23) Affandi, S.; Nelson, J. H.; Alcock, N. W.; Howard, O. W.; Alyea,
E. C.; Sheldrick, G. M. Organometallics 1988, 7, 1724–1734.
(24) Affandi, S.; Green, R. L.; Hsieh, B. T.; Holt, M. S.; Nelson, J. H.;
Alyea, E. C. Synth. React. Inorg., Met.-Org. Chem. 1987, 17, 307–318.
(25) Decken, A. Private Communication 2004, CCDC deposition
number 254271.
(26) Nicholson, R. S. Anal. Chem. 1965, 37, 1351–1355.
(27) See for example: (a) G€unes, S.; Neugebauer, H.; Sariciftci, N. S.
Chem. Rev. 2007, 107, 1324–1338. (b) Peet, J.; Kim, J. Y.; Coates, N. E.;
Ma, W. L.; Moses, D.; Heeger, A. J.; Bazan, G. C. Nat. Mater. 2007,
6, 497–500. (c) Park, S. H.; Poy, A.; Beauprꢀe, S.; Cho, S.; Coates, N.;
Moon, J. S.; Moses, D.; Leclerc, M.; Lee, K.; Heeger, A. J. Nat. Photonics
2009, 3, 297–302.
(28) Matano, Y.; Imahori, H. Org. Biomol. Chem. 2009, 7,
1258–1271.
(29) (a) Norel, L.; Rudolph, M.; Vanthuyne, N.; Williams, J. A. G.;
Lescop, C.; Roussel, C.; Autschbach, J.; Crassous, J.; Rꢀeau, R. Angew.
Chem., Int. Ed. 2010, 49, 99–102. (b) Hudson, Z. M.; Sun, C.; Helander,
M. G.; Amarne, H.; Lu, Z.-H.; Wang, S. Adv. Funct. Mater. 2010,
20, 3426–2439. (c) Wong, W.-Y.; He, Z.; So, S.-K.; Tong, K.-L.; Lin,
Z. Organometallics 2005, 24, 4079–4082.
(30) Still, B. M.; Kumar, P. G. A.; Aldrich-Wright, J. R.; Price, W. S.
Chem. Soc. Rev. 2007, 36, 665–686.
(31) Rajput, J.; Moss, J. R.; Hutton, A. T.; Hendricks, D. T.; Arendse,
C. E.; Imrie, C. J. Organomet. Chem. 2004, 689, 1553–1568.
(32) Anbalagan, V.; Srinivasan, R.; Pallavi, K. S. Transition Met.
Chem. 2001, 26, 603–607.
(33) Durben, S.; Linder, T.; Baumgartner, T. New J. Chem. 2010,
34, 1585–1592.
(34) (a) Textor, M.; Ludwig, W. Helv. Chim. Acta 1972,
55, 184–198. (b) Miskowski, V. M.; Holding, V. H. Inorg. Chem.
1989, 28, 1529–1533.
(35) (a) Welch, G. C.; Coffin, R.; Peet, J.; Bazan, G. C. J. Am. Chem.
Soc. 2009, 131, 10802–10803. (b) Welch, G. C.; Bazan, G. C. J. Am.
Chem. Soc. 2011, 133, 4632–4644.
6836
dx.doi.org/10.1021/ic200951x |Inorg. Chem. 2011, 50, 6823–6836