Pyridyl-Functionalised 3H-1,2,3,4-Triazaphospholes: Synthesis, Coordination Chemistry and Photophysical Properties of Low-Coordinate Phosphorus Compounds

Article abstract of DOI:10.1002/chem.201500988

Novel conjugated, pyridyl-functionalised triazaphospholes with either tBu or SiMe₃ substituents at the 5-position of the N₃PC heterocycle have been prepared by a [3+2] cycloaddition reaction and compared with structurally related, triazole-based systems. Photoexcitation of the 2-pyridyl-substituted triazaphosphole gives rise to a significant fluorescence emission with a quantum yield of up to 12 %. In contrast, the all-nitrogen triazole analogue shows no emission at all. DFT calculations indicate that the 2-pyridyl substituted systems have a more rigid and planar structure than their 3- and 4-pyridyl isomers. Time-dependent (TD) DFT calculations show that only the 2-pyridyl-substituted triazaphosphole exhibits similar planar geometry, with matching conformational arrangements in the lowest energy excited state and the ground state; this helps to explain the enhanced emission intensity. The chelating P,N-hybrid ligand forms a Re^I complex of the type [(N^N)Re(CO)₃Br] through the coordination of nitrogen atom N² to the metal centre rather than through the phosphorus donor. Both structural and spectroscopic data indicate substantial π-accepting character of the triazaphosphole, which is again in contrast to that of the all-nitrogen-containing triazoles. The synthesis and photophysical properties of a new class of phosphorus-containing extended π systems are described. Mix and match: Hitherto unknown pyridyl-functionalized triazaphospholes have been synthesized by a [3+2] cycloaddition reaction starting from phosphaalkynes and pyridyl-substituted azides (see figure). Both experiments and theoretical calculations established these compounds as novel π-conjugated organophosphorus derivatives for future optoelectronic applications.

Full text of DOI:10.1002/chem.201500988

DOI: 10.1002/chem.201500988
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&
Synthesis Design
Pyridyl-Functionalised 3H-1,2,3,4-Triazaphospholes: Synthesis,
Coordination Chemistry and Photophysical Properties of Low-
Coordinate Phosphorus Compounds
Julian A. W. Sklorz,[a] Santina Hoof,[a] Nadine Rades,[a] Nicolas De Rycke,[b] Lµszló Kçnczçl,[c]
DØnes Szieberth,[c] Manuela Weber,[a] Jelena Wiecko,[a] Lµszló Nyulµszi,*[c] Muriel Hissler,*[b]
and Christian Müller*[a]
Dedicated to Professor Manfred Scheer on the occasion of his 60th birthday
Abstract: Novel conjugated, pyridyl-functionalised triaza-
phospholes with either tBu or SiMe3 substituents at the 5-
position of the N3PC heterocycle have been prepared by
a [3+2] cycloaddition reaction and compared with structur-
ally related, triazole-based systems. Photoexcitation of the 2-
pyridyl-substituted triazaphosphole gives rise to a significant
fluorescence emission with a quantum yield of up to 12%.
In contrast, the all-nitrogen triazole analogue shows no
emission at all. DFT calculations indicate that the 2-pyridyl
substituted systems have a more rigid and planar structure
than their 3- and 4-pyridyl isomers. Time-dependent (TD)
DFT calculations show that only the 2-pyridyl-substituted tri-
azaphosphole exhibits similar planar geometry, with match-
ing conformational arrangements in the lowest energy excit-
ed state and the ground state; this helps to explain the en-
hanced emission intensity. The chelating P,N-hybrid ligand
forms a ReI complex of the type [(N^N)Re(CO)3Br] through
the coordination of nitrogen atom N2 to the metal centre
rather than through the phosphorus donor. Both structural
and spectroscopic data indicate substantial p-accepting
character of the triazaphosphole, which is again in contrast
to that of the all-nitrogen-containing triazoles. The synthesis
and photophysical properties of a new class of phosphorus-
containing extended p systems are described.
interesting reactivities and structural motifs.[2] Another class of
low-coordinate phosphorus heterocycles are 3H-1,2,3,4-triaza-
phospholes. These compounds have a conjugated p system
with a high degree of aromaticity and possess a rather high p
density at the phosphorus atom due to significant N-C=P$N+
=C-PÀ conjugation.[3,4] We have recently demonstrated that
methylene-bridged, pyridyl-functionalised triazaphospholes of
type B (Figure 1) can be used to develop transition-metal com-
plexes with different properties from the analogous triazole-
based systems.[5] However, it should be noted that the pyridine
and five-membered ring are not in direct conjugation in com-
pound B.
Introduction
Low-coordinate phosphorus compounds have recently re-
gained noticeable interest because the very peculiar electronic
and steric properties of such l3,s2-species differ significantly
from classical trivalent l3,s3-phosphanes. Their special charac-
teristics can lead to interesting properties in more applied re-
search fields, such as homogeneous catalysis or molecular ma-
terials science.[1] For example, pyridyl-functionalised phosphi-
nines (phosphabenzenes) of type A (Figure 1) have been used
for the development of coordination compounds that present
Coordination compounds containing chelating N^N ligands,
such as 2,2’-bipyridine (bipy) or phenanthroline (phen; C,
Figure 2) have been exploited, to a large extent, as functional
components in electronic and luminescent materials, as well as
[a] J. A. W. Sklorz, S. Hoof, N. Rades, M. Weber, Dr. J. Wiecko, Prof. Dr. C. Müller
Institut für Chemie und Biochemie, Anorganische Chemie
Freie Universität Berlin, Fabeckstr. 34/36, 14195 Berlin (Germany)
E-mail: c.mueller@fu-berlin.de
[b] Dr. N. De Rycke, Prof. Dr. M. Hissler
Institut des Sciences Chimiques de Rennes
UMR 6226 CNRS - UniversitØ de Rennes 1, Campus de Beaulieu
35042 Rennes Cedex (France)
E-mail: muriel.hissler@univ-rennes1.fr
[c] L. Kçnczçl, Dr. D. Szieberth, Prof. Dr. L. Nyulµszi
Budapest University of Technology and Economics
Department of Inorganic and Analytical Chemistry
Szt. GellØrt tØr 4, 1521 Budapest (Hungary)
E-mail: nyulaszi@mail.bme.hu
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201500988.
Figure 1. 2-(2’-Pyridyl)-4,6-arylphenylphosphinine A and 2-[((5-R)-3H-1,2,3,4-
triazaphosphole-3-yl)methyl]pyridine B.
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photocatalysts for the reduction of CO2. Consequently, it could
be interesting to develop novel ligand systems with the pyri-
dine and the triazaphosphole moieties in direct conjugation.[6]
Those compounds could be derived from pyridyl-functional-
ised triazoles of type D (Figure 2), which have recently
emerged as readily modified bipy and phen surrogates as well.
Triazoles are generally accessible in a facile manner by a CuI-
catalysed 1,3-cycloaddition reaction, starting from 2-ethynyl-
pyridine and organic azides (RÀN3).[7] In this respect, it is impor-
tant to note that the related reaction towards N-heterocycle-
substituted 1,2,3-triazoles of type E (inverse click product rela-
tive to D), starting from 2-azidopyridine, is not straightforward
because this azide exists in equilibrium between a closed form
(tetrazole F) and the open form (azide G; Figure 2). Indeed, it
has been shown that pyridotetrazole F is inert towards click re-
actions under standard conditions because the equilibrium for
this particular compound is shifted far to the left (Figure 2).[8]
However, few examples have been reported in the literature
on successful click reactions of alkynes with pyridotetrazoles at
T=1208C, and the coordination chemistry of such inverse 2-
pyridyl-triazoles has been investigated to some extent.[9]
This inherent drawback seems to be particularly problematic
for the synthesis of pyridyl-functionalised triazaphospholes be-
cause one has to start from pyridotetrazole as an azide surro-
gate, since pyridine-derived phosphaalkynes are not available.
Nevertheless, we envisaged access to a family of novel pyridyl-
functionalised, conjugated triazaphospholes of type H, with
the nitrogen atom in either the 2-, 3- or 4-positions of the pyr-
idyl-moiety (Figure 3).
holes, such as I (Figure 3). These five-membered phosphorus
heterocycles, as well as their corresponding transition-metal
complexes, have gained tremendous interest as p-conjugated
components in organic light-emitting diodes (OLEDs).[10] It thus
appeared surprising to us that no studies on the photophysical
properties of 3H-1,2,3,4-triazaphospholes had appeared in the
literature to date. It should, however, be mentioned that 2-pyr-
idylphospholes contain an exocyclic P substituent and are less
aromatic than triazaphospholes, which should certainly have
an impact on the respective properties.
We report herein on a detailed investigation into the synthe-
sis of pyridyl-substituted, conjugated 3H-1,2,3,4-triazaphosp-
hole derivatives 1a/b–3a, as well as on the coordination
chemistry of chelates 1a/b towards ReI. Moreover, the photo-
physical properties of these compounds are evaluated by
measuring the excitation and emission spectra and the results
are interpreted by means of DFT calculations. Selected com-
pounds are compared with the reference compounds 4a/
b and 5a/b to gain information on the influence of the heter-
oatoms and on the importance of conjugation between het-
erocycles with respect to their luminescence properties. As
such, the triazaphosphole is attached directly to a phenyl
moiety in 4a/b, which allows p conjugation, but lacks the ni-
trogen atom in the six-membered ring. In 5a/b, p conjugation
with the phenyl moiety is interrupted (Figure 4). Considering
the diagonal relationship of the phosphorus carbon, triaza-
phospholes are also compared with structurally related tria-
zoles.[11]
The chelating version of H (2-pyridyl-H) should not only be
interesting from a coordination chemistry point of view, but it
also closely resembles structurally donor-functionalised phosp-
Figure 4. Pyridyl-functionalised triazaphospholes and reference compounds.
Results and Discussion
Synthesis and characterisation
Figure 2. Common chelating N^N ligands and pyridotetrazole-2-azidopyri-
dine equilibrium.
For the preparation of compound 1a, pyridotetrazole F
(Figure 2) was synthesised according to a literature procedu-
re.[9a] We first attempted the reaction of F with tert-butylphos-
phaalkyne (PꢀCÀtBu) at T=1258C in toluene. This temperature
was chosen with the intention of shifting the equilibrium F/G
sufficiently to the azide form (Scheme 1).[12] The 31P{1H} NMR
spectrum of the dark red–brown reaction mixture revealed the
presence of one main product at d= +167.5 ppm, but several
unidentified by-products appeared, which could not be sepa-
rated from the main product. Subsequently, the [3+2] cycload-
dition reaction was carried out at lower temperature (T=60–
808C) and the conversion was again followed by means of
Figure 3. Comparison between pyridyl-functionalised triazaphospholes (H)
and phospholes (I).
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31P{1H} NMR spectroscopy. Much to our surprise, the reaction
was selective and ran to completion after one week. The novel
triazaphosphole 1a was obtained in 98% yield (determined
spectroscopically) as a pale-yellow solid after removal of the
solvent (Scheme 1). Similarly, the SiMe3-substituted triaza-
phosphole 1b was formed within 1 h through the reaction of
the pyridotetrazole and PꢀCÀSiMe3 in toluene at T=658C; the
product was isolated as an orange oil.[13] The SiMe3 group had
a great influence on the chemical shift of the product: the res-
onance of 1b was observed at d= +211.6 ppm in the
31P{1H} NMR spectrum.
(Figure S2 in the Supporting Information). The molecular struc-
tures of 5a and 5b are very similar concerning the location of
the benzyl group with respect to the planar triazaphosphole
heterocycle (Figures S3 and S4 in the Supporting Information).
Interestingly, although known for many years, only a few 3H-
1,2,3,4-triazaphospholes have so far been characterised crystal-
lographically by Jones et al.[15] All available structural parame-
ters indicate significant conjugation within the heterocycles. In
case of 1a, the P(1)ÀC(1) distance (1.7133(19) Š) is slightly
shorter than the PÀC bond lengths in 2,4,6-triarylphosphinines
(ꢁ1.75 Š). It thus lies between the values of a localised P=C
Scheme 1. Synthesis of 1a/b starting from pyridotetrazole.
The pyridyl-functionalised triazaphospholes 2a/b, 3a, 4a/
b and 5a/b[14] could be prepared as well, starting from the cor-
responding azides. The [3+2] cycloaddition reaction with both
phosphaalkynes proceeded smoothly at room temperature in
toluene within several minutes in each case (Scheme 2). Com-
pound 3b (R=SiMe3) could not be obtained in a pure form. It
should be noted here that the Me3Si-substituted triazaphosp-
holes seemed to be light sensitive.
Figure 5. Molecular structure of a crystal of 1a. Displacement ellipsoids are
shown at the 50% probability level. Selected bond lengths [Š] and angles
[8]: P(1)ÀC(1): 1.7133(19), P(1)ÀN(1): 1.7012(16), C(1)ÀN(3): 1.368(2), N(3)ÀN(2):
1.300(2), N(2)ÀN(1): 1.353(2), N(1)ÀC(2): 1.436(2), C(2)ÀN(4): 1.321(2), C(2)À
C(3): 1.383(3), N(4)ÀC(6): 1.344(3), C(1)ÀC(7): 1.519(3); C(1)-P(1)-N(1): 85.77(8),
N(1)-N(2)-N(3): 110.54(15), N(2)-N(1)-C(2)-C(3): 0.0.
Scheme 2. Synthesis of pyridyl-functionalised triazaphospholes and refer-
ence compounds.
Crystals of 1a, 2a, 3a, 4a, 5a and 5b suitable for a crystallo-
graphic characterisation were obtained from a saturated solu-
tion in pentane at T=À208C. Although the two ring systems
are coplanar in 1a (Figure 5) and 3a (Figure S1 in the Support-
ing Information), they are considerably twisted in 2a and 4a,
with dihedral angles of 38.7 (Figure 6) and 46.58, respectively
Figure 6. Molecular structure of a crystal of 2a. Displacement ellipsoids are
shown at the 50% probability level. Selected bond lengths [Š] and angles
[8]: P(1)ÀC(1): 1.717(6), P(1)ÀN(1): 1.696(4), C(1)ÀN(3): 1.370(8), N(3)ÀN(2):
1.320(7), N(2)ÀN(1): 1.358(6), N(1)ÀC(2): 1.444(7), C(2)ÀC(3): 1.376(8), C(2)À
C(6): 1.388(7), N(4)ÀC(6): 1.341(8), C(1)ÀC(7): 1.513(8); C(1)-P(1)-N(1): 86.6(3),
N(2)-N(1)-C(2)-C(3): À38.7(8).
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double bond ((diphenylmethylene)(mesityl)phosphine; MesP= triazaphospholes I (2-py), II (3-py) and III (4-py) were calculated
CPh2: 1.692 Š) and a PÀC single bond (PPh3: 1.83 Š).[16] The N-
P-C angle is, at 85.77(8)8, almost 908 and differs significantly
from the C-P-C angle in the aromatic six-membered phospho-
rus heterocycles (ꢁ1008).[17]
with different DFT functionals and basis sets to probe the relia-
bility of our results (Table 2).
Clearly, the most stable structure is I, with the pyridyl nitro-
gen and phosphorus atoms in the cis position. This is in agree-
ment with results obtained from the crystallographic character-
isation of 1a (Figure 5). The energetic preference is approxi-
mately 5 kcalmolÀ1 with respect to all other isomeric structures
at each investigated level of theory. Since this relative stability
remains unchanged when functionals with a dispersion correc-
tion were used, it seems that this energetic preference is not
a consequence of steric repulsion. Also, no pnictogen interac-
tions between phosphorus and pyridyl nitrogen atoms are
present. In fact, neither a bond critical point was located be-
tween the phosphorus and nitrogen atoms, nor was any stabil-
ising interaction found in the second-order perturbation analy-
sis carried out on the basis of natural bond orbitals (NBOs).[19]
By considering the nearly uniform destabilisation of the other
structures, it seems that a NÀP repulsive interaction is simply
smaller than N···N or (C)H···N/P non-bonded repulsive interac-
tions. By calculating planar trans-I with P and N atoms in the
trans position with respect to one another, a saddle point with
an additional destabilisation of 1.6 kcalmolÀ1 was obtained,
which was in agreement with the expected repulsive N···N in-
teraction.
The near 908 bond angle, which is characteristic for these
phosphorus compounds, can apparently more easily be ach-
ieved in a planar pentagon (ideally 1078) than in a hexagon
(ideally 1208). This can be explained by the fact that the lighter
sp2-hybridised ring atoms strive for the trigonal planar arrange-
ment. A similar effect contributes to the planarisation of the
s3-P atom in polyphosphaphospholes.[18] As suggested by
Nyulµszi et al., all of these observations are in agreement with
significant aromaticity within 1,2,3,4-triazaphospholes.[3]
Because the co-planarity of the two aromatic rings is clearly
related to p conjugation and is supposed to affect the optical
properties (see below), the relevant structural parameters in
the triazaphosphole rings of 1a–5a/b are compared in Table 1.
Table 1. Interatomic distances [Š] in the triazaphosphole rings of 1a–5a
and 5b (for numbering of the atoms see Figure 5).
N1ÀC2
N2ÀN1
N3ÀN2
C1ÀN3
P1ÀC1
P1ÀN1
1a
2a
3a
4a
5a
5b
1.436
1.444
1.435
1.436
1.484
1.485
1.353
1.358
1.352
1.350
1.340
1.345
1.300
1.320
1.303
1.309
1.314
1.314
1.368
1.370
1.353
1.351
1.351
1.368
1.713
1.717
1.704
1.711
1.712
1.709
1.701
1.696
1.694
1.689
1.683
1.679
Although the planarity of I is in agreement with structural
analysis of 1a, the optimised structure of III is non-planar,
which is in contrast with the planarity of 3a in the crystal (Fig-
ure S1 in the Supporting Information). Thus, we further deter-
mined the rotational barrier around the interconnecting N(1)
and C(pyridyl) atoms of 1a, 2a and 3a and the results are de-
picted in Figure 7. The rotational barrier is largest for 2-pyridyl-
substituted triazaphosphole 1a. In this case, the minimum
energy is related to a planar structure, in which phosphorus
and nitrogen atoms of 1a in the cis position (dihedral angle is
08) is the most stable conformation. We found an additional
non-planar minimum near to the trans arrangement of the
phosphorus and nitrogen atoms, which was less stable by
about 5 kcalmolÀ1. In the case of 2a (3-pyridyl), the energy dif-
ference between the twisted minimum structure and the
planar (transition) structure is 0.4 kcalmolÀ1, whereas it is even
It is noteworthy that the structural parameters for the conju-
gated rings in 1a–4a remain virtually unchanged, considering
experimental error, irrespective of whether the two rings are
coplanar or not. Likewise, the interatomic triazaphosphole ring
distances in non-conjugated 5a are similar to those in 1a–4a.
However, in this case, both formally single bonded P(1)ÀN(1)
and N(2)ÀN(1) distances are slightly shorter, which indicates
some enhancement of delocalisation of the nitrogen lone pair
within the five-membered ring. Accordingly, the N1ÀC2 dis-
tance in 5a is significantly longer than those in conjugated
compounds 1a–4a. Here, the
distance between the two rings
is similar, within experimental
error, for both planar and non-
planar systems. By taking these
observations into account, it can
be concluded that some conju-
gation remains effective between
the five- and six-membered het-
erocycles, even in the partially
twisted forms.
Table 2. Comparison of the relative energies (Erel) of the minimised structures of triazaphospholes with differ-
ent functionals and basis sets.
Erel [kcalmolÀ1
]
wB97xD/aug-cc-pVTZ
wB97xD/6-31+G*
B3LYP/aug-cc-pVTZ
0.0
0.0
0.0
cis-2-pyridyltriazaphosphole (I)
5.5
4.9
5.5
4.9
5.6
5.0
To investigate the extent of
co-planarity in 1a–4a in more
detail, quantum chemical calcu-
lations were carried out. The
structures of the H-substituted
cis-3-pyridyltriazaphosphole (II)
4-pyridyltriazaphosphole (III)
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We also computed the dimeric structure of 3a at the
wB97xD/6-311+G** level to investigate further the effect of
this interaction. Although the two rings within one molecule
did not remain fully planar, a significant 14 kcalmolÀ1 (basis set
superposition error (BSSE)-corrected wB97xD/6-311+G**) inter-
action energy was obtained, which indicated that intermolecu-
lar interactions played a significant role in the crystalline
phase. Atoms in molecules (AIM) analysis of the electron densi-
ty did not reveal any bond critical points between the phos-
phorus atom and the six-membered ring of the neighbouring
molecule.[20]
To compare triazaphospholes 1a and 1b, in particular, with
the corresponding phosphorus-lacking triazoles, which had
otherwise identical substitution patterns, we also carried out
the click reaction of pyridotetrazole with either HCꢀC-tBu or
HCꢀC-SiMe3 at T=1408C in toluene in the presence of
CuOTf·C6H6 (Tf=triflyl) as the Cu catalyst, according to a modi-
fied literature procedure.[9g] The pyridyl-functionalised triazoles
6a and 6b could be obtained straightforwardly in good yields
as colourless, pure solids after removal of the solvent
(Scheme 3).
Figure 7. wB97xD/aug-cc-pVDZ rotational barriers for the different pyridyl-
triazaphospholes (1a–3a). The reference energy is the lowest energy mini-
mum for each compound, which shows the difference in the barriers; how-
ever, it should be noted that 1a is more stable than 2a or 3a by 5 kcal
molÀ1
.
less than 0.1 kcalmolÀ1 between 0 and 308 for 3a (4-pyridyl).
The planar structure is a first-order saddle point in both cases.
The contrast between the calculated non-planar structure of
3a and the observed planarity in X-ray crystal-structure analy-
sis is understandable in light of the very small energy differ-
ence, when considering in particular that the calculations refer
to the gas phase.
To understand the preference of a coplanar arrangement of
the two heterocycles in the crystalline phase of 3a, which is in
contrast to the calculations, it is also noteworthy that 3a
shows interesting packing of the molecules in the crystal lat-
tice (Figure 8). The two closest molecules are stacked in such
a way that the phosphorus atoms lie above or below the re-
spective pyridyl moiety and vice versa (Figure 8, upper left and
lower right). The distance between the phosphorus atom of
one triazaphosphole and the centroid of the pyridyl moiety of
the second triazaphosphole is in the range of 3.58 Š. It should
be noted here that this type of stacking is not observed in the
crystal lattice of compound 1a, despite the fact that the two
rings are coplanar (Figure 8).
Scheme 3. Synthesis of pyridyl-functionalised triazoles 6a/b from 2-azidopyr-
idine.
We were able to obtain crystals of 6a that were suitable for
XRD. The molecular structure of the 2-pyridyl-functionalised tri-
azole is depicted in Figure 9.
Similar to the structurally related triazaphosphole, a cis align-
ment of the pyridyl nitrogen atom and C(2)ÀH group can be
observed. This arrangement appears to be necessary to mini-
mise non-bonded repulsive N···N and (C)H···N interactions.
Moreover, the two nitrogen heterocycles are only slightly twist-
ed with a dihedral angle of À19.42(17)8. The inter-ring distance
of N(1)ÀC(3) (1.4273(16) Š) is only slightly shorter than that in
triazaphosphole 1a (1.436(2) Š), which again indicates signifi-
cant conjugation between the five- and six-membered nitro-
gen heterocycles.
According to our calculations, the wB97xD/aug-cc-pVTZ ro-
tational surface of triazole 6a is similar to that of triazaphosp-
hole 1a. The most stable minimum is a planar structure with
a cis arrangement of the N(4)C(3)N(1)N(2) units. The rotational
barrier is 6 kcalmolÀ1, and a second non-planar minimum also
exists close to the highest energy point of the rotational po-
tential energy surface.
Figure 8. Packing in a crystal of 3a. View along the b axis.
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Figure 10. Possible coordination modes of 1a/b.
Figure 9. Molecular structure of a crystal of 6a. Displacement ellipsoids are
shown at the 50% probability level. Selected bond lengths [Š] and angles
[8]: C(2)ÀC(1): 1.3639(17), C(1)ÀN(3): 1.3704(16), N(3)ÀN(2): 1.3136(15), N(2)À
N(1): 1.3537(15), N(1)ÀC(2): 1.3541(16), N(1)ÀC(3): 1.4273(16), C(3)ÀN(4):
1.3281(16), C(3)ÀC(4): 1.3867(17), C(4)ÀC(5): 1.3836(18), C(5)ÀC(6): 1.3875(19),
C(6)ÀC(7): 1.3817(19); C(1)-C(2)-N(1): 105.02(11), N(1)-N(2)-N(3): 106.71(10),
N(2)-N(1)-C(3)-C(4): À19.42(17).
Coordination chemistry
Figure 11. Molecular structure of a crystal of 7a. Displacement ellipsoids are
shown at the 50% probability level. Only one independent molecule is
shown and the non-coordinated CH2Cl2 solvent molecules are omitted for
clarity. Selected bond lengths [Š] and angles [8]: P(2)ÀC(14): 1.706(11), P(2)À
N(5): 1.714(8), N(5)ÀN(6): 1.349(12), N(6)ÀN(7): 1.302(13), N(7)ÀC(14):
1.336(13), N(5)ÀC(15): 1.413(12), N(8)ÀRe(2): 2.179(11), N(6)ÀRe(2): 2.147(9);
N(5)-P(2)-C(14): 85.4(5), N(8)-Re(2)-N(6): 73.6(4).
We recently demonstrated that methylene-bridged triaza-
phospholes of type B (Figure 1) and the corresponding phos-
phorus-lacking triazoles underwent a facile reaction with
Re(CO)5Br to form complexes [(N^N)Re(CO)3Br].[5] We therefore
also decided to explore the coordination chemistry of 1a and
6a towards ReI because those bidentate ligands were expected
to coordinate in a chelating manner to a transition-metal
centre, in contrast to compounds 2–4. At the same time, the
[Re(CO)3Br] metal fragment offers the possibility of investigat-
ing the electronic properties of the ligands by means of IR
spectroscopy of the resulting coordination compounds. We
first paid attention to the coordination chemistry of the triaza-
phosphole, which could coordinate in either a P^N (J) or an
N^N (K) fashion (Figure 10). Compound 1a was thus reacted
with an equimolar amount of [Re(CO)5Br] in dichloromethane
at T=808C in a sealed NMR tube and the reaction was moni-
tored by means of 31P{1H} NMR spectroscopy. After 8 h the con-
version was complete and the reaction product showed a reso-
nance in the 31P{1H} NMR spectrum at d= +191.3 ppm. From
the chemical shift difference of Dd=23.8 ppm it is, however,
not conclusive whether the triazaphosphole moiety coordi-
nates through the phosphorus or nitrogen lone pairs to the
metal centre because s-coordinated phosphinines show a simi-
lar chemical shift difference upon coordination to a metal
centre (Figure 10).[21]
From crystallographic characterisation, it is clear that the
chelating ligand 1a coordinates to the ReI centre through the
nitrogen atom N(6) of the triazaphosphole moiety, rather than
through the phosphorus atom. Interestingly, the coordination
of the least nucleophilic nitrogen atom N(6) to a metal centre
has only recently been observed for the first time for triaza-
phospholes and is apparently enforced by the chelate effect.[5]
In agreement with our wB97xD/6-31+G* calculations (by
using the def2-TZVP basis at Re) on 7a, the K-type structure is
more stable than structure J by 9.9 kcalmolÀ1. This stability dif-
ference is essentially due to the preferred binding of rhenium
to nitrogen. In accordance, a P-bound mono-coordinated
[Re(CO)4Br] complex of tert-butyltriazaphosphole as a model is
less stable than its N bound isomer by 12.4 kcalmolÀ1 at the
wB97xD/6-31+G* level (def2-TZVP basis at Re). Interestingly,
the 1.336(13) Š bond length N(7)ÀC(14) is much shorter than
the corresponding distance (C(1)ÀN(3)) in the free ligand 1a.
Also, the inter-ring distance N(5)ÀC(15) shortens significantly
upon coordination (1.413(12) versus 1.436(2) Š). These differen-
ces nicely correlate with the shape of the LUMO of 1a (see Fig-
ure S5 in the Supporting Information), which has a significant
bonding character between the two rings. Once the ligand is
coordinated to an electron-rich transition-metal centre, the
low-lying ligand LUMO gains electron density, which results in
an increase of the bond order and a shortening of the C(15)À
N(5) bond.
Crystals of 7a, suitable for X-ray crystal-structure analysis,
were obtained from cooling a hot saturated solution of the
compound in dichloromethane slowly to T=À218C. Com-
¯
pound 7a crystallises in the space group P1 and the molecular
structure of the crystal, along with selected bond lengths and
angles, is depicted in Figure 11; this shows the expected facial
geometry of the [L2Re(CO)3Br] complex.
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To compare the stereoelectronic properties of triazaphosp-
hole 1a with triazole 6a, a ReI complex containing the chelat-
ing triazole was prepared accordingly. Since a phosphorus
probe was absent, the reaction of 6a with an equimolar
amount of [Re(CO)5Br] in dichloromethane at T=808C was
monitored by means of 1H NMR spectroscopy until full con-
sumption of the ligand was observed. Crystals of 8a (space
group P21/c), suitable for XRD, were obtained by slowly cool-
ing a concentrated solution of 8a in dichloromethane. The mo-
lecular structure, along with selected bond lengths and angles,
is depicted in Figure 12.
Table 3. IR spectroscopic data for ReI–carbonyl complexes 7a and 8a.
À1
À1
À1
~
~
~
n1(CO) [cm
]
n2(CO) [cm
]
n3(CO) [cm
]
7a (tBu/P)
8a (tBu/N)
2023
2026
1992
1913
1900
1870
nificantly to higher wavenumbers relative to triazole-based ReI
complex 8a. This is in agreement with the observations made
above and indicates that triazaphosphole 1a has a higher p-
accepting capacity than that of 6a. However, this is in clear
contrast to the observations made for the non-conjugated,
methylene-bridged triazaphospholes of type B (Figure 1), for
which an inverse situation was observed.[5]
Apparently, conjugation between the pyridyl and triaza-
phosphole moieties considerably affects the electron density
of the phosphorus heterocycle in such way that the p-acceptor
properties are increased, although differences in the steric con-
straints might also play a role.
During the preparation of our manuscript, Crowley et al. re-
ported the crystallographic characterisation of the first ReI
complexes containing inverse phenyl- and benzyl-substituted
2-pyridyltriazole ligands. The bond lengths and angles report-
ed for those coordination compounds are very similar to those
observed for complex 8a (Scheme 4).[9a]
Figure 12. Molecular structure of a crystal of 8a. Displacement ellipsoids are
shown at the 50% probability level. A non-coordinated CH2Cl2 solvent mole-
cule is omitted for clarity. Selected bond lengths [Š] and angles [8]: C(2)À
C(1): 1.365(7), C(2)ÀN(1): 1.356(6), N(1)ÀN(2): 1.352(6), N(2)ÀN(3): 1.313(5),
N(3)ÀC(1): 1.367(6), N(1)ÀC(3): 1.417(6), N(4)ÀRe(1): 2.189(4), N(2)ÀRe(1):
2.146(4); N(4)-Re(1)-N(2): 73.93(15).
Scheme 4. Synthesis of ReI complexes 7a and 8a from [Re(CO)5Br].
Similar to compound 7a, the graphical representation of 8a
reveals the facial geometry of complex [(6a)Re(CO)3Br] with ni-
trogen atom N(2) of the triazole units coordinated to the ReI
centre. Apparently, exchanging the phosphorus atom in 7a for
an isoelectronic CÀH group in 8a has only a marginal effect on
the bite angle N(4)-ReI-N(2), since values of 83.31 (7a) and
82.488 (8a) were found. Likewise, the NÀRe distances are virtu-
ally unchanged. These observations are again in agreement
with the carbon–phosphorus analogy.
Scheme 4 provides a summary of the reaction of ligands 1a
and 6a with [Re(CO)5Br], leading to the corresponding ReI
complexes 7a and 8a, in which coordination exclusively
through the least nucleophilic nitrogen atom N(2) occurs.[22]
Photophysical properties
To establish the structure–property relationship for this novel
series of P-based p-conjugated systems (Figure 3), we started
to investigate the photophysical properties of triazaphospholes
1a/b–3a in comparison with reference compounds 4a/b and
5a/b, phosphorus-lacking triazoles 6a/b and ReI complexes 7a
and 8a. The luminescence measurements were performed in
dichloromethane at room temperature and the results are
listed in Table 4 (see also Figures S6–S12 in the Supporting In-
formation).
Nevertheless, the changes in the bond lengths upon coordi-
nation of 6a to the ReI fragment are not as pronounced as
those observed for phosphorus derivative 1a. The N(3)ÀC(1)
and inter-ring N(1)ÀC(3) distances in 8a (1.367(6) and
1.417(6) Š, respectively) are only slightly shorter than those in
free ligand 1a (1.3704(16) and 1.4273(16) Š). The p-accepting
character of 6a seems to be much less pronounced than that
of the phosphorus analogue 1a.
To probe this, we further investigated the ReI complexes 7a
and 8a by means of IR spectroscopy and Table 3 provides
a summary of the observations made.
The absorption spectra of triazaphosphole derivatives 1a/b,
2a/b, 3a and 4a/b exhibit broad, medium-intensity bands in
the UV part of the spectrum (see Figure 13 and Table 4). The
wB97xD/aug-ccPVDZ TD-DFT calculations performed on 1a/b,
2a/b and 3a/3b at their minimum energy structures (see
~
~
From the results in Table 3, it is clear that n2 and n3, in partic-
ular, in the triazaphosphole-based complex 7a are shifted sig-
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Illumination of compounds 1a/1b gave rise to a significant
fluorescence emission with quantum yields of 12 and 11 %. Ex-
change of the tBu group for a SiMe3 substituent results in
a blueshift as the emission wavelength changes from l=370
to 334 nm with a marginal effect on the quantum yield. In this
respect, it is noteworthy that, likewise for 1a, our calculated
structure for 1b was planar, and the rotational potential
energy surface was also similar to that of 1a. The blueshift is
much smaller in case of the absorption band maximum; never-
theless, it might be in agreement with the p-electron-with-
drawing character of the ÀSiMe3 group bonded directly to an
aromatic system. Clearly, the planarity of 1a is related to the
high quantum yield. Accordingly, the non-planar 3-pyridyl de-
rivative (2a) shows little fluorescence. Unexpectedly, however,
the 4-pyridyl-substituted triazaphosphole 3a, which exhibits
a planar X-ray structure, is very weakly emissive. To understand
this behaviour, the rotational energy profile shown in Figure 7
should be considered. The rotational energy profile is steep in
the case of 1a, whereas it is much shallower for both 2a and
3a; this makes the last two systems more flexible, which facili-
tates the radiationless deactivation of the excited state.
Table 4. Photophysical features of the prepared compounds.
[a]
lmax
e
lem
F
[nm]
[LmolÀ1 cmÀ1
]
[nm]
[%][b]
1a
1b
2a
2b
3a
285
290
275
278
271
3800
1900
9400
6700
5900
370
334
370
338
360
12
11
3
[c]
–
0.4
8
–
–
4a
4b
5a
5b
270
268
261
258
9300
6800
3900
5400
371
-
–
–
[d]
[d]
[d]
–
[d]
6a
6b
7a
276
275
295
420
266
379
21400
11 300
12200
3100
14900
4700
–
–
365
–
–
1.4
[d]
8a
591
15[e]
[a] Measured in CH2Cl2. [b] Fluorescence quantum yields were measured
relative to quinine sulfate (H2SO4, 0.1m), Æ15%. [c] The compound is not
stable and undergoes decomposition. [d] Not determined; this emission
was too low. [e] Emission quantum yields were measured relative to
Exchange of the pyridyl functionality for a phenyl group in
tBu-substituted reference compound 4a leads to a low quan-
tum yield compared with that of 1a; furthermore, replacing
the tBu group for a SiMe3 substituent in 4b results in no emis-
sion at all. Also, the benzyl-substituted reference compounds
5a/b show no emission, which is apparently related to the lack
of conjugation between the aryl group and triazaphosphole
moiety.
2+
[Ru(bpy)]3 in H2O, f[Ru(bpy)3]2+ =4.2%.
above) allow us to assign this feature to four electronic transi-
tions (Table S1 in the Supporting Information). At higher wave-
lengths, a very low intensity (f=0.002–0.02) p*–n transition
(mainly HOMOÀ3–LUMO) is predicted, typically between l=
270 and 280 nm for tBu derivatives and l=280–290 nm for
SiMe3 derivatives. Three further transitions are predicted in
a 10 nm range at around l=250 nm. One of them has a high
HOMO–LUMO contribution and it also has about one order of
magnitude higher calculated oscillator strength (f=0.2–0.3)
than the other two. Apparently, this transition determines the
observed spectrum. Indeed, the position of this intense transi-
tion is redshifted by l=8 nm for 1a with respect to 2a and
3a, in accordance with the l=10 nm redshift in the spectra
shown in Figure 13. The redshift for 1a/1b indicates increased
p conjugation, in accordance with increased planarity (see
below).
Most interestingly, however, we found that the triazoles 6a/
b again had no emission at all, in contrast to structurally relat-
ed 2-pyridyl-triazaphospholes 1a/b. This observation is striking,
since the rotational surface, and consequently, the preference
for planarity of the conjugated p system, was similar for the
two molecules. Thus with similar behaviour in the ground
state, we decided to investigate the geometry of the first excit-
ed state, which is of importance from the point of view of
emission. Time-dependent (TD) B3LYP/cc-PVTZ geometry opti-
misations of the first excited state converged (depending on
the starting geometry) to two planar structures for both 1a
and 6a. Interestingly, however, although for phosphorus-con-
taining fluorescent 1a the arrangement of the two rings is the
same as that in the ground state (cis-NCNP structure), in the
case of 6a the more stable excited-state geometry differs from
the ground state by a rotation of 1808 (Figure 14). Because
fluorescence proceeds from the lowest excited state, and is
governed by Frank–Condon factors, it is completely under-
standable that the difference in the ground- and excited-state
geometries of 6a results in a low probability of emission.
If these results are translated to photophysical observations,
a coplanar arrangement of the two heterocycles seems to be
necessary for good emission properties, as indeed observed
for 1a. The coplanar arrangement as the minimum structure
points to a maximum degree of delocalisation within the p-
conjugated system and is also observed in the molecular struc-
ture of 1a in the crystal (Figure 5). In contrast, compound 2a
(3-pyridyl) shows very little emission and this compound has
Figure 13. Normalised UV/Vis absorption spectra of compounds 1a, 2a, 3a
and 4a in CH2Cl2 at room temperature.
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Replacement of the CH unit by P in the five-membered ring
(complex 7a; Figure 15) results in a redshift of the absorption
band maxima. The spectrum of 7a presents an intense band
centred at l=295 nm, along with a redshifted shoulder and
the MLCT feature (band maximum at l=420 nm) tailing down
to l=525 nm (Figure 15).
To rationalise the observed properties, DFT and TD-DFT cal-
culations were carried out on complexes 7a and 8a. Analysis
of the molecular orbitals of complexes 7a and 8a shows that
the orbitals between HOMO and HOMO-5 are mainly localised
at the {Re(CO)3Br} fragment and have similar energies and
shapes for the two related molecules (see Figures S13 and S14
in the Supporting Information). In contrast, the LUMO (see Fig-
ure S13 and S14 in the Supporting Information) is localised at
the ligand core, and is stabilised by 0.5 eV in 7a with respect
to 8a. Furthermore, the LUMO exhibits significant pyridine
character for complex 8a and triazaphosphole character for
complex 7a. This behaviour is in accordance with the known
stabilisation of the p*P energy levels with respect to their
Figure 14. Schematic representation of the TD-DFT-optimised excited states
and the ground-state geometries of 1a and 6a. The thickness of the arrows
is related to the probability of the transition.
a twisted structure, according to XRD analysis (Figure 7) and
our DFT calculations (see above). The calculations predict
a twisted conformation as the minimum structure, with re-
duced conjugation. From the calculated data summarised in
Table 2, a twisted conformation as the minimum structure is
also predicted, which again is in agreement with reduced con-
jugation. The molecular structure of 3a in the crystal, however,
revealed a coplanar alignment of both heterocycles in the
solid state. Nevertheless, as already mentioned above, this ar-
rangement could be due to packing effects, which result in
a coplanar arrangement of the two heterocycles in the crystal-
line phase in an otherwise flexible system (Figure 8).
=
C
p*C counterparts, as shown by a comparative investigation of
=
C
the electron transmission spectra of the corresponding ben-
zene, phosphabenzene and triphosphabenzene deriva-
tives.[23,24]
The TD-DFT computations performed on complexes 7a and
8a predict 15 transitions for both complexes at wavelengths
higher than l=250 nm. Most of these transitions are of low in-
tensity (f=0.0001–0.02); thus having only a small contribution
to the spectrum. There are three features, however, that have
higher intensity and we assign those to the observed band
Next, we investigated the photophysical properties of the
ReI complexes 7a and 8a. The electronic absorption and emis-
sion spectra were recorded in CH2Cl2 at room temperature and
are shown in Figure 15. The absorption spectrum of 8a shows
similar absorption bands to those of rhenium complexes re-
ported previously.[9a] The absorption spectrum presents an in-
tense intra-ligand charge-transfer (ILCT) band centred at l=
266 nm, along with a redshifted, broad and less intense metal
to ligand charge-transfer (MLCT) band tailing down to l=
450 nm (Figure 15). The MLCT band maximum is centred at
l=379 nm, which is similar to the corresponding rhenium
complex that incorporates 2-(4-phenyl-1H-1,2,3-triazol-1-yl)pyri-
dine as a ligand. This behaviour indicates that the substituent
on the triazole ring (phenyl versus tBu) is not involved in the
MLCT transition.[9a]
!
maxima. The corresponding transitions are LUMO HOMO-1 at
l=444 nm (f=0.0607) for 7a and l=394 nm (f=0.053) for
8a; these can be assigned to the l=420 and 379 nm MLCT
bands, respectively. Also, the transition at l=310 nm (f=
0.0762) of 7a may be assigned to the shoulder at lꢁ350 nm
in the spectrum. The corresponding transition for 8a is at l=
285 nm (f=0.0645). These transitions belong to an excitation
from a metal dÀp(CO) bonding orbital to the LUMO. The third
intense pairs of transitions are located at l=263 (f=0.2147)
and 250 nm (f=0.0668) for 7a and 8a, respectively. These
transitions are due to p*Àp excitations of the ligand. Because
all of these dominant transitions belong to excitations to the
LUMO, their energy shift between 7a and 8a should be related
to the energy difference of the LUMOs of the ligands. Accord-
ingly, the LUMO level for complex 7a is more stabilised than
the LUMO level of complex 8a, as discussed above.
Illumination of complexes 7a and 8a in deoxygenated
CH2Cl2 at the maximum of the MLCT band gave rise to phos-
phorescence emission with a maximum centred at l=591 nm
for compound 8a only. No triplet emission was observed for
compound 7a (Table 4). Moreover, no further emissions were
detected at low temperature. These photophysical data indi-
cate that radiation-less deactivation pathways are mainly re-
sponsible for the deactivation of the MLCT excited states for
complex 7a.
The excitation of complex 8a at the maximum of the ILCT
band gave rise to the triplet emission centred at l=591 nm,
Figure 15. Electronic absorption and emission spectra for the ReI complexes
7a (dashed lines) and 8a (solid lines) in CH2Cl2 at room temperature.
3
which indicated efficient relaxation to the MLCT excited state.
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Most interestingly, compound 7a shows different behaviour
when it is excited at l=295 nm (at the ILCT band). A fluores-
cent emission centred at l=365 nm is recorded, which resem-
bles ligand fluorescence. These results indicate that energy
transfer from the ILCT state to the MLCT band is not efficient.
Currently, a straightforward explanation for the emissive
properties of complex 7a remains elusive. However, the major
difference between complexes 7a and 8a lies in the localisa-
tion of the electron density in the LUMO level. The DFT calcula-
tions showed that the LUMO of complex 7a had an important
triazaphosphole character with a strong contribution from the
phosphorus atom because complex 8a had strong electron
density on pyridine, which indicated different deactivation
pathways for the MLCT excited state. Experiments to clarify this
aspect are currently being performed in our laboratories.
good emissive properties. We showed that, although 2-pyridyl-
substituted triazole 6a had a similarly rigid structure to its ana-
logue 1a, since its excited-state conformational preference dif-
fered from that of the ground state, its emissive properties
were much less favourable. Our experimental and theoretical
findings establish, for the first time, triazaphospholes as a new
class of phosphorus-containing extended p systems. Further
experiments are currently being undertaken to optimise the
structure of p-conjugated systems that incorporate triaza-
phospholes to generate visible emissions for future optoelec-
tronic applications.
Experimental Section
General
All reactions were performed in an argon atmosphere by using
Schlenk techniques, unless stated otherwise. All glassware was
dried prior to use by heating under vacuum. All common chemi-
cals were commercially available and purchased from Aldrich
Chemical Co., ABCR, Alfa Aesar or Acros, as well as Eurisol, and
were used as received. All solvents were dried and degassed by
using standard techniques or used as directly obtained from Braun
Conclusion
Due to the modular synthetic procedure for the preparation of
3H-1,2,3,4-triazaphosphole derivatives, we demonstrated, for
the first time, access to pyridyl-functionalised triazaphospholes
with either tBu or SiMe3 substituents at the 5-position of the
N3PC heterocycle. The tBu-substituted compounds were char-
acterised by means of X-ray crystal-structure analysis, which
demonstrated significant differences in the torsion angles be-
tween the two heterocycles. DFT calculations showed that the
rotation of the two rings was more hindered in the 2-pyridyl-
substituted triazaphosphole than in its 3- and 4-pyridyl-substi-
tuted analogues. To compare the 2-pyridyl-functionalised tria-
zaphospholes, in particular, with the corresponding phospho-
rus-lacking systems, 2-pyridyl-functionalised triazole derivatives
were prepared and structurally characterised. Starting from
[Re(CO)5Br], it turned out that the chelating triazaphospholes
formed complexes of the type [(N^N)Re(CO)3Br)], with the pyr-
idyl nitrogen and least nucleophilic nitrogen atom N(6) of the
triazaphosphole moiety bound to the ReI atom, rather than
through the phosphorus atom. Both structural and IR spectro-
scopic investigations of the ReI–carbonyl complexes revealed
that the chelating triazaphosphole had a significantly higher p-
accepting capacity than the structurally related triazole deriva-
tive. Irradiation of the 2-pyridyl-substituted triazaphospholes
gave rise to a significant fluorescence emission, whereas the
structurally related triazole (tBu) showed no emission at all. In
this respect, there was a clear influence of the phosphorus
atom on the photophysical properties of the corresponding
compounds. We further found that the emission capability of
the triazaphospholes strongly depended on the position of the
nitrogen atom within the pyridine heterocycle. To explain the
experimental findings, DFT calculations were performed, the re-
sults for which suggested that a coplanar arrangement of the
two heterocycles was a necessary prerequisite for good emis-
sion properties, as indeed observed for the 2-pyridyl-function-
alised triazaphosphole. However, a planar structure as an
energy minimum might also exist in a flexible structure (e.g.,
in 3a), resulting in bad emission properties. A further impor-
tant observation was that matching of the ground- and excit-
ed-state rotational energy surfaces was also of importance for
1
Solvent systems. The H, 13C{1H} and 31P{1H} NMR spectra were re-
corded on JEOL ECX400 (400 MHz), JEOL ECP500 (500 MHz), Bruker
AVANCE500 (500 MHz), or Bruker AVANCE700 (700 MHz) spectrome-
ters, and all chemical shifts were reported relative to the residual
resonance in the deuterated solvents. IR spectra were obtained by
using a Nicolet iS10 MIR FTIR spectrometer. Arylbromides (Aryl=
Ph, 2-Py, 3-Py, 4-Py) were obtained from Acros Organics and Sigma
Aldrich, and were used without any additional purification. Rheni-
um pentacarbonyl bromide was purchased from ABCR. ESI-TOF-MS
was performed on an Agilent 6210 ESI-TOF instrument, Agilent
Technologies, Santa Clara, CA, USA (5 mLminÀ1, 4 kV, 15 psi.). The
voltage was optimised during measurements of the maximum
abundance of the [M+X] signal (X: H, Na, K). Microwave reactions
were performed with an Anton Paar Monowave 300 microwave.
DFT calculations
DFT calculations were carried out with the Gaussian 09 suite of pro-
grams.[25] Geometry optimisation was performed at the wB97xD/
aug-cc-pVTZ level[26] to account for dispersion effects, which were
likely to contribute significantly to interactions that influenced the
rotational energy surface. The complexes were calculated at the
wB97xD/6-31+G* level (for the transition metals, the def2-TZVP
basis set was used). Geometries were fully optimised and at the
minima second derivatives were calculated to ensure that real
minima were obtained. To find the rotational energy surfaces, re-
laxed scan calculations were carried out at 308 intervals. The com-
puted molecular structures and orbitals were visualised by means
of the MOLDEN program.[27]
General synthetic procedure for aryl azides
Aryl azides were synthesised by using a related protocol reported
by Liang et al.[28] The corresponding bromide (10 mmol) was dis-
solved in a degassed mixture of water/EtOH (100 mL; 7:3 v/v).
Sodium azide (2 equiv), copper iodide (10 mol%) and N,N’-dime-
thylethylenediamine (30 mol%) were added. The reaction mixture
was heated at reflux under an argon atmosphere for 2 h, cooled to
RT and diluted with H2O (50 mL). The organic compounds were ex-
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2
3
tracted by washing with Et2O (3”100 mL), and the combined or-
ganic phases were washed with brine, dried over MgSO4, concen-
trated and filtered through a SiO2 plug (ø=6,5 cm”3 cm). The sol-
vent was removed in vacuo and the crude products were used
without additional purification. There was one exception (see
below): tetrazolo[1,5-a]pyridine F (“2-azido pyridine”, see above)
was purified by column chromatography (SiO2, dichloromethane/
ethyl acetate 9:1 v/v).
C10), 36.0 (d, J(C,P)=15.5 Hz; tBu-C7), 116.1 (d, J(C,P)=8.3 Hz; Ar-
2
C3, Ar-C6), 147.8 (d, J(C,P)=11.4 Hz; Ar-C2), 152.1 (s; Ar-C4, Ar-C5),
199.8 ppm (d, J=55.4 Hz; Ar-C1); 31P{1H} NMR (162 MHz, CD2Cl2):
d=174.7 ppm (s); HR-ESI-TOF-MS (+, 150.0 V): m/z calcd for
C10H13N4P [M+H]+: 221.0951; found: 221.0965; elemental analysis
calcd (%) for C10H13N4P: N 25.44, C 54.54, H 5.95; found: N 25.76, C
54.41, H 5.84.
Compound 4a: White crystalline solid (715.21 mg, 3.26 mmol,
87%); 1H NMR (400 MHz, CD2Cl2): d=1.49 (d, 4J(H,P)=1.5 Hz, 9H;
Me-H9, Me-H10, Me-H11), 7.42 (m, 1H; Ar-H5), 7.48 (m, 2H; Ar-H4,
Ar-H6), 7.76 ppm (m, 2H; Ar-H3, Ar-H7); 13C NMR (176 MHz, CD2Cl2):
d=31.8 (d, 3J(C,P)=7.6 Hz; Me-C9, Me-C10, Me-C11), 35.9 (d,
2J(C,P)=16.2 Hz; tBu-C8), 122.8 (d, 3J(C,P)=7.3 Hz; Ar-C3, Ar-C7),
Compound 1a
Tetrazolo[1,5-a]pyridine (450.0 mg, 3.75 mmol, 1 equiv) was added
to
a
solution of (2,2-dimethyllidyne)phosphine (412.9 mg,
4.13 mmol, 1.5 equiv) in toluene (30 mL). The reaction mixture was
heated for 1 week at T=808C. After full conversion of the starting
material, the solvent and excess (2,2-dimethylpropylidyne)phos-
phine were removed in vacuo. The crude product was redissolved
in toluene at RT and crystallised by slow cooling to T=À208C.
Compound 1a was obtained as slightly yellow needles (437.7 mg,
1.99 mmol, 53%). 1H NMR (400 MHz, CD2Cl2): d=1.48 (d, 4J(H,P)=
1.6 Hz, 9H; Me-H9, Me-H10, Me-H11), 7.31 (ddd, 3J(H,H)=7.5 Hz,
3J(H,H)=4.9 Hz, 4J(H,H)=1.1 Hz, 1H; Ar-H5), 7.88 (td, 3J(H,H)=
7.8 Hz, 4J(H,H)=1.9 Hz, 1H; Ar-H4), 8.08 (dt, 3J(H,H)=8.3 Hz,
4J(H,H)=1.0 Hz, 1H), 8.44 ppm (ddd, 3J(H,H)=4.9 Hz, 4J(H,H)=
2
129.0 (s; Ar-C5), 130.1 (s; Ar-C4, Ar-C6), 141.6 (d, J(C,P)=10.4 Hz;
Ar-C2), 199.0 ppm (d, 1J(C,P)=55.5 Hz; Ar-C1); 31P{1H} NMR
(162 MHz, CD2Cl2): d=174.3 ppm (s); HR-ESI-TOF-MS (+, 200.0 V):
m/z calcd for C11H14N3P [M+H]+: 220.0998; found: 220.1013; ele-
mental analysis calcd (%) for C11H14N3P: N 19.17, C 60.27, H 6.44;
found: N 18.59, C 60.06, H 6.46.
Compound 5a: White crystalline solid (776.39 mg, 3.30 mmol,
88%); 1H NMR (500 MHz, CD2Cl2): d=1.43 (d, 4J(H,P)=1.6 Hz, 9H;
Me-H), 5.69 (d, 3J(H,P)=6.8 Hz, 2H; CH2), 7.36 ppm (m, 5H; Ar-
H);13C NMR (176 MHz, CD2Cl2): d=31.9 (d, J(C,P)=8.0 Hz; Me-C10,
Me-C11, Me-C12), 35.7 (d, 2J(C,P)=16.2 Hz; tBu-C9), 56.6 (d,
2J(C,P)=13.0 Hz; CH2-C2), 128.9 (s; Ar-C5, Ar-C7), 129.0 (s; Ar-C6),
129.4 (s; Ar-C4, Ar-C8), 137.9 (d, 4J(C,P)=1.9 Hz; Ar-C3), 199.3–
198.2 ppm (d, 1J(C,P)=56.3 Hz; Ar-C1); 31P{1H} NMR (162 MHz,
CD2Cl2): d=171.4 ppm (s); HR-ESI-TOF-MS (+, 200 V): m/z calcd for
C12H16N3P [M+H]+: 234.1155; found: 234.1151; elemental analysis
calcd (%) for C12H16N3P: N 18.02, C 61.79, H 6.91; found: N 17.79, C
61.79, H 6.91.
3
5
1.9 Hz, J(H,H)=0.9 Hz, 1H; Ar-H6); 13C NMR (176 MHz, CD2Cl2): d=
31.1 (d, 3J(C,P)=8.3 Hz; Me-C8, Me-C9, Me-C10), 35.3 (d, 2J(C,P)=
3
15.3 Hz; tBu-C7), 113.4 (d, J(C,P)=2.6 Hz; Ar-C3), 123.5 (s; Ar-C5),
139.1 (s; Ar-C4), 148.5 (s; Ar-C6), 153.3 (d, 2J(C,P)=8.4 Hz; Ar-C2),
199.0 ppm (d, 1J(C,P)=57.2 Hz; Ar-C1); 31P{1H} NMR (162 MHz,
CD2Cl2): d=167.51 ppm; HR-ESI-TOF-MS (+, 150.0 V): m/z calcd for
C10H13N4P [M+H]+: 221.0951; found: 221.0967; elemental analysis
calcd (%) for C10H13N4P: N 25.44, C 54.54, H 5.95; found: N 25.36, C
54.56, H 5.97.
General synthesis procedure of 5-TMS-substituted triaza-
phospholes
General synthesis of compounds 2a–5a
Aryl and benzyl azides (3.75 mmol) were mixed with a stirring bar
in a 250 mL Normag flask. Subsequently, the azide was frozen and
the flask was evacuated, followed by the addition of dry [(trime-
thylsilyl)methylidyne]phosphine (ꢁ100 mL) in toluene (large
excess). The reaction solution was allowed to warm to RT and was
stirred for 24 h. The solvent and excess alkyne were removed in
vacuo.
Aryl and benzyl azides (3.75 mmol) were mixed with a stirring bar
in a 100 mL Normag flask. Subsequently, the azide was frozen and
the flask was evacuated, followed by the addition of dry toluene
(ꢁ50 mL) and (dimethylidyne)phosphine (412.9 mg, 4.13 mmol,
1.5 equiv). The reaction solution was allowed to warm to RT and
was stirred for 24 h. The solvent and excess alkyne were removed
in vacuo. The resulting solid was recrystallised from a hot saturated
solution in n-pentane.
Compound 1b: Orange oil (806.34, 3.41 mmol, 91%); 1H NMR
(400 MHz, CD2Cl2): d=8.49 (ddd, J=4.9, 1.8, 0.9 Hz, 1H; HAr), 8.14
(dt, J=8.2, 0.9 Hz, 1H; HAr), 7.95–7.89 (m, 1H; HAr), 7.35 (ddd, J=
7.4, 4.9, 1.0 Hz, 1H; HAr), 0.44 ppm (d, J=0.6 Hz, 9H; CH3); 13C NMR
(101 MHz, CD2Cl2): d=186.4 (d, 1J(P,C)=74.0 Hz; C=P), 153.6 (d,
Compound 2a: White crystalline needles (668.89 mg, 3.04 mmol,
81%); 1H NMR (400 MHz, CD2Cl2): d=1.51 (d, 4J(H,P)=1.5 Hz, 9H;
tBu), 7.47 (ddd, 3J(H,H)=8.2 Hz, 3J(H,H)=4.8 Hz, 4J(H,H)=0.8 Hz,
1H; Ar-H4), 8.12 (dddd, 3J(H,H)=8.2 Hz, 4J(H,P)=2.5, 4J(H,H)=
1.5 Hz, 5J(H,H)=1.0 Hz, 1H; Ar-H3), 8.65 (dd, 3J(H,H)=4.8 Hz,
4
2J(P,C)=7.1 Hz; C2, Ar), 149.2, 139.8 (s; CAr), 124.2 (d, J(P,C)=1.1 Hz;
C4, Ar), 114.6 (d, 3J(P,C)=2.2 Hz; C3, Ar), À0.19 ppm (d, 3J(P,C)=3.8;
4
4
4J(H,H)=1.5 Hz, 1H; Ar-H5), 9.03 ppm (dt, J(H,P)=2.3 Hz, J(H,H)=
CH3); 31P{1H} NMR (162 MHz, CD2Cl2): d=211.6 ppm (s).
1.0 Hz, 1H; Ar-H6); 13C NMR (101 MHz, CD2Cl2): d=31.2 (d, J(C,P)=
7.9 Hz; Me-C8, Me-C9, Me-C10), 35.4 (d, 2J(C,P)=15.5 Hz; tBu-C7),
3
1
Compound 2b: Orange solid, (824.1 mg, 3.49 mmol, 93%). H NMR
3
2
124.1 (s; Ar-C4), 129.4 (d, J(C,P)=6.0 Hz; Ar-C3), 137.5 (d, J(C,P)=
9.4 Hz; Ar-C2), 143.4 (d, 3J(C,P)=8.6 Hz; Ar-C7), 149.7 (s; Ar-C5),
199.0 ppm (d, 1J(C,P)=56.5 Hz; Ar-C1); 31P{1H} NMR (162 MHz,
CD2Cl2): d=170.9 ppm (s); HR-ESI-TOF-MS (+, 250.0 V): m/z calcd
for C10H13N4P [M+H]+: 221.0951; found: 221.0969; elemental anal-
ysis calcd (%) for C10H13N4P: N 25.44, C 54.54, H 5.95; found: N
25.50, C 54.51, H 5.89.
(400 MHz, CD2Cl2): d=9.14–8.99 (m, 1H; HAr), 8.66 (dd, J=4.8,
1.4 Hz, 1H; HAr), 8.17–8.12 (m, 1H; HAr), 7.48 (ddt, J=8.2, 4.8,
0.8 Hz, 1H; HAr), 0.45 ppm (s, 9H; CH3); 13C NMR (101 MHz, CD2Cl2):
1
4
d=186.4 (d, J(P,C)=75.5 Hz; C=P), 150.3 (d, J(P,C)=1.2 Hz; C5, Ar),
2
3
144.1 (d, J(P,C)=7.7 Hz; C3, Ar), 130.2 (d, J(P,C)=5.3 Hz; C4, Ar), 124.7
(s; C6, Ar), À0.21 ppm (d, 3J(P,C)=3.6 Hz; CH3); 31P{1H} NMR
(162 MHz, CD2Cl2): d=213.7 ppm(s); HR-ESI-TOF-MS (+, 330 V): m/z
calcd for C9H13N4PSi [M+Na]+: 259.0539; found: 259.1177.
Compound 3a: White crystalline needles (685.4 mg, 3.11 mmol,
83%); 1H NMR (500 MHz, CD2Cl2): d=1.51 (d, 4J(H,P)=1.7 Hz, 9H;
Compound 4b: Red oil (803.0 mg, 3.41 mmol, 91%); 1H NMR
(400 MHz, CD2Cl2): d=7.82 (dt, J=8.4, 1.2 Hz, 2H; HAr), 7.55–7.50
(m, 2H; HAr), 7.48–7.42 (m, 1H; HAr), 0.46 ppm (d, J=0.6 Hz, 9H;
3
4
Me-H8, Me-H9, Me-H10,), 7.79 (dt, J(H,H)=4.6 Hz, J(H,P)=1.4 Hz,
2H; Ar-H4, Ar-H5), 8.70 ppm (m, 2H; Ar-H3, Ar-H6); 13C NMR
(176 MHz, CD2Cl2): d=31.6 (d, 3J(C,P)=8.1 Hz; Me-C8, Me-C9, Me-
1
Me); 13C NMR (101 MHz, CD2Cl2): d=185.7 (d, J(P,C)=74.7 Hz; C=
Chem. Eur. J. 2015, 21, 11096 – 11109
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11106
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
2
4
P), 141.3 (d, J(P,C)=9.3 Hz; C1, Ar), 130.2 (s; C4, Ar), 129.1 (d, J(P,C)=
1.1 Hz; C3,3’, Ar), 123.1 (d, 3J(P,C)=6.5 Hz; C2,2’ Ar), À0.13 ppm (d,
3J(P,C)=3.6 Hz; Me); 31P{1H} NMR (162 MHz, CD2Cl2): d=213.0 ppm
(s).
Compound 7a: Red needles (44.2 mg, 0.08 mmol, 63%); 1H NMR
(700 MHz, CD2Cl2): d=1.57 (d, 4J(H,P)=1.5 Hz, 9H; Me-H11, Me-
3
4
5
H12, Me-H13), 7.35 (ddd, J(H,H)=7.3 Hz, J(H,H)=5.6 Hz, J(H,H)=
3
1.1 Hz, 1H; Ar-H5), 8.06 (d, J(H,H)=8.2 Hz, 1H; Ar-H3), 8.16 (ddd,
3J(H,H)=8.2 Hz, 4J(H,H)=7.6 Hz, 5J(H,H)=1.7 Hz, 1H; Ar-H4),
Compound 5b: White crystalline solid (876.5 mg, 3.49 mmol,
93%); 1H NMR (400 MHz, CD2Cl2): d=0.38 (d, 4J(H,P)=0.5 Hz, 9H;
Me-H9, Me-H10, Me-H11), 5.81 (d, 3J(H,P)=6.0 Hz, 2H), 7.37 ppm
(m, 1H); 13C NMR (101 MHz, CD2Cl2): d=À0.13 (d, 3J(C,P)=3.5 Hz;
Me-C9, Me-C10, Me-C11), 56.1 (d, 2J(C,P)=12.1 Hz; CH2-C2), 128.9
(d, 4J(C,P)=1.2 Hz; Ar-C4, Ar-C5), 129.0 (s; Ar-C6), 129.4 (s; Ar-C5,
Ar-C7), 137.9 (d, 3J(C,P)=2.0 Hz; Ar-C3), 185.5 ppm (d, 1J(C,P)=
74.8 Hz; Ar-C1); 31P NMR (162 MHz, CD2Cl2): d=214.7 ppm (s); HR-
ESI-TOF-MS (+, 200 V): m/z calcd for C11H16N3PSi [M+H]+:
250.0924; found: 250.0909; elemental analysis calcd (%) for
C11H16N3PSi: N 16.85, C 52.99, H 6.47; found: N 16.67, C 52.69, H
6.48.
3
4
8.92 ppm (dd, J(H,H)=5.4 Hz, J(H,H)=1.4 Hz, 1H; Ar-H6); 13C NMR
(176 MHz, CD2Cl2): d=31.4 (d, 3J(C,P)=9.1 Hz; Me-C11, Me-C12,
Me-C13), 36.7 (d, 2J(C,P)=14.6 Hz), 116.7 (d, 3J(C,P)=13.5 Hz; Ar-
C3), 126.2 (s; Ar-C5), 142.3 (s; Ar-C4), 152.9 (s; Ar-C6), 153.0 (d,
2J(C,P)=10.0 Hz), 188.1 (s; CO), 195.2 (s; CO), 197.1 (s; CO),
201.6 ppm (d, 1J(C,P)=60.9 Hz), 31P NMR (162 MHz, CD2Cl2): d=
184.1 ppm (s); HR-ESI-TOF-MS (+, 200 V): m/z calcd for
C13H13BrN4O3PRe [MÀBr+MeCN]+: 532.0543; found: 532.0583; ele-
mental analysis calcd (%) for C13H13BrN4O3PRe: N 8.55, C 25.66, H
2.31; found: N 8.89, C 26.15, H 2.32; one molecule of CH2Cl2 is
found in the lattice of the molecular structure in the crystal.
Compound 8a: Yellow needles (38.7 mg, 0.07 mmol, 57%);
1H NMR (700 MHz, CDCl3): d=1.45 (s, 9H; Me-H12, Me-H13, Me-
H14), 7.35 (ddd, J=7.6, 5.6, 1.0 Hz, 1H; Ar-H5), 7.81 (d, 3J(H,H)=
General synthesis of 1,2,3-triazoles
3
8.2 Hz, 1H; Ar-H4), 8.15 (s, 1H; ArTriazol-H2), 8.19 (ddd, J(H,H)=8.3,
Copper(I) trifluoromethanesulfonate benzene complex (188.7 mg,
0.375 mmol, 10 mol%) was added to tetrazolo[1,5-a]pyridine (F;
450 mg, 3.75 mmol) in a 20 mL microwave reaction vessel. Dry tol-
uene (20 mL) was added along with substituted alkyne
(4.125 mmol, 1.1 equiv). The mixture was heated to 1408C for 4 h
in the microwave. After cooling the reaction vessel to RT, the sol-
vent was removed in vacuo and column chromatography (SiO2,
CH2Cl2/ethyl ether 9:1 v/v) gave the pure title compounds.
4J(H,H)=7.6 Hz, 5J(H,H)=1.6 Hz, 1H; Ar-H6), 8.97 ppm (ddd,
3J(H,H)=5.5 Hz, 4J(H,H)=1.5 Hz, 5J(H,H)=0.6 Hz, 1H; Ar-H7);
13C NMR (176 MHz, CDCl3): d=30.1 (s; Me-C12, Me-C13, Me-C14),
31.7 (s; tBu-C11), 113.2 (s; Ar-C4), 118.0 (s), 125.7 (s; Ar-C5), 142.0
(s; Ar-C6), 147.7 (s; Ar-C3), 153.3 (s; Ar-C7), 161.7 (s; Ar-C1), 187.6
(s; CO), 193.9 (s; CO), 195.9 ppm (s; CO); HR-ESI-TOF-MS (+,
150.0 V): m/z calcd for C14H14BrN4O3Re [M+Na]+: 574.9699; found:
574.9704; elemental analysis calcd (%) for C14H14BrN4O3Re: N 10.14,
C 30.44, H 2.55; found: N 9.76, C 30.08, H 2.67.
1
Compound 6a: White solid (583.62 mg, 2.89 mmol, 77%); H NMR
(500 MHz, CDCl3): d=1.41–1.38 (s, 9H; Me-H12, Me-H13, Me-H14),
3
3
4
7.29 (ddd, J(H,H)=7.4 Hz, J(H,H)=4.9 Hz, J(H,H)=1.0 Hz, 1H; Ar-
H6), 7.87 (ddd, 3J(H,H)=8.2 Hz, 3J(H,H)=7.4 Hz, 4J(H,H)=1.8 Hz,
1H; Ar-H5), 8.16 (dt, 3J(H,H)=8.2 Hz, 4J(H,H)=1.0 Hz, 1H; Ar-H4),
8.27 (s, 1H; ArTriazol-H2), 8.46 ppm (ddd, 3J(H,H)=4.9 Hz, 4J(H,H)=
X-ray crystal-structure determination of 1a
Crystals suitable for XRD were obtained by cooling a saturated so-
lution of 1a in toluene. Crystallographic data: C10H13N4P; Mr =
220.21; 0.50”0.37”0.29 mm3; colourless blocks; orthorhombic;
Pnma; a=7.9500(10), b=6.8020(8), c=20.732(3) Š; a=90, b=90,
5
1.9 Hz, J(H,H)=0.9 Hz, 1H; Ar-H7); 13C NMR (126 MHz, CDCl3): d=
30.3 (s; Me-C12, Me-C13, Me-C14), 31.0 (s; tBu-C11), 113.9 (s; Ar-
C4), 116.1 (s; ArTriazol-C2), 123.3 (s; Ar-C6), 139.2 (s; Ar-C5), 148.5 (s;
Ar-C7), 149.6 (s; Ar-C3), 158.2 ppm (s; ArTriazol-C1); HR-ESI-TOF-MS
(+, 100.0 V): m/z calcd for C11H14N4 [M+Na]+: 225.11107; found:
225.1126; elemental analysis calcd (%) for C11H14N4: N 27.70, C
65.32, H 6.98; found: N 28.17, C 65.15, H 6.79.
g=908; V=1121.1(3) Š3; Z=4; Dx =1.305 gcmÀ3; m=0.218 mmÀ1
;
6647 reflections were measured by using a Stoe IPDS 2T diffrac-
tometer with a rotating anode (MoKÀa1radiation; l=0.71073 Š) up
to a resolution of sinq/l)max =0.69 Š at a temperature of 210 K;
1607 reflections were unique (Rint =0.035). The structures were
solved with SHELXS-2013[31] by using direct methods and refined
with SHELXL-2013[31] on F2 for all reflections. Non-hydrogen atoms
were refined by using anisotropic displacement parameters. The
positions of the hydrogen atoms were calculated for idealised posi-
tions. 89 parameters were refined with one restraint. R1 =0.037 for
1136 reflections with I>2s(I) and wR2 =0.097 for 1607 reflections,
S=0.937, residual electron density was between À0.26 and
0.19 eŠÀ3. Geometry calculations and checks for higher symmetry
were performed with the PLATON program.[32]
1
Compound 6b: White solid (483.0 mg, 2.21 mmol, 59%); H NMR
(500 MHz, CDCl3): d=0.37 (s, 9H; Me-H11, Me-H12, Me-H13), 7.32
(ddd, 3J(H,H)=7.4 Hz, 3J(H,H)=4.9 Hz, 4J(H,H)=1.0 Hz, 1H; Ar-H6),
3
3
4
7.90 (ddd, J(H,H)=8.2 Hz, J(H,H)=7.4 Hz, J(H,H)=1.8 Hz, 1H; Ar-
H5), 8.20 (dt, 3J(H,H)=8.2 Hz, 4J(H,H)=1.0 Hz, 1H; Ar-H4), 8.49
(ddd, 3J(H,H)=4.9 Hz, 4J(H,H)=1.9 Hz, 5J(H,H)=0.9 Hz, 1H; Ar-H7),
8.55 ppm (s, 1H; ArTriazol-H2); 13C NMR (126 MHz, CDCl3): d=À1.1 (s;
Me-C12, Me-C13, Me-C14), 114.4 (s; Ar-C4), 123.4 (s; Ar-C6), 126.5
(s; ArTriazol-C2), 139.3 (s; Ar-C5), 147.3 (s; Ar-C3), 148.6 (s; Ar-C7),
149.5 ppm (s; ArTriazol-C1); HR-ESI-TOF-MS (+, 150.0 V): m/z calcd for
C10H14N4Si [M+Na]+: 241.0880; found: 241.0881; elemental analysis
calcd (%) for C10H14N4Si: N 25.66, C 55.01, H 6.46; found: N 25.59, C
54.92, H 6.52.
CCDC 1046565 (1a) contains the supplementary crystallographic
data for this paper. These data are provided free of charge by The
Cambridge Crystallographic Data Centre
X-ray crystal-structure determination of 2a
General synthesis of ReI complexes
Crystals suitable for XRD were obtained by cooling a saturated so-
lution of 2a in pentane. Crystallographic data: C10H13N4P; Mr =
220.21; 0.45”0.09”0.09 mm3; colourless needles; monoclinic; P21;
a=6.2161(13), b=11.251(3), c=8.1840(19) Š; a=90, b=
92.885(18), g=908; V=571.6(2) Š3; Z=2; Dx =1.280 gcmÀ3; m=
0.214 mmÀ1; 6489 reflections were measured by using a Stoe IPDS
2T diffractometer with a rotating anode (MoKa radiation; l=
[Re(CO)5Br] (50 mg, 0.123 mmol) was mixed with ligand 5a or 6a
(0.123 mmol) in a Young NMR tube and suspended in dry CD2Cl2
(0.5 mL). The reaction mixture was heated for 8 h at 808C, leading
1
to full conversion (as determined by H/31P NMR spectroscopy). The
precipitated product was recrystallised by cooling a hot saturated
solution of 7a or 8a slowly, yielding single-crystalline pure com-
pounds.
À1
0.71073 Š) up to a resolution of sinq/l)max =0.69 Š at a tempera-
Chem. Eur. J. 2015, 21, 11096 – 11109
www.chemeurj.org
11107
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
ture of 200 K; 1796 reflections were unique (Rint =0.159). The struc-
tures were solved with SHELXS-2013[31] by using direct methods
and refined with SHELXL-2013[31] on F2 for all reflections. Non-hy-
drogen atoms were refined by using anisotropic displacement pa-
rameters. The positions of the hydrogen atoms were calculated for
idealised positions. 140 parameters were refined with one restraint.
R1 =0.070 for 1796 reflections with I>2s(I) and wR2 =0.188 for
3082 reflections, S=0.906, residual electron density was between
À0.50 and 0.58 eŠÀ3. Geometry calculations and checks for higher
symmetry were performed with the PLATON program.[32]
CCDC 1046567 (7a) contains the supplementary crystallographic
data for this paper. These data are provided free of charge by The
Cambridge Crystallographic Data Centre.
X-ray crystal-structure determination of 8a
Crystals suitable for XRD were obtained by cooling a hot saturated
solution of 8a in dichloromethane. Crystallographic data:
C14H14BrN4O3Re·CH2Cl2; Mr =637.33; 0.13”0.10”0.08 mm3; yellow
rhombus; monoclinic; P21/c; a=12.5797(10), b=8.8545(5), c=
19.1529(15) Š; a=90, b=106.558(6), g=908; V=2043.9(3) Š3; Z=
4; Dx =2.071 gcmÀ3; m=8.183 mmÀ1. 15327 reflections were mea-
sured by using a Stoe IPDS 2T diffractometer with a rotating anode
CCDC 1046566 (2a) contains the supplementary crystallographic
data for this paper. These data are provided free of charge by The
Cambridge Crystallographic Data Centre.
(MoKa radiation; l=0.71073 Š) up to a resolution of sinq/l)max
=
À1
0.69 Š at a temperature of 200 K. The reflections were corrected
for absorption and scaled on the basis of multiple measured reflec-
tions by using the X-Red program (0.47–0.58 correction range);[30]
5482 reflections were unique (Rint =0.054). The structures were
solved with SHELXS-2013[31] by using direct methods and refined
with SHELXL-2013[31] on F2 for all reflections. Non-hydrogen atoms
were refined by using anisotropic displacement parameters. The
positions of the hydrogen atoms were calculated for idealised posi-
tions; 239 parameters were refined with one restraint. R1 =0.034
for 3653 reflections with I>2s(I) and wR2 =0.069 for 5482 reflec-
tions, S=0.986, residual electron density was between À1.33 and
1.18 eŠÀ3. Geometry calculations and checks for higher symmetry
were performed with the PLATON program.[32]
X-ray crystal-structure determination of 3a
Crystals suitable for XRD were obtained by cooling a saturated so-
lution of 3a in pentane. Crystallographic data: C10H13N4P; Mr =
220.21; 0.34”0.09”0.08 mm3; colourless cylinders, monoclinic;
P21/m; a=6.8490(7), b=7.0770(12), c=12.248(4) Š; a=90, b=
106.236(13), g=908; V=570.0(2) Š3; Z=2; Dx =1.283 gcmÀ3; m=
0.215 mmÀ1; 2965 reflections were measured by using a Stoe IPDS
2T diffractometer with a rotating anode (MoKa radiation; l=
À1
0.71073 Š) up to a resolution of sinq/l)max =0.69 Š at a tempera-
ture of 200 K. 1684 reflections were unique (Rint =0.059). The struc-
tures were solved with SHELXS-2013[31] by using direct methods
and refined with SHELXL-2013[31] on F2 for all reflections. Non-hy-
drogen atoms were refined by using anisotropic displacement pa-
rameters. The positions of the hydrogen atoms were calculated for
idealised positions. 89 parameters were refined with one restraint.
R1 =0.040 for 1154 reflections with I>2s(I) and wR2 =0.094 for
1627 reflections, S=0.947, residual electron density was between
À0.25 and 0.26 eŠÀ3. Geometry calculations and checks for higher
symmetry were performed with the PLATON program.[32]
CCDC 1046568 (8a) contains the supplementary crystallographic
data for this paper. These data are provided free of charge by The
Cambridge Crystallographic Data Centre.
Determination of optical data
UV/Vis spectra were recorded at room temperature on a Varian
Cary 5000 UV/Vis/near-IR spectrophotometer. Luminescence spec-
tra were recorded at room temperature with a FS920 Steady State
Fluorimeter (M300, UC920, CD920/CD930, S900) equipped with
a xenon lamp (Xe900). All spectra were recorded in CH2Cl2 (SDS,
CCDC 1046564 (3a) contains the supplementary crystallographic
data for this paper. These data are provided free of charge by The
Cambridge Crystallographic Data Centre.
HPLC grade) stabilised with ethanol, with concentrations of 5.10À6
,
10À5, 5.10À5 and 10À4 m. Quantum yields were calculated relative to
quinine sulfate (f=0.55 in 0.1n H2SO4)[29] or to [Ru(bpy)3]2+ in
H2O, f[Ru(bpy)3]2+ =4.2%)[29] by using Equation (1):
X-ray crystal-structure determination of 7a
Crystals suitable for XRD were obtained by cooling a hot saturated
solution of 7a in dichloromethane. Crystallographic data:
C13H13BrN4O3PRe·CH2Cl2; Mr =655.28; 0.34”0.09”0.08 mm3; yellow
Â
Ã
Qx=Qr ¼ ½ArðlÞ=Axðl0ފ nx2=nr2 ½Dx=DrŠ
ð1Þ
¯
needles, triclinic; P1; a=13.4120(11), b=18.0785(18), c=
in which A is the absorbance at the excitation wavelength (l), n is
the refractive index and D is the integrated luminescence intensity;
r and x represent reference and sample, respectively. Excitations of
reference and sample compounds were performed at the maxi-
mum wavelength of the molecules.
8.6707(8) Š; a=89.999(8), b=91.816(7), g=89.998(7)8; V=
570.0(2) Š3; Z=4; Dx =2.071 gcmÀ3; m=8.0355 mmÀ1; 22878 re-
flections were measured by using a Stoe IPDS 2T diffractometer
with a rotating anode (MoKÀa1radiation; l=0.71073 Š) up to a reso-
lution of sinq/l)max =0.69 Š at a temperature of 200 K. The reflec-
tions were corrected for absorption and scaled on the basis of mul-
tiple measured reflections by using the X-Red program (0.73–0.91
correction range).[30]11 254 reflections were unique (Rint =0.222). Acknowledgements
The structures were solved with SHELXS-2013[27] by using direct
methods and refined with SHELXL-2013[31] on F2 for all reflections.
Financial support from OTKA
K 105417, Balaton PHC
Non-hydrogen atoms were refined by using anisotropic displace-
(830386K)–FR_12_TET_A044DF3B and COST CM10302 (SIPS)
and the Bolyai Fellowship for D.S. is gratefully acknowledged.
C.M. thanks the Deutsche Forschungsgemeinschaft (DFG), the
European Initial Training Network SusPhos (317404) and the
Free University of Berlin, Institute of Chemistry and Biochem-
istry, for financial support.
ment parameters. The positions of the hydrogen atoms were calcu-
lated for idealised positions. 475 parameters were refined with one
restraint. R1 =0.054 for 4608 reflections with I>2s(I) and wR2 =
0.082 for 11 254 reflections, S=0.774, residual electron density was
between À0.25 and 0.26 eŠÀ3. Geometry calculations and checks
for higher symmetry were performed with the PLATON program.[32]
Chem. Eur. J. 2015, 21, 11096 – 11109
www.chemeurj.org
11108
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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Keywords: coordination
calculations · heterocycles · luminescence · phosphorus
modes
·
density
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Received: March 12, 2015
Published online on June 26, 2015
Chem. Eur. J. 2015, 21, 11096 – 11109
www.chemeurj.org
11109
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim