Bipyridyl– and pyridylquinolyl–phenothiazine structures as potential photoactive ligands: Syntheses and complexation to palladium

Article abstract of DOI:10.1016/j.tetlet.2017.06.073

Three new bipyridyl– and pyridylquinolyl–phenothiazine structures were synthesized through Pd-catalyzed C–N couplings between phenothiazine and the corresponding bromo-heteroaryls. For the 2-(N-phenothiazine)-bipyridine, boat conformation was determined for the phenothiazine moiety by X-ray diffraction analysis. Single well-defined palladium acetate complexes were observed by ¹H NMR analysis with the 4-(N-phenothiazine)-bipyridine and the pyridyl-5-(N-phenothiazine)-quinoline. Compared to the naked ligands, the UV–visible absorption spectra showed, in these cases, significantly red shifted λ_max upon coordination. Preliminary modeling experiments with the free and the coordinated 4-(N-phenothiazine)-bipyridine suggested for both the occurrence of electronic transfers from the phenothiazine to the bipyridine. Potentially enabling the tuning of the electron density of the coordinating moiety upon near-UV irradiation, this bipyridyl–phenothiazine structure could be the origin of a novel class of photo-active ligands for applications in organometallic catalysis.

Full text of DOI:10.1016/j.tetlet.2017.06.073

Accepted Manuscript
Bipyridyl– and pyridylquinolyl–phenothiazine structures as potential photoac-
tive ligands: syntheses and complexation to palladium.
Alexis Tabey, Jonathan Mendy, Philippe Hermange, Eric Fouquet
PII:
S0040-4039(17)30811-0
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.06.073
TETL 49065
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
27 April 2017
9 June 2017
23 June 2017
Please cite this article as: Tabey, A., Mendy, J., Hermange, P., Fouquet, E., Bipyridyl– and pyridylquinolyl–
phenothiazine structures as potential photoactive ligands: syntheses and complexation to palladium., Tetrahedron
Letters (2017), doi: http://dx.doi.org/10.1016/j.tetlet.2017.06.073
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Graphical Abstract
Bipyridyl– and pyridylquinolyl–
phenothiazine structures as potential
photoactive ligands: syntheses and
complexation to palladium.
Leave this area blank for abstract info.
Alexis Tabey, Jonathan Mendy, Philippe Hermange* and Eric Fouquet*

1
Tetrahedron Letters
Bipyridyl– and pyridylquinolyl–phenothiazine structures as potential photoactive
ligands: syntheses and complexation to palladium.
Alexis Tabey, Jonathan Mendy, Philippe Hermange* and Eric Fouquet*
Univ. Bordeaux, Institut des Sciences Moléculaires, UMR-CNRS 5255, 351, Cours de la Libération, 33405 Talence Cedex, France.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Three new bipyridyl– and pyridylquinolyl–phenothiazine structures were synthesized through
Pd-catalyzed C–N couplings between phenothiazine and the corresponding bromo-heteroaryls.
For the 2-(N-phenothiazine)-bipyridine, boat conformation was determined for the phenothiazine
moiety by X-ray diffraction analysis. Single well-defined palladium acetate complexes were
1
Available online
observed by H NMR analysis with the 4-(N-phenothiazine)-bipyridine and the pyridyl-5-(N-
phenothiazine)-quinoline. Compared to the naked ligands, the UV-visible absorption spectra
showed, in these cases, significantly red shifted λmax upon coordination. Preliminary modeling
experiments with the free and the coordinated 4-(N-phenothiazine)-bipyridine suggested for both
the occurrence of electronic transfers from the phenothiazine to the bipyridine. Potentially
enabling the tuning of the electron density of the coordinating moiety upon near-UV irradiation,
this bipyridyl–phenothiazine structure could be the origin of a novel class of photo-active
ligands for applications in organometallic catalysis.
Keywords:
Photo-redox catalysis
Redox-active ligands
Palladium
Phenothiazine
C-N coupling
2
009 Elsevier Ltd. All rights reserved
1
2
13
Tremendous attention has been recently focused on the
development of novel efficient, mild and green synthetic methods
using visible-light photoredox catalysis, and the field is now
well-established as a powerful strategy in the toolbox of organic
Applied in numerous field like solar cells, sensors, atom
14,15
transfer radical polymerization (ATRP),
or photoredox
16
catalysis, the phenothiazine moiety (PTZ) was selected as light
17
absorbing entity and its Pd-catalyzed C–N coupling was
envisaged with bromo-substituted bipyridyl or pyridylquinolyl
backbones (Scheme 1).
1
chemists. Indeed, excited states of metal- or organic-based
photosensitizers (PS) are generally suitable for single electron
transfers (SET) with a wide range of substrates. As a result,
photoredox catalysis facilitates the access to highly reactive
2
radicals, prone to consecutive chemical transformations, or can
be combined to other organic- or organometallic-catalytic cycles,
3
increasing exponentially the synthetic possibilities. For instance,
previously inaccessible elementary steps can be achieved by in
situ modification of the oxidation state of an organometallic
intermediate, through SET between the photo-excited PS* and
Scheme 1. Retro-synthetic route envisaged for the preparation of
the bipyridyl– and pyridylquinolyl– phenothiazine ligands.
4
the metallic center. In all cases, concomitantly with oxidation
and reduction potentials, lifetime of the photo-excited species is
an essential parameter in these intermolecular electron transfers,
and can sometimes be a restrictive point in the development of
Commercial 6-bromo-2,2-bipyridine 1 was firstly selected as
substrate and reacted with phenothiazine employing Pd(dba)
2
(2
t
mol%) as palladium source, HP Bu
3
. BF
4
(10 mol%) as ligand
5
new synthetic methods. Thus, intramolecular processes would
t
18
and BuOK (1.5 equiv.) as base in toluene at 80°C for 24h.
allow to suppress this constraint, and could improve the overall
efficiency of the reaction. For example, the design of novel
unimolecular photosensitizer – catalyst structures has already6
proved to be a successful strategy for double bond isomerisation,
However, only traces of products could be detected in this case.
t
Thus, keeping BuOK (1.5 equiv.) as base, RuPhos-Pd-G2 was
selected as precatalyst (10 mol%) and the reaction was run in
14
dioxane at 110°C for 18h. With this new set of conditions, the
7
8
thioether oxidation or C-C bond formation. Ru(bpy)
Ir(bpy) -derivatives were used in most of these studies for their
ideal photo-physical properties.
x
and
desired product was secured in a correct yield of 48% after
column chromatography on silica gel (Figure 1, A). Interestingly,
x
1b
However, organic-based
slow evaporation of a CDCl
3
solution of L1 allowed to produce
9
moieties also showed promising properties, avoiding the using of
costly metals. In this context, we aimed to design new bipyridyl-
based ligands directly coupled to a full-organic photosensitive
unit. Indeed, after complexation to the metal catalyst, internal
electronic transfers might occur under irradiation, which could
suitable monocrystals for X-ray diffraction analysis (Figure 1,
19
B). The expected boat conformation of the phenothiazine was
confirmed by this solid-state structure, and bond lengths / angles
were similar to previously described values for N-heteroaryl-
20
phenothiazine. Especially, the torsion angles measured at the
1
0,11
tune finely the catalytic synthetic activity of the complex.
PTZ nitrogen indicated a more important lone pair delocalization

2
Tetrahedron
8,24
into the 2,2’-bipyridyl functionality than into the two ortho-
phenylene groups of the phenothiazine.
ligands, we decided to evaluate this potential issue by studying
the complexation of our set of molecules to Pd(II). L1, L2, L3
and the reference compound 2,2'-bipyridine (bpy) were mixed
with equimolar quantities of Pd(OAc)
2
in deuterated chloroform,
1
A)
and sonicated for 60 min before recording the H NMR spectra of
2
5
the resulting solutions (Figure 2). A mixture of two species in a
0/60 ratio was observed in the case of L1, probably due to the
4
presence of rotamers or to the various bidentate complexation
possibilities for the palladium in this potential tri-or tetra-dentate
ligand. On the contrary, single well-defined species were
observed for both ligands L2 and L3.
B)
A)
B)
(
A) Method A: 6-bromo-2,2-bipyridine (0.65 mmol), phenothiazine (1.1
t
equiv), Pd(dba)
2
(2 mol %), HP Bu
3
. BF
4
(10 mol%), t-BuOK (1.5 equiv),
toluene (1 mL) at 80 °C for 24 h. Method B: 6-bromo-2,2-bipyridine (0.3
mmol), phenothiazine (1.3 equiv), RuPhos-Pd-G2 (10 mol %), t-BuOK (1.5
equiv), dioxane (1 mL) at 110 °C for 18 h. (B) Drawings with 50% thermal
ellipsoids. Selected torsion angles: (C7)-(N14)-(C15)-(N20) 15.65°, (C11)-
(
N14)-(C15)-(C16) -7.22°, (C15)-(N14)-(C11)-(C12) 71.84°, (C15)-(N14)-
C7)-(C6) -72.59°, (N20)-(C19)-(C21)-(N26) -166.32°.
(
C)
D)
Figure 1. Synthesis of ligand L1 and Mercury drawings of its
structure obtained by X-Ray diffraction analysis.
Then, the same synthetic procedure was applied to two other
bromo-heteroaryls. Firstly, 4-bromo-2,2-bipyridine
2
was
2
1
prepared according to the literature
and reacted with
phenothiazine to obtained the desired coupling product L2 with
an excellent yield of 93% (Scheme 2). Then, the 5-
bromoquinoline derivative 3 was synthesized by a Friedländer
condensation between 2-amino-6-bromobenzaldehyde 4 and 2-
22
acetylpyridine 5. Quinoline 3 was isolated in an excellent yield
of 92% and engaged in the following C-N bond formation step to
2
3
obtain ligand L3 in 56% yield.
Figure 2. Proton NMR spectra in CDCl
3
of bpy (A) , L1 (B) , L2
(
C) , L3 (D) and signal shifts upon complexation with one equivalent
2
of Pd(OAc) .
1
The H NMR spectra of the L2 - palladium acetate complex
(
1:1) was very similar to (bpy)Pd(OAc) , supporting common
2
26
structural parameters for the two species. Upon complexation,
both lead to deshielded signals of 4’ and shielding of the 6,6’ /
3,3’ protons. Interestingly, all the signals of the protons of the
phenothiazine group were also shifted downfield (up to 0.1 ppm),
which indicated a decrease of the electron density in this moiety.
The same tendency was observed for L3, with a deshielding of
the PTZ signals ranging from 0.02 to 0.08 ppm. However, in this
case, the overall electron density remains higher in this part of
2
the molecule when compared to (L2)Pd(OAc) . This was
consistent with the more important delocalization of the lone pair
of the PTZ nitrogen into the two ortho-phenylene groups, which
can be observed with more hindered N-heteroaryl-
Scheme 2. Syntheses of ligands L2 and L3.
Sulfur is known to be an excellent coordinating atom for
metals, and adding a phenothiazine group might disturb the
desired bidentate ligation expected from the bipyridyl moiety. As
palladium has already demonstrated interesting synthetic
applications when combined to photo- and redox-active
27
phenothiazine.
Having demonstrated the coordinating abilities of the L2 and
L3 ligands, the potential behavior upon photoexcitation of the
resulting complexes with palladium acetate were examined. After

3
2
8
switching the solvent to acetonitrile, UV-visible absorption of
these species were measured and compared to the free ligands, as
summarized in Figure 3.
G2 as precatalyst. Structural parameters for L1 were obtained
by X-ray diffraction analysis and the boat conformation of its
phenothiazine was confirmed. Their abilities to form defined
1
complexes with Pd(OAc)
2
were examined by H NMR analysis
In both cases, the number of local extrema between 300 to 500
nm was identical for the free and the coordinated ligands. For
example, one absorption band at 314 nm was observed for L2,
which could be assigned to a π-π* transition, and this λmax was
red shifted to 354 nm upon complexation, indicating a strong
decrease of the energy gap of this electronic transition. Similarly,
a bathochromic effect appeared when forming (L3)Pd(OAc) .
2
Indeed, the 322 nm and 337 nm peaks of L3 were shifted to 343
nm and 358 nm, respectively. It should be noted that no specific
and proved for ligands L2 and L3. Significant bathochromic
shifts were observed in the UV-visible absorption spectra upon
complexation, and preliminary modeling experiments realized for
29
2
L2 and (L2)Pd(OAc) suggested an electronic transfer from the
PTZ to the coordinating bipyridyl moiety. Further fundamental
studies and applications of this potential photo-electronically
tunable ligand are currently explored and will be reported in due
time.
2
transition could be detected for (bpy)Pd(OAc) in this range of
wavelengths, proving the benefits of the PTZ moiety when
employing near-ultraviolet or visible light irradiations.
Figure 4. Frontier and selected molecular orbitals of L2 and
(
2
L2)Pd(OAc) .
Acknowledgments
This study was supported by a public grant from the French
Agence Nationale de la Recherche (AAP JCJC 2015), referenced
ANR-15-CE18-0015-01 and named SuCarB. We thank Dr. Raphaël
Méreau for his help for the modeling experiments.
Figure 3. UV-visible absorption spectra of L2, L3,
(
(
L2)Pd(OAc)
300 to 500 nm, relative scale to the absorbance at 300 nm for L2,
(L3)Pd(OAc) and at 310 nm for
2 2 2
, (L3)Pd(OAc) and (bpy)Pd(OAc) in acetonitrile
L3, (L2)Pd(OAc)
bpy)Pd(OAc) ).
2
,
2
References and notes
(
2
Attempting to understand these effects, simple preliminary
modeling experiments were realized to compare the HOMO and
LUMO in L2 and (L2)Pd(OAc) (Figure 4). For the naked
2
ligand, the highest occupied molecular orbital was mainly
centered onto the phenothiazine, whereas its lowest unoccupied
molecular orbital was localized in the bipyridyl part of the
molecule. Thus, the electron transfer from the PTZ moiety to the
bpy could likely occur upon photo-excitation, and probably
correspond to the observed π-π* transition absorbing at 314 nm.
1. For selected recent reviews on photoredox catalysis, see: (a) Shaw, M.
H.; Twilton, J.; MacMillan, D. W. C. J. Org. Chem. 2016, 81, 6898–
6926. (b) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem. Rev.
30
2
2
013, 113, 5322–5363. (c) Romero, N. A.; Nicewicz, D. A. Chem. Rev.
016, 116, 10075–10166.
2. For selected recent reviews, see: (a) Yoon, T. P. ACS Catal. 2013, 3,
895–902. (b) Goddard, J.-P.; Ollivier, C.; Fensterbank, L. Acc. Chem.
Res. 2016, 49, 1924–1936. (c) Hering, T.; Meyer A. U., Köning, B. J.
Org. Chem. 2016, 81, 6927–6936.
3
.
For selected recent reviews on dual transition metal-photoredox
catalysis, see: (a) Hopkinson, M. N.; Sahoo, B.; Li, J.-L.; Glorius, F.
Chem. Eur. J. 2014, 20, 3874–3886. (b) Skubi, K. L.; Blum, T. R.;
Yoon, T. P. Chem. Rev. 2016, 116, 10035–10074. (c) Tóth, B. L.;
Tischler, O.; Novák, Z. Tetrahedron Lett. 2016, 57, 4505–4513.
For a case example, see: Terrett, J. A.; Cuthbertson, J. D.; Shurtleff, V.
W; MacMillan, D. W. C. Nature 2015, 524, 330–334.
2
After coordination to Pd(OAc) , the shape of the LUMO of the
resulting complex was highly similar to the one observed for the
free L2, but the HOMO was exclusively localized at the Pd-
center and the acetate ligands. Decreasing in energy, three other
MO were similarly centered onto the palladium atom before
reaching the highest molecular orbital implying the
phenothiazine. Interestingly, despite the coordination of the
4
5
.
.
For an example, see: Lévêque, C.; Chenneberg, L.; Corcé, V.; Ollivier,
C.; Fensterbank, L. Chem. Commun. 2016, 52, 9877–9880.
6. Osawa, M.; Hoshino, M.; Wakatsuki, Y. Angew. Chem. Int. Ed. 2001,
0, 3472–3474.
4
2
Pd(OAc) , this HOMO - 4 had an almost identical shape when
7
.
(a) Hamelin, O.; Guillo, P.; Loiseau, F.; Boissonnet, M.-F.; Ménage, S.
Inorg. Chem. 2011, 50, 7952–7954. (b) Guillo, P.; Hamelin, O.; Batat,
P.; Jonusauskas, G.; McClenaghan, N. D.; Ménage, S. Inorg. Chem.
2012, 51, 2222–2230. (c) Kozawa, K.; Inagaki, A.; Akita, M. Chem.
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Jouvenot, D.; Loiseau, F.; Lebrun, C.; Hamelin, O.; Ménage, S.
Angew. Chem. Int. Ed. 2015, 54, 8415–8419.
compared to the HOMO of L2. Thus, the electron transfer from
the PTZ to the 2,2’-bipyridine could still potentially occur under
photo-irradiation. Modifying the electron density of the
coordinating moiety upon near-UV irradiation, this could open
the way to a novel class of photo-electronically tunable ligands,
and more precise studies of this phenomenon are under
investigation through DFT modeling.
8
.
(a) Inagaki, A.; Yatsuda, S.; Edure, S.; Suzuki, A.; Takahashi, T.;
Akita, M. Inorg. Chem. 2007, 46, 2432–2445. (b) Nitadori, H.;
Takahashi, T.; Inagaki, A.; Akita, M. Inorg. Chem. 2012, 51, 51–62.
In conclusion, three new bipyridyl– and pyridylquinolyl–
phenothiazine structures were synthesized in correct to good
yields, through Pd-catalyzed C–N couplings using RuPhos-Pd-
(c) Murata, K.; Inagaki, A.; Akita, M.; Halet, J.-F.; Costuas, K. Inorg.
Chem. 2013, 52, 8030–8039. (d) Murata, K.; Araki, M.; Inagaki, A.;
Akita, M. Dalton Trans. 2013, 42, 6989–7001. (e) Shiba, Y.; Inagaki

4
Tetrahedron
A.; Akita, M. Organometallics 2015, 34, 4844–4853. (f) Murata, K.;
Saito, K.; Akita, M.; Inagaki, A. Chem. Commun. 2015, 51, 5717–
saturated NaCl solution were added. The aqueous layer was
extracted three times with dichloromethane (3 x 10 mL). The
5
720. (g) Son, C.; Inagaki, A. Dalton Trans. 2016, 45, 1331–1334.
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Ben-Moshe, T.; Cohen, R.; Leitus, G.; Shimon, L. J. W.;
Rybtchinski, B. Inorg. Chem. 2007, 46, 4790–4792. (b) Cook, R. E.;
Phelan, B. T.; Shoer, L. E.; Majewski, M. B.; Wasielewski, M. R.
Inorg. Chem. 2016, 55, 12281–12289.
combined organic layers were dried with MgSO
removed under reduced pressure. The residue was purified by silica
gel flash chromatography (CH Cl as eluent) affording 99.0 mg of
L2 (0.28 mmol, 93%) as an amorphous pale yellow solid. H NMR
(300MHz, CDCl ): 8.60 (d, J = 4.2 Hz, 1H); 8.36 (d, J = 5.9 Hz,
1H); 8.31 (d, J = 8.0 Hz, 1H); 8.07 (d, J = 2.6 Hz, 1H); 7.78 (td, J =
7.6 Hz, J = 1.7 Hz, 1H); 7.60 (dd, J = 7.9 Hz, J = 0.9 Hz, 2H); 7.52
(dd, J = 7.7 Hz, J = 1.3 Hz, 2H); 7.44 (td, J = 7.6 Hz, J = 1.3 Hz,
4
and the solvent was
9
1
.
2
2
1
3
0. For selected reviews on redox-active ligands, see: (a) Praneeth, V. K.
K.;. Ringenberg, M. R; Ward, T. R. Angew. Chem. Int. Ed. 2012, 51,
1
2
4
0228–10234. (b) Lyaskovskyy, V.; de Bruin, B. ACS Catal. 2012,
, 270–279. (c) Luca, O. R.; Crabtree, R. H. Chem. Soc. Rev. 2013,
2, 1440–1459. (d) Jacquet, J.; Desage-El Murr, M.; Fensterbank, L.
2H); 7.31-7.25 (m, 3H); 6.91 (dd, J = 5.9 Hz, J = 2.6 Hz, 1H).
+
HRMS (ESI) C22
H
15
N
3
S, calculated for [M+Na] : 376.0878, found:
376.0893. 10-(2-(Pyridin-2-yl)quinolin-5-yl)-10H-phenothiazine L3.
To a solution of 2-amino-6-bromobenzaldehyde (100 mg, 0.5 mmol,
1 equiv.) in 3 mL of ethanol were added 2-acetylpyridine (56 µL, 1
equiv.) and KOH (30 mg, 1.2 equiv.). The mixture was stirred at
reflux for 48h, cooled to room temperature and filtered. The filtrate
was collected and the solvent was removed under reduced pressure,
affording 131 mg of 5-bromo-2-(pyridin-2-yl)quinolone 3 (0.28
ChemCatChem 2016, 8, 3310–3316.
1
1
1. For selected reviews on the related field of photochromic catalysts,
see: (a) Stoll, R. S.; Hecht, S. Angew. Chem. Int. Ed. 2010, 49,
5
054–5075. (b) Akita, M. Organometallics 2011, 30, 43–51.
2. (a) Iqbal, Z.; Wu, W.-Q.; Huang, Z.-S.; Wang, L.; Kuang, D.-B.;
Meier, H.; Cao, D. Dyes Pigment. 2016, 124, 63–71. (b) Chen, C.;
Liao, J.-Y.; Chi, Z.; Xu, B.; Zhang, X.; Kuang, D.-B.; Zhang, Y.;
Liu, S.; Xu, J. J. Mater. Chem. 2012, 22, 8994–9005.
mmol, 93%) as an off-white solid used in the next step without
1
further purification. H NMR (300MHz, CDCl
3
): 8.78 (ddd, J = 4.8
1
1
3. Bishnoi, S.; Milton, M. D. Tetrahedron Lett. 2015, 56, 6633–6638.
4. Pan, X.; Fang, C.; Fantin, M.; Malhotra, N; So, W. Y.; Peteanu, L.
A.; Isse, A. A.; Gennero, A.; Liu, P.; Matyjaszewski, K .J. Am.
Chem. Soc. 2016, 138, 2411–2425.
5. For recent reviews on ATRP, see: (a) Lalevée, J.; Telitel, S.; Xiao,
P.; Lepeltier, M.; Dumur, F.; Morlet-Savary, F.; Gigmes, D.;
Fouassier, J.-P. Beilstein J. Org. Chem. 2014, 10, 863–876. (b)
Teator, A. J.; Lastovickova, D. N.; Bielawski, C. W. Chem. Rev.
Hz, J = 1.8 Hz, J = 0.9 Hz, 1H); 8.70-8.64 (m, 3H); 8.16 (d, J = 8.6
Hz, 1H); 7.91 (td, J = 7.8 Hz, J = 1.8 Hz, 1H); 7.85 (dd, J = 7.5 Hz, J
= 1.0 Hz, 1H); 7.61 (dd, J = 8.5 Hz, J = 7.6 Hz, 1H); 7.41 (ddd, J =
7.5 Hz, J = 4.8 Hz, J = 1.2 Hz, 1H). Then, following the procedure
for L1 with 3 instead (85.5 mg, 0.3 mmol, 1 equiv.), the residue was
1
1
purified by silica
CH Cl /cyclohexane) affording 67.9 mg of L3 (0.168 mmol, 56%) as
an amorphous yellow solid. H NMR (300MHz, CDCl
gel
flash chromatography (40/60:
2
2
1
3
): 8.74 (ddd,
2
016, 116, 1969–1992.
J = 4.9 Hz, J = 1.8 Hz, J = 0.9 Hz, 1H); 8.68 (dt, J = 8.0 Hz, J = 1.0
Hz, 1H); 8.56 (d, J = 8.8 Hz, 1H); 8.51 (d, J = 8.8 Hz, 1H); 8.37 (dt,
J = 8.5 Hz, J = 0.9 Hz, 1H); 7.98-7.87 (m, 2H); 7.73 (dd, J = 7.4 Hz,
J = 1.0 Hz, 1H); 7.38 (ddd, J = 7.5 Hz, J = 4.9 Hz, J = 1.2 Hz, 1H);
7.08 (dd, J = 7.4 Hz, J = 1.8 Hz, 2H); 6.82 (td, J = 7.4 Hz, J = 1.4
6. (a) Discekici, E. H.; Treat, N. J.; Poelma, S. O.; Mattson, K. M.;
Hudson, Z. M.; Luo, Y.; Hawker, C. J.; Read de Alaniz, J . Chem.
Commun. 2015, 51, 11705–11708. (b) Poelma, S. O.; Burnett, G. L.;
Discekici, E. H.; Mattson, K. M.; Treat, N. J.; Luo, Y.; Hudson, Z.
M.; Shankel, S. L.; Clarck, P. G.; Kramer, J. W.; Hawker, C. J.;
Read de Alaniz, J. J. Org. Chem. 2016, 81, 7155−7160.
7. For recent reviews, see: (a) Bariwal, J.; Van der Eycken, E. Chem.
Soc. Rev. 2013, 42, 9283–9303. (b) Ruiz-Castillo, P.; Buchwald, S.
L. Chem. Rev. 2016, 116, 12564–12649.
Hz, 2H); 6.76 (td, J = 7.7 Hz, J = 1.8 Hz, 2H); 6.07 (dd, J = 8.0 Hz, J
+
= 1.5 Hz, 2H). HRMS (ESI) C26
426.1035, found: 426.1045.
H
17
N
3
S, calculated for [M+Na] :
1
1
24. Broere, D. L. J.; de Bruin, B.; Reek, J. N. H.; Lutz, M.; Dechert, S.;
van der Vlugt, J. I. J. Am. Chem. Soc. 2014, 136, 11574–11577.
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H. L.; Monkman, A. P.; Bryce, M. R. J. Polym. Sci. Pol. Chem.
25. In a NMR tube were added Pd(OAc)
equiv.), the ligand (1 equiv.) and 0.7 mL of CDCl
sealed and sonicated at room temperature for 1h. The H NMR
2
(5.6 mg, 0.025 mmol, 1
3
. The tube was
1
2
011, 49, 1129–1137.
9. 10-(2,2'-bipyridin-6-yl)-10H-phenothiazine L1: In a tube were added
-bromo-2,2-bipyridine (70.5 mg, 0.3 mmol, equiv.),
1
1
spectra was consecutively recorded. (bpy)Pd(OAc)
(300MHz, CDCl ): 8.46 (dt, J = 7.7 Hz, J = 1.1 Hz, 2H); 8.15-8.07
(m, 4H); 7.35 (ddd, J = 7.7 Hz, J = 5.5 Hz, J = 1.3 Hz, 2H); 2.13 (s,
2
.
H NMR
6
1
3
phenothiazine (77.7 mg, 1.3 equiv.), RuPhos-Pd-G2 (23.4 mg, 10
mol %) and t-BuOK (50.5 mg, 1.5 equiv). The tube was sealed,
purged three times with argon and 1 mL of anhydrous dioxane was
added. The reaction mixture was stirred at 110 °C for 18 h. After
1
2 3
6H). (L2)Pd(OAc) . H NMR (300MHz, CDCl ): 8.19 (dd, J = 5.7
Hz, J = 1.2 Hz, 1H); 8.00 (td, J = 8.0 Hz, J = 1.5 Hz, 1H); 7.82 (d, J
= 8.1 Hz, 1H); 7.74 (d, J = 6.7 Hz, 1H); 7.64-7.60 (m, 4H); 7.51 (td,
J = 7.7 Hz, J = 1.5 Hz, 2H); 7.46 (d, J = 2.8 Hz, 1H); 7.42-7.36 (m,
cooling to room temperature, 10 mL of H
aqueous layer was extracted three times with ethyl acetate (3 x 10
mL). The combined organic layers were dried with MgSO and the
solvent was removed under reduced pressure. The residue was
purified by silica gel flash chromatography (50/50:
CH Cl /cyclohexane) affording 51.2 mg of L1 (0.145 mmol, 48%) as
an amorphous pale yellow solid. H NMR (300MHz, CDCl
2
O were added and the
3H); 6.89 (dd, J = 6.7 Hz, J = 2.8 Hz, 1H); 2.11 (s, 3H); 2.08 (s, 3H).
1
4
(L3)Pd(OAc)
2
. H NMR (300MHz, CDCl
3
): 9.18 (d, J = 8.5 Hz, 1H);
8.87 (d, J = 8.7 Hz, 1H); 8.66-8.52 (m, 1H); 8.46-8.36 (m, 1H); 8.24-
8.16 (m, 1H); 8.03 (t, J = 8.3 Hz, 1H); 7.91 (d, J = 7.1 Hz, 2H); 7.13
(d, J = 7.5 Hz, 2H); 7.08-7.02 (m, 1H); ); 6.95-6.80 (m, 4H); 6.09
(d, J = 7.6 Hz, 2H); 2.16 (s, 3H); 2.14 (s, 3H).
2
2
1
3
): 8.66
d, J = 4.6 Hz, 1H); 8.25 (d, J = 8.0 Hz, 1H); 8.04 (d, J = 7.3 Hz,
(
26. Milani, B.; Alessio, E.; Mestroni, G.; Sommazzi, A.; Garbassi, F.;
Zangrando, E.; Bresciani-Pahor, N.; Randaccio, L. J. Chem. Soc.,
Dalton Trans. 1994, 1903–1911.
27. For the molecular structure of the related 10-(acridin-9-yl)-10H-
phenothiazine, see: Koshima, H.; Wang, Y.; Matsuura, T.; Miyahara
I.; Mizutani, H.; Hirotsu, K.; Asahi, T.; Masuhara, H. J. Chem. Soc.,
Perkin Trans. 2 1997, 2033–2038.
1
H); 7.91-7.71 (m, 3H); 7.63 (t, J = 7.9 Hz, 1H); 7.44 (dd, J = 7.7
Hz, J = 1.2 Hz, 2H); 7.36 (td, J = 7.7 Hz, J = 1.5 Hz, 2H); 7.30-7.25
m, 1H); 7.21 (td, J = 7.6 Hz, J = 1.2 Hz, 2H); 6.97 (d, J = 8.3 Hz,
H). Slow evaporation from CDCl afforded suitable crystals for X-
(
1
3
Ray diffraction analysis. Crystallographic data for this structure has
been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC 1544934. Copies of the data
can be obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK, (fax: +44-(0)1223-336033 or e-
mail: deposit@ccdc.cam.ac.uk).
28. Absorption spectra of the aerated CH
compounds were recorded on a Varian Cary 5000 spectrophotometer
at concentrations of 2µM for L2, L3, (L2)Pd(OAc) , (L3)Pd(OAc)
and of 50µM for (bpy)Pd(OAc)
3
CN solutions of the
2
2
,
2
.
2
0. For structural data for the related 10-(2’-pyrazyl)phenothiazine, see:
Jovanovic, M. V.; Biehl, E. R. J. Heterocyclic Chem. 1983, 20,
29. Jovanovic, M. V.; Biehl, E. R.; Rosenstein, R. D.; Chu, S. S. C. J.
Heterocyclic Chem. 1984, 21, 661–667.
1
677–1680.
1. He, Y.; Bian, Z.; Kang, C.; Gao, L. Chem. Commun. 2010, 46,
695–5697.
2. Tong, L.; Zong, R.; Thummel, R. P. J. Am. Chem. Soc. 2014, 136,
881–4884.
30. Molecular structures were reconstructed using crystallographic data
2
2
2
2 2
from L1 and from (bpy)Pd(OAc) .5H O: Bercaw, J. E.; Day, M. W.;
5
Golisz, S. R.; Hazari, N.; Henling, L. M.; Labinger, J. A.; Schofer, S.
J.; Virgil, S. Organometallics 2009, 28, 5017–5024. The B3LYP
DFT functional (Becke, A. D. J. Chem. Phys. 1993, 198, 5648-5652)
and the following basis sets were used in the ground-state geometry
optimization in Gaussian 09 program packages (Revision A.02,
Gaussian, Inc., Wallingford CT, 2016): Lanl2DZ for Pd and 6-
31G+(d,p) for all other atoms.
4
3. 10-(2,2'-Bipyridin-4-yl)-10H-phenothiazine L2. Following the
procedure for L1 with 4-bromo-2,2-bipyridine instead (70.5 mg, 0.3
mmol, 1 equiv.), the reaction mixture was stirred at 110 °C for 18 h.
2
After cooling to room temperature, 5 mL of H O and 5 mL of

5
-
-
-
Easy to-synthesize bipyridyl– and
pyridylquinolyl–phenothiazine structures.
Ligand complexation to Pd(OAc)
absorption studied.
2
and UV-visible
Molecular modeling suggesting intramolecular
electronic transfers upon irradiation.
-
Potential photo-electronically tunable ligands.
3
1.