SelectIVe synthesis, reactIVity and luminescence of unsymmetrical bis-cyclometalated Pt(IV) complexes

Article abstract of DOI:10.1039/c9dt02431j

Pt(ii) complexes cis-N,N-[PtCl(C^N)(N′^C′H)], where C^N represents a monocyclometalated 2,6-diaryl-or 2-arylpyridine ligand and N′^C′H is an N-coordinated 2-arylpyridine, are selectively obtained from bridge-cleavage reactions of dimers [Pt₂(μ-Cl)₂(C^N)₂] with excess N′^C′H at room temperature; isolation and characterization of derivatives of this kind is reported for the first time. Oxidation with PhICl₂ affords Pt(iv) complexes [PtCl₂(C^N)(C′^N′)], bearing two cyclometalated ligands in an unsymmetrical arrangement. The abstraction of the two chlorides using AgOTf at 120 °C in the presence of an additional 2-arylpyridine ligand leads to mer isomers of tris-cyclometalated Pt(iv) complexes if C^N derives from a 2-arylpyridine, whereas it results in a reductive C-C coupling if C^N is a monocyclometalated 2,6-diarylpyridine. Complexes [PtCl₂(C^N)(C′^N′)] show phosphorescence in frozen PrCN glasses arising from essentially ³LC excited states localized on the cyclometalated ligand with the lowest π-π? transition energy. The combined photophysical data and computational results substantiate a variable degree of MLCT admixture into the emitting state depending on the atom trans to the metalated carbon of the chromophoric ligand (Cl or N), which has an appreciable effect on the characteristics of the observed luminescence.

Full text of DOI:10.1039/c9dt02431j

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PAPER
Selective synthesis, reactivity and luminescence
of unsymmetrical bis-cyclometalated Pt(IV)
complexes†
Cite this: Dalton Trans., 2019, 48,
14367
Ángela Vivancos, a Dionisio Poveda,a Alonso Muñoz,a Julia Moreno,a
a
Delia Bautistab and Pablo González-Herrero
*
Pt(II) complexes cis-N,N-[PtCl(C^N)(N’^C’H)], where C^N represents a monocyclometalated 2,6-diaryl-
or 2-arylpyridine ligand and N’^C’H is an N-coordinated 2-arylpyridine, are selectively obtained from
bridge-cleavage reactions of dimers [Pt2(μ-Cl)2(C^N)2] with excess N’^C’H at room temperature; isolation
and characterization of derivatives of this kind is reported for the first time. Oxidation with PhICl2 affords
Pt(IV) complexes [PtCl2(C^N)(C’^N’)], bearing two cyclometalated ligands in an unsymmetrical arrange-
ment. The abstraction of the two chlorides using AgOTf at 120 °C in the presence of an additional 2-aryl-
pyridine ligand leads to mer isomers of tris-cyclometalated Pt(IV) complexes if C^N derives from a 2-aryl-
pyridine, whereas it results in a reductive C–C coupling if C^N is a monocyclometalated 2,6-diarylpyri-
dine. Complexes [PtCl2(C^N)(C’^N’)] show phosphorescence in frozen PrCN glasses arising from essen-
tially 3LC excited states localized on the cyclometalated ligand with the lowest π–π* transition energy. The
combined photophysical data and computational results substantiate a variable degree of MLCT admix-
ture into the emitting state depending on the atom trans to the metalated carbon of the chromophoric
ligand (Cl or N), which has an appreciable effect on the characteristics of the observed luminescence.
Received 7th June 2019,
Accepted 10th September 2019
DOI: 10.1039/c9dt02431j
rsc.li/dalton
may combine two cyclometalated C^N ligands in a C2-sym-
metrical or unsymmetrical arrangement with diverse neutral or
Introduction
The synthesis and photophysical properties of late transition- anionic ancillary ligands,15–22 or contain three C^N ligands in a
metal complexes with chelating heteroaromatic ligands have meridional (mer) or facial ( fac) configuration14,23,24 (Chart 1). In
been the subject of intensive research owing to the wide appli- addition, luminescent Pt(IV) complexes bearing cyclometalated
cability of their long-lived excited states, including the develop- aryl-N-heterocyclic carbene and bi- or terdentate 2,6-diaryl-
ment of electrophosphorescent materials,1,2 chemical and bio- pyridine ligands have been recently reported by us.25
logical sensors,3–5 photocatalysts,6,7 and photosensitizers in
The phosphorescence of cyclometalated Pt(IV) complexes
photodynamic therapy.8,9 The use of cyclometalated 2-arylpyri- usually arises from triplet ligand-centred (3LC or 3π–π*) excited
dines (C^N) and related ligands has proved particularly fruit-
ful, because it has allowed to obtain complexes with broad
colour-tuning possibilities and high emission efficiencies,
most often with the Ir(III)10 and Pt(II)11–13 ions. Pt(IV) complexes
bearing cyclometalated heteroaromatic ligands are still rela-
tively scarce and only very recently has their potential as
efficient phosphorescent emitters begun to be uncovered.14
The reported phosphorescent Pt(IV) complexes of this class
aDepartamento de Química Inorgánica, Facultad de Química, Universidad de
Murcia, Apdo. 4021, 30071 Murcia, Spain. E-mail: pgh@um.es
bSAI, Universidad de Murcia, Apdo. 4021, 30071 Murcia, Spain
†Electronic supplementary information (ESI) available: 1H and 13C{1H} NMR
spectra of new compounds, crystallographic information, and computational
data. CCDC 1913441 (6·0.5CH2Cl2) 1913448 (2af), 1913449 (2ed), 1913450 (3af),
1913451 (3bd), 1913452 (3cd) and 1913453 (4·Et2O). For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c9dt02431j
Chart 1 Structural types of phosphorescent cyclometalated Pt(IV) com-
plexes. C^N = cyclometalated 2-arylpyridine. X = halide or carboxylate.
R = alkyl or C6F5. N^N = aromatic diimine.
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states mainly localized on the C^N ligands with a very small 2,6-diaryl- or 2-arylpyridine, can be employed to selectively syn-
but critical metal-to-ligand charge-transfer (MLCT) character thesize Pt(IV) complexes of the type [PtCl2(C^N)(C′^N′)],
mixed in. Emission lifetimes are typically very long (from tens bearing two different or equal cyclometalated ligands in an
to hundreds of microseconds), which make them interesting unsymmetrical arrangement, via bridge-cleavage reactions
candidates for applications that benefit from long-lived excited with different 2-arylpyridines (N′^C′H) at room temperature
states, such as photosensitizing, photocatalysis or chemosen- and subsequent oxidation. The isolation and characterization
sing. The development of colour-tunable complexes of this of intermediate cis-N,N-[PtCl(C^N)(N′^C′H)] complexes is
class relies on the availability of suitable methods for the intro- reported for the first time and chloride substitution reactions
duction of cyclometalated C^N ligands with different π–π* on [PtCl2(C^N)(C′^N′)] complexes are evaluated. A photo-
transition energies. With the aim of finding alternative syn- physical and computational study on
a selected set of
thetic routes that both make use of easily accessible platinum [PtCl2(C^N)(C′^N′)] complexes is also presented, which pro-
precursors and allow a straightforward variation of the C^N vides a unique demonstration of the variability of the MLCT
ligands, we set out to examine the potential of dichloro- contribution to the essentially 3LC emitting state of cyclometa-
bridged Pt(II) dimers [Pt2(μ-Cl)2(C^N)2] as versatile starting lated Pt(IV) complexes and its effects on their luminescence.
materials for the synthesis of cyclometalated Pt(IV) complexes.
Dimers of this kind with cyclometalated 2-arylpyridines have
been known for a long time26,27 and serve as excellent precur-
Results and discussion
Synthesis and characterization
sors of luminescent Pt(II) complexes.28–31 Their synthesis typi-
cally involves the reaction of K2PtCl4 with the 2-arylpyridine
The treatment of suspensions of dichloro-bridged dimers
ligand (N^CH) in 1 : 1 molar ratio at 80 °C. If the reaction is
performed in the presence of an excess of N^CH, mononuclear
[Pt2(μ-Cl)2(C^N)2] (1) in CH2Cl2 with a 2-arylpyridine (N′^C′H;
1–3 equiv. per Pt) led to yellow or orange solutions containing
monomeric Pt(II) species 2 that result from bridge-cleavage
reactions (see Scheme 2 for the employed ligands and com-
pound numbering). Isolation of complexes 2 was successful in
some cases (2af, 2cd, 2dd and 2ed), which allowed their
unequivocal identification as cis-N,N-[PtCl(C^N)(N′^C′H)]
Pt(II) complexes trans-N,N-[PtCl(C^N)(N^CH)] are obtained
(Scheme 1),32–35 and therefore the ligand : metal ratio must be
carefully controlled. When 2,6-diarylpyridines are employed,
dimers bearing the monocyclometalated ligand are obtained
exclusively, even in the presence of a ligand excess.36
Previous works have examined bridge-cleavage reactions of
[Pt2(μ-Cl)2(C^N)2] dimers with pyridine ligands (L).26,37,38 The
through X-ray diffraction studies and/or NMR (see below).
Although a previous study reported that the reaction of
monomeric complexes cis-N,N-[PtCl(C^N)(L)] are formed first,
as a result of the preferential cleavage of the Pt–Cl bond trans
to the metalated aryl because of the strong kinetic trans effect of
this carbon–donor moiety. Subsequent isomerization to the
[Pt2(μ-Cl)2(tpy)2] with tpyH gave a mixture of cis- and trans-N,N-
[PtCl(tpy)(tpyH)] isomers,38 our results demonstrate that the
cis-N,N isomer forms exclusively in all the studied cases.39
thermodynamically more stable trans-N,N-[PtCl(C^N)(L)] com-
plexes may take place in the presence of an excess of L through
an associative mechanism if this ligand lacks bulky substituents;
otherwise, the kinetic cis-N,N isomers were reported to be stable
at room temperature (Scheme 1).26 Two of these works employed
2-arylpyridines as the L ligand, showing that the trans-N,N isomer
is obtained exclusively at high temperatures,26,37 whereas a
mixture of the cis- and trans-N,N isomers was observed in one
case by performing the reaction at room temperature;38 however,
to the best of our knowledge, cis-N,N complexes bearing
N-coordinated 2-arylpyridines have never been isolated.
In the present work, we show that [Pt2(μ-Cl)2(C^N)2]
dimers, where C^N represents
a
monocyclometalated
Scheme 2 Synthetic route to unsymmetrical bis-cyclometalated com-
plexes 3.
Scheme 1 HC^N = 2-arylpyridine. L = (substituted) pyridine.
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Several experimental facts indicate that complexes 2 are in
equilibrium with the parent dimers 1 and free N′^C′H in solu-
tion, which appears to be more or less shifted toward the pro-
ducts depending on the properties of the C^N ligand. Thus, in
all cases, the precursor 1 slowly precipitated from solutions of
2 in the absence of added N′^C′H. For this reason, precipi-
tation of pure samples or single-crystal formation of complexes
2af and 2ed from CH2Cl2/Et2O were only possible in the pres-
1
ence of an excess of the corresponding N′^C′H ligand. The H
NMR spectrum of pure 2af in CD2Cl2 in the absence of ppyH
showed very broad signals that indicate the existence of a
mixture or a dynamic process (Fig. S1†). The attempts to
isolate complex 2bd resulted in the precipitation of 1b.
Complexes 2cd, 2dd and 2ed proved more stable than 2af or
2bd and their 1H NMR spectra showed well-defined reso-
nances, although small amounts of free tpyH were present too. Fig. 1 Structure of 2af (thermal ellipsoids at 50% probability). Hydrogen
atoms are omitted. Selected bond distances (Å) and angles (°): Pt–C1,
1.982(2); Pt–N1, 2.0447(19); Pt–N2, 2.159(2); Pt–Cl, 2.3004(6); C1–Pt–
N1, 80.87(9); C1–Pt–Cl, 93.25(7); N1–Pt–N2, 100.72(8); N2–Pt–Cl,
84.88(6).
Thus, it is clear that the formation of complexes 2 is more
difficult from precursors 1a or 1b, which bear a monocyclome-
talated 2,6-diarylpyridine ligand that places the non-metalated
aryl group in the vicinity of the coordination position of the
incoming N′^C′H ligand.
The 1H NMR spectra of complexes 2cd, 2dd and 2ed are
consistent with a cis-N,N configuration. A low-field shifted
resonance at around 9.10 ppm arises from the aromatic
proton ortho to the nitrogen of the coordinated tpyH ligand,
while the resonance of the analogous proton in the cyclometa-
lated C^N ligand is significantly high-field shifted, appearing
together with the rest of aromatic signals, because it is
directed toward the shielding region of the pyridine ring of the
coordinated tpyH ligand. The NMR data also proved the
absence of the trans-N,N isomers, which would give rise to a
strongly shielded aromatic signal with platinum satellites at
around 6 ppm corresponding to the proton ortho to the meta-
lated carbon of the C^N ligand, which is directed toward the
pyridine group of the tpyH ligand in these isomers.32 The
crystal structures of 2af (Fig. 1) and 2ed (Fig. 2) provided
further confirmation of their cis-N,N configuration. In complex
Fig. 2 Structure of one of the two independent molecules of 2ed in
the asymmetric unit (thermal ellipsoids at 50% probability). Hydrogen
atoms are omitted. Selected bond distances (Å) and angles (°): Pt–C1,
2af, the steric repulsion between the nonmetalated phenyl
group of the dppyH ligand and the pyridine moiety of the
ppyH ligand causes an appreciable deviation from the copla-
narity between the three aromatic rings of the dppyH ligand
and also determines the orientation of the coordinated pyri-
dine ring of the ppyH ligand, which forms an angle of 55.8°
with the Pt coordination mean plane. A similar twisted confor-
1.975(2); Pt–N1, 2.1538(19); Pt–N2, 2.0321(18); Pt–Cl, 2.3041(6); C1–
Pt–N2, 80.81(8); C1–Pt–Cl, 93.48(6); N1–Pt–N2, 97.51(7); N1–Pt–Cl,
88.15(6).
mation of the dppyH ligand has been found for cis-[Pt yields. Similar oxidation reactions have been previously
(dppyH)2]40 and [Pt(dppyH)(dmbpy)]+ (dmbpy = 5,5′-dimethyl- employed for the synthesis of different types of bis-cyclometa-
2,2′-bipyridine).41 In contrast, in 2ed the thpy ligand and the lated Pt(IV) complexes.15,17–19,42,43 The formation of complexes
coordination plane are practically coplanar (mean deviation 3 entails the liberation of one equivalent of HCl, which is
from plane: 0.040 Å) and the pyridine group of the tpyH ligand trapped by the excess of N′^C′H ligand present in the reaction
forms an angle of 77° with the coordination plane.
mixture to give the corresponding 2-arylpyridinium salt that
Treatment of CH2Cl2 solutions of in situ generated com- can be removed by washing the crude solids with methanol.
1
plexes 2 with one equivalent of PhICl2 led to the oxidation to The main distinctive feature found in the H NMR spectra of
Pt(IV) and the electrophilic metalation of the pendant aryl complexes 3 is a resonance in the range 6.06–6.28 ppm
group of the coordinated N′^C′H ligand to give unsymmetrical flanked by platinum satellites, corresponding to the proton
bis-cyclometalated complexes of the type [PtCl2(C^N)(C′^N′)] ortho to the metalated carbon of the C′^N′ ligand, which is
(3; Scheme 2), which could be isolated in moderate to good considerably shielded by the ring current of the aryl ring of the
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C^N ligand, indicating that the two metalated carbon atoms
are mutually cis in all cases. The NMR data also ruled out
ligand scrambling at room temperature.
The crystal structures of 3af (Fig. 3), 3bd (Fig. 4) and 3cd
(Fig. 5) are consistent with the NMR data and also confirm
that these derivatives retain the cis-N,N configuration of their
precursors. The nonmetalated aryl ring of the dppyH or dtpyH
ligand in complexes 3af or 3bd is rotated by about 67° with
respect to the pyridine ring of the same ligand to minimize
steric repulsions with the pyridine ring of the C′^N′ ligand;
still, these repulsions lead to some deviation from planarity in
Fig. 5 Structure of complex 3cd (thermal ellipsoids at 50% probability).
Hydrogen atoms are omitted. Selected bond distances (Å) and angles (°):
Pt–C1, 2.005(2); Pt–C21, 2.014(2); Pt–N1, 2.0190(18); Pt–N2, 2.1168(19);
Pt–Cl2, 2.3142(5); Pt–Cl1, 2.4522(5); C1–Pt–N1, 81.06(9); C21–Pt–N2,
80.49(9); N1–Pt–N2, 96.48(7); Cl2–Pt–Cl1, 93.511(19).
the cyclometalated portion of these ligands and longer Pt–N
bond distances trans to Cl [3af, 2.0731(16) Å; 3bd, 2.079(2) Å]
as compared to the corresponding distance in 3cd [2.0190(18)
Å]. In the three cases, the Pt–C bond from the C^N ligand
(trans to N) is appreciably shorter than the one from the C′^N′
ligand (trans to Cl), suggesting that in these complexes the Cl
ligand exerts a higher trans influence compared to the pyridine
moiety of the C′^N′ ligand.
Chloride substitution and C–C coupling reactions
Fig. 3 Structure of complex 3af (thermal ellipsoids at 50% probability).
Hydrogen atoms are omitted. Selected bond distances (Å) and angles (°):
Pt–C1, 2.006(2); Pt–Cl2, 2.4410(5); Pt–C18, 2.0179(19); Pt–N1, 2.0731
(16); Pt–N2, 2.1402(17); Pt–Cl1, 2.3133(5); C1–Pt–N1, 81.39(7); C18–Pt–
N2, 79.91(7); N1–Pt–N2, 100.15(6); Cl1–Pt–Cl2, 90.923(17).
Chloride substitution reactions in complexes 3 were investi-
gated to evaluate their suitability as precursors of fac isomers
of tris-cyclometalated Pt(IV) complexes, fac-[Pt(C^N)3]+. The
only known route to this class of complexes involves the
abstraction of the chloride ligands from the C2-symmetrical
isomers of complexes [PtCl2(C^N)2] with 2 equiv. of AgOTf in
the presence of a third 2-arylpyridine ligand at high tempera-
tures in noncoordinating solvents, affording exclusively the
meridional isomers, mer-[Pt(C^N)3]+, which must then be
photoisomerized to the fac isomers by irradiating with UV
light.14,23,24 Since the mer-to-fac photoisomerization step often
results in low yields, direct synthetic routes to the fac-[Pt
(C^N)3]+ complexes are desirable. We hypothesized that the
chloride ligand trans to the metalated carbon of the C′^N′
ligand would be abstracted first upon reaction with AgOTf,
allowing the coordination of a third 2-arylpyridine ligand to
form an intermediate with a fac-N,N,N configuration that
would finally give the desired tris-cyclometalated complex.
Toward testing this hypothesis, we first carried out the reaction
of complex 3cd with one equiv. of AgOTf in the presence of
γ-picoline (γ-pic) at 120 °C in 1,2-dichlorobenzene, which gave
[PtCl(dfppy)(tpy)(γ-pic)]OTf (4) in 65% yield (Scheme 3). The
crystal structure of this complex (Fig. 6) showed that the co-
ordinated nitrogen atoms are in a fac arrangement, demon-
strating that the chloride trans to a metalated carbon in 3cd
was selectively substituted.
Fig. 4 Structure of complex 3bd (thermal ellipsoids at 50% probability).
Hydrogen atoms are omitted. Selected bond distances (Å) and angles (°):
Pt–C1, 2.012(3); Pt–C21, 2.024(3); Pt–N1, 2.079(2); Pt–N2, 2.160(2); Pt–
Cl2, 2.3166(6); Pt–Cl1, 2.4368(6); C1–Pt–N1, 80.85(9); C21–Pt–N2,
79.97(10); N1–Pt–N2, 103.09(8); Cl2–Pt–Cl1, 91.35(2).
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Scheme 3 Chloride substitution reactions of 3cd. DCB = 1,2-Dichlorobenzene.
to the fac isomer (Fig. S15†). The selective formation of two
mer isomers in this reaction suggests that the intermediate
species resulting from the abstraction of the chloride ligands,
which must contain coordinated triflate anions, is unstable
and isomerizes to a trans-N,N configuration under the reaction
conditions (Scheme 3). We note that the C2-symmetrical
complex [Pt(OTf)2(ppy)2] is stable in noncoordinating sol-
vents.16 The isomerization process must be faster than the
coordination of the tpyH ligand through the N atom, which is
probably hindered due to the presence of the p-tolyl substitu-
ent. Analogously, the reaction of 3dd with two equiv. of AgOTf
and an excess tpyH in 1,2-dichlorobenzene at 120 °C for 72 h
gave mer-[Pt(tpy)3]OTf (mer-5dd), which has been already
reported14 and was identified by its 1H NMR data.
Drastically different results were obtained when starting
from complexes with dppyH or dtpyH ligands. The reaction of
complex 3af with 2 equiv. of AgOTf and an excess tpyH (3–5
equiv.) in 1,2-dichloroethane at 90 °C for 48 h afforded a
mixture from which the yellow Pt(II) complex [Pt(C^N^N)
(tpyH)]OTf (6) could be isolated (23% yield), containing a ter-
dentate C^N^N ligand that results from a reductive C–C coup-
ling between the metalated carbon of the ppy ligand and an
ortho carbon from one of the phenyl groups of the dppyH
ligand (Scheme 4). The identity of 6 was established by means
Fig. 6 Structure of complex 4·Et2O (thermal ellipsoids at 50% prob-
ability). The triflate anion, hydrogen atoms and crystallization solvent are
omitted. Selected bond distances (Å) and angles (°): Pt–C1, 2.009(2); Pt–
C12, 2.020(2); Pt–N1, 2.0365(17); Pt–N2, 2.1283(18); Pt–N3, 2.1718(18);
Pt–Cl, 2.3081(6); C1–Pt–N1, 81.25(8); C12–Pt–N2, 80.46(8); N1–Pt–N2,
98.04(7); N3–Pt–Cl, 91.64(5).
We then attempted the synthesis of tris-cyclometalated of X-ray diffraction studies (Fig. 7). The C^N^N ligand forms 5-
complexes from a subset of complexes 3 by abstracting the two and 9-membered chelate rings. The coordination environment
chloride ligands in the presence of tpyH. Contrary to our around the metal deviates from the ideal square planar geome-
expectations, the reaction of 3cd with two equiv. of AgOTf and try because of the narrow bite angle of the C^N fragment of
an excess tpyH in 1,2-dichlorobenzene at 120 °C for 72 h gave the C^N^N ligand [N2–Pt–C21, 81.59(12)°] and the strain
a mixture of tris-cyclometalated complexes with a mer con- caused by the 9-membered ring [N3–Pt–N2, 105.36(10)°]. As
figuration, mer-[Pt(dfppy)(tpy)2]OTf (mer-5cd). The 1H NMR expected, the longest Pt–N bond distance corresponds to the
spectrum of mer-5cd shows two sets of aromatic resonances nitrogen trans to the metalated carbon [Pt–N3, 2.155(3) Å]. The
corresponding to two different species in a 1 : 0.7 ratio 1H NMR spectrum of 6 confirms the presence of a coordinated
(Fig. S14 and S15†), each one containing three inequivalent tpyH ligand, which gives a resonance at 8.78 ppm due to the
cyclometalated ligands, that we assign to two of the four poss- proton ortho to the coordinated nitrogen atom. It also corro-
ible isomers with a mer configuration (Scheme 3). Support for borates that a phenyl group of the ppy fragment remains meta-
this assignment was obtained by irradiating a solution of this lated, as evidenced by the resonance at 5.78 ppm with Pt satel-
mixture in CD3CN in a quartz NMR tube with UV light, where- lites arising from the proton ortho to the metalated carbon,
upon a single set of resonances gradually arose, also corres- which is shielded because of its proximity to the ring current
ponding to three inequivalent ligands, which are attributable of the pyridine group of the tpyH ligand. The attempt to
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Scheme 5 Proposed reaction pathway for the formation of complex 6.
Scheme 4 Chloride substitution reactions of 3af and 3bd. DCE = 1,2-
dichloroethane. DCB = 1,2-dichlorobenzene.
mediate C. At this point, the reductive coupling of two
mutually cis metalated carbon atoms would take place, result-
ing in the formation of the nine-membered ring (D). Finally,
the substitution of the triflate ligand in D for tpyH would give
the cationic complex 6. This process is closely related to the
reductive C–C couplings involving a dicyclometalated 2,6-di-
arylpyridine ligand and a cyclometalated tribenzylphosphine
ligand on the coordination sphere of Pt(IV), which have been
recently reported by Rourke et al.44
When a higher temperature was employed (120 °C in 1,2-
dichlorobenzene for 48 h), the reactions of 3af or 3bd with
AgOTf (2 equiv.) and tpyH (5 equiv.) gave [Pt(tpy)(tpyH)2]OTf
(7), resulting from a reduction to Pt(II) and the replacement of
all the ligands present in the Pt(IV) precursor by tpy or tpyH
ligands (Scheme 4). Complex 7 could also be obtained by
heating a mixture of 6 and tpyH (5 equiv.) in 1,2-dichloroben-
zene at 120 °C for 48 h, suggesting that its formation involves
a transcyclometalation step in which the C^N^N ligand is
replaced by tpy. A complex analogous to 7 containing 1-phenyl-
isoquinoline ligands [Pt(piq)(piqH)2]OTf has been previously
reported to result from the reaction of [PtCl2(piq)2] (C2-sym-
metrical isomer) with 2 equiv. of AgOTf in the presence of an
excess of piqH.23
Fig. 7 Structure of complex 6·0.5CH2Cl2 (thermal ellipsoids at 50%
probability). Hydrogen atoms and crystallization solvent are omitted.
Selected bond distances (Å) and angles (°): Pt–N1, 2.042(3); Pt–N2,
2.062(3); Pt–N3, 2.155(3); Pt–C21, 1.983(3); N1–Pt–N3, 81.09(10); N3–
Pt–N2, 105.36(10); N2–Pt–C21, 81.59(12); N1–Pt–C21, 91.21(12).
Photophysical study
The Pt(IV) complexes 3bd, 3cd, 3ce, 3de, 3ed and 4 were
selected for a photophysical study. Their electronic absorption
obtain a derivative analogous to 6 by reacting complex 3bd data in CH2Cl2 solution at 298 K are compiled in Table 1 and
with 2 equiv. of AgOTf and an excess tpyH under the same con- the spectra are shown in Fig. 8. The lowest-energy absorption
1
ditions afforded a product mixture; although its H NMR data bands in the range 300–400 nm apparently result from the
suggested the presence of the C–C coupling product, all efforts overlap of ligand-centred (1LC) absorptions from the individ-
to isolate it were unsuccessful.
ual C^N and C′^N′ ligands, as has been observed for other
A possible reaction pathway for the formation of complex 6 Pt(IV) complexes containing different cyclometalated 2-arylpyri-
is shown in Scheme 5. The abstraction of the chloride ligands dines.23 Thus, complexes 3bd, 3cd, 3ed and 4, bearing tpy as
in 3af would lead to species A, containing labile triflate the C′^N′ ligand, give rise to a common absorption feature at
ligands, which would isomerize to give a species with a trans- around 320 nm. Similarly, the lowest-energy shoulder at
N,N configuration (B). The metalation of the second phenyl around 350 nm in the spectra of complexes 3ce and 3de is
ring of the dppyH ligand would then be possible, giving inter- attributable to the cyclometalated thpy, which is the C′^N′
14372 | Dalton Trans., 2019, 48, 14367–14382
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Table 1 Electronic absorption data for the studied complexes in
CH2Cl2 solution (ca. 5 × 10−5 M) at 298 K
Table 2 Emission data of the studied complexes
Complex
Medium (T/K)
λem a/nm
τb/μs
Complex λmax/nm (ε × 10−2/M−1 cm−1
)
3bd
3cd
3ce
3de
3ed
PrCN (77)
PrCN (77)
PrCN (77)
PrCN (77)
CH2Cl2 (298)
PrCN (77)
PrCN (77)
460, 494, 523
272
447, 480, 506, 518, 543
503, 521, 543, 564, 589
505, 523, 543, 564, 589
518, 558
512, 530, 552, 573, 600
447, 480, 508, 518, 543
662
497
496
14.3
269
906
3bd
3cd
3ce
264 (211), 320 (148), 353 (sh, 72)
264 (163), 309 (sh, 117), 320 (126), 332 (sh, 100)
262 (151), 286 (144), 296 (138), 327 (119), 335 (123), 354 (sh,
62)
3de
3ed
4
267 (196), 297 (73), 338 (75), 347 (sh, 69)
272 (195), 303 (172), 328 (sh, 117), 359 (65)
257 (237), 320 (202)
4
a The most intense peak is italicized. b Emission lifetime.
Fig. 8 Electronic absorption spectra of complexes 3bd, 3cd, 3ce, 3de,
3ed and 4 in CH2Cl2 solution at 298 K.
Fig. 9 Excitation (left) and emission (right) spectra of complex 3ed in
CH2Cl2 solution at 298 K.
ligand in these derivatives and has the lowest π–π* transition
energy. Notably, the thpy absorption has a lower energy in in this medium could arise from photodecomposition pro-
complex 3ed, where it can be distinguished as an individual ducts. In contrast, CH2Cl2 solutions of complex 3ed proved
band (359–371 nm), revealing that the same ligand gives a photostable at 298 K. Its emission spectrum shows a vibration-
lower energy absorption when it occupies the C^N position. ally structured band (Fig. 9), with a large Stokes shift and a
The long tails extending to ca. 450 nm that can be most clearly lifetime of 14.3 μs, consistent with a triplet ligand-centred
observed in the spectra of derivatives 3bd, 3de and 3ed are (3LC) emitting excited state. This emission is very similar in
typical of LMCT and/or LLCT absorptions, as observed for energy and shape to those of [PtMe(Cl)(thpy)2]15 or mer-[Pt
other bis-cyclometalated Pt(IV) complexes with halide (C^N)2(thpy)]+ (C^N = dfppy, ppy),23 meaning that the chromo-
ligands.16
The luminescence of the selected subset of complexes was
phoric ligand is the thpy.
All of the studied complexes showed sharply structured
examined in deaerated CH2Cl2 solution at 298 K and in butyro- emissions in PrCN glasses at 77 K (Fig. 10), with lifetimes in
3
nitrile (PrCN) frozen glasses at 77 K. The emission data are the range 269–906 μs, which are typical of LC emissions from
summarized in Table 2 and the emission spectra are plotted in cyclometalated Pt(IV) complexes.14,23,24 The vibrational struc-
Fig. 9 and 10. Complexes 3bd, 3ce and 3de showed no detect- tures and emission energies indicate that the observed lumine-
able emissions in fluid CH2Cl2 solution at 298 K, in line with scence arises from the cyclometalated ligand with the lowest
the previously studied unsymmetrical isomers of complexes π–π* transition energy, namely dtpyH (3bd), tpy (3cd, 4) or
[PtX2(ppy)2] (X = halide or carboxylate), whose emissions are thpy (3ce, 3de, 3ed). The emission energy of 3ed is lower than
totally quenched at room temperature due to the thermal that of its isomeric complex 3de, meaning that the essentially
population of dissociative or distorted excited states of LMCT LC transition within the chromophoric thpy ligand has a lower
character.16 Complexes 3cd, 3ed and 4 showed a weak but mea- energy when it occupies the C^N position (C trans to N′) than
surable luminescence in these conditions, but only in the case when it is in the C′^N′ position (C′ trans to Cl). This is consist-
of 3ed was the excitation spectrum compatible with the ent with the lower energy observed for the thpy absorption
absorption profile (Fig. 9). Irradiation of diluted solutions of band observed for 3ed with respect to 3de (see above). It is
3cd and 4 in CH2Cl2 with UV light (310 nm) led to substantial also noteworthy that complexes that emit from the ligand in
changes in their absorption spectra, and thus their emissions the C^N position (3bd and 3ed) display significantly shorter
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Fig. 11 Orbital energy diagrams from DFT calculations.
the other complexes. The dtpyH complex 3bd presents the
smallest HOMO–LUMO gap, mainly because of its low LUMO
energy, which can reasonably be connected to the weaker σ-
donation from the pyridine moiety of the dtpyH ligand as a
consequence of the longer Pt–N(dtpyH) bond distance.
Frontier orbital energies in complex 4 are lower than in com-
plexes 3 because of its cationic nature, but its HOMO–LUMO
gap is similar to that of its precursor 3cd.
Fig. 10 Emission spectra of the studied complexes in PrCN frozen
glasses at 77 K.
Excitation energies at the ground-state geometries were cal-
culated by TDDFT in CH2Cl2 solution. The data for selected
singlet and triplet excitations are given in the ESI.† The lowest-
energy singlet excitations have low oscillator strengths and
correspond to primarily LMCT transitions from the HOMO or
HOMO−1 to the LUMO, and are consistent with the long tails
observed in the absorption spectra. The excitations with the
highest oscillator strengths correspond to 1LC (π–π*) tran-
emission lifetimes compared to the rest of studied complexes,
which could be associated with a higher effectiveness of the
spin–orbit coupling induced by the metal, resulting in faster
radiative decays.1,10,45,46
Computational study
For a better understanding of their photophysical properties, sitions within the C^N or C′^N′ ligands with some LMCT char-
DFT and TD-DFT calculations have been performed for acter. Consistent with the experimental observations, the
complexes 3bd, 3cd, 3ce, 3de, 3ed and 4 at the B3LYP/ lowest 1LC excitation in complexes 3ce, 3de and 3ed involves
(6-31G**+LANL2DZ) level considering solvent effects (CH2Cl2). the thpy ligand and has a lower energy for 3ed, where the thpy
Fig. 11 shows a diagram comparing frontier orbital energies ligand occupies the C^N position.
and a simplified, color-coded representation of their compo-
A diagram showing the lowest vertical triplet excitation
sition. Detailed compositions and isodensity surfaces of fron- energies at the ground-state geometries and their main charac-
tier orbitals are given in the ESI.† The highest occupied mole- ter is shown in Fig. 12. The T1 excitation in complexes 3bd and
cular orbital (HOMO) and the HOMO−1 are essentially π orbi- 3ed corresponds to a HOMO–LUMO+1 transition, and there-
3
tals of the C^N or C′^N′ ligands with little metal orbital invol- fore can be described as LC involving the C^N ligand (dtpyH
vement (1–4%). The lowest unoccupied molecular orbital or thpy, respectively), with some LMCT character. In the rest of
(LUMO) is a dσ* orbital mainly distributed along the N–Pt–Cl complexes, the T1 arises from a HOMO–LUMO+2 excitation,
axis, while the LUMO+1 is a π* orbital of the C^N ligand with which is a π–π* transition within the C′^N′ ligand [tpy (3cd, 4)
significant dσ* character along the mentioned axis. Essentially or thpy (3ce, 3de)], and can be described as almost purely 3LC.
π* orbitals of the C^N and C′^N′ ligands lie at higher energies. Thus, in all cases the lowest triplet excitation involves the
Among complexes 3, the largest HOMO–LUMO energy gap is cyclometalated ligand with the lowest π–π* transition energy,
found for 3cd, mainly because its tpy-based HOMO has a which agrees with the experimental emission data. The lower
lower energy compared to the dtpyH- or thpy-based HOMOs of T1 excitation energy predicted for complex 3ed relative to the
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Fig. 13 Spin density distributions (0.001 e per bohr3) for the lowest
triplet excited state of complexes 3de and 3ed.
Notably, there is an appreciably higher spin density on the
metal in the T1 state of 3ed with respect to the other com-
plexes, which can be visually appreciated by comparing the
spin density distributions for the T1 state of the isomeric com-
plexes 3de and 3ed (Fig. 13). Consistently, the calculated
natural spin density on the Pt atom (Table 3) is appreciably
higher for the T1 state of 3ed, which implies a higher metal-
orbital contribution to the excited state. This fact can be
reasonably ascribed to a stronger π-donation from the aryl
group of the chromophoric thpy ligand in 3ed, where it
occupies the C^N position (C trans to N′) and has a shorter Pt–
C bond distance, resulting in a higher energy of the involved
dπ orbital and hence it can be associated with a higher degree
of MLCT admixture into the relaxed 3LC state, which is consist-
ent with its lower energy relative to 3ce and 3de. In the other
complexes, the chromophoric ligand occupies the C′^N′ posi-
tion (C′ trans to Cl) and the corresponding Pt–C′ distance is
longer, resulting in a much lower spin density on the metal
and hence a markedly decreased MLCT contribution. This
implies also that complexes that emit from the C^N ligand
(3bd and 3ed) may exhibit shorter emission lifetimes due to an
enhancement of the spin–orbit coupling effects induced by
the metal, which are known to accelerate the radiative tran-
sition to the ground state.1,10,45,46
Fig. 12 Lowest triplet excitation energies from TDDFT calculations at
the ground-state geometry.
other thpy-based emitters is also consistent with the experi-
mental observations. All the studied complexes present low-
3
lying LMCT excited states, whose energies approximately cor-
relate with the HOMO–LUMO energy gaps, and therefore are
lower for the complexes bearing the dtpyH (3bd) or thpy (3ce,
3de, 3ed) ligands. The energy differences between the lowest
3LMCT state and the T1 state range from 0.19 (3bd) to 0.49
(3ed) eV. These differences are smaller compared with those
found for other cyclometalated Pt(IV) complexes that are mod-
erately emissive in fluid solution, e.g. [PtCl2(ppy)2] (C2-sym-
metrical isomer, 0.60 eV)16 or mer-[Pt(ppy)2(thpy)]+ (1.15 eV),23
meaning that thermal population of the LMCT state from the
emitting state should provide an effective nonradiative de-
activation mechanism, resulting in largely or totally quenched
emissions at room temperature.
The geometry of the lowest triplet excited state (T1) was opti-
mized for 3cd, 3ce, 3de, 3ed and 4. In the case of 3bd, the T1
state could not be optimized because it collapsed to a dissocia-
tive LMCT state. The calculated electronic energies relative to
the ground state (adiabatic energy differences, Table 3) are in
good agreement with the observed sequence of emission ener-
gies. The spin density distributions correspond to π–π* exci-
tations mainly localized on the cyclometalated ligands
(Fig. 13 and S37†) with little metal orbital participation.
On the basis of these computational results, the fact that
3ed is the only complex of the studied series that emits in
fluid solution at 298 K is a consequence of two favourable
factors: (1) it is the derivative with the largest energy difference
between the emitting state and the lowest 3LMCT state, and
therefore its emission should be less effectively quenched, and
(2) the chromophoric thpy ligand occupies the C^N position,
having a higher metal orbital involvement in the emitting state,
which implies a faster radiative transition to the ground state.
Table 3 Adiabatic energy differences between the T1 and S0 states and
natural spin densities at the Pt atom in the optimized T1 state
Conclusions
Complex
ΔE(T1–S0)/eV
Spin density on Pt
Dichloro-bridged dimers [Pt2(μ-Cl)2(C^N)2], bearing a mono-
cyclometalated 2,6-diaryl- or 2-arylpyridine ligand (C^N) undergo
bridge-cleavage reactions upon reaction with different 2-aryl-
pyridines (N′^C′H) at room temperature to give exclusively
complexes cis-N,N-[PtCl(C^N)(N′^C′H)]; isolation and structural
3cd
3ce
3de
3ed
4
2.81
2.38
2.38
2.32
2.79
0.0062
0.0082
0.0094
0.0347
0.0017
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characterization of derivatives of this class have been achieved mer-5cd was carried out using a 36 W Philips UVB Narrowband
for the first time. Subsequent oxidation with PhICl2 leads to lamp centred at 310 nm. UV-vis absorption spectra were
the electrophilic metalation of the pendant aryl group of the recorded on a PerkinElmer Lambda 750S spectrophotometer.
N′^C′H ligand to give Pt(IV) complexes [PtCl2(C^N)(C′^N′)], Excitation and emission spectra were recorded on a Jobin Yvon
bearing two different or equal cyclometalated ligands in an Fluorolog 3–22 spectrofluorometer with a 450 W xenon lamp,
unsymmetrical arrangement.
double-grating monochromators, and a TBX-04 photomulti-
Chloride-abstraction reactions on a subset of complexes plier. Measurements were carried out in a right angle configur-
[PtCl2(C^N)(C′^N′)] using AgOTf at 120 °C have been investi- ation using 10 mm quartz fluorescence cells (298 K) or 5 mm
gated to evaluate their suitability for the synthesis of tris-cyclo- quartz NMR tubes (77 K). A liquid nitrogen Dewar with quartz
metalated Pt(IV) complexes. The selective substitution of the windows was employed for the low-temperature measure-
chloride ligand trans to C′ can be achieved by using one equiv. of ments. Solutions of the samples were degassed by bubbling
AgOTf. However, when both chloride ligands are abstracted in argon for 30 min. Lifetimes were measured using an IBH
the presence of a 2-arylpyridine, isomerization to intermediate FluoroHub controller in MCS mode and the Fluorolog’s
complexes with a trans-N,N configuration occurs, resulting in the FL-1040 phosphorimeter pulsed xenon lamp as excitation
formation of mer isomers of tris-cyclometalated Pt(IV) complexes source; the estimated uncertainty is 10% or better.
if C^N is a monoarylpyridine, or in a reductive C–C coupling reac-
tion if C^N is a monocyclometalated 2,6-diarylpyridine.
General procedure for the synthesis of [Pt2(μ-Cl)2(C^N)2]
(C^N = dfppy (1c), tpy (1d), thpy (1e). The following procedure
Complexes of the type [PtCl2(C^N)(C′^N′)] exhibit phosphor- is a modification of that reported for the ppy26 and tpy38
escence in frozen PrCN glasses arising from 3LC states loca- derivatives. K2PtCl4 and the appropriate N^CH ligand in
lized on the cyclometalated ligand with the lowest π–π* tran- 1 : 1 molar ratio were placed in a Carius tube under a N2 atmo-
sition energy, which can be either in the C^N (C trans to N′) or sphere and a previously degassed 3 : 1 (v/v) mixture of 2-ethox-
C′^N′ position (C′ trans to Cl). The emissions are largely or yethanol and H2O (50 mL) was added. The mixture was stirred
totally quenched in fluid CH2Cl2 solution at room temperature at 80 °C for 24 h, whereupon a yellow suspension formed.
because of the thermal population of low-lying, dissociative After cooling to room temperature, H2O (50 mL) was added to
excited states of LMCT character. Interestingly, the complexes complete the precipitation. The solid was collected by fil-
in which the chromophoric ligand occupies the C^N position tration, washed with MeOH (2 × 5 mL), CH2Cl2 (3 × 5 mL) and
exhibit shorter emission lifetimes and can have a lower emis- Et2O (2 × 5 mL) and vacuum-dried to give 1. All complexes 1
sion energy with respect to those with the chromophoric are insoluble in noncoordinating organic solvents.
ligand in the C′^N′ position. On the basis of the computational
[Pt2(μ-Cl)2(dfppy)2] (1c). Yellow solid, obtained from K2PtCl4
analysis, this effect can be ascribed to a higher MLCT admix- (1008 mg, 2.43 mmol) and dfppyH (370 μL, 2.43 mmol). Yield:
ture into the essentially 3LC emitting state for the ligands in 694 mg, 68%. Elemental analysis calcd for C22H12Cl2F4N2Pt2:
the C^N position, because of the shorter Pt–C bond distance C, 31.40; H, 1.44; N, 3.33; found: C, 31.68; H, 1.35; N, 3.23.
trans to N′ and a stronger π-donation from the aryl group,
[Pt2(μ-Cl)2(tpy)2] (1d). Yellow solid, obtained from K2PtCl4
which increases the energy of the occupied dπ orbitals. Thus, (1643 mg, 3.96 mmol) and tpyH (677 μL, 3.96 mmol). Yield:
the present results show that, although the metal orbital con- 905 mg, 57%. Elemental analysis calcd for C24H20Cl2N2Pt2: C,
tribution to the emitting state in cyclometalated Pt(IV) com- 36.15; H, 2.53; N, 3.51; found: C, 36.28; H, 2.40; N, 3.50.
plexes is small, it can be modulated by varying the ligand trans
[Pt2(μ-Cl)2(thpy)2] (1e). Yellow solid, obtained from K2PtCl4
to the metalated carbon of the chromophoric ligand and can (1000 mg, 2.41 mmol) and thpyH (420 mg, 2.53 mmol). Yield:
have an appreciable impact on their emission properties.
745 mg, 79%. Elemental analysis calcd for C18H12Cl2N2Pt2S2:
C, 27.66; H, 1.55; N, 3.58; S, 8.20; found: C, 27.59; H, 1.45; N,
3.43; S, 8.44.
General procedure for the synthesis of cis-N,N-[PtCl(C^N)(N′
^C′H)] (2). To a suspension of 1 (0.10 mmol) in CH2Cl2
(10 mL) was added the N′^C′H ligand (1–3 equiv. per Pt) and
Experimental section
General considerations, materials and instrumentation
Unless otherwise noted, preparations were carried out at room the mixture was stirred until a clear solution was obtained
temperature under atmospheric conditions using synthesis (0.5–1 h). The mixture was concentrated under reduced
grade solvents. The dichloro-bridged dimers 1a36 and 1b25 and pressure (1 mL) and Et2O (15 mL) was added, whereupon a
47
the PhICl2
reagent were prepared following reported pro- yellow solid precipitated, which was collected by filtration and
cedures. NMR spectra were recorded on Bruker Advance 300, vacuum dried to give 2.
400 or 600 MHz spectrometers at 298 K. Chemical shifts (δ)
cis-N,N-[PtCl(dppyH)(ppyH)] (2af). Yellow solid, obtained
were referenced to residual signals of non-deuterated solvent from 1a (80 mg, 0.09 mmol) and ppyH (80 μL, 0.56 mmol).
and are given in ppm downfield from tetramethylsilane. Yield: 97 mg, 88%. Elemental analysis calcd for C28H21ClN2Pt:
Elemental analyses were carried out with
CHNS-932 microanalyzer. High-resolution electrospray ioniza- NMR data could not be obtained (see main text and Fig. S1†).
tion mass spectra (ESI-MS) were recorded on an Agilent 6220 cis-N,N-[PtCl(dfppy)(tpyH)] (2cd). Yellow solid, obtained
Accurate-Mass time-of-fight (TOF) LC/MS. The irradiation of from 1c (60 mg, 0.07 mmol) and tpyH (40 μL, 0.24 mmol).
a
LECO C, 54.59; H, 3.44; N, 4.55; found: C, 54.36; H, 3.57; N, 4.53.
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1
Yield: 47 mg, 56%. H NMR (400 MHz, CD2Cl2): δ = 9.09 (br d, immediate colour change to pale yellow was observed. The
J = 5.7 Hz, 1H, CH), 8.03–7.97 (m, 3H, CH), 7.93–7.86 (m, 1H, mixture was concentrated under reduced pressure (2 mL) and
CH), 7.75 (td, J = 7.9, 1.7 Hz, 1H, CH), 7.71 (br d, J = 7.9 Hz, Et2O (15 mL) was added to give a pale-yellow precipitate, which
1H, CH), 7.64–7.45 (m, 3H, CH), 7.18 (d, J = 7.8 Hz, 2H, CH), was collected by filtration, washed with MeOH (3 × 4 mL) and
6.81 (ddd, J = 7.4, 5.8, 1.5 Hz, 1H, CH), 6.56 (ddd, J = 12.6, 8.9, vacuum-dried to give the corresponding complex 3 (complex
2.5 Hz, 1H, CH), 2.27 (s, 3H, CH3). 13C{1H} NMR (100 MHz, 3ce precipitated directly from the CH2Cl2 solution as a white
CD2Cl2): δ = 164.4 (d, JFC = 7 Hz, C), 162.6 (dd, JFC = 255, solid after the addition of PhICl2).
13 Hz, C), 161.3 (s, C), 160.0 (dd, JFC = 258, 12 Hz, C), 153.0 (s,
[PtCl2(dppyH)(ppy)] (3af). Pale yellow solid, obtained from
CH), 148.2 (s, CH), 143.0 (d, JFC = 8 Hz, C), 140.3 (s, C), 139.2 1a (80 mg, 0.09 mmol), ppyH (80 μL, 0.56 mmol) and PhICl2
1
(s, CH), 138.9 (s, CH), 136.5 (s, C), 130.0 (s, CH), 129.3 (s, CH), (50 mg, 0.18 mmol). Yield: 101 mg, 86%. H NMR (400 MHz,
127.7 (s, CH), 124.2 (s, CH), 122.8 (d, JFC = 19 Hz, C), 122.6 (s, CD2Cl2): δ = 8.78 (ddd with satellites, JHH = 5.5, 1.3, 1.1 Hz,
CH), 117.1 (d with satellites, JFC = 19 Hz, JPtC ∼ 47 Hz, CH), JPtH = 9 Hz, 1H, CH), 8.21–8.13 (m, 1H, CH), 8.00 (dd, JHH
=
99.6 (t, JPtC = 27 Hz, CH), 21.6 (CH3); the resonance of one of 8.2, 1.6 Hz, 1H, CH), 7.83–7.78 (m, 2H, CH), 7.70–7.65 (m, 3H,
the quaternary carbon atoms was not observed. Elemental ana- CH), 7.60 (dd, JHH = 7.7, 1.4 Hz, 1H, CH), 7.43 (dtd, JHH = 16.8,
lysis calcd for C23H17ClF2N2Pt: C, 46.83; H, 2.90; N, 4.75; 7.3, 1.6 Hz, 2 H, CH), 7.28 (tdd, JHH = 7.6, 1.4, 0.6 Hz, 1H, CH),
found: C, 46.78; H, 2.84; N, 4.67.
7.14–7.04 (m, 2H, CH), 7.02 (td, JHH = 5.4, 3.5 Hz, 1H, CH),
cis-N,N-[PtCl(tpy)(tpyH)] (2dd). Yellow solid, obtained from 6.89 (ddd, JHH = 7.9, 7.3, 1.5 Hz, 1H, CH), 6.83 (dd with satel-
1d (80 mg, 0.10 mmol) and tpyH (102 μL, 0.60 mmol). Yield: lites, JHH = 7.5, 1.6 Hz, JPtH = 12 Hz, 1H, CH), 6.74–6.64 (m,
1
54 mg, 48%. H NMR (600 MHz, CD2Cl2): δ = 9.11 (br d, JHH
=
=
1H, CH), 6.35 (dddd, JHH = 7.6, 2.0, 1.2, 0.6 Hz, 1H, CH), 6.28
5.5 Hz, 1H, CH), 8.04 (d, JHH = 7.7 Hz, 2H, CH), 7.99 (td, JHH
(dd with satellites, JHH = 7.9, 1.1 Hz, JPtH = 36 Hz, 1H, CH). 13
C
7.8, 1.7 Hz, 1H, CH), 7.75 (s with satellites, JPtH = 17 Hz, 1H, NMR data could not be obtained because of the very low solu-
CH), 7.73–7.59 (m, 2H, CH), 7.53–7.45 (m, 3H, CH), 7.23 (d, bility of this complex in common solvents. Elemental analysis
JHH = 7.9 Hz, 1H, CH), 7.19 (d, JHH = 7.9 Hz, 2H, CH), 6.87 (d, calcd for C28H20Cl2N2Pt: C, 51.70; H, 3.10; N, 4.31; found: C,
JHH = 7.8 Hz, 1H, CH), 6.75–6.70 (m, 1H, CH), 2.34 (s, 3H, 51.57; H, 3.07; N, 4.54.
CH3), 2.27 (s, 3H, CH3). 13C{1H} NMR (151 MHz, CD2Cl2): δ =
[PtCl2(dppyH)(tpy)] (3ad). Pale yellow solid, obtained from
167.9 (C), 161.3 (C), 153.1 (CH), 148.0 (CH), 142.5 (C), 140.2 1a (80 mg, 0.09 mmol), tpyH (80 μL, 0.47 mmol) and PhICl2
(C), 138.9 (C), 138.9 (CH), 138.1 (CH), 136.7 (C), 135.7 (CH), (50 mg, 0.18 mmol). Yield: 72 mg, 60%. 1H NMR (400 MHz,
130.1 (CH), 129.2 (CH), 127.5 (CH), 124.9 (CH), 124.0 (CH), CD2Cl2): δ = 8.75 (br d, JHH = 4.9 Hz, 1H, CH), 8.16 (d with sat-
123.4 (CH), 122.0 (CH), 118.9 (CH), 22.1 (CH3), 21.6 (CH3). ellites, JHH = 7.6 Hz, JPtH = 25 Hz, 1H, CH), 8.01 (d, JHH = 8.1
Elemental analysis calcd for C24H21ClN2Pt: C, 50.75; H, 3.73; Hz, 1H, CH), 7.83–7.77 (m, 2H, CH), 7.68–7.59 (m, 3H, CH),
N, 4.93; found: C, 50.74; H, 3.75; N, 4.80.
cis-N,N-[PtCl(thpy)(tpyH)] (2ed). Orange solid, obtained from JHH = 7.6, 6.4 Hz, 1H, CH), 7.00–6.95 (m, 1H, CH), 6.91 (d, JHH
1e (150 mg, 0.19 mmol) and tpyH (90 μL, 0.53 mmol). Yield: = 7.9 Hz, 1H, CH), 6.83 (d, JHH = 7.4 Hz, 1H, CH), 6.68 (t, JHH
7.49–7.38 (m, 3H, CH), 7.27 (t, JHH = 7.6 Hz, 1H, CH), 7.08 (td,
=
1
173 mg, 80%. H NMR (300 MHz, CD2Cl2): δ = 9.10 (ddd with 7.6 Hz, 1H, CH), 6.35 (d, JHH = 7.4 Hz, 1H, CH), 6.06 (s with
satellites, JHH = 5.7, 1.7, 0.8 Hz, JPtH = 18 Hz, 1H, CH), 8.04 (d satellites, JPtH = 37 Hz, 1H, CH), 2.06 (s, 3H, CH3). 13C{1H}
with satellites, JHH = 8.2 Hz, JPtH = 8 Hz, 2H, CH), 7.98 (td, JHH NMR (100 MHz, CD2Cl2): δ = 166.3 (C), 149.7 (CH), 143.5 (C),
= 7.8, 1.7 Hz, 1H, CH), 7.69 (ddd, JHH = 7.9, 1.4, 0.8 Hz, 1H, 141.9 (C), 140.3 (C), 139.9 (CH), 138.4 (CH), 135.7 (C), 133.0
CH), 7.59 (td, JHH = 7.8, 1.5 Hz, 1H, CH), 7.48 (ddd, JHH = 7.2, (C), 132.7 (JPtC = 26 Hz, CH), 131.9 (JPtC = 34 Hz, CH), 130.7
5.6, 1.5 Hz, 1H, CH), 7.42 (d with satellites, JHH = 4.8 Hz, JPtH
∼
(CH), 130.3 (CH), 129.8 (C), 128.3 (CH), 128.2 (CH), 127.6 (CH),
6 Hz, 1H, CH), 7.35 (ddd, JHH = 5.9, 1.5, 0.8 Hz, 1H, CH), 7.32 127.4 (CH), 126.4 (CH), 126.1 (JPtC = 24 Hz, CH), 125.2 (JPtC
=
=
(d, JHH = 4.8 Hz, 1H, CH), 7.23–7.18 (m, 3H, CH), 6.60 (ddd, 27 Hz, CH), 123.8 (CH), 120.2 (JPtC = 33 Hz, CH), 119.3 (JPtC
JHH = 7.4, 5.9, 1.5 Hz, 1H, CH), 2.28 (s, 3H, CH3). 13C{1H} NMR 13 Hz, CH), 22.0 (CH3). Elemental analysis calcd for
(75 MHz, CD2Cl2): δ = 163.3 (C), 161.3 (C), 153.1 (CH), 148.3 C29H22Cl2N2Pt: C, 52.42; H, 3.34; N, 4.22; found: C, 52.42; H,
(CH), 143.5 (C), 140.3 (C), 139.0 (CH), 138.9 (CH), 136.6 (C), 3.41; N, 4.09.
133.3 (JPtC = 93 Hz, CH), 130.0 (CH), 129.3 (CH), 127.4 (CH),
124.2 (JPtC = 19 Hz, CH), 120.0 (JPtC = 36 Hz, CH), 117.9 (JPtC
42 Hz, CH), 21.2 (CH3). Elemental analysis calcd for (65 mg, 0.24 mmol). Yield: 111 mg, 75%. H NMR (300 MHz,
[PtCl2(dtpyH)(tpy)] (3bd). Pale yellow solid, obtained from
=
1b (105 mg, 0.11 mmol), tpyH (92 μL, 0.54 mmol) and PhICl2
1
C21H17ClN2PtS: C, 45.04; H, 3.06; N, 5.00; S, 5.73; found: C, CD2Cl2): δ = 8.71 (ddd with satellites, JHH = 5.6, 1.6, 0.7 Hz,
45.13; H, 3.06; N, 4.85; S, 5.41.
JPtH = 10 Hz, 1H, CH), 7.98 (s with satellites, JPtH = 25 Hz, 1H,
General procedure for the synthesis of complexes 3. The CH), 7.93 (dd, JHH = 8.2, 1.7 Hz, 1H, CH), 7.78–7.64 (m, 3H,
following procedure was applied in all cases except 3ed. To a CH), 7.58 (d, JHH = 8.1 Hz, 1H, CH), 7.50 (dd, JHH = 7.9, 2.0 Hz,
suspension of the dimer 1 (0.10 mmol) in CH2Cl2 (10 mL) was 1H, CH), 7.47 (d, JHH = 8.1 Hz, 1H, CH), 7.25 (ddd, JHH = 8.0,
added the appropriate N′^C′H ligand (1–3 equiv. per Pt). After 1.8, 0.9 Hz, 1H, CH), 7.06–7.01 (m, 1H, CH), 6.98 (ddd, JHH
=
stirring for 0.5–1 h, a clear yellow solution was obtained (in 7.2, 5.6, 1.4 Hz, 1H, CH), 6.90 (ddd, JHH = 7.8, 1.7, 0.6 Hz, 1H,
the synthesis of 3ce, this mixture remained a suspension after CH), 6.79 (dd with satellites, JHH = 7.4, 1.6 Hz, JPtH = 12 Hz,
18 h). PhICl2 (1 equiv. per Pt) was then added, whereupon an 1H, CH), 6.42–6.37 (m, 1H, CH), 6.20 (dd, JHH = 7.8, 2.0 Hz,
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1H, CH), 6.08 (dd with satellites, JHH = 1.5, 0.8 Hz, JPtH = 37 8.07–8.04 (m, 1H, CH), 8.04 (dd with satellites, JHH = 1.7, 0.8
Hz, 1H, CH), 2.50 (s, 3H, CH3), 2.20 (s, 3H, CH3), 2.07 (s, 3H, Hz, JPtH = 26 Hz, 1H, CH), 7.87–7.82 (m, 1H, CH), 7.78 (ddd,
CH3). 13C NMR data could not be obtained for this complex JHH = 8.2, 7.3, 1.4 Hz, 1H, CH), 7.62–7.59 (m, 3H, CH), 7.43
because of its very low solubility. Elemental analysis calcd for (ddd with satellites, JHH = 6.0, 1.4, 0.7 Hz, JPtH = 33 Hz, 1H,
C31H26Cl2N2Pt: C, 53.76; H, 3.78; N, 4.05; found: C, 53.64; H, CH), 7.24 (ddd, JHH = 7.9, 1.6, 0.6 Hz, 1H, CH), 6.93 (ddd, JHH
3.71; N, 3.93.
= 7.5, 6.0, 1.5 Hz, 1H, CH), 6.91 (ddd, JHH = 7.9, 1.6, 0.8 Hz,
[PtCl2(dfppy)(tpy)] (3cd). Pale yellow solid, obtained from 1c 1H, CH), 6.20 (dd with satellites, JHH = 1.6, 0.8 Hz, JPtH = 40 Hz
(150 mg, 0.18 mmol), tpyH (92 μL, 0.54 mmol) and PhICl2 1H, CH), 2.55 (s, 3H, CH3), 2.07 (s, 3H, CH3). 13C{1H} NMR
1
(99 mg, 0.36 mmol). Yield: 173 mg, 77%. H NMR (600 MHz, (151 MHz, CD2Cl2): δ = 165.5 (JPtC = 58 Hz, C), 161.8 (JPtC = 40
CD2Cl2): δ = 9.77 (ddd with satellites, J = 5.5, 1.6, 0.7 Hz, JPtH
∼
Hz, C), 148.4 (CH), 146.5 (CH), 144.2 (JPtC = 775 Hz, C), 144.0
8 Hz, 1H, CH), 8.29–8.23 (m, 1H, CH), 8.12 (ddd, J = 8.2, 7.4, (JPtC = 36 Hz, C), 142.9 (JPtC = 48 Hz, C), 140.8 (CH), 140.6
1.7 Hz, 1H, CH), 8.07 (dt, J = 8.1, 1.0 Hz, 1H, CH), 7.92–7.83 (CH), 138.9 (JPtC = 24 Hz, C), 138.5 (C), 137.0 (JPtC = 754 Hz, C),
(m, 2H, CH), 7.63–7.60 (m, 2H, CH), 7.49 (ddd with satellites, J 132.9 (JPtC = 37 Hz, CH), 132.5 (JPtC = 24 Hz, CH), 127.4 (CH),
= 6.0, 1.6, 0.7 Hz, JPtH = 33 Hz, 1H, CH), 7.02 (ddd, J = 7.5, 6.1, 127.3 (CH), 125.7 (JPtC = 29 Hz, CH), 125.5 (JPtC = 28 Hz, CH),
1.4 Hz, 1H, CH), 6.99–6.93 (m, 3H, CH), 6.22 (dd with satel- 124.7 (CH), 123.7 (JPtC = 29 Hz, CH), 121.1 (JPtC = 34 Hz, CH),
lites, J = 1.6, 0.7 Hz, JPtH = 39 Hz, 1H, CH), 2.12 (s, 3H, CH3). 120.8 (CH), 22.5 (CH3), 22.0 (CH3). Elemental analysis calcd
13C{1H} NMR (151 MHz, CD2Cl2): δ = 163.9 (dd, JFC = 259, 13 for C24H20Cl2N2Pt: C, 47.85; H, 3.35; N, 4.65; found: C, 47.70;
Hz, C), 162.0 (dd, JFC = 23, 5 Hz, C), 161.0 (dd, JFC = 261, 13 Hz, H, 3.47; N, 4.44.
C), 148.4 (s, CH), 146.8 (s, CH), 145.5 (d with satellites, JFC = 9
Hz, JPtH = 788 Hz, C), 143.4 (s with satellites, JPtH = 47 Hz, C), (100 mg, 0.13 mmol), thpyH (133 mg, 0.82 mmol) and PhICl2
141.4 (CH), 141.2 (CH), 138.4 (C), 137.1 (s with satellites, JPtH
(83 mg, 0.30 mmol). Yield: 84 mg, 54%. 1H NMR (600 MHz,
[PtCl2(tpy)(thpy)] (3de). Pale yellow solid, obtained from 1d
=
741 Hz, C), 132.6 (s with satellites, JPtC = 37 Hz, CH), 127.7 CD2Cl2): δ = 9.56 (ddd, JHH = 5.5, 1.6, 0.8 Hz, 1H, CH), 8.03 (td,
(CH), 125.9 (s with satellites, JPtC = 28 Hz, CH), 125.1–124.7 (m, JHH = 7.8, 1.7, 1H, CH), 8.01 (dd with satellites, JHH = 1.7, 0.9
2 CH), 124.4 (s with satellites, JPtC = 28 Hz, CH), 121.0 (s with Hz, JPtH ∼ 29 Hz, 1H, CH), 7.86–7.77 (m, 2H, CH), 7.71 (dt, JHH
satellites, JPtC ∼ 14 Hz, CH), 115.3 (d with satellites, JFC = 21 = 8.0, 1.0 Hz, 1H, CH), 7.59 (d, JHH = 7.9 Hz, 1H, CH), 7.54
Hz, JPtC = 21 Hz, CH), 102.4 (t, JFC = 26 Hz, CH), 22.0 (CH3). 19
F
(ddd with satellites, JHH = 6.0, 1.3, 0.7 Hz, JPtH ∼ 30 Hz, 1H,
NMR (282.4 MHz, CD2Cl2): −102.21 (m, 1F), −108.95 (m, 1F); CH), 7.51 (ddd, JHH = 7.6, 5.5, 1.3 Hz, 1H, CH), 7.25 (d, JHH
=
the resonances of two of the quaternary carbon atoms were 5.0 Hz, 1H, CH), 7.21 (ddd, JHH = 8.0, 1.5, 0.7 Hz, 1H, CH),
not observed. Elemental analysis calcd for C23H16Cl2F2N2Pt: C, 6.98 (ddd, JHH = 7.9, 6.1, 1.8 Hz, 1H, CH), 6.11 (d with satel-
44.24; H, 2.58; N, 4.49; found: C, 44.15; H, 2.77; N, 4.29.
lites, JHH = 5.0 Hz, JPtH ∼ 17 Hz, 1H, CH), 2.52 (s, 3H, CH3). 13
C
[PtCl2(dfppy)(thpy)] (3ce). White solid, obtained from 1c {1H} NMR (151 MHz, CD2Cl2): δ = 165.0 (JPtC = 59 Hz, C), 157.7
(100 mg, 0.12 mmol), thpyH (104 mg, 0.64 mmol) and PhICl2 (JPtC = 32 Hz, C), 148.3 (CH), 146.9 (CH), 143.8 (JPtC = 36 Hz,
1
(78 mg, 0.28 mmol). Yield: 127 mg, 86%. H NMR (600 MHz, C), 141.2 (CH), 140.8 (CH), 139.9 (JPtC = 770 Hz, C), 139.3 (JPtC
CD2Cl2): δ = 9.57 (ddd with satellites, JHH = 5.6, 1.6, 0.8 Hz, ∼ 27 Hz, C), 136.9 (C), 134.8 (JPtC ∼ 795 Hz, C), 133.0 (JPtC = 26
JPtH ∼ 14 Hz, 1H, CH), 8.26–8.21 (m, 1H, CH), 8.06 (ddd, JHH
=
Hz, CH), 129.4 (JPtC = 65 Hz, CH), 129.2 (JPtC = 56 Hz, CH),
8.0, 7.6, 1.6 Hz, 1H, CH), 7.89 (dddd, JHH = 8.2, 7.5, 1.5, 0.6, 127.5 (CH), 125.4 (JPtC = 28 Hz, CH), 124.0 (JPtC = 28 Hz, CH),
1H, CH), 7.84 (ddd with satellites, JFH = 8.6, 0.9 Hz, JHH = 2.4 123.2 (CH), 120.9 (JPtC = 33 Hz, CH), 120.2 (CH), 22.5 (CH3).
Hz, JPtH ∼ 36 Hz, 1H, CH), 7.74 (ddd, JHH = 8.0, 1.3, 0.9, 1H, Elemental analysis calcd for C21H16Cl2N2PtS: C, 42.43; H, 2.71;
CH), 7.60 (ddd with satellites, JHH = 6.1, 1.6, 0.7 Hz, JPtH ∼ 31 N, 4.71; S, 5.39; found: C, 42.18; H, 2.72; N, 4.64; S, 5.31.
Hz, 1H, CH), 7.53 (ddd, JHH = 7.6, 5.6, 1.3 Hz, 1H, CH), 7.32 (d
with satellites, JHH = 5.0 Hz, JPtH ∼ 6 Hz, 1H, CH), 7.08 (ddd, 0.16 mmol) in CH2Cl2 (5 mL) was added PhICl2 (43 mg,
JHH = 7.6, 6.0, 1.5, 1H, CH), 6.95 (ddd, JFH = 12.2, 8.8 Hz, JHH 0.16 mmol) and the mixture was stirred for 10 min. The result-
[PtCl2(thpy)(tpy)] (3ed). To a solution of 2ed (87 mg,
=
2.4 Hz, 1H, CH), 6.18 (d with satellites, JHH = 5.0 Hz, JPtH ∼ 16 ing solution was concentrated under reduced pressure (1 mL)
Hz, 1H, CH). 13C{1H} NMR (151 MHz, CD2Cl2): δ = 148.4 (CH), and Et2O (20 mL) was added, whereupon a pale-yellow precipi-
147.2 (CH), 141.6 (CH), 129.8 (CH), 129.0 (CH), 124.8 (CH), tate formed, which was collected by filtration and vacuum-
124.7 (CH), 123.4 (CH), 120.3 (CH), 115.9 (CH), 115.8 (CH), dried to give 3ed. Yield: 80 mg, 87%. 1H NMR (600 MHz,
102.7 (t, JFC = 27 Hz, CH); quaternary carbon atoms were not CD2Cl2): δ = 9.80 (ddd with satellites, JHH = 5.5, 1.6, 0.8 Hz,
observed. 19F NMR (282.4 MHz, CD2Cl2): δ = −102.29 (m, 1H), JPtH ∼ 9 Hz, 1H, CH), 8.13–8.09 (ddd, JHH = 8.1, 7.4, 1.6 Hz, 1H,
−108.88
C20H12Cl2F2N2PtS: C, 38.97; H, 1.96; N, 4.54; S, 5.20; found: C, 1H, CH), 7.73 (ddd, JHH = 8.1, 7.4, 1.5 Hz, 1H, CH), 7.66 (d, JHH
38.88; H, 2.04; N, 4.60; S, 5.16. = 4.9 Hz, JPtH = 11 Hz, 1H, CH), 7.62–7.56 (m, 3H, CH), 7.31
(m,
1H).
Elemental
analysis
calcd
for CH), 8.05 (br d, JHH = 8.1 Hz, 1H, CH), 7.80 (d, JHH = 4.9 Hz,
[PtCl2(tpy)2] (3dd). Pale yellow solid, obtained from 1d (ddd with satellites, JHH = 6.1, 1.4, 0.7 Hz, JPtH = 34 Hz, 1H,
(59 mg, 0.07 mmol), tpyH (25 μL, 0.15 mmol) and PhICl2 CH), 6.93 (ddd, JHH = 7.9, 1.6, 0.7 Hz, 1H, CH), 6.82 (ddd with
(47 mg, 0.17 mmol). Yield: 68 mg, 81%. 1H NMR (600 MHz, satellites, JHH = 7.5, 6.1, 1.5 Hz, JPtH ∼ 8 Hz, 1H, CH), 6.12 (dd
CD2Cl2): δ = 9.77 (ddd with satellites, JHH = 5.5, 1.7, 0.8 Hz, with satellites, JHH = 1.5, JHH = 0.7 Hz, JPtH = 39 Hz, 1H, CH),
JPtH ∼ 7 Hz, 1H, CH), 8.10 (ddd, JHH = 8.2, 7.3, 1.6 Hz, 1H, CH), 2.11 (s, 3H). 13C{1H} NMR (75 MHz, CD2Cl2): δ = 162.2 (C),
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160.6 (C), 148.4 (CH), 146.7 (CH), 145.1 (C), 143.1 (C), 141.2
Irradiation of mer-5cd. A solution of the isomer mixture mer-
5cd (5 mg) in CD3CN (0.4 mL) was placed in a quartz NMR
(CH), 141.0 (CH), 138.4 (C), 136.6 (C), 136.5 (C), 132.9 (JPtC
=
35 Hz, CH), 130.5 (JPtC = 50 Hz, CH), 130.1 (CH), 127.6 (CH), tube and irradiated with UV light (310 nm) for 27 h. The result-
125.7 (CH), 124.6 (JPtC = 12 Hz, CH), 121.9 (JPtC = 27 Hz, CH), ing NMR spectrum is shown in Fig. S15.† HRMS (ESI+, m/z)
120.8 (JPtC = 15 Hz, CH), 120.3 (JPtC = 30 Hz, CH), 22.1 (CH3). calcd for [C35H26F2N3Pt]+: 721.1746; found: 721.1743; error:
Elemental analysis calcd for C21H16Cl2N2PtS: C, 42.43; H, 2.71; 0.4 ppm.
N, 4.71; S, 5.39; found: C, 42.45; H, 2.58; N, 4.56; S, 5.47.
mer-[Pt(tpy)3]OTf (mer-5dd). A Carius tube was charged with
[PtCl(dfppy)(tpy)(γ-pic)]OTf (4). A Carius tube was charged 3dd (74 mg, 0.12 mmol), tpyH (51 µL, 0.30 mmol), AgOTf
with complex 3cd (65 mg, 0.10 mmol), AgOTf (25 mg, (76 mg, 0.30 mmol) and 1,2-dichlorobenzene (5 mL) and the
0.10 mmol), γ-picoline (10 µL, 0.10 mmol) and 1,2-dichloro- mixture was stirred at 120 °C under a N2 atmosphere for 48 h.
benzene (5 mL) under a N2 atmosphere and the mixture was The resulting suspension was filtered through Celite. The
stirred at 120 °C for 72 h. The resulting suspension was filtered addition of Et2O (20 mL) to the filtrate led to the formation of
through Celite. The addition of pentane (20 mL) to the filtrate a precipitate, which was collected by filtration, washed with
led to the precipitation of a white solid, which was collected by Et2O (3 × 4 mL) and vacuum-dried to give mer-5dd as white
1
filtration, recrystallized from CH2Cl2/Et2O and vacuum-dried solid (77 mg, 76%). The H NMR data are in agreement with
to give 4 as a white solid. Yield: 57 mg, 65%. 1H NMR those previously reported.23
(600 MHz, CD2Cl2): δ = 8.46 (br s, 2H), 8.26 (dt, J = 8.3, 1.9 Hz,
[Pt(C^N^N)(tpyH)]OTf (6). Complex 3af (115 mg,
1H), 8.21–8.15 (m, 3H), 8.06 (td, J = 8.0, 1.3 Hz, 1H), 7.99 0.18 mmol), AgOTf (136 mg, 0.53 mmol) and a degassed solu-
(d with satellites, J = 6.3 Hz, JPtH = 31, 1H), 7.92–7.85 (m, 1H), tion of tpyH (150 μL, 0.88 mmol) in 1,2-dichloroethane (8 mL)
7.67 (d, J = 8.0 Hz, 1H), 7.60–7.54 (m, 1H), 7.48 (ddd, J = 7.5, were placed in a Carius tube and the resulting mixture was
5.9, 1.4 Hz, 1H), 7.40 (d, J = 6.1 Hz, 2H), 7.04–6.95 (m, 2H), stirred at 90 °C under a N2 atmosphere for 48 h. After cooling
6.18 (s with satellites, JPtH = 35 Hz, 1H), 2.43 (s, 3H), 2.13 (s, to room temperature, CH2Cl2 (10 mL) was added and the sus-
3H). 13C{1H} NMR (151 MHz, CD2Cl2): δ = 164.2 (dd, JFC = 261, pension was filtered through Celite. The filtrate was concen-
13 Hz, C), 161.3–161.0 (m, C), 161.0 (dd, JFC = 262, 13 Hz, C), trated under reduced pressure (3 mL) and Et2O (20 mL) was
154.2 (s, C), 148.8 (s, CH), 148.5 (s, CH), 148.1 (s, CH), 146.8 (s, added, whereupon a solid precipitated, which was filtered off
CH), 144.7 (d, JFC = 8 Hz, C), 143.8 (s with satellites, JPtC
43 Hz, C), 143.3 (s, CH), 142.1 (s, CH), 138.8 (s, C), 133.4 (s CH2Cl2/Et2O afforded 6 as a pale-yellow solid. Yield: 37 mg,
with satellites, JPtC = 37 Hz, CH), 130.0 (s with satellites, JPtC
23%. 1H NMR (600 MHz, CD2Cl2): δ = 8.78 (ddd, JHH = 6.0, 1.6,
707 Hz, C), 128.9 (s, CH), 128.7 (s, CH), 127.5 (s with satellites, 0.7 Hz, 1H, CH), 7.99 (t, JHH = 8.0 Hz, 1H, CH), 7.93 (td, JHH
=
and washed with Et2O (3 × 4 mL). Recrystallization from
=
=
JPtC = 28 Hz, CH), 126.4 (s with satellites, JPtC = 25 Hz, CH), 7.8, 1.6 Hz, 1H, CH), 7.86 (d, JHH = 8.2 Hz, 2H CH), 7.81 (dd,
126.0 (s, C), 125.5 (s with satellites, JPtC ∼ 32 Hz, CH), 125.4 JHH = 8.3, 1.6 Hz, 1H, CH), 7.73 (ddd, JHH = 7.5, 1.3, 0.6 Hz,
(s with satellites, JPtC ∼ 33 Hz, CH), 122.1 (s with satellites, 1H, CH), 7.61 (td, JHH = 7.6, 1.2 Hz, 1H, CH), 7.54–7.50 (m, 3H,
JPtC ∼ 14 Hz, CH), 121.6 (q, JFC ∼ 320 Hz, C), 114.7 (d with sat- CH), 7.41 (td, JHH = 7.6, 1.3 Hz, 1H, CH), 7.35–7.31 (m, 2H,
ellites, JFC = 22 Hz, JPtC ∼ 22 Hz, CH), 103.9 (t, JFC = 27 Hz, CH), 7.28 (d, JHH = 8.2 Hz, 2H, CH), 7.23–7.19 (m, 2H, CH),
CH), 22.1 (s, CH3), 21.7 (s, CH3). 19F (282.4 MHz, CD2Cl2): 7.15–7.10 (m, 2H, CH), 7.05 (ddd, JHH = 7.6, 1.1, 0.5 Hz, 1H,
−78.73 (s, 3F), −100.43 (m, 1F), −106.81 (m, 1F). HRMS CH), 6.88 (td, JHH = 7.6, 1.4 Hz, 1H, CH), 6.87 (td, JHH = 7.6, 1.4
(ESI+, m/z) calcd for [C29H23ClF2N3Pt]+: 682.1195; found: Hz, 1H, CH), 6.64 (ddd, JHH = 7.7, 5.4, 1.4 Hz, 1H, CH), 6.55
682.1183; error: 1.8 ppm. Elemental analysis calcd for (ddd, JHH = 5.3, 1.6, 0.8 Hz, 1H, CH), 6.27 (ddd, JHH = 7.7, 1.2,
C30H23ClF5N3O3PtS: C, 43.35; H, 2.79; N, 5.06; S, 3.86; found: 0.4 Hz, 1H, CH), 5.78 (dd, JHH = 7.8, 1.0 Hz, 1H, CH), 2.42 (s,
C, 43.32; H, 2.61; N, 4.92; S, 3.88.
3H, CH3). 13C{1H} NMR (151 MHz, CD2Cl2): δ = 168.2 (C), 162.9
mer-[Pt(dfppy)(tpy)2]OTf (mer-5cd; mixture of mer isomers). (C), 160.5 (C), 160.4 (C), 154.3 (CH), 152.1 (CH), 145.7 (C),
A Carius tube was charged with 3cd (80 mg, 0.13 mmol), tpyH 142.1 (C), 141.8 (C), 140.8 (C), 140.3 (CH), 140.1 (CH), 139.2
(108 µL, 0.64 mmol), AgOTf (66 mg, 0.26 mmol) and 1,2- (C), 139.0 (C), 138.7 (CH), 136.5 (C), 135.2 (C), 132.6 (CH),
dichlorobenzene (5 mL) and the mixture was stirred at 120 °C 130.9 (CH), 130.3 (CH), 130.2 (CH), 129.9 (CH), 129.3 (CH),
under a N2 atmosphere for 72 h. The resulting suspension was 129.1 (CH), 129.0 (CH), 128.9 (CH), 127.9 (CH), 127.6 (CH),
filtered through Celite. The addition of pentane (20 mL) to the 126.5 (CH), 126.2 (CH), 125.6 (CH), 125.1 (CH), 124.8 (CH),
filtrate led to formation of a sticky precipitate, which was 123.3 (CH), 118.7 (CH), 21.8 (CH3); the CF3 resonance was not
washed with Et2O (5 × 5 mL) and dissolved in CH2Cl2 (2 mL). observed. 19F NMR (282.4 MHz, CD2Cl2): δ = −78.86 (s). HRMS
The addition of Et2O (15 mL) afforded an off-white solid, (ESI+, m/z) calcd for [C40H30N3Pt]+: 747.2091; found: 747.2086;
which was collected by filtration and vacuum-dried to give error: 0.7 ppm. Elemental analysis calcd for C41H30F3N3O3PtS:
mer-5cd (37 mg, 33%). The complete NMR data could not be C, 54.91; H, 3.37; N, 4.69; S, 3.57; found: C, 54.71; H, 3.16; N,
extracted because of the complexity of the signals (see Fig. S14 4.61; S, 3.60.
and S15†). HRMS (ESI+, m/z) calcd for [C35H26F2N3Pt]+:
[Pt(tpy)(tpyH)2]OTf (7). Complex 3af (100 mg, 0.15 mmol),
721.1746; found: 721.1734; error: 1.7 ppm. Elemental analysis AgOTf (93 mg, 0.36 mmol) and a degassed solution of tpyH
calcd for C36H26F5N3O3PtS: C, 49.66; H, 3.01; N, 4.82; S, 3.68; (130 μL, 0.76 mmol) in dry 1,2-dichlorobenzene (5 mL) were
found: C, 49.46; H, 3.19; N, 4.69; S, 3.48.
placed in a Carius tube, and the resulting mixture was stirred
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at 120 °C under a N2 atmosphere for 48 h. After cooling to Computational methods
room temperature, CH2Cl2 (15 mL) was added and the suspen-
DFT calculations were carried out with the Gaussian 09
package,51 using the hybrid B3LYP functional52,53 together
with the 6-31G** 54,55 basis set for the light atoms and the
LANL2DZ56 basis set and effective core potential for the Pt
atom. All geometry optimizations were carried out without
symmetry restrictions, using “tight” convergence criteria and
“ultrafine” integration grid. Vertical excitation energies were
obtained from TDDFT calculations at the ground-state opti-
mized geometries. Triplet state geometry optimizations were
carried out following a reported strategy.57 The solvent effect
(CH2Cl2) was accounted for in all cases by using the integral
equation formalism variant of the polarizable continuum sol-
vation model (IEFPCM).58 All the optimized structures were
confirmed as minima on the potential energy surface by per-
forming frequency calculations (zero imaginary frequencies).
Natural spin densities were obtained from natural population
analyses using the NBO 5.9 program.59
sion was filtered through Celite. The filtrate was concentrated
under reduced pressure (3 mL) and Et2O was added (30 mL).
The precipitate was collected by filtration, washed with Et2O (3
× 3 mL) and vacuum-dried to give 7 as a pale-yellow solid.
Yield: 78 mg, 61%. Using the same procedure, complex 7 was
also obtained from 3bd (97 mg, 0.14 mmol), AgOTf (74 mg,
0.29 mmol) and tpyH (0.12 mL, 0.70 mmol). Yield: 57 mg,
48%. 1H NMR (300 MHz, CD2Cl2): δ = 8.00 (ddd, JHH = 8.6,
7.5, 1.5 Hz, 1H, CH), 7.93–7.78 (m, 5H, CH), 7.59 (ddd, JHH
=
5.6, 1.6, 0.7 Hz, 1H, CH), 7.56–7.44 (m, 4H, CH), 7.43–7.36 (m,
3H, CH), 7.22–7.10 (m, 5H, CH), 7.06–6.98 (m, 2H, CH), 6.87
(ddd, JHH = 7.5, 6.0, 1.5 Hz, 1H, CH), 6.18 (s with satellites,
JPtH = 41 Hz, 1H, CH), 2.41 (s, 6H, CH3), 2.18 (s, 3H, CH3).
13C{1H} NMR (75 MHz, CD2Cl2): δ = 168.3 (C), 161.1 (C), 160.9
(C), 154.5 (CH), 151.7 (CH), 149.0 (CH), 142.8 (C), 141.7 (C),
141.1 (C), 141.0 (C), 140.5 (CH), 139.5 (C), 139.5 (CH), 139.0
(CH), 136.5 (C), 136.1 (C), 133.6 (JPtC = 56 Hz, CH), 130.0
(2CH), 129.8 (2CH), 129.2 (2CH), 129.1 (2CH), 127.4 (JPtC
=
63 Hz, CH), 127.1 (JC–Pt = 32 Hz, CH), 126.2 (CH), 125.0
(CH), 124.9 (CH), 124.5 (JPtC = 40 Hz, CH), 123.4 (JPtC = 35 Hz,
CH), 120.1 (JPtC = 43 Hz, CH), 22.1 (CH3), 21.7 (CH3),
21.6 (CH3); the CF3 resonance was not observed.
19F (282.4 MHz, CD2Cl2): δ = −78.88 (s). HRMS (ESI+, m/z)
calcd for [C36H32N3Pt]+: 701.2247; found: 701.2260; error:
1.8 ppm. Elemental analysis calcd for C37H32F3N3O3PtS: C,
52.23; H, 3.79; N, 4.94; S, 3.77; found: C, 52.20; H, 3.84; N,
4.71; S, 3.83.
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
We thank the Spanish Ministerio de Economía
Competitividad (CTQ2015-69568-P), Fundación Séneca (19890/
GERM/15) and Ministerio de Ciencia, Innovación
y
y
Universidades (PGC2018-100719-BI00) for financial support. Á.
Vivancos and D. Poveda thank Fundación Séneca for a
Saavedra Fajardo Fellowship (20398/SF/17) and a predoctoral
fellowship (20725/FPI/18), respectively.
X-ray structure determinations
Single crystals of 2af, 2ed, 3af, 3bd, 3cd, 4·Et2O and
6·0.5CH2Cl2 suitable for X-ray diffraction were obtained by the
liquid–liquid diffusion method from CH2Cl2/Et2O. In the cases
of 2af or 2ed, crystallization required the presence of an excess
ppyH or tpyH, respectively. Numerical details are presented in
the ESI (Tables S1 and S2†). The data were collected on a
Bruker D8 QUEST diffractometer with monochromated Mo-Kα
radiation performing ω scans (2af, 3bd and 3cd) or φ and ω
scans (rest of complexes). The structures were solved by dual
methods48 and refined anisotropically on F2 using the
program SHELXL-2018 (G. M. Sheldrick, University of
Göttingen).49 Methyl hydrogens were included as part of rigid
idealized methyl groups allowed to rotate but not tip; other
hydrogens were included using a riding model. Special fea-
tures of refinement: In 3bd, there is a poorly resolved region of
residual electron density that could not be adequately mod-
elled and therefore the program SQUEEZE,50 which is part of
the PLATON system, was employed to mathematically remove
the effects of the solvent; the void volume per cell was 335 Å3,
with a void electron count per cell of 79; this additional
solvent was not taken into account when calculating derived
parameters such as the formula weight, because its nature was
uncertain. In 6·0.5CH2Cl2, the triflate anion is disordered over
two positions, approximately 54 : 46%.
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