Cyclometalated complexes of platinum(II) with 2-vinylpyridine

Article abstract of DOI:10.1002/ejic.201400052

The electron-rich platinum(II) derivatives [Pt(R)₂(DMSO) ₂] (R = Me, Ph) react with 2-vinylpyridine (L) to give the cyclometalated complexes [Pt(L-H)(R)(DMSO)] through C-H bond activation. Cyclometalation also occurs with [Pt(Me)(Cl)(DMSO)₂]. From the starting compounds, a series of cyclometalated complexes was obtained and characterised by analytical and spectroscopic methods. The molecular structures of [Pt(L-H)(Me)(PPh₃)] and [Pt(L-H)(Ph)(PCy₃)] were solved by X-ray diffraction analysis, and the results unambiguously demonstrate cyclometalation of 2-vinylpyridine. The five-membered cyclometalated ring is particularly stable, likely due to partial electronic delocalisation. Copyright

Full text of DOI:10.1002/ejic.201400052

FULL PAPER
DOI:10.1002/ejic.201400052
Cyclometalated Complexes of Platinum(II) with
2-Vinylpyridine
Antonio Zucca,*[a] Luca Maidich,[a] Veronica Carta,[a]
Giacomo L. Petretto,[a] Sergio Stoccoro,[a] Maria Agostina Cinellu,[a]
Maria I. Pilo,[a] and Guy J. Clarkson[b]
Keywords: Metallacycles / Metalation / C–H activation / Platinum / Vinylidene ligands
The electron-rich platinum(II) derivatives [Pt(R)2(DMSO)2]
(R = Me, Ph) react with 2-vinylpyridine (L) to give the cyclo-
metalated complexes [Pt(L–H)(R)(DMSO)] through C–H
bond activation. Cyclometalation also occurs with [Pt(Me)-
(Cl)(DMSO)2]. From the starting compounds, a series of cy-
clometalated complexes was obtained and characterised by
analytical and spectroscopic methods. The molecular struc-
tures of [Pt(L–H)(Me)(PPh3)] and [Pt(L–H)(Ph)(PCy3)] were
solved by X-ray diffraction analysis, and the results unam-
biguously demonstrate cyclometalation of 2-vinylpyridine.
The five-membered cyclometalated ring is particularly
stable, likely due to partial electronic delocalisation.
Introduction
Results and Discussion
The electron-rich PtII complex cis-[Pt(Me)2(DMSO)2] is
a well-known cyclometalating precursor that is able to acti-
vate C–H bonds under mild conditions with methane evol-
ution.[19] In the case of 2-vinylpyridine as L, reaction with
cis-[Pt(Me)2(DMSO)2] follows different routes depending
on the reaction conditions. Under mild conditions, i.e., in
acetone at room temperature, only displacement of one
DMSO ligand by L occurs, to give the corresponding ad-
duct cis-[Pt(Me)2(L)(DMSO)] (1), whereas under harsher
conditions, such as in toluene at 80 °C, activation of a vin-
ylic C–H bond occurs to give the cyclometalated species
[Pt(L–H)(Me)(DMSO)] (2), with loss of methane
(Scheme 1).
Cyclometalation is a widely studied reaction[1] and the
synthesis of new cyclometalated complexes continues to at-
tract interest due to their promising applications in many
fields.[2] In this context, five-membered cyclometalated
platinum(II) complexes containing a C,N backbone have
been extensively studied due to their cytotoxicity and lumi-
nescence properties.[3] Cyclometalated PtII complexes have
also been studied as sensors, switches, and catalysts.[4] In
addition, cyclometalation is also widely studied as an intra-
molecular analogue of intermolecular C–H bond acti-
vation.[1b,5] One of the most studied pro-ligands in this field
is 2-phenylpyridine, the five-membered cyclometalated
complexes of which have been the subject of a considerable
number of papers.[6] Despite this, 2-vinylpyridine, a ligand
that is able to give a similar five-membered cyclometalated
ring with the same sequence of C(sp2) atoms, has been the
subject of a relatively limited number of studies involving
Pd,[7] Pt,[6a,8] Co,[9] Rh,[10] Ir,[11] Ru,[12] Os,[12d–13] plati-
num(II) derivatives cis-[Pt(R)2(DMSO)2] (R = Me, Ph) and
trans-[Pt(Me)(Cl)(DMSO)2].
[a] Dipartimento di Chimica e Farmacia, Università degli Studi di
Sassari,
Via Vienna 2, 07100 Sassari, Italy
E-mail: zucca@uniss.it
http://dcf.uniss.it/ws.php?mod=staff&usrid=257&page=
itext&tag=curriculum&lang=en
Scheme 1.
[b] Department of Chemistry, University of Warwick,
CV4 7AL Coventry, United Kingdom
Adduct 1, which is likely to be an intermediate species in
the synthesis of 2, was characterised by 1H NMR spec-
troscopy. In particular, coordination of nitrogen was dem-
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201400052.
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onstrated by the downfield shift of the H-6 proton and, tive reaction, as previously reported for other cyclomet-
mostly, by its coupling with the 195Pt nucleus (δ = 8.83 ppm, alation reactions involving [Pt(Me)2(DMSO)2].[19]
3JPt,H = 20 Hz). Two methyl groups (δ = 0.47 ppm, 2JPt,H
=
The reaction, however, was not clean, and other second-
2
89 Hz; 0.33 ppm, JPt,H = 79 Hz) and a DMSO (δ = ary species were present in solution. In toluene heated to
2.79 ppm, JPt,H = 14 Hz) complete the coordination around reflux the conversion occurred with high yield, allowing the
the metal. The coupling of the DMSO hydrogen atoms with isolation of 2 in the solid state and its characterization by
the 195Pt nucleus is very small, confirming a trans DMSO- means of analytical and spectroscopic methods. In particu-
1
Pt-Me arrangement. The signal of the Hα vinylic proton is lar, the H NMR spectrum clearly showed the absence of
strongly deshielded and coupled with platinum (δ = one olefinic proton and an AX system with satellites for
8.21 ppm, JPt,H = 10 Hz), with both factors suggesting an the remaining two hydrogen atoms of the substituent. Pt–
anagostic interaction[20] with the metal centre.
H coupling constants for these protons were particularly
2
3
When rotation of the pyridine ligand around the Pt–N high, JPt,H = 171 Hz for Hβ (δ = 7.42 ppm) and JPt,H
=
bond is restricted, the DMSO methyl groups should be dia- 108 Hz for Hα (δ = 6.94 ppm). As a comparison, the analo-
1
stereotopic; however, they appear instead in the H NMR gous protons in the cationic complex [Pt(N,N)(L–H)]+ [N,N
spectrum as a singlet with satellites, suggesting free rotation being ArN=C(Me)–C(Me)=NAr] have 195Pt–1H coupling
of the pyridine on the NMR time-scale. The NOESY spec- constants of 89 and 82 Hz for Hβ and Hα, respectively.[8]
trum of complex 1 is in line with this observation, showing
The coordinated methyl (δ = 0.69 ppm, 2JPt,H = 82.5 Hz)
3
no NOE contacts between pyridine protons and the other and DMSO (δ = 3.07 ppm, JPt,H = 17 Hz) groups showed
ligands, as may be expected in the case of free rotation. signals that were consistent with a Me trans to a nitrogen
Furthermore, the NOESY spectrum showed clear cross- and a DMSO trans to a carbon, respectively. Coordination
peaks between the three olefinic protons, as well as between of the nitrogen was demonstrated by the shift of the H-6
the methyl group at δ = 0.48 ppm and the DMSO hydrogen signal and by its coupling to platinum (δ = 9.24 ppm, 3JPt,H
atoms at δ = 2.90 ppm, allowing the assignment of Pt- = 12 Hz), which was consistent with a trans N–Pt–CH3 ar-
bonded methyl signals. The methyl signal at δ = 0.33 ppm rangement. The coordination geometry was confirmed by a
appears shifted to lower frequency, likely due to the shield- 1D-NOE spectrum, which showed contacts of the coordi-
ing effect of the adjacent pyridine ring (Scheme 2).
nated methyl with the Hβ proton and the DMSO group
(Scheme 3).
Scheme 3. Complex 2: NOE contacts supporting the proposed ge-
ometry.
Scheme 2. Complex 1 with selected NMR spectroscopic data.
Further data for the characterisation was provided by
13C NMR spectroscopic analysis, which showed two
1
The progress of the metalation was investigated by H metalated carbon atoms: the methyl group, at –19.9 ppm,
NMR spectroscopic analysis at room temperature and at and the olefinic carbon, at δ = 163.2 ppm, both being cou-
40 °C. After addition of 2-vinylpyridine to [Pt(Me)2- pled to platinum (1JPt,C = 756 and 1035 Hz, respectively).
(DMSO)2] (0.05 m solution) rapid formation of the adduct The coordination sphere is completed by DMSO
2
1 was observed in both cases, but complete conversion of (δC(DMSO) = 43.5 ppm, JPt,C = 40 Hz) and pyridine
2
[Pt(Me)2(DMSO)2] into the adduct 1 was slow, requiring [δ(C6) 150.5 ppm, JPt,C = 116 Hz]. It should be noted that
more than one day at 40 °C, even in the presence of a slight the metalated olefinic carbon was strongly deshielded (δ =
excess of ligand. At 40 °C, conversion of the adduct 1 into 163.2 ppm) with respect to the free ligand (δ = 118.1 ppm,
the metalated complex 2 was observed; a conclusion that Δδ = 45.1 ppm).
was supported by the appearance of methane in the spec-
When cis-[Pt(Ph)2(DMSO)2] was used in place of cis-
trum at δ = 0.17 ppm. The concentration of 1 reached a [Pt(Me)2(DMSO)2] the corresponding cyclometalated com-
maximum after approximately 30 minutes, then decreased plex [Pt(L–H)(Ph)(DMSO)] (3) could be isolated with high
1
as the concentration of 2 increased. After 3 h, [Pt(Me)2- yields and characterised. The H NMR spectrum of 3 was
(DMSO)2], 1 and 2 are present in an approximate 2:1.5:1 similar to that of 2, with some differences: five additional
molar ratio. Conversion of 1 into 2 also occurred at room aromatic protons, two of which strongly coupled to plati-
3
temperature, but this was extremely slow. On the whole, the num (Hortho: δ = 7.39 ppm, JPt–H = 71 Hz), demonstrate
progress of the reaction was typical of a two-step consecu- that a phenyl group is still coordinated to platinum. In this
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case, also the absence of one olefinic proton accounts for
C–H bond activation, and the remaining two signals dem-
onstrate cyclometalation (Hβ: δ = 7.38 ppm, d with sat,
3
2JPt,H = 180 Hz; Hα: δ = 6.90 ppm, d with sat, JPt,H
=
117 Hz). The DMSO resonates at low frequency compared
to 2 (δ = 2.89 vs. 3.07 ppm in 2) likely due to the shielding
effect of the adjacent phenyl ring, which is probably nearly
perpendicular to the square planar plane. The H-6 proton
is also deshielded (δ = 9.29 ppm) and coupled with plati-
num, with the 195Pt–1H coupling constant (12 Hz) being
very small, as for 2, due to the strong trans-influence of the
C(sp2) phenyl carbon atom.
Cyclometalation of 2-vinylpyridine can be compared to
that of 2-phenylpyridine (Phpy), which reacts easier, giving
the corresponding five-membered cycloplatinated com-
plexes [Pt(Phpy-H)(Me)(DMSO)] even at room temperature
(1H NMR proof).
Activation of a vinylic C–H bond also occurs with the
less electron-rich complex trans-[Pt(Me)(Cl)(DMSO)2] to
give, in toluene at 80 °C, the cyclometalated complex [Pt(L–
H)(Cl)(DMSO)] (4), also in this case with loss of methane.
In complex 4 the DMSO ligand is coordinated trans to the
nitrogen, instead of to the carbon; this is shown by the
195Pt–1H coupling constant value of the DMSO hydrogen
atoms (3JPt,H = 26 Hz), which are typical of DMSO coordi-
nated trans to a nitrogen atom. In this case, the pattern of
Figure 1. Isomers of complexes 2–4 and their relative stabilities.
Values are DFT calculated differences in enthalpy (ΔH) and Gibbs
free energy (ΔG) between the isomeric form A and B (298 K,
kJmol–1, corrected for ZPE, in vacuo at PBE0/def2-SVP level of
theory).
1
the two remaining olefinic protons in the H NMR spec-
trum also confirms metalation. These protons give rise to
2
an AX system (δ = 6.65 ppm, JPt,H = 97 Hz, Hα; δ =
The effect of the stabilisation is predominantly enthalpic,
3
7.26 ppm, JPt–H = 84 Hz, Hβ). It is worth noting that in as can be seen from the values in Figure 1, with less than
the electron poorer complex 4 the coupling constants be- 8% of the stabilisation energy being ascribable to the en-
tween the olefinic protons and the platinum are smaller tropic contribution; these findings are consistent with pre-
than the corresponding constants in the electron-rich spe- viously reported data on analogous complexes.[22] Another
2
cies 2 and 3. In particular, JPt,H is almost halved in 4. The interesting trend that is worth noting concerns the nature
H-6 proton is shifted to low fields and coupled to 195Pt (δ of the anionic ligand. Apparently, groups having a carbon
2
= 9.10 ppm, JPt,H = 35 Hz). Complex 4 was also obtained donor, i.e., methyl and phenyl, lead to a larger difference in
from 2 by reaction with HCl in acetone. The cyclometalated the energies between the A and B forms compared to the
ring in complexes 2 and 4 is extremely stable; reaction of chloride. This result can be justified in terms of the trans-
complex 2 with 1 or 2 equiv. of HCl only results in Pt-CH3 influence: for complexes 2–3 in form B a C-trans-C/S-trans-
protonolysis, with complex 4 being formed as the only reac- N arrangement is observed that is highly unstable (ca.
tion product, even after prolonged reaction times.
50 kJmol–1); on the other hand, in 4A a S-trans-C/Cl-trans-
The isolation of different geometric isomers in the corre- N situation is found that is less unstable due to the smaller
sponding methyl and chloride cyclometalated complexes trans influence of the groups involved (ca. 12 kJmol–1). An
[Pt(N,C)(Me)(DMSO)] and [Pt(N,C)(Cl)(DMSO)] is well- analysis of the energy values permits the following trans-
known[21] and is attributable to the stronger trans-influence influence scale to be established: Me ≈ PhϾDMSOϾCl,
of Me compared to Cl. When possible, the ligand with the which is perfectly consistent with the classic energy val-
stronger trans-influence coordinates trans to the ligand with ues.[23]
the weaker trans-influence, this leads to a DMSO coordi-
We also explored the potential energy surface (PES) as-
nated trans to metalated vinylic carbon in 2 and 3, with sociated with rotation of the DMSO ligand around the Pt–
DMSO trans to nitrogen in 4. To verify this result, we per- S bond in complexes 2–4 in both A and B forms (Figure 2).
formed DFT calculations on the two geometric isomers, A Analysis of the energy profiles obtained for form A did not
and B, of complexes 2–4, depicted in Figure 1 with their indicate anything unusual, and the most stable conforma-
respective relative ΔH values (in kJmol–1, ZPE corrected, tions were always those with the oxygen of the DMSO
in vacuo). Full optimisation without constraints at the pointing towards the H-6 of the pyridine. On the other
PBE0/def2-SVP level gave data that were consistent with hand, complexes of form B showed smaller activation ener-
experimental results, showing that the more stable isomers gies for rotation around the Pt–S bond, which is reasonable
for complexes 2–3 have the A geometry; the opposite was considering the distance between the DMSO and the group
observed for complex 4.
of the cyclometalated ligand in the cis position.
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C(sp2) atom, as evidenced by the low value of the 195Pt–31P
coupling constant (ca. 1800–2000 Hz; 5: JPt,P = 2020 Hz; 6:
JPt,P = 1873 Hz; 8: JPt,P = 1990 Hz; 9: JPt,P = 1843 Hz); the
coupling is stronger for PPh3 (5, 8) than for PCy3 (6, 9), and
for Me-derivatives compared to Ph-derivatives. In species 5
and 6 the protons of the methyl groups appear as doublets
with satellites, due to coupling both to 31P and to 195Pt
(complex 5: δ = 0.80 ppm, 3JP,H = 8.1, 2JPt,H = 84 Hz; com-
3
3
plex 6: δ = 1.04 ppm, JP,H = 6.0, JPt,H = 85 Hz), confirm-
ing the proximity of the CH3 and PR3 ligands. The geome-
try of complex 5 in solution was confirmed by a 1D-NOE
experiment, which showed enhancement of signals at δ =
7.90 ppm (Hβ) and 7.79 (Ho PPh3) by irradiation of the
methyl signal at δ = 0.80 ppm.
Figure 2. Potential energy surface calculated for rotation around
the Pt–S bond in complexes 2–4 in forms A and B (VWN5/SBKJC
level). Structures of form A are depicted to highlight the dihedral
angle explored.
The finding that the most stable conformer of complexes
of the type A has the oxygen of the DMSO close to H-6 is
in agreement with its typical resonance in 2A and 3A.
A charge decomposition analysis (CDA)[24] was per-
formed on complexes 2–4 to investigate the interaction en-
ergy of the DMSO with the remaining fragment of the com-
plex. In all cases, the interaction energy was negative, with
values ranging from –1.58 eV for 2 to –1.63 eV for 3 and
–2.66 eV for 4. Overall, however, the net charge donation is
very similar in all three cases (ca. 0.27 e–). A comparison
Complex [Pt(L–H)(Me)(CO)] (7), has a strong absorp-
tion in the IR spectrum at 2046 cm–1, which is consistent
with absorption bands found for analogous cyclometalated
complexes (e.g., [Pt(bipy-H)(Me)(CO)] at 2044 cm–1).[21]
Interestingly, attempts to prepare the corresponding com-
plex derived from 2-phenylpyridine, which should be similar
in terms of electronic and steric properties, were not suc-
cessful.[25] Complex 7 is stable in solution and in the solid
state, even in the presence of water and air.
3
between the interaction energies and the JPt,H coupling
constants for the protons of the DMSO show a reasonable
qualitative agreement. We did not look for quantitative cor-
relations between experiment and theory due to the re-
quired approximations involved in the calculations, but also
because multiple bond coupling constants cannot be inter-
preted in a straightforward way because they are dependent
on many different factors (i.e., angles, dihedrals, effects in
space, etc.).
For chloride complex 4, the coordinated DMSO trans to
a nitrogen atom can be easily displaced by PPh3 under mild
conditions to give the corresponding phosphane complex
[Pt(L–H)(Cl)(PPh3)] (10), with high yields. Analytical and
spectroscopic data are consistent with the proposed formu-
lation, with a P–Pt–N trans arrangement, as indicated by
1
Substitution Reactions
the high JPt,P value (4194 Hz). Due to the close proximity
of the Cl ligand, the H-6 proton is strongly deshielded (δ =
DMSO is a good leaving group and, in complexes 2–4,
can be easily substituted by two-electron donor ligands to
obtain a series of complexes with different electronic and
steric properties. Substitution is particularly easy for com-
plexes 2 and 3, in which the DMSO is coordinated trans to
a C(sp2), a donor atom that has both high trans influence
and trans effect. Reaction of 2 with PPh3, PCy3 or CO gives,
under mild conditions, complexes [Pt(L–H)(Me)(PPh3)] (5),
[Pt(L–H)(Me)(PCy3)] (6), and [Pt(L–H)(Me)(CO)] (7),
respectively. Analogously, complexes [Pt(L–H)(Ph)(PPh3)]
(8) and [Pt(L–H)(Ph)(PCy3)] (9), were obtained from 3. An-
alytical and spectroscopic data for compounds 5–9 were
9.45 ppm) with a coupling constant value (3JPt–H
=
26.3 Hz) higher than that of complex 5, due to the lower
trans influence of PPh3 with respect to Me. Coupling con-
stants of the olefinic protons are smaller than in 5 (JPt,H
=
138.6 and 95.1 Hz for Hβ and Hα, respectively), and the
signals are strongly shielded by the presence of PPh3 in the
cis position (δ = 6.39 ppm, Hβ, 6.63 ppm, Hα).
X-ray Structural Determinations
Crystals of 5 and 9 suitable for X-ray analysis were
grown from acetone solutions. The crystal structures, shown
consistent with the proposed formulations. In particular 31
P
NMR spectra account for phosphanes being coordinated in Figures 3 and 4, confirm the geometries predicted from
trans to a donor atom with high trans-influence, such as a NMR spectroscopy. The methyl and the phenyl ligands in
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5 and 9, respectively, are coordinated trans to the pyridine
nitrogen, and the phosphane is coordinated trans to the cy-
clometalated carbon. In particular, crystals of 5 are com-
posed of discrete molecules separated by van der Waals dis-
tances, in the monoclinic space group P21/n. The complex
shows a remarkable planarity both in the coordination
plane and in the cyclometalated moiety; the largest devia-
tion from the best plane comprising the metal and its
bounded atoms is for C108, which is 0.014 Å away from the
plane.
Figure 4. X-ray crystal structure of 9. Thermal ellipsoids are drawn
at 50% probability. Hydrogen atoms have been removed for clarity
and only selected atoms are labelled. Selected bond lengths [Å] and
angles [°]: Pt1–P301 2.3534(9); Pt1–N101 2.170(3); Pt1–C108
2.010(5); Pt1–C201 2.000(4); C107-C108 1.334(7); C106–C107
1.440(6); C106–N101 1.376(5); P301–Pt1–C201 91.9(1); C108–Pt1–
C201 86.1(2); C108–Pt1–N101 78.2(2); N101–Pt1–P301 103.78(9);
P301–Pt1–C108 175.1(1); N101–Pt1–C201 164.3(1).
Figure 3. X-ray crystal structure of 5. The thermal ellipsoids are
drawn at 50% probability. Hydrogen atoms have been removed for
clarity and only selected atoms are labelled. Selected bond lengths
[Å] and angles [°]: Pt1–P1 2.3086(6); Pt1–N101 2.159(3); Pt1–C108
2.013(3); Pt1–C1 2.041(4); C107–C108 1.313(5); C106–C107
1.442(5); C106–N101 1.370(3); P1–Pt1–C1 92.7(1); C108–Pt1–C1
88.2(1); C108–Pt1–N101 78.1(1); N101–Pt1–P1 100.94(6); P1–Pt1–
C108 178.51(9); N101–Pt1–C1 166.4(1).
Angles around the platinum are similar to those in [Pt(L–
H)(CH3)(PPh3)]: the cyclometalated ligand has a bite angle
of 78.21°, whereas the angles involving the PCy3 are wider
[N(101)–Pt(1)–C(108) = 195.69°], compared with 5, due to
the increased cone angle of the phosphane. Steric strain is
somewhat relieved by the presence of the phenyl group,
which bends away from the phosphane taking advantage of
its almost perpendicular coordination with respect to the
cyclometalated plane.
The structure of 9 has a slight pyramidal distortion,
highlighted by the angle between the planes passing
through N(101)–Pt(1)–C(108) and P(301)–Pt(1)–C(201) of
only 4.5°. Moreover, the best plane drawn through the cy-
clometalated ligand (all eight non-hydrogen atoms) has an
angle of 6.3° with the fragment comprising the metal centre
and the two other donors (N101 and C201). No unusual
interactions due to packing or particular contacts were
noted.
Angles around platinum are in line with the steric
requirements of the ligands. The cyclometalated ligand has
a bite of 78.13(11)°, which is a low value that is consistent
with those usually found for five-membered cyclometalates.
As a comparison, the N–Pt–C angle in the analogous five-
membered cyclometalated complex [Pt(bipy-H)(Me)(PPh3)]
(11),[26] in which bipy-H is a cyclometalated “rollover” bi-
pyridine, is 79.61(9)°. Correspondingly, the angles involving
phosphorus are larger than 90°, which seems reasonable
considering the hindrance exerted by the PPh3 group
(N101–Pt1–C1 193.64°). The structure has a very slight py-
ramidal distortion, which is highlighted by the angle be-
tween the best planes calculated through N1–Pt–C108 and
P1–Pt–C1 (1.2°). Moreover, the best plane drawn through
the cyclometalated ligand has an angle of 3.8° with the frag-
ment comprising the metal centre and the two other ligands.
Electronic Spectroscopy and Electrochemical Behaviour
[Pt(L–H)(Me)(PPh3)] (5) and [Pt(L–H)(Cl)(PPh3)] (10)
There are no unusual interactions or short contacts revealed were characterised by UV/Vis spectroscopy in CH2Cl2 solu-
in the packing of 5. Overall, the distances and angles tion. Both derivatives showed spin-allowed π–π* ligand-
around the metal are typical of similar species, such as 11.
centred transitions at 237 (ε ≈ 18000 mol–1 Lcm–1) and 279
The solid-state structure of complex 9 consists of discrete nm (shoulder) for 5 and 265 (ε ≈ 10000 mol–1 Lcm–1) and
molecules separated by van der Waals distances, in the or- 292 nm (shoulder) for 10. Furthermore, in the lower energy
thorhombic space group Pbca. The complex is planar, with region of the spectra, weaker transitions were evident that
the largest deviation from the best plane comprising the were ascribed to dPt–π* metal-to-ligand charge-transfers;
metal and its bounded atoms again found for C108, which these bands occurred at 336 (ε≈ 3000 mol–1 Lcm–1) and
is 0.061 Å away from the plane.
386 nm (ε≈ 2500 mol–1 Lcm–1) for 5, and 400 (ε≈
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2000 mol–1 Lcm–1) and 420 nm (shoulder) for 10. Analysis cently reported by Esteruelas and co-workers.[32] Analysis
of UV/Vis spectra allowed evaluation of the Eg values for of the five-membered metallacycle in metallapyrroles and
5 and 10 as 2.88 and 2.81 eV, respectively.
metallaindolizines (A and B, see below) show elongated C1–
The electrochemical behaviour of 5 and 10 was investi- C2 bonds associated with short C2–C3 bond lengths, in
gated by cyclic voltammetry in CH2Cl2/TEAPF6 (0.1 m) sol- particular when compared to non-cyclic analogous species
vent system, with a Pt (Figure 5) and a GC working elec- (species C, see below). Short M–N and M–C1 bond lengths
trode. No reductive processes were evident in the available have also been reported for these delocalised metallacycles.
potential range. Both derivatives show an anodic process,
located at 1.14 V on Pt (1.03 V on GC) and 1.45 V on Pt
(1.43 V on GC), respectively, that were irreversible on the
experimental time-scale (20Ϭ500 mVs–1). The process can
reasonably be assumed to stem from mono-electronic
charge transfer located mainly on the metal centre, with a
chemical reaction following the charge transfer.[27] Because
PtIII complexes are unstable species, oxidation processes
that are mainly located on the metal centre are expected to
∧
be irreversible. Furthermore, oxidation processes in N C
complexes may also involve the heteroatom and are
The analysis of bond lengths in compounds 5 and 9
irreversible.[28] A comparison of the responses confirms that shows a short C1–C2 bond in 5 [1.313(5) Å] and a longer
in the Me derivative the metal centre is more electron-rich bond [1.334(7) Å] in 9. The C2–C3 bond length is shorter
than in the Cl derivative, as suggested from the different than expected for a single C–C sp2 bond [1.442(5) and
electron-withdrawing/donating ability of the Me and Cl 1.440(6) Å, respectively], and is close to an aromatic C–C
substituents. As confirmation, the HOMO energy values bond length. For comparison, in the aromatic ruthenaind-
obtained from the cyclic voltammetric responses on the Pt olizine complex [Ru(L–H)(PR3)(Tp)] [R = isopropyl, Tp =
working electrode are –5.22 eV for 5 and –5.44 eV for 10. hydridotris(pyrazolyl)borate],[32] C1–C2 1.35(2) and C2–C3
Evaluation of the LUMO energy from (Eg + EHOMO) con- 1.428(3) Å, and in the non-cyclic complex [Ru(CH3){(E)-
firms that the cyclometalated ligand in 5 has a higher elec- CH=CHPh}(CO)2(PiPr3)2] (species C, above), C1–C2
tron density than in 10.
1.311(6) Å and C2–C3 1.497(5) Å.[33] Analysis of the Pt–C1
bond in 5 and 9 (2.013 and 2.010 Å, respectively) reveal
normal values for Pt–C bonds in a five-membered cycle;
however, partial delocalisation should always be taken into
account.
In contrast, in non-cyclic complexes or in non-planar cy-
clometalates (e.g., six- or seven-membered cycles), Pt–
C(sp2) bonds are usually longer. As an example of Pt–
C(sp2) bonds trans to PPh3 we may cite the non-cyclic trans-
Pt(H)(SAr)(PPh3)2 (Ar = C6H4Cl-p),[34] which has a Pt–C
bond length of 2.066 Å, and the non-planar six-membered
metallacycle [{η6–2-MeBTPt(PPh3)2}Mn(CO)3]-BF4 (BT =
benzothiophene),[35] in which the Pt–C bond length is
2.056 Å. Interestingly, the Pt–C1 bond lengths in 5 and 9
are short even when compared with the analogous cyclo-
metalated complex [Pt(NC)(Me)(PPh3)] (NC = cyclo-
metalated “rollover” 2,2Ј-bipyridine), in which the same
bond is 2.043(3) Å.[26]
Figure 5. Cyclic voltammetric responses of [Pt(L–H)(Me)(PPh3)]
(5; black line) and [Pt(L–H)(Cl)(PPh3)] (10; red line) in CH2Cl2/
TEAPF6 (0.1 m) solvent system on a Pt working electrode. Potential
scan rate 100 mVs–1. Potential values referred to SCE.
On the whole, the metallacycle in complexes 5 and 9
seems to have a certain degree of delocalisation, with short
C2–C3 and Pt–C1 bonds; in contrast, in complex 9 the C1–
C2 bond seems to be slightly elongated.
Interestingly, 1H NMR spectra show large 195Pt–1H cou-
pling constants for the olefinic protons in the electron-rich
Cyclometalation, Delocalisation and Aromaticity
Five-membered cyclometalated rings are often reported complexes (e.g., 2 and 5) and weaker couplings in the elec-
to have a certain degree of aromaticity. Such metallacycles, tron-poorer compounds (e.g., 4 and 10), which may be
which include metallapyrroles,[29] metallafurans[30] and correlated with partial π-delocalisation favoured by electron
metallathiophenes,[31] have received much attention in re- density on the metal. In agreement with such partial π-de-
cent years. Among the vast number of systems, cyclo- localisation, 1H NMR signals of Hα and Hβ in most of the
metalated 2-vinylpyridine may be described as a metallain- complexes reported here are strongly deshielded, resonating
dolizine, and a 3-ruthenaindolizine complex has been re- in the aromatic region of the spectra.
Eur. J. Inorg. Chem. 2014, 2278–2287
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Comparison with 2-Ethylpyridine
Experimental Section
General: All the solvents were purified and dried according to stan-
dard procedures.[36] cis-[Pt(Me)2(DMSO)2], trans-[Pt(Me)(Cl)-
(DMSO)2] and [Pt(Ph)2(DMSO)2] were synthesised according to
reported procedures.[37] Elemental analyses were performed with a
Perkin–Elmer elemental analyzer 240B.
In an attempt to extend the study, we also tried to cyclo-
metalate 2-ethylpyridine (LЈ), to compare C(sp2)–H and
C(sp3)–H bond activation in the formation of five-mem-
bered cyclometalated rings. However, we were not able to
cyclometalate LЈ starting from cis-[Pt(CH3)2(DMSO)2], and
only obtained the adduct [Pt(LЈ)(Me)2(DMSO)] (12), a spe-
cies analogous to complex 1.
1H, 13C{1H} and 31P{1H} NMR spectra were recorded with Varian
VXR 300 or Bruker Avance III 400 spectrometers. Chemical shifts
are given in ppm relative to internal TMS for 1H and 13C{1H} and
1
Complex 12 was characterised based mainly on its H
1
external 85% H3PO4 for 31P{1H}; J values are given in Hz. H-1H
NMR spectrum. The H-6 proton (δ = 8.70 ppm) showed
satellites that were indicative of coordination of the nitro-
gen (3JPt,H = 20 Hz) trans to a carbon atom. Two coordi-
nated methyl groups were present: on the basis of 195Pt–1H
coupling constants and a comparison with complex 1, the
signals may be assigned to a methyl trans to N (δ =
0.40 ppm; 3JPt,H = 84.9 Hz) and to a methyl trans to DMSO
COSY, 1H-1H NOESY and 1H 1D-NOE experiments were per-
formed by using standard pulse sequences.
UV/Vis spectra were recorded with a Fulltech T80+ spectropho-
tometer. Cyclic voltammetric tests were performed with a comput-
erised electrochemical system CHI-650 (CH Instruments, Austin,
TX, USA) using its specific software, employing a single-compart-
ment, three-electrode cell, at room temperature, under an Ar atmo-
sphere, at a potential scan rate of 100 mVs–1. A 2 mm diameter Pt
or a 3 mm diameter glassy carbon (GC) disk electrode was used as
working electrode, an aqueous SCE with suitable salt bridge was
used as the reference electrode, and a graphite rod was used as the
3
(δ = 0.43 ppm; JPt,H = 77.9 Hz). In contrast to complex 1,
the DMSO ligand generated two singlets with satellites (δ =
2.87 ppm, JPt,H = 15.3 Hz; δ = 2.83 ppm, JPt,H = 15.3 Hz),
indicating that the methyl groups are diastereotopic. This
implies that the pyridine does not rotate around the Pt–N auxiliary electrode. All the experiments were carried out in CH2Cl2
(Sigma–Aldrich, anhydrous, Ն 99.8%) using 0.1 m tetraethylammo-
nium hexafluorophosphate (TEAPF6, Sigma–Aldrich, for electro-
chemical analysis, Ն 99.0%) as supporting electrolyte, with sample
concentration of ca. 2ϫ10–3 m. Energy-gap values (Eg) were evalu-
ated from the λonset in the UV/Vis spectra. HOMO energy values
were evaluated from the equation EHOMO [eV] = –e(Eonset + 4.4).[38]
bond on the NMR time-scale, in contrast to the motion
proposed for complex 1. Hence, on the NMR time-scale,
complex 12 is a chiral species (an example of planar chiral-
ity). Accordingly, the CH2 protons are also diastereotopic,
and appear as two multiplets at δ = 3.51 and 3.45 ppm,
each integrating one proton; both signals are strongly
shifted with respect to the free ligand (δ = 2.76 ppm).
DFT calculations were carried out with the Firefly QC package,[39]
which is partially based on the GAMESS (US)[40] source code. Full
details are given in the Supporting Information.
Preparations
[Pt(CH3)2(L)(DMSO)] (1): To
a solution of cis-[Pt(CH3)2-
(DMSO)2] in [D6]acetone in an NMR tube was added an excess of
2-vinylpyridine. The reaction was followed in solution by means of
1H NMR spectroscopy, at 25 and 40 °C. 1H NMR (400 MHz, [D6]-
acetone, room temp.): δ = 8.83 (ddd sat, JH,H = 5.5, 1.6, 1.0 Hz,
JPt,H = 20 Hz, 1 H, H-6), 8.21 (dd sat, JH,H = 17.8, 11.3 Hz, JPt,H
= 10 Hz, 1 H, Hα), 7.91 (m, 2 H, H-3 + H-5), 7.37 (td, 1 H, H-4),
6.12 (d, JH,H = 17.8 Hz, 1 H, Hβtrans), 5.70 (d, JH,H = 11.3 Hz, 1
H, Hβcis), 2.79 (s sat, JPt,H = 14.4 Hz, 6 H, DMSO), 0.48 (s sat,
Attempts to obtain cyclometalated complexes analogous
to 2 failed, even at high temperatures and after prolonged
reaction times, indicating that C–H bond activation in the
ethyl substituent is not easy. It is worth noting that the cor-
2
2JPt,H = 88.8 Hz, 3 H, CH3), 0.33 (s sat, JPt,H = 79.2 Hz, 3 H,
responding 2,2Ј-bipyridine ligand, 6-ethyl-2,2Ј-bipyridine, CH3) ppm. 1H NMR (400 MHz, [D6]acetone, 40 °C): δ (selected
reacts easily with PtII complexes to give the terdentate cy-
signals) = 0.17 (CH4), 9.40 (dd sat, JH,H = 5.5, JPt,H = 11 Hz, 1 H,
2
clometalated complex [Pt(N,N,C)Cl].[18b]
H-6), 6.93 (d, JH,H = 8.8 Hz, 1 H, Hβ), 0.68 (s sat, JPt,H = 82 Hz,
3 H, CH3) ppm.
[Pt(L–H)(CH3)(DMSO)] (2): To
a solution of cis-[Pt(CH3)2-
(DMSO)2] (0.264 mmol, 1 equiv.) in toluene (15 mL) was added 2-
vinylpyridine (34 μL, 0.316 mmol, 1.2 equiv.). The solution was
stirred under a nitrogen atmosphere for 2 h at 80 °C, then evapo-
rated to dryness and vacuum pumped to give an analytical sample
as a yellow solid, yield 88.1 mg (85%). 1H NMR (300 MHz,
Conclusions
We have shown that 2-vinylpyridine easily gives five-
membered cycloplatinated complexes. At variance with the
well-known cyclometalating pro-ligand 2-phenylpyridine,
however, cyclometalation of 2-vinylpyridine requires
harsher conditions. The species obtained are extremely
stable and show interesting features, such as remarkable
195Pt–1H coupling constants inside the metallacycle. Such
coupling constants are particularly large for the electron-
rich complexes of the series (e.g., 2 and 5) and this may due
to partial π-delocalisation inside the cycle.
3
CDCl3): δ = 9.24 (d sat, JH,H = 5.5 Hz, JPt,H = 12 Hz, 1 H, H-6),
3
4
7.63 (td, JH,H = 7.5 Hz, JH,H = 1.6 Hz, 1 H, H-4), 7.42 (d sat,
3JH,H = 8.7 Hz, 2JPt,H = 171 Hz, 1 H, Hβ), 7.08 (d, 3JH,H = 7.5 Hz,
1 H, H-3), 7.00 (m, 1 H, H-5), 6.94 (d sat, JH,H = 8.7 Hz, JPt,H
3
3
3
= 108 Hz, 1 H, Hα), 3.07 (s sat, JPt,H = 16.8 Hz, 6 H, CH3 of
DMSO), 0.69 (s sat, 2JPt,H = 82.5 Hz, 3 H, Pt-CH3) ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 166.9 (s sat, JPt,C = 115 Hz, C2), 163.2 (s
sat, JPt,C = 1035 Hz, Cβ), 150.5 (s sat, 2JPt,C = 15.6 Hz, C6), 139.3,
Eur. J. Inorg. Chem. 2014, 2278–2287
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3
2
138.4 (s sat, JPt,C = 4.0 Hz, C4), 121.2 (s sat, JPt,C = 5.2 Hz, C3 or PCy3), 1.04 (d sat, JP,H = 6.0 Hz, JPt,H = 84.9 Hz, 3 H, Pt-
2
C5), 119.5 (s sat, JPt,C = 18.6 Hz, C3 or C5), 43.5 (s sat, JPt,C
=
CH3) ppm. 31P NMR (121.4 MHz, CDCl3): δ = 26.2 (s sat, JPt,P
=
1875 Hz) ppm.
40 Hz, CH3 of DMSO), –19.9 (s sat, 1JPt,C = 756 Hz, Pt-CH3) ppm.
C10H15NOPtS (392.38): calcd. C 30.61, H 3.85, N 3.57; found C
30.84, H 3.63, N 3.68.
[Pt(L–H)(Me)(CO)] (7): Obtained by Method B (R = Me). In this
case, CO was bubbled into the solution for 1 h. 1H NMR
3
[Pt(L–H)(Ph)(DMSO)] (3): Complex 3 was synthesised as de-
scribed for complex 2, using cis-[Pt(Ph)2(DMSO)2] in place of cis-
(300 MHz, CDCl3): δ = 8.49 (d br. sat, JH,H = 5.4 Hz, JPt,H
=
16.2 Hz, 1 H, H-6), 7.12 (m, JH,H = 5.4 Hz, JH,H = 7.0 Hz, 1 H,
1
[Pt(CH3)2(DMSO)2], at 80 °C for 3 h, yield 70%; m.p. 133 °C. H
H-5), 7.78 (td, JH,H = 2.0 Hz, JH,H = 7.0 Hz, 1 H, H-4), 7.17 (d,
NMR (300 MHz, CDCl3): δ = 9.29 (d sat, 3JH,H = 5.4 Hz, 3JPt,H
=
JH,H = 8.0 Hz, 1 H, H-3), 7.35 (d sat, JH,H = 9.7 Hz, JPt,H
=
2
3
12.6 Hz, 1 H, H-6), 7.72 (td, JH,H = 8.7 Hz, 1 H, H-4), 7.39 (m
156 Hz, 1 H, Hβ), 7.26 (d sat, JH,H = 9.7 Hz, 3JPt,H = 106 Hz, 1 H,
3
sat, JPt,H = 71 Hz, 2 H, partially overlapping, Ho), 7.38 (d with Hα), 1.21 (s sat, 2JPt,H = 87.0 Hz, 3 H, Pt-CH ) ppm. IR (Nujol): ν
˜
3
3
2
sat, JH,H = 7.9 Hz, JPt,H = 180 Hz, 1 H, partially overlapping, = 2046 (vs, ν CO) cm–1.
3
Hβ), 7.20 (d, JH,H = 7.9 Hz, 1 H, H-3), 7.17 (td, 1 H, H-5), 7.06
[Pt(L–H)(Ph)(PPh3)] (8): Obtained by Method A, yield 70%; m.p.
(m, 2 H, Hm), 6.95 (td, 1 H, Hp), 6.90 (d sat, 3JH,H = 8.7 Hz, 4JPt,H
154 °C. 1H NMR (300 MHz, CDCl3): δ = 7.79 (td, 3JH,H = 7.7 Hz,
3JH,H = 1.5 Hz, 1 H, H-4), 7.70–7.20 (m, 21 H, Ar-H, Hβ), 7.01 [d
2
= 118 Hz, 1 H, Hβ), 2.89 [s sat, JPt,H = 16.8 Hz, 6 H, CH3 of
DMSO] ppm. C15H17NOPtS (454.35): C, 39.64; H, 3.77; N, 3.08;
found C, 39.42; H, 3.62, N, 3.29.
3
3
sat, JH,H = 6.3 Hz, JPt,H = 70.1 Hz, 2 H, Ho(Ph)], 6.60 (m, 3 H),
6.43 (td, 3JH,H = 5.7 Hz, 3JH,H = 1.5 Hz, 1 H, H-5) ppm. 31P NMR
(121.4 MHz, CDCl3): δ = 31.46 (s sat, JPt,P = 1990 Hz) ppm.
1
[Pt(L–H)(Cl)(DMSO)] (4); Method A: To a solution of trans-
[Pt(CH3)(Cl)(DMSO)2] (165 mg, 0.410 mmol, 1 equiv.) in acetone
(10 mL) was added under vigorous stirring 2-vinylpyridine (48 mg,
0.456 mmol, 1.10 equiv.). The solution was stirred at 55 °C for 6 h,
then concentrated to small volume and treated with n-hexane. The
precipitate formed was filtered off, washed with n-hexane and vac-
uum pumped to give an analytical sample as a yellow solid, yield
152.3 mg (90%).
[Pt(L–H)(Ph)(PCy3)] (9): Obtained by Method A, yield 75%; m.p.
1
3
147 °C. H NMR (300 MHz, CDCl3): 8.43 (d sat, JH,H = 5.4 Hz,
3JPt,H = 17.0 Hz, 1 H, H-6), 7.59 (td, JH,H = 7.6 Hz, JH,H
=
3
3
3
1.3 Hz, 1 H, H-4), 7.33 (d, 1 H, Hα), 7.01 (d, JH,H = 7.6 Hz, 1 H,
H-3), 6.90 (m, 1 H, H-5), 6.71 (d sat, 1 H, Hβ), 2.00–0.90 (m, 11
H, PCy3) ppm. 31P NMR (121.4 MHz, CDCl3): δ = 24.1 (s sat,
1JPt,P = 1843 Hz) ppm.
Method B: To a solution of 2 in acetone was added aqueous 0.1 m
HCl (1:1 Pt/acid molar ratio). The mixture was stirred at room
temperature for 1 h then evaporated to dryness. Complex 4 was
obtained by crystallisation of the resulting crude material from
CH2Cl2/n-hexane, yield 90%, m.p. 124 °C. 1H NMR (300 MHz,
[Pt(L–H)(Cl)(PPh3)] (10): Obtained by Method B, yield 90%; m.p.
1
3
164 °C. H NMR (300 MHz, CDCl3): δ = 9.45 (s br. sat, JPt,H
=
26.3 Hz, 1 H, H-6), 7.77–7.67 (m, 7 H, H-4, Ho(PPh3)), 7.49–7.40
2
[m, 9 H, Hm, Hp (PPh3)], 7.20 (m, JH,H = 6.8 Hz, 1 H, H-5), 7.12
2
3
3
(d, JH,H = 7.3 Hz, 1 H, H-3), 6.63 (dd sat, JH,H = 8.3 Hz, JPt,H
3
CDCl3): δ = 9.10 (ddd sat, JH,H = 5.8, 1.6, 0.8 Hz, JPt,H = 33 Hz,
4
3
= 95 Hz, JP,H = 0.5 Hz, 1 H, Hα), 6.39 (t sat, JH,H
= =
3JP,H
3
3
1 H, H-6), 7.75 (td, JH,H = 7.7 Hz, 1 H, H-4), 7.26 (d sat, JH,H
8.3 Hz, JPt,H = 139 Hz, 1 H, Hβ) ppm. 31P NMR (121.4 MHz,
CDCl3): δ = 17.9 (s sat, JPt,P = 4194 Hz) ppm. C25H21ClNPPt
(596.95): calcd. C 51.42; H 3.62; N 2.39; found C 50.20; H 3.29; N
2.51.
2
3
3
= 7.5 Hz, JPt,H = 84 Hz, 1 H, Hα), 7.18 (d, JH,H = 7.7 Hz, 1 H,
H-3), 7.14 (m, 1 H, H-5), 6.65 (d sat, JH,H = 7.5 Hz, JPt,H
97 Hz, 1 H, Hβ), 3.54 [s sat, JPt,H = 25.6 Hz, 6 H, CH3 of
DMSO] ppm. C9H12ClNOPtS (412.80): calcd. C 26.19, H 2.93, N
3.39; found C 26.32, H 2.68, N 3.29.
3
2
=
3
[Pt(LЈ)(Me)2(DMSO)] (12): Complex 12 may be obtained as com-
plexes 1 or 2, using 2-ethylpyridine (LЈ) in place of 2-vinylpyridine
(L). 1H NMR (300 MHz, [D6]acetone): δ = 8.70 (dd sat, 1 H, 3JH,H
General Method for the Synthesis of Complexes [Pt(L–H)(R)(L)] (R
= Me, Ph, L = Phosphane or CO) 5–9; Method A (one pot): To a
solution of [Pt(R)2(DMSO)2] (R = Me or Ph, 0.25 mmol, 1 equiv.)
in toluene (10 mL), was added under a nitrogen atmosphere, 2-
vinylpyridine (34 μL, 0.316 mmol, 1.26 equiv.). The solution was
stirred at 80 °C for 2 h, then heating was turned off and the phos-
phane (0.30 mmol, 1.2 equiv.) was added. The solution was stirred
for 1 h, then concentrated to a small volume and treated with n-
hexane. The precipitate formed was filtered off, washed with n-
hexane and vacuum pumped to give the analytical sample.
3
= 5.6 Hz, JPt,H = 20 Hz, H-6), 7.56 (td, JH,H = 7.8 Hz, 1 H, H-4),
3
7.34 (d, JH,H = 7.8 Hz, 1 H, H-3), 7.09 (m, 1 H, H-5), 3.51 (m,
3
2
2JH,H = 15.0 Hz, JH,H = 7.5 Hz, 1 H, CH2), 3.45 (m, JH,H
=
3
3
15.0 Hz, JH,H = 7.5 Hz, 1 H, CH2), 2.87 (s sat, JPt,H = 15.3 Hz,
3
3 H, DMSO), 2.83 (s sat, JPt,H = 15.3 Hz, 3 H, DMSO), 1.36 (t,
3JH,H = 7.5 Hz, 3 H, CH3CH2), 0.40 ppm (s sat, JPt,H = 84.9 Hz,
3
3 H, Pt-CH3), 0.43 ppm (s sat, 3JPt,H = 77.9 Hz, 3 H, Pt-CH3) ppm.
X-ray Experimental Data
[Pt(L–H)(Me)(PPh3)] (5): Obtained by Method A (R = Me), yield
Complex 5: Single crystals of C26H24NPPt (5) were grown from
1
92%; m.p. 162 °C. H NMR (300 MHz, CDCl3): δ = 7.90 (dd sat,
acetone. A suitable crystal was selected and mounted on a glass
3
2
3JH,H = 9.2 Hz, JP,H = 7.8 Hz, JPt,H = 163 Hz, 1 H, Hβ), 7.65– fibre with Fromblin oil and placed on an Oxford Diffraction Xcali-
7.42 (m, 18 H, Ar-H), 7.33 (dd sat, 3JH,H = 9.2 Hz, 4JP,H = 15.2 Hz,
bur Gemini diffractometer with a Ruby CCD area detector. The
crystal was kept at 150(2) K during data collection. The structure
was solved by using Olex2,[41] with the XS[42] structure solution
3JPt,H = 94 Hz, 1 H, Hα), 7.14 (d, JH,H = 7.8 Hz, 1 H, H-3), 6.45
3
2
(t, JH,H = 6.3 Hz, 1 H), 0.80 (d sat, JP,H = 8.1, JPt–H = 84 Hz, 3
H, Pt-CH3) ppm. 31P NMR (121.4 MHz, CDCl3): δ = 28.5 (s sat, program using direct methods and refined with the ShelXL[42] re-
1JPt,P = 2020 Hz) ppm.
finement package using least squares minimisation (Table 1).
[Pt(L–H)(Me)(PCy3)] (6): Obtained by Method A (R = Me), yield
Complex 9: Single crystals of C31H44NPPt (9) were grown from
acetone. A suitable crystal was selected and mounted on a glass
fibre with Fromblin oil and placed on an Oxford Diffraction Xcali-
1
3
3
95%. H NMR (CDCl3): δ = 8.46 (d sat, JH,H = 5.2 Hz, JPt,H
=
17.1 Hz, 1 H, H-6), 7.73 (dd, JH,H = 9.1 Hz, JP,H = 7.8 Hz, 1 H,
JPt,H = 155 Hz, Hβ), 7.62 (td, 1 H, H-4), 7.39 (dd, JH,H = 9.1 Hz, bur Gemini diffractometer with a Ruby CCD area detector. The
JP,H = 14.1 Hz, JPt,H = 86 Hz, 1 H, Hα), 7.11 (t sat, 3JH,H = 8.2 Hz, structure was solved by using Olex2,[41] with the XS[42] structure
1 H), 6.90 (td, 1 H, H-5), 2.00–1.05 (m, 33 H, CH and CH2 of solution program using direct methods and refined with the
Eur. J. Inorg. Chem. 2014, 2278–2287
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Inorg. Chem. 2012, 51, 11665–11679; d) T. Okada, I. M. El-
Mehasseb, M. Kodaka, T. Tomohiro, K.-I. Okamoto, H.
Okuno, J. Med. Chem. 2001, 44, 4661–4667.
For example, see: M. Albrecht, G. van Koten, Angew. Chem.
Int. Ed. 2001, 40, 3750–3781; Angew. Chem. 2001, 113, 3866.
a) C. P. Newman, K. Casey-Green, G. J. Clarkson, G. W. V.
Cave, W. Errington, J. P. Rourke, Dalton Trans. 2007, 3170–
3182.
For examples, see: a) P. Jolliet, M. Gianini, A. von Zelewsky, G.
Bernardinelli, H. Stoeckli-Evans, Inorg. Chem. 1996, 35, 4883–
4888; b) F. Niedermair, K. Waich, S. Kappaun, T. Mayr, G.
Trimmel, K. Mereiter, C. Slugovc, Inorg. Chim. Acta 2007, 360,
2767–2777; c) T. Yagyu, J.-I. Ohashi, M. Maeda, Organometal-
lics 2007, 26, 2383–2391.
a) A. Kasahara, K. Tanaka, T. Izumi, Bull. Chem. Soc. Jpn.
1969, 42, 1702–1704; b) G. R. Newkome, K. J. Theriot, B. K.
Cheskin, D. W. Evans, G. R. Baker, Organometallics 1990, 9,
1375–1379.
Table 1. X-ray data for complexes 5 and 9.
5
9
[4]
[5]
Crystal shape
Dimensions [mm]
Empirical formula
M
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
brown block
0.30ϫ0.30ϫ0.22 0.20ϫ0.04ϫ0.02
C26H24NPPt
576.52
monoclinic
P21/n
9.33289(13)
19.1459(2)
12.87984(19)
90
brown block
C31H44NPPt
656.73
orthorhombic
Pbca
8.64617(12)
18.0240(2)
35.5920(5)
90
[6]
β [°]
101.3736(14)
90
2256.26(5)
150(2)
90
90
[7]
γ [°]
U [Å3]
5546.62(13)
150(2)
8
1.54184
1.573
2640
10.135 (Cu-Kα)
77.56
20284
5794
0.0276
T [K]
Z
λ [Å]
4
[8]
[9]
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CCDC-980421 (for 5) and -980422 (for 9) contain the supplemen-
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Supporting Information (see footnote on the first page of this arti-
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[13]
Acknowledgments
Financial support from Università di Sassari (FAR) is gratefully
acknowledged. L. M. gratefully acknowledges a PhD fund, fi-
nanced on POR/FSE 2007-2013, from Regione Autonoma della
Sardegna. The authors acknowledge support from the Advantage
West Midlands (AWM) (partially funded by the European Regional
Development Fund) for the purchase of the XRD system that was
used to solve the crystal structure of 5 and 9.
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