New trans-configured acetylide-cyanide platinum(II) anions: Spectroscopic and optical studies

Article abstract of DOI:10.1021/om301134k

A novel series of phosphorescent stable mixed acetylide-cyanide anionic (NBu₄)₂[trans-Pt(C≡CR)₂(CN)₂] (R = Tol (1), C₆H₄CF₃-4 (2), C ₅H₄N-4 (3), Np (4)) complexes were prepared by reactions of the neutral [trans-Pt(C≡CR)₂(PPh₃)₂] precursors with excess (NBu₄)CN. The formation of 1-4 takes place through monoanionic [trans-Pt(C≡CR)₂(CN)(PPh₃)] ^- intermediate species, as confirmed by the isolation of the naphthyl derivative (NBu₄)[trans-Pt(C≡CNp)₂(CN)(PPh ₃)] (5). Further substitution of PPh₃ in 5 by CN ^tBu gives (NBu₄)[trans-Pt(C≡CNp)₂(CN) (CN^tBu)], containing three different isoelectronic ligands. The complexes have been characterized (¹H, ¹³C, ¹⁹⁵Pt NMR, IR, MALDI-TOF), including X-ray crystallography for 2, 4, and 6, and their spectroscopic and optical properties compared to those of the related homoleptic [Pt(C≡CR)₄]^2- complexes. Time-dependent density functional theory (TD-DFT) calculations were performed for anions 1^2- and 4^2- and three different conformers of 6^- to provide further insight into the nature of the electronic transitions.

Full text of DOI:10.1021/om301134k

Article
pubs.acs.org/Organometallics
New Trans-Configured Acetylide−Cyanide Platinum(II) Anions:
Spectroscopic and Optical Studies
Jesus R. Berenguer, Julio Fernandez,* Elena Lalinde,* and Sergio Sanchez
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́
́ ́
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Departamento de Quımica−Centro de Investigacion en Sıntesis Quımica, Universidad de La Rioja, 26006 Logrono, Spain
̃
S
* Supporting Information
ABSTRACT: A novel series of phosphorescent stable mixed
acetylide−cyanide anionic (NBu4)2[trans-Pt(CCR)2(CN)2] (R =
Tol (1), C6H4CF3-4 (2), C5H4N-4 (3), Np (4)) complexes were
prepared by reactions of the neutral [trans-Pt(CCR)2(PPh3)2]
precursors with excess (NBu4)CN. The formation of 1−4 takes place
through monoanionic [trans-Pt(CCR)2(CN)(PPh3)]− intermediate
species, as confirmed by the isolation of the naphthyl derivative
(NBu4)[trans-Pt(CCNp)2(CN)(PPh3)] (5). Further substitution of
PPh3 in 5 by CNtBu gives (NBu4)[trans-Pt(CCNp)2(CN)-
(CNtBu)], containing three different isoelectronic ligands. The complexes have been characterized (1H, 13C, 195Pt NMR, IR,
MALDI-TOF), including X-ray crystallography for 2, 4, and 6, and their spectroscopic and optical properties compared to those
of the related homoleptic [Pt(CCR)4]2− complexes. Time-dependent density functional theory (TD-DFT) calculations were
performed for anions 12− and 42− and three different conformers of 6− to provide further insight into the nature of the electronic
transitions.
application in materials science. Several recent reviews cover
different aspects of these compounds.12
INTRODUCTION
■
The synthesis of transition-metal complexes with cyanide
ligands has been a widely studied field for many years.1 Their
high stability and structural and bond characteristics, together
with their interesting properties, have increased their attraction
not only for chemistry but also for materials science.2 In
particular, cyanometalates have been extensively employed to
prepare and study discrete or supramolecular heteronuclear
cyanide-bridged arrays, exhibiting fascinating structures and
tunable magnetic or photophysical properties facilitated by the
presence of short bridges, which maximize the magnitude of
magnetic exchange couplings and favor energy transfer
processes.3 Furthermore, owing to the ability of the cyanide
groups to act as hydrogen bond acceptors, these negatively
charged cyanometalate units have been also successfully
incorporated into hydrogen-bonded supramolecular assem-
blies.4 In platinum chemistry, particularly relevant are the
widely studied tetracyanoplatinate ([Pt(CN)4]2−, TCP) based
systems5 and some recent heteroleptic derivatives, such as the
extended networks [cis-Pt(CN)2(CNR)2],6 K(H2O)x[Pt-
(C∧N)(CN)2] (C∧N = bzq, ppy; x = 0, 1),7 Na2[Pt-
(CN)2(dcpy)]·nH2O (H2dcpy = 4,4′-dicarboxy-2,2′-bypiridine;
n = 2, 5),8 and [PtTl(L)(CN)2] (L = bzq,9 C4H9N410) and
{Tl[Tl{cis-Pt(C6F5)2(CN)2}](H2O)]n and [trans,trans,trans-
Tl2Pt(C6F5)2(CN)2(acetone)2]n,11 in which additional metal-
lophillic interactions (Pt···Pt, Pt−Tl) play a remarkable role in
their structures and associated optical properties.
In the realm of photophysics we12a,c,13 and others14 have
been interested in using homoleptic and heteroleptic alkynyl
platinates as precursors of clusters or supramolecular
assemblies, which are stabilized by a synergistic combination
of alkynyl σ/π bonding and metallophilic (Pt···Pt, Pt···M,
M···M) interactions. This has allowed us to prepare fascinating
high-nuclearity arrays having interesting properties, including
luminescence,12a,c thermochromism,9 mechanochromism,13f
and solvatochromism.12c,13e,15
Following our interest in both cyanide and alkynyl
luminescent platinum-based systems, we decided to explore
the chemistry and properties of new platinum derivatives
simultaneously containing these two kinds of ligands (alkynyl
and cyanide), which have been essentially unexplored. Several
years ago we reported (from Pt(CCR)2COD as precursors)
the cis-configured mixed anionic complexes [cis-Pt(C
t
CR)2(CN)2]2− (R = Ph, Bu) as oily materials, which were
combined with d8 (PtII, RhI, IrI) metal ions to construct
multimetallic (triangle, square hexametallic) assemblies,16 and,
more recently,17 the successful synthesis of the first novel trans-
configured derivative (NBu4)2[trans-Pt(CCTol)2(CN)2] (1),
by using the neutral derivative [trans-Pt(CCTol)2(PPh3)2] as
precursor. (NBu4)2[trans-Pt(CCTol)2(CN)2] (1) was found
to be not only an interesting blue emitter but also an adequate
tecton to construct two different PtTl2 and PtPb2 supra-
molecular heterometallic luminescent materials.17 As a
On the other hand, transition-metal alkynyl complexes have
been also attracting widespread interest for many years, largely
due to their interesting reactivity, structural diversity, and
photoluminescent properties, as well as their potential
Received: November 26, 2012
Published: January 31, 2013
© 2013 American Chemical Society
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continuation, in this report, we present the synthesis, structure,
and photophysical properties of a family of dianionic
bis(cyanide)bis(acetylide)platinum complexes (NBu4)2[trans-
Pt(CCR)2(CN)2] (R = C6H4CF3-4 (2), C5H4N-4 (3), Np
(4)). These complexes are generated through the monoanionic
derivatives [trans-Pt(CCR)2(CN)(PPh3)]− as intermediate
species, from which the complex (NBu4)[trans-Pt(C
CNp)2(CN)(PPh3)] (5) has been isolated and fully charac-
terized. We sought to probe that, in complex 5, PPh3 can also
be substituted by an isocyanide ligand, which has allowed us to
prepare and structurally characterize the very unusual derivative
(NBu4)[trans-Pt(CCNp)2(CN)(CNtBu)] (6) stabilized by
three distinct isoelectronic ligands.
observed increase in the 31P−195Pt coupling constant are
consistent with the excess of electronic density in the Pt atom
and the lower trans influence of the incoming CN− group in
relation to the replaced PPh3 ligand. We note that the
displacement of the second PPh3 occurs more slowly and, by
using the stoichiometric amount of cyanide (2 equiv), is only
complete in the case of complex 1 (R = Tol). For the other
systems, mixtures of the monoanionic intermediates, PPh3, and
the final dianionic complexes 2−4 were always found, even
after prolonged reaction times (1−2 days). However, in the
presence of excess of CN− the reactions go easily to completion
(see the Experimental Section). We note that treatment of
these dianionic complexes 2−4 with 2 equiv of PPh3 does not
evolve with substitution of cyanide by phosphine, even with
long reaction times (3 days).
RESULTS AND DISCUSSION
■
Synthesis and Characterization. As detailed in the
Experimental Section, complexes (NBu4)2[trans-Pt(C
CR)2(CN)2] (2−4) were conveniently synthesized following
a strategy similar to that previously communicated for complex
117 (eq 1), which has been also included in this work for
comparative purposes.
Analytical and spectroscopic data (vide infra) confirm, in all
cases, the retention of the trans geometry of the precursor, and,
with the aim of confirming the monosubstitution step, we
decided to isolate and characterize the monoanionic
intermediate with the naphthylacetylide ligand.
Monitoring of this reaction (Scheme 1) by NMR spectros-
copy at different stoichiometries showed that the formation of
the monosubstituted anion [trans-Pt(CCNp)2(CN)-
(PPh3)]− (5−) takes place rapidly, but the disubstituted dianion
42− always appears before the neutral precursor [trans-Pt(C
CNp)2(PPh3)2] is consumed. The best conditions for the
synthesis of 5− were obtained by minimizing the formation of
42−, because their final separation is not an easy task. This was
achieved by carrying out the reaction of [trans-Pt(C
CNp)2(PPh3)2] with 1 equiv of (NBu4)CN in acetone and
using a short reaction time. As detailed in the Experimental
Section, after 15 min, the reaction mixture is mainly formed by
the desired monosubstituted anion [trans-Pt(CCNp)2(CN)-
(PPh3)]− (5−) and free PPh3, together with only small amounts
of 42− and the neutral precursor [trans-Pt(CCNp)2(PPh3)2],
which is still present. This starting material has very low
solubility in acetone, allowing its elimination by filtration.
Subsequent evaporation of the filtrate and treatment of the oily
residue obtained with i-Pr2O generates (NBu4)[trans-Pt(C
CNp)2(CN)(PPh3)] (5) as a white solid in moderate yield
(46%). As is shown in Scheme 1, the PPh3 ligand in complex 5
can be easily replaced by an isocyanide ligand. Thus, treatment
of complex 5 with an excess of CNtBu allows access to the
unusual heteroleptic complex (NBu4)[trans-Pt(C
CNp)2(CN)(CNtBu)] (6), containing three isoelectronic
ligands (acetylide, cyanide, and isocyanide) in the coordination
sphere of the PtII center.
In all cases, a suspension of the appropriate precursor [trans-
Pt(CCR)2(PPh3)2] in acetone was treated with an excess of
(NBu4)CN (molar ratio 1:4), to drive the reaction to
completion in ca. 15 min. The final solution was evaporated
to dryness and the corresponding dianionic complex obtained
as detailed in the Experimental Section. Thus, while the
naphthyl derivative 4 precipitated as a pure pink solid by
treating the residue with an i-PrOH/Et2O mixture, complexes 2
and 3, which are more soluble, required a previous extraction in
an equimolecular CH2Cl2/H2O mixture to remove the excess
(NBu4)CN. They are isolated as white solids from solvent
mixtures (CH2Cl2/MeOH/n-hexane, 2; i-PrOH/Et2O, 3) only
in a moderate yield (∼40%).
Monitoring all reactions by 31P{1H} NMR spectroscopy
revealed that the substitution of PPh3 by cyanide takes place
rapidly through the initial formation of the monoanionic
species [trans-Pt(CCR)2(CN)(PPh3)]−, which exhibit the
phosphorus resonance shifted to high field by ca. 5 ppm (δ
(ppm)/1J(31P−195Pt) (Hz) = 13.4/2696 (R = Tol),18 13.8/
2682 (R = C6H4CF3-4), 13.9/2668 (R = C5H4N-4), 13.7/2709
(R = Np)) in relation to the corresponding precursor [trans-
Pt(CCR)2(PPh3)2] (δ (ppm)/1J(31P−195Pt) (Hz) = 18.6/
2657 (R = Tol), 18.9/2620 (R = C6H4CF3-4), 18.8/2598 (R =
C5H4N-4), 18.8/2648 (R = Np)). This fact and the slight
It is worth noting that these dianionic complexes are very
stable both in the solid state and even in solution (at room
temperature for several months). This fact is in contrast with
the relatively low stability of the related homoleptic
(NBu4)2[Pt(CCR)4] complexes.19
Scheme 1
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Table 1. Selected IR (cm−1, in Nujol) and NMR Data (δ/ppm [JPt−C/Hz]) of Complexes 1−6
1
2
3
4
5
6
ν(CN)
ν(CC)
δ(C−CN)
δ(Cα)
2114
2093
2111
2088
2111
2097
2107
2079
2129
2133
2100, 2088
2105, 2092
b
129.7 [1029]
111.9 [934]
104.0 [255]
−4437.6
128.2 [1032]
119.0 [934]
104.2 [279]
−4439.4
127.8 [1031]
122.4 [967]
103.5 [279]
−4427.1
128.7 [1028]
120.1 [970]
102.6 [278]
−4417.4
a
a
a
a
108.2 [970]
102.8 [278]
−4469.1
δ(Cβ)
c
δ(195Pt)
a
b
c
Not soluble enough. Not observed. Shifts are relative to Na2[PtCl6].
All complexes have been characterized by the usual
spectroscopic and analytical techniques (see the Experimental
Section and Table 1), and the crystal structures of complexes 2,
4 and 6 were determined by X-ray crystallography. The
negative MALDI(−) mass spectra of 1−4 show the
corresponding peaks due to the ions [M − NBu4]− and [M
− 2NBu4]−, respectively, and those of 5 and 6 show the
expected [M − NBu4]− peak (100% m/z 785.1 (5), 606.2 (6))
from the loss of the tetrabuthylammonium ion. The IR spectra
of 1−4 confirm the presence of one strong ν(CN) (2107−
2114 cm−1) and one ν(CC) (2079−2097 cm−1) stretching
band in the expected regions,1,20 consistent with the trans
geometry of the ligands (local D2h symmetry). The ν(CC)
bands appear slightly shifted to higher energies in relation to
the corresponding homoleptic (NBu4)2[Pt(CCR)4]19a com-
plexes (Δν = 12 cm−1 (R = Tol), 13 cm−1 (R = C6H4CF3-4), 4
cm−1 (C5H4N-4), 14 cm−1 (Np)), whereas the ν(CN)
stretches are found at low energies in relation to that for
[Pt(CN)4]2− (2122 cm−1). This result is in accordance with the
electronic perturbation in the Pt center, taking into account the
better π*-acceptor properties of cyanide groups. For the
complexes (NBu4)[trans-Pt(CCNp)2(CN)(PPh3)] (5) and
(NBu4)[trans-Pt(CCNp)2(CN)(CNtBu)] (6), in addition
to the ν(CN) stretch (2129 cm−1, 5; 2133 cm−1, 6), two
ν(CC) bands (2100, 2088 cm−1, 5; 2105, 2092 cm−1, 6) are
observed, in accordance with the expected two active modes
(A1 + B1, C2v symmetry). Complex 6 displays an additional
high-energy ν(CN, CNtBu) absorption at 2209 cm−1.6,21
The small shifts to higher energies in the ν(CN) and ν(C
C) bands in complex 6, in relation to complex 5, can be
primarily attributed to the occurrence of a lesser electronic π
back-donation from the PtII center to the cyanide and acetylide
ligands, caused by the substitution of the PPh3 by the CNtBu
(a better π-accepting ligand).
The most relevant data in the NMR spectra of 1−4 are the
signals due to the CN groups and to the Cα and Cβ acetylenic
carbons compiled in Table 1. A comparison of the chemical
shifts of the acetylenic carbons, which are easily assigned due to
distinct couplings to the 195Pt center (see Figure 1 as an
illustration), with those of the homoleptic complexes
(NBu4)2[Pt(CCR)4]19a reveals that the signal due to the
Cα atom is shifted upfield (Δδ(Cα) (ppm) = −6.5 (1), −6.0
(2), −0.9 (3)), whereas the signal due to Cβ appears shifted
slightly downfield (Δδ(Cβ) (ppm) = 1.9 (1), 1.2 (2), 0.9 (3)).
We attribute this, primarily, to the decrease in the net π back-
bonding component from platinum to π*(CCR) orbitals
caused by the electron-withdrawing effect of CN ligands, which
likely decreases the so-called paramagnetic contribution to the
shift. This result is also in accordance with previous theoretical
and experimental data,22 which suggest that a downfield 13C
NMR shift of the Cα carbon in metal σ-acetylides might reflect
Figure 1. Carbon resonances of [trans-Pt(CCNp)2(CN)2]2− (42−)
extracted from the 13C{1H} NMR spectrum of complex 4 in
CD3COCD3 at 293 K.
the cumulenic character associated with the resonant form II
(Chart 1).
Chart 1
The C(CN) resonance is observed in the narrow region from
127.8 to 129.7 ppm. The 195Pt−C(cyanide) coupling constants
(∼1030 Hz) are higher than that reported by us in [cis-Pt(C
CtBu)2(CN)2]2− (δ 132.5 ppm, JPt−C = 916 Hz),16 pointing to a
greater trans influence for the CCR ligand. Accordingly,
these values are also higher than those observed for 1J(Pt−Cα)
bonds (see Table 1), suggesting a stronger Pt−C (Pt−C(CN)
> Pt−CαCβ) spin−spin interaction. The proton spectra of
complexes 5 and 6 exhibit only one set of naphthyl resonances,
which supports the proposed trans geometry. The 13C{1H}
spectrum of 5 was not recorded due to its limited solubility. For
t
complex 6, in addition to Np and Bu groups, the expected
resonances due to acetylenic carbons with the corresponding
195Pt satellites were observed, but despite prolonged accumu-
lation, the quaternary CN (CN, CNtBu) carbons were not
found. Interestingly, the Cα carbon is observed (δ 108.2 ppm)
remarkably shifted to lower frequencies in relation to 4 (δ 120.1
ppm), reflecting again the lower electron density on the Pt
center. We have also recorded the 195Pt{1H} NMR spectra of
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Figure 2. ORTEP views of the anions (a) [trans-Pt(CCC6H4CF3-4)2(CN)2]2− (22−), (b, c)[trans-Pt(CCNp)2(CN)2]2− (42−), and (d, e)
[trans-Pt(CCNp)2(CN)(CNtBu)]− (6−). Ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity.
complexes 1−4 and 6. As can be seen in Table 1, all complexes
exhibit a singlet resonance in the expected range (from
−4427.1 to −4469.1 ppm).23 For complex 1 this signal (δ
CD3COCD3 −4437.6 ppm) is shifted upfield (Δδ 250 ppm)
with respect to the homoleptic (NBu4)2[Pt(CCTol)4]
complex (δ CD2Cl2 −4187 ppm), the only available
reference.13a
Table 2. Selected Bond Distances (Å) and Angles (deg) for
2, 4, and 6
2·3/4(CH3)2CO and 4·2/3EtOH·1/3H2O
2·3/4(CH3)2CO
4·2/3EtOH·1/3H2O
Pt−Cα
2.004(8)
2.000(9)
Pt−C(CN)
1.992(10), 2.006(11)
1.199(9)
1.993(9)
Cα-Cβ
1.187(12)
1.147(11)
178.0(11)
178.9(8)
X-ray Crystal Structures. Suitable crystals for X-ray
diffraction studies were obtained for (NBu4)2[trans-Pt(C
CC6H4CF3-4)2(CN)2] (2), (NBu4)2[trans-Pt(C
CNp)2(CN)2] (4) and (NBu4)[trans-Pt(CCNp)2(CN)-
(CNtBu)] (6) (see the Experimental Section), which
crystallize with solvent molecules as 2·3/4(CH3)2CO,
4·2/3EtOH·1/3H2O, and 6·3/4(CH3)2CO, respectively. Perspec-
tive drawings of anions 22−, 42−, and 6− are depicted in Figure
2. Table S1 (Supporting Information) shows the most
important crystallographic information, and selected lengths
and angles are summarized in Table 2. To our knowledge, these
are the first structurally characterized examples of Pt complexes
simultaneously containing these types of isoelectronic ligands,
which show the expected structural details. The Pt centers were
found to adopt essentially a trans-square-planar geometry with
the Cα−Pt−C(CN or CNtBu) angles close to 90° (89.4(2)−
90.7(2)°). The Pt−Cα(acetylide) (1.999(7)−2.007(6) Å), Pt−
C(CN) (1.989(7)−2.006(11) Å), and CC bond lengths
(1.187(12)−1.219(9) Å) do not differ significantly for the three
complexes, with values comparable to those found in other
mononuclear platinum(II) σ-alkynyl19,20 or cyanide6 com-
plexes. In complex 6, the Pt−C(CNtBu) bond displays the
shortest distance (1.946(7) Å), but also lies within the range of
other Pt−isocyanide complexes.21
C−N
1.145(12), 1.149(11)
178.8(7)
Pt−Cα−Cβ
Pt−C−N
180.0(8), 180.0(9)
177.0(8)
Cα−Cβ−Cγ
Cα−Pt−C(CN)
Cα−Pt−Cα
C(CN)−Pt−C(CN)
178.4(12)
89.9(3), 90.1(3)
180.0(4)
89.4(2), 90.6(2)
178.8(4)
180.0(3)
180.000(1)
6·(CH3)2CO
Pt−Cα
Pt−C26
Pt−C27
1.9997(7), 2.001(7) Cα−Cβ
1.210(9), 1.219(9)
1.159(8)
1.989(7)
C26−N1
C27−N2
1.946(7)
1.161(8)
Pt−Cα−Cβ
179.0(7), 179.1(7)
Cα−Pt−C26
Cα−Pt−C27
C1−Pt−C13
89.8(3), 90.1(3)
90.4(3), 89.7(3)
178.3(3)
Pt−C26−N1 176.6(6)
Pt−C27−N2 177.7(6)
Cα−Cβ−Cγ
172.5(8), 175.6(7)
C26−Pt−C27 177.0(3)
C−H···C = 148.3−124.5°; C···N = 3.35−3.55 Å, H···N =
2.63−2.90 Å, C−H···N = 129.6−115.6°) hydrogen interactions.
+
The NBu4 cations also show C−H···π(aromatic or CC)
bonding interactions with the arylacetylide ligands (aromatic
C···C = 3.58−3.85 Å, H···C = 2.82−2.95 Å, C−H···C =
169.04−134.4°; acetylide C···C = 3.57−3.62 Å, H···C = 2.69−
2.82 Å, C−H···C = 175.0−117.9°), to give, in the case of 4, an
extended 3D architecture with channels of ca. 6.4 Å diameter
along the crystallographic c axis (Figure S1, Supporting
Information), which connect voids of 429 Å3 containing the
ethanol and water crystallization molecules.
In the dianions, both aryl (22−) and naphtyl (42−) groups are
nearly perpendicular to the platinum coordination plane (89.2°
(2), 89.9° (4)) but essentially coplanar between them
(deviation angles 9.44° (2) and 0° (4); see Figure 2c). Not
unexpectedly, in both complexes, the supramolecular crystal
packing is deeply influenced by the presence of the two
tetrabuthylammonium counterions,24 which interact with the
cyanide ligands through weak C−H···N (C···N = 3.11−3.45 Å,
H···N = 2.33−2.51 Å, C−H···N = 169.3−118.5°) and T-shaped
C−H···π(CN) (C···C = 3.40−3.54 Å, H···C = 2.64−2.81 Å,
Curiously, in contrast with the mutually anti parallel
orientation of both Np substituents seen in complex 4, in the
heteroleptic monoanion 6−, both Np groups adopt a syn
disposition, oriented to the side of the bulkiest ligand (CNtBu).
In addition, as can be seen in Figure 2e, while one of the Np
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Table 3. Absorption of 1−6 in CH2Cl2 (5 × 10−5 M) and 1−4 in a 70/30 MeOH/H2O Mixture (5 × 10−5 M)
solvent
abs/nm (103ε/M−1 cm−1
)
1
CH2Cl2 (5 × 10−5 M)
235 (23.3), 264 sh (30.6), 276 (37.2), 318 (38.5), 327 sh (36.0)
MeOH/H2O (5 × 10−5 M) 250 (39.4), 262 sh (29.5), 274 sh (23.5), 310 (22.8), 322 sh (19.3)
a
[Pt(CCTol)4]2−
CH2Cl2
CH2Cl2 (5 × 10−5 M)
285 (49.5), 334 (38.6), 345 sh (34.8)
2
231 (19.1), 266 (28.5), 286 (36.9), 327 (30.2), 344 sh (21.8)
MeOH/H2O (5 × 10−5 M) 222 (18.0), 233 sh (14.6), 262 sh (20.4), 279 (25.0), 315 (23.2)
a
[Pt(CCC6H4CF3-4)4]2−
CH2Cl2
CH2Cl2 (5 × 10−5 M)
309 (48.5), 350 (44.7), 365 sh (35.5)
3
231 (22.5), 264 (25.4), 290 (38.7), 325 (30.0)
MeOH/H2O (5 × 10−5 M) 223 (15.6), 234 (13.3), 260 sh (13.7), 285 (21.6), 321 (22.7)
a
[Pt(CCC5H4N-4)4]2−
CH2Cl2
CH2Cl2 (5 × 10−5 M)
345 (48.4), 398 (34.0)
4
233 (42.5), 252 (25.4), 285 (15.0), 366 (32.3)
MeOH/H2O (5 × 10−5 M) 225 (46.4), 243 sh (26.9), 275 (14.5), 293 sh (11.4), 340 (19.5), 350 (19.4)
b
[Pt(CCNp)4]2−
CH2Cl2
240 (54.96), 260 (38.91), 282 sh (25.49), 340 sh (26.32), 360 sh (35.72), 378 sh (43.32), 398 (51.47)
232 (34.6), 247 (22.5), 272 (7.7), 311 (6.9), 359 (18.7)
5
6
CH2Cl2 (5 × 10−5 M)
CH2Cl2 (5 × 10−5 M)
231 (26.6), 246 (18.7), 303 (5.2), 358 (17.4)
a
b
See ref 19a. See ref 13f.
groups forms a small angle with the Pt coordination plane
(deviation 33.5°), the second is nearly coplanar (deviation
7.4°). Inspection of the extended crystal structure (Figure S2,
Supporting Information) reveals that, in contrast to the
structures of the dianionic complexes 2 and 4, the presence
accepting CN ligands. This would lower the energy of the
mixed alkynyl/Pt based HOMO and significantly raise the
transition energy. Along the same lines, the lower negative
charge in the naphthylacetylide derivatives 5 and 6 is reflected
in the slight hypsochromic shift of ca. ∼10 nm, observed in the
low-energy band in comparison to 4. However, in both
complexes the profiles are essentially identical, indicating that
the change of PPh3 by CNtBu has no significant effect on the
transition energy. In these complexes, because of the presence
of the extended aromatic naphthyl groups, the low-energy band
would be predominantly located on the CC−Np chromo-
phores.27
Previous studies in polypyridyl cyano metalate complexes
have shown that intermolecular O−H(solvent)···NC inter-
actions exert a remarkable effect on the 1MLCT absorption and
3MLCT emission bands.28 These interactions increase the π-
acceptor ability of the CN groups and the ligand field strength
at the metal center, giving rise to larger HOMO−LUMO gaps
and inducing significant hypsochromic shifts in comparison to
the case where such interactions are absent. Accordingly, we
investigated the absorption spectra of complexes 1−4 in a
MeOH/H2O (70/30) mixture, and the data are given in Table
3. In all complexes there is a blue shift of the lowest energy
manifold. The observed effect is relatively small in complexes 1
(475 cm−1) and 3 (383 cm−1) but significant in 2 (2676 cm−1)
and 4 (1249 cm−1) (see Figure 4), which can be compared to
that observed in [Ir(ppy)2(CN)2]− (1829 cm−1).28e,f These
hypsochromic shifts are consistent with the decrease in the
electron density around the PtII caused by the formation of
cyanide−hydrogen bonding interactions, which could likely
lower the energy of the mixed alkynyl/Pt HOMO and, hence,
increase the transition energy.
+
of only one NBu4 counterion lets the monoanionic platinates
get closer to each other. As a consequence, one aromatic
hydrogen atom of the Np groups of different platinate units is
involved in C−H···N hydrogen interactions (C···N = 3.38, 3.42
Å; H···N = 2.53, 2.65 Å; C−H···N = 136.1, 158.4°) with the N
of the cyanide ligand, which also supports a third C−H···N
interaction (C···N = 3.59 Å, H···N = 2.63 Å, C−H···N =
+
169.7°) with the NBu4 cation. As can be seen in Figure S2
(Supporting Information), other types of noncovalent inter-
actions, including C−H···π(aromatic or CC) and C−H···O,
are observed. The sum of all these interactions could favor the
distinct disposition in the solid state of the Np groups in 6 with
respect to that observed for 2 and 4.
Photophysical Properties. The photophysical properties
of the dianionic complexes (NBu4)2[trans-Pt(CCR)2(CN)2]
(1−4) are summarized in Tables 3 and 4. For comparison, the
absorption data of the homoleptic derivatives (NBu4)2[Pt(C
CR)4]19a are also included in Table 3. Complexes 1−4 (Figure
3) display in CH2Cl2 intense high-energy absorptions (230−
290 nm), which are likely of mixed configuration, including
intraligand (1IL CCR), metal to ligand (CCR, CN), and
ligand to ligand (CN → CCR) character. The broad
absorption band located in the near-UV region, which lies out
of the absorption range seen for (NBu4)2[Pt(CN)4]25 and is
sensitive to the alkynyl substituent, is ascribed to transitions
associated with the trans-Pt(CCR)2 fragment. On the basis of
theoretical calculations (see below) and previous assignments
in related complexes,14a,19a,22b,26 this low-energy band is
assigned to a mixed 1IL/1MLCT (π(CCR)/dπ(Pt) →
π*(CCR)) transition, having a predominant intraligand
character. This assignment is consistent with the trend found in
its maximum (318 nm (1) > 325 nm (3) ≈ 327 nm (2) > 366
nm (4)), which correlates with the energy of the π*(CCR)
orbitals (C6H4CH3-4 > C6H4CF3-4 ≈ C5H4N-4 > Np).22 As
detailed in Table 3 and illustrated in Figure S3 (Supporting
Information), this band appears blue-shifted with respect to the
related band in the corresponding homoleptic (NBu4)[Pt(C
CR)4] derivatives,13f,19a most likely because of the stabilization
of the Pt d(π) orbitals due to the coordination of the π-
The luminescence data, including emission wavelengths in
rigid and fluid media (CH2Cl2, MeOH), lifetimes, and quantum
yields in the solid state, are summarized in Table 4. All
complexes exhibit luminescence in the solid state and in
solution, at room and at low temperature, which is enhanced
and is brighter at 77 K. As an illustration, the emission spectra
for 1−4 in glassy media are shown in Figure 5 (CH2Cl2, 77 K)
and Figure S4 (MeOH, 77 K; Supporting Information). The
spectra display typical vibronically structured alkynyl based
profiles, which in all cases are blue-shifted and better resolved at
77 K. With reference to previous works14a,19a,22b,26 and the long
lifetimes observed, indicative of phosphorescence, the origin of
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Table 4. Emission Properties of 1−6 in the Solid State and in
Solution (CH2Cl2 and MeOH, 10−3 M) at 298 and 77 K
τ/μs (λem
/
complex
medium
solid
T/K
λem/nm (λex/nm) {ϕ/%}
nm)
1
298 452 max (137), 473 sh (348) 137
1
{12}
(452)
77 446 max, 467, 481, 493, 518 sh 296
1
(341)
(467)
CH2Cl2
298 445 max, 462 sh (345)
a
(10−3 M)
77 437 max, 459, 469, 481, 501 sh 460
1
(333)
(437)
MeOH
298 440 max, 457, 479 sh (330)
(10−3 M)
77 434 max, 455, 476 sh (330)
298 460 max, 470 sh (327)
b
2
CH2Cl2
12.1 0.7
(460)
(10−3 M)
Figure 3. Absorption spectra of complexes 1 (black), 2 (green), 3
(blue), and 4 (orange) in CH2Cl2 (5 × 10−5 M).
77 441 max, 467, 477, 491, 514 sh 16.2 0.8
(330)
(447)
MeOH
298 452 max, 471 (330)
(10−3 M)
77 446 max, 467, 488 (330)
3
solid
298 441 max, 458, 480, 504 sh
13.3 0.6
(441)
(300−430) {21}
77 439 max, 456, 465, 476, 501
18.4 1.2
(439)
(295−400)
c
CH2Cl2
298 440, 467 max (330)
15.1 0.5
(440)
(10−3 M)
77 431 max, 446 sh, 470 sh (330) 17.5 1.1
(431)
MeOH
298 439 max, 460 sh (330)
(10−3 M)
77 434 max, 456, 471, 500 sh
(330)
4
solid
298 552 max, 605, 662 (387) {4}
8.6 0.5
(552)
Figure 4. Absorption spectra of complexes 2 (green) and 4 (orange)
in CH2Cl2 (5 × 10−5 M) (solid line) vs MeOH/H2O (70:30, 5 ×
10−5) (dashed line), highlighting the energetic difference between the
lowest energy absorptions in each solvent.
77 557 max, 605, 654 (300−420) 120
1
(557)
CH2Cl2
298 552 max, 596, 640 sh (388)
8.5 0.7
(552)
(10−3 M)
77 548 max, 560 sh, 596, 612 sh, 48.9 1.1
641 (375, 400−450)
(548)
MeOH
298 543, 590 sh (365)
(10−3 M)
77 540 max, 551 sh, 584, 599 sh,
632 (365)
5
6
solid
298 545 max, 618 br (365)
a
77 551, 588 max, 630 sh (400)
175
2
(585)
CH2Cl2
298 547 max, 591, 632 sh (386,
426)
7.2 0.9
(547)
(10−3 M)
77 545 max, 558 sh, 591 (375)
242
1
(545)
solid
298 545 max, 590, 650 (380)
77 547, 576 br (380)
a
83.0 1.3
(547)
CH2Cl2
298 545 max, 588, 627 (378)
8.5 0.3
(545)
(10−3 M)
77 544 max, 558 sh, 592 (378)
43.7 0.8
(544)
Figure 5. Normalized emission spectra of 1 (black), 2 (green), 3
(blue), and 4 (orange) in CH2Cl2 (10−3 M) at 77 K.
a
b
Too weak for an accurate measurement. Oily sample, not measured
c
in the solid state. A weak fluorescence band at 409 nm is also
observed.
(431 nm (3), 437 nm (1), 441 nm (2)) and 3 ≈ 1 > 2 in
MeOH at 77 K (434 nm (1, 3) > 446 nm (2)). The observed
lower energy emission in the p-trifluoromethylphenyl derivative
2 related to those of 1 and 3 is consistent with the involvement
of the π*(CCR) character in the LUMO. Obviously, the
presence of the two low-lying extended polyaromatic napthyl
groups in complexes 4−6 lowers the energy of the transition,
thus inducing a remarkable red shift of the emission. The nearly
the emission is ascribed to a mixed 3IL(π → π*(C
CR))/3MLCT(dπ(Pt) → π*(CCR)) excited state, having
a predominant intraligand character. Accordingly, the emission
energies were found to be sensitive to the alkynyl substituent.
The aryl (1, 2) and pyridyl (3) derivatives emit in the blue
region, following the energy order 3 > 1 > 2 in CH2Cl2 at 77 K
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identical yellow-orange emission bands found for complexes 4−
observed in Table 4, only slight blue shifts were observed for
the bis(cyanide) derivatives 1−4 in fluid methanol relative to
CH2Cl2 (5 nm (411 cm−1), 1; 8 nm (385 cm−1), 2; 1 nm (52
cm−1), 3; 9 nm (300 cm−1), 4). This fact is not unexpected and
3
6 (Figure 6) are suggestive of an emissive state of mainly IL
3
has been also previously observed in MLCT emissions of
cyanopolypyridyl d6 systems.28 The lesser solvent dependence
in the emission relative to the absorption has been attributed to
the fact that the electron density on the CN ligands is smaller in
the triplet than in the singlet state and, hence, the direct
donor−acceptor CN···H(solvent) interactions are weaker in
the triplet state.
Theoretical Calculations. In order to get a further insight
into the photophysics of these complexes, theoretical
calculations were performed for 4 and 6. The absorption and
emission spectra of both complexes were examined on the
optimized geometries (for the S0 and T1 states) of the
corresponding anions of both complexes at the B3LYP/
LanL2DZ(Pt)/6-31G**(ligand atoms) level. The equilibrium
geometries, the coordinates, and the most important geo-
metrical parameters, together with the experimental values for
comparison, are given in the Supporting Information (Tables
S2−S6). In the anion 42−, the optimized ground-state geometry
is in fair agreement with the structural data, with both Np
groups coplanar and orthogonal to the NC−Pt−CN axis (see
Figure S5, Supporting Information). In the case of the
monoanion 6−, the X-ray analyses show that both Np groups
adopt a syn disposition, with deviation angles of 33.5 and 7.40°
to the Pt coordination plane. That disposition, with both Np
groups oriented toward the most bulky ligand and the
difference from the disposition observed in complex 4, incited
us to perform geometry optimizations using as starting points
three different geometries of 6−. When the starting structure of
6− had both Np groups oriented toward the CN ligands, the
geometry optimization resulted in a transition state structure
with both Np ligands almost coplanar with the Pt coordination
plane. When the optimizations were performed starting from
the X-ray data (Np groups oriented toward the CNtBu ligand)
or starting with both Np groups orthogonal to the Pt
coordination plane (as observed in the X-ray structure of 4),
two different energy minima were found (see Figure S6,
Figure 6. Normalized emission spectra of 4 (orange), 5 (violet), and 6
(pink) in CH2Cl2 (10−3 M) at 77 K.
character. However, the slight bathochromic shift in the
dianionic complex 4 in relation to 5 and 6 (see Table 4)
reflects the increase of electronic density on the PtII atom,
which is generally involved in the π system of the HOMO;
3
thus, the emission of 4−6 has also some MLCT character, as
has been further supported by TD-DFT calculations (vide
infra). It is worth noting that, in comparison with the emission
observed for the homoleptic complexes (NBu4)2[Pt(CCR)4]
(λmax/nm CH2Cl2, 77 K: 447 (R = Tol), 463 (R = C6H4CF3-4),
471 (R = C5H4N-4), 565 (R = Np)), the emissions of 1−4 are
significantly blue-shifted to higher energies. The change of two
electron-rich alkynyl fragments for cyanide ligands stabilizes the
dπ(PtII) orbitals, which, by orbital mixing, stabilizes the Pt−
alkynyl-based HOMO, thus increasing the gap of the transition.
The measured lifetimes and quantum yields for 1−4 in the
solid state are relatively longer than those reported for [Pt(C
CR)4]2−, a result which is indicative of a greater intraligand
3
contribution in the mixed IL/3MLCT manifold. We have also
examined the emissions of 1−4 in MeOH as solvent. As can be
Figure 7. Experimental UV−vis spectra in CH2Cl2 (5 × 10−5 M) and calculated absorption spectra (blue bars) in CH2Cl2, together with frontier
orbital plots obtained by DFT, for (a) 4 and (b) 6.
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Supporting Information), as established by subsequent
frequency calculations. As the two obtained minimum are
close in energy (ΔE = 0.67 kcal/mol), we carried out TD-DFT
calculations with both geometries. The calculated absorption
spectrum obtained using the geometry with both Np groups
oriented orthogonal to the NC−Pt−CNC axis fits better with
the experimental UV−vis spectrum, even though the
interpretation of this is not straightforward. The distances
and angles of the ground-state optimized structure compare
well with the X-ray data obtained for complex 6 (see Table S6),
the only remarkable difference being the angles between the Np
groups and the Pt coordination plane (86.77, 73.86° in S0 vs
7.4, 33.5° in the X-ray structure). Some selected frontier
molecular orbitals of both anions are depicted in Figures S7 and
S8 (Supporting Information), and the composition in terms of
ligands and metals are collected in Table S7 (Supporting
Information). For comparison, the recently reported data of the
anion 12− have been also included. The HOMOs of all
complexes are delocalized over the platinum and the acetylide
ligands, with a higher contribution of the Pt center in both
dianionic derivatives (41% (1), 43% (4)) than in the
monoanionic derivative (9% (6)), thus reflecting the influence
of the charge of the anion. The LUMOs are mainly centered on
the alkynyl fragments (98% (1), 99% (4 and 6)). The next low-
energy unoccupied orbitals in 1 and 4 are also centered on the
alkynyl fragments (from LUMO+1 to LUMO+3 in 1; from
LUMO+1 to LUMO+5 in 4); whereas in 6 LUMO+1 is
localized on the alkynyl moieties, but LUMO+2 is delocalized
on the alkynyl (11%), isocyanide (49%), and Pt center (34%).
To examine the UV−vis absorption spectra, the lowest lying
vertical singlet excitation energies were calculated by TD-DFT
calculations with the consideration of the solvation effect
(CH2Cl2) using the PCM method. Data including energy gaps
(nm) and corresponding assignments of the transitions with
strong oscillator strengths are given in Table S8 (Supporting
Information). As can be seen in Figure 7, the computed lowest
energy transitions at 372 nm (4) and 354 nm (6) closely
resemble the observed experimental bands (366 nm (4), 358
nm (6)). These transitions mainly arise from the HOMO →
LUMO excitation (89% (4), 72% (6)); therefore, the lowest
Figure 8. Frontier orbital plots obtained by DFT for the first triplet
state of the anions of complexes 4 and 6.
CONCLUSIONS
■
In summary, a method of generating stable anionic trans-
configured heteroleptic alkynyl platinate complexes [trans-
Pt(CCR)2(CN)2]2− is reported. Neutral trans-bis(alkynyl)-
bis(triphenylphosphine) platinum(II) substrates were reacted
with (NBu4)CN, producing the disubstituted dianionic
complexes with retention of the configuration, through the
monoanionic [trans-Pt(CCR)2(CN)(PPh3)]− as intermedi-
ate species. As illustration, the naphthylacetylide derivative (5,
R = Np) was isolated and has allowed us to access to
(NBu4)[trans-Pt(CCNp)2(CN)(CNtBu)] (6) by subsequent
displacement of the phosphine ligand. Their spectroscopic and
photophysical properties were examined and compared to
those found for the homoleptic [Pt(CCR)4]2− derivatives,
which has demonstrated that substitution of two alkynyl ligands
for two π-acceptor groups produces a stabilization of the
platinum−alkynyl-based HOMO Pt(dπ)/π(CCR), giving
rise to a significant blue shift in both the absorption and
emission. The arylacetylide compounds 1−3 display bright blue
emissions and the naphthylacetylide compounds 4−6 orange
3
emissions, originating mainly from a mixed IL(π → π*C
CR)/3MLCT(5d(Pt) → π*CCR) excited state with
predominant intraligand character. According to TD-DFT
calculations, the metal to ligand (acetylide) charge transfer
contribution decreases with the charge of the anion on going
from [trans-Pt(CCR)2(CN)2]2− (42−) to [trans-Pt(C
CR)2(CN)(CNtBu)] (6−).
1
lying absorption can be assigned as a mixture of IL/1MLCT
transitions in both derivatives, with a stronger MLCT character
in 4.
The nature of the phosphorescent emission was addressed by
optimization of the first triplet state of the anions of 4 and 6.
For 42−, the geometrical parameters of the computed triplet
state are similar to those found for the corresponding ground
state (Table S6, Supporting Information). However, in the case
of 6− the anion adopts a more planar configuration in the
optimized T1 state, pointing to a higher degree of conjugation
in relation to the nonplanar S0 ground state. The SOMO and
SOMO-1 of both anions are depicted in Figure 8, together with
their composition in terms of metal and ligands. The lowest
energy emission calculated as ΔET1‑S0 at 515.2 nm (4) and
600.0 nm (6) are qualitatively close to the experimental values
(552 nm (4), 545 nm (6)). The compositions of the singly
occupied orbitals are mainly centered on the alkynyl fragments
It is hoped that these new platinate systems, having three
distinct basic sites (Pt, CCR, and CN), will behave as
excellent building blocks for the design of novel high-
dimensionality systems. The interaction of these modular
chromophoric precursors with different cations or electrophilic
fragments will stimulate future investigations aiming to generate
or even harness new interesting and useful properties.
EXPERIMENTAL SECTION
■
Materials and Methods. All reactions were carried out under Ar
using dried solvents purified by known procedures and distilled prior
to use. IR spectra were recorded on a FT-IR Nicolet Nexus
spectrometer as Nujol mulls between polyethylene sheets, and NMR
spectra were recorded on Bruker ARX 300 and DRX 400
spectrometers. Chemical shifts are reported in ppm relative to external
standards (SiMe4, CFCl3, and 85% H3PO4). Elemental analyses were
carried out with a Perkin-Elmer 2400 CHNS/O microanalyzer, and
MALDI-TOF spectra on a Microflex MALDI-TOF Bruker spec-
3
in both complexes (89−99%), suggesting an essentially IL
character of the emission, although the participation of the Pt
3
center in SOMO-1 (11% (4), 7% (6)) confirms some MLCT
character. Therefore, the emission can be assigned as an
3IL/3MLCT mixture of transitions.
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trometer operating in the linear and reflector modes using dithranol as
matrix. Conductivities were measured in acetone solutions (ca. 5 ×
10−4 mol L−1) using a Crison GLP31 conductimeter. UV−vis
absorption spectra were recorded on a Hewlet-Packard 8453
spectrometer. Excitation and emission spectra were obtained on a
Jobin-Yvon Horiba Fluorolog 3-11 Tau-3 spectrofluorimeter. The
lifetime measurements were performed operating in the phosphorim-
eter mode using a 450 W Xe lamp (with a F1-1029 lifetime emission
photomultiplier tube assembly). Lifetime measurement errors, which
correspond to deviation of the experimental data with respect to the
theoretical decay function, are included in Table 4. Quantum yields in
the solid state were measured using a F-3018 Integrating Sphere
mounted on a Fluorolog 3-11 Tau-3 spectrofluorimeter. The estimated
relative error of the quantum yields is about 10%. Emission data have
been fitted using the Jobin Yvon software package and Origin 5.
Literature methods were used to prepare the starting materials [trans-
Pt(CCR)2(PPh3)2],18,29 and other reagents were obtained from
commercial sources.
(revision B.01).36 Geometries in the S0 ground state were optimized
using the B3LYP method and in the T1 excited state using the
unrestricted U-B3LYP (T1) Becke three-parameter functional
combined with the Lee−Yang−Parr correlation functional.37 In the
case of 6−, the geometry of the ground state was optimized starting
from three different geometries. No negative frequency was found in
the vibrational frequency analysis of the final equilibrium geometries.
The basis set used for the platinum centers was the LanL2DZ effective
core potential38 and 6-31G(d,p) for the ligand atoms. The solvent
effect of dichloromethane in the TD-DFT calculations was taken into
consideration by the polarizable continuum model (PCM).39
Preparation of (NBu4)2[trans-Pt(CCTol)2(CN)2] (1). (NBu4)-
CN (0.268 g, 1 mmol) was added to a suspension of trans-Pt(C
CTol)2(PPh3)2 (0.475 g, 0.5 mmol) in acetone. After 1 h of stirring at
room temperature, a yellow solution was obtained. The solvent was
removed under vacuum and the yellow oily residue treated with ∼30
mL of Et2O. The mixture was stirred for 1 h, which dissolved free PPh3
and caused the separation of 1 as a pale -yellow solid. The solid was
filtered off and repeatedly washed with Et2O (0.414 g, 86%). Anal.
Calcd for C52H86N4Pt (962.36): C, 64.90; H, 9.01; N, 5.82. Found: C,
64.85; H, 8.74; N, 6.02. MS MALDI(−): m/z 719.3 ([M − NBu4]−,
49%), 477.0 ([M − 2NBu4]−, 100%). IR (cm−1): ν(CN) 2114 (vs),
Data for the complex [trans-Pt(CCC6H4CF3-4)2(PPh3)2] are as
1
follows. H NMR (δ, 300.13 MHz, CDCl3, 293 K): 7.76 (m, 12H,
H2,6, PPh3), 7.35 (m, 18H, PPh3), 7.11 (d, J = 8.1 Hz, 4H, C6H4,
C6H4CF3-4), 6.28 (d, J = 8.1 Hz, 4H, C6H4, C6H4CF3-4). 31P{1H}
1
1
ν(CC) 2093 (vs). H NMR (δ, 300.13 MHz, CDCl3, 293 K): 7.15
NMR (δ, 121.5 MHz, CDCl3, 293 K): 18.9 (s, JP−Pt = 2620 Hz, P,
PPh3). 19F{1H} NMR (δ, 282.4 MHz, CDCl3, 293 K): −136.2 (s, CF3,
C6H4CF3-4).
(d, J = 7.8 Hz, 4H, C6H4, Tol), 6.90 (d, J = 7.8 Hz, 4H, C6H4, Tol),
3.43 (m, 16H, NCH2, NBu4), 2.23 (s, 6H, CH3, Tol), 1.66 (m, 16H,
CH2, NBu4), 1.50 (m, 16H, CH2, NBu4), 0.94 (t, 24H, CH3, NBu4).
13C{1H} NMR (δ, 100.14 MHz, CD3COCD3, 293 K): 133.0 (s, C4,
Tol), 131.8 (s, CH, 4JC−Pt ≈ 9 Hz, Tol), 129.7 (s, C1, 3JC−Pt ≈ 24 Hz,
Data for the complex [trans-Pt(CCNp)2(PPh3)2] are as follows.
1
IR (cm−1): ν(CC) 2098 (vs). H NMR (δ, 300.13 MHz, CDCl3,
293 K): 7.87 (d, J = 5.2 Hz, 12H, H2,6, PPh3), 7.58 (d, J = 8.0 Hz, 2H,
H2, Np), 7.41 (d, J = 8.1 Hz, 2H, Np), 7.29−7.20 (m, 2H, Np
overlapped with 18H, PPh3), 7.16 (d, J = 8.3 Hz, 2H, Np), 7.03 (m,
2H, Np), 6.93 (m, 2H, Np), 6.35 (d, J = 7.1 Hz, 2H, Np). 31P{1H}
1
Tol), 129.7 (s, C-CN, JC−Pt = 1029 Hz, CN), 129.1 (s, CH, Tol),
1
2
111.9 (s, JC−Pt = 934 Hz, Cα, CC), 104.0 (s, JC−Pt = 255 Hz, Cβ,
CC), 59.6 (s, N−CH2, NBu4), 24.9 (s, −CH2−, NBu4), 21.3 (s,
−CH3, Tol), 20.5 (s, −CH2−, NBu4), 14.2 (s, −CH3, NBu4). 195Pt
NMR (δ, 85.68 MHz, CDCl3, 293 K): −4437.67. ΛM ((CH3)2CO):
174.5 Ω−1 cm2 mol−1.
1
NMR (δ, 121.5 MHz, CDCl3, 293 K): 18.8 (s, JP−Pt = 2648 Hz, P,
PPh3).
X-ray Crystallography. Details of the structural analyses for all
complexes are summarized in Table S1 (Supporting Information).
Colorless crystals of complex 2 were obtained by slow evaporation of a
saturated acetone solution of the complex. Pink (4) or white (6)
crystals were obtained by slow diffusion of Et2O into EtOH (4) or
acetone (6) saturated solutions of the corresponding compound. X-ray
intensity data were collected with a NONIUS-κCCD area-detector
diffractometer, using graphite-monochromated Mo Kα radiation.
Images were processed using the DENZO and SCALEPACK suite
of programs,30 and the absorption corrections were performed with
MULTI-SCAN31 (2 and 4) or XABS32 (6), using the program suite
WINGX.33 The structures were solved by direct methods using
SHELXS-9734 and refined by full-matrix least squares on F2 with
SHELXL-97.34 All non-hydrogen atoms were assigned anisotropic
displacement parameters. All the hydrogen atoms were constrained to
idealized geometries, fixing isotropic displacement parameters 1.2
times the Uiso value of their attached carbon for the aromatic and 1.5
times that value for the methyl groups. For complexes 2 and 4,
disordered crystallization molecules of acetone (2) or ethanol and
water (4) were observed. Despite many attempts, we could not resolve
the disorders adequately.
Preparation of (NBu4)2[trans-Pt(CCC6H4CF3-4)2(CN)2] (2).
This complex was prepared in a way similar to that described for 1,
starting from trans-Pt(CCC6H4CF3-4)2(PPh3)2 (0.600 g, 0.57
mmol) and (NBu4)CN (0.608 g, 2.28 mmol). In this case, the
reaction mixture was stirred for 15 min. The solvent was removed
under vacuum, and the complex was extracted with a CH2Cl2/H2O
mixture (20/20). The dichloromethane solution was dried with
anhydrous MgSO4 and filtered through Celite. The filtrate was
evaporated to dryness, and ∼10 mL of a CH2Cl2/MeOH/hexane
mixture (∼1/19/80) was added to the flask. The slow evaporation (up
to 7 days) of this mixture at −30 °C caused the crystallization of 2 as
an oily solid. This solid was filtered, washed with cold hexane, and
dried (0.244 g, 40%). Anal. Calcd for C52H80N4F6Pt (1070.30): C,
58.35; H, 7.53; N, 5.23. Found: C, 58.54; H, 7.91; N, 5.05. MS
MALDI(−): m/z 827.3 ([M − NBu4]−, 21%), 585.0 ([M − 2NBu4]−,
1
51%). IR (cm−1): ν(CN) 2111 (vs) ν(CC) 2088 (vs). H NMR
(δ, 300.13 MHz, CD3COCD3, 293 K): 7.45 (d, J = 7.9 Hz, 4H, C6H4,
C6H4CF3-4), 7.34 (d, J = 7.9 Hz, 4H, C6H4, C6H4CF3-4), 3.51 (m,
16H, NCH2, NBu4), 1.81 (m, 16H, CH2, NBu4), 1.47 (m, 16H, CH2,
NBu4), 0.96 (t, 24H, CH3, NBu4). 19F NMR (282.4 MHz,
CD3COCD3, 293 K): −145.6 (s, CF3, C6H4CF3-4). 13C{1H} NMR
(δ, 100.14 MHz, CD3COCD3, 293 K): 135.8 (s, C1, C6H4CF3-4),
Thus, we have used the SQUEEZE program35 as an alternative to
the modeling of the solvent. For the structure of complex 2, the use of
SQUEEZE revealed the existence in the unit cell of four voids of 157
Å3 containing 23 e each, which fits well with the presence of 0.75
acetone molecules in each of them. In the case of 4, the presence of
three voids of 430 Å3 with 63 e (which fits well for two molecules of
ethanol and one water in each void) were observed. Therefore, we
have included them as crystallization solvents in the corresponding
empirical formula, to give the final stoichiometries 2·3/4(CH3)2CO
and 4·2/3EtOH·1/3H2O. Complex 6 also crystallizes with 0.75
molecules of acetone (6·3/4(CH3)2CO). In both cases, several
restraints have been used to model the NBu4 counteranion, and the
three structures present some residual peaks greater than 1 e A−3, but
without chemical meaning.
1
131.8 (s, CH, C6H4CF3-4), 128.2 (s, C-CN, JC−Pt = 1032 Hz, CN),
1
125.7 (q, CF3, JC−F = 271 Hz, C6H4CF3-4), 125.1 (s, CH, C6H4CF3-
4), 125.1 (q, 2JC−F = 32 Hz, C4, C6H4CF3-4), 119.0 (s, 1JC−Pt = 934 Hz,
2
Cα, CC), 104.2 (s, JC−Pt = 279 Hz, Cβ, CC), 59.2 (s, N−CH2,
NBu4), 24.5 (s, −CH2−, NBu4), 20.2 (s, −CH2−, NBu4), 13.9 (s,
−CH3, NBu4). 195Pt NMR (δ, 85.68 MHz, CDCl3, 293 K): −4439.4.
ΛM ((CH3)2CO): 180.2 Ω−1 cm2 mol−1.
Preparation of (NBu4)2[trans-Pt(CCC5H4N-4)2(CN)2] (3).
This complex was prepared in a way similar to that for 2 starting
from trans-Pt(CCC5H4N-4)2(PPh3)2 (0.500 g, 0.52 mmol) and
(NBu4)CN (0.556 g, 2.08 mmol). In this case, after the extraction with
CH2Cl2/H2O, the white oily residue was treated with an i-PrOH/Et2O
mixture (5/95) to give 3 as a white solid (0.212 g, 42%). Anal. Calcd
for C48H80N6Pt (936.28): C, 61.58; H, 8.61; N, 8.98. Found: C, 61.95;
Computational Details for DFT Calculations. DFT calculations
were performed on the anions of complexes 4 and 6 with Gaussian 09
843
dx.doi.org/10.1021/om301134k | Organometallics 2013, 32, 835−845

Organometallics
Article
H, 8.92; N, 9.12. MALDI(−): m/z 693.2 ([M − NBu4]−, 80%), 451.0
([M − 2NBu4]−, 100%). IR (cm−1): ν(CN) 2111 (vs), ν(CC)
2097 (vs). 1H NMR (δ, 300.13 MHz, CDCl3, 293 K): 8.30 (d, J = 5.5
Hz, 4H, C5H4, C5H4N-4), 7.08 (d, J = 5.5 Hz, 4H, C5H4, C5H4N-4),
3.39 (m, 16H, NCH2, NBu4), 1.67 (m, 16H, CH2, NBu4), 1.50 (m,
16H, CH2, NBu4), 0.94 (t, 24H, CH3, NBu4). 13C{1H} NMR (δ,
100.14 MHz, CD3COCD3, 293 K): 149.6 (s, CH, C5H4N-4), 139.0 (s,
C1, 4JC−Pt = 24 Hz, C5H4N-4), 127.8 (s, C-CN, 1JC−Pt = 1031 Hz, CN),
126.4 (s, CH, C5H4N-4), 122.4 (s, 1JC−Pt = 967 Hz, Cα, CC), 103.5
tBu), 1.43 (m, 8H, CH2, NBu4), 0.98 (t, 12H, CH3, NBu4). 13C{1H}
NMR (δ, 100.14 MHz, CD3COCD3, 293 K): 136.1 (s, C, Np), 135.1
(s, C, Np), 130.0 (s, C, Np), 129.4 (s, CH, Np), 129.2 (s, CH, Np),
3
128.2 (s, C, JPt−C = 24 Hz, Np), 127.3 (s, CH, Np), 127.1 (s, CH,
1
Np), 126.6 (s, CH, Np), 108.2 (s, JC−Pt = 970 Hz, Cα, CC), 102.8
(s, 2JC−Pt = 278 Hz, Cβ, CC), 60.4 (s, N−CH2, NBu4), 58.5 (s, CH3,
tBu, CNtBu), 31.6 (C-CH3, CNtBu), 25.5 (s, −CH2−, NBu4), 21.2 (s,
−CH2−, NBu4), 15.0 (s, −CH3, NBu4). Resonances due to the
quaternary carbon atoms of CN and CNtBu groups were not observed.
195Pt NMR (δ, 85.68 MHz, CDCl3, 293 K): −4469.1.
2
(s, JC−Pt = 279 Hz, Cβ, CC), 59.5 (s, N−CH2, NBu4), 24.7 (s,
−CH2−, NBu4), 20.3 (s, −CH2−, NBu4), 14.0 (s, −CH3, NBu4). 195Pt
NMR (δ, 85.68 MHz, CDCl3, 293 K): −4427.1. ΛM ((CH3)2CO):
169.7 Ω−1 cm2 mol−1.
ASSOCIATED CONTENT
* Supporting Information
■
S
Preparation of (NBu4)2[trans-Pt(CCNp)2(CN)2] (4). This
complex was prepared in a way similar to that for 2, starting from
trans-Pt(CCNp)2(PPh3)2 (1.250 g, 1.22 mmol) and (NBu4)CN
(1.5 g, 4.88 mmol). An oily pink residue was obtained, which was
treated with i-PrOH (∼10 mL) and Et2O (∼20 mL), giving rise to 4 as
a pink solid (0.723 g, 57%). Anal. Calcd for C58H86N4Pt (1034.43): C,
67.35; H, 8.38; N, 5.42. Found: C, 67.84; H, 8.40; N, 5.30.
MALDI(−): m/z 791.4 ([M − NBu4]−, 73%), 549.1 ([M − 2NBu4]−,
100%). IR (cm−1): ν(CN) 2107 (vs), ν(CC) 2079 (vs). 1H
NMR (δ, 300.13 MHz, CD3COCD3, 293 K): 8.99 (d, J = 7.9 Hz, 2H,
H4, Np), 7.74 (d, J = 8.2 Hz, 2H, H2, Np), 7.52 (d, J = 8.0 Hz, 2H,
Np), 7.45−7.30 (m, 6H, Np), 7.28 (m, 2H, Np), 3.48 (m, 16H,
NCH2, NBu4), 1.74 (m, 16H, CH2, NBu4), 1.42 (m, 16H, CH2,
NBu4), 0.88 (t, 24H, CH3, NBu4). 13C{1H} NMR (δ, 100.14 MHz,
Figures S1−S8, Tables S1−S7, and CIF files giving additional
structural data, characterization data, details of the calculations,
and crystallographic data. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: elena.lalinde@unirioja.es (E.L.); julio.fernandez@
unirioja.es (J.F.).
■
Notes
The authors declare no competing financial interest.
3
CD3COCD3, 293 K): 136.1 (s, C1, JC−Pt ≈ 6 Hz, Np), 134.7 (s, C,
1
ACKNOWLEDGMENTS
Np), 130.1 (s, C, Np), 129.9 (s, CH, Np), 128.7 (s, C-CN, JC−Pt
=
■
1028 Hz, CN), 128.4 (s, CH, Np), 128.1 (s, CH, 4JC−Pt ≈ 10 Hz, Np),
126.4 (s, CH, Np), 126.3 (s, CH, Np), 125.8 (s, CH, Np), 124.2 (s,
CH, Np), 120.1 (s, 1JC−Pt = 970 Hz, Cα, CC), 102.6 (s, 2JC−Pt = 278
Hz, Cβ, CC), 59.6 (s, N−CH2, NBu4), 24.6 (s, −CH2−, NBu4),
20.5 (s, −CH2−, NBu4), 14.2 (s, −CH3, NBu4). 195Pt{1H} NMR (δ,
85.68 MHz, CDCl3, 293 K): −4417.4. ΛM ((CH3)2CO): 171.1 Ω−1
cm2 mol−1.
This work was supported by the Spanish MICINN (Project
CTQ2008-06669-C02-02/BQU) and the CAR (COLABORA
project 2009/05). S.S. thanks the CSIC for a grant.
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