Remarkable influence of the cyclometalating ligand on the nuclearity and properties of heterobridged (μ-X)(μ-C=CR) platinum(II) complexes

Article abstract of DOI:10.1021/om101172p

Partial dehalogenation reaction of [Pt(C^N)(μ-Cl)]₂ [C^N = 2,6-diphenylpyridinate (dppyH), 7,8-benzoquinolate (bzq)] with NaC=C ^tBu (or HC=C^tBu/NEt₃/CuI) proceeds with formation of binuclear ([{Pt(dppyH)}_2<

Full text of DOI:10.1021/om101172p

ARTICLE
pubs.acs.org/Organometallics
Remarkable Influence of the Cyclometalating Ligand on
the Nuclearity and Properties of Heterobridged (μ-X)(μ-CtCR)
Platinum(II) Complexes
ꢀ
Jesꢀus R. Berenguer, Alvaro Díez, Ana García, Elena Lalinde,* M. Teresa Moreno, Sergio Sꢀanchez, and
Javier Torroba
Departamento de Química, Grupo de Síntesis Química de La Rioja, UA-CSIC, Universidad de La Rioja, 26006, Logro~no, Spain
S Supporting Information
b
ABSTRACT: Partial dehalogenation reaction of [Pt(C∧N)(μ-Cl)]2 [C∧N = 2,6-diphenyl-
pyridinate (dppyH), 7,8-benzoquinolate (bzq)] with NaCtCtBu (or HCtCtBu/NEt3/CuI)
proceeds with formation of binuclear ([{Pt(dppyH)}2(μ-Cl)(μ-CtCtBu)], 1) or tetra-
nuclear ([Pt2(bzq)2(μ-Cl)(μ-CtCtBu)]2, 4) complexes, depending on the nature of the
cyclometalated ligand. Similar halide-bridged complexes 2, 3, 5, and 6 have also been
prepared. The X-ray structures of 1, 4, and 5 reveal the selective formation in all cases of
the isomer having the bridging chlorine atom located in a trans position to the metalated
carbon atoms of two Pt(C∧N) units. In 4 and 5, the tetrahedral Pt4 core is additionally
stabilized by short Pt Pt and π π intramolecular bonding interactions, which have
3 3 3
3 3 3
influence on their photophysical properties. The lower lying absorption bands are ascribed to
mixed MLCT [PtfdppyH]/1LL0CT [CtCR/XfdppyH] (complexes 1-3) or to
1
1MMLL0CT transitions (L = CtCR, L0 = bzq) (complexes 4-6, TD-DFT). Complexes
1-3 are nonemissive. By contrast, the tetranuclear clusters are brightly emissive at 77 K (solid state, frozen CH2Cl2), exhibiting an
unstructured orange emission (560-580 nm). This emission has been attributed, according to computational studies of the frontier
orbitals in the optimized T1 state of 5, to an excited state of large [Pt(d)/π(CtCR)/Pt(d)fbzq/bzq] character, with the LUMO
delocalized on the adjacent Pt(bzq) fragments. In frozen CH2Cl2, an additional low-energy shoulder (∼640-675 nm) is also
detected, probably due to the presence of close distinct emissive states originating in small modifications in the ground-state
structure in frozen solution.
’ INTRODUCTION
with their propensity to engage in interplanar stacking through
the occurrence of Pt Pt and/or π π interactions.11,17-20
3 3 3
3 3 3
Square-planar Pt(II) complexes combining strong ligand field
cyclometalating groups and ancillary ligands such as acetylides
have drawn great attention in the past decade, mainly because of
their impressive and versatile photophysical properties.1-6 Apart
from the fundamental interest in their intrinsic emissive states,
these compounds have shown potential in a variety of applica-
tions such as light-emitting materials,7-10 photocatalysts and
hydrogen production,11 dye-sensitized solar cells, biosensors,
photoswitches,12-15 and singlet O2 sensitization.16 To date,
there have been considerable efforts devoted to mononuclear
complexes in which excited-state properties can be easily tuned
through structural modification of either the cyclometalated
group and/or the electronic nature of the alkynyl substituent
ligand. As reported in the literature for most of the alkynyl-
cycloplatinate complexes, the luminescence origins are usually
from excited states of metal-to-ligand (cyclometalated) charge
transfer (3MLCT) mixed with some ligand-to-ligand charge
transfer (3LLCT) character. In addition, some of these com-
plexes show rich polymorphism in the solid state and also
intriguing spectroscopic and photophysical properties associated
In this area, the employment of diethynyls of type HCt
C-R-CtCH or polypyridyl-substituted acetylide groups has also
allowed the study of bi- and polymetallic systems with interesting
photophysical properties.21-24 However, despite the well-estab-
lished ability of alkynyl groups to act as bridging ligands leading
to bi- and multinuclear complexes25-43 and the numerous
studies on their optical properties,34-43 the chemistry of cyclo-
platinated fragments connected by μ-CtCR groups remains to
be fully explored. To our knowledge, only the C∧N bimetallic
complexes [anti-{Pt(κ2C,N-N∧C∧N)(μ-CtCSiMe3)}2] [N∧C∧N
= 2,6-(CdNR)2C6H3, R = C6H4OCH3-4]44 and C∧P complexes
[Pt(C∧P)(μ-CtCPh)]2 and [Pt(C∧P)(μ-CtCPh)2Pt(C6F5)2]-
[C∧P = κ2C,P-CH2C6H4P(o-tolyl)2]45 have been reported, but with
a focus on their structural characteristics and reactivity.
In this context, recent research has shown that the spectro-
scopic properties (absorption and luminescence) of binuclear
cycloplatinated Pt(II) complexes containing different types of
Received: December 15, 2010
Published: February 28, 2011
r
2011 American Chemical Society
1646
dx.doi.org/10.1021/om101172p Organometallics 2011, 30, 1646–1657
|

Organometallics
ARTICLE
Scheme 1
single or double bridging groups such as pyrazolates,46-53
diphosphines20,48,54-60 or bidentate organic anions53,60-67 are
’ RESULTS AND DISCUSSION
As summarized in Scheme 1i, the synthesis of complex 1 takes
place following a classical dehydrohalogenation reaction. Thus,
the reaction of the insoluble chloride binuclear complex
[Pt(dppyH)(μ-Cl)]2, in which dppyH- is the monodeproto-
nated 2,6-diphenylpyridinate, with excess tert-butylacetylene in
the presence of NaOMe (4 equiv of HCtCtBu/NaOMe), in
acetone at room temperature for 48 h, evolves through a
monodehydrohalogenation process to give the diplatinum com-
plex [{Pt(dppyH)}2(μ-Cl)(μ-CtCtBu)] (1) as a yellow micro-
crystalline solid in moderate yield (61%). A similar result was
obtained by using Sonogashira’s conditions [excess of HCt
CtBu in the presence of the catalytic mixture (CuI/NEt3) in
chloroform (see Experimental Section for details)]. Although the
expected second chloride/acetylide exchange does not occur,
subsequent metathesis of the chloride bridging ligand with excess
KBr or KI yielded the corresponding bromide (2) and iodide (3)
derivatives (Scheme 1ii).
very interesting, because the degree of intramolecular Pt Pt
3 3 3
and/or π π interactions in these systems can control the
3 3 3
nature of the excited state. For instance, Thompson and co-
workers have reported the influence of the pyrazolate substitu-
ents on the Pt Pt separation and on the photophysical
3 3 3
properties in a series of doubly bridged complexes [(C∧N)Pt-
(μ-pz)]2 [C∧N = 2-(4,6-difluorophenyl)pyridine].49,52 Cur-
iously, the intramolecular metal-metal-to-ligand charge transfer
(MMLCT) excited state can be tuned through regulation of the
Pt Pt spacing, but due to the larger interplanar separation
3 3 3
between the cyclometalated C∧N ligands, the intramolecular
π
π interaction between its C∧N ligands is negligible.
Our group has recently reported the first preparation of
3 3 3
monoanionic luminescent cycloplatinated complexes Q[Pt-
(bzq)(CtCR)2]68 and Q[Pt(dppy)(CtCR)]4 (Q = NBu4,
bzqH = 7,8-benzoquinoline, dppyH2 = 2,6-diphenylpyridine).
These complexes are useful precursors for the synthesis of cluster
complexes, and in previous works, we have demonstrated that the
photophysical properties of [Pt(bzq)(CtCR)2]- are signifi-
1
Complexes 1-3 were fully characterized by IR and H NMR
spectroscopy, elemental analysis, and MALDI spectrometry, and, in
the case of 1, its molecular structure has been confirmed by X-ray
crystallography. The three complexes show a characteristic νCtC
band (1956 1, 1955 2, 1963 3 cm-1) in the typical range of η2-
alkynyl CtCtBu bridging groups.71-77 Due to their limited
solubility, good 13C{1H} and 195Pt{1H} NMR spectra could not
be acquired; however, the well-resolved 1H NMR spectra reveal the
presence of only one set of dppyH signals and one resonance due to
cantly modified by neutralization with Tlþ69 or Pb2þ 70
Con-
.
tinuing our studies on polymetallic alkynyl-bridging cyclopla-
tinate systems, in this contribution we report the synthesis and
preparation of three diplatinum complexes [{Pt(dppyH)}2-
(μ-X)(μ-CtCtBu)] (X = Cl 1, Br 2, I 3) and three tetranuclear
t
clusters [Pt2(bzq)2(μ-Cl)(μ-CtCR)]2 (R = Bu 4, Ph 5,
C6H4CF3-4 6), the latter containing an unusual tetrahedral Pt4
core generated by two alkynyl and two chloride bridging ligands
t
the Bu alkynyl substituent. This pattern is consistent with a syn
orientation of the metalated dppyH ligands and a fast σ/πexchange
and stabilized by two pairs of additional intramolecular Pt Pt
3 3 3
of the CtCtBu group between both Pt centers. The molecular
and π π bonding interactions.
3 3 3
1647
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
Chart 1
Figure 1. Molecular structure of [{Pt(dppyH)}2(μ-Cl)(μ-CtCtBu)]
3
0.5CH2Cl2 (1 0.5CH2Cl2).
3
Table 1. Selected Bond Lengths and Bond Angles for
1 0.5CH2Cl2
3
Distances [Å]
Pt-NdppyH
Pt-Corth
2.058(4), 2.097(4)
1.980(4)-1.985(5)
2.4728(11)
Pt(2)-C(1)
Pt(2)-C(2)
C(1)-C(2)
C(2)-C(3)
2.191(4)
2.198(5)
1.236(6)
1.477(7)
3.1542(3)
Pt(1)-Cl(1)
Pt(2)-Cl(1)
Pt(1)-C(1)
2.5017(12)
1.960(5)
Pt(1) Pt(2)
3 3 3
complexes containing the Pt(μ-CtCR)2Pt core.34,44,45,71-80
However, the symmetrical Pt(2)-C(acetylide) side-on dis-
tances of 2.191(4) and 2.198(5) Å are relatively shorter when
compared with values previously found in related anionic
([{Pt(C6F5)2(μ-CtCPh)}2]2- [2.263(12)-2.369(15) Å]71)
or neutral ([anti-Pt(C6F5)L(μ-CtCR)]2 [L = PPh3; R = Ph,
C(OH)Ph2, C(OMe)MeEt] [2.261(6)-2.362(6) Å],74,75 [anti-
Pt(C∧P)(μ-CtCPh)]2 [2.311(3), 2.368(3) Å]45) doubly
bridged bis(alkynyl) complexes. These short distances, which
can be attributed to the small trans influence of the N(2) pyridine
atom, suggest a very strong interaction of the Pt(2) center with the
alkynyl unit [C(1)tC(2)]. The distortion form linearity of the
Pt(1)-C(1)tC(2) unit (angles at C(1) 167.3(4)° and C(2)
159.7(5)°) andtheC(1)tC(2) distance (1.236(6) Å) are, however,
within the range found in previous μ-(1κCR:η2) alkynyl bridging
complexes.34,44,45,71-80 The Pt-Cl bridging distances (2.4728(11),
2.5017(12) Å) are slightly longer than those found in [trans-Pt-
(C∧N)(μ-Cl)]2 (C∧NH = 2-(4-fluorophenyl)-6-propylpyridine;
Pt-Cl = 2.3100(6) Å (trans to N), 2.4620(6) Å (trans to C))85
and in the long end-range of chloride-bridged Pt(II) complexes.86
The angle at the chlorine atom is very acute (78.70(3)°), forcing a
Angles [deg]
NdppyH-Pt-Corth
C(1)-Pt(1)-C(7)
81.15(18),
81.47(18)
96.36(19)
C(1)-Pt(2)-C(2)
32.71(16)
Pt(1)-Cl(1)-Pt(2) 78.70(3)
98.74(18)
C(1)-Pt(2)-C(24) 101.9(18)
N(1)-Pt(1)-Cl(1) 103.48(10) Pt(1)-C(1)-Pt(2)
C(1)-Pt(1)-Cl(1) 78.19(13)
N(1)-Pt(1)-Pt(2) 134.11(10) N(2)-Pt(2)-Cl(1)
99.46(11)
73.64(12)
130.55(10)
Pt(1)-C(1)-C(2)
C(1)-C(2)-C(3)
167.3(4)
159.7(5)
C(1)-Pt(2)-Cl(1)
N(2)-Pt(2)-Pt(1)
structure of complex 1 (Figure 1, Table 1) confirmed the syn
orientation of the orthometalated groups and allowed to establish
thatofthe twopossiblesyn isomers (B, D, Chart 1); the one formed
has the chlorine atom trans to both metalated carbon atoms (B).
The selective formation of isomer B is in accordance with that
which would be expected, taking into account the known greater
trans influence of the CtCtBu relative to the chlorine. In addition,
as can be seen in Figure S1 (in the Supporting Information), the
expected larger steric interactions between the bulky tert-butyl
group and the hanging phenyl groups are also probably disfavoring
the other syn isomer (D) and the anti configuration A.
rather short Pt Pt distance of 3.1542(3) Å, and, probably due to
3 3 3
the steric demands of the hanging phenyl groups, the central
diplatinacycle is quite puckered with a dihedral angle of 71.94°
between the best platinum coordination planes. Curiously, these
values are comparable to those found in [anti-{Pt(κ2C,N-N∧C∧N)-
(μ-CtCSiMe3)}2] (3.15573(13) Å and 75.07(12)°),44 which also
contains a bulky substituent attached to the cyclometalated ligand.
However, remarkably less puckered (∼45-49.6°) or even planar
It is worth noting that although numerous examples of double
34,44,45,71-80
(μ-CtCR)2
and mixed (μ-CtCR)(μ-X) (X =
hydride,81-84 PPh2CtCR72,78) diplatinum complexes have
been reported, as far as we know, complexes 1-3 are the first
representative examples in platinum chemistry of homobimetal-
lic complexes stabilized by a rare heterobridged mixed (μ-X)-
(μ-CtCR) system. As is shown in Figure 1, due to the σ/π
coordination of the acetylide ligand, the coordination environ-
ment of both Pt atoms is different. Thus, Pt(1) completes a
distorted square-planar coordination with a σ-bonded alkynyl
carbon (Pt(1)-C(1) 1.960(5) Å), while Pt(2) is side-on bonded
to both alkynyl carbon atoms. The Pt(1)-C(1) bond distance is
comparable to those found in the anti binuclear cyclometalated
complex [anti-{Pt(κ2C,N-N∧C∧N)(μ-CtCSiMe3)}2] (1.945(3),
1.935(4) Å) reported by Elsevier et al.44 and in many other
structures with longer Pt Pt separations (3.22-3.65 Å) have been
3 3 3
observed in other bis(alkynyl) bridging complexes,75 thus reflecting
the role played by the steric demands of co-ligands in the final
geometry. The hanging Ph rings adopt a face-to-face configuration
(C(20)-C(39) 4.16(3) Å), forming a dihedral angle of about 51.05°
(see also Figure S1). This allows the chlorine atom to form two close
intramolecular contacts with both electrophilic ipso-C atoms, with
Cl C distances (3.22(1) and 3.234(9) Å) shorter than the sum of
3 3 3
the corresponding van der Waals radii (3.45 Å).87
1648
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
Figure 2. (a) View of the dimers formed for 1 0.5CH2Cl2 by intermolecular π π (black, dotted lines) and T-shaped (light blue, dotted lines)
3
3 3 3
noncovalent interactions. (b) Space-filling diagram of the extended crystal lattice of 1 0.5CH2Cl2 showing the formation of channels along the c axis.
3
Figure 3. Molecular structure of [Pt2(bzq)2(μ-Cl)(μ-CtCtBu)]2
3
1.6CHCl3 1.5CH3CH2OH (4 1.6CHCl3 1.5CH3CH2OH, A molecule).
3
3
3
Figure 4. Molecular structure of [Pt2(bzq)2(μ-Cl)(μ-CtCPh)]2
As shown in Figure 2a, the molecules associate in dimers in a
3
3CH3COCH3 (5 3CH3COCH3).
3
head-to-tail manner through intermolecular π π interactions,
3 3 3
which involve the central pyridine ring and the metalated phenyl
group of two distinct dppyH ligands (interplanar distance 3.46 Å,
dihedral angle between planes 0°), assisted by two secondary
examined similar reactions using the 7,8-benzoquinolate diplati-
num complex [Pt(bzq)(μ-Cl)]2 as starting precursor. Interest-
ingly, this change afforded the synthesis of related chloride/
alkynyl bridging complexes, which form unprecedented tetra-
nuclear photoluminescent [Pt4(bzq)4(μ-Cl)2(μ-CtCR)2] com-
pounds. As is shown in Scheme 1iii, the reactions of [Pt(bzq)-
T-shaped C-H π interactions (C C 3.53 Å, H
C
3 3 3
3 3 3
3 3 3
2.78 Å, C-H C 139.1°). In the extended crystal lattice, these
3 3 3
dimers arrange to yield circular void channels along the c axis
(Figures 2b and S2), in which the dichloromethane solvent
molecules are located.
t
(μ-Cl)]2 in acetone with 2 equiv of HCtCR (R = Bu, Ph,
The photoluminescence properties of all binuclear complexes
1-3 were investigated in solution (CH2Cl2, NCMe) and in the
solid state, both at room and low temperature (77 K). To our
surprise, despite the presence of cyclometalating and alkynyl
groups (strong field ligands), which could raise the energy of
deactivating metal-centered d-d* states, or even the relatively
C6H4CF3-4) and NaOMe at low temperature (0 °C) for 3 h
allowed the compounds [Pt2(bzq)2(μ-Cl)(μ-CtCR)]2 (R = tBu
4, Ph 5, C6H4CF3-4 6) to be obtained in low yield (14-28%), as
yellow (4) or pale orange (5, 6) microcrystalline solids. Similar
yields wereobtainedusing differentstoichiometries. Theirspectro-
scopic(1H NMR, IR), high-resolution MALDI(þ), and elemental
analyses results were consistent with the formulation given in
Scheme 1, and the molecular structures of 4 and 5 were un-
ambiguously confirmed by single-crystal X-ray diffraction (see
Figures 3, 4, S3 and Tables 2, 3, S1). Distinctive νCtC stretching
frequencies in the typical range of alkynyl bridging (1906-1922
cm-1) groups were observed in the IR spectra, and their 1H NMR
spectra showed the expected two sets of proton resonances for the
two nonequivalent types of benzoquinolate groups. Worth noting
are the two proton H2 resonances at very low field (δ 9.44, 8.67 4;
9.39, 8.67 5; 9.40, 8.73 6), as illustrated in Figure S4 for complex 5.
Complex 4 shows a singlet resonance at δ 1.34, proving the
chemical equivalence of both CtCtBu groups. The tetranuclear
short Pt Pt separation found in 1, complexes 1-3 were
3 3 3
nonemissive. At present, it is not straightforward to explain the
lack of emissive properties in these bimetallic complexes. The
nature of the possible quenching process is not clear, although it
could be attributed to easy deactivation due to the simultaneous
presence of a hanging phenyl group and weak field chloride
bridging ligand. However, the insoluble precursor [Pt(ddpyH)-
(μ-Cl)]2 exhibits in the solid state a bright orange emission [λmax
585 nm (λexc 430 nm)].
Therefore, looking for better emissive properties, and also to
further investigate the influence of the steric constraints of the
cyclometalated group on the structure of these complexes, we
1649
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
Table 2. Selected Bond Lengths and Bond Angles for 4 1.6CHCl3 1.5CH3CH2OH (A molecule)
3
3
Distances [Å]
Pt-Nbzq
2.080(7)-2.090(6)
1.982(8)-1.988(8)
1.954(8)
Cl(2)-Pt(3,4)
C(53)-C(54)
C(59)-C(60)
2.491(2), 2.477(2)
1.254(11)
1.224(11)
3.2764(4)
3.3450(7)
3.7046(4)
4.3139(4)
3.6669(6)
3.6633(5)
Pt-Corth
Pt(1)-C(53)
Pt(2)-C(59)
Pt(3)-C(59)
Pt(3)-C(60)
Pt(4)-C(53)
Pt(4)-C(54)
Cl(1)-Pt(1,2)
1.956(8)
Pt(1) Pt(3)
3 3 3
2.241(8)
Pt(2) Pt(4)
3 3 3
2.129(8)
Pt(2) Pt(3)
3 3 3
2.187(7)
Pt(2) Pt(1)
3 3 3
2.135(8)
Pt(1) Pt(4)
3 3 3
2.424(2), 2.436(2)
Pt(3) Pt(4)
3 3 3
Angles [deg]
Nbzq-Pt-Corth
80.7(3)-82.8(4)
173.0(3)
Corth-Pt-Cl
170.8(3)-174.4(3)
89.6(2)-94.2(2)
164.5(7)
N(1)-Pt(1)-C(53)
N(2)-Pt(2)-C(59)
Pt(3)-Cl(2)-Pt(4)
Pt(1)-Cl(1)-Pt(2)
Cl(1)-Pt(1)-C(53)
Cl(1)-Pt(2)-C(59)
Nbzq-Pt-Cl
171.0(3)
Pt(1)-C(53)-C(54)
Pt(2)-C(59)-C(60)
C(53)-C(54)-C(55)
C(59)-C(60)-C(61)
95.03(8)
167.1(7)
125.17(9)
95.6(2)
160.5(8)
160.1(8)
96.9(2)
Table 3. Selected Bond Lengths and Bond Angles for 5 3CH3COCH3
3
Distances [Å]
Pt-Nbzq
2.074(5)-2.106(5)
1.985(6)-1.999(7)
1.945(7)
Cl(2)-Pt(2,4)
C(27)-C(28)
C(61)-C(62)
2.4098(16), 2.4263(17)
1.253(9)
Pt-Corth
Pt(2)-C(27)
Pt(4)-C(61)
Pt(1)-C(61)
Pt(1)-C(62)
Pt(3)-C(27)
Pt(3)-C(28)
Cl(1)-Pt(1,3)
1.249(9)
1.929(7)
Pt(1) Pt(2)
3.2342(4)
3 3 3
2.218(6)
Pt(3) Pt(4)
3 3 3
3.3850(4)
2.106(6)
Pt(1) Pt(3)
3.5550(3)
3 3 3
2.262(6)
Pt(2) Pt(4)
3 3 3
4.2709(4)
2.124(6)
Pt(1) Pt(4)
3.7210(4)
3 3 3
2.4601(17), 2.4483(17)
Pt(2) Pt(3)
3 3 3
3.7448(4)
Angles [deg]
Nbzq-Pt-Corth
81.4(3)-82.4(2)
174.0(2)
Corth-Pt-Cl
170.2(2)-175.0(2)
89.15(17)-93.03(18)
166.8(5)
N(2)-Pt(2)-C(27)
N(4)-Pt(4)-C(61)
Pt(1)-Cl(1)-Pt(3)
Pt(2)-Cl(2)-Pt(4)
Cl(2)-Pt(4)-C(61)
Cl(2)-Pt(2)-C(27)
Nbzq-Pt-Cl
171.9(2)
Pt(2)-C(27)-C(28)
Pt(4)-C(61)-C(62)
C(27)-C(28)-C(29)
C(61)-C(62)-C(63)
92.81(6)
164.2(5)
124.04(8)
97.11(19)
94.61(19)
160.6(7)
160.6(7)
nature of all complexes is further confirmed by their MALDI(þ)
spectra, which exhibited the expected cluster peak (m/z 1726 4,
1766 5, and 1902 for 6), corresponding to Mþ.
The X-ray structures of 4 and 5 reveal that they are formed by
four Pt(bzq) units linked by two μ-chloride and two μ-κCR:η2-
acetylide bridging groups. In 4, the asymmetric part of the crystal
structure shows two formula units, but due to their similarity,
only one of them will be discussed (Figure 3, Table 2; see Table
S1 and Figure S3 for complete data). In both complexes, the
resulting tetrahedral platinum core is additionally stabilized by
bzq ligands, 3.232(9), 3.296(9) Å 4; 3.294(9), 3.325(9) Å 5)
bonding interactions, which are probably the driving force of the
observed final dimerization. To the best of our knowledge,
the tetrahedral Pt4 motif is unknown in platinum(II) chemistry.88
The remaining four single-bridged edges of the tetrahedral array
exhibit Pt Pt distances (3.6633(5)-4.3139(4) Å 4, 3.5550(3)-
3 3 3
4.2709(4) Å 5; see Tables 2, 3 and S1) longer than the van der
Waals limit (3.5 Å),87 excluding bonding interactions. Due to the
side-on coordination of the CtCR groups, there are two types of Pt
environments (Pt(1)/Pt(2) and Pt(3)/Pt(4) 4, Pt(2)/Pt(4) and
Pt(1)/Pt(3) 5), which, following the transphobia effect, exhibit an
analogous structural disposition to that seen in the binuclear
complex 1. Thus, Pt(1) and Pt(2) in 4 and Pt(2) and Pt(4) in 5
two short intramolecular Pt Pt (Pt(1)-Pt(3) 3.2764(4), Pt-
3 3 3
(2)-Pt(4) 3.3450(7) Å 4; Pt(1)-Pt(2) 3.2342(4), Pt(3)-
Pt(4) 3.3850(4) Å 5) and π π (minimum distance between
3 3 3
1650
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
are σ-bonded to the CR alkynyl carbon (Pt-CR 1.929(7)-
1.956(8) Å), which is located trans to the cycloplatinate N atoms
N(1), N(2) and N(2), N(4), respectively. The other two platinum
atoms are asymmetrically π-bonded (2.129(8)-2.241(8) Å 4;
2.106(6)-2.262(6) Å 5) to the triple bonds of the alkynyl units
(C(53)tC(54), C(59)tC(60) 4; C(27)tC(28), C(61)tC-
(62) 5), which adopt a trans disposition to the cycloplatinate N
atoms. As a consequence, the cyclometalated C of each Pt(bzq) unit
is coordinated trans to the chlorine atom of the corresponding
single-bridging μ-Cl group with Pt-Cl distances (2.424(2)-
2.491(2) Å 4; 2.4098(16)-2.4601(17) Å 5) that are comparable
to those seen in 1. The Pt(3)-Cl(2)-Pt(4) (4) and Pt(1)-
Cl(1)-Pt(3) (5) angles (95.03(8)° 4, 92.81(6)° 5) are more
optimal than Pt(1)-Cl(1)-Pt(2) (4, 125.17(9)°) and Pt(2)-
Cl(2)-Pt(4) (5, 124.04(8)°), and all of them wider than that
observed in complex 1 (78.70(3)°).
Table 4. Absorption Data for 1-6
a
compound
absorption, λmax/nm (103 ε M-1 cm-1
)
1
237 (46.0), 273 (36.5), 307 (22.3), 325sh (17.8), 342 (14.8),
390 (9.6), 430sh (4.1)
2
3
4
5
6
236 (39.9), 270 (30.4), 306 (16.6), 340 (13.0), 395 (7.1),
435sh (3.6)
235 (34.7), 267 (26.6), 312 (12.9), 341 (10.9), 402 (4.7),
440sh (1.9)
225 (163.7), 252sh (110.5), 310 (52.0), 370 (24.6),
379 (23.7), 425 (12.9)
223 (263.2), 240sh (168.8), 305 (73.4), 380 (25.3),
420 (19.4)
215 (196.2), 241sh (145.4), 309 (66.4), 333sh (54.0),
400 (29.1)
As can be seen, the two pairs of unbridged Pt(bzq) units adopt
an eclipsed configuration being nearly coplanar (dihedral angles
of 4.50° and 6.13° 4; 5.37° and 7.75° 5), thus favoring the
simultaneous presence of close Pt Pt and π π bonding
a Measurements were made on samples in CH2Cl2, 5 ꢀ 10-5 M.
Table 5. Emission Data for 4-6 at 77 Ka
3 3 3
3 3 3
interactions, whereas the angles between adjacent μ-bridging
Pt(bzq) units range from 70.93° ([Pt(1)] vs [Pt(2)]) to 75.74°
([Pt(3)] vs [Pt(4)]) in 4 and 76.32° ([Pt(2)] vs [Pt(4)]) to
81.50° ([Pt(1)] vs [Pt(3)]) in 5. As noted in the Introduction,
compound
media
λem/nm
τ/μs (λmax)
4
solid
575 (λexc 360-490)
580max, 675sh
23.5 (575)
20.1 (580)
CH2Cl2 5 ꢀ
10-5 M
π
π stacking is an important structural feature in platinum
(λexc 360-480)
3 3 3
chemistry with chelating N-donor ligands.11,17-20 In these
systems offset, slipped, or parallel displaced configurations are
usually preferred over eclipsed configurations to reduce the
electrostatic repulsions. Platinum complexes exhibiting a face-
5
6
solid
580 (λexc 365-485)
575 (λexc 360-460)
10.9 (580)
18.8 (575)
CH2Cl2 5 ꢀ
10-5 M
575, 640max (λexc 490)
570 (λexc 360-500)
560max, 660sh
14.2 (640)
28.3 (570)
27.5 (560),
11.0 (660)
to-face eclipsed π π stacking disposition are far less common.
3 3 3
solid
Although the factors that influence the preference for an eclipsed
configuration are still unclear, it is worth pointing out that in the
cyclometalated complexes [(RCNN)2Pt2(μ-dppm)2] reported
by Che et al.10,20,55,58 the preference for an eclipsed configuration
has been noted to increase with the extent of π conjugation in the
cyclometalating ligand.
CH2Cl2 5 ꢀ
10-5 M
(λexc 360-480)
a In the solid state, at 298 K, a weak emission was detected (600 nm 4;
630 nm 5; 560 nm 6).
We expected that the structural characteristics of these cumules
wavelength tail of each complex, the absorption, in part, could be
attributed to a triplet charge transfer transition, which becomes
partially allowed due to the enhancement of spin-orbit coupling
via the heavy metal center,4,89-91 though some contribution of
transitions due to ground-state intramolecular π π/Pt Pt
(4-6), containing η2-alkynyl bridging and both Pt Pt and
3 3 3
π
π intramolecular interactions, allow us to get more insight
3 3 3
into their relationship with the photophysical properties.
3 3 3
3 3 3
interactions could not be excluded. This suggestion is in line with
’ PHOTOPHYSICAL PROPERTIES
the presence of short Pt Pt [3.1542(3) Å] in 1 and close
3 3 3
Absorption Spectroscopy. The spectroscopic (1-6) and
photophysical (4-6) data are listed in Tables 4 and 5, respec-
tively. Room-temperature electronic spectra of complexes 1-3
and 4-6 in CH2Cl2 are given in the Supporting Information
(Figure S5) and in Figure 5, respectively. With reference to
previous Pt(II) cyclometalated acetylide complexes,3-6 the in-
tense absorption bands at λ < 350 nm are attributed to
Pt Pt [3.2342(4)-3.3850(4) Å] and π π [3.23(9)-
3 3 3
3 3 3
3.296(9) Å] interactions in 4 and 5, as revealed from X-ray
diffraction studies. It is worth noting that, in both series, the
maximum of the low-energy broad band is affected by the nature
of the bridging ligands. Thus, the band bathochromically shifts to
lower energies (402, 440sh 3< 395, 435sh 2 < 390, 430sh nm 1;425
4 < 420 5 < 400 nm 6) as the electron donor ability of the co-ligand
halide (I > Br > Cl 3-1) and acetylide (CtCtBu > CtCPh >
CtCC6H4CF3-4) increases, supporting the ligand (X/CtCR) to
ligand (cyclometalating) charge transfer contribution.
1
intraligand (ππ*) transitions located on the cyclometalated
and alkynyl ligands. The broad low-energy absorptions (with a
shoulder in 1-3) tailing to 475-500 nm are mainly ascribed to
charge transfer (CT) transitions, composed of both metal-to-
ligand (Ptfbzq) and ligand-to-ligand (alkynyl/halidefbzq)
contributions. According to time-dependent TD-DFT calcula-
tions (vide infra) on complex 5, the low-energy bands in the
Emission Spectroscopy. As commented before, the binuc-
lear halide-acetylide bridged complexes 1-3 are nonemissive.
By contrast the tetranuclear complexes are brightly emissive at
low temperatures, in both the solid state (77 K) and solution
(CH2Cl2, 77 K). At room temperature, no emission was detected
in solution, and in the solid state all three complexes exhibit only
very weak orange emissions (560-630 nm). Upon cooling the
solids at 77 K, complexes 4-6 produce brightly slightly blue-
shifted orange unstructured photoluminescence in the range
1
tetranuclear derivatives (4-6) have a remarkable MMLL0CT
character (L = alkynyl, L0 = bzq). These transitions involve
transfer of electronic charge from the system formed by the Pt
centers connected through the alkynyl group, [Pt(μ-CtCR)Pt],
to the bzq ligand bonded to the π(CtC) Pt atom. At the long-
1651
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
570-580 nm (Figure 6). The relatively long lifetimes (10.9-
28.3 μs) suggest that the emissive states are triplet in nature. In
frozen CH2Cl2 solution, the emission profile for complexes 4 and
6 is not dependent on the wavelength. Upon exciting in the range
360-480 nm, both complexes show an asymmetrical band with
the peak maximum slightly red-shifted in the case of 4 (λem 580
nm) or blue-shifted for 6 (560 nm) from that observed in the
solid state (77 K). A low-energy shoulder better resolved in
compound 6 (660 nm) is also detected (Figure S6). This fact
suggests the contribution of two close emissive states to the
emission profile, further confirmed by the measurement of different
lifetimes monitoring at 560 (27.5 μs) and 660 nm (11.0 μs) for this
complex. Dual phosphorescence is more evident in the phenylace-
tylide derivative 5. As can be seen in Figure 7, complex 5 shows a
structureless symmetrical band, slightly blue-shifted (575 nm) from
that of the solid, upon exciting in the range 360-460 nm. However,
by increasing the excitation wavelength the intensity of the emission
profile decreases and is resolved into two bands with different
lifetimes (575 nm (18.8 μs) and 640 nm (14.2 μs)), the relative
intensity of which depends on the excitation wavelength. The
excitation spectra monitoring both maxima are different, excluding
excimer-type emission formation and suggesting the presence of
close distinct emissive states, which may be attributed to a small
modification in the ground-state structure in the frozen glass. It is
likely that the freezing process causes the formation of slightly
different entities, having small intramolecular differences in the
separation of the Pt(bzq) fragments, although the presence of
intermolecular aggregates cannot be completely excluded. It is not
straightforward to assign the nature of the emissive state in these
clusters. However, the observed emissions are largely red-shifted in
relation to typical monomeric benzoquinolate complexes, such as
the anionic bis(chloride) (NBu4)[Pt(bzq)Cl2]46 (CH2Cl2, 77 K,
494 nm) or bis(alkynyl) (NBu4)[Pt(bzq)(CtCR)2]5 (CH2Cl2,
77 K, λmax R = tBu 512, Ph 505, C6H4CF3-4 492 nm) derivatives,
and appear in the range of aggregate and/or excimeric induced
emissions ascribed to ligand-ligand (π π)/Pt Pt interac-
3 3 3
3 3 3
tions (3ππ*/3MMLCT manifolds),11,17-20,46-52,54-60 suggesting
that they are likely involved in the emissive state. As shown in
Table 5, although the influence of the alkynyl group is small, the
energy maxima follow the same trend (580 nm 4 < 575 nm 5 < 560
nm 6) as that observed in the absorption maxima, which is
consistent with its contribution to the metal-alkynyl-based HOMO
[Pt(5d)/π(CtCR)]. Taking into account these observations, and
the salient features of the frontier orbitals in the optimized T1 state
on complex 5 (see below), we suggest that the emission comes from
an excited state of largely [Pt(d)/π(CtCR)/Pt(d)fbzq/bzq]
character, with the LUMO widely delocalized onto the adjacent
Figure 5. Normalized absorption spectra of 4-6 in CH2Cl2, 5 ꢀ 10-5 M.
Figure 7. Emission spectra of 5 in CH2Cl2 (5 ꢀ 10-5 M) at 77 K.
Figure 6. (a) Normalized emission spectra of 4-6 in the solid state at 77 K. (b) Normalized emission spectra of 4 at 298 (weak) and 77 K.
1652
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
Figure 8. Frontier orbital plot for [Pt2(bzq)2(μ-Cl)(μ-CtCPh)]2
Figure 9. Selected transitions and bars with the experimental spectrum
of 5 in CH2Cl2.
3
3CH3COCH3 (5 3CH3COCH3) for the ground state and excited state.
3
CH2Cl2. The calculated energy gap of the S0fS1 transition at
432 nm is close to the observed maximum found at 420 nm, and
the triplet S0fT1 centered at 472 nm lies within the visible
extended tail of the band. The S1 state is mainly characterized by
the HOMOfLUMO transition (88%), and therefore, the lowest
lying absorption can be assigned as a charge transfer from the
Pt(μ-CtCPh)Pt system to the benzoquinolate ligand located
trans to the η2-alkynyl bond (MMLL0CT). The triplet is more
complex, being attributed to the sum of several transitions (includ-
ing the HOMOfLUMO) with contribution mainly from occupied
orbitals having participation of Pt and bzq ligands to unoccupied
orbitals located on the bzq groups. Other excited states such as S3-
S5 (395-393 nm) also have additional contribution from intrali-
gand transitions between opposite bzq groups.
Pt(bzq) fragments. The intramolecular stacking of the planar “Pt-
(bzq)” units is enhanced in the excited state, playing a key role in the
emissive manifold.
DFT Calculations. The photophysics of lumophores can be
better understood by revealing the electronic structures of the
excited states. In this work, density functional theory (DFT)
calculations were performed on one of the tetranuclear com-
plexes (5), in order to get some insight into the electronic
character of this type of cluster. The geometry of complex 5 in the
ground state (S0) and excited state (T1) was optimized without
any symmetry constraints, including the phenyl groups of the
acetylide ligands. The most important geometrical parameters
are given in Table S2, together with the corresponding experi-
mental values for comparison. In the optimized ground-state
geometry, the σ Pt-C (bzq, alkynyl) and Pt-N bond lengths are
in very good agreement with those found in the structure, and the
Pt-Cl and η2-Pt-C(alkynyl) bridging bond lengths are only
slightly elongated (0.5-11%). However, the two observed
The nature of the phosphorescent emission was addressed by
optimization of the first triplet state. For comparison with the
optimized ground state S0 (and the X-ray diffraction structure),
their geometric details are also included in Table S2. In the T1 opti-
mized geometry, which exhibits a C2 symmetry, the Pt-C (σ and
Pt Pt contacts in the crystal structure are clearly overesti-
3 3 3
π) bond distances and the Pt Pt separation between the stacked
mated (3.6934; 3.6929 Å calculated vs 3.2342(4) and 3.3850(4)
Å experimental). We note that this result is not unexpected, as
dispersion and correlation effects have an important role in
3 3 3
fragments are slightly shortened. These decreases could be the
result of transferring one electron from the antibonding platinum-
alkynyl bridging based HOMO toward the two stacking Pt(bzq)
fragments. The calculated emission energy as the difference
between the energy of the T1 and the energy of the singlet state
with the triplet state optimized is 538 nm, which is only qualitatively
close to the experimental value (5 580 nm solid; 575 nm glass). As
can be seen in Figure 8, the SOMO-1 is essentially analogous to
the HOMO in the ground state, being located on the four platinum
centers (33%) and the two CtCPh groups (58%). The highest
singly occupied molecular orbital SOMO resembles the LUMO in
S0, but now is more uniformly localized on the four π* orbitals of
the bzq (22% bzq trans to σ-alkynyl and 52% bzq trans to η2-CtC)
and exhibits slightly higher Pt (15%) and alkynyl contribution
(11%). From these results it can be suggested that due to the close
proximity of the adjacent Pt(bzq) fragments, the two pairs of
stacked bzq/bzq ligands participate in the excited state. The T1 to
S0 de-excitation in the gas phase corresponds to ligand-ligand
(bzq/bzq) to metal-ligand (alkynyl) charge transfer transition.
noncovalent M M interactions,92-94 and they are not cur-
3 3 3
rently accurately accounted for in commercial DFT programs.95
Some selected frontier molecular orbitals (HOMO-3 to
LUMOþ3), together with their composition in terms of ligands
and metals, are collected in the Supporting Information (Figure
S7, Table S3). As an illustration, the HOMO and LUMO are
shown in Figure 8. As can be seen, the HOMO is mainly
delocalized over the four platinum centers (32%) and the two
phenylacetylide groups (60%), with a negligible contribution of
chloride (3%), and the LUMO is essentially localized on the π*
orbitals of the two benzoquinolate groups located in trans
disposition to the η2-alkynyl bonds.
To examine the UV-vis absorption spectrum, the lowest lying
vertical singlet excitation (50) energies and the first triplet
manifold were calculated by TD-DFT calculations based on
the optimized structure, together with the consideration of the
solvation effect (CH2Cl2). Data including energy gaps calculated
and corresponding assignments of the transitions with strong
oscillator strengths are listed in Table S4 of the Supporting
Information, and, as an illustration, Figure 9 depicts the selected
transitions as bars with the experimental spectrum of 5 in
’ CONCLUSIONS
In summary, we present here two different types of hetero-
bridged (μ-X)(μ-CtCR) assemblies based on chromophoric
1653
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
cycloplatinated “Pt(C∧N)” units and the study of their photo-
physical properties.
and near-UV ranges. Emission and excitation spectra were obtained on a
Jobin-Yvon Horiba Fluorolog 3-11 Tau-3 spectrofluorimeter, with the
lifetime measured in phosphorimeter mode. The starting materials
[Pt(bzq)(μ-Cl)]296 and [Pt(dppyH)(μ-Cl)]297 were prepared accord-
ing to reported procedures with slight modifications.
It has been shown that typical dehalogenation reactions of
[Pt(C∧N)(μ-Cl)]2 with excess NaCtCR evolve with partial
substitution, leading to selective (Cl trans to Cmetalate) hetero-
bridged (μ-Cl)(μ-CtCR) complexes, whose nuclearity strongly
depends on the steric and electronic characteristics of the
cyclometalating group. Thus, the presence of sterically demand-
ing phenyl substituents in the monoanionic dppyH ligand
generates the strongly bent diplatinum complex [{Pt(dppyH)}2-
Preparation of [{Pt(dppyH)}2(μ-Cl)(μ-CtCtBu)] (1). Method
A: Complex [Pt(dppyH)(μ-Cl)]2 (0.15 g, 0.16 mmol) in acetone (25
mL) was treated with excess HCtCtBu (80 μL, 0.65 mmol) and NaOMe
(0.035 g, 0.65 mmol) for 48 h under anhydrous conditions at room
temperature. The resulting crude was evaporated to dryness, 50 mL of
dichloromethane was added, and the mixture was filtered through Celite.
The yellow solution obtained was evaporated to ∼2 mL and treated with
15 mL of cooled iPrOH, yielding complex 1 as a yellow microcrystalline
solid (0.096 g, 61%). Method B: 80 μL ofHCtCtBu(0.65 mmol), 5 mgof
CuI (0.03 mmol), and 1 mL of distilled NEt3 were added to a
[Pt(dppyH)(μ-Cl)]2 suspension (0.15 g, 0.16 mmol) in 40 mL of
anhydrous CHCl3. After 24 h of stirring, the resulting suspension was
filtered under Ar and the clear yellow solution evaporated to dryness. The
treatment ofthe residuewith 5 mLofcoolediPrOHyielded complex 1asa
yellow microcrystalline product (0.093 g, 59%). Anal. Found: C, 49.43; H,
3.35; N, 2.66. C40H33ClN2Pt2 requires: C, 49.67; H, 3.44; N, 2.90. MS
MALDI(þ): m/z (%) 931 [M - Cl]þ (100). MS MALDI(-): m/z (%)
35 Cl- (100). IR (cm-1, Nujol): ν(CtC) 1956(w). 1H NMR (δ, 300.13
MHz, CDCl3): 7.85 (t, J ≈ 8, 2H, dppyH), 7.69 (m, 6H, dppyH), 7.45 (m,
2H, dppyH), 7.27 (m, 6H, dppyH), 7.15 (m, 4H, dppyH), 7.03 (m, 4H,
dppyH), 1.54 (s, 9H, tBu).
(μ-Cl)(μ-CtCtBu)] (1), which displays a short Pt Pt dis-
3 3 3
tance (3.15 Å). Further π π and T-shaped C-H π inter-
3 3 3
3 3 3
molecular interactions, in a head-to-tail manner, form dimers,
which additionally arrange through weak secondary hydrogen
bonds, affording a final supramolecular network having circular
channels. Similar bromide (2) and iodide (3) complexes were
accessible by simple halide-exchange reactions. Surprisingly, the
presence of the planar and more delocalized benzoquinolate
ligand leads to discrete tetranuclear aggregates [Pt2(bzq)2-
(μ-CtCR)(μ-Cl)]2 (4-6), as confirmed by X-ray studies,
having an original and new tetrahedral platinum core. The
formation of 4-6 implies a formal dimerization of the expected
monomer, which may be associated with a more favorable
orientation of the two monomers driven by the occurrence of
two pairs of simultaneous strong Pt Pt and π π stacking
3 3 3
interactions, leading to the final Pt4 core.
3 3 3
Preparation of [{Pt(dppyH)}2(μ-Br)(μ-CtCtBu)] (2). A 25
mg amount of KBr (0.20 mmol) was added to an acetone (20 mL)
suspension of [{Pt(dppyH)}2(μ-Cl)(μ-CtCtBu)] (1) (0.10 g, 0.10
mmol). After stirring for 5 h, the crude was evaporated to dryness and
treated with 50 mL of dichloromethane. The mixture was filtered
through Celite and evaporated to dryness again. Complex 2 was
obtained as a yellow solid by adding 10 mL of diethyl ether (0.066 g,
65%). Anal. Found: C, 47.63; H, 3.22; N, 2.68. C40H33BrN2Pt2 requires:
C, 47.48; H, 3.29; N, 2.77. MS MALDI(þ): m/z (%) 931 [M - Br]þ
(100). MS MALDI(-): m/z (%) 79 Br- (100). IR (cm-1, Nujol):
ν(CtC) 1955(w). 1H NMR (δ, 300.13 MHz, CDCl3): 7.84 (t, J ≈ 8,
2H, dppyH), 7.67 (m, 6H, dppyH), 7.45 (m, 2H, dppyH), 7.25 (m, 6H,
dppyH), 7.15 (m, 4H, dppyH), 7.03 (m, 4H, dppyH), 1.54 (s, 9H, tBu).
Preparation of [{Pt(dppyH)}2(μ-I)(μ-CtCtBu)] (3). Complex
[{Pt(dppyH)}2(μ-I)(μ-CtCtBu)] (3) was obtained (0.074 g, 70%) as a
microcrystalline yellow product using an identical procedure to that for 2,
treating the precursor material [{Pt(dppyH)}2(μ-Cl)(μ-CtCtBu)]
(0.10 g, 0.10 mmol) with excess KI (33 mg, 0.20 mmol). Anal. Found:
C, 45.10; H, 3.10; N, 2.71. C40H33IN2Pt2 requires: C, 45.38; H, 3.14; N,
2.65. MS MALDI(þ): m/z (%) 931 [M - I]þ (100). MS MALDI(-):
m/z (%) 127 I- (100). IR (cm-1, Nujol): ν(CtC) 1963(w). 1H NMR
(δ, 300.13 MHz, CDCl3): 7.82 (t, J ≈ 8, 2H, dppyH), 7.69 (m, 4H,
dppyH), 7.56 (m, 2H, dppyH), 7.43 (m, 2H, dppyH), 7.33-7.18 (m,
10H, dppyH), 7.05 (m, 4H, dppyH), 1.54 (s, 9H, tBu).
Both series display different photophysical properties. Thus,
while the diplatinum complexes 1-3 are nonemissive, the
tetranuclear aggregates 4-6 exhibit an interesting luminescence
behavior. The role of the alkynyl bridging group in the electronic
properties of these clusters (4-6) is supported by TD-DFT
calculations on complex 5, allowing us to assign the lowest lying
absorption mainly to a charge transfer from the Pt(μ-CtCR)Pt
system to the bzq ligand trans-disposed to the η2-alkynyl bond
(1MMLL0CT). On the other hand, the computational studies
suggest that the intramolecular stacking of the eclipsed Pt(bzq)
fragments is enhanced in the excited state, playing a key role in
the emissive manifold. The phosphorescent emission observed in
rigid media (560-580 nm, solid, CH2Cl2 glassy, 77 K) has been
attributed, according to the frontier orbitals in the optimized
T1 state of 5, to an excited state of large [Pt(d)/π(CtCR)/
Pt(d)fbzq/bzq] character, with the LUMO delocalized on the
adjacent stacked Pt(bzq) fragments. The intriguing structures
and properties of complexes 1-6 invite further investigation to
examine related systems by simple modifications of bridging and
cyclometalating groups.
’ EXPERIMENTAL SECTION
Preparation of [Pt2(bzq)2(μ-Cl)(μ-CtCtBu)]2 (4). HCtCtBu
(54 μL, 0.367 mmol) and NaOCH3 (0.020 g, 0.367 mmol) were added
over a yellow suspension of [Pt(bzq)(μ-Cl)]2 (0.150 g, 0.183 mmol) in
acetone (25 mL) at 0 °C. After 5 h of stirring, the suspension was
evaporated to dryness and the residue was treated with CH2Cl2 (25 mL).
The mixture was stirred for 30 min and filtered through Celite. The
resultant yellow solution was evaporated to ca. 2 mL, and 1 mL of EtOH
was added. After 10 h at -30 °C, 4 was obtained as a yellow solid (0.022 g,
14%). Anal. Found: C, 44.40; H, 3.01; N, 3.00. C64H50Cl2N4Pt4 requires:
C, 44.53; H, 2.92; N, 3.25. MS MALDI(þ): m/z (%) 1236 [M -
Pt(bzq)Cl(CtC-tBu)]þ (31), 1282 [M - Pt(bzq)Cl2]þ (100), 1690
[M - Cl]þ (1), 1726 [M]þ (0.5). IR (cm-1, Nujol): ν(CtC) 1922(m).
1H NMR (δ, 400.17 MHz, CDCl3, 223 K): 9.44 (d, 3JH-H = 5.2, 2H2,
bzq), 8.67 (d, 3JH-H = 5.2, 2H2, bzq), 8.29 (d, 3JH-H =7.2, 2H9, bzq), 8.08
General Comments. All reactions were carried out under an
atmosphere of dry argon, using standard Schlenk techniques and
solvents from a solvent purification system (MBraun MB SPS-800).
NMR spectra were recorded at 293 K on Bruker ARX 300 or ARX 400
spectrometers. Chemical shifts are reported in ppm relative to external
standards (SiMe4, CFCl3), and all coupling constants are given in Hz. IR
spectra were obtained on a Nicolet Nexus FT-IR spectrometer, using
Nujol mulls between polyethylene sheets. Elemental analyses were carried
out with Perkin-Elmer 2400 CHNS/O or Carlo Erba EA1110 CHNS-O
microanalyzers. Mass spectra were recorded on a Microflex MALDI-TOF
Bruker (MALDI) spectrometer operating in the linear and reflector modes
using dithranol as matrix. The optical absorption spectra were recorded
using a Hewlett-Packard 8453 (solution) spectrophotometer in the visible
1654
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
(d, 3JH-H = 7.6, 2H4, bzq), 7.85 (d, 3JH-H = 7.2, 2H9, bzq), 7.49 (AB,
3JH-H = 8.8, 2H5/6, bzq), 7.40 (pt, 2H4, 2H7, bzq), 7.28 (d, 2H5/6, bzq)
(only one of the signals is seen, the other one is overlapped with the
CHCl3 signal), 7.19 (t, 3JH-H = 9.6, 2H8, bzq), 7.00 (m, 2H8, 2H3, bzq),
of programs,100 carrying out the absorption correction at this point for
complex 5. The other absorption corrections were performed using
SORTAV101 (1) or XABS2102 (4). The structures were solved by
Patterson and Fourier methods using DIRDIF92 (1 and 5)103 or direct
methods using SHELXS-97 (4).104 The structures were refined by full-
matrix least-squares on F2 with SHELXL-97,104 and all non-hydrogen
atoms were assigned anisotropic displacement parameters. The hydro-
gen 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 for the methyl groups. For
complex 4, inspection of the symmetry (using PLATON105) suggests no
obvious space group change. Also, for complexes 4 and 5, the correct
assignment of the position of the orthometalated carbon atom of all the
bzq ligands (always in a transoidal disposition to the bridging chlorine
atoms) was confirmed by examination of the ΔMSDA values for bonds
involving these atoms105,106 (after refining the structures with the iden-
tities of the C and N atoms of each benzoquinolate group in one
position, reversed, and with 50/50 hybrid scattering factors at each of the
affected atomic sites). Several restraints have been used to model one
acetone molecule in 5. Finally, all the structures present some residual
peaks greater than 1 e Å-3 in the vicinity of the metal atoms (or the
crystallization solvent for 5), but with no chemical meaning.
Computational Details for Theoretical Calculations. DFT
and TD-DFT calculations were performed on complex 5 with Gaussian
03 (revision E.01).107 Geometries in the S0 ground state and T1 excited
state were optimized using the restricted B3LYP (S0) or unrestricted
U-B3LYP (T1) Becke’s three-parameter functional combined with
Lee-Yang-Parr’s correlation functional.108-110 The basis set used
for the platinum centers was the LanL2DZ effective core potential111
and 6-31G(d,p) for the ligand atoms. The solvent effect of the
dichloromethane in the TD-DFT calculation was taken into considera-
tion by the polarizable continuum model (PCM),112 using CPCM.113
3
6.88 (t, JH-H = 5.6, 2H3, bzq), 6.74 (m, 2H5/6, 2H7, bzq), 6.57 (AB,
3JH-H = 8.8, 2H5/6, bzq), 1.34 (s, 18H, tBu).
Preparation of [Pt2(bzq)2(μ-Cl)(μ-CtCPh)]2 (5). HCtCPh
(27 μL, 0.245 mmol) and NaOMe (0.013 g, 0.245 mmol) were added to
a suspension of [Pt(bzq)(μ-Cl)]2 (0.100 g, 0.122 mmol) in 20 mL of
acetone at 0 °C. The resulting suspension was stirred for 3 h, the volatiles
were removed in vacuo, and CH2Cl2 (20 mL) was added. After 30 min of
vigorous stirring, the mixture was filtered through Celite and the yellow
solution was evaporated to ca. 3 mL to yield 5 as a pale orange solid
(0.028 g, 26%). Anal. Found: C, 46.49; H, 2.68; N, 2.98. C68H42-
Cl2N4Pt4 requires: C, 46.24; H, 2.40; N, 3.17. MS MALDI(þ): m/z (%)
847 [Pt2(bzq)2(CtCPh)]þ (100), 1256 [M - Pt(bzq)Cl(CtCPh)]þ
(68), 1321 [M - Pt(bzq)Cl2]þ (89), 1358 [M - Pt(bzq)Cl þ Hþ]þ
(10), 1730 [M - Cl]þ (10), 1766 [M]þ (2). IR (cm-1, Nujol):
1
ν(CtC) 1937sh, 1916(m). H NMR (δ, 400.17 MHz, CDCl3): 9.39
3
3
(d, JH-H = 5.2, 2H2, bzq), 8.67 (d, JH-H = 5.2, 2H2, bzq), 7.99 (d,
3JH-H = 7.2, 2H9, bzq), 7.89 (m, 4H, Ph), 7.83 (d, JH-H = 8.0, 2H3,
3
bzq), 7.58 (d, JH-H = 7.4, 2H9, bzq), 7.51 (AB, JH-H = 8.8, 2H5/6
,
3
3
bzq), 7.41 (d, 3JH-H = 7.8, 2H7, bzq), 7.35 (d, 3JH-H = 7.8, 2H4, bzq),
7.27 (d, 2H5/6, bzq) (only one of the signals is seen, the other one is
overlapped with the CHCl3 signal), 7.11 (m, 2H8 bzq þ Ph), 6.92 (t,
3JH-H = 7.6, 2H8, bzq), 6.83 (m, 4H3, 2H5/6, bzq), 6.76 (d, 3JH-H = 7.8,
2H7, bzq), 6.63 (AB, 3JH-H = 8.8, 2H5/6, bzq).
Preparation of [Pt2(bzq)2(μ-Cl)(μ-CtCC6H4CF3-4)]2 (6).
Complex 6 was prepared as a pale orange solid in a similar way to
complex 4 starting from [Pt(bzq)(μ-Cl)]2 (0.150 g, 0.183 mmol),
HCtCC6H4CF3-4 (60 μL, 0.367 mmol), and NaOMe (0.020 g,
0.367 mmol), but in this case it was stirred for 3 h (0.049 g, 28%).
Anal. Found: C, 44.39; H, 2.33; N, 2.63. C70H40Cl2F6N4Pt4 requires: C,
44.20; H, 2.12; N, 2.95. MS MALDI(þ): m/z (%) 1324 [M -
Pt(bzq)Cl(CtCC6H4CF3-4)]þ (100), 1457 [M - Pt(bzq)Cl2]þ (60),
1866 [M - Cl]þ (22), 1902 [M]þ (5). IR (cm-1, Nujol): ν(CtC)
1914sh, 1906(s). 1H NMR (δ, 300.13 MHz, CDCl3): 9.40 (d, 3JH-H = 5.0,
’ ASSOCIATED CONTENT
S
Supporting Information. Selected bond lengths and
b
bond angles for 4 1.6CHCl3 1.5CH3CH2OH (B molecule,
Table S1). Complete reference for Gaussian 03 (revision
E.01). Comparative geometrical parameters of the experimental
3
3
3JPt-H = 30.9, 2H2, bzq), 8.73 (d, JH-H = 5.1, JPt-H = 28.8, 2H2,
bzq), 7.95 (m, 4H, bzq/C6H4CF3-4), 7.83 (d, 3JH-H = 7.8, 2H, bzq),
7.53 (m, 4H bzq/C6H4CF3-4), 7.41 (pd, 4H, bzq/C6H4CF3-4), 7.32
3
3
and the DFT-calculated structures of 5 3CH3COCH3 (Table
3
3
(pt, 4H, bzq/C6H4CF3-4), 7.12 (t, JH-H = 7.8, 4H, bzq), 6.86 (m,
S2). Composition (%) of frontier MOs in the ground state for 5
in the gas phase (Table S3). Selected low-lying singlet excited
states (Sn) and first triplet computed by TD-DFT/CPCM
(CH2Cl2) with the orbitals involved, vertical excitation energies
(nm), and assignments for 5 (Table S4). DFT-optimized co-
ordinates of 5 in the ground state (S0) (Table S5) and in the
excited state (T1) (Table S6). Crystallographic data for com-
plexes 1, 4, and 5 (Table S7). View of the molecular structure of
[{Pt(dppyH)}2(μ-Cl)(μ-CtCtBu)] 0.5CH2Cl2 (1 0.5CH2Cl2)
12H, bzq/C6H4CF3-4), 6.67 (d, 3JH-H = 8.7, 2H5/6, bzq). 19F NMR
(δ, 282.41 MHz, CDCl3): -136.3 (s, C6H4CF3-4).
X-ray Crystallography. Details of the structural analyses for all
complexes are summarized in Table S7 (in the Supporting Information).
Yellow crystals of 1, 4, and 5 were obtained by slow diffusion at -30 °C of
n-hexane (1, 5) or ethanol (4) into the respective solutions of the
complexes in CH2Cl2 (1), CHCl3 (4), or acetone (5). Three molecules
of acetone were found in the asymmetric unit of complex 5. For complexes
1 and 4, disordered solvent crystallization molecules (CH2Cl2 1, CHCl3
and EtOH 4) were observed. In spite of many attempts, we could not
resolve the disorders adequately, and both of the situations were modeled
using the program SQUEEZE.98,99 For 1, the program found three clear
voids of 747 Å3 containing 134 electrons in the unit cell, which fits well with
the presence of 0.5 molecule of dichloromethane in each asymmetric unit,
3
3
along the b axis (Figure S1). View of the supramolecular organiza-
tion of complex 1along the caxis (Figure S2). Molecular structure of
4 1.6CHCl3 1.5CH3CH2OH (B molecule, Figure S3). 2D corre-
3
3
1
lation H-1H spectrum (COSY) of 5 in CDCl3 (Figure S4).
Normalized absorption spectra of 1, 2, and 3 in CH2Cl2, 5 ꢀ 10-5
M (Figure S5). Normalized emission spectra of 6 in CH2Cl2 at 77 K
which has been, thus, included in the empirical formula (1 0.5CH2Cl2). In
3
the case of 4, the program found four voids of 1127 Å3 with 375 electrons
and another four voids of 394 Å3 with 148 electrons (which fit well with 3.2
molecules of CHCl3 and 3 molecules of CH3CH2OH in each asymmetric
unit). Thus, we have assigned 4 1.6CHCl3 1.5CH3CH2OH as the
(Figure S6). Representative frontier orbitals for 5 3CH3COCH3
3
(Figure S7). This material is available free of charge via the Internet
at http://pubs.acs.org.
3
3
empirical formula.
’ AUTHOR INFORMATION
X-ray intensity data were collected with a NONIUS-κCCD area-
detector diffractometer, using graphite-monochromated Mo KR radia-
tion. Images were processed using the DENZO and SCALEPACK suite
Corresponding Author
*Fax: (þ34) 941 299 621. E-mail: elena.lalinde@unirioja.es.
1655
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
’ ACKNOWLEDGMENT
(34) Berenguer, J. R.; Lalinde, E.; Moreno, M. T. Coord. Chem. Rev.
2010, 254, 832.
This work was supported by the Spanish MICINN (Project
CTQ2008-06669-C02-02/BQU and a grant for A.D.). S.S.
thanks the CSIC for a grant. We also thank CESGA for computer
support.
(35) Wong, W. Y. Coord. Chem. Rev. 2007, 251, 2400.
(36) Yam, V. W. W. Acc. Chem. Res. 2002, 35, 555.
(37) Yam, V. W. W.; Lo, K. K. W. Chem. Soc. Rev. 1999, 28, 323.
(38) Yam, V. W. W.; Lo, K. K. W.; Wong, K. M. C. J. Organomet.
Chem. 1999, 578, 3.
(39) Yam, V. W. W.; Lo, W. Y.; Lam, C. H.; Fung, W. K. M.; Wong,
K. M. C.; Lau, V. C. Y.; Zhu, N. Coord. Chem. Rev. 2003, 245, 39.
(40) Yam, V. W. W. J. Organomet. Chem. 2004, 689, 1393.
(41) Wong, W. Y. Dalton Trans. 2007, 4495.
(42) Chen, Z. N.; Zhao, N.; Fan, Y.; Ni, J. Coord. Chem. Rev. 2009,
253, 1.
(43) Chen, Z. N.; Fan, Y.; Ni, J. Dalton Trans. 2008, 573.
(44) Hoogervorst, W. J.; Elsevier, C. J.; Lutz, M.; Spek, A. L.
Organometallics 2001, 20, 4437.
(45) Casas, J. M.; Forniꢀes, J.; Fuertes, S.; Martín, A.; Sicilia, V.
Organometallics 2007, 26, 1674.
(46) Lai, S. W.; Chan, M. C. W.; Cheung, K. K.; Peng, S. M.; Che,
C. M. Organometallics 1999, 18, 3991.
(47) Koo, C. K.; Ho, Y. M.; Chow, C. F.; Lam, M. H. W.; Lau, T. C.;
Wong, W. Y. Inorg. Chem. 2007, 46, 3603.
(48) Lai, S. W.; Chan, M. C. W.; Cheung, T. C.; Peng, S. M.; Che,
C. M. Inorg. Chem. 1999, 38, 4046.
’ REFERENCES
(1) Muro, M. L.; Rachford, A. A.; Wang, X.; Castellano, F. N. Top.
Organomet. Chem. 2010, 29, 159.
(2) Lai, S. W.; Che, C. M. Top. Curr. Chem. 2004, 241, 27.
(3) Clark, M. L.; Diring, S.; Retailleau, P.; McMillin, D. R.; Ziessel, R.
Chem.—Eur. J. 2008, 14, 7168.
(4) Berenguer, J. R.; Lalinde, E.; Torroba, J. Inorg. Chem. 2007, 46, 9919.
(5) Fernꢀandez, S.; Forniꢀes, J.; Gil, B.; Gꢀomez, J.; Lalinde, E. Dalton
Trans. 2003, 822.
(6) Liu, R.; Chang, J.; Xiao, Q.; Li, Y.; Chen, H.; Zhu, H. Dyes Pigm.
2011, 88, 88.
(7) Yersin, H. Top. Curr. Chem. 2004, 241, 1.
(8) Evans, R. C.; Douglas, P.; Wiscom, C. J. Coord. Chem. Rev. 2006,
250, 2093.
(9) Lu, W.; Mi, B. X.; Chan, M. C. W.; Hui, Z.; Zhu, N.; Lee, S. T.;
Che, C. M. Chem. Commun. 2002, 206.
(49) Ma, B.; Li, J.; Djurovich, P. I.; Yousufuddin, M.; Bau, R.;
Thompson, M. E. J. Am. Chem. Soc. 2005, 127, 28.
(50) Rachford, A. A.; Castellano, F. N. Inorg. Chem. 2009, 48, 10865.
(51) Saito, K.; Nakao, Y.; Sakaki, S. Inorg. Chem. 2008, 47, 4329.
(52) Ma, B.; Djurovich, P. I.; Garon, S.; Alleyne, B.; Thompson,
M. E. Adv. Funct. Mater. 2006, 16, 2438.
(53) Saito, K.; Nakao, Y.; Umakoshi, K.; Sakaki, S. Inorg. Chem.
2010, 49, 8977.
(54) Koo, C. K.; Wong, K. L.; Lau, K. C.; Wong, W. Y.; Lam,
(10) Lu, W.; Mi, B. X.; Chan, M. C. W.; Hui, Z.; Che, C. M.; Zhu, N.;
Lee, S. T. J. Am. Chem. Soc. 2004, 126, 4958.
(11) Schneider, J.; Du, P.; Jarosz, P.; Lazarides, T.; Wang, X.;
Brennessel, W. W.; Eisenberg, R. Inorg. Chem. 2009, 48, 4306.
(12) Yam, V. W. W.; Tang, R. P. L.; Wong, K. M. C.; Lu, X. X.;
Cheung, K. K.; Zhu, N. Chem.—Eur. J. 2002, 8, 4066.
(13) Yang, Q. Z.; Wu, L. Z.; Zhang, H.; Chen, B.; Wu, Z. X.; Zhang,
L. P.; Tung, C. H. Inorg. Chem. 2004, 43, 5195.
(14) Siu, P. K. M.; Lai, S. W.; Lu, W.; Zhu, N.; Che, C. M. Eur.
J. Inorg. Chem. 2003, 2749.
M. H. W. Chem.—Eur. J. 2009, 15, 7689.
(55) Kui, S. C. F.; Chui, S. S. Y.; Che, C. M.; Zhu, N. J. Am. Chem. Soc.
2006, 128, 8297.
(15) Lano€e, P. H.; Le Bozec, H.; Williams, J. A. G.; Fillaut, J. L.;
Guerchais, V. Dalton Trans. 2010, 39, 707.
(56) Sun, W.; Zhu, H.; Barron, P. M. Chem. Matter 2006, 18, 2602.
(57) Lu, W.; Chan, M. C. W.; Zhu, N.; Che, C. M.; Li, C.; Hui, Z. J.
Am. Chem. Soc. 2004, 126, 7639.
(58) Kui, S. C. F.; Sham, I. H. T.; Cheung, C. C. C.; Ma, C. W.; Yan,
B.; Zhu, N.; Che, C. M.; Fu, W. F. Chem.—Eur. J. 2007, 13, 417.
(59) Shao, P.; Sun, W. Inorg. Chem. 2007, 46, 8603.
(60) Ding, J.; Pan, D.; Tung, C. H.; Wu, L. Z. Inorg. Chem. 2008,
47, 5099.
(61) Hu, J.; Lin, R.; Yip, J. H. K.; Wong, K. Y.; Ma, D. L.; Vittal, J. J.
Organometallics 2007, 26, 6533.
(62) Jude, H.; Bauer, J. A. K.; Connick, W. B. Inorg. Chem. 2005,
44, 1211.
(16) Djurovich, P. I.; Murphy, D.; Thompson, M. E.; Hernandez, B.;
Gao, R.; Hunt, P. L.; Selcke, M. Dalton Trans. 2007, 3763.
(17) Yuen, M. Y.; Roy, V. A. L.; Lu, W.; Kui, S. C. F.; Tong, G. S. M.;
So, M. H.; Chui, S. S. Y.; Muccini, M.; Ning, J. Q.; Xu, S. J.; Che, C. M.
Angew. Chem., Int. Ed. 2008, 47, 9895.
(18) Chen, Y.; Li, K.; Lu, W.; Chui, S. S. Y.; Ma, C. W.; Che, C. M.
Angew. Chem., Int. Ed. 2009, 48, 9909.
(19) Shao, P.; Li, Y.; Sun, W. J. Phys. Chem. A 2008, 112, 1172.
(20) Lu, W.; Chan, M. C. W.; Cheung, K. K.; Che, C. M. Organo-
metallics 2001, 20, 2477.
(21) Bai, F. Q.; Zhou, X.; Xia, B. H.; Liu, T.; Zhang, J. P.; Zhang,
H. X. J. Organomet. Chem. 2009, 694, 1848.
(22) Seneclanze, J. B.; Retailleau, P.; Ziessel, R. New J. Chem. 2007,
31, 1412.
(63) Ma, B.; Djurovich, P. I.; Yousufuddin, M.; Bau, R.; Thompson,
M. E. J. Phys. Chem. C 2008, 112, 8022.
(64) Develay, S.; Williams, J. A. G. Dalton Trans. 2008, 4562.
(65) Guo, Z.; Chan, M. C. W. Chem.—Eur. J. 2009, 15, 12585.
(66) Koshiyama, T.; Omura, A.; Kato, M. Chem. Lett. 2004, 33, 1386.
(67) Tzeng, B. C.; Chiu, T. H.; Lin, S. Y.; Yang, C. M.; Chang, T. Y.;
Huang, C. H.; Chang, A. H. H.; Lee, G. H. Cryst. Growth Des. 2009,
9, 5356.
(23) Shao, P.; Li, Y.; Yi, J.; Pritchett, T. M.; Sun, W. Inorg. Chem.
2010, 49, 4507.
(24) Shao, P.; Li, Y.; Azenkeng, A.; Hoffmann, M. R.; Sun, W. Inorg.
Chem. 2009, 48, 2407.
(25) Belluco, U.; Bertani, R.; Michelin, R. A.; Mozzon, M.
J. Organomet. Chem. 2000, 600, 37.
(26) Lang, H.; George, D. S. A.; Rheinwald, G. Coord. Chem. Rev.
2000, 206-207, 101.
(27) Lang, H.; Stein, T. J. Organomet. Chem. 2002, 641, 41.
(28) Buschbeck, R.; Low, P. J.; Lang, H. Coord. Chem. Rev. 2011,
255, 241.
(68) Fernꢀandez, S.; Forniꢀes, J.; Gil, B.; Gꢀomez, J.; Lalinde, E. Dalton
Trans. 2003, 822.
(69) Forniꢀes, J.; Fuertes, S.; Martín, A.; Sicilia, V.; Gil, B.; Lalinde, E.
Dalton Trans. 2009, 2224.
(70) Berenguer, J. R.; Díez, A.; Fernꢀandez, J.; Forniꢀes, J.; García, A.;
Gil, B.; Lalinde, E.; Moreno, M. T. Inorg. Chem. 2008, 47, 7703.
(71) Forniꢀes, J.; Gꢀomez-Saso, M. A.; Lalinde, E.; Martínez, F.;
Moreno, M. T. Organometallics 1992, 11, 2873.
(72) Ara, I.; Falvello, L. R.; Fernꢀandez, S.; Forniꢀes, J.; Lalinde, E.;
Martín, A.; Moreno, M. T. Organometallics 1997, 16, 5923.
(73) Falvello, L. R.; Forniꢀes, J.; Gꢀomez, J.; Lalinde, E.; Martín, A.;
Martínez, F.; Moreno, M. T. J. Chem. Soc., Dalton Trans. 2001, 2132.
(29) Long, N. J.; Williams, C. K. Angew. Chem., Int. Ed. 2003,
42, 2586.
(30) Bruce, M. I.; Low, P. J. Adv. Organomet. Chem. 2004, 50, 179.
(31) Rosenthal, V. Angew. Chem., Int. Ed. 2003, 42, 1794.
(32) Mak, T. C. W.; Zhao, L. Chem. Asian J. 2007, 2, 456.
(33) Mathur, P.; Chatterjee, S.; Avasare, V. D. Adv. Organomet.
Chem. 2008, 55, 201.
1656
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657

Organometallics
ARTICLE
(74) Berenguer, J. R.; Forniꢀes, J.; Lalinde, E.; Martín, A.; Serrano, B.
J. Chem. Soc., Dalton Trans. 2001, 2926.
(108) Becke, A. D. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38, 3098.
(109) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B: Condens. Matter
Phys. 1988, B37, 785.
(110) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(111) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284.
(112) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995.
(113) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. J. Comput. Chem.
2003, 24, 669.
(75) Berenguer, J. R.; Forniꢀes, J.; Martínez, F.; Cubero, J. C.; Lalinde,
E.; Moreno, M. T.; Welch, A. J. Polyhedron 1993, 12, 1797.
(76) Falvello, L. R.; Forniꢀes, J.; Martín, A.; Gꢀomez, J.; Lalinde, E.;
Moreno, M. T.; Sacristꢀan, J. Inorg. Chem. 1999, 38, 3116.
(77) Forniꢀes, J.; Lalinde, E.; Martín, A.; Moreno, M. T. J. Chem. Soc.,
Dalton Trans. 1994, 135.
(78) García, A.; Lalinde, E.; Moreno, M. T. Eur. J. Inorg. Chem.
2007, 3553.
(79) Aullꢀon, G.; Alvarez, S. Organometallics 2002, 21, 2627.
(80) Berenguer, J. R.; Forniꢀes, J.; Lalinde, E.; Martínez, F. J.
Organomet. Chem. 1994, 470, C15.
(81) Ara, I.; Falvello, L. R.; Forniꢀes, J.; Lalinde, E.; Martín, A.;
Martínez, F.; Moreno, M. T. Organometallics 1997, 16, 5392.
(82) Berenguer, J. R.; Bernechea, M.; Forniꢀes, J.; Lalinde, E.;
Torroba, J. Organometallics 2005, 24, 431.
(83) Berenguer, J. R.; Bernechea, M.; Lalinde, E. Organometallics
2007, 26, 1161.
(84) Berenguer, J. R.; Bernechea, M.; Lalinde, E. Dalton Trans.
2007, 2384.
(85) Crosby, S. H.; Clarkson, C. J.; Deeth, R. J.; Rourke, J. P.
Organometallics 2010, 29, 1966.
(86) Aullꢀon, G.; Ujaque, G.; Lledꢀos, A.; Alvarez, S.; Alemany, P.
Inorg. Chem. 1998, 37, 804.
(87) Winter, M. In WebElementsTM; The Periodic Table of the www;
http://www.webelements.com: University of Scheffield: UK, accesed
Nov 2010.
(88) Jain, V. J.; Jain, L. Coord. Chem. Rev. 2010, 254, 2848.
(89) Díez, A.; Forniꢀes, J.; Fuertes, S.; Larraz, C.; Lalinde, E.; Lꢀopez,
J. A.; Martín, A.; Moreno, M. T.; Sicilia, V. Organometallics 2009,
28, 1705.
(90) Díez, A.; Forniꢀes, J.; Larraz, C.; Lalinde, E.; Lꢀopez, J. A.; Martín,
A.; Moreno, M. T.; Sicilia, V. Inorg. Chem. 2010, 49, 3239.
(91) Develay, S.; Blackburn, O.; Thompson, A. L.; Williams, J. A. G.
Inorg. Chem. 2008, 47, 11129.
(92) Grimme, S.; Djukic, J. P. Inorg. Chem. 2010, 49, 2911.
(93) Schwabe, T.; Grimme, S.; Djukic, J. P. J. Am. Chem. Soc. 2009,
131, 14156.
(94) Hyla-Kryspin, I.; Grimme, S.; Djukic, J. P. Organometallics
2009, 28, 1001.
(95) Phillips, V.; Willard, K. J.; Golen, J. A.; Moore, C. J.; Rheingold,
A. L.; Doerrer, L. H. Inorg. Chem. 2010, 49, 9265.
(96) Pregosin, P. S.; Wombacher, F.; Albinati, A.; Lianza, F. J.
Organomet. Chem. 1991, 418, 249.
(97) Cave, G. W. V.; Fanizzi, F. P.; Deeth, R. J.; Errington, W.;
Rourke, J. P. Organometallics 2000, 19, 1355.
(98) Van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(99) Spek, A. L. SQUEEZE, incorporated into PLATON: A Multi-
purpose Crystallographic Tool; Utrecht University: Utrecht, The Neth-
erlands, 2005.
(100) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter,
C. V., Jr., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol.
276A, p 307.
(101) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(102) Parkin, S.; Moezzi, B.; Hope, H. J. Appl. Crystallogr. 1995,
28, 53.
(103) Beursken, P. T.; Beursken, G.; Bosman, W. P.; de Gelser, R.;
García-Granda, S.; Gould, R. O.; Smith, J. M. M.; Smykalla, C. The
DIRDIF92 Program System; University of Nijmegen: The Netherlands,
1992.
(104) Sheldrick, G. M. SHELX-97 a Program for the Refinement of
Crystal Structures; University of G€ottingen: Germany, 1997.
(105) Speck, A. L. Acta Crystallogr., Sect. A 1990, 46, c34.
(106) Hirshfeld, F. L. Acta Crystallogr., Sect. A 1976, 32, 239.
(107) Frisch, M. J.; et al. Gaussian 03, Revision E.01; Gaussian, Inc.:
Wallingford, CT, 2004 (see Supporting Information for complete
citation).
1657
dx.doi.org/10.1021/om101172p |Organometallics 2011, 30, 1646–1657