Synthesis, characterization, and computational study of complexes containing Pt···H hydrogen bonding interactions

Article abstract of DOI:10.1021/ic402036p

Complexes [Pt(C₆F₅)(bzq)L] (bzq = 7,8-benzoquinolinate; L = 8-hydroxyquinoline, hqH (1); 2-methyl-8- hydroxyquinoline, hqH′ (2)) have been prepared by replacing the labile acetone ligand in the starting material [Pt(C₆F₅)(bzq) (Me₂CO)]. The ¹H NMR spectra of 1 and 2 show that the signals attributable to the hydroxyl proton of the hqH or hqH′ ligands are displaced downfield 2.64 ppm for 1 and 2.74 ppm for 2 with respect to the respective free ligands. Moreover, in both complexes the signals present platinum satellites with J(Pt,H) coupling constant of 67.0 Hz for 1 and 80.6 Hz for 2. All these features are indicative of the existence of Pt···H-O hydrogen bonds in solution for these complexes. The structures of complexes 1 and 2 have been established by an X-ray diffraction study and allow us to confirm the existence of these interactions in the solid state too. Thus, in both cases the hydroxyl hydrogen atom is pointing toward the metal center, and the measured geometric parameters involving this hydrogen are Pt-H = 2.09(4) A, O-H = 0.94(4) A, Pt-H-O 162(4), for 1, and Pt-H = 2.10(4) A, O-H = 0.91(4) A, Pt-H-O 162(4), for 2, all of which are fully compatible with a hydrogen bond system. Complexes 1 and 2 and the analogues [Pt(C₆F₅)₃(hqH)]^- (A) and [Pt(C₆F₅)₃(hqH′)]^- (B), prepared some time ago in our laboratory and also showing Pt·· ·H-O hydrogen bonds, have been the object of theoretical calculations to obtain better insight into the Pt···H interactions. Their density functional theory (DFT) calculated structures show excellent agreement with the X-ray determined ones (1, 2, and B). Topological analyses of the electron density function (ρ(r)) have been performed on the four complexes according to Bader's Atoms In Molecules theory. These analyses reveal a bond path that relates the platinum atom and the hydroxyl hydrogen atom, as well as the corresponding bond critical points. The values of the Laplacian ?²ρ(r) and local energy density H(r) indicate that these are closed shell, electrostatic interactions, but with partial covalence. The deprotonation of the OH fragment in 1 and 2 with BuLi leads to the formation of the unexpected trinuclear complexes (NBu₄)[Li{Pt(C₆F ₅)(bzq)(L)}₂] (L = hq (3), hq′ (4)). The X-ray structures of these have shown a change in the coordination of the deprotonated hq and hq′, which are now bonded to the Pt atoms through their O atoms, and which are bridging the Pt and Li metal atoms.

Full text of DOI:10.1021/ic402036p

Article
pubs.acs.org/IC
Synthesis, Characterization, And Computational Study of Complexes
Containing Pt···H Hydrogen Bonding Interactions
́
Miguel Baya, Ursula Belío, and Antonio Martín*
́ ́ ́
Instituto de Síntesis Química y Catalisis Homogenea (ISQCH), Departamento de Química Inorganica, Universidad de
Zaragoza−CSIC, 50009 Zaragoza, Spain
S
* Supporting Information
ABSTRACT: Complexes [Pt(C6F5)(bzq)L] (bzq = 7,8-benzoquino-
linate; L = 8-hydroxyquinoline, hqH (1); 2-methyl-8-hydroxyquinoline,
hqH′ (2)) have been prepared by replacing the labile acetone ligand in
the starting material [Pt(C6F5)(bzq)(Me2CO)]. The 1H NMR spectra
of 1 and 2 show that the signals attributable to the hydroxyl proton of
the hqH or hqH′ ligands are displaced downfield 2.64 ppm for 1 and
2.74 ppm for 2 with respect to the respective free ligands. Moreover, in
both complexes the signals present platinum satellites with J(Pt,H)
coupling constant of 67.0 Hz for 1 and 80.6 Hz for 2. All these features
are indicative of the existence of Pt···H−O hydrogen bonds in solution
for these complexes. The structures of complexes 1 and 2 have been
established by an X-ray diffraction study and allow us to confirm the
existence of these interactions in the solid state too. Thus, in both cases
the hydroxyl hydrogen atom is pointing toward the metal center, and
the measured geometric parameters involving this hydrogen are Pt−H = 2.09(4) Å, O−H = 0.94(4) Å, Pt−H−O 162(4)°, for 1,
and Pt−H = 2.10(4) Å, O−H = 0.91(4) Å, Pt−H−O 162(4)°, for 2, all of which are fully compatible with a hydrogen bond
system. Complexes 1 and 2 and the analogues [Pt(C6F5)3(hqH)]− (A) and [Pt(C6F5)3(hqH′)]− (B), prepared some time ago in
our laboratory and also showing Pt···H−O hydrogen bonds, have been the object of theoretical calculations to obtain better
insight into the Pt···H interactions. Their density functional theory (DFT) calculated structures show excellent agreement with
the X-ray determined ones (1, 2, and B). Topological analyses of the electron density function (ρ(r)) have been performed on
the four complexes according to Bader’s Atoms In Molecules theory. These analyses reveal a bond path that relates the platinum
atom and the hydroxyl hydrogen atom, as well as the corresponding bond critical points. The values of the Laplacian ∇2ρ(r) and
local energy density H(r) indicate that these are closed shell, electrostatic interactions, but with partial covalence. The
deprotonation of the OH fragment in 1 and 2 with BuLi leads to the formation of the unexpected trinuclear complexes
(NBu4)[Li{Pt(C6F5)(bzq)(L)}2] (L = hq (3), hq′ (4)). The X-ray structures of these have shown a change in the coordination
of the deprotonated hq and hq′, which are now bonded to the Pt atoms through their O atoms, and which are bridging the Pt
and Li metal atoms.
in solution5 mention the possibility of metal centers being
INTRODUCTION
■
involved in hydrogen bridging, these M···H−X systems have
been recognized and understood from the early 1990s and now
they are well established.2,3,6−10 They are substantially similar
to “classic” hydrogen bonds, that is, the metal atom is the Lewis
base that has a filled orbital with an electron pair that can
interact with an electropositive hydrogen atom. Using a
molecular orbital method language, the electron pair is donated
to create a 3-center−4-electron (3c-4e) system. These
hydrogen bonds therefore are favored by electron rich metals
such as late transition metals, especially in low oxidation states.
Pt(II) complexes have been found to be particularly suited to
this interaction because of their planar nature and the electron
The existence of interactions between metal centers and
hydrogen atoms attached to main group elements (especially C,
N, and O) has been recognized since the early 1980s.1−3 The
first of these types of interactions to be studied and understood
were the “agostic” interactions.1,4 In these, the metal center acts
as a Lewis acid, generally receiving electron density from a C−
H bond and resulting in a 3-center−2-electron (3c-2e) bond
system. The three centers are the metal and the C and H atoms,
and the two electrons are those in the C−H bond. An empty
orbital of the metal is involved to house the donated electron
density. A characteristic of agostic interactions is the upfield
1
displacement in the H NMR spectra of the signal of the
2
pair housed in the 5dz orbital, available to participate in the
hydrogen involved.
In the second type of M···H interactions a transition metal
atom is acting as a proton acceptor in a formally hydrogen
bonding interaction. Although some early reports on IR studies
Received: August 7, 2013
© XXXX American Chemical Society
A
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Pt···H−X 3c-4e system of the hydrogen bond. The signal of the
proton involved in the M···H−X hydrogen bonding moves
molecule has been reported in the complex trans-[PtCl2(NH3)-
(N-Glycine)].9 The structure also presents an intramolecular
Pt···H−N interaction. Interestingly, theoretical studies of this
system conclude that dispersion forces constitute the main
component of the intermolecular Pt···H−O contact9,18,20 and
also support the persistence of this interaction in solution.19,20
In the course of previous research, we prepared anionic tris
pentafluorophenyl Pt(II) complexes containing Pt···H−X (X =
O, C) hydrogen bonds.6 In this paper we have explored the use
of neutral Pt(II) pentafluorophenyl complexes which also
contain the 7,8-benzoquinolate chelate planar ligand as
precursors for complexes containing Pt···H−O hydrogen
bonding with success. The overall charge in the complex and
the different steric requirements of the ligands surrounding the
metal center might influence the characteristics of the Pt···H
interactions, which have been studied both in the solid state (X-
ray) and in solution (NMR). Moreover, theoretical calculations
have been performed to obtain a greater insight into the nature
of the Pt···H interaction. For comparative purposes, studies on
A and B, a couple of similar complexes previously prepared in
our laboratory6 (see Scheme 1) have also been included in this
paper. The study of the reactivity of the Pt···H complexes
toward hydrogen abstractors has resulted in unexpected
polynuclear complexes which have also been fully characterized.
Synthesis and Characterization of the Complexes
[Pt(C6F5)(bzq)L] {L = hqH, 8-hydroxyquinoline (1); L =
hqH′, 2-methyl-8-hydroxyquinoline (2)}. Complex [Pt-
(C6F5)(bzq)(Me2CO)] (bzq = 7,8-benzoquinolinate) has
proven to be a suitable precursor for the preparation of
complexes [Pt(C6F5)(bzq)L] because the acetone group is
easily replaced with other L ligands.22,23 Thus, the addition of
equimolecular amounts of 8-hydroxyquinoline (hqH) or 2-
methyl-8-hydroxyquinoline (hqH′) to dichloromethane solu-
tions of [Pt(C6F5)(bzq)(Me2CO)] under protective Ar
atmosphere and at 273 K allows one to obtain, after 15 min
of stirring, the corresponding complexes [Pt(C6F5)(bzq)L] {L
= hqH (1), hqH′ (2), see Scheme 1} as yellow solids which
precipitate after partial evaporation of the solvent.
1
downfield in the H NMR spectra, which is a common feature
of all hydrogen bond systems.
The terms “anagostic”1,11 or “pregostic”12 have been used to
refer to M···H−C interactions which clearly do not fit the
“agostic” definition. Structurally and spectroscopically, they are
more similar to the hydrogen bonding M···H−X systems, but
given the low ability of the C atom to act as a proton donor in a
C−H fragment, their bonding description is still unclear.
Nevertheless, some theoretical studies would seem to indicate
8
2
that the dz orbital in d square planar complexes is not involved
in the interaction in certain cases.11
While a fair amount of structural solid state studies have been
carried out by X-ray or neutron diffraction,9,13,14 there is
relatively scarce evidence of the existence of M···H hydrogen
bridging in solution achieved through simultaneous observation
of the downfield on the H signal and M-H coupling.6,15−17 The
highest value of a J(Pt,H) coupling constant (180 Hz) has been
found in complex [PtBr{1-C10H6(NMe2)-8-C,N}{1-
C10H6(NHMe2)-8-C,H}].15 In this example, the hydrogen
involved is very acidic because of the ammonic nature of the N
donor fragment. Smaller values of the coupling constants have
been reported for amino donor fragments, such as in [Pt(C6H3-
2,6E2)(8-acetylaminequinoline)]+ (E = PPh2, J(Pt,H) = 55 Hz;
NMe2, J(Pt,H) = 33 Hz).16 Intermediate values of J(Pt,H) (69
and 88 Hz, respectively) have been found in anionic complexes
[Pt(C6F5)3(hqH)]− (A) and [Pt(C6F5)3(hqH′)]− (B, see
Scheme 1),6 which contain the 8-hydroxyquinoline (hqH) or
Scheme 1
The IR spectra of complexes 1 and 2 confirm the
replacement of the acetone in the starting material, since the
νCO vibration band corresponding to this ligand which appears
at 1669 cm−1 is no longer present, and bands assignable to the
hqH and hqH′ ligands can now be observed (see Experimental
Section).
2-methyl-8-hydroxyquinoline (hqH′) ligands, with a O−H
donor fragment. Usually, with even less acidic C−H protons
such as the ones contained in the 7,8-benzo[h]quinoline
(bzqH) ligand of complex [Pt(C6F5)3(bzqH)]−,6 the value
observed for the Pt−H coupling constant is even lower (22
Hz). Nevertheless, higher J(Pt,H) can be observed when the
C−H group is strongly oriented toward the Pt atoms by the
geometry of the ligand. This is the case of the complexes
[Pt(Me3Si-BAM)Me2] and [Pt(Me3Si-BAM)Ph2] (BAM =
bis(7-azaindol-1-yl)methane)17 for which values of 61.0 and
44.1 Hz, respectively, have been reported. Theoretical studies
have also been carried on these complexes containing M···H−X
hydrogen bonds.2,9,11,18−21 They indicate that most systems
show an important electrostatic contribution interaction, as in
“classic” hydrogen bonds. Nevertheless, it has been suggested
that the importance of a covalent contribution increases as the
M···H distance shortens and thus the strength of the interaction
increases.2,11
The 19F NMR spectra of 1 and 2 present the same pattern of
five signals, indicating that all the five fluorine atoms of the
C6F5 ligands are inequivalent. The two ortho-F appear at lower
field with platinum satellites. At higher field, one signal for the
para-F and one for each of the meta-F can be observed. The
inequivalence of the fluorine atoms in analogous positions of
the pentafluorophenyl rings indicates the difficulty of this group
to rotate around the Pt−Cipso, probably because of the bulkiness
and rigidity of the neighboring chelating bzq ligand.
The 1H NMR spectra of these complexes are more
interesting. Figures 1 and 2 show these spectra for complexes
1 and 2, respectively. They show the signals corresponding to
the hydroxyquinoline ligands in the aromatic area besides the
ones attributed to the bzq ligand with the expected relative
intensity. Moreover, in the case of complex 2, a singlet signal
corresponding to the methylic hydrogen atoms appears at 3.40
ppm. However, the most striking feature of these spectra is the
presence at low field of a sharp signal with platinum satellites
assignable to the hydroxylic proton of the hydroxyquinoline
Recently, the first crystallographic evidence by neutron
difraction of intermolecular hydrogen bonding involving a d8
metal center and a hydrogen atom of a crystallization water
B
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1
Figure 1. H NMR spectrum of 1. Inset: Detail of the signal of the OH hydrogen atom showing the 195Pt satellites.
1
Figure 2. H NMR spectrum of 2. Inset: Detail of the signal of the OH hydrogen atom showing the 195Pt satellites.
ligands. This signal appears at 10.92 ppm in 1, with a coupling
constant J(Pt,H) = 67.0 Hz, and at 10.99 ppm in 2, with a
coupling constant J(Pt,H) = 80.6 Hz. The downfield displace-
ment of these signals with respect to the free ligands6 (2.64
ppm for 1 and 2.74 ppm for 2) and, most importantly, the
existence of the Pt−H coupling, accounts for the existence of
the Pt···H−O hydrogen bond in solution for complexes 1 and
2. Similar Pt−H coupling constants have been reported for the
related complexes [Pt(C6F5)3(hqH)]− (A) and [Pt-
(C6F5)3(hqH′)]− (B),6 (69 Hz, and 88 Hz, respectively, see
Table 1). Nevertheless, the chemical displacement of the signal
of the hydrogen involved in the interaction is greater (3.70 ppm
and 4.09 ppm respectively).
C
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Table 1. Relevant Structural and Magnetic Parameters
Illustrating the Pt···H−O Contacts in Complexes 1, 2, A, and
a
B
b
b
complex
Pt···H (X-ray), Å
1
2
A
B
2.09(4)
2.18
2.10(4)
2.14
2.19
2.11
Pt···H (DFT calculations, gas
2.16
phase), Å
1
δ H NMR (CD2Cl2), ppm
10.92
10.99
10.95
12.22
11.95
12.34
12.07
δ 1H NMR (DFT calculations, gas 10.71
phase), ppm
1
Δδ H NMR (CD2Cl2), ppm
+2.64
+3.02
+2.74
+2.89
+3.70
+4.26
+4.09
+4.01
1
Δδ H NMR (DFT calculations,
gas phase), ppm
JPt−H, Hz
67.0
80.6
1.47
1.28
69
88
c
T1, min central signal, s
1.55
c
T1, min satellites, s
1.45
ΔT1, min
−0.10
−0.19
a
b
c
See Experimental Section for further details. Reference 6. T1, min
Figure 4. View of the molecular structure of the complex
[Pt(C6F5)(bzq)(hqH′)] (2). Ellipsoids are drawn at their 50%
probability level.
found at 193 K.
The close vicinity of the platinum center and the hydroxylic
hydrogen atom is also manifest in another magnetic property of
the latter, the relaxation rate.24 Thus the I = 1/2 platinum
isotope in the 195Pt···H−O isotopomer makes an additional
contribution to the relaxation rate of the corresponding
hydrogen atom. As a consequence, the T1(min) values measured
for the satellite signals (which are due to the 195Pt···H−O
isotopomer) are slightly shorter than those measured for the
central signal (which belong to the rest of the platinum
isotopomers).25 In CD2Cl2 as solvent, the measured T1(min)
values for the central singlet are 1.55 (1) and 1.45 (2) s,
whereas those measured for the doublet corresponding to the
195Pt isotopomers are 1.45 (1) and 1.28 (2) s. All those
magnetic parameters are summarized in Table 1
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
[Pt(C6F5)(bzq)(hqH)]·CH2Cl2 (1·CH2Cl2) and
[Pt(C6F5)(bzq)(hqH′)]·CHCl3 (2·CHCl3)
1·CH2Cl2
1.995(3)
2·CHCl3
1.990(2)
Pt−C(17)
Pt−C(1)
Pt−N(1)
Pt−N(2)
Pt−H(1)
O−C(27)
O−H(1)
2.012(3)
2.089(2)
2.144(2)
2.09(4)
2.011(2)
2.083(2)
2.176(2)
2.10(4)
1.355(4)
0.94(4)
1.357(3)
0.91(4)
C(17)−Pt−C(1)
C(17)−Pt−N(1)
C(1)−Pt−N(1)
C(17)−Pt−N(2)
C(1)−Pt−N(2)
N(1)−Pt−N(2)
Pt−H(1)−O
91.76(12)
81.96(11)
173.52(10)
174.89(10)
93.17(10)
93.14(9)
92.57(9)
81.80(8)
174.24(8)
174.90(8)
90.03(8)
95.67(7)
The structures of complexes 1 and 2 have been established
by single crystal X-ray diffraction studies. Figures 3 and 4 show
162(4)
162(4)
coplanar to the Pt basal square planes (dihedral angle 3.4(1)°
for 1 and 4.4(1)° for 2), while hqH and C6F5 ligands are almost
perpendicular to the latter (dihedral angles are 80.7(1)° and
78.5(1)° respectively for 1 and 84.0(1)° and 84.6(1)° for 2).
With these dispositions, the OH fragments of the hqH and
hqH′ ligands have optimal orientations for the hydrogen atoms
to establish interactions with the Pt centers. It is noteworthy
that the quality of the X-ray diffraction data collected has
allowed, in both structures, to find and refine the position of
these hydrogen atoms (H(1)) without restraints, and that from
all the possible orientations, the hydrogen atoms are pointing
toward the metal centers. Thus, the measured geometric
parameters involving H(1) are Pt−H(1) = 2.09(4) Å, O−H(1)
= 0.94(4) Å, Pt−H(1)−O 162(4)° for 1 and Pt−H(1) =
2.10(4) Å, O−H(1) = 0.91(4) Å, Pt−H(1)−O 162(4)° for 2. If
the O−H(1) distances are normalized to 0.993,26 then the Pt−
H(1) distances are 2.04 Å in 1 and 2.07 Å in 2. In any case,
these parameters are fully consistent with the existence of Pt···
H(1)−O hydrogen bond systems in the solid state;2,3 in fact,
the Pt−H(1) distances found in 1 and 2 (2.09(4) Å, 2.10(4) Å)
are the shortest reported for this kind of hydrogen bonding.
Figure 3. View of the molecular structure of the complex
[Pt(C6F5)(bzq)(hqH)] (1). Ellipsoids are drawn at their 50%
probability level.
views of the structures of 1 and 2 respectively, and Table 2 lists
a selection of relevant bond distances and angles for both
complexes. As expected, 1 and 2 are square planar complexes in
which the pentafluorophenyl ligand is located trans to the
nitrogen donor atom of the cyclometalated bzq ligand, as has
previously been found in complexes with the formula
[Pt(C6F5)(bzq)L].23 In both structures, the bzq planes are
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Table 3. Comparison of Selected Distances (Å) and Angles (deg) Obtained for 1 (X-ray, DFT), 2 (X-ray, DFT),
[Pt(C6F5)3(hqH)]− A (DFT), and B (X-ray,6 DFT)
Pt···H
H−O
O−C
Pt···H−O
H−O−C
Pt···H−O−C
1 (X-ray)
1-DFT
2.09(4)
2.18
0.94(4)
0.983
0.91(4)
0.983
0.99
1.355(4)
1.338
162(4)
153.6
162(4)
152.4
157.8
160.7
153.9
110.2
112.7
109.8
111.7
113.0
108.4
113.1
−29.1
−45.3
−29.3
−50.1
−20.8
−32.0
−33.7
2 (X-ray)
2-DFT
2.10(4)
2.15
1.357(3)
1.343
A-DFT
2.16
1.329
B (X-ray)6
B-DFT
2.19
0.84
1.354(6)
1.331
2.11
0.99
Slightly longer distances have been found in complexes
that the hydrogen atom of the hydroxyl fragment is oriented
toward the platinum atom resulting in a very short distance of
2.11 Å (2.19 Å, X-ray), and all the Pt···H−O structural
parameters are consistent with a hydrogen bonding 4e-3c type
interaction (see Table 3). The optimized geometry of the
analogous A (A-DFT) is very similar, thus supporting the
existence of a Pt···H−O hydrogen bonding system.
[PtBr{1-C10H6(NMe2)-8-C,N}{1-C10H6(NHMe2)-8-C,H}]
(2.11(5) Å),15 B (2.19 Å),6 and [Pt(C6H3-2,6(PPh2)2)(8-
acetylaminequinoline)](CF3SO3) (2.2(1) Å).16 Nevertheless,
fine comparisons of the Pt−H distances must be performed
with caution because of the inherent uncertainty of the location
of the hydrogen atoms from single crystal X-ray diffraction
studies. As expected, the Pt−H distance found in the structure
of trans-[PtCl2(NH3)(N-Glycine)]·H2O, determined by neu-
tron diffraction,9 is much longer (2.885(3) Å), since it arises
from an intermolecular interaction between the Pt center and a
crystallization water molecule.
Computational Studies. The molecular structures of the
complexes 1, 2, A, and B have been optimized by density
functional theory (DFT) methods, at the M06 level of theory
(see Experimental Section for further details). A comparison of
the most relevant structural parameters of 1, 1-DFT, 2, 2-DFT,
A-DFT, B, and B-DFT is included in Table 3. Views of the
optimized structures for 1-DFT, 2-DFT, A-DFT, and B-DFT
are included in Figure 5. The geometries of 1-DFT and 2-DFT
The coherence observed for these structures has led us to
investigate the Pt···H contacts in more detail through DFT
methods. Topological analyses of the electron density function
(ρ(r)) obtained for 1-DFT, 2-DFT, A-DFT, and B-DFT have
been performed. According to Bader’s Atoms In Molecules
theory,27−31 the critical points (CPs) in the ρ(r) function are
the points in space at which the first derivatives of the function
vanish (i.e., each individual derivative in the gradient operator is
zero). CPs indicate chemically meaningful points and are
classified according to their rank and signature. The rank is the
number of nonzero curvatures of the electron density ρ(r) at
the CP, whereas the signature is the algebraic sum of the signs
of the curvatures. For example, CPs of the (3,-3) type are
indicative of the nuclear positions, whereas CPs of the (3,-1)
type are evidence of chemical bonds. Complementarily, a bond
path (BP) is a single line of maximum electron density linking
the nuclei of two chemically bonded atoms. A BP is an
indicator of chemical bonding of all kinds; weak, strong, closed-
shell, and open-shell interactions. The point on the BP with the
lowest electron density value (minimum along the path) is the
bond critical point (BCP).
The analyses of the electron density functions in 1-DFT, 2-
DFT, A-DFT, and B-DFT reveal a BP relating the platinum
atom and the hydroxyl hydrogen atom in all four cases, as well
as the corresponding BCPs. Observation of the properties of
the electron density at the referred CPs sheds light onto the
nature and properties of the discussed contacts. Cremer et al.
have stated that to provide a thorough description of the CP,
electrostatic and also energetic aspects must be considered.32
Thus, a negative value of ∇2ρ(r) indicates a covalent (shared
electron) interaction, while a positive value is associated with a
closed-shell, electrostatic interaction. Complementarily, a
negative value of the local energy density function H(r)
corresponds to partial covalence, while a positive H(r) indicates
a purely closed-shell, electrostatic interaction.11,27,28
Figure 5. Optimized structures (DFT) for 1, 2, A, and B.
are consistent with the structures found by X-ray diffraction
(see Figures S1 and S2, Supporting Information). In agreement
with the existence of a Pt···H short contact, the Pt···H(1)
distance is 2.18 Å, the H(1)−O bond length is 0.98 Å, and the
Pt−H(1)−O is 153.6° for 1-DFT, while for 2-DFT the
calculated parameters are 2.15, 0.98 Å, and 152.4°, respectively.
These Pt−H distances are slightly longer than those
determined crystallographically and support 4e-3c type
interactions. The optimized geometry of B (B-DFT) is also
consistent with the X-ray determined structure.6 It also shows
The results of our study on the referred BCPs found for 1-
DFT, 2-DFT, A-DFT, and B-DFT are shown in Table 4. The
electron density ρ(r) at a BCP correlates with the strength of
an atomic interaction. For a typical C−C covalent bond the
value of ρ(r) is about 1.7 au.33 For conventional purely organic
hydrogen bonding, values of between 0.0123 and 0.0276 au
̀
have been reported.33 Berges et al.20 have found ρ(r) values of
about 0.020 au for the intermolecular Pt···H interactions
between d8 square planar Pt(II) complexes and the water
E
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NMR spectra.11 In the case of the four complexes studied here,
the calculated or measured values of the Pt−H distances are
very similar, ranging from 2.09 Å to 2.19 Å (see Table 1).
Nevertheless, the value of the downfield displacement of the
signal of the interacting hydrogen in the 1H NMR with respect
to the free ligand is significantly greater for the complexes A
and B (3.70 and 4.09 ppm, respectively) than it is for 1 and 2
(2.64 and 2.74 ppm, respectively). Thus, in these cases the Pt−
H distance would seem to be not the only factor determining
the magnitude of the downfield displacement in the signal of
the hydrogen involved in the interaction.
Table 4. Topological Characteristics of Critical Point Pt···
a
H−O in Complexes 1-DFT, 2-DFT, A-DFT, and B-DFT
complex
1-DFT
2-DFT
A-DFT
B-DFT
ρ(r) (au)
0.034
0.070
0.028
2.18
0.036
0.076
0.034
2.15
0.035
0.070
0.028
2.16
0.039
0.079
0.034
2.11
∇2ρ(r)
Ellipt
Pt···H (Å)
BP length (Å)
Pt−CP (Å)
CP−H (Å)
G(r) (au)
V(r) (au)
2.21
2.18
2.20
2.14
1.51
1.49
1.51
1.47
0.70
0.69
0.69
0.67
0.022
−0.026
−0.004
0.648
−8.15
0.024
−0.029
−0.005
0.661
−9.11
0.022
−0.027
−0.005
0.630
−8.34
0.026
−0.032
−0.006
0.655
−9.92
Natural Bond Orbital (NBO) analyses have been performed
for 1-DFT, 2-DFT, A-DFT, and B-DFT (see Supporting
Information, Table S7). As a result of the anionic nature of the
latter pair of complexes, the atomic charges on the platinum
centers of 1-DFT and 2-DFT (+0.23 and +0.22) are higher
than those in A-DFT and B-DFT (+0.11 and +0.09). This
trend is also observed in the Mulliken charges (+0.09 in 1-
DFT, +0.06 in 2-DFT, −0.09 in A-DFT, and −0.11 in B-DFT).
Oppositely, the calculated charges on the hydroxyl hydrogen
and on the oxygen atoms are almost identical in the series of
four cases under study (average values are +0.52 for the
hydrogen and −0.70 for the oxygen atoms according to NBO,
and +0.41 for the hydrogen and −0.56 for the oxygen atoms
H(r) (au)
G(r)/ρ(r)
E(HB, kcal mol−1
)
a
BP: Bond path; CP: Critical point.
molecules discussed above. In the complexes studied in this
paper, the values of ρ(r) are higher, ranging from 0.034 to
0.039, and also higher that those reported by Oldfield and co-
workers11 for d8 square planar complexes containing intra-
molecular M···H−X (X = C, N) interactions (range 0.012−
0.025), or by Per
́
ez-Prieto and co-workers34 in intramolecular
1
according to Mulliken). The H chemical shifts of the free
M···H−C (M = Pd, Ag, Mo) interactions (range 0.019−0.034).
Thus, these values of ρ(r) at the BCP seem to indicate a
significant Pt···H interaction in the complexes studied here.
According to the Econt = 1/2V(rCP) relationship, the energies of
the hydrogen bonds can be estimated to be between −8.1 and
−10.0 kcal mol−1.35,36
quinoline and quinaldine molecules and of the 1-DFT, 2-DFT,
A-DFT, and B-DFT complexes have also been calculated by
DFT methods and compared to the experimental values (see
Table 1). The calculated shifts for the hydroxylic hydrogen
atoms in the organic substrates (7.69 and 8.06 ppm
respectively) and in the four organometallic complexes
(10.71, 10.95, 11.95, and 12.07 ppm respectively) are in a
good agreement with the experimental ones, from both a
qualitative and a quantitative point of view (see Table 1).
Remarkably, the computed shifts reproduce the experimentally
observed downfield delta shifts upon formation of the Pt···H
interactions, and predict higher deshieldings for the hydroxylic
proton of the aromatic ligands when coordinated to the anionic
[Pt(C6F5)3]− fragment (+4.26 for A-DFT and +4.01 for B-
DFT), than when coordinated to the neutral [Pt(C6F5)(bzq)]
(+3.02 for 1-DFT and +2.89 for 2-DFT). The sum of these
observations suggests that the strengths of the Pt···H
interactions and the extent of the downfield shifts of the
hydroxylic hydrogen atoms participating in the platinum−
hydrogen contacts are determined not only by the short values
of the Pt···H distances but also by the charges of the platinum
centers in these sets of compounds. According to this, a more
negative charge on the platinum center would favor stronger
hydrogen bonds as well as more downfield chemical 1H shifts in
the resulting complexes.
With respect to the sign of the Laplacian ∇2ρ(r), in all four
cases their values are positive (see Table 4), thus indicating
closed-shell, electrostatic interactions. This same result is also
observed in conventional organic hydrogen bonds,33 in the
referred Pt(II)··H−OH interactions20,21 or in other studies on
M···H−X systems11,34 Nevertheless, and as stated before,11,33,34
considering the values and signs of ∇2ρ(r) and H(r) together
allows a better understanding of these interactions. Thus, in the
four examples studied here, all the H(r) values are negative (see
Table 4), which means that the Pt···H−O hydrogen bonds have
partial covalence. Analogous results have been found in other
pregostic or hydrogen bonded M···H−X interactions,11,34 in
contrast to conventional organic hydrogen bond systems for
which positive values of H(r) are always calculated, and thus no
covalent component is deduced in the interaction.33
It has been observed that a more negative value of H(r) is
related to the decrease in the distance between the interacting
atoms, both in certain specific organic hydrogen bonding
systems33,37 and in other nonbonded interactions.38 In these
specific hydrogen bonding systems the donor or proton
acceptors are ylides37 or organic acids,33 and when known,
the X···H distances have been shown to be very short. These
“special” hydrogen bonds are sometimes termed “Low Barrier
Hydrogen Bonds” (LBHB) and are postulated as transition
states in several organic and enzyme catalytic events.33,37 The
values of H(r) reported for the complexes investigated here are
the most negative ones calculated for M···H−X interactions11,34
(see Table 4), and certainly, the Pt−H distances calculated or
measured by X-ray (complexes 1 and B, see Table 3), are
among the shortest reported for this kind of complexes6,15,16
Some authors have stated that the shorter the Pt···H contact,
the more negative the value of H(r) is and the greater the
downfield displacement of the interacting hydrogen is in the 1H
Reactivity of Complexes 1 and 2 toward Bases. The
hydrogen bridging M···H interactions have been described as
the first step in processes of protonation of the metal and
possible migration of the proton to a ligand with elimination of
the protonated ligand.2 For example, complex [Pt-
(C6F5)3(bzqH)]−, which shows evidence of the existence of
1
the Pt···H interaction through Pt−H coupling in its H NMR
spectrum (see above), undergoes cyclometalation of the bzq
ligand with elimination of C6F5H when it is refluxed in 1,2-
dichloroethane for 3 h, giving rise to [Pt(C6F5)2(bzq)].39
Furthermore, the preparation of the starting material [Pt-
(C6F5)(bzq)(Me2CO)] is achieved via this pathway, with
coordination of the Hbzq ligand to the platinum center in reflux
F
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of acetone solutions of cis-[Pt(C6F5)2(THF)2]23 However,
complexes 1 and 2 do not undergo a similar process, with the
cyclometalation of the hqH ligand, when their solutions are
refluxed for several hours, even in relatively high boiling point
solvents such as 1,2-dichloroethane.
Since the “internal” deprotonation, chelation, and corre-
sponding formation of C6F5H do not take place, we tested the
acidity of the OH hydrogen of the hydroxyquinoline ligands in
1 and 2 toward several “external” deprotonating reagents.
Successful abstraction of the proton from the hydroxyl
fragment should afford a monoanionic complex with a formally
negative oxygen atom that could be used as a building block for
preparing compounds of higher nuclearity, for example, by
reaction with acidic metals such as Ag(I), Au(I), or Tl(I).
Although no deprotonation was achieved using KOH,
K(Me3CO), or 1,8-bis(dimethylamino)naphthalene (proton
sponge), the reactions with BuLi led to unexpected results.
Thus, the treatment of tetrahydrofuran (THF) solutions of 1 or
2 with equimolar amounts of BuLi for 1 h at 198 K and the
subsequent room temperature addition of (NBu4)ClO4
afforded, after workup, two yellow solids in good yields (see
Figure 7. View of the molecular structure of the anion of the complex
(NBu4)[Li{Pt(C6F5)(bzq)(hq′)}2] (triclinic pseudopolymorph, 4a).
their relevant bond distances and angles. A figure, a table of
selected bond distances and angles, and crystallographic data
for 4b are included as Supporting Information.
1
Experimental Section for details). The H NMR spectra of
these yellow solids do indeed show the absence of the
downfield signal corresponding to the OH hydrogen atoms of
the hydroxyquinoline ligands, with signals corresponding to the
other protons of these and the bzq ligands in 1:1 ratio. They
Complexes 3, 4a, and 4b are isostructural, with the obvious
difference of the methyl substituent on the 2-methyl-
hydroxyquinolinate ligand, and small differences mainly in the
conformation of the pentafluorophenyl and hydroxyquinolinate
ligands that probably can be accounted by the flexibility of the
molecules in the crystalline environment.41 The three
complexes are trinuclear, with two “Pt(C6F5)(bzq)(L)”
subunits bridged by a lithium atom. The most remarkable
feature of the structures is the change of coordination mode of
the hydroxyquinolinate ligands. Thus, the deprotonation of the
hydroxyl group and the presence of the lithium atom cause a
change in the bond between the platinum center and the
hydroxyquinolinate ligand, which now is established through a
Pt−O bond. This change in the donor atom allows the oxygen
atom to act as a bridge between the two metals. Furthermore,
in this way, the lithium also coordinates to the now available
nitrogen atom and is able to reach the four coordination with a
distorted tetrahedral environment. A few lithium hydroxyqui-
nolate complexes have been previously described in the
literature, which are tetrametallic or hexametallic with cyclic
structures in which the Li atoms are bridged by three oxygen
atoms of the hq ligand and only the fourth coordination
position is occupied by a N atom.42,43
+
also show signals for NBu4 , but with half the intensity expected
for a (NBu4)[Pt(C6F5)(bzq)(hq)] or (NBu4)[Pt(C6F5)(bzq)-
(hq′)] stoichiometry. Their 19F NMR spectra show signals for
five fluorine atoms in the region and intensity expected.
The nature of the yellow solids could only be established
when their structures were determined by single crystal X-ray
diffraction. These studies concluded that the stoichiometry of
the prepared complexes was in fact (NBu4)[Li{Pt(C6F5)(bzq)-
(L)}2] (L = hq (3), hq′ (4)). For complex 4, two sets of
different crystals have been obtained, corresponding to two
pseudopolymorphs,40 one triclinic (P1) which incorporates two
̅
CH2Cl2 solvent molecules in the asymmetric unit, and one
monoclinic (P21/n) with one CH2Cl2 molecule. The structural
parameters for both pseudopolymorphs are very similar and will
be denoted 4a and 4b, respectively. Figures 6 and 7 show views
of the complexes 3 and 4a, and Tables 5 and 6 list a selection of
The two Pt square planes are nearly coplanar, in a disposition
that is probably optimal to reduce the steric repulsions of the
bulky benzoquinolinate chelate ligands. Furthermore, the two
bzq planes are separated about 3.4 Å, a distance that could
indicate the existence of π···π interactions of the planar
aromatic rings in a similar fashion to that previously reported
for other complexes containing the bzq ligand.23,44−46
CONCLUSION
■
The combination of the 8-hydroquinoline type ligands and
square planar Pt(II) complexes has shown to be a good way to
design complexes which contain Pt···H−O hydrogen bonds.
Thus, 1 and 2 are examples of complexes exhibiting this kind of
1
interaction both in solution and in the solid state. Their H
NMR spectra show the two expected features that prove the
interactions, namely, (a) downfield displacements of the signals
of the involved hydrogen atoms and, even more conclusive, (b)
Figure 6. View of the molecular structure of the anion of the complex
(NBu4)[Li{Pt(C6F5)(bzq)(hq)}2] (3).
G
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Table 5. Selected Bond Lengths (Å) and Angles (deg) for (NBu4)[Li{Pt(C6F5)(bzq)(hq)}2]·1.875CH2Cl2 (3·1.875CH2Cl2)
Pt(1)−C(17)
Pt(1)−O(1)
Pt(2)−N(3)
Li−O(1)
1.978(4)
2.110(3)
2.071(3)
1.910(7)
Pt(1)−C(1)
Pt(2)−C(45)
Pt(2)−O(2)
Li−N(4)
2.003(4)
1.981(4)
2.122(3)
2.030(7)
Pt(1)−N(1)
Pt(2)−C(29)
Li−O(2)
2.076(3)
2.012(4)
1.886(7)
2.057(7)
Li−N(2)
C(17)−Pt(1)−C(1)
97.23(16)
C(17)−Pt(1)−N(1)
81.88(14)
C(1)−Pt(1)−N(1)
C(1)−Pt(1)−O(1)
C(45)−Pt(2)−C(29)
C(29)−Pt(2)−N(3)
C(29)−Pt(2)−O(2)
O(2)−Li−O(1)
173.30(14)
87.99(14)
95.78(16)
174.15(15)
87.70(13)
113.4(4)
C(17)−Pt(1)−O(1)
N(1)−Pt(1)−O(1)
C(45)−Pt(2)−N(3)
C(45)−Pt(2)−O(2)
N(3)−Pt(2)−O(2)
O(2)−Li−N(4)
174.75(13)
93.01(11)
82.00(15)
175.70(13)
94.29(12)
85.5(3)
O(1)−Li−N(4)
129.1(4)
O(2)−Li−N(2)
130.8(4)
O(1)−Li−N(2)
84.4(3)
N(4)−Li−N(2)
119.4(4)
Table 6. Selected Bond Lengths (Å) and Angles (deg) for (NBu4)[Li{Pt(C6F5)(bzq)(hq′)}2]·2CH2Cl2 (4a·2CH2Cl2)
Pt(1)−C(17)
Pt(1)−O(1)
Pt(2)−N(3)
Li−O(1)
1.973(3)
2.111(2)
2.076(3)
1.903(6)
Pt(1)−C(1)
Pt(2)−C(46)
Pt(2)−O(2)
Li−N(2)
2.003(3)
1.976(3)
2.100(2)
2.028(6)
Pt(1)−N(1)
Pt(2)−C(30)
Li−O(2)
2.078(3)
2.002(4)
1.888(6)
2.058(6)
Li−N(4)
C(17)−Pt(1)−C(1)
96.04(13)
C(17)−Pt(1)−N(1)
81.98(12)
C(1)−Pt(1)−N(1)
C(1)−Pt(1)−O(1)
C(46)−Pt(2)−C(30)
C(30)−Pt(2)−N(3)
C(30)−Pt(2)−O(2)
O(2)−Li−O(1)
174.03(12)
88.09(11)
95.92(14)
175.35(12)
87.66(11)
115.0(3)
C(17)−Pt(1)−O(1)
N(1)−Pt(1)−O(1)
C(46)−Pt(2)−N(3)
C(46)−Pt(2)−O(2)
N(3)−Pt(2)−O(2)
O(2)−Li−N(2)
175.51(11)
94.09(10)
81.75(13)
176.02(11)
94.55(10)
128.2(3)
O(1)−Li−N(2)
85.1(2)
O(2)−Li−N(4)
84.8(2)
O(1)−Li−N(4)
127.2(3)
N(2)−Li−N(4)
121.7(3)
the existence of Pt−H couplings with values of J of appreciable
magnitude, indeed some of the largest reported so far.
Moreover, the X-ray structures of 1 and 2 have revealed that
the structural parameters of the fragment Pt−H−O are typical
of a hydrogen bonding system. In particular, the Pt−H
distances are very short, 2.09(4) and 2.10(4) Å, and indicate
a quite strong interaction. The Atoms in Molecules study on
complexes 1 and 2, and also of the related complexes A and B
(see Scheme 1), confirms the existence of interactions between
the metal centers and the OH hydrogen atoms of electrostatic
nature but with a partial covalence. This description is derived
from the values of the Laplacian ∇2ρ(r) and the local energy
density function H(r) calculated for the Pt···H−O systems. In
particular, besides their sign, the magnitude of the value of H(r)
has also been directly related with the distance Pt−H, which
correlates well with the observations for 1, 2, A, and B, and with
EXPERIMENTAL SECTION
■
General Comments. Literature methods were used to prepare the
starting material [Pt(C6F5)(bzq)(Me2CO)].22 Elemental analyses were
carried out with a Perkin-Elmer 2400 CHNS analyzer. IR spectra were
recorded on a Perkin-Elmer Spectrum 100 FT-IR spectrometer (ATR
in the range 250−4000 cm−1). Mass spectrometry was performed with
the Microflex matrix-assisted laser desorption ionization-time-of-flight
(MALDI-TOF) Bruker or an Autoflex III MALDI-TOF Bruker
instruments. NMR spectra in solution were recorded at 298 K on
Bruker Avance 400 spectrometer with SiMe4 and CFCl3 as external
1
references for H, 13C, and 19F. The signal attributions and coupling
constant assessment was made on the basis of a multinuclear NMR
analysis of each compound including 1H COSY, 1H-13C HMQC,
1H-13C HMBC, and APT.
Preparation of [Pt(C6F5)(bzq)(8-hydroxyquinoline)] (1). To a
solution of [Pt(bzq)(C6F5)(Me2CO)] (0.150 g, 0.251 mmol) in
CH2Cl2 (20 mL) at 273 K and under Ar atmosphere, 0.251 mmol
(0.036 g) of 8-hydroxyquinoline were added. After 15 min of stirring
the solution was concentrated to about 2 mL. The yellow precipitate
which appeared was filtered off, washed with n-hexane (10 mL), and
air-dried. Yield 0.148 g (0.216 mmol), 86% yield. IR υ = 2946 (w,
υOH), 1576 (vw), 1497 (m), 1450 (m), 1438 (m), 1208 (w), 1059
(m), 952 (s), 801 (m, C6F5, X-sensitive vibr.)47 cm−1. 1H NMR
(400.132 MHz, CD2Cl2, 298 K): δ = 10.92 (1H, s, J(H,Pt) = 67.0 Hz,
1
the magnitude of the downfield displacement of the H NMR
signal of the hydrogen.11 Nevertheless, in the cases studied in
this paper the magnitude of this NMR displacement seems to
be also related to the difference of charge between the Pt and
the H, as suggested by NBO analyses of the complexes.
Several reagents have been tested as deprotonating agents for
the hydroxyl OH in 1 and 2, and only BuLi has proved to work
properly. Nevertheless, the process evolves toward the
formation of unexpected trinuclear Pt2Li complexes, in which
the coordination mode of the deprotonated 8-hydroquinolinate
type ligands changes. The hq and hq′ ligands are now O-
coordinated to the Pt atom, and O,N-chelate to the Li atom, in
such a way that the Li is tetracoordinated and bridges two
platinum subunits.
3
3
H; hqH′−OH), 9.62 (1H, d, J(H2,H3) = 5.1 Hz, J(H2,Pt) 23.4
=
Hz, H2, see Scheme 2 for the hydrogen and carbon numbering
3
4
scheme), 8.44 (1H, dd, J(H4,H3) = 8.4 Hz, J(H4,H2) = 1.6 Hz,
3
4
H4), 8.37 (1H, dd, J(H17,H16) = 8.1 Hz, J(H17,H15) = 1.3 Hz,
H17), 7.85 (1H, d, 3J(H6,H5) = 8.8 Hz, H6), 7.65 (1H, d, 3J(H6,H5)
3
4
= 8.8 Hz, H5), 7.64 (1H, dd, J(H7,H8) = 7.9 Hz, J(H7,H9) = 0.8
3
3
Hz, H7), 7.62 (1H, t, J(H19,H20) = J(H19,H18) = 7.7 Hz, H19),
7.60−7.52 (3H, m, overlapped signals of H15, H18 and H3), 7.39
(1H, dd, 3J(H8,H9) = 7.9 Hz, 3J(H8,H7) = 7.9 Hz, H8), 7.33 (1H, dd,
4
3J(H20,H19) = 7.7 Hz, J(H20,H18) = 1.5 Hz, H20), 7.29 (1H, dd,
3
3J(H16,H17) = 8.1 Hz, J(H16,H15) = 5.2 Hz, H16), 7.00 (1H, d,
H
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mmol), 68% yield. IR υ = 2964 (vw), 1567 (vw), 1493 (m), 1450 (m),
Scheme 2
1436 (m), 1276 (vw), 1055 (m), 951 (s), 880 (w), 796 (m, C6F5, X-
sensitive vibr.),47 409 (w) cm−1. H NMR (400.132 MHz, CD2Cl2,
1
298 K): δ = 9.10 (2H, dd, 3J(H2,H3) = 5.1 Hz, 4J(H2,H4) = 0.9, H2,
see Scheme 2 for the hydrogen and carbon numbering scheme), 8.14
3
4
(2H, dd, J(H17,H16) = 8.4 Hz, J(H17,H15) = 1.4 Hz, H17), 7.90
3
4
(2H, dd, J(H15,H16) = 4.1 Hz, J(H15,H17) = 1.4 Hz, H15), 7.74
3
3
(2H, d, J(H20,H19) = 7.8 Hz, H20), 7.44 (2H, d, J(H6,H5) = 8.7
Hz, H6), 7.38 (2H, d, 3J(H7,H8) = 7.6 Hz, H7), 7.22 (2H, t,
3J(H19,H20) = 3J(H19,H18) = 8.0 Hz, H19), 7.20 (2H, dd,
3J(H16,H17) = 8.4 Hz, J(H16,H15) = 4.1 Hz, H16), 7.11 (2H, t,
3
3J(H8,H9) = 3J(H8,H7) = 7.5 Hz, H8), 6.97 (2H, dd, 3J(H18,H19) =
8.0 Hz, 4J(H18,H20) = 0.8 Hz, H18), 6.86 (4H, d, overlapped signals
of H5 and H9), 6.67 (2H, d, 3J(H4,H3) = 8.0 Hz, H4), 6.17 (2H, dd,
3J(H9,H8) = 7.8 Hz, 3J(H9,Pt) = 62.5 Hz, H9) ppm. 19F NMR
3
(376.479 MHz, CD2Cl2, 298 K): δ = −117.9 (o-F, m, J(F,Pt) = 515
3J(H3,H4) = 8.0 Hz, J(H3,H2) = 5.1 Hz, H3), 2.70 (16H, m, α-
3
Hz), −121.2 (o-F, m, 3J(F,Pt) = 444 Hz), −163.3 (p-F, t), −164.5 (m-
F, br m), −165.0(m-F, br m) ppm. 13C{1H} NMR (100.624 MHz,
CD2Cl2, 298 K): δ = 155.4 (s, C12), 153.2 (s, C2), 152.2 (s, C21),
146.2 (s, C15), 142.7 (s, C11), 140.3 (s, C4), 138.6 (s, C17), 136.4 (s,
+
+
CH2−NBu4 ), 1.28 (16H, m, β-CH2−NBu4 ), 1.13 (16H, m, γ-CH2−
+
+
NBu4 ), 0.84 (24H, t, CH3−NBu4 ) ppm. 19F NMR (376.479 MHz,
CD2Cl2, 298 K): δ = −117.5 (2o-F, m, 3J(F,Pt) = 597 Hz), −166.6 (m-
F, br m), −167.0 (m-F, br m), −167.3 (p-F, t) ppm. 13C {1H} NMR
(100.624 MHz, CD2Cl2, 298 K): δ = 166.2 (s, C21), 153.6 (s, C12),
148.7 (s, C2), 146.0 (s, C15), 145.2 (s, C22), 142.8 (s, C11), 137.6 (s,
C10), 136.7 (s, C17), 134.0 (s, C4), 133.4 (s, C14), 133.3 (s, 2J(C,Pt)
= 139 Hz, C9), 130.2 (s, C23), 129.0 (s, C8), 128.6 (s, C19), 127.8 (s,
C6), 125.0 (s, C13), 123.8 (s, C5), 122.3 (s, C3), 121.0 (s, C16),
2
C22), 135.9 (s, C10), 134.7 (s, J(C,Pt) = 114 Hz, C9), 134.2 (s,
C14), 132.3 (s, C23), 130.2 (s, C5), 129.8 (s, C8), 129.4 (s, C19),
123.5 (s, C6), 123.2 (s, C7), 122.2 (s, C16), 122.0 (s, C18), 120.3 (s,
C3), 117.3 (s, C20) ppm. Mass spectra MALDI+ DCTB: m/z = 517.0
[Pt(C13H8N)(C9H7NO)], 684.0 [Pt(C13H8N)(C6F5)(C9H6NOH)-
H]+. Elemental analysis calcd (%) for C28H15F5N2OPt: C 49.06, H
2.21, N 4.09; found: C 48.72, H 2.25, N 4.02.
+
119.7 (s, C7), 114.9 (s, C20), 111.4 (s, C18), 59.0 (s, α-CH2−NBu4 ),
+
+
Preparation of [Pt(C6F5)(bzq)(2-methyl-8-hydroxyquino-
line)] (2). To a solution of [Pt(bzq)(C6F5)(Me2CO)] (0.150 g,
0.251 mmol) in CH2Cl2 (20 mL) at 273 K and under Ar atmosphere,
0.251 mmol (0.040 g) of 2-methyl-8-hydroxyquinoline were added.
After 15 min of stirring the solution was concentrated to about 2 mL.
The yellow precipitate which appeared was filtered off, washed with n-
hexane (10 mL), and air-dried. Yield 0.154 g (0.220 mmol), 88% yield.
IR υ = 2938 (w, υOH), 1569 (w), 1504 (m), 1450 (m), 1438 (m), 1258
24.1 (s, β-CH2−NBu4 ), 20.0 (s, γ-CH2−NBu4 ), 13.8 (s, CH3−
+
NBu4 ). Mass spectra MALDI− DCTB: m/z = 557.0 [Pt(C13H8N)-
(C6F5)(OH)], 684.0 [Pt(C13H8N)(C6F5)(C9H8NOH)-H]+, 1375.0
[(Pt(C1 3 H8 N)(C6 F5 )(C9 H6 NO))Li(Pt(C1 3 H8 N)(C6 F5 )-
(C9H6NO))]−. Elemental analysis calcd (%) for C72H64F10LiN5O2Pt2:
C 53.43, H 3.99, N 4.33; found: C 53.19, H 3.88, N 3.92.
Preparation of (NBu4)[Li{Pt(C6F5)(bzq)(2-methyl-8-hydroxy-
quinolinate)}2] (4). To a solution of 2 (0.350 g, 0.500 mmol) in
tetrahydrofuran (60 mL) at 195 K and under Ar atmosphere, BuLi
(2.5 M solution in hexane; 0.220 mL, 0.550 mmol) was added. After
60 min of stirring the solution was allowed to reach room temperature,
and the solution was hydrolyzed for 10 min to remove the excess of
BuLi. The solution was evaporated to dryness, and the yellow solid
(m), 1060 (m), 955 (s), 797 (m, C6F5, X-sensitive vibr.)47 cm−1. H
1
NMR (400.132 MHz, CD2Cl2, 298 K): δ = 10.99 (1H, s, J(H,Pt) =
80.6 Hz, H; hqH′−OH), 8.42 (1H, dd, 3J(H4,H3) = 8.1 Hz,
4J(H4,H2) = 1.2 Hz, H4, see Scheme 2 for the hydrogen and carbon
3
numbering scheme), 8.27 (1H, d, J(H17,H16) = 8.5 Hz, H17), 8.10
3
4
3
i
(1H, dd, J(H2,H3) = 5.3 Hz, J(H2,H4) = 1.2 Hz, J(H2,Pt) = 19.4
Hz, H2), 7.88 (1H, d, 3J(H6,H5) = 8.8 Hz, H6), 7.67 (1H, d,
3J(H5,H6) = 8.8 Hz, H5), 7.66 (1H, dd, 3J(H7,H8) = 7.9 Hz,
4J(H7,H9) = 0.7 Hz, H7), 7.52 (1H, t, 3J(H19,H20) = 3J(H19,H18) =
7.8 Hz, H19), 7.44−7.38 (3H, m, overlapped signals of H18,H8 and
H3), 7.42 (1H, d, 3J(H16,H17) = 8.5 Hz, H16), 7.28 (1H, dd,
was treated with PrOH (10 mL) and NBu4ClO4 (0.085 g, 0.250
mmol) was added. The resultant yellow suspension was filtered off,
washed with n-hexane (10 mL), and air-dried. Yield 0.284 g (0.173
mmol), 69% yield. IR υ = 2963 (vw), 1562 (vw), 1496 (m), 1450 (m),
1435 (m), 1274 (vw), 1057 (m), 952 (s), 880 (w), 796 (m, C6F5, X-
sensitive vibr.),47 356 (w) cm−1. H NMR (400.132 MHz, CD2Cl2,
1
4
3J(H20,H19) = 7.8 Hz, J(H20,H18) = 1.6 Hz, H20), 7.02 (1H, d,
3
298 K): δ = 9.10 (2H, d, J(H2,H3) = 5.1 Hz, H2, see Scheme 2 for
3
3J(H9,H8) = 7.2 Hz, J(H,Pt) = 62.0 Hz, H9), 3.40 (3H,s, H; hqH′-
the hydrogen and carbon numbering scheme), 8.03 (2H, d,
CH3) ppm. 19F NMR (376.479 MHz, CD2Cl2, 298 K): δ = −117.8 (o-
F, m, 3J(F,Pt) = 435 Hz), −118.5 (o-F, 3J(F,Pt) = 468 Hz), −163.5 (p-
F, t), −164.9 (m-F, br m), −165.1 (m-F, br m) ppm. 13C{1H} NMR
(100.624 MHz, CD2Cl2, 298 K): δ = 163.5 (s, C15), 155.6 (s, C12),
152.8(s, C21), 146.8 (s, C2), 142.3 (s, C11), 140.8 (s, C17), 138.7 (s,
C4), 137.2 (s, C22), 136.5 (s, C10), 134.6 (s, 2J(C,Pt) = 110 Hz, C9),
134.4 (s, C14), 130.7 (s, C23), 130.4 (s, C6), 130.1 (s, C8), 128.4 (s,
C19), 127.7 (s, C13), 124.5 (s, C16), 123.7 (s, C5), 123.2 (s, C7),
122.6 (s, C3), 120.5 (s, C18), 118.4 (s, C20) ppm. Mass spectra
MALDI+ DCTB: m/z = 531.0 [Pt(C13H8N)(C10H8NOH)-H]+, 699.0
[Pt(C13H8N)(C6F5)(C10H8NOH)-H]+. Elemental analysis calcd (%)
for C29H17F5N2OPt: C 49.79, H 2.45, N 4.01; found: C 49.87, H 2.14,
N 4.10.
3
3J(H17,H16) = 8.4 Hz, H17), 7.74 (2H, d, J(H20,H19) = 7.8 Hz,
H20), 7.42 (2H, d, 3J(H6,H5) = 8.7 Hz, H6), 7.38 (2H, d, 3J(H7,H8)
3
3
= 7.8 Hz, H7), 7.15 (2H, t, J(H19,H20) = J(H19,H18) = 7.8 Hz,
3
3
H19), 7.11 (2H, t, J(H8,H9) = J(H8,H7) = 7.8 Hz, H8), 7.09 (2H,
3
3
d, J(H16,H17) = 8.4 Hz, H16), 6.90 (2H, d, J(H18,H19) = 7.8 Hz,
H18), 6.84 (2H, d, 3J(H5,H6) = 8.7 Hz, H5), 6.82 (2H, d, 3J(H9,H8)
3
= 7.8 Hz, H9), 6.65 (2H, d, J(H4,H3) = 8.0 Hz, H4), 6.21 (2H, dd,
3J(H3,H4) = 8.0 Hz, J(H3,H2) = 5.1 Hz, H3), 2.71 (16H, m, α-
4
+
+
CH2−NBu4 ), 1.29 (16H, m, β-CH2−NBu4 ), 1.14 (16H, m, γ-CH2−
NBu4 ), 0.85 (24H, t, CH3−NBu4 ) ppm. 19F NMR (376.479 MHz,
+
+
CD2Cl2, 298 K): δ = −117.2 (o-F, m, 3J(F,Pt) = 557 Hz), −117.7 (o-F,
3
m, J(F,Pt) = 549 Hz), −166.8 (m-F, br m), −167.1 (m-F, br m),
−167.6 (p-F, t) ppm. 13C {1H} NMR (100.624 MHz, CD2Cl2, 298 K):
δ 165.6 (s, C21), 155.5 (s, C15), 153.5 (s, C12), 148.7 (s, C2), 144.3
(s, C22), 142.8 (s, C11), 138.0 (s, C10), 137.1 (s, C17), 134.0 (s, C4),
133.4 (s, C14), 133.1 (s, 2J(C,Pt) = 101 Hz, C9), 129.0 (s, C8), 128.3
(s, C23), 127.7 (s, C6), 127.6 (s, C19), 125.0 (s, C13), 124.0 (s, C5),
122.4 (s, C3), 121.7 (s, C16), 119.6 (s, C7), 115.1 (s, C20), 111.4 (s,
Preparation of (NBu4)[Li{Pt(C6F5)(bzq)(8-hydroxyquinoli-
nate)}2] (3). To a solution of 1 (0.343 g, 0.500 mmol) in
tetrahydrofuran (60 mL) at 195 K and under Ar atmosphere, BuLi
(2.5 M solution in hexane; 0.220 mL, 0.550 mmol) was added. After
60 min of stirring the solution was allowed to reach room temperature,
and the solution was hydrolyzed for 10 min to remove the excess of
BuLi. The solution was evaporated to dryness, and the yellow solid
+
+
C18), 58.9 (s, α-CH2−NBu4 ), 24.1 (s, β-CH2−NBu4 ), 23.5 (s, γ-
+
+
CH2−NBu4 ), 20.0 (s, CH3−NBu4 ). Mass spectra MALDI− DCTB:
m/z = 698.0 [Pt(C13H8N)(C6F5)(C10H8NOH)-H]+, 1403.0 [(Pt-
(C13H8N)(C6F5)(C10H8NO))Li(Pt(C13H8N)(C6F5)(C10H8NO))]−.
i
was treated with PrOH (10 mL) and NBu4ClO4 (0.085 g, 0.250
mmol) was added. The resultant yellow suspension was filtered off,
washed with n-hexane (10 mL), and air-dried. Yield 0.281 g (0.174
I
dx.doi.org/10.1021/ic402036p | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 7. Crystal Data and Structure Refinement for Complexes 1·CH2Cl2, 2·CHCl3, 3·1.875CH2Cl2, and 4a·2CH2Cl2
1·CH2Cl2
2·CHCl3
3·1.875CH2Cl2
4a·2CH2Cl2
formula
C28H15F5N2OPt
·CH2Cl2
770.44
C29H17F5N2OPt
·CHCl3
818.90
C72H64F10LiN5O2Pt2
·1.875CH2Cl2
1777.64
C74H68F10LiN5O2Pt2
·2CH2Cl2
1816.31
Mt
crystal system
space group
a/Å
monoclinic
P21/c
monoclinic
P21/n
triclinic
triclinic
P1
P1
̅
̅
10.3728(2)
16.5660(3)
15.0527(2)
90
10.9721(2)
15.5286(2)
16.6883(2)
90
14.3558(2)
14.5503(2)
17.2806(3)
78.609(1)
81.501(1)
80.284(1)
3463.2(1)
2
13.8434(1)
14.2761(2)
18.7328(2)
79.406(1)
86.245(1)
81.744(1)
3598.4(1)
2
b/Å
c/Å
α/deg
β/deg
96.075(2)
90
107.556(2)
90
γ/deg
V/Å3
2572.1(1)
4
2710.9(1)
4
Z
Dc/g cm−3
1.990
2.006
1.705
1.676
T/K
100(1)
100(1)
100(1)
100(1)
μ/mm−1
F(000)
5.728
5.536
4.257
4.108
1480
1576
1750
1792
2θ range/deg
collected reflections
unique reflections
Rint
8.4−57.7
28470
8.8−57.9
30600
8.3−57.8
76190
8.4−57.8
77177
6142
6571
16370
17183
0.0249
0.0226
0.0337
0.0340
a
R1, wR2 (I > 2σ(I))
0.0217, 0.0515
0.0246, 0.0523
0.0174, 0.0424
0.0191, 0.0432
0.0290, 0.0796
0.0402, 0.0813
0.0276, 0.0745
0.0396, 0.0769
1.024
a
R1, wR2 (all data)
b
GOF (F2)
1.048
1.059
1.040
a
b
2
2
2
R1 = ∑(|Fo| − |Fc|)/∑|Fo|. wR2 = [∑w (Fo − Fc2)2/∑w(Fo )2]1/2. Goodness-of-fit = [∑w(Fo − Fc2)2/(nobs − nparam)]1/2
.
Elemental analysis calcd (%) for C74H68F10LiN5O2Pt2: C 53.98, H
4.16, N 4.25; found: C 53.66, H 4.33, N 3.99.
Computational Details. Quantum mechanical calculations were
performed with the Gaussian09 package50 at the DFT/M06 level of
theory.51 SDD basis set and its corresponding effective core potentials
(ECPs) were used to describe the platinum atom.52 An additional set
of f-type functions was also added.53 Carbon, fluorine, hydrogen,
nitrogen, and oxygen atoms were described with a 6-31G* basis set54
except for the hydrogen atoms close to the metal (hydroxyl and
methyl hydrogen atoms), which were described with a 6-31G** basis
set.55 The structures of the platinum complexes and hydroxyquinoline
ligands were fully optimized with these basis sets and with no
symmetry restrictions. All minima were subsequently characterized by
analytically computing the Hessian matrix. Atomic coordinates (x, y, z)
for the optimized structures are collected in the Supporting
Information, Tables S3−S6. Topological analyses of the electron
density distribution functions ρ(r) were performed by using the
AIMAll program package56 based on the extended wave function
obtained by M06 calculations. The AIM extended wave function
format allows QTAIM analyses of molecular systems containing heavy
atoms described with ECPs. Atomic charges were calculated by using
the NBO analysis option as incorporated in Gaussian 09.57 NMR
chemical shifts were calculated in the previously optimized structures,
but using the 6-311++g(d) basis set for all the light atoms in the
molecules.58,59
X-ray Structure Determinations. Crystal data and other details
of the structure analyses are presented in Table 7. Suitable crystals for
X-ray diffraction studies were obtained by slow diffusion of n-hexane
into concentrated solutions of the complexes in 3 mL of CH2Cl2 (1, 3,
and 4) or CHCl3 (2). Crystals were mounted at the end of quartz
fibers. X-ray intensity data were collected on an Oxford Diffraction
Xcalibur diffractometer. The diffraction frames were integrated and
corrected for absorption using the CrysAlis RED program.48 The
structures were solved by Patterson and Fourier methods and refined
by full-matrix least-squares on F2 with SHELXL-97.49 All non-
hydrogen atoms were assigned anisotropic displacement parameters
and refined without positional constraints, except as noted below. For
1·CH2Cl2, 3·1.875CH2Cl2, and 4a·2CH2Cl2, all hydrogen atoms were
constrained to idealized geometries and assigned isotropic displace-
ment parameters equal to 1.2 times the Uiso values of their attached
parent atoms (1.5 times for the methyl hydrogen atoms), with the
exception of the position of the hydrogen attached to the OH group of
the hydroxyquinoline ligand (H(1)) in complex 1·CH2Cl2, which was
found in the electron density maps and allowed to refine with no
positional or thermal restraints. For 2·CHCl3, the positions of all
hydrogen atoms were found in the electron density maps and allowed
to refine with no positional or thermal restraints. In the structure of 3·
1.875CH2Cl2, the dichloromethane solvent molecules were very
diffuse, and restraints in their geometry and thermal parameters
were used. In the structure of 4a·2CH2Cl2, the γ-CH2 and CH3 groups
of two of the butyl chains of the cation are disordered over two sets of
positions refined with occupancy 0.7/0.3 and 0.6/0.4. Restraints were
used in the geometry parameters involving these atoms. Full-matrix
least-squares refinement of these models against F2 converged to final
residual indices given in Table 7.
ASSOCIATED CONTENT
■
S
* Supporting Information
Further details of the structure determinations of 1·CH2Cl2, 2·
CHCl3, 3·1.875CH2Cl2, 4a·2CH2Cl2, and 4b·CH2Cl2 in cif
format. Tables of selected bond lengths and angles, crystal data
and structure refinement, and a view of the molecular structure
for 4b. Tables of atomic coordinates for the optimized
structures of 1-DFT, 2-DFT, A-DFT, and B-DFT. Table of
calculated NBO and Mulliken atomic charges for complexes 1-
DFT, 2-DFT, A-DFT, and B-DFT. Overlay drawings of the X-
ray diffraction and DFT calculated structures of 1 and 2. This
CCDC-950300 (1), CCDC-950301 (2), CCDC-950302 (3),
CCDC-950303 (4a), and CCDC-950304 (4b) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
J
dx.doi.org/10.1021/ic402036p | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(22) Berenguer, J. R.; Lalinde, E.; Moreno, M. T.; San
́
chez, S.;
material is available free of charge via the Internet at http://
pubs.acs.org.
Torroba, J. Inorg. Chem. 2012, 51, 11665−11679.
(23) Martín, A.; Belío, U.; Fuertes, S.; Sicilia, V. Eur. J. Inorg. Chem.
2013, 2231−2247.
AUTHOR INFORMATION
Corresponding Author
*E mail: tello@unizar.es.
■
(24) Bakhmutov, V. I. Practical Nuclear Magnetic Resonance
Relaxation for Chemists; John Wiley & Sons: Chichester, U.K., 2004.
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1985, 24, 1949−1950.
Notes
(26) Mercury CSD 3.1.1; Cambridge Crystallographic Data Centre:
Cambridge, U.K., 2013.
The authors declare no competing financial interest.
(27) Bader, R. F. W. Atoms in Molecules-a Quantum Theory; Oxford
University Press: Oxford, U.K., 1990.
ACKNOWLEDGMENTS
This work was supported by the Spanish MICINN (DGPTC/
FEDER) (Project CTQ2008-06669-C02-01/BQU) and MINE-
■
(28) Bader, R. F. W. J. Phys. Chem. A 1998, 102, 7314−7323.
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CO (CTQ2012-35251), the Gobierno de Aragon
́
(Grupo
ica y de los Compuestos
́
Consolidado E21: Quimica Inorgan
Organometal
(JIUZ2012-CIE-02). The authors thank the Instituto de
́
́
icos), and the Universidad de Zaragoza
́
Biocomputacion
́
y Fisica de Sistemas Complejos (BIFI) and
de Galicia (CESGA) for
the Centro de Supercomputacion
́
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DEDICATION
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Dalton Trans. 2009, 5077−5082.
Dedicated to Prof. Antonio Laguna on the occasion of his 65th
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