Diacetylplatinum(II) complexes with κ2-coordinated tris(pyridyl)methanol and tris(pyridyl)methyl ether ligands: Structural insight into the ligand dynamics in solution

Article abstract of DOI:10.1021/om400091h

Reactions of the bis(benzylamine)platinum(II) complex [Pt(COMe) ₂(NH₂Bn)₂] (2; Bn = benzyl) with (2-py) ₃COR (2-py = 2-pyridyl), (2-py)₂PhCOR, and (2-py) ₂(m-Tol)COR (m-Tol = 3-methylphenyl

Full text of DOI:10.1021/om400091h

Article
pubs.acs.org/Organometallics
Diacetylplatinum(II) Complexes with κ2‑Coordinated
Tris(pyridyl)methanol and Tris(pyridyl)methyl Ether Ligands:
Structural Insight into the Ligand Dynamics in Solution
Martin Bette,† Tim Kluge,† Jurgen Schmidt,‡ and Dirk Steinborn*,†
̈
†Institute of Chemistry-Inorganic Chemistry, Martin Luther University of Halle-Wittenberg, Kurt-Mothes-Straße 2, D-06120 Halle,
Germany
‡Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120 Halle, Germany
S
* Supporting Information
ABSTRACT: Reactions of the bis(benzylamine)platinum(II)
complex [Pt(COMe)2(NH2Bn)2] (2; Bn = benzyl) with (2-
py)3COR (2-py = 2-pyridyl), (2-py)2PhCOR, and (2-py)2(m-
Tol)COR (m-Tol = 3-methylphenyl) afforded the neutral
diacetylplatinum(II) complexes [Pt(COMe)2{(2-py)3COR}]
(R = H (3a), Me (3b), Et (3c), Bn (3d)), [Pt(COMe)2{(2-
py)2PhCOR}] (R = H (4a), Me (4b)), and [Pt(COMe)2{(2-
py)2(m-Tol)COR}] (R = H (5a) Me (5b)), respectively,
having, due to a κ2 coordination of the ligands, a 2-pyridyl (3), a
phenyl (4), or a m-tolyl (5) ring as the pendant group. The
identities of all complexes were unambiguously proved by high-
resolution mass spectrometric investigations and by NMR (1H,
13C, 195Pt) and IR spectroscopy as well as by single-crystal X-ray
diffraction analyses (3a−d). In methanol solution, complexes 3b−d and 5b show a dynamic behavior. The thermodynamic
parameters of these dynamics have been determined by variable-temperature 1H NMR measurements (Eyring plots).
Furthermore, extensive DFT calculations will be presented, which indicate that the dynamics are caused by the interplay of
hindered and respectively unhindered rotations of the substituent R and/or the pendant group.
(Scheme 1, d and e).5,6 Due to its substitution-labile
1. INTRODUCTION
benzylamine ligands, the bis(benzylamine)platinum(II) com-
plex 2, accessible by the reaction of II in neat benzylamine
The dinuclear platina-β-diketone [Pt2{(COMe)2H}2(μ-Cl)2]
(1), being accessible by the reaction of hexachloridoplatinic
(Scheme 1, f), was found to be another useful precursor
complex for the synthesis of diacetylplatinum(II) complexes.7
In this reaction pathway diacetylplatinum(II) complexes III
bearing scorpionate ligands could also be synthesized but,
unexpectedly, not the type IV complexes (Scheme 1, g and
h).5,6
Both types of ligands, the anionic tris(pyrazolyl)borates as
well as the isoelectronic neutral tris(pyrazoyl)methanes, are
due to the tetrahedral geometry at their central B or C
backbone atomrestricted to a facial κ3N,N′,N″ coordination
in octahedral complexes. For the same reason the coordination
mode of these ligands in type III and IV square-planar
complexes is κ2N,N′ with a pendant third pyrazolyl ring.4,8
Although these ligands are isoelectronically and structurally
very similar, their diacetylplatinum(II) and -platinum(IV)
complexes may exhibit great differences in reactivity and
chemical behavior.5,6
acid with n-butyl alcohol and bis(trimethylsilyl)acetylene, can
be considered as a hydroxycarbene complex, where the
hydroxycarbene ligands are stabilized by intramolecular O−
H···O hydrogen bonds to neighboring acetyl ligands (Scheme
1, a).1 Due to its electronic unsaturation (16 valence electrons)
and kinetically labile ligand sphere, the platina-β-diketone 1
exhibits a unique reactivity and thus is a suitable precursor
complex for the synthesis of a great variety of acetyl
platinum(II) and platinum(IV) complexes with bidentate
N∧N, P∧P, S∧S, and N∧O ligands.2 Thus, the reaction of
complex 1 with the bidentate N-donor 2,2′-bipyridine leads to
the formation of the thermally extraordinarily stable diacetyl-
(hydrido)platinum(IV) complex I (Scheme 1, b), which affords
with NaOH a reductive elimination of HCl to form the
respective diacetylplatinum(II) complex II (Scheme 1, c).3
Reactions of 1 with tris(pyrazolyl)borates (so-called scorpio-
nates)4 and tris(pyrazolyl)methanes, which represent examples
of tridentate N-donor ligands, followed by the addition of a
base led in an analogous manner to the formation of the
diacetylplatinum(II) complexes III and IV bearing the tripodal
ligand only κ2N,N′ coordinated with a pendant pyrazolyl ring
Received: February 1, 2013
© XXXX American Chemical Society
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Scheme 1. Synthesis of Diacetylplatinum(II) Complexes Bearing κ2-Bonded Scorpionate (III) and Tris(pyrazolyl)methane
Ligands (IV)
Scheme 2. Syntheses of the Diacetylplatinum(II) Complexes 3−5
Another class of facially coordinating tripodal ligands, which
has received considerable attention in both coordination and
organometallic chemistry in recent years, are the neutral tris(2-
pyridyl)methanol ligands ((2-py)3COH) and the respective
tris(2-pyridyl)methyl ether ligands ((2-py)3COR).9 The main
difference from the aforementioned ligand classes is the change
of the donating group from pyrazole to pyridine, which is
reported to be both a better σ donor and π acceptor ligand than
pyrazole.9,10 Here, we report on the synthesis and character-
ization of diacetylplatinum(II) complexes bearing κ2N,N′-
coordinated tris(2-pyridyl)methanol and tris(2-pyridyl)methyl
ether ligands as well as on the molecular dynamics of these
complexes. Furthermore, for comparison, ligands are included
which bear a phenyl or m-tolyl group instead of the pendant
third pyridine ring.
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2. RESULTS AND DISCUSSION
2.1. Synthesis of Diacetylplatinum(II) Complexes.
Reactions of [Pt(COMe)2(NH2Bn)2] (2) with (2-py)3COR
afforded in facile ligand exchange reactions the
diacetylplatinum(II) complexes [Pt(COMe)2{(2-py)3COR}]
(R = H (3a), Me (3b), Et (3c), Bn (3d)) bearing κ2 bonded
tris(2-pyridyl)methanol (3a) and tris(2-pyridyl)methyl ether
(3b−d) ligands (Scheme 2). By the same pathway the
structurally similar complexes [Pt(COMe)2{(2-py)2PhCOR}]
(R = H (4a), Me (4b)) and [Pt(COMe)2{(2-py)2(m-
Tol)COR}] (R = H (5a), Me (5b)) were prepared, where
the pendant pyridyl group of type 3 complexes is replaced by a
phenyl (4) and a m-tolyl group (5), respectively (Scheme 2).
Thus, in type 4 and 5 complexes the pendant group is
symmetrically and unsymmetrically replaced, respectively. All
compounds were isolated in good yields between 68 and 90%
as yellow solids, which were characterized by NMR (1H, 13C,
195Pt) and IR spectroscopy as well as by high-resolution mass
spectrometric (HRMS-ESI) investigations and single-crystal X-
ray diffraction analyses (3). All complexes are soluble in
methanol, methylene chloride, and chloroform. At room
temperature under anaerobic conditions, solutions of com-
pounds 3 are stable for several days, while for solutions of
complexes 4 and 5 the start of decomposition can be detected
by NMR spectroscopy within 2 days.
Figure 1. Structure of [Pt(COMe)2{(2-py)3COH}] (3a) in crystals of
3a·CH2Cl2. Ellipsoids are shown at the 30% probability level. H atoms
are omitted for clarity, except for that at O3. The broken line indicates
an intermolecular O−H···O hydrogen bond in crystals of 3a·CH2Cl2.
Selected structural parameters (distances in Å, angles in deg): Pt−C1
= 1.975(4), Pt−C3 = 1.997(4), Pt−N1 = 2.140(3), Pt−N2 =
2.139(3), C1−Pt−C3 = 87.1(2), C1−Pt−N2 = 92.7(1), C3−Pt−N1 =
95.9(1), N1−Pt−N2 = 84.3(1), C1−Pt−N1 = 175.4(1), C3−Pt−N2
= 178.4(2), O1···O3′ = 2.652(4).
As an alternative route to prepare diacetylplatinum(II)
complexes, in general, reactions of the respective bi- or
tridentate ligands with the platina-β-diketone 1 followed by
the reduction of the formed diacetyl(hydrido)platinum(IV)
complexes induced by proton abstraction by a base can be
envisoned. This is shown in Scheme 1 for the analogous
diacetylplatinum(II) complexes bearing scorpionate (III) or
tris(pyrazolyl)methane ligands (IV). Here, in this pathway, only
complexes bearing etherified ligands (R = Me, Et, Bn; 3b−d,
4b, 5b) could be synthesized. Reactions with the alcohol
derivatives (R = H) failed. Due to, in general, poorer yields and
a more time-consuming workup procedure, this pathway was
not further pursued.
2.2. Structures of [Pt(COMe)2{(2-py)3COR}] (R = H (3a),
Me (3b), Et (3c), Bn (3d)). Crystals of [Pt(COMe)2{(2-
py)3COR}] (R = H (3a), Me (3b), Et (3c), Bn (3d)) suitable
for X-ray diffraction analyses were obtained from a saturated
methylene chloride solution at −7 °C (3a·CH2Cl2) and from
THF solutions layered with n-pentane (3b−d). The molecular
structures are shown in Figures 1−4, respectively. Selected
structural parameters are given in the figure captions. The
platinum atoms are coordinated in a square-planar fashion by
two acetyl ligands and the κ2N,N′-coordinated (2-py)3COR
ligand. The angles between neighboring ligands are all close to
90° (84.3(1)−95.9(1)°, 3a; 84.4(2)−93.2(2)°, 3b; 84.2(2)−
93.7(2)°, 3c; 84.2(2)−94.0(2)°, 3d). The C(μ-py)2Pt units
adopt a boat conformation with the backbone carbon atom of
the (2-py)3COR ligand (C10) and the platinum atom at the
apexes. The noncoordinated pyridine ring is situated in an axial
position of this boat structure and oriented pseudo-parallel to
the coordination plane (Pt,C1,C3,N2,N4). The angles between
the complex plane and the plane of the noncoordinated
pyridine ring are between 46.2(2) and 50.7(2)°, resulting in
distances of 3.769 Å (3a), 3.656 Å (3b), 3.681 Å (3c), and
3.770 Å (3d) between the platinum atom and the center of
gravity of the noncoordinated ring. In crystals of complexes
3b−d, the torsion angles C21−O3−C10−C16 (44.3(7)°, 3b;
Figure 2. Molecular structure of [Pt(COMe)2{(2-py)3COMe}] (3b).
Ellipsoids are shown at the 30% probability level. Broken lines indicate
intermolecular C−H···O hydrogen bonds in crystals of 3b. Selected
structural parameters (distances in Å, angles in deg): Pt−C1 =
2.016(7), Pt−C3 = 2.014(6), Pt−N1 = 2.140(5), Pt−N2 = 2.147(4),
C1−Pt−C3 = 91.2(3), C1−Pt−N2 = 91.1(2), C3−Pt−N1 = 93.2(2),
N1−Pt−N2 = 84.4(2), C1−Pt−N1 = 175.5(2), C3−Pt−N2 =
174.0(4), C21−O3−C10−C16 = 44.3(7), C6···O1′ = 3.35(1),
H···O1′ = 2.49, C6−H···O1′ = 151, C14′···O2 = 3.277(8), H···O2
= 2.51, C14′−H···O2 = 139.
47.8(7)°, 3c; 41.2(7)°, 3d) demonstrated that the non-
coordinated pyridine rings and the substituents R at the
oxygen atoms O3 are gauche to each other.
In all structures, the carbonyl oxygen atoms of the two acetyl
ligands were found to lie on the same side of the complex
plane. Thus, the diacetyl moieties represent a “cisoid”
conformation as a result of intermolecular hydrogen bonds:
in crystals of the complex 3a·CH2Cl2 the O1···O3′ distance of
2.652(4) Å indicates the presence of an intermolecular O−
H···O hydrogen bond11 between the acetyl ligand and the
hydroxyl group at the backbone C atom of the (2-py)3COH
ligand (Figure 1), such that the crystals are threaded by one-
dimensional strands. In crystals of 3b,c the oxygen atoms of the
acetyl ligands were found to act as H acceptors in weak
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Figure 5. Wire model showing the zigzag arrangement of the
molecules in crystals of 3b.
Figure 3. Molecular structure of [Pt(COMe)2{(2-py)3COEt}] (3c).
Ellipsoids are shown at the 30% probability level. Broken lines indicate
intermolecular C−H···O hydrogen bonds in crystals of 3c. Selected
structural parameters (distances in Å, angles in deg): Pt−C1 =
1.998(6), Pt−C3 = 2.009(6), Pt−N1 = 2.143(4), Pt−N2 = 2.157(4),
C1−Pt−C3 = 89.8(2), C1−Pt−N2 = 92.3(2), C3−Pt−N1 = 93.7(2),
N1−Pt−N2 = 84.2(2), C1−Pt−N1 = 176.5(2), C3−Pt−N2 =
174.3(4), C21−O3−C10−C16 = 47.8(7), C6···O1′ = 3.25(1),
H···O1′ = 2.37, C6−H···O1′ = 155, C14′···O2 = 3.189(9), H···O2
= 2.43, C14′−H···O2 = 137.
broadened, pointing to a dynamic process. Thus, low-
temperature and temperature-dependent NMR measurements
in CD3OD were also performed.
At room temperature, the 1H NMR spectrum of [Pt-
(COMe)2{(2-py)3COH}] (3a) displayed one signal for both
acetyl ligands and two sets of signals with a 2:1 intensity in the
aromatic area reflecting a mirror-symmetric structure of the
1
complex in solution. In contrast, at room temperature, the H
NMR spectra of [Pt(COMe)2{(2-py)3COR}] (R = Me (3b),
Et (3c), Bn (3d)) exhibited broad signals for the protons both
of the acetyl ligands and of the coordinated pyridine rings, as
shown in Figure 6 for complex 3b. At −20 °C, these signals
were found to be split up, indicating a dynamic process that
leads to a loss of the mirror-symmetric structure of the
1
complexes in solution (Table 1). In contrast, the H NMR
spectrum of 3a (R = H) recorded even at −80 °C still displayed
only one sharp signal for the acetyl ligands andin addition to
the signals of the pendant pyridyl grouponly one set of
signals for the protons of the two coordinated pyridine rings.
The similar type 4 and 5 complexes [Pt(COMe)2{(2-
py)2PhCOR}] (R = H (4a), Me (4b)) and [Pt(COMe)2{(2-
py)2(m-Tol)COH}] (5a), where the pendant pyridyl group is
replaced by a phenyl or m-tolyl group, do not show any
dynamics, whereas the complex [Pt(COMe)2{(2-py)2(m-Tol)-
COMe}] (5b) shows a dynamics (although not all proton
signals are split up) analogous to that of complexes 3b−d
(Table 1). Thus, in compliance with complexes 3, the dynamics
depend on both the symmetry of the pendant group
(unsymmetrically substituted as py, m-Tol versus symmetrically
substituted as Ph) and the substitution pattern at the backbone
C atom (OR with R = Me, Et, Bn versus OH).
Figure 4. Molecular structure of [Pt(COMe)2{(2-py)3COBn}] (3d).
Ellipsoids are shown at the 30% probability level. Broken lines indicate
intermolecular C−H···O hydrogen bonds in crystals of 3d. Selected
structural parameters (distances in Å, angles in deg): Pt−C1 =
2.007(6), Pt−C3 = 2.010(6), Pt−N1 = 2.142(4), Pt−N2 = 2.156(4),
C1−Pt−C3 = 88.6(2), C1−Pt−N2 = 93.2(2), C3−Pt−N1 = 94.0(2),
N1−Pt−N2 = 84.2(2), C1−Pt−N1 = 176.9(2), C3−Pt−N2 =
177.9(2), C21−O3−C10−C16 = 41.2(7), C7′···O2 = 3.272(8),
H···O2 = 2.44, C7′−H···O2 = 147, C14″···O1 = 3.313(8), H···O1 =
2.38, C14″−H···O1 = 170.
In general, the same observations were made in the 13C
NMR spectra of compounds 3−5. At room temperature,
spectra of 3b−d and 5b exhibited broad signals (which split up
at lower temperatures) or even two sets of signals for the C
atoms of the acetyl ligands and of the coordinated pyridine
rings. On the other hand, the 13C NMR room-temperature
spectra of 3a, 4, and 5a reflect a mirror-symmetric structure of
the complexes in solution.
The conditions for the existence of mirror-symmetric
structures in solution should be both a fast rotation of the
acetyl ligands and a fast rotation of the substituent R at the
backbone of the (2-py)3COR ligand as well as of the
noncoordinated pyridine/m-tolyl ring. Since a hindered
rotation of the acetyl ligands can be excluded due to experience
with a number of other diacetylplatinum(II) complexes,5,7,13
intermolecular Cpy−H···O hydrogen bonds, so that the crystals
are built up by strands in a zigzag manner, as shown in Figure 5
for complex 3b as an example. The structural parameters of all
these hydrogen bonds (C···O = 3.189(9)−3.35(1) Å, O···H =
2.37−2.51 Å, C−H···O = 137−170°) are in the range expected
for such attractive interactions.12 In contrast, in crystals of 3d
the Cpy−H···O hydrogen bonds built up a three-dimensional
network.
2.3. Spectroscopic Investigations. The 1H, 13C, and
195Pt NMR spectra of the diacetylplatinum(II) complexes 3−5
1
give proof of their identities. At room temperature, in the H
and 13C NMR spectra of 3b−d and 5b some signals are
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Figure 6. Variable-temperature 1H NMR spectra of 3b measured in CD3OD: (A) region related to the acetyl ligands.; (B) aromatic region. Signals of
the noncoordinated pyridyl group are marked with asterisks.
Table 1. Temperature-Dependent Characteristic Proton Shifts (in ppm) of the Acetyl Ligands and of the Coordinated Pyridyl
a
Groups of [Pt(COMe)2{(2-py)3COR}] (R = Me (3b), Et (3c), Bn (3d)) and [Pt(COMe)2{(2-py)2(m-Tol)COMe}] (5b)
T (°C)
δacetyl
1.79
δH3
8.21
δH4
8.11
δH5
7.44
δH6
8.62
b
3b
+27
−20
+27
−20
+27
−20
+27
−20
+27
+27
+27
+27
1.74/1.85
1.79
8.20/8.29
8.21
8.11/8.18
8.11
7.45/7.52
7.44
8.60/8.63
8.62
b
3c
1.73/1.85
1.80
8.19/8.28
8.26
8.11/8.19
8.12
7.45/7.52
7.45
8.60/8.63
8.65
b
3d
5b
1.75/1.85
1.76
8.21/8.33
8.20
8.10/8.18
8.10
7.45/7.52
8.62/8.64
8.65
b
e
ca. 7.4
e
1.72/1.80
1.76
8.22
8.13
ca. 7.4
8.61/8.67
8.59
b
c
3a
4a
8.38
8.10
7.43
7.25
7.25
7.43
1.71
8.43
7.96
8.64
d
4b
1.79
8.04
7.88
8.83
b
5a
1.74
8.40
8.10
8.63
a
b
c
For comparison, the corresponding values of complexes 3a, 4a,b, and 5a without dynamics are shown. Measured in CDOD3. Measured in
d
e
CD2Cl2. Measured in CDCl3. Overlapped with other signals.
these results imply that in complexes 3b−d and 5b at least one
of the other aforementioned rotations is hindered and thus is
the reason for the observed phenomena in NMR spectroscopy.
To get an impression of the thermodynamic parameters of
these potentially hindered rotations, the signals of the acetyl
ligands were used for an analysis of this dynamics by NMR
1
techniques. Thus, variable-temperature H NMR studies were
performed to estimate the coalescence temperatures. Fur-
thermore, from line-shape analyses14 of spectra recorded in a
range close to the coalescence temperatures (283−318 K), the
activation parameters ΔH⧧ and ΔS⧧ have been determined by
Eyring plots (Figure 7). The Gibbs free energies of activation at
the coalescence temperature were calculated according to
ΔGC⧧ = ΔH⧧ − TC·ΔS⧧. The compilation of ΔGC⧧ and related
parameters in Table 2 shows that the coalescence temperatures
(296−303 K) as well as the Gibbs free energies of activation at
the coalescence temperature (14.6−15.8 kcal mol−1) for all
compounds were found in a narrow range. The enthalpies of
activation (ca. 9.2 kcal mol−1) and entropies of activation (ca.
−18.7 cal mol−1 K−1) calculated for complexes 3b−d are in a
narrow range as well. In contrast, the corresponding values of
complex 5b were found to be ΔH⧧ = 12.8 kcal mol−1 and ΔS⧧
= −8.5 cal mol−1 K−1, thus being higher by about 2.6 kcal mol−1
and about 10.2 cal mol−1 K−1, respectively. For comparison, the
requisite values of the well-studied dimethylformamide as the
Figure 7. Eyring plots of complexes [Pt(COMe)2{(2-py)3COR}] (R =
Me (3b), Et (3c), Bn (3d)) and [Pt(COMe)2{(2-py)2(m-Tol)-
COMe}] (5b).
2.4. DFT Calculations. For an additional qualitative and
quantitative analysis of the dynamics found in complexes 3b−d
and 5b, quantum-chemical calculations on the DFT level of
theory were performed using the B3LYP functional and high-
quality basis sets for all atoms and a pseudopotential for Pt
considering relativistic effects (for details, see the Experimental
Section). In all calculations solvent effects (MeOH) were
“benchmark” are given: ΔGC = 21.5 kcal mol−1 at TC = 114
⧧
°C;15 ΔH = 21.2 kcal mol−1, ΔS = −1.6 cal mol−1 K−1.16
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Table 2. Gibbs Free Energies of Activation and Related
Parameters for the Dynamics in Complexes 3b−d and 5b
Table 3. Calculated Standard Gibbs Free Energies (in kcal
mol−1) of the Conformers of 3a*, 3b*, and 5b* Relative to
the Most Stable Conformer
ΔH⧧ (kcal
ΔS⧧ (cal mol−1
ΔGC (kcal
TC
⧧
mol−1
)
K−1
)
mol−1
)
(K)
entry
conformer
3a*
3b*
5b*
a
3b
3c
3d
5b
9.1 0.5
9.3 0.3
9.2 0.4
12.8 0.9
−18.5 1.4
−18.2 1.0
−19.1 1.4
−8.5 3.0
14.6 0.8
14.8 0.6
15.0 0.8
15.4 1.8
296
301
303
302
1
2
3
4
pyax/gauche
0
0
0
a
pyax/anti
4.2
7.2
3.2
5.5
9.5
5.3
5.7
6.9
6.4
b
pyeq/syn
b
pyeq/anti
a
Conformation characterized by the R−O−C−Ci dihedral angle (Ci =
considered according to Tomasi’s polarized continuum
model.17 To analyze the dynamics, the complexes [Pt-
(COMe)2{(2-py)3COMe}] (3b) and [Pt(COMe)2{(2-
py)2(m-Tol)COMe}] (5b) were chosen. Furthermore, for
comparison, the complex [Pt(COMe)2{(2-py)3COH}] (3a)
showing a mirror-symmetric structure even at −80 °C was
included into the calculations.
ipso-C atom of the pyridine and tolyl ring, respectively).
b
Conformation determined by the N−Ci−C−O (for 5b* C2−Ci−
C−O) dihedral angle.
As discussed in section 2.3, the dynamics observed may be
caused by a hindered rotation of the asymmetric pendant group
and/or of the substituent R. In Figure 9 the Gibbs free energy
diagram for the rotation of the pendant pyridyl group is shown
starting from the most stable gauche conformers of 3a* and
3b*. Here and in the following, the dynamics of 5b* are very
similar to those of 3b*; thus, the diagrams for 5b* are only
given in the Supporting Information. Apart from these
conformers (pyax/gauche; Figure 9, a) only one further
equilibrium structure each could be located. They are also
pyax/gauche conformers (Figure 9, c), their energies being only
slightly above the global minima. In the case of 3a* (R = H),
the two activation barriers (Figure 9, b/d) are significantly
different; thus, a flip-flop-type motion could be operative: the
activation barrier of the flip-flop-type motion where the N atom
of the pendant pyridine ring is directed toward the substituent
R = H (Figure 9, a → c via b) is 4.2 kcal mol−1, whereas that
where the 3-C−H group of the pendant pyridine ring is
directed toward the substituent R = H (Figure 9, a → c via d) is
13.7 kcal mol−1. In the case of 3b* (R = Me) the two activation
barriers (Figure 9, b/d) are of the same order of magnitude
(17.8/19.5 kcal mol−1) and are significantly higher than that for
3a*. Thus, for 3b*, even at room temperature, a rotation of the
pendant pyridine group is expected to be hindered.
At first the equilibrium structures of reasonable conformers
(four for each complex) were calculated: see Figure 8 for 3b*27
and the Supporting Information for 3a* and 5b*. The standard
Gibbs energies (ΔG⧧) are given in Table 3. As expected, in all
structures the C(μ-py)2Pt units adopt a boat conformation with
the platinum atom and the backbone carbon atom of the (2-
py)3COR or the (2-py)2(m-Tol)COMe ligand at the apexes. In
the global minimum (Table 3, entry 1), the OR groups are
equatorially positioned, while the asymmetric pendant groups
(py in 3a*/3b*, m-Tol in 5b*) are in an axial position and are
thus curled toward the platinum center. Moreover, the
substituents R and the pendant rings (py/m-Tol) are in
mutually gauche positions. These conformations (R = H
(3a*(pyax/gauche)); R = Me (3b*(pyax/gauche), 5b*(Tolax/
gauche))) were found in crystals of type 3 complexes except for
the transoid position of the acetyl ligands which isin
generalfavored over a cisoid position.6 The cisoid position
found in crystals of 3 is a consequence of intermolecular
hydrogen bonds (see section 2.2).
The conformers having an anti (fully staggered) conforma-
tion of the R−O−C−Ci dihedral angle (instead of a gauche
conformation) are 4.2−5.7 kcal mol−1 higher in their standard
Gibbs free energies (Table 3, entry 2), which might be caused
by steric interactions. Furthermore, two conformers, each with
an inverted boat unit, have to be considered. This results in an
equatorial position of the pendant pyridyl/m-tolyl groups
(pyeq/Toleq). Moreover, the N−Ci−C−O dihedral angles (for
5b* C2−Ci−C−O) can be syn or anti. All these conformers are,
at least, 3.2 kcal mol−1 higher in their standard Gibbs energies
(Table 3, entries 3 and 4).
In Figure 10 the Gibbs free energy diagram for the rotation
of R for the complexes 3a* and 3b* is shown. An inspection of
the Newman projections makes it clear that a rotation of the
substituent R by 360° includes the following conversions:
gauche (Figure 10, a; global minimum; R pointed toward the N
atom of the pyridine ring) → anti (Figure 10, c) → gauche
(Figure 10, e; lone electron pair of the O atom pointed toward
the N atom) → gauche (Figure 10, a; global minimum).
Obviously, the activation barriers (Figure 10, b/d) are mainly a
Figure 8. Calculated equilibrium structures of different conformers of [Pt(COMe)2{(2-py)3COMe}] (3b*). The conformers are designated with
indices showing an axial (pyax) or equatorial (pyeq) position of the noncoordinated pyridine group and characterizing the dihedral angles R−O−C−
Ci (gauche, anti) and N−Ci−C−O (syn, anti) (Ci = ipso-C atom of the noncoordinated pyridine ring), respectively. The standard Gibbs free energies
(in kcal mol−1) are given in parentheses relative to the most stable conformer.
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Figure 9. Gibbs free energy diagram for the rotation of the noncoordinated pyridyl group in [Pt(COMe)2{(2-py)3COR}] (R = H (3a*) Me (3b*)).
The Gibbs energies (in kcal mol−1) are given in parentheses relative to the most stable isomer (ts = transition state). The Newman projections (lp =
lone electron pair; pyc = coordinated pyridyl) are along the O−C vector of the backbone of the (2-py)3COR (R = H, Me) ligands.
Figure 10. Gibbs free energy diagram for the rotation of the substituent R in [Pt(COMe)2{(2-py)3COR}] (R = H (3a*), Me (3b*)). The Gibbs
energies (in kcal mol−1) are given in parentheses relative to the most stable isomer (ts = transition state). The Newman projections (lp = lone
electron pair; pyc = coordinated pyridyl) are along the O−C vector of the backbone of the (2-py)3COR (R = H, Me) ligands.
consequence of steric repulsion between the substituent R and
the 3-CH groups of the coordinated pyridine rings (pyc). Thus,
as expected, for R = H (3a*) the barriers are remarkably lower
than for R = Me (3b*): 6.2/6.8 vs 13.6/13.8 kcal mol−1.
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Figure 11. Calculated equilibrium structure of the anti conformer 3b*(pyax/anti) with the N atom of the pendant pyridine ring aligned toward the Pt
atom.
Figure 12. Gibbs free energy diagram for the dynamics in [Pt(COMe)2{(2-py)3COMe}] (3b*). The Gibbs energies (in kcal mol−1) are given in
parentheses relative to the most stable isomer (ts = transition state). The Newman projections (lp = lone electron pair; pyc = coordinated pyridyl)
are along the O−C vector of the backbone of the (2-py)3COMe ligand.
Since for the gauche conformer of 3b* the activation barriers
for the rotation of the pendant pyridine ring (Figure 9, b/d) are
significantly higher than those calculated for the gauche−anti
isomerization (17.8/19.5 vs 13.6/13.8 kcal mol−1), calculations
concerning the rotation of the pendant groups of the anti
conformers were performed. In addition to the equilibrium
structure of the thermodynamically most stable anti conformer
described above (3b*(pyax/anti) in Figure 8), another one
(3b*(pyax/anti′′)) was found lying 0.9 kcal mol−1 over the
aforementioned one (Figure 11). In this structure the pendant
pyridyl group is positioned perpendicular to the complex plane
while the N atom is aligned toward the Pt atom. The rotation
of 90° both clockwise and anticlockwise was found to be almost
barrierless; thus, a flip-flop-type motion could be operative
(Figure 11). In contrast, a similar structure having the C−H
group oriented toward the Pt atom is a transition state, which
lies in its Gibbs free energy 3.6 kcal mol−1 above the most
stable anti conformer (see the Gibbs free energy diagram in
Figure S2 (Supporting Information)).
For the rotation of the m-tolyl group in the anti conformer of
5b* only insignificant activation barriers were found, and thus,
a 360° rotation could be operative in this case. Although
irrelevant (because the gauche−anti isomerization is higher in
Gibbs free energy than the flip-flop-type motion of the pyridyl
group in the gauche conformer), the rotation of the pyridine
ring in the anti conformer of 3a* was calculated. In this case
two activation barriers of 6.2 and 7.3 kcal mol−1 were found
(see the Gibbs free energy diagram in Figure S1 (Supporting
Information)).
All structures of the conformers with the inverted boat
structure (pyeq/syn and pyeq/anti) lie between 3.2 and 6.9 kcal
mol−1 above the global minimum equilibrium structures (pyax/
gauche). Furthermore, for the inversion of the boat structure
(which might proceed according a dissociative mechanism),18 a
relatively high barrier can be assumed. Thus, although it cannot
H
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be strictly ruled out, these conformers should not play a role in
the dynamics observed.
tris(pyrazolyl)methane ligands, and complexes of type 3 with
neutral tris(pyridyl)methanol and tris(pyridyl)methyl ether
ligands discussed here. In type IV complexes, molecular
rearrangement (exchange of coordinated and noncoordinated
pyrazolyl rings via intermediates having only κ1N-coordinated
ligands) was observed, pointing to a weak coordination of the
neutral tris(pyrazolyl)methane ligands.6 Type III complexes do
not show any molecular dynamics, indicating, as expected, a
stronger coordination of the scorpionate ligands due to their
negative charge.5 In the neutral type 3 complexes discussed
here, which have pyridine type donor sites, the molecular
dynamics observed are due to a rotation or a flip-flop-type
motion of the pendant (noncoordinated) pyridine group but
not due to a decoordination/recoordination mechanism as in
type IV complexes. This is in accord with a stronger σ donor
ability of pyridine in comparison with that of pyrazole.9 Thus,
the donor ability of such ligands depends both on the overall
charges of the ligands and complexes, respectively, and on the
nature of the donor N atoms.
2.5. Conclusions. Within this work, the synthesis and
characterization of diacetylplatinum(II) complexes bearing κ2-
bonded ligands of type (2-py)3COR (R = H, Me, Et, Bn), (2-
py)2PhCOR, and (2-py)2(m-Tol)COR (R = H, Me) have been
described. Furthermore, both a qualitative and quantitative
analyses of the dynamics found in complexes 3b−d and 5b
bearing asymmetric pendant groups (py/m-Tol) and etherified
ligands (R ≠ H) by NMR techniques and DFT calculations
have been presented. The results of the DFT calculations
indicate that the dynamics observed is caused by an interplay of
a hindered and unhindered rotation, respectively, of the
substituent R and/or of the pendant py/m-Tol group.
(1) For complexes with an etherified ligand (R ≠ H) and an
asymmetric pendant pyridyl group (3b−3d; in the following
discussed with 3b* as an example) it can be stated that, starting
from the gauche conformer, the activation barrier for the
gauche−anti isomerization (Figure 12, a → c) is remarkably
lower than that for the rotation of the pendant pyridyl group
(Figure 12, a → b). For the anti conformer a flip-flop-type
motion of the pendant group (py) has an insignificant
activation barrier and thus is favorable (Figure 12, c → e via
d). In accordance with the NMR experiments, the mirror
symmetry of complexes in solution is retained, at least at higher
temperatures, due to the activation barrier of 13.6 kcal mol−1
(3b*) for the gauche−anti isomerization.
(2) The situation of complex 5b having an etherified ligand
(R = Me) and an asymmetric pendant m-tolyl group is
analogous to that described above, butinstead of a flip-flop-
type motion of the pendant group in the anti conformera full
360° rotation takes place, which proved to be nearly barrierless
(see Figure S5 (Supporting Information) for 5b*).
(3) For complexes with an alcohol group (R = H) and an
asymmetric pendant pyridyl or m-tolyl group (3a, 5a; in the
following discussed with 3a* as an example, see Figures 12 and
10) it can be stated that a flip-flop-type motion of the pendant
group of the gauche conformer (global minimum) retains the
mirror symmetry, whereas the gauche−anti isomerization does
not play a role. In accordance with the NMR experiments, due
to the activation barrier of 4.2 kcal mol−1, the dynamics are
operative even at lower temperatures.
3. EXPERIMENTAL SECTION
3.1. General Comments. All reactions were performed under an
argon atmosphere using standard Schlenk techniques. Solvents were
dried (diethyl ether and THF over Na/benzophenone) and distilled
prior to use. If not otherwise stated, NMR spectra were recorded at 27
°C with Varian VXR 400 and Unity 500 spectrometers. Chemical
shifts are relative to solvent signals (CDCl3, δH 7.24, δC 77.0; CD2Cl2,
δH 5.32, δC 53.8; CD3OD δH 3.31, δC 49.0) as internal references;
δ(195Pt) is referenced to Na2[PtCl6]. If necessary, 2D NMR techniques
(H,H C,H COSY, HMBC, and NOESY) were used to assign the
signals in 1H and 13C NMR spectra. Temperature calibration for
variable-temperature measurements was performed using CD3OD.19
IR spectra were recorded with a Bruker Tensor 28 spectrometer with a
Platinum ATR unit. Microanalyses were performed by the University
of Halle microanalytical laboratory using a CHNS-932 (LECO)
elemental analyzer. The high-resolution ESI mass spectra were
obtained from a Bruker Apex III Fourier transform ion cyclotron
resonance (FT-ICR) mass spectrometer (Bruker Daltonics) equipped
with an Infinity cell, a 7.0 T superconducting magnet (Bruker), an rf-
only hexapole ion guide, and an external APOLLO electrospray ion
source (Agilent, off-axis spray). The sample solutions were introduced
continuously via a syringe pump with a flow rate of 120 μL h−1. The
complexes [Pt2 {(COMe)2 H}2 (μ-Cl)2 ] (1) and [Pt-
(COMe)2(NH2Bn)2] (2) were prepared according to literature
methods.1,7 Syntheses and spectroscopic data of the ligands, which,
in part, have not yet been described in the literature, are reported in
the Supporting Information.
(4) For complexes with a symmetric pendant phenyl group
(4a,b), irrespective whether the ligand is etherified (R = Me) or
not (R = H), mirror-symmetric structures were observed NMR
spectroscopically. Obviously, the situation is analogous to the
m-tolyl complex 5b*, but due to the symmetric pendant phenyl
group a loss of the complex symmetry due to hindered rotation
is irrelevant.
The present study gives a detailed insight into the nature of
the dynamics in diacetylplatinum(II) complexes bearing
κ2N,N′-coordinated ligands of types (2-py)3COR, (2-
py)2PhCOR, and (2-py)2(m-Tol)COR. Moreover, a very
good agreement between the values obtained from NMR
experiments (ΔG298 = 14.6 kcal mol−1 (3b), 14.7 kcal mol−1
(3c), 14.9 kcal mol−1 (3d), 15.3 kcal mol−1 (5b)) and from
DFT calculations (ΔG298 = 13.6/14.5 kcal mol−1 (3b*/5b*))
was found.
3.2. Syntheses of the Diacetylplatinum(II) Complexes (3−5).
[Pt(COMe)2(NH2Bn)2] (2; 100 mg, 0.2 mmol) and an equimolar
amount of the respective ligand were dissolved in THF (5 mL) and
stirred for 30 min. The volume of the yellow solution was reduced in
vacuo to about 2 mL, and diethyl ether (8 mL) was added. The yellow
precipitate that formed was filtered off, washed with diethyl ether (3 ×
2 mL), and dried in vacuo.
3.2.1. [Pt(COMe)2{(2-py)3COH}] (3a). Yield: 87 mg (80%). HRMS
(ESI): m/z calcd for [C20H19O3N3PtH]+ 545.11487, found for [M −
H]+ 545.11456. 1H NMR (400 MHz, CD3OD): δ 1.76 (s, 6H,
COCH3), 7.10 (m, 1H, H9 py), 7.43 (m, 2H, H5/5′ py), 7.49 (m, 1H,
H11 py), 7.89 (m, 1H, H10 py), 8.10 (m, 2H, H4/4′ py), 8.38 (m, 2H,
H3/3′ py), 8.56 (m, 1H, H12 py), 8.59 (m, 2H, H6/6′ py). 13C NMR
3
(100 MHz, CD3OD): δ 43.9 (s + d, JPt,H = 343.7 Hz, COCH3), 85.0
(s, (2-py)3COH), 124.6 (s, C11 py), 125.0 (s, C3/3′ py), 125.5 (s, C5/5
′
Thus, overall there are three types of diacetylplatinum(II)
complexes with κ2N,N′-coordinated ligands having an addi-
tional pendant N-donor site at their disposal, namely type III
complexes (see Scheme 1) with anionic tris(pyrazolyl)borate
ligands, type IV complexes (see Scheme 1) with neutral
+ C9 py), 138.8 (s, C10 py), 140.7 (s, C4/4′ py), 150.5 (s, C12 py), 152.2
(s, C6/6′ py), 162.5 (s, C2/2′ py), 164.8 (s, C8 py), 236.5 (s + d, 3JPt,H
=
1286.9 Hz, COCH3). Here and in the following, the two coordinated
pyridine rings are numbered 1−6 and 1′−6′, respectively; non-
coordinated pyridine rings are numbered 7−12. 195Pt NMR (107
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MHz, CD2Cl2): δ −3221.8 (s). IR: ν(CO) 1624, ν(CO) 1601, ν(CO)
1576, ν(CO) 1562 cm−1.
230.2 (s, 2 × COCH3). 13C NMR (125 MHz, CDCl3, +27 °C): δ
43.3/43.6 (s (br), 2 × COCH3), 67.9 (s, OCH2Ph), 89.1 (s, (2-
py)3COBn), 122.8/123.0 (s (br), C3/3′ py), 123.5 (s, C11 py), 123.7/
124.5 (s (br), C5 + C5′ py), 126.6 (s, C9 py), 127.1 (s, m-CH Ph),
128.0 (s, o-CH Ph), 128.6 (s, p-CH Ph), 136.6 (s, C10 py), 137.2 (s, i-C
Ph), 138.6 (s (br), C4/4′ py), 149.5 (s, C12 py), 151.5/153.1 (s (br), C6
+ C6′ py), 158.4/160.8 (s (br), C2 + C2′ py), 158.8 (s, C8 py), 226.4/
229.5 (s (br), 2 × COCH3). 195Pt NMR (107 MHz, CD2Cl2): δ
−3213.4 (s). IR: ν(CO) 1614, ν(CO) 1583 cm−1.
3.2.2. [Pt(COMe)2{(2-py)3COMe}] (3b). Yield: 82 mg (73%). HRMS
(ESI): m/z calcd for [C21H21O3N3PtH]+ 559.13053, found for [M −
1
H]+ 559.13046. H NMR (500 MHz, CD3OD, −20 °C): δ 1.74 (s,
3H, COCH3), 1.85 (s, 3H, COCH3), 3.29 (s, 3H, OCH3), 7.28 (m,
1H, H9 py), 7.45/7.52 (m, 2H, H5 + H5′ py), 7.64 (m, 1H, H11 py),
8.00 (m, 1H, H10 py), 8.11/8.18 (m, 2H, H4 + H4′py), 8.20/8.29 (m,
2H, H3 + H3′py), 8.60/8.63 (m, 2H, H6 + H6′ py), 8.69 (m, 1H, H12
1
py). H NMR (500 MHz, CD3OD, +27 °C): δ 1.79 (s (br), 6H,
3.2.5. [Pt(COMe)2{(2-py)2PhCOH}] (4a). Yield: 98 mg (90%).
COCH3), 3.29 (s, 3H, OCH3), 7.22 (m, 1H, H9 py), 7.44 (s (br), 2H,
H5/5′ py), 7.59 (m, 1H, H11 py), 7.96 (m, 1H, H10 py), 8.11 (s (br),
2H, H4/4′ py), 8.21 (s (br), 2H, H3/3′ py), 8.62 (m, 2H, H6/6′ py), 8.66
(m, 1H, H12 py). 13C NMR (50 MHz, CD2Cl2, −80 °C): δ 43.4/43.5
(s, 2 × COCH3), 53.6 (s, OCH3), 88.2 (s, (2-py)3COMe), 122.6/
123.1/123.2/123.6/124.2/125.7 (s, C3 + C3′ + C9 + C5 + C5′ + C11
py), 136.2 (s, C10 py), 138.3/138.7 (s, C4 + C4′ py), 149.2/150.4/
151.3 (s, C6 + C6′ + C12py), 156.9/158.2/159.6 (s, C2 + C2′ + C8 py),
229.0/230.3 (s, 2 × COCH3). 13C NMR (100 MHz, CD2Cl2, +27 °C):
δ 43.5 (s (br), COCH3), 54.1 (s, OCH3), 89.4 (s, (2-py)3COMe),
123.5 (s (br), C3/3′ py), 123.8 (s, C11 py), 124.1/124.6 (s (br), C5 +
C5′ py), 126.5 (s, C9 py), 136.8 (s, C10 py), 138.8 (s (br), C4/4′ py),
149.8 (s, C12 py), 151.5/152.6 (s (br), C6 + C6′ py), 158.9/161.1 (s
(br), C2 + C2′ py), 159.3 (s, C8 py), 226.6/227.8 (s (br), 2 × COCH3).
195Pt NMR (107 MHz, CD2Cl2): δ −3221.8 (s). IR: ν(CO) 1600,
ν(CO) 1583, ν(CO) 1564 cm−1.
HRMS (ESI): m/z calcd for [C21H20O3N2PtH]+ 544.11965, found
1
for [M − H]+ 544.11945. H NMR (500 MHz, CD2Cl2): δ 1.71 (s,
6H, COCH3), 6.92 (m, 2H, o-CH Ph), 7.25 (m, 2H, H5/5′ py), 7.32
(m, 2H, m-CH Ph), 7.39 (m, 1H, p-CH Ph), 7.96 (m, 2H, H4/4′ py),
8.43 (m, 2H, H3/3′ py), 8.64 (m, 2H, H6/6′ py). 13C NMR (125 MHz,
2
+27 °C, CD2Cl2): δ 43.2 (s + d, JPt,C = 355.2 Hz, COCH3), 82.9 (s,
(2-py)2PhCOH), 123.7 (s, C3/3′ py), 124.0 (s, C5/5′ py), 128.3 (s, p-
CH Ph), 128.4 (s, o-CH Ph), 128.8 (s, m-CH Ph), 138.7 (s, C4/4′ py),
145.8 (s, i-C Ph), 151.4 (s, C6/6′ py), 161.2 (s, C2/2′ py), 230.5 (s + d,
1JPt,C = 1304.7 Hz, COCH3). 195Pt-NMR (107 MHz, CD2Cl2): δ
−3249.4 (s). IR: ν(CO) 1599, ν(CO) 1576 cm−1.
3.2.6. [Pt(COMe)2{(2-py)2PhCOMe}] (4b). Yield: 87 mg (78%).
HRMS (ESI): m/z calcd for [C22H22O3N2PtH]+ 558.13531, found for
1
[M − H]+ 558.13487. H NMR (400 MHz, CDCl3): δ 1.79 (s, 6H,
COCH3), 3.18 (s, 3H, OCH3), 6.95 (m, 2H, o-CH Ph), 7.25 (m, 2H,
H5/5′ py), 7.39−7.44 (m, 3H, m-CH + p-CH Ph), 7.88 (m, 2H, H4/4
′
3.2.3. [Pt(COMe)2{(2-py)3COEt}] (3c). Yield: 97 mg (85%). HRMS
py), 8.04 (m, 2H, H3/3′ py), 8.83 (m, 2H, H6/6′ py). 13C NMR (125
MHz, +27 °C, CDCl3): δ 43.5 (s + d, 2JPt,C = 377.6 Hz, COCH3), 88.4
(s, (2-py)2PhCOH), 122.8 (s, C3/3′ py), 123.9 (s, C5/5′ py), 128.6 (s,
(ESI): m/z calcd for [C22H23O3N3PtH]+ 545.14619, found for [M −
1
H]+ 573.14627. H NMR (500 MHz, CD3OD, −20 °C): δ 1.40 (t,
3H, OCH2CH3), 1.73 (s, 3H, COCH3), 1.85 (s, 3H, COCH3), 3.30
(m, 2H, OCH2CH3), 7.25 (m, 1H, H9 py), 7.45/7.52 (s, 2H, H5 +
H5′), 7.63 (m, 1H, H11 py), 7.99 (m, 1H, H10 py), 8.11/8.19 (s, 2H, H4
+ H4′ py), 8.19/8.28 (s, 2H, H3 + H3′ py), 8.60/8.63 (m, 2H, H6 + H6′
py), 8.67 (m, 1H, H12 py). 1H NMR (500 MHz, CD3OD, +27 °C): δ
1.33 (t, 3H, OCH2CH3), 1.79 (s (br), 6H, COCH3), 3.33 (s, (br), 2H,
OCH2CH3), 7.19 (m, 1H, H9 py), 7.44 (s (br), 2H, H5/5′ py), 7.57 (m,
1H, H11 py), 7.94 (m, 1H, H10 py), 8.11 (s (br), 2H, H4/4′ py), 8.21 (s
m-CH Ph), 128.8 (s, p-CH Ph), 130.4 (s, m-CH Ph), 138.3 (s, C4/4
′
py), 139.2 (s, i-C Ph), 152.5 (s, C6/6′ py), 160.0 (s, C2/2′ py), 230.5 (s
1
+ d, JPt,C = 1304.7 Hz, COCH3). 195Pt NMR (107 MHz, CDCl3): δ
−3206.3 (s). IR: ν(CO) 1599, ν(CO) 1576 cm−1.
3.2.7. [Pt(COMe)2{(2-py)2(m-Tol)COH}] (5a). Yield: 80 mg (72%).
HRMS (ESI): m/z calcd for [C22H22O3N2PtH]+ 558.13531, found for
1
[M − H]+ 558.13508. H NMR (400 MHz, CD3OD): δ 1.74 (s, 6H,
COCH3), 2.30 (s, 3H, 3-CH3Ph), 6.72 (m, 1H, H6 m-Tol), 6.76 (s,
1H, H2 m-Tol), 7.27−7.34 (m, 2H, H4 + H5 m-Tol), 7.43 (m, 2H,
H5/5′ py), 8.10 (s, 2H, H4/4′ py), 8.40 (m, 2H, H3/3′ py), 8.63 (s, 2H,
H6/6′ py). 13C NMR (100 MHz, CD3OD): δ 21.6 (s, 3-CH3Ph), 43.9
(s, COMe), 53.5 (s, OCH3), 82.3 (s, (2-py)2(m-Tol)COH), 124.9 (s,
C3/3′ py), 125.4 (s, C5/5′ py), 126.9 (s, C6 m-Tol), 130.0 (s, C4 + C5 m-
Tol), 130.6 (s, C2 m-Tol), 139.6 (s, C3, m-Tol), 140.5 (s, C4/4′ py),
147.1 (s, C1 m-Tol), 152.4 (s, C6/6′ py), 163.2 (s, C2/2′ py), 236.9 (s,
COCH3). 195Pt NMR (107 MHz, CD2Cl2): δ −3244.8 (s). IR: ν(CO)
1618, ν(CO) 1600, ν(CO) 1574 cm−1.
3.2.8. [Pt(COMe)2{(2-py)2(m-Tol)COMe}] (5b). Yield: 78 mg (68%).
HRMS (ESI): m/z calcd for [C23H24O3N2PtH]+ 545.15097, found for
[M − H]+ 572.15109. 1H NMR (500 MHz, CD3OD, −20 °C): δ 1.72
(s, 3H, COCH3), 1.80 (s, 3H, COCH3), 2.34 (s, 3H, 3-CH3Ph), 3.24
(s, 3H, OCH3), 6.77 (m, 1H, H6 m-Tol), 6.84 (s, 1H, H2 m-Tol),
7.32−7.49 (m, 4H, H4 + H5 m-Tol + H5/5′ py), 8.13 (s, 2H, H4/4′ py),
8.22 (m, 2H, H3/3′ py), 8.61/8.67 (m, 2H, H6/H6′ py). 1H NMR (500
MHz, CD3OD, +27 °C): δ 1.76 (s (br), 6H, COCH3), 2.33 (s, 3H, 3-
CH3Ph), 3.25 (s, 3H, OCH3), 6.76 (m, 1H, H6 m-Tol), 6.81 (s, 1H, H2
m-Tol), 7.31−7.45 (m, 4H, H4 + H5 m-Tol + H5/5′ py), 8.10 (s, 2H,
H4/4′ py), 8.20 (m, 2H, H3/3′ py), 8.65 (s (br), 2H, H6/6′ py). 13C
NMR (125 MHz, −20 °C, CD3OD): δ 21.7 (s, 3-CH3Ph), 43.4/44.1
(s, 2 × COMe), 54.2 (s, OCH3), 89.6 (s, (2-py)2(m-Tol)COH),
125.0/125.2 (s, C3 + C3′ py), 125.7/125.8 (s, C5 + C5′ py), 128.7 (s, C6
m-Tol), 130.0 (s, C5 m-Tol), 130.8 (s, C4 m-Tol), 132.5 (s, C2 m-Tol),
139.6 (s, C3, m-Tol), 140.9/141.0 (s, C4 + C4′ py), 139.1 (s, C1 m-
Tol), 152.6/152.9 (s, C6 + C6′ py), 160.9/161.5 (s, C2 + C2′ py),
236.4/237.3 (s, 2 × COCH3). 13C NMR (125 MHz, +27 °C, CDCl3):
δ 21.5 (s, 3-CH3Ph), 43.4 (s (br), COMe), 53.5 (s, OCH3), 88.4 (s, (2-
py)2(m-Tol)COH), 122.8 (s (br), C3/3′ py), 123.8 (s (br), C5/5′ py),
127.4 (s, C6 m-Tol), 128.5, (s, C5 m-Tol), 129.5 (s, C4 m-Tol), 131.1
(s, C2 m-Tol), 138.2 (s, C3 m-Tol), 138.3 (s (br), C4/4′ py), 139.1 (s,
C1 m-Tol), 152.4 (s (br), C6/6′ py), 159.9/160.2 (s (br), C2 + C2′ py),
(br), 2H, H3/3′ py), 8.62 (m, 2H, H6/6′ py), 8.64 (m, 1H, H12 py). 13
C
NMR (100 MHz, CD3OD, −20 °C): δ 15.5 (s, OCH2CH3), 43.9/44.2
(s, 2 × COCH3), 63.0 (s, OCH2CH3), 89.9 (s, (2-py)3COEt), 125.0/
125.1/125.3/125.6/126.2/127.9 (s, C3 + C3′ + C9 + C5 + C5′ + C11
py), 138.9/140.9/141.3 (s, C4 + C4′ + C10 py), 150.5/152.0/153.1 (s,
C6 + C6′ + C12 py), 159.8/160.8/161.7 (s, C2 + C2′ + C8 py), 235.4/
237.7 (s, 2 × COCH3).13C NMR (100 MHz, CD2Cl2, +27 °C): δ 15.4
(s, OCH2CH3), 43.5 (s (br), COCH3), 62.0 (s, OCH2CH3), 89.2 (s,
(2-py)3COEt), 123.4 (s (br), C3/3′ py), 123.6 (s, C11 py), 124.1/124.7
(s (br), C5 + C5′ py), 126.3 (s, C9 py), 136.8 (s, C10 py), 138.8/139.9
(s (br), C4 + C4′ py), 149.7 (s, C12 py), 151.4/152.5 (s (br), C6 + C6′
py), 159.2/161.3 (s (br), C2 + C2′ py), 159.9 (s, C8 py), 227.2/228.4 (s
(br), 2 × COCH3). 195Pt NMR (107 MHz, CD2Cl2): δ −3213.4 (s).
IR: ν(CO) 1615, ν(CO) 1585 cm−1.
3.2.4. [Pt(COMe)2{(2-py)3COBn}] (3d). Yield: 89 mg (70%). HRMS
(ESI): m/z calcd for [C27H25O3N3PtH]+ 635.16188, found for [M −
1
H]+ 635.16155. H NMR (500 MHz, CD3OD, −20 °C): δ 1.75 (s,
3H, COCH3), 1.85 (s, 3H, COCH3), 4.42 (m, 2H, OCH2Ph), 7.30
(m, 1H, H9 py), 7.33 (m, 1H, p-CH Ph), 7.39 (m, 2H, m-CH Ph), 7.44
(m, 2H, o-CH Ph), 7.45/7.52 (s, 2H, H5 + H5′ py), 7.61 (m, 1H, H11
py), 7.96 (m, 1H, H10 py), 8.10/8.18 (s, 2H, H4 +H4′ py), 8.21/8.33
(s, 2H, H3 + H3′ py), 8.62/8.64 (m, 2H, H6 + H6′ py), 8.68 (m, 1H,
1
H12 py). H NMR (500 MHz, CD3OD, +27 °C): δ 1.80 (s (br), 6H,
COCH3), 4.44 (s (br), 2H, OCH2Ph), 7.23 (m, 1H, H9 py), 7.30 (m,
1H, p-CH Ph), 7.35−7.42 (m, 4H, o-CH + m-CH Ph), 7.45 (s (br),
2H, H5/5′ py), 7.56 (m, 1H, H11 py), 7.90 (m, 1H, H10 py), 8.12 (s
(br), 2H, H4/4′ py), 8.26 (s (br), 2H, H3/3′ py), 8.65 (m, 3H, H6/6′ +
H12 py). 13C NMR (50 MHz, CDCl3, −80 °C): δ 43.5/43.6 (s, 2 ×
COCH3), 67.0 (s, OCH2Ph), 88.2 (s, (2-py)3COBn), 122.7/123.1/
123.4/123.7/124.3/125.3 (s, C3 + C3′ + C9′ + C5′ + C5 + C11 py),
126.4/128.1 (s, m- + o-CH Ph), 127.4 (s, p-CH Ph), 136.6 (s, C10 py),
136.7 (s, i-C Ph), 138.5/138.7 (s, C4′ + C4 py), 149.2/150.6/151.3 (s,
C6 + C6′ + C12 py), 157.2/158.5/159.1 (s, C2 + C2′ + C8 py), 229.2/
J
dx.doi.org/10.1021/om400091h | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 4. Crystal Data and Structure Refinement for 3a−d
3a·CH2Cl2
3b
3c
3d
empirical formula
formula wt
cryst syst
space group
a (Å)
C21H21Cl2N3O3Pt
629.4
C21H21N3O3Pt
558.5
C22H23N3O3Pt
572.5
C27H25N3O3Pt
634.6
monoclinic
P21/c
orthorhombic
P212121
orthorhombic
P212121
monoclinic
P21/c
8.3991(9)
15.800(1)
17.095(2)
100.74(1)
2228.4(4)
4
8.1635(3)
13.7797(6)
17.8650(7)
8.2151(7)
13.932(1)
18.546(2)
14.315(3)
10.722(1)
16.602(2)
108.82(2)
2412.1(6)
4
b (Å)
c (Å)
β (deg)
V (Å3)
2009.6(1)
4
2122.5(3)
4
Z
Dcalcd (g cm−3
)
1.876
1.846
1.792
1.747
μ(Mo Kα) (mm−1
)
6.563
7.008
6.638
5.851
F(000)
1216
1080
1112
1240
θ range (deg)
2.43−26.01
15455
2.28−28.00
11935
2.64−25.93
12293
2.30−25.84
16605
no. of rflns collected
nol of obsd rflns (I > 2σ(I))
no. of indep rflns
3603
4395
3848
3736
4306 (Rint = 0.0741)
4306/0/274
0.978
4757 (Rint = 0.0424)
4757/0/256
1.037
4080 (Rint = 0.0333)
4080/0/264
1.047
4640 (Rint = 0.0569)
4640/0/309
1.010
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R1 = 0.0312
wR2 = 0.0551
R1 = 0.0393
wR2 = 0.0572
0.893, −0.782
R1 = 0.0293
wR2 = 0.0546
R1 = 0.0349
wR2 = 0.0558
0.776, −0.917
R1 = 0.0250
wR2 = 0.0562
R1 = 0.0280
wR2 = 0.0570
1.064, −0.430
R1 = 0.0317
wR2 = 0.0729
R1 = 0.0439
wR2 = 0.0768
1.418, −1.260
R indices (all data)
largest difference peak, hole (e Å−3
)
227.8/227.9 (s (br), 2 × COCH3). 195Pt NMR (107 MHz, CD2Cl2): δ
−3205.2 (s). IR: ν(CO) 1618, ν(CO) 1600, ν(CO) 1573 cm−1.
3.3. X-ray Crystallography. Data for X-ray diffraction analyses of
single crystals were collected on a Stoe-IPDS (3a,b,d) or a Stoe-IPDS
2T diffractometer (3b) at 200 K using Mo Kα radiation (λ = 0.71073
Å, graphite monochromator). A summary of the crystallographic data,
the data collection parameters, and the refinement parameters is given
in Table 4. Absorption corrections were applied empirically with the
PLATON program package (Tmin/Tmax: 0.04/0.15, 3a·CH2Cl2; 0.23/
0.47, 3b; 0.10/0.17, 3c; 0.45/0.71, 3d).20 The structures were solved
with direct methods using SHELXS-9721 and refined using full-matrix
least-squares routines against F2 with SHELXL-97.22 All non-hydrogen
atoms were refined with anisotropic displacement parameters and
hydrogen atoms with isotropic parameters. H atoms were placed in
calculated positions according to the riding model.
3.4. Computational Details. DFT calculations were performed
with the Gaussian09 program package23 using the functional B3LYP.24
The 6-311++G(d,p) basis sets as implemented in Gaussian09 were
employed for main-group atoms, while the relativistic pseudopotential
of the Ahlrichs group and related basis functions of TZVPP quality
were employed for the Pt atom.25 The appropriateness of the
functional in combination with the basis sets and effective core
potential used for reliable interpretation of structural and energetic
aspects of related platinum complexes has been demonstrated.26 All
systems were fully optimized without any symmetry restrictions. The
resulting geometries were characterized as equilibrium structures and
transition states, respectively, by the analysis of the force constants of
normal vibrations. Solvent effects (methanol) were considered
according to Tomasi’s polarized continuum model.17 The method
was used as implemented in Gaussian 09,23 which is much more
sophisticated than in previous Gaussian versions, especially because
solvent effects are considered in each optimization step.
diagrams for 5b* and 3a*/3b* (anti conformer), and
crystallographic data for 3a·CH2Cl2 and 3b−d. This material
is available free of charge via the Internet at http://pubs.acs.org.
Supplementary crystallographic data (3a·CH2Cl2, CCDC
922887; 3b, CCDC 922888; 3c, CCDC 922889; 3d, CCDC
922890) can also be obtained free of charge via http://www.
ccdc.cam.ac.uk/deposit.
AUTHOR INFORMATION
■
Notes
The authors declare no competing financial interest.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Text, tables, figures, and CIF files giving synthesis details and
spectroscopic data of the ligands, energies and Cartesian
coordinates of all calculated molecules, Gibbs free energy
K
dx.doi.org/10.1021/om400091h | Organometallics XXXX, XXX, XXX−XXX

Organometallics
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8.
L
dx.doi.org/10.1021/om400091h | Organometallics XXXX, XXX, XXX−XXX