Five-coordinate [PtII(bipyridine)2(phosphine)] n+ complexes: Long-lived intermediates in ligand substitution reactions of [Pt(bipyridine)2]2+ with phosphine ligands

Article abstract of DOI:10.1021/ic403089j

The reaction of [Pt(N-N)₂]²⁺ [N-N = 2,2′-bipyridine (bpy) or 4,4′-dimethyl-2,2′-bipyridine (4,4′-Me₂bpy)] with phosphine ligands [PPh₃ or PPh(PhSO₃)₂^2-] in aqueous or methanolic solutions was studied by multinuclear (¹H, ¹³C, ³¹P, and ¹⁹⁵Pt) NMR spectroscopy, X-ray crystallography, UV-visible spectroscopy, and high-resolution mass spectrometry. NMR spectra of solutions containing equimolar amounts of [Pt(N-N)₂]²⁺ and phosphine ligand give evidence for rapid formation of long-lived, 5-coordinate [Pt^II(N-N)₂(phosphine)]ⁿ⁺ complexes. In the presence of excess phosphine ligand, these intermediates undergo much slower entry of a second phosphine ligand and loss of a bpy ligand to give [Pt ^II(N-N)(phosphine)₂]ⁿ⁺ as the final product. The coordination of a phosphine ligand to the Pt(II) ion in the intermediate [Pt(N-N)₂(phosphine)]ⁿ⁺ complexes is supported by the observation of ³¹P-¹⁹⁵Pt coupling in the ³¹P NMR spectra. The 5-coordinate nature of [Pt(bpy)₂{PPh(PhSO ₃)₂}] is confirmed by X-ray crystallography. X-ray crystal structural analysis shows that the Pt(II) ion in [Pt(bpy) ₂{PPh(PhSO₃)₂}]·5.5H₂O displays a distorted square pyramidal geometry, with one bpy ligand bound asymmetrically. These results provide strong support for the widely accepted associative ligand substitution mechanism for square planar Pt(II) complexes. X-ray structural characterization of the distorted square planar complex [Pt(bpy)(PPh₃)₂](ClO₄)₂ confirms this as the final product of the reaction of [Pt(bpy)₂]²⁺ with PPh₃ in CD₃OD. The results of density functional calculations on [Pt(bpy)₂]²⁺, [Pt(bpy) ₂(phosphine)]ⁿ⁺, and [Pt(bpy)(phosphine)₂] ⁿ⁺ indicate that the bonding energy follows the trend of [Pt(bpy)(phosphine)₂]ⁿ⁺ > [Pt(bpy) ₂(phosphine)]ⁿ⁺ > [Pt(bpy)₂]²⁺ for stability and that the formation reactions of [Pt(bpy) ₂(phosphine)]ⁿ⁺ from [Pt(bpy)₂]²⁺ and [Pt(bpy)(phosphine)₂]ⁿ⁺ from [Pt(bpy) ₂(phosphine)]ⁿ⁺ are energetically favorable. These calculations suggest that the driving force for the formation of [Pt(bpy)(phosphine)₂]ⁿ⁺ from [Pt(bpy)₂] ²⁺ is the formation of a more energetically favorable product.

Full text of DOI:10.1021/ic403089j

Article
pubs.acs.org/IC
Five-Coordinate [PtII(bipyridine)2(phosphine)]n+ Complexes: Long-
Lived Intermediates in Ligand Substitution Reactions of
[Pt(bipyridine)2]2+ with Phosphine Ligands
Warrick K. C. Lo,† German Cavigliasso,‡ Robert Stranger,‡ James D. Crowley,*,†
́
and Allan G. Blackman*,†,§
†Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
‡Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia
§School of Applied Sciences, Auckland University of Technology, Private Bag 92006, Auckland 1142, New Zealand
S
* Supporting Information
ABSTRACT: The reaction of [Pt(N−N)2]2+ [N−N = 2,2′-bipyridine (bpy) or 4,4′-dimethyl-
2,2′-bipyridine (4,4′-Me2bpy)] with phosphine ligands [PPh3 or PPh(PhSO3)22−] in aqueous or
methanolic solutions was studied by multinuclear (1H, 13C, 31P, and 195Pt) NMR spectroscopy, X-
ray crystallography, UV−visible spectroscopy, and high-resolution mass spectrometry. NMR
spectra of solutions containing equimolar amounts of [Pt(N−N)2]2+ and phosphine ligand give
evidence for rapid formation of long-lived, 5-coordinate [PtII(N−N)2(phosphine)]n+ complexes.
In the presence of excess phosphine ligand, these intermediates undergo much slower entry of a
second phosphine ligand and loss of a bpy ligand to give [PtII(N−N)(phosphine)2]n+ as the final
product. The coordination of a phosphine ligand to the Pt(II) ion in the intermediate [Pt(N−
N)2(phosphine)]n+ complexes is supported by the observation of 31P−195Pt coupling in the 31P
NMR spectra. The 5-coordinate nature of [Pt(bpy)2{PPh(PhSO3)2}] is confirmed by X-ray
crystallography. X-ray crystal structural analysis shows that the Pt(II) ion in [Pt(bpy)2{PPh-
(PhSO3)2}]·5.5H2O displays a distorted square pyramidal geometry, with one bpy ligand bound
asymmetrically. These results provide strong support for the widely accepted associative ligand substitution mechanism for
square planar Pt(II) complexes. X-ray structural characterization of the distorted square planar complex [Pt(bpy)(PPh3)2]-
(ClO4)2 confirms this as the final product of the reaction of [Pt(bpy)2]2+ with PPh3 in CD3OD. The results of density functional
calculations on [Pt(bpy)2]2+, [Pt(bpy)2(phosphine)]n+, and [Pt(bpy)(phosphine)2]n+ indicate that the bonding energy follows
the trend of [Pt(bpy)(phosphine)2]n+ > [Pt(bpy)2(phosphine)]n+ > [Pt(bpy)2]2+ for stability and that the formation reactions of
[Pt(bpy)2(phosphine)]n+ from [Pt(bpy)2]2+ and [Pt(bpy)(phosphine)2]n+ from [Pt(bpy)2(phosphine)]n+ are energetically
favorable. These calculations suggest that the driving force for the formation of [Pt(bpy)(phosphine)2]n+ from [Pt(bpy)2]2+ is the
formation of a more energetically favorable product.
ligand) complexes;13,15,16 evidence for this has come from
INTRODUCTION
The unusually facile reactivity of the [Pt(bpy)2]2+ (bpy = 2,2′-
■
NMR, UV−vis spectroscopy, and mass spectrometry, but again,
a lack of X-ray crystal structural data renders these data open to
bipyridine) ion toward a variety of nucleophiles has been a
other interpretations.
topic of interest ever since Gillard and Lyons first reported
The closely related complex cation [Pt(phen)2]2+ reacts with
some 40 years ago that dissolution of [Pt(bpy)2]2+ in alkaline
CN− in aqueous solutions to give the 5-coordinate [Pt-
aqueous solution gave UV−visible spectral changes that were
(phen)2(CN)]+ ion, as shown by Wernberg and Hazell, who
reversible on addition of acid.1 The considerable amount of
reported the X-ray crystal structure of [Pt(phen)2(CN)](NO3)·
data that has been collected by numerous groups since this time
H2O in 1980.17 The observation of 195Pt satellites in the 13C
has variously been used as evidence that these spectral changes
NMR spectrum of this complex showed that the 5-coordinate
arise from either OH− attack at the coordinated bpy ligand to
structure persists in solution.
give a covalent hydrate or from OH− coordination to the Pt(II)
Of all the ligands studied in these types of reactions, those
ion to give a 5-coordinate complex (Scheme 1).1−13 However,
having P donor atoms have been surprisingly absent, given that
despite the use of numerous physical techniques, it appears
31P NMR should be potentially useful in the characterization of
that, in the absence of crystal structural data, a definitive
products formed from such ligands. Herein we report the
experiment to distinguish unequivocally between the two
results of studies of the reactions of [Pt(N−N)2]2+ [N−N =
possibilities (see 1 and 2 of Scheme 1) has yet to be devised.14
It has also been proposed that [Pt(bpy)2]2+ reacts with a variety
of anions other than OH− and heterocyclic nitrogenous bases
to give 5-coordinate [PtII(bpy)2(L)]n+ (L = monodentate
Received: December 19, 2013
Published: March 21, 2014
© 2014 American Chemical Society
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Scheme 1. Proposed Products from the Reaction of
Scheme 2. Synthesis of the 5-Coordinate [Pt(N−
a
a
[Pt(bpy)2]2+ and OH− in Aqueous Solution
N)2(L)](NO3)n Complexes
a
Reaction conditions: (i) 1 equiv of K2PPh(PhSO3)2·2H2O, H2O
solvent and (ii) 1 equiv of PPh3, CH3OH solvent.
calculations on [Pt(bpy)2]2+, [PtII(bpy)2(L)]n+, and [PtII(bpy)-
(L)2]n+ complexes.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of [Pt(N−N)2{PPh-
(PhSO3)2}] Complexes. Addition of 1 equiv of the water-
soluble phosphine ligand K2PPh(PhSO3)2·2H2O to a pale
yellow aqueous solution of [Pt(bpy)2](NO3)2·H2O at room
temperature results in a rapid intensification of the yellow color.
The UV−vis absorption spectrum of an aqueous solution of
[Pt(bpy)2](NO3)2·H2O shows two maxima in the UV region,
at 245 and 323 nm. On addition of increasing amounts of
K2PPh(PhSO3)2·2H2O the intensity of the former decreases,
while that of the latter increases; three isosbestic points are also
observed (Supporting Information, Figure S35). These
absorbance changes are similar to those observed in the
reaction of [Pt(bpy)2](NO3)2·H2O and OH− in water,1
suggesting that they arise from analogous processes in both
complexes.
a
Pathway a gives the 5-coordinate complex 1, [Pt(bpy)2(OH)]+,
through coordination of OH− to the Pt(II) ion, while compound 2, a
covalent hydrate, is formed via pathway b as a result of nucleophilic
attack by OH− at the bpy ligand.
2,2′-bipyridine (bpy) or 4,4′-dimethyl-2,2′-bipyridine (4,4′-
Me2bpy)] toward the phosphine ligands triphenylphosphine
(PPh3) and its water-soluble derivative bis(p-sulfonatophenyl)-
phenylphosphine [PPh(PhSO3)22−] (Figure 1) in both aqueous
and methanolic solutions.
1H, 13C, 31P, and 195Pt NMR data were collected from an
equimolar mixture of K2PPh(PhSO3)2·2H2O and [Pt(bpy)2]-
(NO3)2·H2O in D2O, while various two-dimensional NMR
1
experiments were also carried out. Both the H and 13C NMR
spectra of the solution gave evidence for chemical reaction, with
noticeable changes in the chemical shifts of the signals due to
2−
the bpy ligands and the PPh(PhSO3)2 ligand (Supporting
Information, Figures S6, S7). The 31P and 195Pt NMR spectra
of the solution exhibited signals having chemical shifts
significantly different from those of the starting materials (31P
NMR, K2PPh(PhSO3)2·2H2O, −6.79 ppm, singlet; product,
11.13 ppm, singlet with 195Pt and 13C satellites: 195Pt NMR,
[Pt(bpy)2](NO3)2·H2O, −2270 ppm, singlet; product, −3176
ppm, doublet). In addition, 31P−195Pt coupling of approx-
imately 3800 Hz was observed in both spectra, showing
unequivocally that coordination of phosphorus to the Pt(II) ion
had occurred (Figure 2). The observation of a doublet in the
31P NMR spectrum indicates only one phosphorus atom is
coordinated to the Pt(II) ion in the product, while the 195Pt
NMR chemical shift of −3176 ppm, upfield from that of the
starting material, is consistent with coordination of a soft donor
atom to the Pt(II) ion.13 The 1H and 13C NMR spectra
strongly suggest that the two bpy ligands in the product are
chemically equivalent on the NMR time scale. These
observations are consistent with the formation of a 5-
coordinate species in aqueous solution, which is either fluxional
on the NMR time scale or in which the Pt(II) ion adopts a
square pyramidal geometry that renders the two bpy ligands
equivalent. Regardless of the geometry, the P donor atom
remains bonded to the Pt(II) ion in solution. The 1H diffusion-
ordered spectroscopic (DOSY) NMR spectrum showed that
Figure 1. [Pt(N−N)2]2+ complexes and phosphine ligands used in this
study.
We detail the synthesis of the 5-coordinate Pt(II) complexes
[Pt(N−N)2(L)](NO3)n (N−N = bpy, 4,4′-Me2bpy; L =
PPh(PhSO3)22−, n = 0: L = PPh3, n = 2: Scheme 2) and the
X-ray crystal structures of both [Pt(bpy)2{PPh(PhSO3)2}]·
5.5H2O, the first example of a crystallographically characterized
monomeric 5-coordinate [PtII(bpy)2(L)]n+ complex, and [Pt-
(bpy)(PPh3)2](ClO4)2·0.5(C6H14O), the product deriving
from the 5-coordinate [Pt(bpy)2(PPh3)]2+ intermediate. We
present multinuclear (1H, 13C, 31P, 195Pt) NMR and mass
spectral data from solution studies of the [Pt(N−N)2(L)]-
(NO3)n complexes and show that these complexes are fluxional
5-coordinate species in solution at room temperature. Finally,
we report the results of density functional theory (DFT)
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Figure 2. (a) 195Pt (107 MHz) and (b) 31P NMR (202 MHz) spectra of an equimolar mixture of [Pt(bpy)2](NO3)2·H2O and K2PPh(PPhSO3)2·
1
1
2H2O in D2O at 25 °C. J coupling of approximately 3800 Hz between 195Pt and 31P was observed in both spectra, while J coupling of 63.5 Hz
between 31P and 13C was observed in the 31P NMR spectrum.
the reaction of [Pt(bpy)2]2+ and PPh(PhSO3)22− in D2O gave a
1:1 adduct that has a diffusion coefficient of 2.72 × 10−10 m2
s−1, a much smaller value than those of the reactants
([Pt(bpy)2]2+, 4.23 × 10−10 m2 s−1; PPh(PhSO3)22−, 4.03 ×
10−10 m2 s−1: Supporting Information, Figures S18, S19),
indicative of the formation of a compound of higher molar
mass. All of the NMR data are consistent with the formation of
a 5-coordinate complex of the type [Pt(bpy)2{PPh(PhSO3)2}],
in which the bpy ligands are equivalent. High-resolution mass
spectral data also support the proposed formula, with peaks
corresponding to [Na(Pt(bpy)2{PPh(PhSO3)2})]+ and [K(Pt-
(bpy)2{PPh(PhSO3)2})]+ observed at m/z = 950.0812 and
966.0387, respectively (Supporting Information, Figures S23,
S24), as well as lower mass fragments derived from these.
The 5-coordinate nature of the product was confirmed by X-
ray crystallography. Yellow, X-ray quality crystals of [Pt(bpy)2-
{PPh(PhSO3)2}]·5.5H2O were obtained by vapor diffusion of
acetonitrile into an aqueous solution containing equimolar
amounts of [Pt(bpy)2](NO3)2·H2O and K2PPh(PhSO3)2·
2H2O. Figure 3 shows an Oak Ridge thermal-ellipsoid plot
(ORTEP) diagram of [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O, with
Figure 3. ORTEP diagram of [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O;
the waters of crystallization omitted for clarity. The neutral
solvent water molecules and hydrogen atoms are omitted for clarity.
complex contains a central 5-coordinate Pt(II) ion that is
Thermal ellipsoids are drawn at the 30% probability level. Selected
bond lengths (Å) and angles (deg): Pt1−N1 2.049(9), Pt1−N2
2.092(8), Pt1−N3 2.050(11), Pt1−N4 2.753(14), Pt1−P1 2.260(2);
N1−Pt1−N2 79.6(3), N1−Pt1−N3 170.9(4), N1−Pt1−P1 97.7(3),
N2−Pt1−N3 92.1(3), N2−Pt1−P1 176.6(2), N3−Pt1−P1 90.5(2),
N3−Pt1−N4 68.4(5).
bound to the N atoms of two chemically inequivalent bpy
2−
ligands and the P atom of a PPh(PhSO3)2 ligand. The
geometry about the Pt(II) ion is best described as distorted
square pyramidal (τ5 = 0.095)18,19 with three N atoms (N1, N2,
and N3) from the bpy ligands and the P atom from the
2−
PPh(PhSO3)2 ligand defining the square plane. The Pt(II)
ion sits very slightly (0.054 Å) above this plane. The “apex” of
of a bpy ligand, although it is not positioned directly above the
the square pyramid is occupied by the remaining N atom (N4)
metal ion, as reflected in the N3−Pt1−N4 bond angle of 68.4°.
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Table 1. NMR Chemical Shifts of Phosphine Ligands, [Pt(N−N)2]2+, and [Pt(N−N)2(phosphine)]n+ Complexes
compound
solvent
31P NMR δ, ppm (1JPt−P, Hz)
195Pt NMR δ, ppm (1JPt−P, Hz)
a
K2PPh(PhSO3)2·2H2O
PPh3
D2O
−6.79
−4.74
CD3OD
D2O
b
[Pt(bpy)2](NO3)2·H2O
−2270
c,d
CD3OD
D2O
[Pt(4,4′-Me2bpy)2](NO3)2·2H2O
−2242
c
CD3OD
D2O
[Pt(bpy)2{PPh(PhSO3)2}]
[Pt(4,4′-Me2bpy)2{PPh(PhSO3)2}]
[Pt(bpy)2(PPh3)](NO3)2
11.13 (3791)
10.94 (3795)
11.91 (3790)
11.81 (3801)
−3176 (3805)
−3197 (3795)
c
D2O
CD3OD
[Pt(4,4′-Me2bpy)2(PPh3)](NO3)2
CD3OD
c
c
a
b
d
Reference 24 quotes −6.49 ppm. From reference 13. Insufficient solubility in this solvent to obtain a spectrum. A 48 h data collection gives no
195Pt NMR signal.
1
The Pt−N4 distance of 2.753 Å is also much longer than the
Pt−N distances in the square plane (Pt1−N1, 2.049 Å; Pt1−
N2, 2.092 Å; Pt1−N3, 2.050 Å), showing that one bpy ligand is
bound very asymmetrically. A similar asymmetric binding of the
phen ligand in [Pt(phen)2(CN)](NO3)·H2O has also been
observed;17 indeed, the coordination geometry about the Pt(II)
ion in [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O is very similar to that
found in [Pt(phen)2(CN)](NO3)·H2O (τ5 = 0.045),20 and
such a coordination geometry has been predicted for the 5-
coordinate [Pt(bpy)2(OH)]+ and [Pt(bpy)2(py)]2+ complexes
by us15 and Kawanishi et al.,16 respectively, based on the results
of DFT geometry optimization calculations. Although the bpy
ligand, unlike the closely related phen ligand, possesses
rotational freedom about the interannular C−C bond, the
fact that N4 is oriented toward, rather than away from, the
Pt(II) ion strongly suggests that there is a genuine bonding
interaction (albeit weak) between Pt1 and N4 in [Pt(bpy)2-
{PPh(PhSO3)2}]·5.5H2O. Note that this interaction is
reproduced in the optimized structure obtained from DFT
calculations (see below). The small dihedral angle (13.11°)
between the pyridine rings of the asymmetrically bound bpy
ligand is also consistent with both N atoms of the ligand being
bonded to the Pt ion. A similar ligand orientation and long Pt−
N distance (2.625(7) Å) is present in the terpyridine (terpy)
ligand of the [Pt(PNCHP-κ3P,N,P)(terpy-κ2N,N)]2+ cation,21
while the peroxo-bridged dimer [(bpy)2Pt(μ-O2)Pt(bpy)2]-
(BF4)2 also displays an asymmetrically coordinated bpy
ligand.22 However, in the latter compound, the dihedral angle
between the pyridine rings of the nondisordered asymmetrically
bound bpy ligand is 46.58°, and the corresponding “long” Pt−
N distance is 2.975 Å. Both measurements, which are
significantly larger than those in [Pt(bpy)2{PPh(PhSO3)2}]·
5.5H2O, are more consistent with a 4-coordinate square-planar
geometry and are again suggestive of a genuine Pt1−N4
bonding interaction in [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O.
Offset π−π interactions23 are observed in the crystal
structure of [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O. These occur
gave the same H NMR spectrum as that observed initially on
mixing equimolar amounts of [Pt(bpy)2](NO3)2·H2O and
K2PPh(PhSO3)2·2H2O in the same solvent. This observation
suggests that, in contrast to the situation in the solid state, the
two bpy ligands in the complex are equivalent in solution on
the NMR time scale. We therefore propose that the complex is
fluxional in solution.
Similar behavior to that described above is observed when
[Pt(4,4′-Me2bpy)2](NO3)2·2H2O is used as the starting
material. NMR, UV−vis, and mass spectral studies of an
aqueous solution containing equimolar amounts of [Pt(4,4′-
Me2bpy)2](NO3)2·2H2O and K2PPh(PhSO3)2·2H2O are con-
sistent with formation of 5-coordinate [Pt(4,4′-Me2bpy)2{PPh-
(PhSO3)2}]. This complex shows slight decreases in the 31P
and 195Pt NMR chemical shifts compared to those of
[Pt(bpy)2{PPh(PhSO3)2}] (Table 1), presumably due to the
more electron-rich 4,4′-Me2bpy ligands, and it also appears to
be somewhat less fluxional. The latter observation is supported
1
by the presence of broad peaks in the H NMR spectrum of
[Pt(4,4′-Me2bpy)2{PPh(PhSO3)2}] at 25 °C (Supporting
Information, Figure S8), which sharpen significantly with
increasing temperature (Supporting Information, Figure S9).
Synthesis and Characterization of [Pt(N−N)2(PPh3)]2+
Complexes. The reaction of 1 equiv of PPh3 with both
[Pt(bpy)2]2+ and [Pt(4,4′-Me2bpy)2]2+ in CH3OH showed
2−
many similarities to those of PPh(PhSO3)2 in aqueous
solution described above, and 5-coordinate products were
obtained with both Pt(II) starting materials. A bright yellow
solution was formed on mixing equimolar amounts of [Pt(N−
N)2](NO3)2 and PPh3, and chemical shifts different from those
of the starting materials were observed in the 1H and 13C NMR
spectra of these mixtures in CD3OD (Supporting Information,
Figures S11, S12, S18); these spectra also showed the N−N
ligands to be chemically equivalent in solution. 31P−195Pt
coupling of approximately 3800 Hz in the 31P NMR spectra
(Supporting Information, Figures S13, S15) gave evidence for
coordination of the phosphorus atom of PPh3 to the Pt(II) ion.
2−
between a phenyl ring of the PPh(PhSO3)2 ligand and a
1
Furthermore, the H DOSY NMR spectra showed that the
pyridine ring of the asymmetrically bound bpy ligand
(Supporting Information, Figure S37) and also between the
symmetrically bound bpy ligands of two [Pt(bpy)2{PPh-
(PhSO3)2}] molecules (Supporting Information, Figure S38).
The centroid−centroid distances are 3.723 and 3.669 Å,
respectively.
Elemental analysis of the crystals used for the X-ray structural
determination was consistent with the formula of [Pt(bpy)2-
{PPh(PhSO3)2}]·5.5H2O. Dissolution of these crystals in D2O
reaction of [Pt(N−N)2](NO3)2 and PPh3 in CD3OD gave a
product that has a diffusion coefficient of approximately 6 ×
10−10 m2 s−1, consistent with formation of 5-coordinate [Pt(N−
N)2(PPh3)]2+ (Supporting Information, Figures S21, S22).
Mass spectral evidence for the formation of [Pt(N−
N)2(PPh3)]2+ was also obtained (Supporting Information,
Figures S29, S31). Unfortunately, despite many efforts, X-ray
quality crystals of the products could not be obtained.
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Table 2. X-ray Crystallographic Data for [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O and [Pt(bpy)(PPh3)2](ClO4)2·0.5(C6H14O)
compound
[Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O
[Pt(bpy)(PPh3)2](ClO4)2·0.5(C6H14O)
chemical formula
formula weight
temperature, K
wavelength, Å
crystal system
space group
a, Å
C38H40N4O11.5PPtS2
1026.92
100.0(2)
0.71070
monoclinic
P21/c
C49H45Cl2N2O8.5P2Pt
1125.80
100.0(1)
0.71070
monoclinic
P21/c
11.8665(4)
24.5917(7)
15.8557(7)
90
10.4219(2)
25.1945(6)
18.9236(4)
90
b, Å
c, Å
α, deg
β, deg
103.382(4)
90
93.356(2)
90
γ, deg
volume, Å3
4501.3(3)
2
4960.33(18)
2
Z
D
calcd, g cm−3
μ, mm−1
1.515
1.508
3.305
3.055
2
R(Fo or Fo )
0.0836
0.0340
2
Rw(Fo or Fo )
0.2358
0.0897
Formation of [PtII(N−N)(phosphine)2]n+ Complexes.
The aqueous and methanolic solution studies show that the
reactions of [Pt(N−N)2](NO3)2 with 1 equiv of either
phosphine ligand gives the 5-coordinate [Pt(N−
N)2(phosphine)]n+ complexes quantitatively. The [Pt(N−
N)2(phosphine)]n+ complexes are stable in solution for at
least 4 d, as no significant spectral changes were observed in
crystals of [Pt(bpy)(PPh3)2](ClO4)2·0.5(C6H14O) were ob-
tained by vapor diffusion of diisopropyl ether into a solution of
[Pt(bpy)(PPh3)2](ClO4)2 in acetone. Figure 4 shows a diagram
1
either the H or 31P NMR spectra over this time. However,
while reaction of [Pt(bpy)2]2+ with 4 equiv of PPh3 in CD3OD
also gave the 5-coordinate complex initially (Supporting
Information, Figure S16), 1H and 31P NMR data gave evidence
for the formation of a small amount (approximately 15%) of a
new complex after one week. New NMR signals due to a very
small amount of free bpy ligand were observed in the 1H NMR
spectrum recorded 22 h after sample preparation, and after one
week, a new, small 31P NMR signal was observed at 9.33 ppm.
In analogous 31P NMR studies with excess K2PPh(PhSO3)2·
2H2O in D2O, a new singlet, flanked by 195Pt satellites
(31P−195Pt coupling of 3498 Hz), was observed at 8.86 ppm.
Given that [Pt(bpy)2]2+ is known to react with excess pyridine
to give [Pt(bpy)(py)2]2+,15 we suspected these new peaks
might be due to the hitherto unknown complex [Pt(bpy)-
(PPh3)2]2+. We therefore prepared [Pt(bpy)(PPh3)2](ClO4)2
by heating [Pt(bpy)Cl2] with 10 equiv of PPh3 in a 1:2 H2O/
acetone mixture. Removal of unreacted PPh3 and addition of
NaClO4 gave [Pt(bpy)(PPh3)2](ClO4)2 as an off-white solid.
[Pt(bpy)(PPh3)2](ClO4)2 was characterized by elemental
Figure 4. ORTEP diagram of the [Pt(bpy)(PPh3)2]2+ cation;
hydrogen atoms are omitted for clarity. Thermal ellipsoids are
drawn at the 50% probability level. Selected bond lengths (Å) and
angles (deg): Pt1−N1 2.102(3), Pt1−N2 2.110(3), Pt1−P1
2.2753(8), Pt1−P2 2.2849(9); N1−Pt1−N2 77.97(11), N1−Pt1−P2
167.29(8), N1−Pt1−P1 94.34(8), N2−Pt1−P2 94.50(8), N2−Pt1−
P1 166.30(9), P1−Pt1−P2 94.96(3).
of the [Pt(bpy)(PPh3)2]2+ cation. This consists of a central 4-
coordinate Pt(II) ion that is bound to both N atoms of a bpy
ligand and the P atoms of two PPh3 ligands. The geometry
about the Pt(II) ion is best described as distorted square planar
(τ4 = 0.19);25 the two P donor atoms sit on either side of the
plane defined by Pt1, N1, and N2,26 while there is a significant
bowing in the bpy ligand. Presumably, the observed geometry
about the Pt(II) ion minimizes the unfavorable intra- or
interligand proton−proton interactions. In addition, this
geometry allows an interligand, offset π−π interaction between
phenyl rings of the two PPh3 ligands, with a centroid−centroid
distance of 3.531 Å (Supporting Information, Figure S39). No
π−π interactions between the bpy ligands of neighboring
[Pt(bpy)(PPh3)2]2+ cations are observed, presumably due to
the close proximity of two sterically demanding PPh3 ligands
1
analysis, H, 13C, and 31P NMR, mass spectroscopy, and X-
ray crystallography. A single 31P NMR signal at 8.80 ppm,
flanked by 195Pt satellites (31P−195Pt coupling of 3560 Hz) was
observed in the spectrum of [Pt(bpy)(PPh3)2](ClO4)2 in
dimethylformamide (DMF)-d7, suggesting that coordination of
the phosphorus atom(s) of one or two PPh3 ligand(s) to the
Pt(II) ion had occurred (Supporting Information, Figure S5).
In CD3OD, the 31P NMR signal appears as a broad singlet at
9.15 ppm. The formation of [Pt(bpy)(PPh3)2]2+ is supported
by high-resolution mass spectral data, with a peak correspond-
ing to [Pt(bpy)(PPh3)2]2+ observed at m/z = 437.6050
(Supporting Information, Figure S34).
The identity of [Pt(bpy)(PPh3)2](ClO4)2 was confirmed by
X-ray crystallography (Table 2). Colorless, X-ray quality
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Figure 5. Ball-and-stick representations of optimized structures of (a) [Pt(bpy)2(PPh3)]2+, (b) [Pt(bpy)2{PPh(PhSO3)2}], (c) [Pt(bpy){PPh-
(PhSO3)2}2]2−, and (d) [Pt(bpy)(PPh3)2]2+ from density functional calculations; hydrogen atoms are omitted for clarity. Color scheme for each
element: C (gray), N (blue), O (red), P (dark green), Pt (gold), and S (orange).
and a perchlorate anion (Supporting Information, Figure S40).
Interestingly, anion-π interactions27 are observed between a
bpy ligand and the perchlorate anion oxygen atoms O5 and O8
(Supporting Information, Figure S41), with the oxygen−
centroid distances being 3.161 and 2.947 Å, respectively. The
Pt−N distances of 2.102 Å (Pt1−N1) and 2.110 Å (Pt1−N2)
are rather longer than those in [PtII(bpy)2]X (X = (NO3)2·
H2O, (ClO4)2, (CF3SO3)2, {Au(CN)2}2, [C6H4{C-
(CN)2}2]2),28−33 consistent with the significant trans effect
exerted by phosphine ligands.
the aqueous spectrum (8.86 ppm) is due to [Pt(bpy){PPh-
(PhSO3)2}2]2−. This makes intuitive sense, as the asymmetri-
cally bonded bpy ligand in 5-coordinate [Pt(bpy)2-
(phosphine)]n+ might be expected to be relatively easily
substituted. Note also that the 31P NMR data are not consistent
with formation of the recently characterized cyclometalated
complex [Pt(bpy-H-κN,C)(PPh3)2]+.34
Mechanism of the Reaction of [Pt(bpy)2]2+ with
Phosphine Ligands. Extensive studies of the mechanism of
ligand substitution in square planar Pt(II) complexes have
shown this process to have associative character, with only a
few exceptions.35,36 Our study of the reaction of [Pt(N−N)2]2+
with phosphine ligands provides support for the associative
ligand substitution mechanism. NMR studies clearly show that
The similarity in 31P NMR chemical shifts between
[Pt(bpy)(PPh3)2]2+ (9.15 ppm) and the unknown peak (9.33
ppm) in CD3OD strongly suggests that the unknown peak is
indeed due to [Pt(bpy)(PPh3)2]2+, while the peak observed in
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Table 3. Comparison of Calculated and Observed Structural Data for [Pt(bpy)2]2+, [PtII(bpy)2(phosphine)]n+, and
[PtII(bpy)(phosphine)2]n+ Complexes
complex
calculated Pt−N (Å)
experimental Pt−N (Å)
calculated Pt−P (Å)
experimental Pt−P (Å)
[Pt(bpy)2]2+
2.039, 2.039, 2.039, 2.040
2.055, 2.068, 2.114, 2.758
2.136, 2.154
2.023, 2.023, 2.029, 2.029
[Pt(bpy)2(PPh3)]2+
2.310
[Pt(bpy)(PPh3)2]2+
2.102, 2.110
2.322, 2.328
2.311
2.275, 2.285
2.260
[Pt(bpy)2{PPh(PhSO3)2}]
[Pt(bpy){PPh(PhSO3)2}2]2−
2.054, 2.068, 2.109, 2.753
2.130, 2.151
2.049, 2.050, 2.092, 2.753
2.321, 2.330
the reaction of [Pt(N−N)2]2+ with excess phosphine ligand
[PPh3 or PPh(PhSO3)22−] immediately gives quantitative
formation of the 5-coordinate [Pt(N−N)2(phosphine)]n+
complex as a long-lived intermediate, with subsequent rate-
determining entry of a further phosphine ligand to give [Pt(N−
N)(phosphine)2]n+ as the final product. The driving force for
entry of the first phosphine ligand appears to be relief of steric
strain in the [Pt(N−N)2]2+ starting material. Close approach of
the 6 and 6′ bpy protons in the square planar starting material
results in either a bowing of the bpy ligands30−33 or a slight
distortion toward tetrahedral geometry29 in the solid state. Such
unfavorable interactions are not observed in the crystal
structure of [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O, with the
symmetrically bound bpy ligand being essentially planar. It is
likely that this is also the basis of the facile reaction of [Pt(N−
N)2]2+ with OH−, other anions, and aromatic nitrogen bases.
Calculations on [Pt(bpy)2]2+, [PtII(bpy)2(phosphine)]n+,
and [PtII(bpy)(phosphine)2]n+. Density functional calcula-
tions were carried out to optimize the geometries of
[Pt(bpy)2]2+, [Pt(bpy)2(phosphine)]n+, and [Pt(bpy)-
(phosphine)2]n+ (Figure 5). Comparisons of computational
and available experimental data for these complexes are given in
Table 3. The calculated structures of [Pt(bpy)2]2+, [Pt-
(bpy)2{PPh(PhSO3)2}], and [Pt(bpy)(PPh3)2]2+ are in good
agreement with the corresponding crystal structures; the Pt(II)
ion displays a perfect square planar geometry in [Pt(bpy)2]2+, a
distorted square pyramidal geometry in [Pt-
(bpy)2(phosphine)]n+, and a distorted square planar geometry
in [Pt(bpy)(phosphine)2]n+. In addition, interligand π−π
interactions between the phenyl rings of the two phosphine
ligands and between a phenyl ring of a phosphine ligand and a
pyridine ring of the asymmetrically bound bpy ligand are
observed in the calculated structures of [Pt(bpy)-
(phosphine)2]n+ and [Pt(bpy)2(phosphine)]n+, respectively.
Of particular importance are the computational results for
both 5-coordinate complexes, which are predicted to have a
distorted square pyramidal geometry with a bpy N atom in the
apical position; indeed, no convergence could be obtained
when the P atom of the phosphine ligand was placed in this
position. Thus, it is very likely that the observed equivalence of
the bpy ligands of these complexes in solution is due to a
fluxional process involving interconversion of species having
bpy N atoms at the apical position of a square pyramid, rather
than the bpy ligands themselves being truly equivalent.
Table 4. Calculated Bonding Energy Data for [Pt(bpy)2]2+,
[PtII(bpy)2(phosphine)]n+, and [PtII(bpy)(phosphine)2]n+
Complex−Ligand Systems
complex−ligand system
[Pt(bpy)2]2+ + 2PPh3
bonding energy (kJ mol−1
)
−67 604
−67 620
−67 629
−76 885
−76 910
−76 913
[Pt(bpy)2(PPh3)]2+ + PPh3
[Pt(bpy)(PPh3)2]2+ + bpy
[Pt(bpy)2]2+ + 2PPh(PhSO3)2
2−
2−
[Pt(bpy)2{PPh(PhSO3)2}] + PPh(PhSO3)2
[Pt(bpy){PPh(PhSO3)2}2]2− + bpy
The bonding energy data in Table 4 can also be used to
calculate the energy change (ΔE) for the formation of
[Pt(bpy)2(phosphine)]n+ and [Pt(bpy)(phosphine)2]n+ com-
plexes, and the results are summarized in Scheme 3. These
results show that the formation of both [Pt(bpy)2-
(phosphine)]n+ and [Pt(bpy)(phosphine)2]n+ complexes is
characterized by favorable energetics. Interestingly, the
formation of [Pt(bpy)2(phosphine)]n+ is predicted to be
2−
more energetically favorable when PPh(PhSO3)2 is the
ligand, whereas PPh3 is the preferred ligand in the formation
of [Pt(bpy)(phosphine)2]n+.
The isolation of [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O and
NMR solution studies clearly show that [Pt(bpy)2-
(phosphine)]n+ forms rapidly as a stable reaction intermediate,
and this observation is supported by the results from bonding
energy calculations. These calculations suggest that the
formation of [Pt(bpy)(phosphine)2]n+ from [Pt(bpy)2-
(phosphine)]n+ is also an energetically favorable process. The
formation of [Pt(bpy)(phosphine)2]n+ has been observed in
solution NMR studies, and this process has been shown to
occur much more slowly than the formation of [Pt(bpy)2-
(phosphine)]n+ from [Pt(bpy)2]2+. One reason is that both de-
coordination of a bidentate bpy ligand and coordination of a
sterically bulky phosphine ligand are required in the formation
of [Pt(bpy)(phosphine)2]n+; however, only the coordination of
a phosphine ligand is required in the formation of [Pt(bpy)2-
(phosphine)]n+. Furthermore, the Pt(II) ion in [Pt(bpy)2-
(phosphine)]n+ is less exposed to the incoming phosphine
ligand than that in [Pt(bpy)2]2+, and therefore, a larger degree
of preorganization between [Pt(bpy)2(phosphine)]n+ and the
incoming phosphine ligand is required in the formation of
[Pt(bpy)(phosphine)2]n+. As a result, the formation of
[Pt(bpy)(phosphine)2]n+ is much slower than that of [Pt-
(bpy)2(phosphine)]n+.
The calculated bonding energy results for [Pt(bpy)2]2+,
[Pt(bpy)2(phosphine)]n+, and [Pt(bpy)(phosphine)2]2+ pro-
vide some insight into the driving force for the formation of
[Pt(bpy)(phosphine)2]n+ from [Pt(bpy)2]2+. The bonding
energy data listed in Table 4 show that the trend in
thermodynamic stability is [Pt(bpy)2]2+ < [Pt(bpy)2-
(phosphine)]n+ < [Pt(bpy)(phosphine)2]2+, and thus the final
product [Pt(bpy)(phosphine)2]2+ is the most energetically
favored species.
CONCLUSIONS
■
This work provides the first definitive X-ray structural evidence,
in the form of [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O, for the
formation of 5-coordinate species from the reaction of [Pt(N−
N)2]2+ (N−N = bpy, 4,4′-Me2bpy) complexes with mono-
dentate ligands in both aqueous and methanolic solution. Such
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Scheme 3. Formation Reaction Energetics (ΔE) of [PtII(bpy)2(phosphine)]n+ and [PtII(bpy)(phosphine)2]n+ Complexes
K2PPh(PhSO3)2·2H2O. HRESI-MS (positive mode, MeOH): m/z
5-coordinate species are formed rapidly and show significant
stability in both the solid state and solution. Subsequent slow
reaction of these with excess ligand gives [Pt(N−N)-
(phosphine)2]2+ as the final product. These observations
confirm an associative substitution mechanism for these
reactions. It would be remarkable if the formation of 5-
coordinate complexes was limited to phosphine ligands, and it
appears very likely that previously studied heterocyclic
nitrogenous base and anionic ligands react similarly to give 5-
coordinate complexes. Of arguably greatest interest, and
certainly greatest controversy, among these is OH−, and the
results presented above provide more evidence, in addition to
that already collected,15 for coordination of this ligand to the
Pt2+ ion in [Pt(N−N)2]2+ to give 5-coordinate [Pt(N−
N)2(OH)]+. Most notably, we have shown that the UV−vis
spectral changes that occur on formation of the structurally
characterized 5-coordinate species [Pt(bpy)2{PPh(PhSO3)2}]
in aqueous solution are very similar to those observed in the
reaction of [Pt(bpy)2]2+ and OH−.
+
calcd for C18H13K2NaO6PS2 : 520.9058 [K2PPh(PhSO3)2 + Na]+ ([M
+
+ Na]+); found 520.9067 (96%), m/z calcd for C18H13KNa2O6PS2 :
504.9318 [M − K + 2Na]+; found 504.9308 (100%), m/z calcd for
+
C18H13Na3O6PS2 : 488.9579 [M − 2K + 3Na]+; found 488.9563
(52%). ESI-MS (negative mode, MeOH): m/z calcd for
−
C18H13KO6PS2 : 458.9534 ([M − K]−); found 458.9595 (12%), m/
z calcd for C18H13O6PS22−: 209.9951 ([M − 2K]2−); found 210.0002
1
(100%). H NMR (500 MHz, D2O): 7.76−7.81 (m, 4H, Hc), 7.39−
7.51 (m, 9H, Hb, Hf, Hg, Hh). 13C NMR (126 MHz, D2O): 145.9 (s,
Cd), 142.9 (d, 1JP−C = 9.5 Hz, Ca), 137.5 (d, 1JP−C = 6.3 Hz, Ce), 136.9
(d, 2JP−C = 20.0 Hz, Cf), 136.8 (d, 2JP−C = 19.2 Hz, Cb), 132.8 (s, Ch),
132.0 (d, 3JP−C = 7.7 Hz, Cg), 128.4 (d, 3JP−C = 7.1 Hz, Cc). 31P NMR
2
(202 MHz, D2O): −6.79 (s with satellites; JP−C = 19.0 Hz).
Syntheses. [Pt(bpy)Cl2],38 [Pt(bpy)2](ClO4)2,39 and [Pt(bpy)2]-
(NO3)2·H2O13 were synthesized by reported methods.
Caution! Although no difficulties were experienced with the perchlorate
salts described herein, all perchlorate species should be treated as potentially
explosive and handled with care.
[Pt(bpy)2](NO3)2·H2O.13 To a stirred suspension of [Pt(bpy)2]-
(ClO4)2 (4.44 g, 6.29 mmol) in H2O (200 mL) was added dropwise
an aqueous solution of [AsPh4]Cl·H2O (5.50 g, 12.6 mmol) in H2O
(20 mL). [AsPh4]ClO4 precipitated immediately as a white solid. The
mixture was first stirred at room temperature for 15 min and then on
an ice-bath for 10 min; the solid was then removed by filtration
through Celite and washed with ice-cold H2O (2 × 10 mL). The
yellow filtrate was concentrated (by rotary evaporator (rotavap)) to
low volume (ca. 40 mL) and passed through a column of Dowex anion
EXPERIMENTAL SECTION
■
General Methods. Deuterated solvents were degassed with argon
gas. Unless otherwise stated, all NMR spectra were recorded at 25 °C.
1H and 13C NMR spectra, and two-dimensional gradient correlation
spectroscopy (gCOSY), total correlated spectroscopy (TOCSY),
DOSY, heteronuclear single quantum coherence adiabatic
(HSQCAD), and gradient-selected heteronuclear multiple bond
correlation using adiabatic pulses (gHMBCAD) NMR spectra, were
recorded on either a Varian 400-MR or Varian 500 MHz AR
spectrometer. 31P NMR spectra were recorded on either a Varian 400-
MR or Varian 500 MHz AR spectrometer at 162 and 202 MHz,
respectively. 195Pt NMR spectra were recorded on a Varian 500 MHz
AR spectrometer at 107 MHz. All chemical shifts are reported in parts
per million (ppm). 1H and 13C NMR chemical shifts are referenced to
−
exchange resin (100−200 mesh size, NO3 form), and the yellow
eluate was taken to dryness (rotavap) to give a yellow solid, which was
washed with ice-cold H2O (2 × 5 mL), then acetone (3 × 10 mL), and
finally diethyl ether (3 × 10 mL) and dried under vacuum. Yield: 3.75
g (92%). Anal. Calcd (%) for C20H18N6O7Pt: C 36.99, H 2.79, N
12.94; found C 37.27, H 2.88, N 12.93. HRESI-MS (MeCN): m/z
calcd for C20H16N5O3Pt+: 569.0897 [M + NO3]+; found 569.0859
(2%), m/z calcd for C21H16N5Pt+: 533.1049 [M + CN]+; found
533.1008 (58%), m/z calcd for C20H15N4Pt+: 506.0941 [M − H]+;
found 506.0897 (38%), m/z calcd for C20H16N4Pt2+: 253.5507
[Pt(bpy)2]2+ ([M]2+); found 253.5503 (9%), m/z calcd for
internal standard NaTSP-d4 (in D2O: H δ 0 ppm, 13C δ 0 ppm) or
1
+
1
C10H9N2 : 157.0760 [bpy + H]+; found 157.0804 (100%). H NMR
(400 MHz, DMSO-d6): 9.10 (d, J = 5.5 Hz, 4H, bpyH-6/6′), 8.85 (dd,
J = 8.1, 1.1 Hz, 4H, bpyH-3/3′), 8.64 (td, J = 8.0, 1.0 Hz, 4H, bpyH-4/
4′), 7.99−8.10 (m, 4H, bpyH-5/5′). 1H NMR (500 MHz, D2O): 8.96
(d, J = 5.8 Hz, 4H, bpyH-6/6′), 8.51−8.61 (m, 8H, bpyH-3/3′, bpyH-
4/4′), 7.90−8.03 (m, 4H, bpyH-5/5′). 13C NMR (101 MHz, DMSO-
d6): 156.6 (bpyC-2/2′), 151.6 (bpyC-6/6′), 142.6 (bpyC-4/4′), 128.6
(bpyC-5/5′), 124.7 (bpyC-3/3′). 13C NMR (101 MHz, D2O): 159.9
(bpyC-2/2′), 153.6 (bpyC-6/6′), 145.8 (bpyC-4/4′), 131.3 (bpyC-5/
5′), 127.6 (bpyC-3/3′).
tetramethylsilane (TMS) (in CD3OD, dimethyl sulfoxide (DMSO)-d6,
1
or DMF-d7: H δ 0 ppm, 13C δ 0 ppm). 31P NMR chemical shifts are
reported relative to an external reference of aqueous H3PO4 (40 wt %)
at 0 ppm. 195Pt NMR chemical shifts are reported relative to H2[PtCl6]
at 0 ppm, via an external reference of aqueous K2[PtCl4] (0.1 M in 1
M DCl; −1620 ppm relative to H2[PtCl6]). High-resolution
electrospray ionization mass spectra (HRESI-MS) were recorded on
a Bruker micrOTOF-Q spectrometer. UV−vis absorption spectra were
recorded at room temperature on a Perkin-Elmer Lambda 950 UV−
vis−near-IR spectrophotometer. Elemental analyses were performed at
the Campbell Microanalytical Laboratory, University of Otago.
Reagents. All regents were laboratory reagent grade or better and
used as received. Dipotassium bis(p-sulfonatophenyl)phenylphosphine
dihydrate (K2PPh(PhSO3)2·2H2O) was purchased from Sigma-Aldrich
and used as received. However, while characterizing this commercial
product, we found some discrepancies in the NMR data reported in
the literature. Reference 37 reports correct 13C NMR data for this
compound, but the reported 31P NMR data are incorrect. The latter
are correctly reported in reference 32, but neither reference reports 1H
NMR data. We do so below.
The 4,4′-dimethyl substituted complexes [Pt(4,4′-Me2bpy)Cl2],
[Pt(4,4′-Me2bpy)2](ClO4)2, and [Pt(4,4′-Me2bpy)2](NO3)2·2H2O
were synthesized by methods analogous to those used for the
nonsubstituted bpy complexes. The syntheses of [Pt(4,4′-Me2bpy)-
Cl2] and [Pt(4,4′-Me2bpy)2](ClO4)2 are given in the Supporting
Information.
[Pt(4,4′-Me2bpy)2](NO3)2·2H2O. An aqueous solution of [AsPh4]-
Cl·H2O (2.67 g, 6.11 mmol) in H2O (30 mL) was added dropwise to a
stirred suspension of [Pt(4,4′-Me2bpy)2](ClO4)2 (2.33 g, 3.06 mmol)
in H2O (70 mL). [AsPh4]ClO4 precipitated immediately as a white
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solid. The mixture was first stirred at room temperature for 20 min and
then on an ice-bath for 10 min; the solid was then removed by
filtration through Celite and washed with ice-cold H2O (2 × 25 mL).
The resulting yellow filtrate was passed through a column of Dowex
5/5′), 2.45 (s, 12H, CH3). 13C NMR (126 MHz, D2O): 158.2 (s,
bpyC-2/2′), 157.3 (s, bpyC-4/4′), 152.7−153.8 (broad, bpyC-6/6′),
149.3 (d, 4J = 2.6 Hz, Cd), 137.1−137.9 (m, broad, Cb, Cf), 136.2 (d, 4J
= 2.8 Hz, Ch), 132.4 (d, 3J = 11.7 Hz, Cg), 131.0 (s, bpyC-5/5′), 130.4
(d, 1J = 63.9 Hz, Ca), 129.0 (s, bpyC-3/3′), 128.9 (d, 3J = 12.1 Hz, Cc),
−
anion exchange resin (100−200 mesh size, NO3 form), and the
1
yellow eluate was taken to dryness (rotavap) to give a yellow solid,
which was washed with ice-cold H2O (2 × 3 mL), then acetone (2 × 4
mL), and finally diethyl ether (3 × 10 mL) and dried under vacuum.
Yield: 2.11 g (95%). Anal. Calcd (%) for C24H28N6O8Pt: C 39.84, H
3.90, N 11.61; found C 39.71, H 3.90, N 11.43. HRESI-MS (MeCN):
m/z calcd for C24H24N5O3Pt+: 625.1523 [M + NO3]+; found 625.1507
(6%), m/z calcd for C25H24N5Pt+: 589.1676 [M + CN]+; found
589.1675 (70%), m/z calcd for C24H24N4Pt2+: 281.5820 [Pt(4,4′-
125.6 (d, J = 63.5 Hz, Ce), 23.5 (s, CH3). 31P NMR (202 MHz,
1
1
D2O): 10.94 (s with satellites; JP−Pt = 3795 Hz, JP−C = 63.5 Hz and
2JP−C = 11.8 Hz). 195Pt NMR (107 MHz, D2O): −3197 (d, JPt−P
=
1
3795 Hz).
In Situ Synthesis of [Pt(bpy)2(PPh3)]2+ in CD3OD Solution. A
pale yellow solution of [Pt(bpy)2](NO3)2·H2O in CD3OD (3.0 mM,
1.18 mL) was added to PPh3 (0.93 mg, 3.5 μmol). The mixture was
stirred at room temperature until the PPh3 dissolved, giving a more
intense yellow solution containing [Pt(bpy)2(PPh3)]2+. HRESI-MS
(MeCN): m/z calcd for C21H16N5Pt+: 533.1049 [M − PPh3 + CN]+;
found 533.1039 (100%), m/z calcd for C38H31N4PPt2+: 384.5963
1
Me2bpy)2]2+ ([M]2+); found 281.5839 (100%). H NMR (400 MHz,
DMSO-d6): 8.89 (d, J = 6.2 Hz, 4H, bpyH-6/6′), 8.69 (s, 4H, bpyH-3/
1
3′), 7.85 (d, J = 5.5 Hz, 4H, bpyH-5/5′), 2.66 (s, 12H, CH3). H
1
[Pt(bpy)2(PPh3)]2+ ([M]2+); found 384.5937 (7%). H NMR (500
NMR (400 MHz, D2O): 8.61 (d, J = 6.1 Hz, 4H, bpyH-6/6′), 8.25 (s,
4H, bpyH-3/3′), 7.64 (d, J = 5.9 Hz, 4H, bpyH-5/5′), 2.70 (s, 12H,
CH3). 13C NMR (101 MHz, D2O): 159.5 (bpyC-4/4′), 158.8 (bpyC-
2/2′), 152.3 (bpyC-6/6′), 132.0 (bpyC-5/5′), 128.1 (bpyC-3/3′),
23.9 (CH3). 195Pt NMR (107 MHz, D2O): −2242 ppm.
MHz, CD3OD): 8.41 (d, J = 5.2 Hz, 4H, bpyH-6/6′), 8.33 (d, J = 8.0
Hz, 4H, bpyH-3/3′), 8.21 (td, J = 7.9, 1.5 Hz, 4H, bpyH-4/4′), 7.50−
7.61 (m, 9H, Hb, Hd), 7.48 (ddd, J = 7.2, 5.7, 1.1 Hz, 4H, bpyH-5/5′),
7.38−7.44 (m, 6H, Hc). 13C NMR (126 MHz, CD3OD): 157.1 (s,
In Situ Synthesis of [Pt(bpy)2{PPh(PhSO3)2}] in D2O Solution.
A yellow solution of [Pt(bpy)2](NO3)2·H2O in D2O (32 mM, 0.361
mL) was added to a colorless solution of K2PPh(PhSO3)2·2H2O in
D2O (32 mM, 0.361 mL) at room temperature to give a more intense
yellow solution containing [Pt(bpy)2{PPh(PhSO3)2}]. HRESI-MS
bpyC-2/2′), 152.9 (s, bpyC-6/6′), 142.6 (s, bpyC-4/4′), 135.7 (d,
3
2JC−P = 11.2 Hz, Cb), 134.2 (d, 4JC−P = 2.8 Hz, Cd), 130.8 (d, JC−P
=
11.6 Hz, Cc), 128.9 (s, bpyC-5/5′), 127.0 (s, bpyC-3/3′), 126.1 (d,
1JC−P = 63.7 Hz, Ca). 31P NMR (202 MHz, CD3OD): 11.91 (s with
1
1
2
satellites; JP−Pt = 3790 Hz, JP−C = 63.6 Hz and JP−C = 11.2 Hz).
In Situ Synthesis of [Pt(4,4′-Me2bpy)2(PPh3)]2+ in CD3OD
Solution. A pale yellow solution of [Pt(4,4′-Me2bpy)2](NO3)2·2H2O
in CD3OD (3.0 mM, 1.41 mL) was added to PPh3 (1.1 mg, 4.2 μmol).
The mixture was stirred at room temperature until the PPh3 dissolved,
giving a more intense yellow solution containing [Pt(4,4′-
+
(MeCN): m/z calcd for C38H29KN4O6PPtS2 : 966.0548 [(Pt(bpy)2-
{PPh(PhSO3)2}) + K]+ ([M + K]+); found 966.0387 (12%), m/z
+
calcd for C38H29N4NaO6PPtS2 : 950.0809 [M + Na]+; found 950.0812
(13%), m/z calcd for C22H18N4NaO4Pt+: 620.0870 [M − PPh-
(PhSO3)2 + 2O2CH + Na]+; found 620.0828 (100%), m/z calcd for
C38H29N4Na2O6PPtS22+: 486.5350 [M + 2Na]2+; found 486.5316
Me2bpy)2(PPh3)]2+
. HRESI-MS (MeCN): m/z calcd for
1
C42H39N6NaO6PPt+: 972.2212 [M + 2NO3 + Na]+; found 972.2236
(0.2%), m/z calcd for C42H39N4PPt2+: 412.6276 [Pt(4,4′-
Me2bpy)2(PPh3)]2+ ([M]2+); found 412.6230 (2%), m/z calcd for
(10%). H NMR (500 MHz, D2O): 8.27−8.39 (m, 4H, bpyH-6/6′),
8.24 (d, J = 8.0 Hz, 4H, bpyH-3/3′), 8.18 (td, J = 7.9, 1.4 Hz, 4H,
bpyH-4/4′), 7.67−7.77 (m, 6H, Hf, Hc), 7.65 (td, J = 7.6, 7.1, 1.6 Hz,
1H, Hh), 7.53−7.62 (m, 4H, Hb), 7.44 (m, 6H, bpyH-5/5′, Hg). 13C
NMR (126 MHz, D2O): 158.5 (s, bpyC-2/2′), 154.3 (s, bpyC-6/6′),
149.3 (d, 4JC−P = 2.9 Hz, Cd), 144.2 (s, bpyC-4/4′), 137.4−137.7 (m,
Cb, Cf), 136.3 (d, 4JC−P = 2.7 Hz, Ch), 132.5 (d, 3JC−P = 12.0 Hz, Cg),
C24H24N4Pt2+: 281.5820 [M − PPh3]2+; found 281.5804 (100%). H
1
NMR (400 MHz, CD3OD): 8.06−8.27 (m, 8H, bpyH-6/6′, bpyH-3/
3′), 7.57−7.63 (m, 3H, Hd), 7.52 (dd, J = 11.3, 8.2 Hz, 6H, Hb), 7.41
(td, J = 7.8, 2.8 Hz, 6H, Hc), 7.27 (d, J = 5.7 Hz, 4H, bpyH-5/5′), 2.50
(s, 12H, CH3). 13C NMR (101 MHz, CD3OD): δ = 156.8 (s, bpyC-2/
2′), 155.6 (s, bpyC-4/4′), 152.0 (s, bpyC-6/6′), 135.7 (d, 2JC−P = 11.2
Hz, Cb), 134.0 (d, 4JC−P = 2.7 Hz, Cd), 130.7 (d, 3JC−P = 11.5 Hz, Cc),
129.4 (s, bpyC-5/5′), 127.6 (s, bpyC-3/3′), 126.4 (d, 1JC−P = 63.6 Hz,
Ca), 21.4 (s, CH3). 31P NMR (202 MHz, CD3OD): 11.81 (s with
130.6 (s, bpyC-5/5′), 130.3 (d, 1JC−P = 63.3 Hz, Ca), 129.0 (d, 3JC−P
=
P
12.0 Hz, Cc), 128.5 (s, bpyC-3/3′), 125.3 (d, 1JC−P = 64.0 Hz, Ce). 31
1
NMR (202 MHz, D2O): 11.13 (s with satellites; JP−Pt = 3791 Hz,
2
1JP−C = 63.5 Hz and JP−C = 11.8 Hz). 195Pt NMR (107 MHz, D2O):
1
−3176 (d, JPt−P = 3805 Hz).
1
1
2
satellites; JP−Pt = 3801 Hz, JP−C = 63.3 Hz and JP−C = 11.2 Hz).
Synthesis of [Pt(bpy)(PPh3)2](ClO4)2. PPh3 (1.06 g, 4.06 mmol)
in acetone (40 mL) was added to a stirred suspension of [Pt(bpy)Cl2]
(0.18 g, 0.43 mmol) in H2O (20 mL). The resulting mixture was
stirred at 50 °C for 10 min to give a pale yellow solution. Unreacted
PPh3 precipitated as a white solid upon cooling the mixture on an ice
bath. The white solid was removed by filtration, and the pale yellow
filtrate was extracted with diethyl ether (3 × 15 mL). NaClO4 (1.88 g)
was added to the aqueous layer, and an off-white solid precipitated
immediately. The mixture was cooled on an ice bath, the solid was
collected by filtration, washed with ice-cold H2O (4 × 10 mL), then
ice-cold EtOH (3 × 10 mL) and finally diethyl ether (3 × 10 mL), and
dried under vacuum overnight. Yield: 0.11 g (24%). Anal. Calcd (%)
for C46H38Cl2N2O8P2Pt: C 51.41, H 3.56, N 2.61, Cl 6.60; found C
51.34, H 3.50, N 2.70, Cl 6.79. HRESI-MS (MeCN): m/z calcd for
C28H23ClN2O4PPt+: 712.0729 [M − PPh3 + ClO4]+ (10%); found
712.0695, m/z calcd for C29H23N3PPt+: 639.1274 [M − PPh3 + CN]+;
found 639.1236 (100%), m/z calcd for C46H38N2P2Pt2+: 437.6075
Synthesis of [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O. Yellow crystals of
[Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O suitable for X-ray crystallography
were obtained by vapor diffusion of MeCN into an equimolar mixture
of [Pt(bpy)2](NO3)2·H2O and K2PPh(PhSO3)2·2H2O in aqueous
solution over
a period of 10 d. Anal. Calcd (%) for
C38H40N4O11.5PPtS2: C 44.44, H 3.93, N 5.46, S 6.24; found: C
44.32, H 3.59, N 5.61, S 6.48.
In Situ Synthesis of [Pt(4,4′-Me2bpy)2{PPh(PhSO3)2}] in D2O
Solution. A yellow solution of [Pt(4,4′-Me2bpy)2](NO3)2·2H2O in
D2O (10 mM, 0.790 mL) was added to K2PPh(PhSO3)2·2H2O (4.2
mg, 7.9 μmol). The mixture was stirred at room temperature until the
K2PPh(PhSO3)2·2H2O dissolved, giving a more intense yellow
solution containing [Pt(4,4′-Me2bpy)2{PPh(PhSO3)2}]. HRESI-MS
+
(MeCN): m/z calcd for C42H37KN4O6PPtS2 : 1022.1175 [(Pt(4,4′-
Me2bpy)2{PPh(PhSO3)2}) + K]+ ([M + K]+); found 1022.1203 (3%),
+
m/z calcd for C42H37N4NaO6PPtS2 : 1006.1435 [M + Na]+; found
+
1006.1486 (3%), m/z calcd for C42H38N4O6PPtS2 : 984.1616 [M +
H]+; found 984.1660 (3%), m/z calcd for C25H24N5Pt+: 589.1676 [M
1
− PPh(PhSO3)2 + CN]+; found 589.1670 (100%). H NMR (500
1
[Pt(bpy)(PPh3)2]2+ ([M]2+); found 437.6050 (1%). H NMR (400
MHz, D2O, 65 °C): 8.08 (d, J = 4.9 Hz, 4H, bpyH-6/6′), 7.98 (s, 4H,
bpyH-3/3′), 7.73 (dd, J = 8.4, 2.1 Hz, 4H, Hc), 7.60−7.69 (m, 3H, Hf,
Hh), 7.54 (dd, J = 11.9, 8.3 Hz, 4H, Hb), 7.47 (td, J = 8.1, 2.9 Hz, 2H,
MHz, DMF-d7): 8.97 (d, J = 8.0 Hz, 2H, bpyH-3/3′), 8.52 (t, J = 7.8
Hz, 2H, bpyH-4/4′), 8.14−8.22 (broad, 2H, bpyH-6/6′), 8.05−8.14
(m, 12H, Hb), 7.61 (t, J = 7.4 Hz, 6H, Hd), 7.50 (t, J = 6.8 Hz, 2H,
bpyH-5/5′), 7.44 (t, J = 7.2 Hz, 12H, Hc). 13C NMR (126 MHz,
DMF-d7): 157.8 (s, bpyC-2/2′), 153.2 (s, bpyC-6/6′), 143.6 (s, bpyC-
4/4′), 136.0 (t, 2JC−P = 5.4 Hz, Cb), 133.6 (s, Cd), 130.0 (t, 3JC−P = 5.8
Hz, Cc), 128.5 (s, bpyC-5/5′), 125.8 (d, 1JC−P = 64.6 Hz, Ca), 125.5 (s,
1
Hg), 7.25 (d, J = 5.0 Hz, 4H, bpyH-5/5′), 2.47 (s, 12H, CH3). H
NMR (500 MHz, D2O, 25 °C): 7.85−8.25 (m, broad, 8H, bpyH-6/6′,
bpyH-3/3′), 7.61−7.78 (m, 7H, Hc, Hf, Hh), 7.47−7.61 (broad, 4H,
Hb), 7.43 (dt, J = 7.7, 3.9 Hz, 2H, Hg), 7.05−7.35 (broad, 4H, bpyH-
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Inorganic Chemistry
Article
bpyC-3/3′). 31P NMR (162 MHz, DMF-d7): 8.80 (s with satellites;
1JP−Pt = 3557 Hz). 31P NMR (202 MHz, CD3OD): 9.15 (broad); no
195Pt satellites were observed owing to the low solubility of the
ACKNOWLEDGMENTS
■
The authors are grateful to the National Computational
Infrastructure for access to the Australian National University
supercomputer facilities. We thank Mr. James Lewis for useful
discussions on X-ray crystal structure refinement. W.K.C.L.
thanks the University of Otago for awarding a doctoral
scholarship.
complex in this solvent.
Colorless crystals of [Pt(bpy)(PPh3)2](ClO4)2·0.5(C6H14O) suit-
able for X-ray crystallography were obtained by vapor diffusion of
diisopropyl ether into a solution of [Pt(bpy)(PPh3)2](ClO4)2 in
acetone over 2 d.
X-ray Crystallography. X-ray data were collected at 100.0 K on
an Agilent Technologies Supernova system using Mo Kα radiation,
and data were treated using CrisAlisPro40 software. The structure was
solved using SIR-97,41 and weighted full-matrix refinement on F2 was
carried out using SHELXL-9742 running within the WinGX43 package.
Data Refinement Details for [Pt(bpy)2{PPh(PhSO3)2}]·5.5H2O.
All non-hydrogen atoms were refined anisotropically. Hydrogen atoms
attached to carbons were placed in calculated positions and refined
using a riding model. Hydrogen atoms of solvent water molecules were
placed in calculated positions and orientated with sensible hydrogen-
bonding acceptors (where possible). The two sulfonate groups were
disordered over two sites. One group was modeled with occupancies
of 40% (O1, O2, and O3) and 60% (O10, O11, and O12) over two
sites, and the other group was modeled with occupancies of 50% (O4,
O7, and O8) and 50% (O5, O6, and O9) over two sites. S1 and S2
were full occupancy. A DFIX command was used to restrain the S1−
O2 distance to 1.35 Å. An ISOR command was applied to sulfonate
oxygen atoms O2, O4, O8, O9, and O11 and to the solvent water
molecule oxygen atoms O91 and O94. The half of the bpy ring that
consists of atoms N4 and C16 through C20 was slightly disordered
and modeled with the SIMU command.
Data Refinement Details for [Pt(bpy)(PPh3)2](ClO4)2·0.5-
(C6H14O). All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were placed in calculated positions and refined
using a riding model. The two isopropyl groups of the diisopropyl
ether molecule were slightly disordered. An ISOR command was
applied to all six carbon atoms (C91, C92, C93, C94, C95, and C96)
in the two isopropyl groups. A DFIX command was used to restrain
the O9−C94 distance to 1.44 Å.
Computational Details. All calculations were performed with the
Amsterdam Density Functional (ADF 2010)44−46 package. Func-
tionals based on the generalized gradient approximation (GGA),
proposed by Becke47 and Perdew48 (for exchange and correlation
effects, respectively), and all-electron basis sets of triple-ζ quality plus
one polarization function (TZP)49 were utilized. Relativistic effects
were included by means of the zero order regular approximation
(ZORA),50−52 and the conductor-like screening model (COSMO)53
was used for the treatment of solvation effects, with water as the
solvent.
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ASSOCIATED CONTENT
■
S
* Supporting Information
1
1
Selected H, 13C, 31P, and H DOSY NMR spectra, selected
mass spectra, UV−vis spectra, calculated bonding energy, and
CIFs giving crystallographic data for [Pt(bpy)(PPh3)2](ClO4)2·
0.5(C6H14O) (CCDC 975095) and [Pt(bpy)2(PPh-
(PhSO3)2)]·5.5H2O (CCDC 975096). This material is
available free of charge via the Internet at http://pubs.acs.org.
́
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AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: allan.blackman@aut.ac.nz. Fax: +64 9 921 9627.
Phone: +64 9 921 9642 (A.G.B.).
*Email: jcrowley@chemistry.otago.ac.nz. Fax: +64 3 479 7906.
Phone: +64 3 479 7731 (J.D.C.).
Notes
The authors declare no competing financial interest.
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