Bridging and chelating roles of bis(2-(diphenylphosphino)ethyl) phenylphosphine in stabilizing binuclear platinum(II) complexes

Article abstract of DOI:10.1021/om400322s

The diorganoplatinum(II) complexes [PtR₂(triphos-P,P′)] (1; R = Me, p-MeC₆H₄ and triphos = bis(2- (diphenylphosphino)ethyl)phenylphosphine), containing one free phosphine atom, react with cyclometalated platinum complexes [PtR′(CN) (SMe₂)] (2; R′ = Me, p-MeC₆H₄ and C N is deprotonated 2-phenylpyridine (ppy) or deprotonated benzo[h]quinoline (bhq)) to give the cyclometalated diplatinum(II) complexes [Pt₂R₂R′(CN)(triphos)] (3). In these binuclear platinum(II) compounds, triphos acts as both a chelating and bridging ligand to stabilize the produced diplatinum complexes. The complexes 3 were readily characterized by multinuclear NMR spectroscopy and elemental microanalysis. The crystal structure of complex 3f (R = Me, R′ = p-MeC₆H₄, and CN = bhq) was further determined by X-ray crystallography, giving the first example of an X-ray structural determination of a diplatinum complex with a triphos ligand acting simultaneously as both a chelating and bridging ligand.

Full text of DOI:10.1021/om400322s

Article
pubs.acs.org/Organometallics
Bridging and Chelating Roles of Bis(2-
(diphenylphosphino)ethyl)phenylphosphine in Stabilizing Binuclear
Platinum(II) Complexes
Fatemeh Raoof,† Ahmad R. Esmaeilbeig,*,† S. Masoud Nabavizadeh,*,† Fatemeh Niroomand Hosseini,‡
and Maciej Kubicki§
†Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71467-13565, Iran
‡Department of Chemistry, Shiraz Branch, Islamic Azad University, Shiraz 71993-37635, Iran
§Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland
ABSTRACT: The diorganoplatinum(II) complexes [PtR2(triphos-P,P′)] (1;
R = Me, p-MeC6H4 and triphos = bis(2-(diphenylphosphino)ethyl)-
phenylphosphine), containing one free phosphine atom, react with cyclo-
metalated platinum complexes [PtR′(C∧N)(SMe2)] (2; R′ = Me, p-MeC6H4
and C∧N is deprotonated 2-phenylpyridine (ppy) or deprotonated benzo[h]-
quinoline (bhq)) to give the cyclometalated diplatinum(II) complexes
[Pt2R2R′(C∧N)(triphos)] (3). In these binuclear platinum(II) compounds,
triphos acts as both a chelating and bridging ligand to stabilize the produced
diplatinum complexes. The complexes 3 were readily characterized by
multinuclear NMR spectroscopy and elemental microanalysis. The crystal
structure of complex 3f (R = Me, R′ = p-MeC6H4, and C∧N = bhq) was
further determined by X-ray crystallography, giving the first example of an X-ray structural determination of a diplatinum
complex with a triphos ligand acting simultaneously as both a chelating and bridging ligand.
transition metals.5 In the present work, we have synthesized a
INTRODUCTION
■
series of mixed diorgano and cyclometalated diplatinum(II)
In the past few years, the chemistry of cyclometalated platinum
complexes, [Pt2R2R′(C∧N)(triphos)] (3), in which R, R′ = Me,
complexes has attracted much attention. The most well-studied
p-MeC6H4 and C∧N is deprotonated 2-phenylpyridine (ppy) or
examples of these compounds are five-membered-ring com-
deprotonated benzo[h]quinoline (bhq), using a general
plexes containing nitrogen−Pt and C(phenyl)−Pt bonds.1
synthetic approach involving ligand replacement from the
They exhibit a wide range of applications which range from the
corresponding precursor having the labile ligand SMe2.
synthesis of new organic and organometallic compounds to
mesogenic species and catalytic materials as well as supra-
EXPERIMENTAL SECTION
molecular entities.2 On the other hand, there has been a
■
1
The H NMR spectra were recorded by using either a Bruker Avance
growing interest in the synthesis of platinum complexes
DPX 250 spectrometer or a Varian Mercury 400 spectrometer in
containing polydentate phosphine ligands, due to their
CDCl3 with TMS as reference. The 31P and 195Pt NMR spectra were
applications as homogeneous and heterogeneous catalysts.3
recorded on a Bruker Avance DRX 500 spectrometer in CDCl3 with
In the past, we have been interested in platinum(II)
cyclometalated complexes derived from 2-phenylpyridine
ligands; for example, 2-phenylpyridine, benzo[h]quinoline,
and 2-(p-tolyl)pyridine ligands readily react with platinum(II)
precursor complexes, such as those with the formula
[PtR2(SMe2)2] or [Pt2R4(μ-SMe2)2] through cyclometalation
reactions to give cyclometalated platinum complexes. Treat-
ment of the resulting cycloplatinated complexes with
diphosphine ligands such as 1,1′-bis(diphenylphosphino)-
ferrocene, bis(diphenylphosphino)methane, and bis-
(diphenylphosphino)ethane, in different molar ratios, produces
mono- or dinuclear complexes with biphosphines as mono-
dentate, bidentate, or bridging ligands.4
85% H3PO4 and aqueous Na2PtCl4 as references, respectively. The
microanalyses were performed using a Thermo Finnigan Flash EA-
1112 CHNSO rapid elemental analyzer. [Pt2Me4(μ-SMe2)2]6 and the
monomeric precursors cis-[Pt(p-MeC6H4)2(SMe2)2],7 [PtMe(C∧N)-
(SMe2)] (C∧N = ppy, bhq),4b and [Pt(p-MeC6H4)(C∧N)(SMe2)]
(C∧N = ppy, bhq)4c were prepared by the literature methods. Bis(2-
(diphenylphosphino)ethyl)phenylphosphine (triphos) was purchased
from commercial sources. The NMR labeling of complexes 3 is
depicted in Figure 1.
[PtMe2(triphos-P,P′)] (1a). A solution of [PtMe2(triphos-P,P′)]
(1a) was prepared8 by addition of triphos (186.7 mg, 0.33 mmol) to a
solution of [Pt2Me4(μ-SMe2)2] (100 mg, 0.17 mmol) in acetone at
room temperature. This solution was stirred for 30 min and used
freshly for preparation of complexes 3.
The ligand triphos (=bis(2-(diphenylphosphino)ethyl)-
phenylphosphine) is an interesting and useful ligand in the
synthesis of many chelating, binuclear, and cluster complexes of
Received: April 16, 2013
Published: July 9, 2013
© 2013 American Chemical Society
3850
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Organometallics
Article
[Pt2Me(p-MeC6H4)2(ppy)(triphos)] (3d). To a solution of
[PtMe(ppy)(SMe2)] (2a; 19 mg, 0.04 mmol) in acetone was added
[Pt(p-MeC6H4)2(triphos)] (1b; 41 mg, 0.05 mmol). The mixture was
stirred at room temperature for 20 h. The solvent was removed, and
the residue was purified to a pale yellow powder by treatment with
diethyl ether and drying under vacuum. Yield: 32 mg, 26%. Mp: 160
°C dec. Anal. Calcd for C60H58NP3Pt2; C, 56.5; H, 4.5; N, 1.1. Found:
C, 57.5; H, 4.3; N, 1.2. NMR in CDCl3: δ(1H) 0.68 (d, 3JHP = 7.6 Hz,
JPt H = 83.1 Hz, 3H, MePt), 1.86 (s, 3H, Me of p-MeC6H4 ligand),
a
Figure 1. NMR labeling of complexes 3.
2
a
1.93 (s, 3H, Me of p-MeC6H4 ligand), 1.71−2.53 (m, 8H, CH2 of
triphos), 6.02−7.67 (br, 41H, hydrogens of aromatic region); δ(31P)
[Pt(p-MeC6H4)2(triphos-P,P′)] (1b). To a solution of cis-[Pt(p-
MeC6H4)2(SMe2)2] (100 mg, 0.2 mmol) in dichloromethane was
added triphos (110 mg, 0.21 mmol), and the reaction mixture was
stirred at room temperature for 3 h. The solvent was removed, and the
residue was dissolved in a minimum amount of CH2Cl2. The white
solid product was formed after dropwise addition of n-hexane at 0 °C.
Yield: 60 mg, 66%. Mp: 165 °C dec. Anal. Calcd for C48H47P3Pt: C,
63.2; H, 5.2. Found: C, 63.1; H, 5.2. NMR data in CDCl3: δ(1H) 2.07
(s, 3H, CH3 of p-MeC6H4 ligand), 2.11 (s, 3H, CH3 of p-MeC6H4
3
1
3
24.9 (d, JP P = 45 Hz, JPt P = 2094 Hz, 1P, Pa), 42.1 (d, JP P = 45
a
b
a
a
a b
Hz, JPt P = 1702 Hz, 1P, Pb), 40.8 (s, JPt P = 1708 Hz, 1P, Pc).
[Pt2Me3(bhq)(triphos)] (3e). This was prepared by the method
described above for preparation of complex 3a using the starting
material [PtMe(bhq)(SMe2)]. Yield: 83%. Mp 210 °C dec. Anal.
Calcd for C50H50NP3Pt2; C, 52.3; H, 4.5; N, 1.2. Found: C, 52.4;
1
1
b
b
b c
H,4.3; N, 1.4. NMR in CDCl3: δ(1H) 0.67 (t, JHP = JHP = 7.6 Hz,
3
3
b
c
2
2
3
3
b
b
c
JPt H = 69.0 Hz, 3H, Me trans to P), 0.69 (t, JHP = JHP = 7.0 Hz,
JPt H = 70.0 Hz, 3H, Me trans to P), 1.15 (d, JHP = 7.5 Hz, JPt H
o
ligand), 1.70−2.71 (m, 8H, CH2 of triphos), 6.61 (d, 3JH Hm = 6.8 Hz,
3
2
b
a
a
=
3
2Hm of p-MeC6H4 ligand), 6.73 (d, JH ′H ′ = 7.0 Hz, 2Hm′ of p-
o
m
83.9 Hz, 3H, Me trans to N), 1.80−2.75 (m, 8H, CH2 of triphos),
6.92−8.12 (br, 33H, hydrogens of aromatic region), 9.31 (d, 1H, 3JHH
= 7.2 Hz, CH group adjacent to coordinated N atom); δ(31P) 23.5 (d,
MeC6H4 ligand); δ(31P) 45.7 (t, 1P, JPtP = 1695 Hz, JPP = 20 Hz).
[Pt2Me3(ppy)(triphos)] (3a). To a solution of [Pt2Me4(μ-SMe2)2]
(30 mg, 0.052 mmol) in acetone was added triphos (56 mg, 0.1
mmol). The reaction mixture was stirred at room temperature for 30
min. After this time, [PtMe(ppy)(SMe2)] (45 mg, 0.11 mmol) was
added to the solution, and the reaction mixture was stirred for 2 h. The
solvent was evaporated, and the residue was washed with ether and
dried under vacuum to give a light yellow powder of 3a. Yield: 42 mg,
36%. Mp 179 °C dec. Anal. Calcd for C48H50NP3Pt2; C, 51.2; H, 4.4;
N, 1.2. Found: C, 50.7; H,4.2; N, 1.2. NMR in CDCl3: δ(1H) 0.42 (t,
1
3
3
1
a
3
1
a
b
a
a
a
b
b b
JP P = 45 Hz, JPt P = 2132 Hz, 1P, P ), 47.2 (d, JP P = 45 Hz, JPt P
=
1797 Hz, 1P, Pb), 48.0 (s, JPt P = 1807 Hz, 1P, Pc); δ(195Pt) −2590
1
b
c
(d, 1JPt P = 2131 Hz, 1Pt, Pt ), −3006 (t, JPt P = JPt P = 1800 Hz, 1Pt,
a
1
1
a
a
b
b
b c
Ptb).
[Pt2Me2(p-MeC6H4)(bhq)(triphos)] (3f). This was prepared by
the method used for preparation of complex 3b using [Pt(p-
MeC6H4)(bhq)(SMe2)]. Yield: 82%. Mp 232 °C dec. Anal. Calcd
for C56H54NP3Pt2; C, 54.9; H, 4.4; N, 1.2. Found: C, 54.8; H,4.5; N,
3
3
3
b
3
2
c
b
JHP = JHP = 7.3 Hz, JPt H = 70.0 Hz, 3H, Me trans to P), 0.44 (t,
3
2
1.1. NMR in CDCl3: δ(1H) 0.12 (t, 3JHP3 = JHP = 7.2 Hz, JPt H = 70.1
b
c
b
3
2
b
c
b
JHP = JHP = 7.3 Hz, JPt H = 70.4 Hz, 3H, Me trans to P), 0.71 (d,
2
b
c
b
2
Hz, 3H, Me trans to P), 0.33 (t, 3JHP = JHP = 7.0 Hz, JPt H = 68.9 Hz,
3H, Me trans to P), 2.0 (s, 3H, Me of p-MeC6H4 ligand), 1.91−2.41
(m, 8H, CH2 of triphos), 6.37−7.89 (br, 37H, hydrogens of aromatic
a
a
JHP = 7.5 Hz, JPt H = 85.0 Hz, 3H, Me trans to N), 1.81−2.50 (m, 8H,
CH2 of triphos), 6.30−7.72 (br, 34H, hydrogens of aromatic region);
δ(31P) 23.9 (d, 3JP P = 45 Hz, JPt P = 2076 Hz, 1P, P ), 47.3 (dd, JP P
1
a
3
a
b
a
a
a b
region); δ(31P) 21.7 (d, 3JP P = 46 Hz, 1JPt P = 2070 Hz, 1P, Pa), 48.8
a
b
a a
= 45 Hz, 3JP P = 5 Hz, JPt P = 1798 Hz, 1P, P ), 47.9 (s, JPt P = 1806
1
b
1
b
c
b
b
b c
(d, 3JP P = 46 Hz, JPt P = 1823 Hz, 1P, P ), 48.7 (s, JPt P = 1819 Hz,
1
b
1
a
b
b
b
b c
Hz, 1P, Pc); δ(195Pt) −2559 (d, 1JPt P = 2078 Hz, 1Pt, Pt ), −3005 (t,
a
a
a
1P, Pc); δ(195Pt) −2431 (d, 1JPt P = 2067 Hz, 1Pt, Pt ), −3002 (t, JPt P
a
1
a
a
b b
1
1
JPt P = JPt P = 1802 Hz, 1Pt, Ptb).
b
b
b c
1
= JPt P = 1820 Hz, 1Pt, Ptb).
b
c
[Pt2Me2(p-MeC6H4)(ppy)(triphos)] (3b). To a freshly prepared
[Pt2(p-MeC6H4)3(bhq)(triphos)] (3g). This was prepared by the
method used for preparation of complex 3c using [Pt(p-MeC6H4)-
(bhq)(SMe2)]. Yield: 73%. Mp: 175 °C dec. Anal. Calcd for
C68H62NP3Pt2; C, 59.3; H, 4.5; N, 1.0. Found: C, 59.7; H,4.7; N,
1.1. NMR in CDCl3: δ(1H) 2.02 (s, 3H, Me of p-MeC6H4 ligand), 2.06
(s, 3H, Me of p-MeC6H4 ligand), 2.12 (s, 3H, Me of p-MeC6H4
solution of [PtMe2(triphos-P,P′)] (132 mg, 0.17 mmol in 20 mL of
acetone) was added [Pt(p-MeC6H4)(ppy)(SMe2)] (87.5 mg, 0.17
mmol), and the solution was stirred for 3 h. A pale yellow precipitate
was formed, which was isolated by filtration and dried under vacuum.
Yield: 148 mg, 71%. Mp: 222 °C dec. Anal. Calcd for C54H54NP3Pt2;
C, 54.1; H, 4.5; N, 1.2. Found: C, 54.0; H,4.3; N, 1.1. NMR in CDCl3:
ligand), 1.58−2.82 (m, 8H, CH2 of triphos), 6.50−8.00 (br, 45H,
3
2
δ(1H) 0.10 (t, 3JHP = JHP = 7.4 Hz, JPt H = 70.0 Hz, 3H, Me trans to
b
c
b
3
a
b
a a
3
2
hydrogens of aromatic region); δ(31P) 21.1 (d, JP P = 46 Hz, JPt P
=
P), 0.32 (t, 3JHP = JHP = 7.2 Hz, JPt H = 69.1 Hz, 3H, Me trans to P),
1.90 (s, 3H, Me of p-MeC6H4 ligand), 1.38−2.31 (m, 8H, CH2 of
triphos), 6.30−7.72 (br, 37H, hydrogens of aromatic region); δ(31P)
b
c
b
2089 Hz, 1P, Pa), 43.1 (d, JP cP = 46 Hz, JPt P = 1724 Hz, 1P, Pb),
3
1
a
b
b b
42.1 (s, 1JPt P = 1723 Hz, 1P, P ); δ(195Pt) −2430 (d, 1JPt P = 2086 Hz,
b
c
a a
1Pt, Pta), −2952 (t, JPt P = JPt P = 1723 Hz, 1Pt, Ptb).
1
1
b
b
b c
22.1 (d, JP P = 46 Hz, JPt P = 2008 Hz, 1P, Pa), 48.7 (d, JP P = 46
3
1
3
a
b
a
a
a b
Hz, JPt P = 1822 Hz, 1P, Pb), 48.8 (s, JPt P = 1817 Hz, 1P, Pc);
1
1
[Pt2Me(p-MeC6H4)2(bhq)(triphos)] (3h). This complex was
prepared by the method used for synthesis of complex 3d using the
starting material [PtMe(bhq)(SMe2)]. Yield: 36%. Mp: 165 °C dec.
Anal. Calcd for C62H58NP3Pt2; C, 57.3; H, 4.5; N, 1.1. Found: C, 56.9;
b
b
b c
δ(195Pt) −2406 (d, 1Pt, 1JPt P = 2010 Hz Pt ), −3001 (t, JPt P = JPt P
a
1
1
a
a
b
b
b c
= 1820 Hz, 1Pt, Ptb).
[Pt2(p-MeC6H4)3(ppy)(triphos)] (3c). To a freshly prepared
solution of [Pt(p-MeC6H4)2(triphos-P,P′)] (1b, by addition of triphos
(53.4 mg, 0.1 mmol) to a solution of [Pt(p-MeC6H4)2(SMe2)2] (50
mg, 0.1 mmol) in acetone at room temperature for 3 h) was added a
solution of [Pt(p-MeC6H4)(ppy)(SMe2)] (50.1 mg, 0.1 mmol). The
mixture was stirred for 3 h. The solvent was evaporated, and the
residue was washed with n-hexane and dried under vacuum. Yield: 63
mg, 47%. Mp: 165 °C dec. Anal. Calcd for C66H62NP3Pt2; C, 58.6; H,
4.6; N, 1.0. Found: C, 59.0; H, 4.5; N, 1.0. NMR in CDCl3: δ(1H) 2.05
(s, 3H, Me of p-MeC6H4 ligand), 2.10 (s, 3H, Me of p-MeC6H4
ligand), 2.12 (s, 3H, Me of p-MeC6H4 ligand), 1.49−2.11 (m. 8H, CH2
of triphos), 6.47−8.04 (br, 45H, hydrogens of aromatic region); δ(31P)
3
2
H,4.2; N, 1.1. NMR in CDCl3: δ(1H) 0.89 (d, JHP = 7.4 Hz, JPt H
=
a
a
83.8 Hz, 3H, Me trans to N), 1.86 (s, 3H, Me of p-MeC6H4 ligand),
1.91 (s, 3H, Me of p-MeC6H4 ligand), 1.51−2.49 (m, 8H, CH2 of
triphos), 6.05−8.01 (br, 41H, hydrogens of aromatic region); δ(31P)
a
3
24.4 (d, 3JP P = 45 Hz, JPt P = 2148 Hz, 1P, P ), 42.0 (d, JP P = 45 Hz,
a
b
a
a
a b
JPt P = 1702 Hz, 1P, Pb), 40.7 (s, JPt P = 1709 Hz, 1P, Pc).
1
1
b
b
b c
X-ray Structure Determination. X-ray diffraction data for
complex 3f were collected at 100(1) K by the ω-scan technique on
an Agilent Technologies four-circle Xcalibur (Eos detector)
diffractometer with graphite-monochromatized Mo Kα radiation (λ
= 0.71073 Å). The data were corrected for Lorentz−polarization and
absorption effects.9 Accurate unit-cell parameters were determined by
a least-squares fit of 29756 reflections of highest intensity, chosen from
the whole experiment. The structure was solved with SIR9210 and
refined with the full-matrix least-squares procedure on F2 by
3
1
3
21.5 (d, JP P = 46 Hz, JPt P = 2027 Hz, 1P, Pa), 42.9 (d, JP P = 46
a
b
a
a
a b
Hz, JPt P = 1724 Hz, 1P, Pb), 41.9 (s, JPt P = 1725 Hz, 1P, Pc);
1
1
b
b
b c
δ(195Pt) −2405 (d, 1JPt P = 2030 Hz, 1Pt, Pt ), −2952 (t, JPt P = JPt P
a
1
1
a
a
b
b
b c
= 1724 Hz, 1Pt, Ptb).
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Organometallics
Article
SHELXL97.11 Scattering factors incorporated in SHELXL97 were
used. All non-hydrogen atoms were refined anisotropically, and all
hydrogen atoms were placed in the calculated positions and refined as
a “riding model” with the isotropic displacement parameters set at 1.2
(1.5 for methyl groups) times the Ueq value for the appropriate non-
hydrogen atom. Relevant crystal data are given in Table 1, together
Cambridge CB2 1EZ, UK (fax +44(1223)336-033, e-mail deposit@
ccdc.cam.ac.uk, or web www.ccdc.cam.ac.uk.
Computational Details. Density functional calculations were
performed with the program suite Gaussian0312 using the B3LYP level
of theory.13 The LANL2DZ basis set14 was chosen to describe Pt. The
6-31G(d) basis set was used for other atoms. The geometries of
complexes were fully optimized by employing the density functional
theory without imposing any symmetry constraints. To evaluate and
ensure the optimized structures of the molecules, frequency
calculations were carried out using analytical second derivatives. The
NBO analyses were carried out on the stationary points using the
NBO 3.1 program15 as implemented in the Gaussian 03 suite of
programs.
Table 1. Crystal Data and Structure Refinement for Complex
3f
formula
formula wt
cryst syst
space group
a (Å)
C56H54NP3Pt2
1224.09
monoclinic
P21/c
15.0322(4)
10.3813(3)
32.3098(10)
90
RESULTS AND DISCUSSION
■
b (Å)
Synthesis and Characterization of the Complexes. As
shown in Scheme 1, the reaction of the diorganoplatinum(II)
complexes [Pt2Me4(μ-SMe2)2] and [Pt(p-MeC6H4)2(SMe2)2]
with triphos gave the platinum(II) complexes [PtR2(triphos-
P,P′)] (1a, R = Me; 1b, R = p-MeC6H4).
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
103.450(5)
90
4903.7(2)
4
Although the dimethylplatinum complex 1a has previously
been reported8 through the slow addition of triphos to a
solution of [PtMe2(COD)] (COD = 1,5-cyclooctadiene) in
CH2Cl2, it was easily prepared by the reaction of [Pt2Me4(μ-
SMe2)2] with 2 equiv of triphos at room temperature in
acetone. The new complex 1b was similarly prepared by the
reaction of [Pt(p-MeC6H4)2(SMe2)2] with 1 equiv of triphos at
room temperature in acetone and isolated as a pure and stable
product. As previously reported, the reaction of complexes
[Pt2Me4(μ-SMe2)2] and [Pt(p-MeC6H4)2(SMe2)2] with 2-
phenylpyridine or benzo[h]quinoline gave the cyclometalated
platinum(II) complexes [PtR′(C∧N)(SMe2)] (2a, R′ = Me,
C∧N = ppy; 2b, R′ = p-MeC6H4, C∧N = ppy; 2c, R′ = Me, C∧N
= bhq; 2d, R′= p-MeC6H4, C∧N = bhq).4b,c
The general synthetic route to diplatinum complexes 3 is
described in Scheme 1. The reaction of diorganoplatinum(II)
complexes [PtR2(triphos-P,P′)] (1) with cyclometalated
platinum(II) complexes [PtR′(C∧N)(SMe2)] (2) gave
diplatinum(II) complexes 3a−h. For example, the reaction of
[PtMe(ppy)(SMe2)] (2a), containing a labile SMe2 ligand, with
Z
Dcalcd (g/cm3)
1.66
μ (mm−1
)
5.84
F(000)
2392
no. of rflns
9644
R1 (I >2σ(I))
R1 (all data)
wR2 (I >2σ(I))
wR2 (all data)
S
0.039
0.050
0.082
0.086
1.08
max/min Δρ (e Å−3
)
1.97/−1.35
with refinement details. In the crystal structure of 3f there are relatively
large voids (of ca. 240 Å3); however, no significant and interpretable
electron density has been found in these voids.
Crystallographic data (excluding structure factors) for the structural
analysis have been deposited with the Cambridge Crystallographic
Data Centre as No. CCDC-933960. Copies of this information may be
obtained free of charge from The Director, CCDC, 12 Union Road,
Scheme 1. Synthetic Route for the Preparation of Complexes 3
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1
Figure 2. H (A, in Me region), 31P (B), and 195Pt (C) NMR spectra of the complex [Pt2Me3(ppy)(triphos)] (3a).
2
a
[Pt(p-MeC6H4)2(triphos-P,P′)] (1b), having a dangling P atom
of the triphos ligand, at room temperature yielded the
diplatinum(II) complex [Pt2Me(p-MeC6H4)2(ppy)(triphos)]
(3d). The complexes were fully characterized using multi-
nuclear (1H, 31P, and 195Pt) NMR spectroscopy, and the
structure of complex [Pt2Me2(p-MeC6H4)(bhq)(triphos)] (3f)
was further identified by X-ray crystallography.
considerably higher JPt H = 85.0 Hz, due to the lower trans
influence of the N atom in comparison with that of the P
atom.4a,16 In the 31P NMR spectrum of the Pt(II)−Pt(II)
complex 3a, three different P signals were observed (see Figure
2B). The Pa atom, located trans to the coordinating C atom of
the phenyl ring of the ppy ligand, appeared as a doublet signal
at δ 23.9 (with 3JP P = 45 Hz) which is coupled to the Pt atom
a
a
b
In the 1H NMR spectrum of complex 3a (see Figure 2A), the
Me groups trans to P were observed at δ 0.42 and 0.44 as
to give satellites with JPt P = 2076 Hz. Two other P atoms, Pb
and Pc, each of which is trans to the Me group, were observed at
δ 47.3 and 47.9, respectively. The Pb atom was coupled with Pa
1
a
a
3
2
triplets (3JHP ≈ JHP = 7.3 Hz), with JPt H values being close to
b
c
b
and Pc atoms with JP P = 45 and JP P = 5 Hz,17 respectively,
3
3
a
b
b c
70 Hz, while the Me group located trans to N ligating atom
appeared as a doublet (3JHP = 7.5 Hz) at δ 0.71, with a
which is further coupled to the Ptb atom, giving a satellite with
a
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Figure 3. Perspective view of the complex [Pt2Me2(p-MeC6H4)(bhq)(triphos)] (3f) together with the numbering scheme. Ellipsoids are drawn at
the 50% probability level, and hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Pt1−N2 = 2.148(5), Pt1−C13
= 2.043(6), Pt1−P16 = 2.3010(15), Pt1−C29 = 2.005(6), Pt2−P37 = 2.2681(15), Pt2−P46 = 2.2799(18), Pt2−C59 = 2.138(5), Pt2−C60 =
2.095(6); N2−Pt1−C29 = 170.4(2), C13−Pt1−P16 = 178.1(2), P37−Pt2−C59 = 178.86(15), P46−Pt2−C60 = 177.57(17).
Table 2. Selected Calculated Bond Distances (Å) and Angles (deg) for Complexes 3a−h Compared to the Experimental Data of
Complex 3f
bond distance or angle
3a
3b
3c
3d
3e
3f
3f (exptl)
3g
3h
Pt01−C100
Pt01−C400
Pt01−N006
Pt01−P03
Pt02−C300
Pt02−C200
Pt02−P04
Pt02−P05
P03−C050
P04−C015
P04−C009
P04−C022
P05−C1
C015−C050
C1−C022
C100−Pt01−C400
C100−Pt01−N006
C400−Pt01−N006
C100−Pt01−P03
C400−Pt01−P03
N006−Pt01−P03
C300−Pt02−C200
C300−Pt02−P04
C200−Pt02−P04
C300−Pt02−P05
C200−Pt02−P05
P04−Pt02−P05
C011−P03−C050
C050−P03−Pt01
C050−C015−P04
C015−C050−P03
2.069
2.046
2.215
2.405
2.103
2.105
2.368
2.368
1.872
1.865
1.842
1.877
1.878
1.535
1.537
91.2
2.028
2.045
2.208
2.421
2.103
2.105
2.373
2.369
1.872
1.865
1.842
1.877
1.878
1.534
1.536
91.8
2.027
2.046
2.211
2.423
2.069
2.067
2.393
2.400
1.875
1.863
1.841
1.871
1.873
1.533
1.535
91.6
2.069
2.046
2.215
2.408
2.069
2.068
2.383
2.405
1.873
1.860
1.841
1.871
1.878
1.535
1.535
91.1
2.067
2.049
2.230
2.399
2.103
2.105
2.367
2.370
1.872
1.865
1.842
1.877
1.878
1.535
1.537
90.6
2.025
2.047
2.223
2.416
2.103
2.105
2.373
2.369
1.871
1.865
1.842
1.877
1.877
1.534
1.536
91.2
2.003(6)
2.043(6)
2.147(5)
2.3010(14)
2.095(6)
2.139(5)
2.2684(15)
2.2799(16)
1.849(5)
1.833(5)
1.840(5)
1.844(6)
1.828(5)
1.526(7)
1.518(7)
90.3(2)
2.024
2.049
2.228
2.418
2.070
2.067
2.393
2.400
1.876
1.863
1.841
1.871
1.873
1.534
1.535
90.9
2.067
2.049
2.229
2.403
2.070
2.068
2.382
2.406
1.873
1.860
1.841
1.871
1.878
1.535
1.535
90.5
168.9
78.9
170.7
79.0
170.3
78.9
169.0
78.9
169.2
79.4
170.7
79.5
170.4(2)
80.8(2)
170.1
79.4
169.3
79.5
92.3
91.3
91.4
92.5
93.0
92.0
91.48(16)
178.1(2)
97.35(14)
85.6(2)
92.3
93.2
175.4
97.9
176.4
98.0
176.5
98.1
175.3
97.7
175.9
97.1
176.3
97.2
176.4
97.4
175.5
97.0
85.9
85.9
86.3
86.4
85.9
85.9
86.3
86.4
95.4
95.3
95.2
94.1
95.4
95.3
94.23(16)
178.82(14)
177.55(16)
94.64(14)
85.61(5)
102.8(3)
121.06(18)
113.0(4)
114.5(4)
95.1
94.1
178.5
179.4
93.7
178.8
179.3
93.8
178.4
177.3
94.1
179.3
176.8
95.0
178.6
179.2
93.7
178.8
179.2
93.8
178.5
177.4
94.1
179.2
176.6
95.0
85.0
85.0
84.5
84.5
84.9
85.0
84.5
84.5
102.0
119.9
111.3
114.3
103.6
120.1
111.0
116.0
104.7
120.6
110.9
117.0
102.8
119.7
111.4
114.3
102.2
119.7
111.3
114.5
103.6
119.8
111.0
116.0
104.7
120.5
110.8
117.0
102.9
119.5
111.4
114.3
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Figure 6. Qualitative frontier molecular orbitals for complex 3a.
Table 4. Energies (eV) of the Relevant Frontier Orbitals of
Complexes 3
complex
orbital
E (eV)
complex
orbital
E (eV)
3a
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
−5.279
−1.299
−5.237
−1.412
−5.106
−1.409
−5.136
−1.295
3e
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
−5.265
−1.467
−5.241
−1.567
−5.107
−1.565
−5.138
−1.463
3b
3c
3d
3f
3g
3h
Figure 4. DFT optimized structures of the diplatinum(II) complexes
3.
Figure 5. Atom numbering of complexes 3.
1
JPt P = 1798 Hz. The Pc atom is also coupled to Ptb with a
b
b
Figure 7. Absorption spectra (1 × 10−4 M) of complexes 1a−3a. The
spectrum for 3a was obtained immediately after addition of complex
1a to 2a under 1:1 stoichiometric conditions.
1
b
c
value of JPt P = 1806 Hz.
The above assignment for phosphorus atoms, shown in
Figure 1 and Scheme 1, is based on the following observations.
First, from the chemical shift values, it can be realized that the
Pc and Pb atoms (47.9 and 47.3 ppm, respectively) are in a five-
membered ring while the Pa atom (23.9 ppm) is in agreement
with a monodentate coordination mode.18 Second, the JPtP
1
1
values for Pa, Pb, and Pc show that the Pa atom (with JPtP
=
Table 3. NPA Charges on Pt Atoms of Complexes 3
Pt atom
3a
3b
3c
3d
3e
3f
3g
3h
Pt01
Pt02
0.082
0.114
0.112
0.080
0.080
0.113
0.112
0.079
−0.198
−0.196
−0.099
−0.101
−0.198
−0.196
−0.099
−0.101
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Scheme 2. Suggested Mechanism for Formation of 3a
2.149(6) and 2.046(7) Å.4b,c Both Pt ions are four-coordinated
and have square-planar environments, which can be shown by
an analysis of the bond angles as well as by the calculations of
the least-squares planes through the four coordinating atoms
(maximum deviations are 0.032(3) Å for Pt1 and 0.035(2) Å
for Pt2). To the best of our knowledge, this is the first X-ray
structural determination of a diplatinum complex having a
triphos ligand simultaneously acting as a chelating and bridging
ligand, although crystal structures of some transition-metal
complexes including triphos as either a bridging or chelating
ligand have been reported.5c,f,22
DFT Investigations of Complexes 3. To perform a
reliable molecular modeling of the newly synthesized
diplatinum complexes containing a triphos ligand and to
analyze correctly their structures, an appropriate DFT method
is needed. During the past decade DFT methods have proven
to be suitable and useful alternatives for calculations of
structures of transition-metal complexes. Thus, it is important
to test the reliability of the computational method employed for
complexes presented in this work. The dinuclear Pt(II)
complex 3f has been structurally characterized by X-ray
diffraction analysis and is used as a standard example to
estimate the reliability of the DFT/B3LYP level of calculations
as to the geometrical parameters. The structures of 3a−h are
schematically presented in Figure 4. Selected calculated bond
lengths of optimized geometries of 3a−h at the B3LYP/6-
31G(d) level (LANL2DZ potential for Pt) and the
corresponding experimental crystallographic data for complex
3f are given in Table 2 (see Figure 5 for atom labeling). The
computed structural details are in good agreement with the
experimental parameters. The mean error for the bond lengths
is 0.036 Å for complex 3f. One reason for the bond length
discrepancy in our calculations is due to a comparison of the
geometrical parameters calculated in the gas phase with those
obtained experimentally in the solid state. Considering the large
molecules under consideration, the B3LYP/6-31G(d) method
appears to be a reasonable compromise between accuracy and
CPU time of calculations and therefore we used it together with
LANL2DZ for Pt for structural characterization of the new
diplatinum complexes 3a−h. The optimized structures are
shown in Figure 4, and calculated results are presented in Table
2.
Figure 8. Calculated structures and energies (kcal mol−1) of
intermediate and compounds in the reaction of 1a with 2a in acetone
solution. Energies are with respect to 1a and 2a; a molecule of free
SMe2 is included in the IM and 3a.
2076 Hz) is trans to the C atom of the ppy ligand (the value
being very close to that obtained for [PtMe(ppy)(PPh31)]19
1
with JPtP = 2105 Hz), while the Pb and Pc atoms (with JPtP
values of 1798 and 1806 Hz, respectively) are trans to Me
ligands, as indicated by 1JPtP values comparable with the value of
1794 Hz in [PtMe2(dppe)]16a (dppe = 1,2-bis-
1
(diphenylphosphino)ethane). Note that the JPtP values
observed for the Pc and Pb atoms are considerably smaller
than the value for the Pa atom, indicating that the Me ligand
exerts a higher trans influence than the C atom of ppy.4a,19,20
This assignment is in agreement with those reported for related
complexes.18,21,22
Consistent with the 31P NMR, in the 195Pt NMR spectrum of
1
1
b
b
b c
3a, a triplet at −3005 with JPt P = JPt P = 1802 Hz and a
doublet at δ −2559 with 1JPt P = 2078 Hz were observed for the
a
a
Ptb and Pta atoms, respectively (see Figure 2C).
The crystal structure of the complex [Pt2Me2(p-MeC6H4)-
(bhq)(triphos)] (3f) was also determined. The molecular
structure of complex 3f is shown in Figure 3. Selected bond
distances and angles for complex 3f are given in Table 2. The
structure of 3f shows that triphos simultaneously acts as a
chelating and bridging ligand. Triphos coordinates to Pt in a
bidentate mode, the chelate ring being similar to that generated
by dppe (dppe = 1,2-bis(diphenylphosphino)ethane). Another
arm of the triphos ligand forms a bridge with the second Pt
atom, giving diplatinum(II) complex 3f. The complex shows
two different Pt−Me distances (2.095(6) and 2.138(5) Å),
As can be seen from Table 2, for complexes containing a bhq
ligand (i.e., 3e−h), the Pt01−P03 (i.e., Pta−Pa; see Figure 1)
bond lengths are shorter than those of the corresponding
platinum(II) products having a ppy ligand (i.e., 3a−d). For
1
which is consistent with the two signals found in the H NMR
example, the Pt01−P03 bond in 3e (2.399 Å) is shorter than
spectrum. The Pt1−P16 bond distance (2.3010(15) Å) is
greater than the Pt2−P37 (2.2681(15) Å) and Pt2−P46
(2.2799(17) Å) bond lengths. This is due to the phosphorus
atoms P37 and P46 being parts of a five-membered chelate ring.
The Pt1−N2 and Pt1−C13 bond lengths are 2.148(5) and
2.043(6) Å, respectively, similar to the literature values of
1
a
a
that in 3a (2.405 Å), complying with the larger JPt P value for
complex 3e as compared with that of complex 3a. These results
suggest that the trans influence of the metalated C atom of the
ppy derivative is greater than that of the bhq analogue.20 Also,
the Pt−P bond lengths for complexes with R′ = p-MeC6H4 (i.e.,
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3b,c,f,g) are longer than those with R′ = Me (i.e., 3a,d,e,h),
donor abilities such as bipyridine and 1,2-(diphenylphosphino)-
ethane, occur through a dissociative path.23 The ligand
dissociation step is facilitated by the strong trans influence of
the alkyl or aryl group, which weakens the metal−ligand bonds,
while the alternative associative mechanism is less favored
because the electron-rich platinum center is resistant to
nucleophilic attack.23
which is in agreement with the trends found for 1JPt P values in
their 31P NMR spectra. This may be attributed to the greater s
character of Pt−C(sp2) and steric hindrance for an aryl ligand
in comparison to Pt−C(sp3) and steric hindrance for Me.
Table 3 shows the atomic charges of the platinum centers for
the complexes 3, obtained from a natural bond orbital (NBO)
analysis.15 The calculated charge on the Pt02 atom is negative
in comparison with the positive charge on the Pt01 atom,
which is the result of the coordination of the nitrogen atom of
C∧N ligands to the Pt01 center. However, the Pt charge values
for both centers in complexes 3 are lower than the formal
charge of +2, as the ligands act as electron donors and therefore
increase the electron density at the metal center. The charge on
the Pt02 atom of complex 3d (−0.101), containing two p-tolyl
ligands, is less negative in comparison with the Pt02 atom of
complex 3a (−0.198), having two methyl ligands, which is
related to the weaker electron donor ability of the p-MeC6H4
ligand compared to the Me ligand.
a
a
CONCLUSION
■
Several diplatinum(II) complexes were prepared, in which one
Pt center contains a bidentate cyclometalated ppy or bhq ligand
and the second Pt center has two methyl or aryl groups. For the
first time, it has been possible to assemble pairs of these units in
any combination by using triphos as the assembling agent. This
triphosphine ligand acts at the same time as a chelating agent
and bridging ligand, forming the complexes [Pt2R2R′(C∧N)-
(triphos)] (3). The first X-ray structural determination of these
diplatinum complexes confirms the square-planar environment
around both platinum centers.
Qualitative representations of the highest occupied and
lowest unoccupied molecular orbitals in complex 3a are
presented in Figure 6. The energies of the relevant frontier
orbitals of complexes 3 are also shown in Table 4. The
HOMO−LUMO gap of 3a is equal to 3.980 eV. The highest
AUTHOR INFORMATION
Corresponding Author
*E-mail: esmaeilbeig@chem.susc.ac.ir (A.R.E.); nabavi@chem.
susc.ac.ir (S.M.N.).
Notes
■
2
occupied MO of 3a is mainly the Pt02 dz orbital (Pt atom
having two alkyl or aryl groups,; see Figure 4). The LUMO is
predominately localized on the d orbitals of the Pt01 atom with
significant contribution of the pπ orbitals of the C∧N ligand.
This means that complex 3a can act as a nucleophile or
electrophile through the Pt02 or Pt01 atoms, respectively. The
values of the energy separations between the HOMO and
LUMO of 3b−h are smaller than that of 3a and are equal to
3.825, 3.697, 3.841, 3.798, 3.674, 3.542, and 3.675 eV,
respectively. The highest occupied molecular orbital of 3b−h
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work has been supported by Shiraz University and the Iran
National Science Foundation (Grant No. 90005160). We are
grateful to Prof. Mehdi Rashidi and Dr. Reza Kia for valuable
assistance and M. Golbon Haghighi for helpful suggestions.
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■
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