Thiacrown PtII complexes with group 15 donor ligands: Pentacoordination in Pt(ii) complexes

Article abstract of DOI:10.1039/b909875e

We report the synthesis and full characterization for a series of thiacrown complexes of Pt(ii) incorporating the fluxional trithiacrown ligand 1,4,7-trithiacyclononane ([9]aneS₃) and several group 15 donors ligands. Reaction of [Pt([9]aneS

Full text of DOI:10.1039/b909875e

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Thiacrown PtII complexes with group 15 donor ligands: pentacoordination in
Pt(II) complexes†
Gregory J. Grant,*a Desire´e A. Benefielda and Donald G. VanDerveerb
Received 20th May 2009, Accepted 13th July 2009
First published as an Advance Article on the web 19th August 2009
DOI: 10.1039/b909875e
We report the synthesis and full characterization for a series of thiacrown complexes of Pt(II)
incorporating the fluxional trithiacrown ligand 1,4,7-trithiacyclononane ([9]aneS3) and several group 15
donors ligands. Reaction of [Pt([9]aneS3)Cl2] with a full stoichiometric equivalent of the group 15
donor (L = 2 ¥ AsPh3, SbPh3 or 1,2-bis(diphenylarsenio) ethane (dpae) followed by metathesis with
NH4PF6 yields [Pt([9]aneS3)L](PF6)2. We also report the analogous Pd(II) complex with dpae. Similar
reactions of the starting Pt complex with one equivalent of XPh3 (X = As or Sb) result in complexes of
the formula [Pt([9]aneS3)(XPh3)(Cl)](PF6). All six new complexes have been fully characterized by
multinuclear NMR, IR, and UV-Vis spectroscopies in addition to elemental analysis and single crystal
structural determinations. The X-ray structures of each complex indicate an axial
M–S interaction formed by the endodentate conformation of the [9]aneS3 ligand. The axial M–S
distance is highly dependent upon the ancillary donor set. The axial M–S distance shortens with the
identity of the group 15 donor ligand according to the trend, Sb < As < P, due to their increasingly
poorer donor qualities. The two bis pnictogen complexes, [Pt([9]aneS3)(AsPh3)2](PF6)2 and
[Pt([9]aneS3)(SbPh3)2](PF6)2 form unusual five-coordinate distorted trigonal bipyramids in contrast to
the pseudo-five coordinate, elongated square pyramidal structures typically observed in Pt(II)
complexes of [9]aneS3. The distortion arises from intramolecular p–p interactions between the phenyl
rings on the two different triphenyl ligands. Chemical shifts in the 195Pt NMR also show similar periodic
relationships which trend progressively upfield as the donor atom becomes larger. As expected, the
coordinated [9]aneS3 ligand shows fluxional behavior in its NMR spectra, resulting in a single 13
C
NMR resonance, despite the asymmetric coordination environment found in both chloro complexes.
The line width for the carbon NMR resonance as well as for the 195Pt NMR peak is highly sensitive to
the nature of the group 15 donor, with poorer donors such as SbPh3 showing significant line
broadening. Measurements from the electronic spectra support that the ligand field strength of the
pnictogen donor decreases with its increasing size.
E–C bond (E = group 15 donor) and is further seen with a decrease
Introduction
in the C–E–C bond angles. In addition to these electronic effects,
steric effects in group 15 ligands can be important and are typically
described in terms of the Tolman cone angle, and the Tolman
cone angles for SbPh3, AsPh3 and PPh3 are 138◦, 142◦ and 145◦,
respectively.6,7
The coordination chemistry of arsine and stibine ligands provides
interesting contrasts with the more commonly studied phosphine
ligands. Transition metal complexes of As and Sb ligands has
been the subject of several reviews1–5 including two recent reviews
by Levason and Reid.1,2 Complexation behavior of the group 15
donor becomes increasingly less well understood as the pnictogen
family is descended due to a more limited set of coordination
complexes. With the increasing size of the pnictogen, the ligand
shows progressively poorer complexation behavior.1,2 Accordingly,
the heavier congeners are both poorer s donors and weaker
p acceptors due to the increasing energy gap between their s
and p atomic orbitals. The increasing p component weakens the
Over the past twenty years, our group and others have
prepared an extensive series of Pt(II) and Pd(II) complexes in-
volving the thiacrown ligand, 1,4,7,-trithiacyclononane ([9]aneS3)
with a wide range of ancillary ligands including diimines,8–11
halides,12–16 cyclometallating ligands,17,18 and of particular rele-
vance for this report, phosphines such as PPh3 and a variety
of chelating diphosphines.19–24 Our goal is to prepare Pt(II)
[9]aneS3 complexes with the heavier group 15 analogues, AsPh3
and SbPh3, and contrast their coordination behavior along with
their spectroscopic and structural properties, to the previously
studied phosphine complexes. In addition, the Pt(II) and Pd(II)
[9]aneS3 complexes with the related bidentate chelator, dpae,
1,2-bis(diphenylarsenio)ethane, the arsenic analog of the popular
diphosphine ligand, dppe, are described. This report complements
a recent paper from our group describing two Pd(II) triphenylar-
sine complexes with the trithiacrown.25
aDepartment of Chemistry, The University of Tennessee at Chattanooga,
Chattanooga, TN, 37403, USA. E-mail: Greg-Grant@utc.edu; Fax: 423-
425-5234; Tel: 423-425-4143
bDepartment of Chemistry, Clemson University, Clemson, SC, 29634, USA
† Electronic supplementary information (ESI) available: NMR spectra
and structural diagrams. CCDC reference numbers 730838–730842 and
733186. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/b909875e
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One interesting feature invariably seen in Pt(II) and Pd(II)
thiacrown complexes is the presence of long distance axial
sulfur–metal interactions. These interactions arise from an orbital
“mismatch” (a term coined by Martin Schro¨der) between the d8
transition metal and the facially coordinating trithiacrown.12 Two
of the three sulfur donors form typical equatorial bonds with
two-electron oxidations10,18,28 and also for associative mechanisms
in ligand substitution reactions in d8 systems.8 In a series of
[9]aneS3 metal complexes with group 15 donor ligands, we will
focus on how the Pt–S axial distance changes with the electron
donating abilities of pnictogen donors and explore periodic
relationships. The six new group 15 donor thiacrown complexes
described in this report are: [Pt([9]aneS3)(AsPh3)2](PF6)2 (1),
[Pt([9]aneS3)(AsPh3)(Cl)](PF6) (2), [Pt([9]aneS3)(SbPh3)2](PF6)2
(3), [Pt([9]aneS3)(SbPh3)(Cl)](PF6) (4), [Pt([9]aneS3)(dpae)](PF6)2
(5), and [Pd([9]aneS3)(dpae)](PF6)2 (6).
˚
Pt–S bond distances in the range of 2.2–2.4 A.‡ However, the third
sulfur donor interacts with Pt(II) at a greater distance which can
˚
vary widely, anywhere between 2.6 to 3.4 A. This distance is highly
dependent upon the donor/acceptor properties of the ancillary
ligand, and thereby serves as a sensitive structural probe to the elec-
tronic nature of the ligand as shown in Scheme 1. Also, the presence
of these axial interactions significantly alters the spectroscopic and
electrochemical properties of the complex with the stabilization of
trivalent oxidation states for Pt and Pd and the presence of unusual
d–d electronic transitions in the visible region.12,26,27 Furthermore,
these types of complexes have been used as models in outer-sphere
Results and discussion
Syntheses
The synthetic procedures used to prepare the complexes in this
study are illustrated in Scheme 2. Ligand substitution by one
stoichiometric equivalent of a monodentate group 15 donor (L =
AsPh3 or SbPh3) results in the displacement of a single chloro
ligand from the parent complex [Pt([9]aneS3)Cl2] at reflux in
nitromethane and readily forms the desired [Pt([9]aneS3)(L)(Cl)]+
complexes in good yields. Similar reactions of the parent complex
with either two equivalents of L (or one equivalent of the bidentate
dpae ligand) yield complexes with the formula [Pt([9]aneS3)(L2)]2+.
All prepared complexes are subsequently metathesized to the
hexafluorophosphate salt which produces better crystalline prod-
ucts. The identities for all six complexes have been confirmed by
elemental analyses, a variety of spectroscopic methods, and single-
crystal X-ray structures. We would highlight that we are not able to
form any isolable Pd(II) complexes with SbPh3, probably due to the
difference in kinetic stability between the Pt and Pd centers. Our
group has previously reported the two Pd(II) ([9]aneS3) complexes
[Pd([9]aneS3)(AsPh3)2](PF6)2 and [Pd([9]aneS3)(AsPh3)(Cl)](PF6)
Scheme 1 Changes of axial Pt–S distances for the [9]aneS3 by ancillary
ligands.
‡ To our knowledge, there have been 47 Pt(II) [9]aneS3 complexes struc-
turally characterized including the five new ones reported here. The Pt–Sax
˚
˚
distances in these structures range from 2.58 A to 3.26 A. Similarly, there
have been 24 Pd(II) [9]aneS3 complexes structurally examined with Pd–Sax
distances ranging from 2.67 A to 3.14 A.
˚
˚
Scheme 2 Synthesis of Pt [9]aneS3 complexes with monodentate group 15 donor ligands.
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Table 1 Crystal data, data collection, and refinement parameters for [Pt([9]aneS3)(AsPh3)2](PF6)2·2CH3NO2 (1), [Pt([9]aneS3)(AsPh3)(Cl)](PF6)·
1.5CH3NO3 (2), [Pt([9]aneS3)(SbPh3)2](PF6)2·2CH3NO2 (3), [Pt([9]aneS3)(SbPh3)(Cl)](PF6) (4), [Pt([9]aneS3)(dpae)](PF6)2·CH3CN (5), and
[Pd([9]aneS3)(dpae)](PF6)2·(CH3)2CO (6)
Compound
Formula
1
2
3
4
5
6
C44H48As2F12N2- C25.5H31.5AsClF6- C44H48F12N2O4P2- C24H27ClF6PPtS3Sb C34H39As2F12NP2PtS3 C35H42As2F12OP2PdS3
O4P2PtS3
Rod, orange
Monoclinic
P21/c
10.6043(13)
39.260(5)
12.614(2)
90
106.48(4)
90
5035.5(14)
4
N1.5O3PPtS3
Chip, orange
Monoclinic
P21/c
8.0987(16)
18.742(4)
20.965(4)
90
94.46(3)
90
3172.5(11)
4
PtS3Sb2
Chip, red
Triclinic
Habit, color
Lattice type
Space group
Plate, red
Orthorhombic
P212121
8.4062(17)
10.862(2)
30.584(6)
90
Chip, red
Monoclinic
P21/n
14.524(3)
16.183(3)
18.869(4)
90
108.97(3)
90
4194.0(14)
4
163(2)
1192.71
1.889
5.218
27 203
Chip, red
Triclinic
P1
¯
¯
P1
˚
a/A
12.893(3)
13.110(3)
15.374(3)
93.67(3)
93.94(3)
91.84(3)
2585.6(9)
2
163(2)
1493.55
1.918
4.005
23 669
11.087(2)
14.193(3)
16.251(3)
108.76(3)
99.61(3)
110.85(3)
2145.3(7)
2
161(2)
854.26
1.735
2.265
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
V/A
Z
90
90
3
˚
2792.7(10)
4
158(2)
908.90
2.162
6.403
15 770
Temperature/K
Fwt/g mol-1
Dc/Mg m-3
m/mm-1
153(2)
1399.89
1.847
4.367
26 762
153(2)
953.63
1.997
5.857
Reflections
23 387
16 481
collected
Unique reflections
8712
5650
10 830 (Rint
=
4908
7405
7603
(Rint = 0.0355)
(Rint = 0.0427)
0.0350)
(Rint = 0.0682)
(Rint = 0.1010)
(Rint = 0.0215)
Max., min.
0.5800, 0.2386
0.3590, 0.1220
0.4670, 0.3951
0.7402, 0.3332
0.7448, 0.2125
0.7728, 0.4426
transmission
Data, restraints,
parameters
8712/0/633
5650/0/398
10 830/0/634
4908/0/334
7405/0/497
7603/0/507
R1, wR2 (I > 2s(I)) 0.0504, 0.1011
0.0304, 0.0688
0.0333, 0.0709
1.130
0.0341, 0.0729
0.0406, 0.0773
1.083
0.0399, 0.0769
0.0453, 0.0804
1.077
0.0816, 0.1696
0.0950, 0.1794
1.097
0.0430, 0.1031
0.0507, 0.1117
1.077
R1, wR2 (all data)
Goodness-of-fit
(F2)
0.0710, 0.1111
1.116
Largest diff. peak,
2.550, -1.707
1.587, -1.479
2.626, -1.356
1.670, -1.584
2.135, -2.024
1.408, -0.789
-3
˚
hole/e A
but had noted difficulties in preparing the former in its pure form.25
However, the Pd(II) [9]aneS3 complex with dpae, as well as its Pt
analogue, was readily prepared, a consequence of the bidentate
nature of the ligand. We also attempted to prepare both the bis
and mono chloro complexes with the heaviest group 15 analogue,
BiPh3, but no isolable products involving the ligand were obtained.
The reactivity we observe with the bismuthine ligand is consistent
with prior reports describing its complexation behavior.1,5,29
X-Ray structures†
A summary of data collection and refinement for all six of the
structures in this report is presented in Table 1. A summary of
key bond distances, M–Sax distances, and bond angles for the
coordination sphere is found in Tables 2 and 3. Fig. 1–6 show the
thermal ellipsoid perspectives for the cations in complexes 1–6,
respectively. With the notable exceptions of the two bis complexes,
[Pt([9]aneS3)(AsPh3)2](PF6)2 and [Pt([9]aneS3)(SbPh3)2](PF6)2 (see
further discussion below), the other four complexes form struc-
tures best described as elongated square pyramids. This is due
to the preferred endodentate conformation of the uncomplexed
[9]aneS3 ligand. As has been observed in virtually all Pt(II) and
Pd(II) complexes of [9]aneS3, the trithiacrown exhibits an axial
Fig.
1 Thermal ellipsoid perspective of cation in [Pt([9]aneS3)-
(AsPh3)2](PF6)2·2CH3NO2 (1). (50% probability, H atoms omitted for
clarity).
as the interplay between the equatorial sulfur bonds and the
corresponding axial interactions. For the six structures presented
in the report, all metal–sulfur distances fall within the range of
those previously observed for [9]aneS3 complexes with Pt(II) and
Pd(II).
M–S interaction that is longer than a formal bond, but less than
30
˚
˚
van der Waals contact (3.5 A for Pt(II), 3.6 A for Pd(II)). We
particularly focused on how the metal–sulfur axial interactions
change as a function of the group 15 donor ligand, as well
The common structural motif for [9]aneS3 in its heteroleptic
Pt(II) and Pd(II) complexes is an elongated square pyramidal
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◦
a
Table 2 Selected structural features for the reported complexes; included are selected bond lengths (A), bond angles ( )a,
t
˚
parameter,bdistances between centroids for phenyl planes, and angles between phenyl planes for [Pt([9]aneS3)(AsPh3)2](PF6)2·2CH3NO2 (1),
[Pt([9]aneS3)(AsPh3)(Cl)](PF6)·1.5CH3NO3 (2), [Pt([9]aneS3)(SbPh3)2](PF6)2·2CH3NO3 (3), [Pt([9]aneS3)(SbPh3)(Cl)](PF6) (4), [Pt([9]aneS3)(dpae)](PF6)2·
CH3CN (5), and [Pd([9]aneS3)(dpae)](PF6)2·(CH3)2CO (6)
Parameter
M–Seq
1
2
3
4
5
6
2.321(2)
2.458(2)
2.584(2)
2.3907(9)
2.3926(9)
N/A
87.82(7)
93.37(3)
N/A
2.246(1)
2.315(1)
3.043(6)
2.3829(6)
2.320(1)
2.450(1)
2.514(1)
2.5486(9)
2.5447(8)
N/A
88.43(4)
90.65(2)
N/A
2.255(2)
2.363(2)
2.787(2)
2.5304(7)
2.324(3)
2.333(4)
2.675(4)
2.3702(14)
2.3849(14)
N/A
88.79(13)
85.16(8)
N/A
2.3574(12)
2.3607(14)
2.6737(16)
2.3686(11)
2.3847(8)
N/A
89.39(5)
83.05(4)
N/A
b
M–Sax
M–E
Pt–Cl
2.330(1)
89.86(4)
N/A
87.34(3)
104.9
0.14
N/A
2.343(2)
88.79(9)
N/A
87.06(6)
101.2
0.30
N/A
Seq–M–Seq
E–M–E
E–Pt–Cl
C–E–C
104.0
0.58
3.84
102.9
0.57
3.91
105.1
0.16
N/A
107.6
0.04
N/A
c
t
Centroid distance
Angles between Ph planes
7.6
N/A
0.60
N/A
N/A
N/A
a Estimated standard deviations are given in parentheses, E = As or Sb. M = Pt or Pd. b For comparative purposes among all [9]aneS3 Pt(II) and Pd(II)
structures, we have consistently defined the axial sulfur in the context of the square pyramidal geometry. In that case, the axial metal–sulfur distance is
the longest of the three. However, in the distorted trigonal bipyramidal structures of 1 and 3, the axial sulfur position will be different since it represents
the longest S–Pt–E bond angle. The Pt–S axial distances in that context are 2.321(2) A in 1 and 2.320(1) A in 3. c For a square pyramidal structure t = 0,
˚
˚
for a trigonal bipyramidal structure t = 1; see ref. 31 for additional information.
Table 3 Selected structural features for related literature Pt(II) and Pd(II) [9]aneS3 complexes; included are metal–sulfur equatorial and axial distances
˚
(A) t parameter, distances between centroids for phenyl planes, and angles between phenyl planes
[Pt([9]aneS3)-
(PPh3)2](PF6)2
[Pt([9]aneS3)-
(PPh3)Cl](PF6)
[Pt([9]aneS3)-
(dppe)(PF6)2
[Pd([9]aneS3)-
(AsPh3)2](PF6)2
[Pd([9]aneS3)-
(AsPh3)Cl](PF6)
[Pd([9]aneS3)-
(PPh3)2](PF6)2
Parameter
M–Seq
2.3258(2)
2.485(3)
2.638(3)
0.58
3.79
8.8
2.2609(9)
2.3365(8)
3.0778(8)
0.07
N/A
N/A
2.366(2)
2.369(2)
2.737(2)
0.01
N/A
N/A
2.351(2)
2.388(2)
2.751(2)
0.24
3.75
12.9
2.262(2)
2.333(2)
3.094(2)
0.08
N/A
N/A
2.376(3)
2.406(3)
2.877(3)
0.27
4.14
24.0
b
M–Sax
t
b
Centroid distance
Angles between Ph planes
Reference
20
22
23
25
25
19
Fig.
2
Thermal ellipsoid perspective of cation in [Pt([9]aneS3)-
Fig. 3 Thermal ellipsoid perspective of cation in [Pt([9]aneS3)(SbPh3)2]-
(PF6)2·2CH3NO2 (3). (50% probability, H atoms omitted for clarity).
(AsPh3)(Cl)](PF3)·1.5CH3NO2 (2). (50% probability, H atoms omitted for
clarity).
structure with a S2X2 + S1 coordination environment (X = an-
cillary ligand donor atom). The geometry has now been observed
in over 60 [9]aneS3 complexes with the two group 10 metals. In
contrast, both bis complexes reported here (compounds 1 and 3)
show structures that are highly distorted towards trigonal bipyra-
mid geometry. We had noted a similar distortion in our previously
8608 | Dalton Trans., 2009, 8605–8615
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0 for an ideal square pyramid and 1 for an ideal trigonal bipyramid.
The t values for the six compounds reported here as well as some
pertinent literature compounds are presented in Tables 2 and 3,
respectively. The distortion towards trigonal bipyramid geometry
can clearly be seen for all three bis EPh3 (E = group 15 donor)
Pt(II) [9]aneS3 complexes. The degree of distortion among the
three complexes is essentially identical despite the differences in
the nature of the group 15 donor atom (0.58).§ Our observation
implies that the distortion towards a trigonal bipyramidal shape
is not a function of the identity of the ligand donor, but rather lies
in another factor.
We propose that the effect originates with intramolecular p–p
interactions between phenyl groups on two different monodentate
triphenylpnictogen ligands. In support of this hypothesis, we note
that none of the mono chloro Pt(II) complexes involving EPh3
ligands show this large degree of trigonal bipyramidal distortion
nor do the analogous Pd(II) [9]aneS3 complexes which contain
two EPh3 ligands. Thus, the distortion requires the presence of
a Pt(II) center along with two group 15 donor ligands bearing
a phenyl group. If either of these conditions are not met, the
[9]aneS3 complex shows the anticipated and common elongated
square pyramidal motif. Also, there are no close contacts that
arise from solvent, anion or packing effects that are unique to the
Pt(II) complexes that could result in the structural distortion. Our
group has previously noted three distinct types of intermolecular
p–p stacking interactions between diimine ligands in Pt(II) and
Pd(II) [9]aneS3 complexes.11 Furthermore, the importance of
intermolecular and intramolecular interactions involving phenyl
Fig.
4
Thermal ellipsoid perspective of cation in [Pt([9]aneS3)-
(SbPh3)(Cl)](PF6) (4). (50% probability, H atoms omitted for clarity).
+
rings in [PPh3]4 structures, termed “phenyl embraces”, has been
highlighted in crystal engineering work by Dance and Scudder.32,33
They had also noted similar interactions between phenyl groups
in arsenic analogues.34 We identify the presence of intramolecular
p–p interactions between phenyl groups in the bis group 15
EPh3 Pt(II) complexes, including importantly the triphenylstibine
complex. The phenyl interactions that we observe are an offset
face-to-face interaction, rather than an edge-to-face interaction,
and are shown in Fig. 7 for the bis SbPh3 complex.32 The calculated
distances between the two centroids for the interacting phenyl rings
are presented in Table 2. It should be noted that complexes which
show the distortion towards a trigonal bipyramidal geometry all
possess two common structural features; phenyl ring centroid
Fig.
5
Thermal ellipsoid perspective of cation in [Pt([9]aneS3)-
(dpae)](PF6)·CH3CN (5). (50% probability, H atoms omitted for clarity).
˚
distances in the 3.79–3.91 A range and relatively small angles
(< 10◦) between the mean least squares planes between the two
phenyl rings.
Interestingly, the Pd(II) [9]aneS3 complexes with two PPh3 or
AsPh3 ligands do not show the trigonal bipyramidal distortion
to the same degree as the analogous Pt(II) complexes. The bis
triphenylphosphine Pd(II) complex has a large distance between
19
˚
its phenyl rings (> 4.0 A). While the bis triphenylarsine has a
˚
short centroid distance (3.75 A), its two phenyl rings are turned
away from a parallel position as the angle between the mean least-
squares planes for the phenyl groups is 12.9◦ which diminishes the
p–p interactions between the rings.25 The PPh3 complex similarly
Fig.
6 Thermal ellipsoid perspective of cation in [Pd([9]aneS3)-
(dpae)](PF6)2·(CH3)2CO (6). (50% probability, H atoms omitted for
clarity).
§ Excluding the three bis EPh3 complexes discussed here, the median
value of t for all heteroleptic Pt(II) [9]aneS3 structures (41 total) is 0.05.
Accordingly, the elongated square pyramidal shape is seen much more
commonly. Examining data for Pd(II) [9]aneS3 structures, excluding the bis
AsPh3 and PPh3 complexes, the median value of t for the other seventeen
heteroleptic Pd(II) [9]aneS3 structures is also 0.05.
reported [Pt([9]aneS3)(PPh3)2](PF6)2 structure.20 The continuum
between a square pyramidal geometry and a trigonal bipyramid
is conveniently represented by the parameter t, developed by
Reedjik, Addison, and coworkers.31 The value of the t parameter is
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five-coordinate complexes has been noted from the infancy of its
complexation chemistry, and our data support that conception.36
The ability of certain ligands to reduce electron density on a metal
center through their p acidity has been cited as a factor favoring
trigonal pyramidal five-coordination.37 Our results suggest that
the same effect can also be achieved by employing a poor s donor
ligand. As the group 15 family donor is changed from P to As to
Sb, the [9]aneS3 ligand clamps down harder on the metal ion via
all three sulfurs to compensate for the increasingly poorer donor
qualities of the ancillary ligand.
The same trend discussed above for the bis pnictogen complexes
is similarly observed in the three related chloro complexes of Pt(II)
with [9]aneS3. That is, the axial Pt–S distances shorten as you
˚
descend the group 15 family, P > As > Sb (P = 3.08 A, As =
˚
˚
3.04 A, Sb = 2.79 A). We had reported the same trend in the
related Pd(II) [9]aneS3 chloro complexes with group 15 donors.25
The two new chloro complexes form elongated square pyramidal
geometries around the Pt center with the anticipated cis-[S2ECl +
S1] (E = group 15 donor) coordination environment. The two cis
donors from the [9]aneS3 ligand, the group 15 donor, and chloride
form the square planar base of the pyramid. In complex 2, the
Fig.
7 Intramolecular p–p interaction between phenyl rings in
[Pt([9]aneS3)(AsPh3)2](PF6)2·2CH3NO2 (1). The distance between cen-
˚
Pt(II) ion is raised 0.156 A above the mean square basal plane
˚
troids for the two phenyl rings is 3.84 A.
defined by the S2AsCl donor set and directed towards the axial
sulfur (S1). Similarly, complex 4 shows the Pt(II) ion is raised
above the mean square plane of the S2SbCl donor set, but to a
has a large angle between the mean least-squares planes for its
phenyl groups (24.0◦). We would underscore, however, that these
two Pd(II) complexes are also the ones that exhibit the greatest
distortion towards trigonal bipyramidal geometry out of any of
the reported structures for Pd(II) complexes with [9]aneS3 ligands
(t values of 0.24 (As complex) and 0.27 (P complex)).35
Other distinctive structural features found in the two bis
complexes, in addition to the distortion towards a trigonal
bipyramidal shape, are their very short Pt–S axial distances
˚
larger degree, 0.230 A. In contrast to the bis EPh3 complexes, the
chloro complexes do show a periodic trend for the distortion from
an ideal square pyramidal shape, with the Sb complex displaying
the largest t value (Sb > As > P; t = 0.30, 0.14, 0.07, respectively).
The better trans directing chloro ligand results in a shorter Pt–S
equatorial bond trans to it as compared to the bond trans to the As
or Sb donor. The effect results in the Pt–S equatorial bond trans
˚
˚
˚
(Pt–S = 2.584(2) A for bis AsPh3 complex; Pt–S = 2.514(1) A
for bis SbPh3 complex). Indeed, these are the two shortest axial
sulfur distances yet observed in all reported Pt(II) [9]aneS3 crystal
structures. As seen in Table 2, there is a notable periodic trend with
the axial Pt–S distances shortening as the group 15 donor changes
in the order, P > As > Sb. We believe that the increasingly poorer
donor qualities of the larger pnictogen ligand are responsible
for the sequence. In earlier papers, we have highlighted the
reciprocal relationship that Pt(II) and Pd(II) [9]aneS3 complexes
with shorter M–S axial distances show longer equatorial bonds
and vice versa.9 The six complexes in this report continue to
demonstrate the correlation. In addition, we have previously
underscored another important structural feature to monitor
[9]aneS3 complexes, the sum of the three metal–sulfur distances.
Like the axial sulfur lengths, the sum of the three metal–sulfur
distances also shortens with the change in the group 15 donor.
Both the bis AsPh3 and bis SbPh3 complexes show the shortest
M–S distance sum of any of the Pt [9]aneS3 structures reported. As
such, these two Pt(II) complexes approach true five-coordination
more than any of the prior complexes involving the [9]aneS3
ligand.¶ The tendency for larger pnicotgen donors like Sb to favor
to the chloro ligand almost 0.02 A shorter in the arsine complex,
˚
but over 0.1 A shorter in the stibine complex. We believe that the
relative poorer donor qualities of the Sb ligand are responsible
for the shorter bond length as well as the greater distortions
towards trigonal bipyramidal geometry in the complex. We also
note that the equatorial Pt–S distances are shorter in the chloro-
EPh3 complexes than for the analogous bis EPh3 complexes due
to the presence of the p-donating chloro ligand. The trend in the
difference between the longer Pt–S equatorial bond lengths in the
[Pt([9]aneS3)(EPh3)2]2+ complexes and the shorter Pt–S bonds in
the [Pt([9]aneS3)(EPh3)(Cl)]+ complexes follows the periodicity of
˚
group 15 with a respective change of 0.13, 0.10, and 0.08 A in
the order of P, As, and Sb. The longer axial Pt–S distances in
the two chloro complexes are balanced with the previously noted
shorter Pt–S equatorial bonds. For the three chloro complexes
with EPh3 ligands, their axial Pt–S distances fall intermediate
between the bis EPh3 complexes and [Pt([9]aneS3)Cl2] (As: 2.58,
3.04, 3.26 A; Sb: 2.51, 2.79, 3.26; P: 2.64, 3.08, 3.26 A), gradually
lengthening as chlorides successively replace pnictogen donors in
the coordination sphere. The axial sulfur (S1) is also angled away
from the pnictogen ligand and directed towards the sulfur trans
to the chloride (S7) (for AsPh3 complex; S1–Pt–S4 = 83.54(7)◦;
S1–Pt–S7 = 79.24(7)◦; for SbPh3 complex; S1–Pt–S4 = 86.94(7)◦;
S1–Pt–S7 = 83.40(7)◦). Among the three chloro EPh3 complexes
with Pt(II), the Pt–Cl bond lengths show surprisingly little change
˚
˚
¶ The difference between the shortest and longest Pt–S distances are
˚
0.28, 0.26, and 0.19 A respectively for the 2 ¥ PPh3, AsPh3, and SbPh3
˚
complexes. These values contrast the median difference of 0.64 A between
the longest and shortest Pt–S distances in all other Pt(II) [9]aneS3 structures,
illustrating how the group 15 donor is effecting the trend towards true five-
coordination.
˚
(2.33–2.34 A), particularly given the large differences in Pt–S
bonds. The observation suggests that the Pt–Cl bond length is
8610 | Dalton Trans., 2009, 8605–8615
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largely affected by the trans thioether sulfur with little contribution
from the cis pnictogen donor. Due to the better p donating chloro
ligand, the trans Pt–S bond is always the shorter of the two bonds,
illustrating both the sensitivity and ability of the coordinated
[9]aneS3 ligand to adapt to changes in the donor/acceptor
properties of whatever ancillary ligand that might be present. Thus,
Pt(II) and Pd(II) complexes with [9]aneS3 are useful structural
probes for examining complexation behaviors in a wide range of
ancillary ligand types.
previously observed for these types of bonds.39–41 However, the
Pt–E distance does decrease as thioether sulfur donors are replaced
by halide donors such that [Pt(EPh3)2X2] (X = Cl or Br) exhibit
shorter metal–pnictogen distances than the Pt thioether complexes
presented here.38–40
The relative trans influence of pnictogen ligands has seen
considerable discussion in the literature.38 In our thiacrown
complexes involving As and P donors, the Pt–S bond that is trans
to the pnictogen donor always shows the shortest bond when E is
an arsenic donor and longest with a phosphorus ligand. The same
sequence is seen for the two bis EPh3 complexes, the two bidentate
dppe and dpae complexes, and both mono chloro complexes. In
the latter complexes, the Pt–S bonds trans to the chloro ligand are
always shorter than any of the pnictogens, suggesting an ordering
of trans influence among the three donor types of P > As > Cl-. We
propose that the ordering is reflective of the ability of the ligand to
function as a s donor. The positioning of the SbPh3 ligand among
the group 15 donor series is difficult. For the chloro complex,
the Pt–S trans bond to SbPh3 is the longest among the three
pnictogen complexes, but in the bis complex it is the shortest. The
noted distortions towards trigonal bipyramidal geometry could
strongly affect the trans influence, making a definitive assignment
of the relative position of SbPh3 in the series of group 15 ligands
difficult.
We would like to highlight two aspects of these p–p intramolec-
ular interactions that are unique to this report. For the first
time, p–p intramolecular interactions in a bis AsPh3 complex as
well as for an analogous SbPh3 complex are noted. A survey
of the Cambridge Structural Database (CSD) shows 128 bis
AsPh3 complexes with any transition metal, of which only 6
show this interaction.35ꢀ Similarly, out of 82 bis SbPh3 complexes
structurally characterized with any transition metal, we have found
only a single example of intramolecular p–p interactions between
phenyl rings.35** There are a decreasing number of examples of
intramolecular p–p interactions in EPh3 complexes (both actual
numbers and proportionally) with the larger group 15 donor. This
is due to a larger number of trans complexes with the ligands
as well as larger E–M–E angles which minimize the approach of
the two phenyl substituents. To our knowledge, there have been
no literature reports of this type of interaction influencing the
stereochemistry of a metal complex and distorting it towards
a trigonal bipyramidal shape. Accordingly, we feel that this is
a rare example of a p–p intramolecular interaction significantly
influencing the stereochemistry at a metal center.
The Pt(II) and Pd(II) complexes with the chelating dpae ligand
exhibit the anticipated square pyramidal geometry. In the Pt(II)
˚
complex with dpae, the Pt ion is raised 0.220 A above the mean
least-squares plane defined by the S2As2 donor set and directed
towards the axial sulfur. The Pd(II) is also raised out of the S2As2
˚
plane towards S1, but to a smaller degree, 0.178 A. It is interesting
to note that the [Pd([9]aneS3)(dpae)]2+ complex has the shortest
known axial Pd–S distance in any of the twenty-four structures
of this type; a consequence of two As donors. Similarly, for the
Pt(II) dpae analog only the previously discussed bis SbPh3 and
AsPh3 complexes (out of all forty-seven Pt(II) structures) have
shorter axial Pt–S distances. Also, both complexes have a three
M–S bond sum that is very short with the Pd(II) dpae complex
being the shortest among Pd(II) [9]aneS3 structures. For the Pt(II)
dpae complex, it has the smallest sum of Pt–S distances for any
complex except for the bis SbPh3 complex. We note the ability of
the trithiacrown ligand to adjust its coordination mode, due to the
poorer s donor abilities of the group 15 donor, regardless of the
denticity of the pnictogen ligand. There is a reduction in charge on
the metal due to the poor sigma donor qualities of the ligand and
similar effects have been observed with Pt(II) [9]aneS3 complexes
containing p-acid ligands.9,10,18 Importantly, we would stress that
neither of the two dpae complexes shows much distortion towards
a trigonal bipyramid geometry, illustrating that the poor donor
properties of the pnictogen alone cannot be responsible for that
distortion (t = 0.16 (Pt) and 0.080 (Pd)).
In prior publications involving [9]aneS3 complexes, the Pd(II)
complexes showed shorter axial metal–sulfur distances, on average
about 0.1 A compared to analogous Pt(II) complexes.12,18 However,
˚
for comparisons of the Pt(II) and Pd(II) complexes in this report,
no general trend emerges with regards to any of the metal–sulfur
distances. We would note that for the two sets of bis EPh3 (E =
P and As) complexes, the Pd(II) complexes show the shorter
equatorial bond distances, but the Pt(II) complexes display shorter
axial lengths and a shorter sum of the three metal–sulfur distances,
possibly due to the trigonal bipyramidal distortion. In comparing
analogous Pt(II) and Pd(II) [9]aneS3 complexes with identical
ancillary group 15 donor ligands, the Pt(II) complex always shows
the greater distortion towards a trigonal bipyramidal geometry.
As typically observed in transition metal complexes with EPh3
complexes, the C–E–C angles for the phenyl rings are compressed
(see Table 2), and the degree of compression increases periodically
with the larger group 15 donor.1–3 In contrast to the anticipated
period trend, the E–Pt–E angles actually decrease with the larger
group 15 donor (P = 95.6◦, As = 93.4◦, Sb = 90.7◦). The source
for the trend is not the trigonal bipyramidal distortion as the
related chloro complexes also follow the same pattern in their
Cl–Pt–X angles, with the antimony complex again showing the
smallest bite angle around the platinum centre. The Pt–As and
Pt–Sb bond lengths for all five [9]aneS3 complexes are in the range
ꢀ A search of the CSD for all transition metal complexes containing at
least two AsPh3 ligands reveals 128 structures.35 We examined all of these
complexes to find structural features similar to the ones presented here. Out
of these, we have identified only six that have both centroid distances less
◦
˚
than 4.0 A and a mean least squares plane angle of 10.0 or less. All involve
Pt(II) (five examples) or Pd(II) centers containing ligands with strongly
electron-withdrawing substituents. We do not mean imply that these values
are defining structural features for an intramolecular p–p interaction, but
the relatively few examples serve to illustrate how uncommon are our
reported structural features. Also, we would note that the interactions do
not appear to have been discussed in the prior structures.
** A similar search of the CSD for all metal complexes containing at least
two SbPh3 reveals 82 structures.35 We have followed the search parameters
described above and found only a single example (JUJBUL) that showed
the described structural features.
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Table 4 Comparative data for 195Pt NMR and visible spectroscopies
Complexa
195Pt NMR d (n1/2
-4489, s(120Hz)
)
l
max/nm d–d trans.
Ref.
[Pt([9]aneS3)(AsPh3)2]2+ (1)
[Pt([9]aneS3)(AsPh3)(Cl)]+ (2)
[Pt([9]aneS3)(SbPh3)2]2+ (3)
[Pt([9]aneS3)(SbPh3)(Cl)]+ (4)
[Pt([9]aneS3)(dpae)]2+ (5)
[Pd([9]aneS3)(dpae)]2+ (6)
[Pt([9]aneS3)(PPh3)2]2+
434
413
454
437
415
466
—
—
—
This work
This work
This work
This work
This work
This work
20
b
—
-4822, s(640Hz)
b
—
-4772, s, (140Hz)
N/A
-4399, t, (49Hz)
-4080, d, (70Hz)
-4069, t, (41Hz)
b
[Pt([9]aneS3)(PPh3)(Cl)]+
[Pt([9]aneS3)(dppe)]2+c
22
23
b
b
-
a All cationic complexes are reported as PF6 salts exclusively to minimize anion effects. b Not observed. c dppe = 1,2-bis(diphenylphosphino)ethane
NMR spectroscopy
and our prior NMR experiences with a number of related Pt(II)
[9]aneS3 complexes.14,23
In the proton NMR spectra for complexes 1, 3, 5, and 6, the
twelve methylene protons of the [9]aneS3 appear as a symmetrical
multiplet with a distinctive AA¢BB¢ splitting pattern observed in
virtually all of its Pt(II) and Pd(II) complexes.12,20 In contrast,
the two chloro complexes, compounds 2 and 4, show a broad
multiplet for the [9]aneS3 (see ESI†). For the Pt(II) complex with
dpae (compound 5), we observe J
spectrum for the ligand’s methylene resonances which results in
195Pt satellites. We see similar carbon–platinum coupling in the
same complex for three of the carbon atoms (dpae methylene
carbons, ortho ring carbons, quaternary ring carbon). The Pt
complexes generally show J
ring carbon atom and J
atoms which allows for the assignment of all peaks in their
13C NMR spectra. The aromatic region in the proton and 13C
NMR spectra for the six group 15 donor complexes is as
expected.
Despite the asymmetric nature of the coordination environment
found in the chloro complexes, the coordinated [9]aneS3 ligand
always displays a single resonance in its 13C NMR spectra due
to the six equivalent methylene carbons which are involved in
a rapid fluxional process. We have previously noted a single
13C NMR resonance in other asymmetrical [9]aneS3 com-
plexes such as ones involving cyclometallating ligands and
related chloro complexes.18,22 The 13C NMR [9]aneS3 singlet
is always shifted 1–2 ppm downfield in the phosphine com-
plexes compared to the analogous arsine complexes. Surpris-
ingly, the line width for the [9]aneS3 13C signal is strongly
affected by the identity of the group 15 donor (see ESI†)
as the peaks become progressively wider as you descend the
family.
As seen in Table 4, there is a clear periodic trend in
195Pt NMR chemical shifts and group 15 donors. The larger group
15 donors result in a progressive upfield chemical shift for the 195Pt
nucleus (see ESI for spectra†) for both monodentate and bidentate
pnictogen ligands, with the dpae complex shifted 750 ppm upfield
relative to the dppe complex. Thus, the 195Pt NMR chemical shift is
quite sensitive to the ligand environment around the metal center.
Curiously, attempts to acquire 195Pt NMR spectra for the two
chloro complexes (complexes 2 and 4) were unsuccessful despite
numerous attempts in concentrated solutions over large chemical
shift ranges and acquisition times (several days in some cases)
Electronic spectroscopy and electrochemistry
Two main types of electronic transitions are observed for all six
complexes, one lower energy and lower intensity transition and
at least one additional band of both higher energy and intensity.
These two transitions are assigned as d–d transitions and metal-
to-ligand charge transfer transitions, respectively. The energy of
the d–d transition allows an apt comparison of the ligand field
strengths among these ligands, and the data are summarized in
Table 4. The antimony donor is a weaker field ligand than the
arsenic which is consistent with the anticipated periodic trend for
the group 15 donors.41 That is, the ligand field strength diminishes
on the order of P > As > Sb. The stronger field phosphine ligands
result in a higher energy d–d band that is then obscured by the more
intense MLCT bands. We note that both AsPh3 or SbPh3 function
as weaker field ligands than chloride since replacement of Cl- by
either of these group 15 donors results in a weaker ligand field, as
seen in a red shift in the absorption of the d–d transition. We also
have recently reported similar trends for Pd [9]aneS3 complexes
with AsPh3.24 As expected, the bidentate dpae ligand is a stronger
field ligand than the monodentate AsPh3. In comparisons between
arsine donor ligands, Pt(II) complexes show stronger ligand fields
than the analogous Pd(II) complexes as expected based upon the
greater ligand interactions with the Pt 5d orbitals.42
We have examined the electrochemistry of the four As complexes
using cyclic voltammetry. None of the complexes exhibit oxidative
electrochemistry except [Pt([9]aneS3)(AsPh3)(Cl)]+ which shows
an irreversible oxidation wave at +626 mV vs. Fc/Fc+. This is
assigned as a one-electron oxidation of the Pt(II) center, and the
oxidation is facilitated by the presence of the anionic chloro ligand
in contrast to the other complexes with exclusively neutral ligands.
All three Pt(II) complexes show an irreversible reduction wave
that is assigned as reduction to Pt(0). The reduction of the dpae
complex occurs at a more negative potential than the bis AsPh3.
Also, the reduction potentials for the arsenic complexes occur
at more negative reduction potentials than the related phosphine
complexes, indicating they are harder to reduce and consistent with
the donor properties of the two pnictogen atoms. The Pd(II) dpae
complex shows a quasi-reversible wave at -952 mV vs. Fc/Fc+
and an irreversible reduction at -1406 mV vs. Fc/Fc+. These are
assigned as a Pd(II)/Pd(I) and Pd(I)/Pd(0) couples respectively.
3
Pt coupling in its 1H NMR
1
195
H–
2
13 195
coupling for the quaternary
C–
Pt
3
13 195
Pt coupling for two ortho ring carbon
C–
8612 | Dalton Trans., 2009, 8605–8615
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C, 39.19; H, 3.50; S, 7.26. C42H42As2F12P2PtS3 requires C, 39.48;
H, 3.31; S, 7.53. dH (400 MHz, CD3NO2): 7.60–7.42 (m, 30H,
Ph), 2.97–2.84, (m, 6H, [9]aneS3). 2.72–2.58 (m, 6H, [9]aneS3). dC
(100 MHz, CD3NO2): 134.59 (3JPt–C = 13 Hz, 12C, Ph), 133.65
(6C, Ph), 131.31 (12C, Ph), 130.16 (2JPt–C = 42 Hz, 6C, Ph), 36.09
(6C, n1/2 = 3 Hz, [9]aneS3). dPt (85.9 MHz, CD3NO2): -4491
(n1/2 = 120 Hz). UV-Vis (CH3CN, nm (e/M-1 cm-1)): 434 (2.12 ¥
102), 264 (9.8 ¥ 104). nmax, cm-1: 3074, 3069, 3041, 3000, 2972,
Conclusion
In summary, we have synthesized and characterized a new series
of heteroleptic platinum(II) complexes containing the thiacrown
[9]aneS3 with monodentate and bidentate group 15 ligands. The
increasing poorer donor qualities of the larger pnictogen ligands
manifest themselves in the structural and spectroscopic properties
of the complex. As expected, the larger pnictogen ligand forms
the weaker ligand field. The trithiacrown compensates for poorer
donor quality with shorter metal–sulfur bond distances, ap-
proaching a pentacoordinate complex with the larger pnictogens.
However, the bis triphenylpnictogen complexes display an unusual
distortion towards a trigonal bipyramidal geometry which arises
from intramolecular p–p interactions between phenyl rings in the
two ligands as opposed to the identity of the group 15 donor.
-
2938, 1559, 1476, 1439, 1290, 1193, 1000, 840 (s, PF6 ), 831, 738,
-
693, 690, 555 (s, PF6 ), 545. The complex shows no oxidative
electrochemistry, but does show an irreversible reduction wave at
-1286 mV vs. Fc/Fc+.
[Pt([9]aneS3)(AsPh3)(Cl)](PF6) (2). This complex was pre-
pared by means of an identical procedure to (1), but using a single
equivalent of AsPh3. The stoichiometric quantities in this reaction
included: [Pt([9]aneS3)Cl2] (51.0 mg, 0.114 mmol), AsPh3 (35.0 mg,
0.114 mmol), and NH4PF6 (20 mg, 0.123 mmol). The color of
the solution was yellow-orange prior to crystallization. Yield:
46 mg, 42%. Anal. Found: C, 32.18; H, 3.33; S, 10.19; Cl, 3.53.
C25.5H31.5AsClF6N1.5O3PPtS3 requires C, 32.11; H, 3.33; S, 10.09;
Cl, 3.72. dH (400 MHz, CD3NO2): 7.79–7.58 (m, 15H, Ph), 3.19–
Methods and materials
All solvents and reagents were purchased from Aldrich Chem-
ical Company and used as received. The starting complexes
[Pt([9]aneS3)Cl2] and its Pd(II) analogue were prepared according
to published methods.43 Elemental analyses were performed by
Atlantic Microlab, Inc. of Atlanta, GA. Fourier transform IR
spectra were obtained as KBr powders using pre-weighed 500 mg
packets and a Nicolet Impact 410 spectrometer equipped with
an ATR accessory. Ultraviolet-visible spectra were obtained in
acetonitrile using a Varian DMS 200 UV-visible spectrophotome-
3.03 (m, 6H, [9]aneS3). dC (100 MHz, CD3NO2): 135.04 (3JPt–C
13 Hz, 6C, Ph), 133.04 (3C, Ph), 130.69, (6C, Ph) 130.55 (2JPt–C
45 Hz, 3C, Ph), (37.69–36.86 (broad, 6C, n1/2 = 29 Hz, [9]aneS3).
We could not detect a 195Pt NMR peak over a total range between
-3000 to -5000 ppm despite obtaining over 20 000 transients (65 h)
in a typical run. UV-Vis (CH3CN, nm (e/M-1 cm-1)): 413 (sh, 9.2 ¥
101), 259 (1.5 ¥ 104). nmax, cm-1: 3074, 3064, 2970, 2918, 2907, 1555,
=
=
1
1
ter. 13C{ H}, 195Pt{ H} and 1H NMR spectra were recorded on a
JEOL ECX-400 NMR spectrometer. Residual solvent peaks were
-
1481, 1435, 1372, 1180, 1162, 1080, 1023, 993, 936, 840 (s, PF6 ),
used for both the deuterium lock and reference for 13C{ H and
1
-
746, 737, 693, 655, 553 (s, PF6 ). The complex shows an irreversible
1H NMR spectra while 195Pt{ H}NMR spectra were exter-
1
oxidation wave at +626 mV and an irreversible reduction wave at
-1680 mV vs. Fc/Fc+. There is also a weak irreversible reduction
at +76 mV vs. Fc/Fc+ associated with the oxidation.
nally referenced to [PtCl4]2- at -1624 ppm.44 Electrochemical
measurements were performed using a Bioanalytical Systems
CV50W analyzer. The supporting electrolyte was 0.1 M tetra-
n-butylammonium tetrafluoroborate in acetonitrile, and sample
concentrations were approximately 2 mM. All voltammograms
were recorded at a scan rate of 100 mV s-1. The standard three-
electrode configuration used is as follows: 1.6 mm diameter Pt disk
working electrode, Pt wire auxiliary electrode, and Ag/AgCl refer-
ence electrode. All reported potentials were internally referenced
[Pt([9]aneS3)(SbPh3)2](PF6)2 (3).
A
mixture of [Pt([9]
aneS3)Cl2] (50.0 mg, 0.112 mmol) and SbPh3 (159 mg, 0.450 mmol)
were refluxed in 50 mL of CHCl3 : CH3NO2 (1 : 1) solvent for
1 h. The stibine ligand quickly dissolved albeit the Pt complex
slowly went into solution. The flask was cooled slightly before
the addition of NH4PF6 (37 mg, 0.23 mmol) which resulted in a
turbid, peach-colored solution. The solution was refluxed for an
additional 30 min. At this point, a clear orange-yellow solution
was present. Cooling overnight at 0◦ precipitated colorless
crystals of NH4Cl which were removed by filtration. The filtrate
was concentrated to 2/3 of its original volume, and three drops
of CHCl3 were added to facilitate solubility. Slow diffusion (1
week) of diethyl ether into the concentrate produced orange
crystals. The clear, colorless supernatant solution was decanted,
and the orange crystals rinsed twice with 10 mL of diethyl ether.
A yield of 71.0 mg (22.8%) of 3 were recovered. Anal. Found: C,
36.32; H, 3.27; S, 6.59. C42H44F12OP2PtS3Sb2 requires C, 36.31;
H, 3.19; S, 6.92. dH (400 MHz, CD3NO2): 7.54–7.45 (m, 30H,
Ph), 2.99–2.94 (m, 6H, [9]aneS3). dC (100 MHz, CD3NO2): 136.68
+
to FeCp2 /FeCp2, which in this solution was found at +0.411 V
relative to the reference electrode.
Preparation of complexes
[Pt([9]aneS3)(AsPh3)2](PF6)2 (1).
A
mixture of [Pt([9]
aneS3)Cl2] (50.0 mg, 0.112 mmol) and AsPh3 (69.0 mg,
0.225 mmol) were refluxed in CH3NO2 (25 mL) for 1 h, producing
a clear, orange solution. The arsine ligand dissolved immediately,
but the Pt complex slowly went into solution. The reaction was
allowed to cool slightly before the addition of solid NH4PF6
(37.0 mg, 0.227 mmol), and the solution was refluxed for another
30 min. The reaction was cooled in ice overnight to precipitate
colorless crystals of NH4Cl which were removed via filtration
from the orange solution. The contents of the reaction flask were
concentrated to 2/3 of its original volume. Slow diethyl ether
diffusion (1 week) into the concentrated solution produced orange
crystals of (1). This were isolated by decantation and rinsed 2 ¥
with 10 mL of diethyl ether. Yield: 0.109 mg, 76.2%. Anal. Found:
(12 C, Ph), 133.62 (6 C, Ph), 131.67 (12C, Ph), 126.93 (2JPt–C
=
56 Hz, 6C, Ph), 37.54 (broad, 6C, n1/2 = 3 Hz, [9]aneS3). dPt
(85.9 MHz, CD3NO2): -4822 (n1/2 = 640 Hz). UV-Vis (CH3CN,
nm (e/M-1 cm-1)): 454 (273), 287 (2.55 ¥ 104), 265 (9.07 ¥ 103).
n
max, cm-1: 3085, 3074, 3023, 2958, 2944, 1475, 1432, 1064, 996,
-
-
840 (s, PF6 ), 747, 685, 668, 560 (s, PF6 ). We also note that yellow
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needles of a second crystalline material were present causing
the low yield of 3. These needles have been identified as the
compound [Pt([9]aneS3)(SbPh3)(Ph)](PF6).45
orange liquid. The reaction flask was allowed to cool slightly
before the addition of the hexafluorophosphate salt. An orange
solution was present which was refluxed for an additional 30 min.
Cooling overnight resulted in the precipitation of NH4Cl. These
crystals were removed by filtration and the solution concentrated
to 2/3 of their original volume. Diethyl ether was slowly diffused
(1 wk) into the concentrated orange-red solution resulting in pink
needles. The clear, colorless supernatant solution was decanted,
and the crystals rinsed twice with 10 mL of diethyl ether. A mass
of 81.0 mg of 6 (79.4%) was recovered. Anal. Found: C, 36.21;
H, 3.37; S, 9.08. C32H36As2F12P2PdS3 requires C, 36.16; H, 3.41; S,
9.05. dH (400 MHz, CD3NO2): 7.77–7.61 (m, 20H, Ph), 3.38 (s, 4H,
–As–CH2–CH2–As–), 3.06–2.95 (m, 6H, [9]aneS3). 2.72–2.60 (m,
6H, [9]aneS3). dC (100 MHz, CD3NO2): 134.36 (4C, Ph), 133.53
(8C, Ph), 131.85 (8C, Ph) 131.33 (4C, Ph), 35.75 (6C, n1/2 = 3 Hz,
[9]aneS3), 30.64 (2C, –As–CH2–CH2–As–). UV-Vis (CH3CN, nm
(e/M-1 cm-1)): 466 (260), 311 (2.4 ¥ 104), 274 (2.0 ¥ 104). nmax, cm-1:
3080, 3053, 2995, 2946, 2925, 2914, 1557, 1471, 1435, 1401, 1294,
[Pt([9]aneS3)(SbPh3)(Cl)](PF6) (4). This complex was pre-
pared by a procedure similar to (3) except one equivalent of SbPh3
was used. The following stoichiometric quantities were employed
in the reaction: [Pt([9]aneS3)Cl2] (50.0 mg, 0.112 mmol); SbPh3
(38.0 mg, 0.108 mmol) and NH4PF6 (20.0 mg, 0.123 mmol).
Following the reflux, the color of the solution was a turbid orange.
Cooling overnight produced colorless crystals of NH4Cl which
were removed by filtration. The filtrate was concentrated to 2/3 of
its original volume. Three drops of CHCl3 were added to facilitate
solubility, and diethyl ether slowly (1 week) diffused into the
solution. Red crystals of 4 were produced. The supernatant was
removed by decantation, and the crystals rinsed twice with 10 mL
of diethyl ether. A yield of 81.0 mg (82.5%) of 4 was obtained. Anal.
Found: C, 31.05; H, 3.06; S, 10.58. C24H27F6PClPtS3Sb requires:
C, 31.09; H, 3.15; S, 10.38. dH (400 MHz, CD3NO2): 7.77–7.75
(m, 6H, Ph), 7.65–7.54 (m, 9H, Ph), 3.27–3.00 (m, 6H, [9]aneS3).
dC (100 MHz, CD3NO2): 137.21 (6C, Ph), 133.00 (3C, Ph), 131.17
-
1181, 1173, 1079, 999, 835 (s, PF6 ), 764, 731, 688, 650, 555 (s,
-
PF6 ). The complex shows no oxidative electrochemistry, but does
show a quasi-reversible reduction wave at -952 mV (ipc/ipa = 0.57)
(6C, Ph), 127.99 (3C, Ph), 37.60–36.22 (very broad, 6C, n1/2
=
and an irreversible wave at -1406 vs. Fc/Fc+.
110 Hz, [9]aneS3). We could not detect a 195Pt NMR peak over a
total range between -3000 to -5000 ppm despite obtaining over
20 000 transients (65 h) in a typical run. UV-Vis (CH3CN, nm
(e/M-1 cm-1)): 437(161), 265(1.74 ¥ 104). nmax, cm-1: 3068, 3051,
3012, 2972, 2887, 2867, 1478, 1430, 1410, 1302, 1186, 1138, 1059,
X-Ray structural determinations†
Crystals suitable for X-ray diffraction studies were obtained by
slow diffusion (several days) of diethyl ether into a concentrated ni-
tromethane solution for compounds 1 and 2, into a nitromethane–
chloroform solution for compounds 3, and 4, into acetonitrile for
compound 5, and into acetone for compound 6. Table 1 contains
crystal data, collection parameters, and refinement criteria for
the structures of 1–6. For all structures, X-ray intensity data
were measured at low temperature with graphite-monochromated
-
-
1019, 835 (s, PF6 ), 732, 689, 665, 551 (s, PF6 ).
[Pt([9]aneS3)(dpae)](PF6)2 (5)
The compound was prepared by
a procedure identical
to compound (1). The following stoichiometric quantities
were used: [Pt([9]aneS3)Cl2] (50.0 mg, 0.112 mmol), 1,2-
bis(diphenylarsenio)ethane (dpae) (55.0 mg, 0.113 mmol), and
NH4PF6 (37.0 mg, 0.227 mmol). Ether diffusion into a concen-
trated deep-yellow CH3NO2 solution produced yellow needle-
like crystals. The crystals were collected, washing with water
(2 ¥ 10 mL) to remove NH4Cl and lastly diethyl ether (2 ¥
10 mL). A yield of 120 mg (92.9%) of yellow crystals of
[Pt([9]aneS3)(dpae)](PF6)2 was obtained. Anal. Found: C, 33.52;
H, 3.08; S, 8.37. C32H36As2F12 P2PtS3 requires C, 33.37; H, 3.15;
S, 8.35. dH (400 MHz, CD3NO2): 7.78–7.62 (m, 20H, Ph), 3.12
(s with 195Pt satellites (3JPt–H = 14 Hz), 4H, –As–CH2–CH2–As–
), 2.99–2.85, (m, 6H, [9]aneS3). 2.72–2.56 (m, 6H, [9]aneS3). dC
(100 MHz, CD3NO2): 134.26 (4C, Ph), 133.57 (3JPt–C = 13 Hz, 8C,
Ph), 131.67 (8C, Ph), 130.40 (2JPt–C = 43 Hz, 4C, Ph), 35.90 (6C,
n1/2 = 3 Hz, [9]aneS3), 29.88 (2JPt–C = 68 Hz), –As–CH2–CH2–
As–). dPt (85.9 MHz, CD3NO2): -4771 (n1/2 = 140 Hz). UV-Vis
(CH3CN, nm (e/M-1 cm-1)): 402 (184), 288 (1.1 ¥ 104), 261 (2.4 ¥
104). nmax, cm-1: 3068, 3051, 3012, 2972, 2887, 2867, 1478, 1430,
˚
radiation (l = 0.71073 A) on a Rigaku AFC8S diffractometer
equipped with a 1 K Mercury CCD detector. The structure was
solved using direct methods and refinement was done using full-
matrix least-squares techniques (on F2).46 Data were corrected
for absorption, using semi-empirical methods. Structure solution,
refinement and the calculation of derived results were performed
with the SHELXTL package of computer programs.47
Acknowledgements
Acknowledgements are made to the following organizations for
their generous support of this research: the donors of the American
Chemical Society Petroleum Research Fund; the Research Corpo-
ration, the Grote Chemistry Fund at the University of Tennessee
at Chattanooga; the National Science Foundation RUI Program.
We thank Professor Daron E. Janzen of St. Catherine’s College
for his comments.
-
1410, 1302, 1186, 1138, 1059, 1019, 835 (s, PF6 ), 732, 689, 665, 551
-
(s, PF6 ). The complex shows no oxidative electrochemistry, but
Notes and references
does show an irreversible reduction wave at -1550 mV vs. Fc/Fc+.
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8614 | Dalton Trans., 2009, 8605–8615
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The Royal Society of Chemistry 2009
©

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This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8605–8615 | 8615
©