Cis-trans ring substituent isomerism in cyano-substituted metallathietane-3,3-dioxide complexes of platinum(II) and palladium(II)

Article abstract of DOI:10.1021/om2011497

Reactions of the platinum complexes cis-[PtCl₂(PPh ₃)₂], [PtCl₂(dppf)], or [PtCl ₂(dppe)], and the palladium complexes, [PdCl₂(PPh ₃)₂] or [PdCl₂(dppe)], with bis(cyanomethyl)sulfone NCCH₂SO₂CH₂CN in methanol with added trimethylamine base gave the new cyano-substituted metallathietane-3,3-dioxide complexes [M{CH(CN)SO₂CH(CN)}L ₂] (M = Pd, Pt) in good yields and purities. ¹H and ³¹P{¹H} NMR spectroscopy indicates that (in the majority of cases) the products are formed as a mixture of cis and trans isomers, with regard to the disposition of the cyano groups across the four-membered ring. An X-ray structure determination on a crystal of [Pd{CH(CN)SO₂CH(CN)} (PPh₃)₂] showed it to be of the cis isomer, the first structurally characterized cis isomer of this type of complex. The four-membered palladacyclic ring is highly planar, in contrast to other metallathietane-3,3- dioxide complexes that have puckered rings. Factors influencing the relative abundances of the two isomers of [Pd{CH(CN)SO₂CH(CN)}(PR ₃)₂] have been investigated by means of NMR spectroscopy and DFT calculations.

Full text of DOI:10.1021/om2011497

Article
pubs.acs.org/Organometallics
Cis−Trans Ring Substituent Isomerism in Cyano-Substituted
Metallathietane-3,3-dioxide Complexes of Platinum(II) and
Palladium(II)
Sacha A. M. Dowling-Mitchell,† William Henderson,*,† Edward R. T. Tiekink,‡ J. Petrakopoulou,§
and Michael P. Sigalas§
†Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
‡Department of Chemistry, University of Malaya, Kuala Lumpur 50603, Malaysia
§Laboratory of Applied Quantum Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, 54 124 Thessaloniki,
Greece
ABSTRACT: Reactions of the platinum complexes cis-[PtCl2(PPh3)2],
[PtCl2(dppf)], or [PtCl2(dppe)], and the palladium complexes, [PdCl2(PPh3)2]
or [PdCl2(dppe)], with bis(cyanomethyl)sulfone NCCH2SO2CH2CN in methanol
with added trimethylamine base gave the new cyano-substituted metallathietane-3,3-
dioxide complexes [M{CH(CN)SO2CH(CN)}L2] (M = Pd, Pt) in good yields and
purities. 1H and 31P{1H} NMR spectroscopy indicates that (in the majority of cases)
the products are formed as a mixture of cis and trans isomers, with regard to the
disposition of the cyano groups across the four-membered ring. An X-ray structure
determination on a crystal of [Pd{CH(CN)SO2CH(CN)}(PPh3)2] showed it to be
of the cis isomer, the first structurally characterized cis isomer of this type of
complex. The four-membered palladacyclic ring is highly planar, in contrast to other
metallathietane-3,3-dioxide complexes that have puckered rings. Factors influencing the relative abundances of the two isomers of
[Pd{CH(CN)SO2CH(CN)}(PR3)2] have been investigated by means of NMR spectroscopy and DFT calculations.
membered M-C-S-C ring.8 In all four crystallographically
characterized metallathietane-3,3-dioxide complexes to date
INTRODUCTION
Small-ring metallacyclic complexes are of fundamental interest
■
(vide infra), the two R substituents have been found to have a
for their structural properties and reactivity, with the best-known
examples of such ring systems being metallacyclobutanes.1,2 The
trans arrangement on the four-membered ring, which is
corroborated by the observation of a single isomer in NMR
metallathietane-3,3-dioxide ring system, M-CHR-SO2-CHR, is
spectroscopic studies. However, in one case involving cycloau-
known for a relatively small number of transition metals,
specifically, platinum(II), palladium(II), nickel(II), and gold-
(III). A series of platinum(II), palladium(II), and nickel(II)
complexes [M(PhCHSO2CHPh)L2] 1 were synthesized from
rated gold(III) complexes, one isolated product derived from
(PhC(O)CH2)2SO2 showed additional signals attributable to the
cis isomer.6
In this contribution, we report the synthesis of new
the parent chloride complexes [MCl2L2] by reaction with the
dianion [PhCHSO2CHPh]2−.3 Complexes [M{CH(COPh)-
metallathietane-3,3-dioxide complexes of platinum(II) and
palladium(II) containing cyano substituents derived from
SO2CH(COPh)}L2] 2 (with electron-withdrawing COPh
NCCH2SO2CH2CN, together with an experimental and
substituents on the ring carbon) have been prepared for
theoretical investigation of the occurrence of cis and trans
platinum(II) and palladium(II) using a convenient method
isomers for these complexes. The only previously reported
employing silver(I) oxide as a mild base and halide-abstracting
agent,4 while gold(III) analogues have been prepared using Ag2O
metallathietane-3,3-dioxide complexes derived from this sulfone
in dichloromethane5 or Me3N in refluxing methanol.6 The nature
of the ring substituent plays a significant role in the chemistry of
the resulting metallacyclic complex. This is exemplified by the
are a series of cycloaurated gold(III) complexes, which were too
insoluble for NMR characterization, and it is unknown if they
exist as cis/trans isomers.6
observation that platinathietane-3,3-dioxide complexes 1 with
RESULTS AND DISCUSSION
Synthesis and Spectroscopic Characterization. The
platinum(II) and palladium(II) starting complexes [MCl2L2]
used in this study were conveniently prepared by ligand
■
phenyl ring substituents undergo ligand substitution reactions
t
with BuNC, but when more strongly electron-withdrawing
COPh substituents are present, ligand substitution and insertion
reactions both occur, giving ring-expanded products.6,7
Metallathietane-3,3-dioxide ring systems are typically slightly
puckered; this has been the subject of a theoretical study, which
found a very low energy barrier to inversion of the four-
Received: November 17, 2011
Published: June 28, 2012
© 2012 American Chemical Society
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substitution of the cyclo-octa-1,5-diene (cod) ligand of
[MCl2(cod)] (M = Pd, Pt) with 2 mol equiv of a monodentate
phosphine (PPh3) or 1 mol equiv of a bis-phosphine [1,2-
bis(diphenylphosphino)ethane (dppe) or 1,1′-bis-
(diphenylphosphino)ferrocene (dppf)]. The [MCl2L2] com-
plexes could be either isolated or generated in situ. Reaction of
[MCl2L2] with 1 mol equiv of bis(cyanomethyl)sulfone
[NCCH2SO2CH2CN] and excess trimethylamine in refluxing
methanol for 30 min, followed by addition of water, gave good
yields of the new cyano-substituted platina- and pallada-thietane-
3,3-dioxide complexes 3a−3e, Scheme 1. The complexes are
white or cream-colored, with the obvious exception of the
ferrocene-derived complex 3b, which is yellow. The complexes
are (surprisingly) poorly soluble in most organic solvents, with
only limited solubility in chlorinated hydrocarbon solvents
(CH2Cl2 and CHCl3) in which other platina- and pallada-
thietane-3,3-dioxide complexes show good solubility. Cycloau-
rated gold(III) complexes of this ligand have also been found to
have low solubility. The complexes were characterized by H
and 31P{1H} NMR spectroscopy, mass spectrometry, IR
spectroscopy, and elemental analysis.
The 2,2′-bipyridine (bipy) complex 3f was similarly prepared
by reaction of [PdCl2(bipy)] with NCCH2SO2CH2CN and
Me3N and was isolated as a cream solid that was very insoluble in
methanol and chlorinated solvents, such that it has not been
possible to obtain satisfactory mass spectra (ESI or MALDI) for
this complex. Evidence for the formation of this complex was
based on satisfactory microanalytical data.
6
1
Scheme 1. Metallathietane-3,3-dioxide Complexes
The IR spectra of complexes 3a−3e showed a medium
intensity sharp absorption due to the cyano groups in the range
of 2213−2218 cm−1 for the platinum complexes 3a−3c, and
slightly lower, around 2202 cm−1, for the palladium complexes
3d and 3e. The symmetric and asymmetric SO2 stretches appear
around 1310 and 1125 cm−1. In comparison, the parent sulfone
NCCH2SO2CH2CN shows a higher CN stretching frequency at
2267 cm−1 (similar to the range for alkyl nitriles, which fall in the
range of 2240−2260 cm−1) and higher SO2 stretches at 1338 and
1149 cm−1.
Positive-ion ESI mass spectrometry was used to characterize
the complexes. However, reproducibility was rather low, and the
observed ions were dependent on the instrument and conditions
used. The best spectra were obtained when ammonium formate
was added as an ionization aid, producing [M + NH4]+ and [2M
+ NH4]+ ions as the dominant ions at low cone voltages.
Increasing fragmentation conditions produced [M + H]+. The
intensity of the [2M + NH4]+ ions decreased, but fragmentation
to [2M + H]+ was not significant, indicating that the ammonium
cation is instrumental in the aggregation of the dimeric species.
The platinum triphenylphosphine complex 3a showed the
fragment ion [Pt(C6H4PPh2)(PPh3)]+ (m/z 718) at cone
voltages > 50 V, this ion being a typical fragment ion observed
for Pt−PPh3 complexes.9−11
Figure 1. Part of the 1H NMR spectrum of [Pt{CH(CN)SO2CH(CN)}(dppf)] 3b showing the Pt−CH resonances of the cis (δ 3.07) and trans (δ 2.87)
isomers of this complex. The inset shows the 1H NMR resonance of the CH protons of the complex trans-[Pt{CH(COPh)SO2CH(COPh)}(PPh3)2]
2a.
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An NMR spectroscopic study on the cyano-substituted
metallathietane-3,3-dioxide complexes reveals the presence of
cis and trans isomers. For example, the 31P{1H} NMR spectrum
of 3a shows major and minor singlet resonances assigned to the
trans and cis isomers at δ 13.5 and 13.4, respectively, showing
1
very similar couplings to 195Pt of 2844 and 2854 Hz. The H
NMR spectrum of a sample of [Pt{CH(CN)SO2CH(CN)}-
(dppf)] 3b is shown in Figure 1 and clearly shows the Pt−CH
resonances due to the cis and trans isomers at ca. δ 3.07 and 2.87,
respectively. These are substantially shielded compared with the
CH2 protons in NCCH2SO2CH2CN (δ 4.33). The trans isomer
is readily identified as the major species, by comparison of its
distinctive resonance (a second-order doublet with satellites due
to 195Pt coupling) with those of [Pt{CH(COPh)SO2CH-
(COPh)}(PPh3)2] 2a, which has been crystallographically
characterized as the trans isomer and found to be isomerically
pure by NMR spectroscopy (see Figure 1, inset).4 The PtCH
protons of the cis isomer of 3b appear also as a doublet, partly
overlapping the 195Pt satellite resonances due to the trans isomer.
Figure 2. Molecular structure of the core of the cis isomer of
[Pd{CH(CN)SO2CH(CN)}(PPh3)2] 3d showing the atom numbering
scheme. Only ipso-C of the phenyl rings are shown, and H atoms are
omitted.
1
The cyano-substituted complexes all give similar H spectro-
theoretical τ4 values of 0 and 1 for a perfect square plane and
tetrahedron, respectively]. This contrasts with the only other
structure of a palladathietane-3,3-dioxide complex 2b, where the
four-membered ring is considerably more puckered [dihedral
angle between the C−Pd−C and C−S−C planes of 30.2(2)°],
but the tetrahedral distortion of the palladium(II) center is
relatively small, with a dihedral angle of 19.09(7)° between the
P−Pd−P and C−Pd−C planes, and a τ4 parameter of 0.167. The
bulky C(O)Ph substituents in the trans isomer 2b adopt pseudo-
axial and pseudo-equatorial positions on the puckered four-
membered ring, in order to minimize steric interactions with the
PMePh2 ligands. The cyano groups of 3d have less steric bulk and
are presumably easily accommodated in either the cis or the trans
isomers. The planar four-membered ring in 3d results in eclipsing
of the S(1)−O(2) bond with the two C−CN bonds, C(1)−C(2)
and C(3)−C(4), such that the O(2)−S(1)−C(1)−C(2) and
O(2)−S(1)−C(3)−C(4) torsion angles are 11.4(3)° and 8.0(3)
°, respectively.
scopic features for the CH protons of the cis and trans isomers.
Different reaction conditions have been employed to
investigate potential changes in the isomer ratios. The reaction
between cis-[PtCl2(PPh3)2] and NCCH2SO2CH2CN was
carried out in dichloromethane solution with Ag2O as the base
(conditions that have been previously used to prepare metal-
lacyclic complexes, including metallathietane-3,3-dioxides4); the
product is easily isolated by precipitation with petroleum spirits.
When the reaction is carried out at room temperature for 1 h
using Ag2O/CH2Cl2, the isolated product contained mainly the
cis isomer, but longer reaction times gave more trans isomer.
Likewise, a shorter reflux time (10 min) using Me3N in MeOH
gave roughly equal amounts of cis and trans isomers. These
observations suggested that the cis isomer may be the kinetically
favored product and that a theoretical study to investigate the
relative stabilities of the cis and trans isomers was warranted
(vide infra).
X-ray Crystal Structure Determination. To date, there
have only been four structure determinations on metallathietane-
3,3-dioxide complexes, these being [Pt(CHPhSO2CHPh)-
(AsPh3)2] 1a,3 [Pt{CH(COPh)SO2CH(COPh)}(PPh3)2] 2a,4
[Pd{CH(COPh)SO2CH(COPh)}(PMePh2)2] 2b,4 and
[(MeOC6H3CH2NMe2)Au{CH(COPh)SO2CH(COPh)}] 4.5
Therefore, an X-ray structure was determined on a cyano-
substituted complex in order to investigate its structural features.
Suitable crystals of the triphenylphosphine−palladium complex
3d were obtained from dichloromethane−diethyl ether.
The molecular structure of the core of the complex is shown in
Figure 2, together with the atom numbering scheme, while
selected bond lengths and angles are given in Table 1. The
structure confirms the complex as a cis cyano-substituted
palladathietane-3,3-dioxide ring system; this is the first
structurally characterized example of a cis-disubstituted metal-
lathietane ring system, all previous examples being the trans
isomers.
The four-membered palladacycle is almost planar, with only a
1.05(12)° angle between the C(1)−S(1)−C(3) and C(1)−Pd−
C(3) planes. However, there is a significant distortion of the
palladium(II) center from the idealized square-planar geometry,
with an angle of 19.09(7)° between the P−Pd−P and C−Pd−C
planes. The distortion from square-planar geometry is
conveniently quantified by the τ4 parameter of Houser and co-
workers,12 which gives a value of 0.258 for 3d [compared to
The Pd−C distances of 3d [2.119(3) and 2.130(3) Å] are
similar to the Pd−C bond distances in 2b [2.148(6) and
2.122(6) Å].4 The bite angle of the NCCHSO2CHCN ligand at
palladium is 75.77(11)°, which also compares favorably with 2b
[74.7(2)°]. Likewise, the C−S−C bond angle at the sulfone
group of 3d is 95.49(13)°, similar to that of 2b [95.9(3)°].
However, the S−C−Pd bond angles in 3d [93.92(13)° and
94.81(13)°] are notably larger than those in 2b [91.1(2)° and
90.0(2)°],4 consistent with the lack of puckering in the cyano-
substituted ring.
The Pd−P bond distances of 3d [Pd−P(1) 2.3225(7) and
Pd−P(2) 2.3307(8) Å] are longer than those of 2b [2.311(2)
and 2.295(2) Å];4 however, the phosphine ligands are different
[PPh3 in 3d versus PMePh2 in 2b]. A comparison of the X-ray
structures of cis-[PtCl2(PPh3)2] (CSD refcode: BISROK)13 and
the monoclinic form of cis-[PtCl2(PMePh2)2] (CSD refcode:
BAZKUI01)14 shows that the Pt−P bonds in the PMePh2
complex are also slightly shorter [2.2458(1) and 2.2445(1) Å]
compared to the PPh3 complex [2.2647(4) and 2.2507(4) Å], so
it is not possible to obtain information on trans influences of the
C donor ligands based on structural data alone. However, from
1
31P NMR data, the value of J(PtP) for the trans isomer of 3a
(2844 Hz) is slightly larger than that of the corresponding
triphenylphosphine complex [Pt{CH(COPh)SO2CH(COPh)}-
(PPh3)2] 2a (2817 Hz),4 indicating that the CH(CN) group has
a slightly smaller trans influence.15
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for [Pd{CH(CN)SO2CH(CN)}(PPh3)2] 3d with Standard Uncertainty
Values in Parentheses
Pd−C(1)
Pd−P(1)
S(1)−O(2)
S(1)−C(3)
C(1)−C(2)
C(3)−C(4)
C(1)−Pd−C(3)
C(1)−Pd−P(2)
O(1)−S(1)−O(2)
O(1)−S(1)−C(3)
O(1)−S(1)−C(1)
C(2)−C(1)−S(1)
S(1)−C(1)−Pd
C(4)−C(3)−S(1)
S(1)−C(3)−Pd
2.130(3)
2.3225(7)
1.442(3)
1.754(3)
1.430(4)
1.418(5)
75.77(11)
93.16(8)
119.15(17)
107.83(15)
109.51(16)
114.4(2)
93.92(13)
115.6(2)
94.81(13)
Pd−C(3)
Pd−P(2)
S(1)−O(1)
S(1)−C(1)
C(2)−N(1)
C(4)−N(2)
C(3)−Pd−P(1)
P(1)−Pd−P(2)
O(2)−S(1)−C(3)
O(2)−S(1)−C(1)
C(1)−S(1)−C(3)
C(2)−C(1)−Pd
N(1)−C(2)−C(1)
C(4)−C(3)−Pd
N(2)−C(4)−C(3)
2.119(3)
2.3307(8)
1.443(3)
1.771(3)
1.155(4)
1.148(5)
92.77(8)
101.11(3)
111.73(15)
110.53(15)
95.49(13)
122.0(2)
179.2(3)
103.5(2)
176.5(4)
Figure 3. A view in projection down the a axis of the unit cell contents for the cis isomer of [Pd{CH(CN)SO2CH(CN)}(PPh3)2] 3d. Molecules
assemble into supramolecular layers in the ac plane via C−H···O (orange dashed lines), C−H···N (blue), and C−H···π (not shown) interactions. Layers
are connected along the b axis via C−H···π (purple dashed lines).
The crystal structure of 3d is stabilized by a combination of C−
H···O, C−H···N, π···π, and C−H···π interactions (refer to the
Experimental Section). The C−H···O and C−H···N contacts
serve to link molecules into a supramolecular array in the ac
plane; additional stabilization to the layers is afforded by C−
H···π interactions. Phenyl rings lie to either side of the layers and
interdigitate with adjacent layers along the b direction, allowing
for the formation of C−H···π interactions. A view of the unit cell
contents for 3d is given in Figure 3.
Theoretical Study. The molecular structure of both cis and
trans conformers of complex 3d, namely, cis-[Pd{CH(CN)-
SO2CH(CN)}(PPh3)2] 3tc and trans-[Pd{CH(CN)SO2CH-
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Figure 4. Optimized geometries of the cis and trans conformers of the actual complex [Pd{CH(CN)SO2CH(CN)}(PPh3)2], 3tc and 3tt, and the model
complex [Pd{CH(CN)SO2CH(CN)}(PH3)2], 3tcm and 3ttm.
(CN)}(PPh3)2] 3tt, have been optimized at the density
functional level of theory using the B3LYP functional. Both
conformers are minima in the potential surface of the molecule,
as the calculation of the Hessian gave no imaginary frequencies.
Figure 4 shows the optimized structures adopting the C1
symmetry point group with an essentially planar [PdCSC]
metallathietane ring. Selected calculated bond lengths and angles
are given in Table 2; experimental bond lengths determined by
X-ray structure analysis for the cis complex 3d are also given for
comparison. An overall agreement has been found between the
calculated and experimental structures of the cis complex. The
Pd−P bond lengths are longer than the experimental values. This
lengthening could be attributed to the fact that, according to
previous theoretical studies, the lengths of metal−ligand bonds
tend to become shorter in the solid state because of interatomic
interactions.16,17 The differences between calculated and
experimental bond angles are not very large and need not be
further discussed. According to the calculation in the gas phase,
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reoptimization of the model complexes 3tcm and 3ttm in the
presence of the methanol solvent starting from the geometries
calculated in the gas phase, the energy difference has been found
to be equal to 0.2 kcal/mol with the trans conformer being again
more stable. The energy difference in the presence of
dichloromethane has been calculated to be equal to that found
in the gas state (0.4 D). Thus, the isolation of the cis or trans
isomer could be attributed to small differences in the reaction and
precipitation conditions. Finally, there are no major differences
between the gas-phase structures and those calculated in the
presence of the solvents. The largest deviation of bond distances
is about 0.02 Å, while that of bond angles is about 2°.
Table 2. Selected Calculated Bond Lengths (Å) and Angles
(deg) for Cis and Trans Conformers of the Actual Complex
[Pd{CH(CN)SO2CH(CN)}(PPh3)2], 3tc and 3tt, and the
Model Complex [Pd{CH(CN)SO2CH(CN)}(PH3)2], 3tcm
ab
,
and 3ttm
c
3tc
3tcm
exptl
3tt
3ttm
Pd−P(1)
Pd−P(2)
Pd−C(1)
Pd−C(2)
S(1)−O(1)
S(1)−O(2)
S(1)−C(1)
S(1)−C(3)
C(1)−C(2)
C(3)−C(4)
C(1)−H(1)
C(3)−H(2)
C(2)−N(1)
C(4)−N(2)
2.380
2.367
2.128
2.154
1.475
1.466
1.808
1.812
1.435
1.433
1.090
1.090
1.166
1.165
74.8
2.395
2.395
2.121
2.121
1.467
1.464
1.820
1.820
1.434
1.434
1.092
1.092
1.165
1.165
75.5
2.330
2.322
2.119
2.130
1.442
1.441
1.754
1.771
1.418
1.430
2.383
2.356
2.147
2.145
1.468
1.471
1.816
1.808
1.432
1.434
1.090
1.089
1.166
1.166
74.4
2.396
2.396
2.118
2.118
1.465
1.465
1.820
1.820
1.434
1.434
1.092
1.092
1.165
1.165
76.0
CONCLUSIONS
■
A series of new platinum(II) and palladium(II) metallathietane-
3,3-dioxide complexes bearing cyano ring substituents have been
synthesized for the first time and shown by NMR spectroscopy to
consist of a mixture of cis and trans isomers, with the first crystal
structure of a cis isomer of such metallacycles being reported.
The energies of the cis and trans isomers were found to be very
similar in this system.
1.147
1.151
75.8
C(1)−Pd−C(3)
C(1)−Pd−P(2)
C(3)−Pd−P(1)
P(1)−Pd−P(2)
C(2)−C(1)−Pd
C(4)−C(3)−Pd
S(1)−C(1)−Pd
S(1)−C(3)−Pd
O(1)−S(1)−O(2)
O(1)−S(1)−C(1)
O(2)−S(1)−C(1)
O(1)−S(1)−C(3)
O(2)−S(1)−C(3)
C(2)−C(1)−S(1)
C(4)−C(3)−S(1)
N(1)−C(2)−C(1)
N(2)−C(4)−C(3)
92.3
92.5
92.8
93.8
76.0
92.3
92.5
93.1
92.7
92.3
EXPERIMENTAL SECTION
■
101.0
107.9
116.0
94.4
99.4
101.1
103.5
122.0
94.8
101.9
112.0
107.4
94.7
99.7
General. 1H and 31P{1H} NMR spectra were recorded at 300.13 and
121.5 MHz, respectively, on a Bruker AC300P spectrometer in CDCl3,
unless otherwise stated. Elemental analyses were obtained by the
Campbell Microanalytical Laboratory at the University of Otago,
Dunedin, New Zealand. Infrared spectra were recorded as KBr disks on a
PerkinElmer Spectrum 100 FT-IR spectrophotometer. Melting points
were determined on a Reichert-Jung hot-stage apparatus and are
uncorrected.
112.3
112.3
95.8
111.8
111.8
96.2
93.4
95.8
93.9
94.9
96.2
120.5
106.4
113.5
107.0
113.6
115.9
115.5
176.8
177.9
121.7
109.2
110.7
109.2
110.7
116.6
116.6
175.5
119.2
107.8
111.8
109.5
110.5
115.6
114.4
176.5
179.2
120.6
111.0
109.8
112.9
107.1
113.2
113.8
178.0
177.2
121.8
108.8
110.9
110.9
108.8
117.0
117.0
175.7
175.7
ESI mass spectra were recorded on a (low-resolution) VG Platform II
instrument, or on a (high-resolution) Bruker MicrOTOF instrument,
the latter calibrated using aqueous sodium formate solution. Samples
(dissolved in a small quantity of dichloromethane) were diluted (to ca.
0.1 mg mL−1) with methanol and centrifuged prior to analysis. In some
cases, a drop of dilute aqueous NaCl or NH4[HCO2] was added as an
ionization aid. Ion identification was facilitated by comparison of
observed and calculated isotope distribution patterns, the latter obtained
from the Isotope program,18 or from proprietary instrument-based
software.
175.5
b
a
Numbering scheme as in Figure 4. Phenyl hydrogens not shown for
c
clarity. Experimental data for complex 3d.
The complexes [PtCl2(cod)],19 [PdCl2(cod)],20 and
[PdCl2(bipy)]21 were prepared by the literature procedures. The
complexes [PtCl2L2] were generated by addition of 2 mol equiv of L to a
stirred suspension of [PtCl2(cod)] in methanol, followed by stirring for
10 min.22 The palladium analogues were prepared in the same way from
[PdCl2(cod)] and the phosphine in dichloromethane, followed by
precipitation with petroleum spirits. NCCH2SO2CH2CN was obtained
from Lancaster Synthesis, or was prepared by the literature procedure,23
and PhC(O)CH2SO2CH2C(O)Ph was prepared as described pre-
viously.4 Aqueous trimethylamine solution (30%) was used as supplied
by BDH. PPh3 (BDH) was used as supplied, whereas dppe24 and dppf25
were prepared by the literature procedures. All reactions were carried
out in laboratory reagent grade methanol without further purification or
attempts to exclude air or moisture.
Synthesis of [Pt{CH(COPh)SO2CH(COPh)}(PPh3)2] 2a. The
complex has been previously synthesized from cis-[PtCl2(PPh3)2] and
PhC(O)CH2SO2CH2C(O)Ph using Ag2O in CH2Cl2.4 A suspension of
cis-[PtCl2(PPh3)2] (356 mg, 0.462 mmol) and PhC(O)CH2SO2CH2C-
(O)Ph (142 mg, 0.470 mmol) in methanol (30 mL) with trimethyl-
amine (1 mL) was refluxed with stirring for 3 h to give a white
suspension in a cream solution. After cooling to room temperature, the
product was filtered, washed with cold methanol (5 mL), and dried
under vacuum to give the product 2a as a white solid (318 mg, 69%) that
was identified by 1H and 31P{1H} NMR spectroscopy as the pure trans
isomer.
the two conformers have actually the same energy. The trans
isomer is found to be the global minimum, whereas the cis
isomer, being experimentally isolated, has been found to be only
0.1 kcal/mol higher in energy.
To explore a possible effect of the steric hindrance of the bulky
phosphine ligands to the cis−trans energy difference, the
molecular structure of both cis and trans conformers of a
model complex, where the PPh3 phosphine ligands have been
replaced by PH3, namely, cis-[Pd{CH(CN)SO2CH(CN)}-
(PH3)2] 3tcm and trans-[Pd{CH(CN)SO2CH(CN)}(PH3)2]
complex 3ttm, has been optimized at the same level of theory.
Although the optimizations had no symmetry constraints, the cis
conformer adopts a planar Cs geometry. The actual symmetry of
the calculated trans conformer is C2 with a small deviation from
planarity, with the angle between the [PdCSC] metallathietane
ring and the [PPdP] plane being equal to 3.9°. The cis-trans
energy difference is very small and in the case of the model
complex 0.4 kcal/mol in favor of the trans isomer.
As the dipole moment of the cis isomer, 3tcm, in the gas phase
(12.2 D) was predicted to be a little larger than that of the trans
isomer 3ttm (11.4 D), one expects that a polar solvent, such as
methanol, would stabilize the cis isomer. After a full
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Organometallics
Article
Synthesis of [M{CH(CN)SO2CH(CN)}L2] − General Method. To
a stirred mixture of [MCl2L2] (either preformed or generated in situ)
and 1 mol equiv of NCCH2SO2CH2CN in methanol (30 mL) was added
aqueous trimethylamine solution (1 mL, excess), and the mixture was
refluxed for 30 min. Water (50 mL) was added, and the product was
isolated by filtration, washed with cold water (10 mL) and diethyl ether
(10 mL), and dried under vacuum.
C14H10N4O2PdS (Mr 404.75) requires C, 41.5; H, 2.5; N, 13.8%. The
complex was too insoluble to record NMR or ESI mass spectra.
X-ray Crystal Structure Determination of [Pd{CH(CN)SO2CH-
(CN)}(PPh3)2] 3d. Colorless crystals of 3d were grown by slow diffusion
of diethyl ether into a dichloromethane solution of the complex at room
temperature. A crystal having dimensions of 0.15 × 0.25 × 0.30 mm was
selected for the study. Data were collected at 103(2) K on a Rigaku
AFC12/SATURN724 diffractometer using Mo Kα radiation so that θmax
= 27.5°. The data set was reduced using CrystalClear26 and corrected for
absorption effects.27 The structure was solved by direct methods with
SHELXS-9728 and refinement (anisotropic displacement parameters,
hydrogen atoms in the riding model approximation, and a weighting
Synthesis of [Pt{CH(CN)SO2CH(CN)}(PPh3)2] 3a. [PtCl2(cod)]
(200 mg, 0.535 mmol) with triphenylphosphine (287 mg, 1.10 mmol)
and NCCH2SO2CH2CN (77 mg, 0.535 mmol) gave 3a (398 mg, 86%)
as a white solid. mp 285−286 °C. Found: C, 56.0; H, 3.6; N, 3.4.
C40H32N2O2P2PtS (Mr 861.25) requires C, 55.8; H, 3.7; N, 3.3%. High-
resolution ESI MS: [M + H]+ (m/z 862.184, calculated 862.138), [M +
Na]+ (m/z 884.166, calculated 884.120). Low-resolution ESI MS: [M +
NH4]+ (m/z 879, 100%), [2M + NH4]+ (m/z 1741, 70%). MALDI-
TOF MS: [M + H]+ (m/z 862), [M + Na]+ (m/z 884). IR ν(CN): 2218
(m) cm−1, ν(SO2) 1312 (vs) and 1129 (vs) cm−1. 31P{1H} NMR: trans
2
2
scheme of the form w = 1/[σ2(Fo ) + (0.037P)2 + 2.594P] for P = (Fo
+
2Fc2)/3) was on F2 by means of SHELXL-97.26 The maximum residual
electron density peak (1.71 e Å−3) was located in the vicinity of the S(1)
atom and is consistent with an alternative site for the O(2) atom being
1.50 Å from S(1) and 1.21 Å from O(2). Despite the low temperature of
the analysis, high thermal motion is also noted in some of the other
positions, in particular, for the N(1) atom. This may indicate an
alternate conformation for the four-membered ring, but none was
discerned. Crystallographic data and final refinement details are given in
Table 3. Figures 2 and 3 were drawn with DIAMOND,29 using arbitrary
spheres. Data manipulation and interpretation were with WinGX30 and
PLATON.31
1
isomer (major), δ 13.5 [s, J(PtP) 2844]; cis isomer (minor), δ 13.4
[1J(PtP) 2854]. 1H NMR: δ 7.65−7.28 (m, PPh3) cis isomer 3.14 [d, br,
J(PH) 4.9, 2J(PtH) 76] and trans isomer 3.06 [d, br, J(PH) 0.9, 2J(PtH)
77].
Synthesis of [Pt{CH(CN)SO2CH(CN)}(dppf)] 3b. [PtCl2(cod)]
(103 mg, 0.275 mmol) with dppf (153 mg, 0.276 mmol) and
NCCH2SO2CH2CN (40 mg, 0.278 mmol) gave 3b as a yellow solid
(184 mg, 75%). Found: C, 50.2; H, 3.3; N, 3.1. C38H30N2FeO2P2PtS (Mr
891.58) requires C, 51.2; H, 3.4; N, 3.1%. MALDI TOF MS: [M + H]+
(m/z 892), [M + Na]+ (m/z 914). High-resolution ESI MS: [M + H]+
(m/z 892.101, calculated 892.058), [M + Na]+ (m/z 914.084, calculated
914.040). Low-resolution ESI MS: [M + NH4]+ (m/z 909, 100%), [2M
+ NH4]+ (m/z 1801, 30%). IR ν(CN): 2218 (m) cm−1, ν(SO2) 1311
(vs) and 1126 (vs) cm−1. 31P{1H} NMR: trans isomer (major), δ 13.9 [s,
1J(PtP) 2912]; cis isomer (minor), δ 13.8 [1J(PtP) ca. 2940]. Selected
1H NMR data: trans isomer (major) δ 2.87 [d, J(PH) 1.2, 2J(PtH) 77];
cis isomer (minor), δ 3.07 [d, 3J(PH) 4.9, 2J(PtH) 78].
Synthesis of [Pt{CH(CN)SO2CH(CN)}(dppe)] 3c. [PtCl2(dppe)]
(130 mg, 0.196 mmol) with NCCH2SO2CH2CN (29 mg, 0.201 mmol)
gave 3c (86 mg, 60%) as a white powder. Found: C, 48.3; H, 3.4; N, 3.8.
C30H26N2O2P2PtS (Mr 735.61) requires C, 49.0; H, 3.6; N, 3.8%. High-
resolution ESI MS: [M + H]+ (m/z 736.128, calculated 736.091), [M +
Na]+ (m/z 758.111, calculated 758.073). Low-resolution ESI MS: [M +
NH4]+ (m/z 753, 100%), [2M + NH4]+ (m/z 1488, 15%). IR ν(CN):
2213 (m) cm−1, ν(SO2) 1312 (vs) and 1124 (vs) cm−1.
Synthesis of [Pd{CH(CN)SO2 CH(CN)}(PPh3 )2 ] 3d.
[PdCl2(PPh3)2] (200 mg, 0.285 mmol) with NCCH2SO2CH2CN (42
mg, 0.292 mmol) gave 3d (183 mg, 83%) as a white powder. Found: C,
62.1; H, 4.1; N, 3.6. C40H32N2O2P2PdS (Mr 773.14) requires C, 62.1; H,
4.2; N, 3.6%. High-resolution ESI MS: [M + H]+ (m/z 773.117,
calculated 773.078), [M + Na]+ (m/z 795.102, calculated 795.060).
Low-resolution ESI MS: [M + NH4]+ (m/z 790, 100%), [2M + NH4 −
PPh3]+ (m/z 1302, 10%), [2M + NH4]+ (m/z 1564, 55%). IR ν(CN):
2203 (m) cm−1, ν(SO2) 1310 (vs) and 1124 (vs) cm−1. 31P{1H} NMR:
trans isomer (major), δ 25.6 (s); cis isomer (minor), δ 25.4 (s). Selected
1H NMR data: trans isomer (major) δ 2.70 (m); cis isomer (minor), δ
2.78 [d, 3J(PH) 3.1].
Synthesis of [Pd{CH(CN)SO2CH(CN)}(dppe)] 3e. [PdCl2(dppe)]
(255 mg, 0.443 mmol) with NCCH2SO2CH2CN (64 mg, 0.444 mmol)
gave 3e as a white solid (266 mg, 93%). Found: C, 55.4; H, 4.1; H, 4.3.
C30H26N2O2P2PdS (Mr 646.98) requires C, 55.7; H, 4.1; N, 4.3%.
MALDI-TOF MS: [M + H]+ (m/z 647), [M + Na]+ (m/z 669). High-
resolution ESI MS: [M + H]+ (m/z 647.061, calculated 647.031), [M +
Na]+ (m/z 669.045, calculated 669.013). Low-resolution ESI MS: [M +
NH4]+ (m/z 664, 100%), [2M + NH4]+ (m/z 1312, 30%). IR ν(CN):
2202 (m) cm−1, ν(SO2) 1309 (vs) and 1121 (vs) cm−1. 31P{1H} NMR:
trans isomer (major), δ 50.7 (s); cis isomer (minor), δ 51.2 (s). Selected
1H NMR data: 2.67−2.31 (m, CH2 of dppe); trans isomer (major) δ
3.01 [d, br, J(PH) 3.7]; cis isomer (minor), δ 3.16 [d, J(PH) 5.2].
Synthesis of [Pd{CH(CN)SO2CH(CN)}(bipy)] 3f. [PdCl2(bipy)]
(158 mg, 0.474 mmol) with NCCH2SO2CH2CN (69 mg, 0.479 mmol)
gave 3f as a cream solid (155 mg, 81%). Found: C, 41.0; H, 2.3; N, 13.4.
Table 3. Crystallographic Details for 3d
formula
molecular wt
T/K
C40H32N2O2P2PdS
773.08
103(2)
cryst syst
space group
a (Å)
triclinic
P1
̅
10.8099(18)
12.655(2)
13.609(2)
103.769(2)
105.322(3)
93.471(2)
1728.7(5)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
D
calc (g cm−3
)
1.485
No. reflns meas.
13 737
No. unique reflns
No. observed reflns [I > 2σ(I)]
R1 [I > 2σ(I)]
7877
7436
0.041
wR2 (all data)
0.095
Intermolecular Interactions in the Crystal Structure of 3d.
Interactions Leading to the Supramolecular Array. C(10)−H-
(10)···O(1)i = 2.30 Å, C(10)···O(1)i = 3.206(4) Å, with angle at
H(10) = 160°; C(31)−H(31)···N(1)ii = 2.57 Å, C(31)···N(1)ii
=
3.444(5) Å, with angle at H(31) = 154°; C(33)−H(33)···N(2)iii = 2.41
Å, C(33)···N(2)iii = 3.277(5) Å, with angle at H(33) = 151°; C(3)−
H(3)···Cg(C17−C22) = 2.81 Å, C(3)···Cg(C17−C22) = 3.653(3) Å,
with angle at H(3) = 143°.
Interactions Linking the Supramolecular Layers. C(25)−H-
(25)···Cg(C35−C40)iv = 2.50 Å, C(25)···Cg(C35−C40)iv = 3.389(3)
Å, with angle at H(25) = 156°; C(13)−H(13)···Cg(C17−C22)v = 2.95
Å, C(13)···Cg(C17−C22)v = 3.842(3) Å, with angle at H(25) = 157°.
Symmetry operations - i: 1 − x, 1 − y, 2 − z; ii: 1 − x, 1 − y, 1 − z; iii: 1 +
x, y, z; iv: −x, −y, 1 − z; v: −x, −y, 2 − z.
Computational Details. For the DFT calculations, the hybrid
B3LYP method was applied with Becke’s three-parameter functional32
and the nonlocal correlation provided by the LYP expression.33 The
geometries of all the studied complexes were fully optimized using
analytical gradient techniques, and a frequency calculation after each
geometry optimization ensured that the calculated structures are real
minima or transition states in the potential energy surface of the
4668
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Organometallics
Article
molecules. Calculations have been carried out on the actual complexes
and on model complexes where the bulky substituents of the phosphine
ligands have been replaced with hydrogen atoms. For the Pd atom, we
used the LANL2DZ small-core relativistic effective core potential of Hay
and Wadt34 and the “Basis set II” (BS II) of Frenking and co-workers,35
which is that of Hay and Wadt contracted to [441/2111/31]. For the
ligand atoms, we used the standard 6-31G(d,p),36−39 except for the
atoms of the phosphines’ substituents, where no polarization functions
were used. These basis sets have been used in our previous theoretical
study of related four-membered palladacycles.8 The calculations in the
presence of solvent were carried out using the polarized continuum
model (PCM) of Tomasi and co-workers40,41 with acetone (ε = 20.7)
and dichloromethane (ε = 8.93). All calculations were carried out using
the Gaussian 03W, version 6.0, system of programs.42
(22) Oliver, D. L.; Anderson, G. K. Polyhedron 1992, 11, 2415.
(23) McCormick, J. E.; McElhinney, R. S. J. Chem. Soc., Perkin Trans. 1
1972, 1335.
(24) Chatt, J.; Hart, F. A. J. Chem. Soc. 1960, 1378.
(25) Bishop, J. J.; Davison, A.; Katcher, M. L.; Lichtenberg, D. W.;
Merrill, R. E.; Smart, J. C. J. Organomet. Chem. 1971, 27, 241.
(26) CrystalClear; Molecular Structure Corporation: The Woodlands,
TX and Rigaku Corporation: Tokyo, Japan, 2005.
(27) Higashi, T. ABSCOR; Rigaku Corporation: Tokyo, Japan, 1995.
(28) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(29) Brandenburg, K. DIAMOND; Crystal Impact GbR: Bonn,
Germany, 2006.
(30) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(31) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
(32) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(33) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(34) Hay, P. J.; Wadt, W. R. J. Phys. Chem. 1985, 82, 299.
AUTHOR INFORMATION
Corresponding Author
*Fax: +64 7 838 4219. E-mail: w.henderson@waikato.ac.nz.
Notes
■
(35) Frenking, G.; Antes, I.; Bohme, M.; Dapprich, S.; Ehlers, A. W.;
̈
Jonas, V.; Neuhaus, A.; Otto, M.; Stegmann, R.; Veldkamp, A.;
Vyboishchikov, S. F. In Reviews in Computational Chemistry; Lipkowitz,
K. B., Boyd, D. B., Eds.; VCH: New York, 1996; Vol. 8, p 63.
(36) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,
2257.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(37) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon,
M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654.
(38) Hariharan, P. C.; Pople, J. A. Chem. Phys. Lett. 1972, 16, 217.
(39) Curtis, L. A.; Redfern, P. C.; Raghavachari, K.; Rassolov, V.; Pople,
J. A. J. Chem. Phys. 1999, 110, 4703.
We thank the University of Waikato for financial support of this
work, Pat Gread for mass spectrometry assistance, and Robert
Appleby for recording the infrared spectra. Support from the
Ministry of Higher Education, Malaysia, High-Impact Research
scheme (UM.C/HIR/MOHE/SC/12) is also gratefully ac-
knowledged. W.H. thanks Oguejiofo T. Ujam for recording some
of the NMR spectra.
(40) Cances
3032.
̀
, E.; Mennucci, B.; Tomasi, J. J. Chem. Phys. 1997, 107,
(41) Barone, V.; Cossi, M.; Tomasi, J. J. Chem. Phys. 1997, 107, 3210.
(42) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratman, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.;
Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.;
Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.;
Salvador, P.; Dannenberg, J. J.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul,
A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.;
Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.;
Replogle, E. S.; Pople, J. A. Gaussian 03; Gaussian Inc.: Pittsburgh, PA,
2003.
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