A bisphosphonite calix[5]arene ligand that stabilizes η6 arene coordination to palladium

Article abstract of DOI:10.1039/c2dt30491k

Treatment of a bis(phenylphosphonite)calix[5]arene ligand with either palladium(ii) chloride or 1,5-cyclooctadieneplatinum(ii) chloride yields square planar metal complexes in which the two phosphorus atoms bind cis to the MCl₂ moiety (M = Pd, Pt). Chloride was removed from the palladium complex to open a coordination site at the metal for catalysis. The chloride removal resulted in a rare and unexpected η⁶ coordination of an arene to the metal. The reaction is reversible upon addition of tetra-n-butyl ammonium chloride.

Full text of DOI:10.1039/c2dt30491k

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PAPER
A bisphosphonite calix[5]arene ligand that stabilizes η6 arene coordination to
palladium†
Beatriz E. Rios,a Paul Sood,a Yaroslav Klichko,a Mohan Koutha,a Douglas Powellb and Michael Lattman*a
Received 1st March 2012, Accepted 2nd April 2012
DOI: 10.1039/c2dt30491k
Treatment of a bis(phenylphosphonite)calix[5]arene ligand with either palladium(II) chloride or 1,5-
cyclooctadieneplatinum(II) chloride yields square planar metal complexes in which the two phosphorus
atoms bind cis to the MCl2 moiety (M = Pd, Pt). Chloride was removed from the palladium complex to
open a coordination site at the metal for catalysis. The chloride removal resulted in a rare and unexpected
η6 coordination of an arene to the metal. The reaction is reversible upon addition of tetra-n-butyl
ammonium chloride.
conformational change of the calixarene accounts for an even
greater variation in P⋯M distance (2.90 to 3.69 Å).
Introduction
Trivalent phosphines and phosphites are some of the most
common ligands in transition metal chemistry, particularly useful
for their applications in catalysis. Other trivalent phosphorus
ligands have been less studied. Over the past few years, reports
on the use of phosphonite [RP(OR)2] ligands suggest that these
might be increasingly important in catalytic reactions such as
hydroformylations,1 isomerizations,2 cross couplings in ionic
liquids,3 phase transfer hydrogenations,4 and azide alkyne
cycloadditions,5 as well as applications in OLED technologies.6
Our current work with bisphosphonite calix[5]arene complexes
of palladium(II) and platinum(II) broadens the scope of these
ligands to include isolation and structural characterization of a
stable η6 arene complex of palladium(II). This is a rare coordi-
nation mode for this metal and, to our knowledge, no such
Results and discussion
complex of palladium(II) has been characterized by X-ray diffrac-
tion until now.
Investigations of metal coordination complexes of the bisphos-
phonite 3 are being carried out to determine utility of the ligand
in catalysis. The X-ray structure of 3 shows it to be in an
approximate cone conformation; the phosphorus lone pairs point
“inside” the cavity7 allowing for bidentate coordination of the
phosphorus atoms to transition metals.
Several calix[5]arene ligands containing one and two phos-
phorus atoms have been reported (Fig. 1).7,8 The calix[5]arene
provides a larger cavity than the common calix[4]arene, while
retaining constraint unavailable in larger calixarenes. The series
of complexes, illustrated by structure A, demonstrate that this
unique combination of “constraint and flexibility” leads to a sig-
nificant variation in ligand–metal interaction. For example,
P⋯M (M = W)8 distances range from 2.74 to 3.15 Å, depending
on the choice of ligand Ln. In another study (M = Ti),9
a
aDepartment of Chemistry, Southern Methodist University, Dallas, Texas
75275, USA. E-mail: mlattman@smu.edu; Fax: +214-768-4089
bDepartment of Chemistry and Biochemistry, University of Oklahoma,
Norman, OK 73019, USA
†Electronic supplementary information (ESI) available: NMR spectra of
3·Pd(O3SCF3)2 and details of crystallography (pdf format), and crystal-
lographic data in cif format. CCDC 836670, 836671 and 869888. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c2dt30491k
Fig. 1 Phosphorus-based calix[5]arene ligands.
Dalton Trans., 2012, 41, 6677–6682 | 6677
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Scheme 1 Synthesis of bisphosphonite calix[5]arene complexes of
square planar palladium and platinum.
Treatment of 3 with palladium(II) chloride (Scheme 1) in THF
1
yields 3·PdCl2 in 78% isolated yield. The H NMR spectrum of
the product shows that the overall Cs symmetry of the ligand is
retained in the complex: three resonances are observed for the
tert-butyl groups (in a 2 : 2 : 1 ratio) and six doublets (due to
2
geminal JHH coupling) are found for the bridging methylene
groups (in a 2 : 2 : 2 : 2 : 1 : 1 ratio). The 31P NMR resonance of
3·PdCl2 at δ 116 is shifted upfield by 38 ppm relative to the free
ligand. An X-ray crystal structure of the complex was obtained
(Fig. 2), and selected distances and angles are shown in Table 1.
Both phosphorus atoms are bound to palladium, with the metal
in a square planar geometry [sum of the cis bond angles around
Pd is 359.6(1)°]. The Pd–P and Pd–Cl bond lengths are in usual
ranges, and the P–Pd–P bite angle is 102.8°. The calix[5]arene
backbone conformation is best described as a “flattened” cone.
One distinctive feature of this complex is the close approach of
the oxygen of the free phenolic group to the metal (O1⋯Pd dis-
tance of 2.80 Å). A similar platinum complex 3·PtCl2 is
obtained in an analogous manner (Scheme 1) using 1,5-cyclo-
octadieneplatinum(II) chloride. The X-ray structure of this
complex is shown in Fig. 2. The geometry of the platinum
complex is very similar to that of palladium with an almost iden-
tical P–Pt–P bite angle. Other bond distances and angles show
only slight differences, and the O1⋯M distance is about 0.1 Å
longer in the platinum complex. The crystals of 3·PdCl2 and
3·PtCl2 are isomorphous.
Fig. 2 Molecular structures of the complexes 3·PdCl2 and 3·PtCl2.
Thermal ellipsoids for the labeled atoms are shown at 50% probability.
The calixarene ligand backbone is in wireframe. Hydrogen atoms are
omitted for clarity.
Table 1 Selected distances (Å) and angles (°) for 3·PdCl2 and 3·PtCl2
3·PdCl2
3·PtCl2
Pd(1)–P(1)
Pd(1)–P(2)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
2.2452(16)
2.2384(16)
2.3342(15)
2.3551(15)
Pt(1)–P(1)
Pt(1)–P(2)
Pt(1)–Cl(1)
Pt(1)–Cl(2)
2.2255(10)
2.2168(9)
2.3400(9)
2.3600(10)
The close proximity of the hydroxyl oxygen to the metal in
these complexes suggests an opportunity for oxygen (O1) to
stabilize an available coordination site suitable for catalysis.
Such a site might be obtained by removal of chloride. Treatment
of 3·PdCl2 with one equivalent of silver trifluoromethanesulfo-
nate consumes half of the starting material; addition of a second
equivalent completely consumes the starting material to give
3·Pd(O3SCF3)2 (Scheme 2). The 31P NMR resonance of the
product at δ 122 is shifted slightly downfield compared to
P(2)–Pd(1)–P(1)
P(2)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
P(2)–Pd(1)–Cl(2)
P(1)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–Cl(2)
102.82(6)
171.68(6)
82.18(6)
82.81(6)
173.08(5)
91.77(6)
P(2)–Pt(1)–P(1)
P(2)–Pt(1)–Cl(1)
P(1)–Pt(1)–Cl(1)
P(2)–Pt(1)–Cl(2)
P(1)–Pt(1)–Cl(2)
Cl(1)–Pt(1)–Cl(2)
102.61(3)
171.80(3)
83.75(3)
84.42(3)
172.32(3)
88.97(3)
Pd(1)⋯O(1)
2.803(4)
Pt(1)⋯O(1)
2.919(3)
1
3·PdCl2. While the H NMR spectrum of this product is still
consistent with an overall Cs symmetry, two peaks appear at
unexpected chemical shifts, and both are due to protons on the
free phenolic ring. There is an upfield shift of the resonance of
the t-butyl protons from δ 1.44 in 3·PdCl2 to −0.07 in 3·Pd
(O3SCF3)2, and an upfield shift from δ 7.28 to 5.90 of the reson-
ance due to the aromatic protons. In addition, this latter
resonance is split into a triplet due to phosphorus coupling
(JPH = 5 Hz).
The X-ray structure of 3·Pd(O3SCF3)2 (Fig. 3) indicates that
both chlorides have been removed. Instead of the hydroxyl
oxygen binding to the metal, the arene of the free phenolic
group π-bonds to palladium in an η6 coordination mode leading
to an 18-electron complex, an unusual count for palladium(II).
The upfield shift of the aryl proton resonance is expected as a
result of this coordination, and the observed three-bond P–H
coupling is reasonable. Because of the arene binding, the t-butyl
6678 | Dalton Trans., 2012, 41, 6677–6682
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Table 2 Selected distances (Å) and angles (°) for 3·Pd(O3SCF3)2
Pd(1)–P(1)
Pd(1)–P(2)
Pd(1)–C(1)
Pd(1)–C(2)
Pd(1)–C(3)
Pd(1)–C(4)
Pd(1)–C(5)
Pd(1)–C(6)
C(1)–C(2)
C(1)–C(6)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
2.263(6)
2.262(6)
2.433(19)
2.381(18)
2.396(18)
2.43(2)
2.367(18)
2.396(18)
1.38(2)
1.37(2)
1.39(2)
1.40(2)
1.41(2)
1.44(2)
P(2)–Pd(1)–P(1)
97.7(2)
Scheme 2 Dechlorination of 3·PdCl2.
deviations in this structure are larger than in the other two struc-
tures due to poorer crystal quality (see Experimental). Neverthe-
less, these values are within previously reported π-bonded arene
Pd–C distances of lower hapticity. For example, an η3-bound
mesitylene shows Pd–C bonding distances of 2.33–2.45 Å;14 an
η5-bound 2,4,6-trimethylphenoxide shows Pd–C bonding dis-
tances of 2.22–2.47 Å.16 Another significant structural feature is
found at the phosphorus atoms. The P–Pd–P bite angle in 3·Pd
(O3SCF3)2 is 98° (5° smaller than in 3·PdCl2), and the phospho-
nite phenyl rings are almost parallel. An interplanar distance of
about 3.3 Å and slightly offset centroids with a distance of
3.55 Å, indicate π–π stacking in the dication.19 This stacking is
not present in 3·PdCl2, since the phenyl rings are too far apart
(centroid to centroid distance of 6.26 Å). The π complex is air
stable at room temperature in the solid-state and in dichloro-
methane solution. The complex remains stable in solution after
addition of diethyl ether, ethanol and methanol, but it decom-
poses upon the addition of water.
Fig. 3 Molecular structure of the metal dication of 3·Pd(O3SCF3)2.
Thermal ellipsoids for the labeled atoms are shown at 50% probability.
The calixarene ligand backbone is in wireframe. Hydrogen atoms are
omitted for clarity. Not shown is a hydrogen bonding interaction
between the hydroxyl group (O1) and the oxygen of a trifluoromethane-
sulfonate group (oxygen⋯oxygen distance of 2.62 Å).
The conversion of 3·PdCl2 to 3·Pd(O3SCF3)2 is reversible.
Addition of tetra-n-butylammonium chloride to a solution of
3·Pd(O3SCF3)2 in dichloromethane forms 3·PdCl2 (Fig. 4).
Subsequent addition of silver trifluoromethanesulfonate regener-
ates 3·Pd(O3SCF3)2.
The reaction of 3·PtCl2 with two equivalents of silver trifluoro-
methanesulfonate is more complex and, as yet, we have not fully
characterized the products. One of the products does appear to
be the platinum analog of 3·Pd(O3SCF3)2, judging by a large
group on that ring is now positioned “inside” the calixarene
cavity and shielded by the π systems of the surrounding calixar-
ene aryl groups. This results in the large upfield shift of this res-
1
1
onance in the H NMR spectrum.10 [Not shown in Fig. 3 is a
upfield shift of one of the t-butyl groups in the H NMR spec-
trum. However, this is not the main product of the reaction.20
hydrogen bonding interaction between the hydroxyl group
(O1) and the oxygen of a trifluoromethanesulfonate group
(oxygen⋯oxygen distance of 2.62 Å).]
Conclusion
Several reported X-ray structures of arene π-coordination to
palladium(II) demonstrate that η6 arene coordination is not
observed in the solid-state.11,12 The hapticities observed are best
described as two,13 three,14 four,15 five,16 and sometimes a com-
bination of these values.17 Some presumed η6 complexes
observed in solution, at low temperatures, decompose at ambient
conditions.18 The palladium atom in 3·Pd(O3SCF3)2 is centered
over the arene ring, with all six Pd–C bond distances in the
range 2.37–2.43 Å (Table 2). The Pd–C(1) and Pd–C(4) dis-
tances of 2.43 Å are slightly longer than the other four Pd–C dis-
tances resulting in a small puckering of the ring. The standard
The constraint and flexibility of the bisphosphonite calixarene
ligand 3 plays a major role in the observed geometry changes.
This ligand is sufficiently flexible to accommodate a 5° change
of the bite angle from the square planar 16-electron complex to
the arene π-bonded 18-electron species, while also providing
constraint to keep the arene in bonding distance to the metal. It
is possible that the π–π stacking of the phosphonite phenyl rings
is responsible for driving the stabilization of the η6 complex.
However, this stacking may be due to the decrease in the P–Pd–
P bite angle that simply forces the rings into a parallel orientation
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cyclooctadieneplatinum(II) chloride, and silver trifluoromethane-
sulfonate were obtained commercially and used without further
purification. Ligand 3 was synthesized by the literature pro-
cedure.7 All NMR spectra were recorded on
a JEOL
ECA-500 multinuclear NMR spectrometer resonating at 500.160
(1H) and 202.468 MHz (31P). 1H NMR resonances were
measured relative to residual proton solvent peaks and referenced
to tetramethylsilane. 31P NMR resonances were measured rela-
tive to external 85% H3PO4. Elemental Analyses were obtained
on a Flash EA 1112 Elemental Analyzer.
Synthesis of 3·PdCl2. Solid palladium(II) chloride (0.250 g,
1.41 mmol) was added to a stirred solution of 3 (1.44 g,
1.41 mmol) in THF (32 mL). The mixture was stirred at room
temperature for 4 d. The product came out of solution as a pale
yellow solid. The solid was filtered and washed with hexane (3 ×
2 mL) and dried under vacuum for 48 hours yielding 3·PdCl2 as
an air- and moisture-stable yellow powder (1.32 g, 78%). Anal
calcd for C67H76Cl2O5P2Pd: C, 67.03; H, 6.38. Found: C, 67.00;
H, 6.27. 1H NMR (CD2Cl2, δ): 1.08 (s, 18H, t-Bu), 1.20 (s,
2
18H, t-Bu), 1.44 (s, 9H, t-Bu), 3.37 (d, 1H, CH2, JHH = 12.5
Hz), 3.44 (d, 2H, CH2, 2JHH = 15.7 Hz), 3.51 (d, 2H, CH2, 2JHH
2
= 15.7), 3.95 (s, 1H, OH), 4.09 (d, 1H, CH2, JHH = 12.5 Hz),
2
2
4.21 (d, 2H, CH2, JHH = 15.7 Hz), 5.22 (d, 2H, CH2, JHH
=
4
15.7 Hz), 7.025 (d, 2H, CH, JHH = 2.5 Hz), 7.026 (d, 2H, CH,
4JHH = 2.5 Hz), 7.12 (d, 2H, CH, JHH = 2.5 Hz), 7.26 (d, 2H,
4
4
CH, JHH = 2.5 Hz), 7.28 (s, 2H, CH), 7.55 (m, 6H, CH), 8.27
(m, 4H, CH). 31P NMR (CD2Cl2, δ): 116.
Synthesis of 3·PtCl2. Solid 1,5-cyclooctadieneplatinum(II)
chloride (0.431 g, 1.14 mmol) was added to a stirred solution of
3 (1.161 g, 1.14 mmol) in toluene (65 mL). The mixture was
stirred at room temperature for 48 hours (only 24 hours is
required for the reaction to reach completion) yielding a white
precipitate. The solution was filtered, the white precipitate
washed with toluene (10 mL) and dried under vacuum for
20 hours yielding 3·PtCl2 as a white, air-stable, pure solid
(1.06 g, 72%). Anal calcd for C67H76Cl2O5P2Pt: C, 62.42; H,
5.94. Found: C, 62.20; H, 6.01. 1H NMR (CDCl3, δ): 1.13 (18H,
s, t-Bu), 1.22 (18H, s, t-Bu), 1.41 (9H, s, t-Bu), 3.42 (1H, d,
Fig. 4 31P NMR (ppm) spectra showing the reversible conversion of
3·PdCl2 (δ 116) to 3·Pd(O3SCF3)2 (δ 122). (a) Pure 3·Pd(O3SCF3)2.
(b) Addition of 2 eq of tetra-n-butylammonium chloride. (c) Addition of
another 2 eq of tetra-n-butylammonium chloride. (d) Addition of 4 eq
AgO3SCF3.
2
2JHH = 12.6 Hz, CH2), 3.45 (2H, d, JHH = 15.5 Hz, CH2), 3.48
2
2
(2H, d, JHH = 14.9 Hz, CH2), 4.22 (2H, d, JHH = 14.9 Hz,
2
2
CH2), 4.32 (1H, d, JHH = 12.6 Hz, CH2), 5.22 (2H, d, JHH
15.5 Hz, CH2), 6.99 (2H, br d, JHH = 2.3 Hz, calix[5]arene
CH), 7.01 (2H, br d, JHH = 2.3 Hz, calix[5]arene CH), 7.13
(2H, br s, CH), 7.17 (2H, br d, JHH = 2.3 Hz, calix[5]arene
=
4
4
4
4
to avoid steric congestion. Clearly, the metal also plays a role,
since platinum does not cleanly form the same complex. Work is
currently being conducted to determine the critical factors stabi-
lizing η6 binding of these ligands.
CH), 7.23 (2H, br d, JHH = 2.3 Hz, calix[5]arene CH), 7.45
(6H, m, PPh CH), 8.30 (4H, m, PPh CH). 31P NMR (CDCl3, δ):
86.4 (1JPPt = 5520 Hz).
Synthesis of 3·Pd(O3SCF3)2. Solid silver trifluoromethanesul-
fonate (0.043 g, 0.17 mmol) was added to a stirred solution of
3·PdCl2 (0.100 g, 0.0833 mmol) in dichloromethane (20 mL).
The flask was sealed with a rubber septum and allowed to stir
overnight. The mixture was transferred to a centrifuge tube and
centrifuged to separate the solids. The solution was decanted
into a clean round bottom flask, and the volatiles were removed
under vacuum resulting in a brown solid. The crude material was
recrystallized by layering pentane on a solution of dichloro-
methane yielding 3·Pd(O3SCF3)2 as an air- and moisture-stable
brown, crystalline solid (0.089 g, 75%). Attempts at elemental
analyses were unsuccessful. Spectra are reproduced in the ESI.†
Experimental
All reactions and manipulations were carried out under an atmos-
phere of nitrogen in a Vacuum Atmospheres drybox or by using
standard Schlenk techniques, unless otherwise indicated. Sol-
vents were dried using standard procedures and distilled under a
nitrogen atmosphere and either used immediately or stored in the
drybox prior to use. Glassware was oven-dried at 140 °C over-
night prior to use. The reagents palladium(II) chloride, 1,5-
6680 | Dalton Trans., 2012, 41, 6677–6682
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Table 3 Crystallographic data
3·PdCl2
3·PtCl2
3·Pd(O3SCF3)2
Empirical formula
Formula weight
Crystal system
(C67H76Cl2O5P2Pd)·3(CH4O)
(C67H76Cl2O5P2Pt)·3(CH4O)
1385.33
C71H80Cl4F6O11P2PdS2
1597.61
Monoclinic
P21/c
1296.64
Triclinic
ˉ
P1
Triclinic
ˉ
Space group
P1
a, Å
b, Å
c, Å
α, °
12.421(2)
15.899(3)
17.188(4)
97.341(3)
12.4596(14)
15.9029(18)
17.1665(18)
97.391(2)
17.467(5)
15.883(4)
25.891(7)
90
β, °
98.159(3)
97.589(4)
3293.2(11)
2, 1
1.308
98.535(2)
97.493(3)
3296.8(6)
2, 1
1.396
0.71073
91.334(14)
90
7181(3)
4, 1
1.478
γ, °
Volume, Å3
Z, Z′
Density (calculated), Mg m−3
Wavelength, Å
0.71073
1.54178
Temperature, K
F(000)
100(2)
1364
0.465
100(2)
1428
2.311
100(2)
3296
5.048
Absorption coefficient, mm−1
Absorption correction
Max. and min. transmission
Theta range for data collection, °
Reflections collected
Independent reflections
Data/restraints/parameters
wR(F2 all data)
R(F obsd data)
Semi-empirical from equivalents
0.9251 and 0.8468
2.35 to 25.50
36340
12001[R(int) = 0.1090]
12001/266/771
wR2 = 0.1509
R1 = 0.0674
0.989
Semi-empirical from equivalents
0.5538 and 0.4162
1.64 to 28.31
46574
16310[R(int) = 0.0389]
16310/254/774
wR2 = 0.0961
R1 = 0.0387
1.000
Semi-empirical from equivalents
0.7516 and 0.2949
5.04 to 32.88
11891
2560[R(int) = 0.1040]
2560/638/945
wR2 = 0.1680
R1 = 0.0602
1.069
Goodness-of-fit on F2
Observed data [I >2σ(I)]
Largest and mean shift/s.u.
Largest diff. peak and hole, e Å−3
7189
0.005 and 0.000
0.755 and −0.811
14365
0.002 and 0.000
2.671 and −1.181
1865
0.000 and 0.000
0.592 and −0.429
2 2
2 2
wR2 = {Σ[w(Fo2 − Fc ) ]/Σ[w(Fo ) ]}1/2, R1 = Σ||Fo| − |Fc||/Σ|Fo|.
1H NMR (CD2Cl2, δ):−0.07 (s, 9H, t-Bu), 1.33 (s, 18H, t-Bu),
1.35 (s, 18H, t-Bu), 3.63 (d, 2H, CH2, 2JHH = 13.5 Hz), 3.80 (d,
3·PtCl2. The asymmetric unit of the cell appeared to contain
one molecule of the metal complex and three methanol solvent
sites. Two of the methanol sites were severely disordered and
were best modeled using the Squeeze program.21 Two of the
t-butyl groups were disordered. The occupancies for atoms C19,
C20, and C21 refined to 0.799(9) and 0.201(9) for the unprimed
and primed atoms. The occupancies for atoms C41, C42, and
C43 refined to 0.567(8) and 0.433(8) for the unprimed and
primed atoms, respectively. Restraints on the positional and dis-
placement parameters of the disordered t-butyl groups were
required.
2
2
1H, CH2, JHH = 15.4 Hz), 3.97 (d of t, 2H CH2, JHH = 18.5
4
2
Hz, JPH = 5 Hz), 4.12 (d, 2H, CH2, JHH = 13.5 Hz), 4.38 (d,
2
2
1H, CH2, JHH = 15.4 Hz), 4.75 (d of t, 2H, CH2, JHH = 18.5
4
3
Hz, JPH = 5 Hz), 5.90 (t, 2H, CH, JPH = 2 Hz), 7.2–7.6 (over-
4
lapping, 12H, CH), 7.66 (m, 4H, CH), 7.90 (d, 2H, CH, JHH
=
2.3 Hz). 31P NMR (CD2Cl2, δ): 122.
Single crystals of 3·PdCl2 and 3·PtCl2 were obtained by
layering methanol on a solution of the compound in dichloro-
methane. Single crystals of 3·Pd(O3SCF3)2 were obtained by
layering pentane on a solution of the compound in dichloro-
methane. Crystals were mounted in the cold stream of the
diffractometer.
3·Pd(O3SCF3)2. The intensity data were truncated to 1.42 Å
resolution because data in higher resolution shells all had Rint
>
0.25. The two methylene chloride groups were disordered. The
occupancies for the S molecule refined to 0.668(6) and 0.332(6)
for the unprimed and primed atoms. The occupancies for the T
molecule refined to 0.619(10) and 0.381(10) for the unprimed
and primed atoms. Restraints on the positional and displacement
parameters of the disordered atoms and the displacement par-
ameters of all atoms were required.
Crystal structure determinations
Crystallographic data are summarized in Table 3.
3·PdCl2. The metal complex contained two t-butyl groups that
were disordered. The occupancies of C19, C20, and C21 refined
to 0.796(12) and 0.204(12) for the unprimed and primed atoms;
the occupancies of atoms C41, C42, and C43 refined to 0.565
(10) and 0.435(10) for the unprimed and primed atoms.
Restraints on the positional and displacement parameters of the
disordered atoms were required. Two methanol solvent sites
were severely disordered and were best modeled using the
Squeeze program.21
Acknowledgements
This work was supported by the Department of Chemistry,
Southern Methodist University. The authors thank Kent Fischer
for obtaining elemental analyses.
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10 This is in agreement with previously reported NMR spectra of monohalo-
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6682 | Dalton Trans., 2012, 41, 6677–6682
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