PtII and PdII complexes with a trans-chelating bis(pyridyl) ligand

Article abstract of DOI:10.1002/ejic.201200442

An atropisomeric bis(pyridyl) chelate ligand bis{3,3'-[N-Ph-2-(2'-py) indolyl]} (bpib) has been found to readily form trans-chelating Pd^II and Pt^II complexes. Two such complexes, Pt(bpib)Cl₂ and Pd(bpib)Cl₂ have

Full text of DOI:10.1002/ejic.201200442

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FULL PAPER
DOI: 10.1002/ejic.201200442
PtII and PdII Complexes with a trans-Chelating Bis(pyridyl) Ligand
Nan Wang,[a] Theresa M. McCormick,[a] Soo-Byung Ko,[a] and Suning Wang*[a]
Keywords: Homogeneous catalysis / Platinum / Palladium / N ligands / Chelates
An atropisomeric bis(pyridyl) chelate ligand bis{3,3Ј-[N-Ph-
2-(2Ј-py) indolyl]} (bpib) has been found to readily form
trans-chelating PdII and PtII complexes. Two such complexes,
Pt(bpib)Cl2 and Pd(bpib)Cl2 have been isolated and their
structures were determined by single-crystal X-ray diffrac-
tion analysis. Both Pt(bpib)Cl2 and Pd(bpib)Cl2 have a chiral
structure with C2 symmetry. Pt(bpib)Cl2 displays a long-lived
phosphorescence with λem = 595 nm in a frozen CH2Cl2 solu-
tion at 77 K. To examine the potential use of the trans chelate
bpib ligand in oxidative coupling reactions catalysed by PdII
compounds, acetoxylation of benzene, chlorobenzene and
toluene by PhI(OAc)2 using Pd(OAc)2/bpib (2:1) as the cata-
lyst was examined and compared with the cis-chelating sys-
tem Pd(OAc)2/2,2Ј-bipyridine (bipy). The bpib system was
found to accelerate the reaction but lower the overall yield.
tain a trans-chelating ligand are still relatively rare but inter-
Introduction
esting since they often display unusual properties[8] and
Due to the broad applications in organic synthesis,[1] cata- have found use in asymmetric catalysis.[9] During the past
lytic processes[2] and biological and pharmacological us- few decades, many trans diphosphane ligands and their cor-
age,[3] PtII and PdII complexes have attracted considerable responding d8 metal complexes have been reported and in-
attention. For bis(chelate) PdII and PtII compounds, the vestigated.[10] Diphosphane ligands that have an intermedi-
most commonly observed binding mode is cis geometry.[4] ate or large bite angle have been found to have a significant
Examples of N,N-cis-chelating PtII and PdII complexes with impact on reactivity of their metal complexes.[10o–10q] In
bipyridyl based ligands are well known[5–7] and their use contrast, PtII or PdII compounds with trans-N,N-chelating
in CϪH activation and catalysis has also been investigated ligands remain scarce. To the best of our knowledge, the
extensively. In contrast, PdII and PtII compounds that con- only examples of trans-chelating bipyridyl ligands are 1,2-
Scheme 1.
bis(2-pyridylethynyl)benzene and its derivatives reported
[a] Department of Chemistry, Queen’s University,
previously by Bosch and others.[11] The use of the trans-
PdCl2 compound with this type of ligands in Heck coupling
Kingston, Ontario, K7L 3N6, Canada
Homepage: http://www.chem.queensu.ca/people/faculty/Wang/
index.html
reactions has been investigated by several research
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200442.
groups.[12]
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N. Wang, T. M. McCormick, S.-B. Ko, S. Wang
FULL PAPER
Recently we reported a class of interesting antropisom- large natural bite angle that spans a considerable range. For
eric ligands that can readily chelate to a CuI or a ZnII centre example, when bound to CuI and ZnII ions,[13] it forms a
forming chiral coordination compounds.[13] One of these li- distorted tetrahedral geometry with an observed bite angle
gands, bpib, is shown in Scheme 1 and it contains two 3,3Ј- of 137° to 141°. Thus, the trans geometry of the PtII and
bis[2-(2Ј-py)-indolyl] binding sites. Compared with phos- PdII compounds is a consequence of the ligand’s large bite
phane ligands, polypyridyl ligands such as bpib are much angle. The Pd(1)–N(2) bond length in Pd(bpib)Cl2 is
harder donors which in turn may enhance the stability of 2.0205(14) Å, which is similar to that[11] of trans-Pd[1,2-
their metal complexes toward oxidation, in addition to the bis(2-pyridylethynyl)benzene]Cl2. The dihedral angle be-
possible introduction of rich photophysical/photochemical tween the two indolyl rings is 103.9° for Pt(bpib)Cl2 and
properties. Based on these considerations, we have synthe- 104.5° for Pd(bpib)Cl2.
sised and investigated the bpib based PdII and PtII com-
plexes. We have found that both PdII and PtII compounds
adapt an unusual trans chelate geometry. We have also con-
ducted a preliminary study on the catalytic activity of the
Pd(OAc)2-bpib (2:1) system in the acetoxylation reaction of
benzene, chlorobenzene and toluene with PhI(OAc)2, a well
known direct C–H bond functionalisation process.[14]
Results and Discussion
Figure 1. The molecular structure of Pt(bpib)Cl2 with 35% thermal
ellipsoids. Selected bond lengths [Å] and angles [°]:Pt(1)–N(1)
Synthesis and Structures
2.019(2), Pt(1)–Cl(1) 2.3061(6), C(7)–C(7Ј) 1.476(5); N(1)–Pt(1)–
N(1Ј) 164.81(12), Cl(1)–Pt(1)–Cl(1Ј) 169.78(4).
The ligand bpib was synthesised by our previously re-
ported procedure.[13] The syntheses of PdII and PtII com-
plexes Pd(bpib)Cl2 and Pt(bpib)Cl2 were accomplished by
the reactions shown in Scheme 1. The PtII compound was
obtained by heating K2PtCl4 and bpib to reflux in a solvent
mixture of H2O/DMSO/CH2Cl2 in a 5:1:5 ratio at 80 °C
for 6 h. The DMSO solvent molecules likely reacted with
K2PtCl4 to first generate Pt(DMSO)2Cl2 which sub-
sequently reacted with the bpib ligand to produce the che-
late complex Pt(bpib)Cl2 which was isolated as orange crys-
tals. Complex Pd(bpib)Cl2 was synthesised by layering an
ethyl acetate solution of a stoichiometric amount of
Pd(PhCN)2Cl2 with a THF solution of bpib at ambient
temperature. Through slow diffusion of these two layers, the
chelating ligand bpib displaced the labile phenylnitrile li-
gands to generate Pd(bpib)Cl2 which precipitated out as a
Figure 2. The molecular structure of Pd(bpib)Cl2 with 35% ther-
mal ellipsoids. Selected bond lengths [Å] and angles [°]: Pd(1)–N(1)
2.0205(14), Pd(1)–Cl(1) 2.3092(4), C(7)–C(7Ј) 1.478(3); N(1)–
Pd(1)–N(1Ј) 165.08(8), Cl(1)–Pd(1)–Cl(1Ј) 165.23(3).
Compared with the previously known trans-chelating li-
red powder. Both compounds were fully characterised by gand, 1,2-bis(2-pyridylethynyl)benzene which has an ex-
NMR spectroscopy and CHN analysis. Single-crystals suit- tended conjugation and a highly rigid structure to reinforce
able for X-ray diffraction analyses for both compounds the trans geometry,[11] the bpib ligand has much rotational
were obtained by recrystallisation of the compounds with freedom, albeit with a high rotation barrier around the
CH2Cl2.
C(7)–C(7Ј) bond.[13] Previously, using DFT computational
The molecular structures of both complexes are shown methods, we established[13a] that the rotation barrier of bpib
in Figures 1 and 2. Both molecules belong to the C2/c space around the C(7)ϪC7Ј bond is ca. 22 kcalmol–1. Our efforts
group with similar unit cell dimensions (see Supporting In- to resolve the enantiomers of bpib were not successful.[13a]
formation). Both molecules are chiral with a crystallograph- Variable-temperature 1H NMR spectra of Pt(bpib)Cl2 show
ically imposed C2 axis, although both enantiomers coexist that this complex retains its structure with no evidence of
in the crystal lattice. The most important feature revealed trans/cis isomerisation in solution. The N-phenyl groups
by the crystal structures is that the bpib ligand is chelated show restricted rotation in solution caused by the ortho-
to PdII and PtII in a rare trans geometry, forming a large hydrogen atom interactions between the phenyl and the pyr-
nine-membered chelate ring. Both compounds show con- idyl ring, as shown by the VT NMR spectra in Figure 3.
siderable distortion from an ideal square-planar geometry The activation energy for the restricted rotation of the N-
with the N(1)–M–N(1Ј) and Cl(1)–M–Cl(1Ј) angles being phenyl ring was estimated to be ca. 62 kJmol–1 using an
ca. 165° to ca. 169°. This distortion can be attributed to the Eyring Equation (1).[16] Pd(bpib)Cl2 possesses similar solu-
1
strain imposed by the bis(N-Ph-indolyl) linker on the che- tion dynamics as established by VT H NMR and its acti-
late ligand, as commonly observed in many previously vation energy for the restricted rotation of the N-phenyl
known trans chelate complexes.[15] The ligand bpib has a ring was estimated to be ca. 61 kJmol–1 (see Supporting
2
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PtII and PdII Complexes with a trans-Chelating Bis(pyridyl) Ligand
Information). Similar restricted rotation of the N-phenyl
groups was also observed in the CuI and ZnII bpib com-
pounds reported previously.[13]
ΔG = RTc [23 + ln(Tc/Δν)]
(1)
Figure 4. UV/Vis spectra of 10–5 m solutions of bpib, Pt(bpib)Cl2
and Pd(bpib)Cl2 recorded in CH2Cl2 at ambient temperature.
Table 1. Absorption and luminescence data.
Compound
Absorption[a]
Emission
τ/μs
λmax/nm
λmax/nm
(quantum yield)
(ε/m–1 cm–1)
bpib
234 (41600)
268 sh (29200)
310 (25200)
340 sh (11400)
237 (49500)
320 (18400)
362 (10100)
233 (54600)
270 sh (27800)
319 (21900)
383 (7920)
441[a]
(0.22)[b]
Pd(bpib)Cl2
Pt(bpib)Cl2
1
Figure 3. Variable temperature H NMR spectra of Pt(bpib)Cl2 in
CD2Cl2 showing the change of the N-phenyl proton chemical shifts
with temperature. The assignments of the peaks for the N-phenyl
protons are based on COSY NMR spectroscopic data.
595[c]
231.8Ϯ2.14[c]
[a] In CH2Cl2 at 298 K. [b] Determined using 9,10-diphenylanthra-
cene as the standard. [c] At 77 K in CH2Cl2 with 150 μs delay.
Photophysical Properties
The absorption spectra of bpib and the two complexes
are shown in Figure 4 and the photophysical data are given
in Table 1. In the absorption spectra there are intense bands
at 234 and 310 nm for ligand bpib which were attributed to
a πǞπ* transition. In addition, a broad shoulder band at
340 nm can also be observed which was attributed to π-π
interactions between the two central pyridyl rings, based on
our earlier investigation on the photophysical properties of
the uncoordinated ligand.[13] The absorption spectra of
Pt(bpib)Cl2 and Pd(bpib)Cl2 are similar to that of the unco-
ordinated bpib except for the presence of a well-resolved
metal-to-ligand-charge-transfer (MLCT) band with a mod-
erate intensity at ca. 360 nm for the PtII compound and ca.
380 nm for the PdII compound. The assignment of the
data (see Supporting Information). The unusually long de-
cay lifetime can be attributed to the involvement of the d-d
transition in the first triplet state and is responsible for the
lack of ambient temperature phosphorescence in solution,
due to quenching by collision with solvent molecules.[17a,17b]
Not surprisingly, complex Pd(bpib)Cl2 shows no lumines-
cence at either ambient temperature or at 77 K which is
common for PdII complexes due to quenching by low lying
d-d states.[17c,17d]
Reactivity of PdII/bpib in Acetoxylation
To examine the impact of the trans-chelating ligand bpib
MLCT band is in agreement with TD-DFT data which on the catalytic properties of PdII compounds, we compared
show that the first three singlet transitions all have signifi- the catalytic activity of bpib/Pd(OAc)2 with that of 2,2Ј-
cant MLCT contributions (see Supporting Information).
bipy/Pd(OAc)2 towards acetoxylation of arenes using
The uncoordinated bpib ligand is blue fluorescent. Com- PhI(OAc)2 as a reagent, where a C–H bond is directly func-
plex Pt(bpib)Cl2 does not display any luminescence in solu- tionalised by an acetoxyl group.[14,18] The choice of using
tion at ambient temperature. However, in a frozen solution Pd(OAc)2 as the Pd reagent is based on the fact that it has
of CH2Cl2 at 77 K, it does emit an orange colour with λmax been commonly used in C–H bond functionalisation in pre-
= 595 nm with a long decay lifetime, 231(2) μs, which is vious studies,[14,18] thus providing a convenient platform for
3
3
attributed to a mixed LC and MLCT transition with sig- us to examine the impact of bpib on Pd catalysis. The mech-
nificant d-d transition contributions, based on TD-DFT anistic aspects of benzene acetoxylation using PhI(OAc)2 as
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N. Wang, T. M. McCormick, S.-B. Ko, S. Wang
FULL PAPER
Scheme 2. Mechanism of Pd-catalysed C–H activation/acetoxylation of arenes with PhI(OAc)2.
the oxidant and Pd(OAc)2 as the catalyst have been well
established previously.[14,18] As shown in Scheme 2, the first
step of the reaction involves CϪH activation at the PdII
centre followed by oxidation of the PdII complex to PdIV
by the oxidant. The subsequent reductive elimination gener-
ates the final product. The selection of PhI(OAc)2 as the
oxidant is based on the fact that it is a common oxidant
used in previous studies[14] which would allow us to follow
the well established procedure of comparing the reactivity
difference of bpib with the standard bipy ligand in PdII cat-
alysed arene acetoxylation.
Standard reaction conditions used in previously reported
PdII catalytic systems[14c] were employed for our study. Pre-
vious studies have shown that the 1:2 ratio of N,N-chelate
ligand/Pd(OAc)2 is the best for arene acetoxylation and that
the catalytic system based on Pd(OAc)2 only is much less
effective.[14c,14e] We therefore adopt the 1:2 ratio of ligand/
Pd(OAc)2 for our study. We used 2,2Ј-bipy/Pd(OAc)2 as the
standard system. The reaction was carried out at 100 °C for
three substrates, benzene, toluene and chlorobenzene and
the results are shown in Figure 5 and Table 2. The active
catalyst bpib-Pd(OAc)2 is generated in situ, following pre-
1
vious established procedures. H NMR spectroscopic stud-
ies show that the bpib ligand rapidly reacts with Pd(OAc)2
to generate the bpib-Pd complex (see Supporting Infor-
mation). Attempts were not made to fully characterise this
complex.
As illustrated in Figure 5, the use of bpib for the acet-
oxylation of benzene appears to significantly accelerate the
reaction in the first 6 h, compared with the standard cata-
lyst 2,2Ј-bipy/Pd(OAc)2 and the maximum yield [ca. 60%,
calculated based on PhI(OAc)2] is achieved after ca. 6 h.
This moderate yield could be attributed to the side reactions
and the formation of by-products such as biphenyl,
IC6H4OAc and C6H4(OAc)2 identified by GC–MS analysis.
The same phenomenon was observed in previously reported
2,2Ј-bipy/PdII systems.[14c] Black Pd0 precipitates were also
observed after about 2 h heating which may be responsible
for side reactions such as CϪC coupling reactions involving
Ph(OAc), thus lowering the overall yield of acetoxylation.
Figure 5. Diagrams showing the yields of acetoxylation products
with time. Top: benzene substrate, middle: toluene substrate, bot-
tom: chlorobenzene substrate. Catalysts: (•) Pd(OAc)2/bpib, 2:1;
(᭢) Pd(OAc)2/2,2Ј-bipy 2:1. The yields are calculated based on
PhI(OAc)2, the limiting reagent.
Similar acceleration effects were also observed in the ace- the Pd(OAc)2/bipy system, the p-isomer is also slightly fav-
toxylation of toluene and chlorobenzene as shown in Fig- oured but the yields of o- and the m-isomers are now sim-
ure 5, although the overall yields obtained by the Pd(OAc)2/ ilar.
bpib catalyst are again lower than the control Pd(OAc)2/
This preliminary study shows that the new trans-chelat-
bipy catalyst for these two substrates. The product distribu- ing bpib ligand does have different behaviour compared
tion study for the Pd(OAc)2/bpib system indicated that the with the 2,2Ј-bipy ligand in PdII catalysis. For the acetoxyl-
p-isomer is somewhat favoured (41% for both toluene and ation reactions we examined, the bpib/PdII system appears
chlorobenzene substrates), compared with the o-isomer to accelerate the reaction rate for the three substrates we
(25% for toluene and 22% for chlorobenzene) and the m- examined compared with the 2,2Ј-bipy ligand and this may
isomer (34% for toluene and 37% for chlorobenzene). For be attributed to the relatively facile binding mode change
4
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PtII and PdII Complexes with a trans-Chelating Bis(pyridyl) Ligand
version 5.00 for windows, GraphPad Software, San Diego Cali-
fornia USA, choosing one phase association equation. Elemental
analyses were performed at the Canadian Microanalytical Service,
Ltd. (Delta, British Columbia, Canada). Ligand bpib was prepared
using methods reported previously.[13]
Table 2. Reaction conditions and product distributions.
Pt(bpib)Cl2: K2PtCl4 (85 mg, 206 μmol) was dissolved in DMSO/
H2O/CH2Cl2 (1 mL/5 mL/5 mL). After stirring for 30 min, a solu-
tion of bpib (100 mg, 187 μmol) in CH2Cl2 (3 mL) was slowly
added. The mixture was heated to reflux at 80 °C for 6 h. The or-
ganic layer was extracted and washed three times with water. Sol-
vent was then removed under vacuum and the residue was redis-
solved in CH2Cl2. The undissolved Pt(DMSO)2Cl2 was removed
by filtration. The resultant yellow solution was allowed to slowly
evaporate to afford an orange powder of Pt(bpib)Cl2 with an over-
all yield of ca. 50%. This compound can be recrystallised from
R
bipy
ortho/metal/para
bpib
ortho/metal/para
CH3
Cl
32:31:37%
32:32:36%
25:34:41%
22:37:41%
of the bpib ligand from chelating to terminal, facilitated by
the large bite angle, thus allowing easy access of the sub-
strate to the PdII centre in the CϪH activation step. The
low yields of the acetoxylation reactions for the substituted
benzenes using bpib/PdII, compared with 2,2Ј-bipy/PdII
may be attributed to the relatively low stability of the trans-
bpib Pd complex, causing irreversible decomposition of the
catalyst and side reactions under the reaction conditions
employed.
1
CH2Cl2. H NMR in CD2Cl2, 500 MHz (263 K): δ = 8.77 (d, J =
5.6 Hz, 1 H), 8.14 (d, J = 7.7 Hz, 1 H), 7.87 (d, J = 7.6 Hz, 1 H),
7.52–7.49 (m, 2 H), 7.47 (d, J = 8 Hz, 1 H), 7.39 (dd, J = 7.5 Hz,
J = 7.5 Hz, 1 H), 7.35 (dd, J = 7 Hz, J = 7 Hz, 1 H), 7.27 (d, J =
7.5 Hz, 1 H), 7.12 (dd, J = 7.5 Hz, J = 7.5 Hz, 1 H), 6.98–6.95 (m,
2 H), 6.73 (d, J = 9 Hz, 1 H) ppm. Due to the poor solubility,
the 13C NMR spectrum was not obtained. C38H26Cl2N4Pt·CH2Cl2:
calcd. C 52.66, H 3.17, N 6.30; found C 52.03, H 3.24, N 6.33.
Pd(bpib)Cl2: A solution of bpib (150 mg, 280 μmol) in THF was
layered with a solution of palladium bis(phenylacetonitrile) dichlo-
ride (108 mg, 280 μmol) in ethyl acetate to give a red precipitate.
The crude product was then purified by recrystallisation from
CH2Cl2. Red crystals of Pd(bpib)Cl2 were obtained in 62% yield.
1H NMR in CD2Cl2, 500 MHz (263 K): δ = 8.43 (d, J = 5 Hz, 1
H), 7.83 (d, J = 10 Hz, 1 H), 7.62 (dd, J = 7.5, J = 7.5 Hz, 1 H),
7.54 (dd, J = 7.5, J = 7.5 Hz, 1 H), 7.41 (d, J = 5 Hz, 2 H), 7.38
(d, J = 5 Hz, 1 H), 7.30 (d, J = 10 Hz, 1 H), 7.26–7.18 (m, 4 H),
Conclusions
In summary, the bpib ligand has been found to be very
effective in forming chiral trans chelate PdII and PtII com-
plexes. When combined with Pd(OAc)2 in a 2:1 ratio
(Pd:bpib) it accelerates the acetoxylation of benzene, tolu-
ene and chlorobenzene by PhI(OAc)2 but the yield is low
for some of the substrates compared with the yields from
the 2,2Ј-bipy-Pd(OAc)2 system. If the enantiomers of the
complexes can be resolved, the trans bpib chelate PdII/PtII
7.10
(dd,
J
=
7.5,
J
=
7.5 Hz,
1
H) ppm.
C38H26Cl2N4Pd·0.25CH2Cl2: calcd. C 62.32, H 3.62, N 7.60; found
C 62.32, H 3.47, N 7.51. Due to the poor solubility, 13C NMR
compounds may find applications in asymmetric catalysis spectra were not obtained.
and further investigation is therefore justified.
Pd-Catalysed Acetoxylation of Benzene. Pd(OAc)2/2,2Ј-bipy: To a
mixture of PhI(OAc)2 (361 mg, 1.12 mmol), Pd(OAc)2 (5.0 mg,
22.4 μmol, 2.0 mol-%) and 0.50 mL (11.2 μmol, 1.0 mol-%) of a
stock solution of 2,2Ј-bipyridine (35.0 mg, 224 μmol) in AcOH
(10 mL) were added glacial acetic acid (0.40 mL) and acetic anhy-
dride (0.10 mL). The suspension was stirred at ambient tempera-
ture for 1 min before benzene (1.00 mL, 875 mg, 11.2 mmol,
10.0 equiv.) was added. The tube was sealed and heated to 100 °C
using a preheated hotplate. At the end of the reaction, the tube
was cooled to ambient temperature and EtOAc (1 mL) solution
containing hexamethylbenzene (8.11 mg, 0.05 mmol) was added as
an internal standard for quantitative GC analysis. The mixture was
diluted with EtOAc (2 mL) and filtered through a plug of Celite.
The filtrate was extracted with a saturated aqueous solution of
K2CO3 (9 m in H2O, 2ϫ2 mL) to quench and separate the acid.
The organic layer was carefully separated and diluted with ad-
ditional EtOAc to a total volume of 25 mL. The resultant solution
was analysed by GC. This same procedure was also used for chloro-
benzene and toluene acetoxylation reactions.
Experimental Section
General: All reactions were performed under dry N2 with standard
Schlenk techniques unless otherwise noted. All starting materials
were purchased from Aldrich Chemical Co. and used without fur-
ther purification. Solvents were freshly distilled from appropriate
drying reagents under an N2 atmosphere. NMR spectra were re-
corded on a Bruker Avance 500 MHz spectrometer as stated. Exci-
tation and emission spectra were recorded on a Photon Technol-
ogies International QuantaMaster Model C-60 spectrometer. UV/
Vis spectra were recorded on an Ocean Optics ISS-UV/Vis spectro-
photometer. Emission lifetimes were measured on a Photon Tech-
nologies International phosphorimeter (Time-Master C-631F)
equipped with a xenon flash lamp and a digital emission photon
multiplier tube, using a band pathway of 5 nm for excitation and
2 nm for emission. GC analyses were performed on an HP 6850
network FID-GC with automatic injector. The column used was
an HP-5 of 30 m in length with an internal diameter of 0.32 mm.
The inlet conditions were 250 °C, 25 psi and a flow rate of
28.9 mLminϪ1 using a splitless injector with helium as the carrier
gas. The method used had an initial temperature of 70 °C with an
immediate increase to 240 °C using a 6°minϪ1 ramp. GC yield was
determined with hexamethylbenzene acting as internal standard.
Raw data for catalytic studies were analysed using GraphPad Prism
Pd-Catalysed Acetoxylation of Benzene. Pd(OAc)2/bpib: The pro-
cedure was identical to the 2,2Ј-bipy system described above.
PhI(OAc)2 (361 mg, 1.12 mmol), Pd(OAc)2 (5.0 mg, 22.4 μmol,
2.0 mol-%), bpib (6 mg, 11.2 μmol, 1.0 mol-%), AcOH (0.90 mL),
acetic anhydride (0.10 mL) and benzene (1.00 mL, 875 mg,
11.2 mmol) were treated at 100 °C. For chlorobenzene and toluene
substrates, the same procedure was used.
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N. Wang, T. M. McCormick, S.-B. Ko, S. Wang
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X-ray Diffraction Analysis: Single-crystals of Pd(bpib)Cl2 and
Pt(bpib)Cl2 were mounted on glass fibres for data collection. Data
were collected on a Bruker Apex II single-crystal X-ray dif-
fractometer with graphite-monochromated Mo-Kα radiation, op-
erating at 50 kV and 30 mA and at 180 K. Data were processed on
a PC with the aid of the Bruker SHELXTL software package (ver-
sion 5.10) and corrected for absorption effects. All structures were
solved by direct methods. Both compounds cocrystallize with
CH2Cl2 solvent molecules (two CH2Cl2 per molecule), which were
modelled and refined successfully.
[7]
CCDC-879680 (for Pd(bpib)Cl2) and -879681 (for Pt(bpib)Cl2)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_requ-
est/cif.
[8]
Molecular Calculation: The computational calculations were per-
formed using the Gaussian09 software package, revision B.01[19]
and the High Performance Computing Virtual Laboratory
(HPCVL) at Queen’s University. The ground-state geometries were
fully optimised at the B3LYP[20] level using the LANL2DZ basis
set for platinum and the 6-31G(d) basis set for all other atoms.[21]
The initial geometric parameters in the calculations were employed
from crystal structure data for geometry optimisation. Time-de-
pendent density function theory (TD-DFT) calculations were per-
formed to obtain the vertical singlet and triplet excitation energies.
[9]
Supporting Information (see footnote on the first page of this arti-
cle): Phosphorescence spectrum of Pt(bpib)Cl2, VT NMR spectra
of Pd(bpib)Cl2, NMR spectra for monitoring the reaction of
Pd(OAc)2 with Bpib, and TD-DFT data.
[10]
Acknowledgments
We thank the Natural Sciences and Engineering Research Council
of Canada (NSERC) for financial support. We are grateful to Dr.
Thomas Wood and Ben Glasspoole at Cathleen Crudden’s labora-
tory for their assistance in recording the GC data.
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6
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Received: May 2, 2012
Published Online: ᭿
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Job/Unit: I20442
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Date: 20-08-12 15:48:41
Pages: 8
N. Wang, T. M. McCormick, S.-B. Ko, S. Wang
FULL PAPER
Chiral Chelate Complexes
PdII and PtII complexes containing a trans-
chelating bis(pyridyl) ligand bpib have been
synthesised. The catalytic reactivity of bpib
in PdII for arene acetoxylation has been
examined and compared with that of 2,2Ј-
bipy.
N. Wang, T. M. MCormick, S.-B. Ko,
S. Wang* .......................................... 1–8
PtII and PdII Complexes with a trans-Chel-
ating Bis(pyridyl) Ligand
Keywords: Homogeneous catalysis / Plati-
num / Palladium / N ligands / Chelates
8
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