Chiral cis-platinum acetylide complexes via diphosphine ligand exchange: Effect of the ligand

Article abstract of DOI:10.1021/om800633h

Chiral, bidentate phosphine ligands (R,R-CHIRAPHOS, R-PROPHOS, S,S-BDPP, R,R-Me-DUPHOS, R,R-NORPHOS) react with trans-platinum acetylide complexes 1a and 1b, (Ph₃P)₂Pt(C≡CR)₂ (R = TTPS, p-MeC₆H₄), via ligand exchange to generate chiral platinum acetylide complexes. The corresponding cis-platinum complexes are formed in all cases except for the reaction of 1b with S,S-BDPP, where the dimeric complex 4d′ is the product. Conversely, the reaction of la and 1b with the ligands S,S-DIOP, R-BINAP, and R-SYNPHOS fails to give the desired product in appreciable yield. Circular dichroism spectroscopy is used to examine the effect of the chiral ligand on the chiroptical properties of the platinum acetylide framework. X-ray crystallographic analyses of achiral complex la and chiral derivative 4e are reported.

Full text of DOI:10.1021/om800633h

Organometallics 2008, 27, 6321–6325
6321
Chiral cis-Platinum Acetylide Complexes via Diphosphine Ligand
Exchange: Effect of the Ligand
Amber L. Sadowy, Michael J. Ferguson,† Robert McDonald,† and Rik R. Tykwinski*
Department of Chemistry, UniVersity of Alberta, Edmonton, AB T6G 2G2, Canada
ReceiVed July 5, 2008
Chiral, bidentate phosphine ligands (R,R-CHIRAPHOS, R-PROPHOS, S,S-BDPP, R,R-Me-DUPHOS,
R,R-NORPHOS) react with trans-platinum acetylide complexes 1a and 1b, (Ph3P)2Pt(Ct CR)2 (R )
TIPS, p-MeC6H4), via ligand exchange to generate chiral platinum acetylide complexes. The corresponding
cis-platinum complexes are formed in all cases except for the reaction of 1b with S,S-BDPP, where the
dimeric complex 4d′ is the product. Conversely, the reaction of 1a and 1b with the ligands S,S-DIOP,
R-BINAP, and R-SYNPHOS fails to give the desired product in appreciable yield. Circular dichroism
spectroscopy is used to examine the effect of the chiral ligand on the chiroptical properties of the platinum
acetylide framework. X-ray crystallographic analyses of achiral complex 1a and chiral derivative 4e are
reported.
Scheme 1. Ligand Exchange Reaction with trans-Platinum
Introduction
Acetylides 1a,b
Platinum acetylide complexes (e.g., 1a and 1b, Scheme 1)
can be easily formed via a number of methods, often through
the simple reaction of a terminal acetylene with (R3P)2PtCl2.1,2
In addition to small-molecule complexes, these versatile alkyn-
ylation reactions have been exploited for the formation of
carbon-rich oligomers,3 polymers,4 macrocycles,5 and supramo-
lecular assemblies.6 Furthermore, the reductive elimination of
platinum from cis-complexes to generate butadiynes has been
established, expanding the usefulness of these compounds.7
It has been shown that when PPh3 is present as the ligands,
trans-acetylides 1 can be transformed smoothly into the corre-
sponding cis-acetylides (e.g, 3 or 4, Scheme 1) via ligand
exchange with cis-bis(diphenylphosphino)ethylene (dppee, 2a,
Figure 1).8 This ligand exchange protocol has also been
successfully used with R,R- or S,S-CHIROPHOS (2b) to
generate chiral products, including a number of macrocycles.9,10
In the present study, the prospect of forming chiral acetylide
complexes via ligand exchange has been explored for two series
* Corresponding author. E-mail: rik.tykwinski@ualberta.ca.
† X-ray Crystallography Laboratory, University of Alberta.
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10.1021/om800633h CCC: $40.75
2008 American Chemical Society
Publication on Web 11/07/2008

6322 Organometallics, Vol. 27, No. 23, 2008
Sadowy et al.
Figure 1. Diphosphine ligands 2a-i.
Table 1. Synthesis of cis-Pt-Acetylides 3 and 4 via Ligand Exchange
of trans-acetylide precursors, 1a and 1b, using a greatly
expanded range of chiral bidentate phosphine ligands 2b-i.
Changes in the CD spectra of the products 3 and 4 are then
used to empirically assay the affect of the various chiral ligands.
The results of this investigation are presented herein.
precursor
ligand 2
2a (dppee)
2b (R,R-CHIRAPHOS)
2c (R-PROPHOS)
2d (S,S-BDPP)
2e (R,R-Me-DUPHOS)
2f (R,R-NORPHOS)
2a (dppee)
2b (R,R-CHIRAPHOS)
2c (R-PROPHOS)
2d (S,S-BDPP)
pdct
yield [%]
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
3a
3b
3c
3d
3e
3f
4a
4b
4c
4d′
4e
4f
95
85
81
68
88
90
48
49
83
44a
81
72
Results and Discussion
Compounds 1a8 and 1b are readily available via the reaction
of either triisopropylsilyl- or p-tolylacetylene with trans-
(PPh3)2PtCl2 (Scheme 1).11 Because the trans-isomer of 1 is
thermodynamically more stable than the corresponding cis-
isomer, the room-temperature reaction of the precursor acetylene
with cis-(Ph3P)2PtCl2 also forms exclusively the trans-complex.
The analogous reaction of a terminal acetylene with trans-
(PEt3)2PtCl2 is also possible, but attempts to effect ligand
exchange with the resulting PEt3 complexes of 1 have not been
successful. Thus, compounds 1a and 1b, with PPh3, have been
utilized for the current study, even though their solubility in
common organic compounds is much reduced versus those with
PEt3 ligands.
2e (R,R-Me-DUPHOS)
2f (R,R-NORPHOS)
a See text for discussion.
R-BINAP (2h) and R-SYNPHOS (2i) did not result in ligand
exchange, even after heating and extended reaction times. The
31P NMR spectra of these latter two reactions showed only
signals of trans-Pt-acetylide complex 1a and the free ligand
R-BINAP (2h) or R-SYNPHOS (2i).
The product of the reaction of 1b with S,S-BDPP (2d)
deserves special comment. The 31P NMR spectrum of the
product isolated from this reaction revealed a signal at 26.9 ppm
for the two equivalent phosphine atoms and showed an
anomalous coupling constant of 1JP-Pt ) 2585 Hz, i.e., one that
was more characteristic of a trans-Pt-acetylide complex. Fur-
thermore, the ESI mass spectral analysis of this product (in the
presence of AgOTf) showed a strong signal at m/z 1837
corresponding to [2M + Ag]+. These observations indicate that
the expected cis-Pt-acetylide depicted in Scheme 1 is not the
likely product, but, rather, a dimeric Pt-containing complex was
formed with two bridging S,S-BDPP ligands, 4d′ (Figure 2).
The analogous dimeric species was not observed in the synthesis
of S,S-BDPP complex 3d, likely due to the greater steric
demands of the bulky TIPS groups in comparison to the planar
tolyl group. A similar bundling effect has been observed by
Gladysz and co-workers, using platinum-endcapped polyynes
in reactions with the achiral 1,3-diphosphine ligand
Ph2P(CH2)3PPh2 to give the dimers 5 (Figure 2).12 In the case
of the triyne derivative 5 (n ) 3), X-ray crystallographic analysis
of three different crystalline solvates was used to confirm the
structure of this species.
Ligand exchange reactions of 1a and 1b with chelating
diphosphines 2a-i (Figure 1) were explored by adding 1 equiv
of the appropriate ligand to a solution of either 1a or 1b in
CH2Cl2 (CD2Cl2) or CHCl3 (CDCl3). Using ligands 2a-f (Table
1), the reactions typically proceeded quickly at room temperature
(hours) and could be easily monitored by thin-layer chroma-
tography or 31P NMR spectroscopy. The 31P NMR spectra
clearly showed the disappearance of the signal of 1a and 1b at
δ 21 (1JP-Pt ) 2728 Hz) and δ 19.7 (1JP-Pt ) 2660 Hz),
respectively, and the appearance of a new signal of the cis-
1
product. The JP-Pt coupling constants were particularly diag-
nostic for confirming ligand exchange: they shifted from
2500-2800 Hz for the trans-acetylides 1a,b to ∼2100-2300
Hz for cis-acetylide products. All complexes could be readily
purified via column chromatography, using either silica gel
(3a-f) or alumina (4a-f).
The reaction of trans-Pt-acetylide complex 1a with S,S-DIOP
(2g) resulted in a mixture of unidentified products based on the
31P NMR spectrum. Surprisingly, the reaction of 1a with
(7) (a) Furusho, Y.; Tanaka, Y.; Yashima, E. Org. Lett. 2006, 8, 2583–
2586. (b) Fuhrmann, G.; Debaerdemaeker, T.; Ba¨uerle, P. Chem. Commun.
2003, 948–949. (c) James, S. L.; Younus, M.; Raithby, P. R.; Lewis, J. J.
Organomet. Chem. 1997, 543, 233–235.
(8) Campbell, K.; McDonald, R.; Ferguson, M. J.; Tykwinski, R. R. J.
Organomet. Chem. 2003, 683, 379–387.
(9) Campbell, K.; Johnson, C. A., II; McDonald, R.; Ferguson, M. J.;
Haley, M. M.; Tykwinski, R. R. Angew. Chem., Int. Ed. 2004, 43, 5967–
5971.
All cis-Pt-acetylide complexes 3a-f and 4a-f have been fully
characterized by 1H, 31P, and 13C NMR and IR spectroscopies,
mass spectral analysis, and microanalysis when possible. The
31P NMR spectra were particularly informative, with signal(s)
1
in the range 5-66 ppm and JP-Pt coupling constants in the
expected range 2100-2300 Hz (with the exception of 4d′, vide
(10) For other examples of ligand exchange at a Pt-acetylide center,
see refs 3a and 7a.
(11) See Supporting Information for details.
(12) Owen, G. R.; Hampel, F.; Gladysz, J. A. Organometallics 2004,
23, 5893–5895.

Chiral cis-Platinum Acetylide Complexes
Organometallics, Vol. 27, No. 23, 2008 6323
Figure 2. Dimeric Pt-acetylide complex 4d′ formed with two bridging S,S-BDPP ligands and dimers 5 synthesized by Gladysz and co-
workers.
Figure 3. ORTEP drawings of (a) compound 1b (20% probability level). Selected bond lengths (Å): Pt-C(1) 2.021(4), C(1)-C(2) 1.192(5),
Pt-P 2.2862(10). Selected bond angles (deg): C(1)-Pt-C(1)′ 180.0(2), C(1)-Pt-P 93.95(11), C(1)-Pt-P′ 86.05(11), P-Pt-P′ 180.0.
(b) Compound 4e (20% probability level, cocrystallized solvent molecule, CH2Cl2, not shown). Selected bond lengths (Å): Pt-C(1) 2.014(4),
Pt-C(3) 2.035(4), C(1)-C(2) 1.209(5), C(3)-C(4) 1.187(6), Pt-P(1) 2.2571(10), Pt-P(2) 2.2513(10). Selected bond angles (deg):
C(1)-Pt-C(3) 93.86(14), C(1)-Pt-P(2) 89.74(11), C(3)-Pt-P(1) 89.66(10), P(1)-Pt-P(2) 86.78(4).
Table 2. X-Ray Crystallographic Details for 1b and 4e
infra). The 13C NMR spectroscopic analysis of the cis-Pt-
1b
4e
acetylide complexes proved to be challenging due to the
complex splitting pattern caused by the magnetically nonequiva-
lent phosphorus atoms and platinum coupling. The analysis was
significantly more complicated for the R-PROPHOS- and R,R-
NORPHOS-containing compounds 3c, 3f, 4c, and 4f, where the
phosphorus atoms are not chemical shift equivalent. Neverthe-
less, the discussion of several assignments is useful. For
complexes 3a-f the R-acetylide (L2Pt(Ct CR)2) carbon signal
has a chemical shift of 122-129 ppm, while for complexes 4a-f
it appears upfield in the range 101-112 ppm (in CDCl3). This
resonance is typically observed as a doublet of doublets (dd),
formula
C54H44P2Pt
949.92
C36H42P2Pt•CH2Cl2
816.65
fw
cryst size, mm
cryst syst
space group
a, Å
0.27 × 0.14 × 0.04 0.60 × 0.48 × 0.27
monoclinic
P21/n (No. 14)
13.6022(8)
8.5341(5)
18.0885(11)
90.4470(10)
2099.7(2)
2
orthorhombic
P212121 (No. 19)
9.8524(9)
b, Å
c, Å
18.9860(18)
19.5240(18)
ꢀ, deg
V, Å3
3652.1(6)
4
Z
Dcalc, g cm-3
T, K
1.502
1.485
2
193
193
with coupling constants JC-P(trans) ) 133-169 Hz and
2JC-P(cis) ) 4-48 Hz. Without an excellent signal-to-noise ratio,
1JC-Pt for the R-acetylide carbon is not usually observed.13 The
ꢀ-acetylide carbon (L2Pt(Ct CR)2) is observed for the cis-
complexes in the range 103-112 ppm with 3JC-P(trans) ) 3-35
2θ limit, deg
µ, mm-1
total data
no indep reflns
no reflns Fo2 g 2σFo
no. params
restraints
52.76
3.455
15 514
4274
3258
52.80
4.099
28 887
7450
7206
2
Hz and JC-P(cis) < 5 Hz (not always observed).14 With
3
260
0
391
3a
sufficient signal-to-noise, coupling constants 2JC-Pt ) 229-307
Hz are also observed for the ꢀ-acetylide carbon.
goodness of fit
1.102
0.0250
0.0736
1.091
2
R(F) [Fo2 g 2σ(Fo )]
0.0203
0.0573
1.069 and -0.771
679335
2
The solid-state structural properties of trans-complex 1b and
R,R-Me-DUPHOS complex 4e have been examined by X-ray
crystallographic analysis (Figure 3, Table 2). Single crystals of
1b suitable for crystallographic analysis were grown by the slow
diffusion of Et2O into a CH2Cl2 solution at 4 °C. Crystals of 4e
were grown by slow evaporation of a CH2Cl2/acetone solution
at room temperature. As a result of its centrosymmetric structure,
wR2 [Fo2 g -3σ(Fo )]
lgst diff peak and hole, e Å-3 0.955 and -0.412
CCDC no.
679334
a Distances within the two sets of atomic positions for the disordered
solvent dichloromethane molecule were constrained to be equal (within
0.001 Å).
the t C-Pt-Ct and P-Pt-P bond angles of 1b are linear at
180°. A slight deviation from overall square-planar geometry
about the Pt center is, however, observed with C(1)-Pt-P and
C(1)-Pt-P′ bond angles of 93.95(11)° and 86.05(11)°, respec-
tively. The geometry about Pt in 4e also deviates slightly from
square planar, with a t C-Pt-Ct bond angle of 93.86(14)°
andaP(1)-Pt-P(2)bondangleof86.78(4)°.15 TheC(1)-Pt-P(2)
and C(3)-Pt-P(1) bond angles are nearly identical at 89.74(11)°
(13) To confirm this signal assignment, a 13C{1H, 31P} NMR spectrum
for 4e was recorded with sufficient signal-to-noise that this coupling was
clearly discernible, providing 1JC-Pt ) 1105 Hz. See Supporting Information
(Figures S45-47).
(14) Compound 4c does not follow this trend, with observed coupling
constants for the alpha acetylenic carbon of 2JC-P ) 85 and 86 Hz (trans)
2
and JC-P ) 3.0 and 2.7 Hz (cis).

6324 Organometallics, Vol. 27, No. 23, 2008
Sadowy et al.
Figure 5. Circular dichroism spectra of compounds 4b-f in CH2Cl2.
Figure 4. Circular dichroism spectra of compounds 3b-f in CH2Cl2.
Similar to complexes 3b-f, tolyl derivatives 4b, 4c, 4e, and
4f all have two absorption maxima in their UV-vis spectra.
The lower energy absorption is observed between 317 and 325
nm and is attributed to the MLCT absorption, while the higher
energy absorption observed between 257 and 263 nm is
presumably due to the π-π* transition for ligands. None of
the complexes have a significant signal in their CD spectra that
appears to correspond to the lower energy absorption (Figure
5), and only the R,R-Me-DUPHOS compound 4e does not
contain a bisignate band corresponding to the higher energy
absorption. These bisignate signals are centered at 252, 252,
and 253 nm for compounds 4b, 4c, and 4f, respectively. The
R,R-NORPHOS compound 4f shows the strongest signal at ∆ε
) -53 M-1 cm-1 (240 nm), followed by 4b (S,S-CHIRAPHOS,
∆ε ) 25 M-1 cm-1 at 241 nm).
In summary, it is clear from the CD spectra that the magnitude
of ∆ε is dependent on the chiral ligand present in the complex,
ranging from nearly zero to 53 M-1 cm-1. Consistently, R,R-
NORPHOS (2f) produced the most substantial ∆ε values,
followed by S,S-CHIRAPHOS (2b). Ligands R-PROPHOS (2c)
and R,R-Me-DUPHOS (2e) provided little or no effect. While
still empirical, these comparisons do suggest that R,R-NOR-
PHOS and S,S-CHIRAPHOS are most effective in providing
for chirality transfer from the diphosphine ligand to the
framework of the platinum acetylide complexes studied. This
outlines a valuable design principle toward the construction of
larger and functional chiral molecules based on platinum
acetylide building blocks.
and 89.66(10)°, respectively. When comparing bond lengths
between the trans- and cis-Pt-acetylide complexes 1b and 4e,
the only noteworthy difference is found for the Pt-P bonds
where the cis-Pt-acetylide bonds of 4e are slightly shorter (by
ca. 0.03 Å).
The electronic absorption characteristics of acetylide com-
plexes 3b-f and 4b-f were examined by UV-vis and CD
spectroscopies.16 The cis-Pt-acetylide complexes 3b-f all have
two absorption maxima in their UV-vis spectra; the lower
energy absorption is observed between 293 and 301 nm and
attributed to the MLCT absorption.17 The higher energy
absorption is observed between 257 and 268 nm, ascribed to a
π-π* transition of the ligands. In the CD spectra, only the S,S-
CHIRAPHOS- and R,R-NORPHOS-containing compounds 3b
and 3f show any remarkable features (Figure 4). Both have a
weak, low-energy band at 291 and 288 nm, respectively, and a
strong, high-energy bisignate band at 254 and 253 nm,
respectively. Complexes 3c-e either do not contain a bisignate
band (3e) or display only a weak signal in the higher energy
region (3c and 3d). The R,R-NORPHOS-containing compound
3f has the most intense signal in the CD spectrum of ∆ε ) 28
M-1 cm-1 (240 nm), and the S,S-CHIRAPHOS-containing
compound 3b has the second largest signal of ∆ε ) 13 M-1
cm-1 (268 nm).
(15) For a discussion of the significance of P-Pt-P bite angles, see
for example: (a) Freixa, Z.; van Leeuwen, P. W. N. M. Dalton Trans. 2003,
1890–1901. (b) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.;
Dierkes, P. Chem. ReV. 2000, 100, 2741–2769. (c) Casey, C. P.; Whiteker,
G. T. Isr. J. Chem. 1990, 30, 299–304.
Experimental Section
(16) The UV-vis spectra were recorded for pure ligands 2b-f, and all
show a high-energy absorption between 254 and 263 nm corresponding to
the π-π* transition for the phenyl chromophores with ε < 16 000 M-1
cm-1. These absorptions are also present in all of the cis-Pt-acetylide
complexes that contain these ligands. The circular dichroism (CD) spectral
analysis of the pure ligands R-PROPHOS (2c) and S, S-BDPP (2d) show
weak signals at 228 and 243 nm, respectively, while the CD spectra of
S,S-CHIRAPHOS (2b), R,R-Me-DUPHOS (2e), and R,R-NORPHOS (2f)
contain stronger signals at 229, 317, and 233 nm, respectively. The CD
spectra of all five ligands show at least one cross-over point in the range
236-275 nm. In all cases the absolute signal intensity of the pure ligand is
∆ε < 10 M-1 cm-1 for absorptions g225 nm; see Supporting Information
for spectra (Figures S1 and S2).
(17) For discussion of MLCT in Pt-acetylides, see: (a) Ref 2e. (b) Saha,
R.; Qaium, M. A.; Debnath, D.; Younus, M.; Chawdhury, N.; Sultana, N.;
Kociok-Ko¨hn, G.; Ooi, L.-L.; Raithby, P. R.; Kijima, M. Dalton Trans.
2005, 2760, 2765. (c) D’Amato, R.; Furlani, A.; Colapietro, M.; Portalone,
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Reagents were purchased reagent grade from commercial sup-
pliers and used without further purification. THF was distilled from
sodium/benzophenone ketyl; hexanes and CH2Cl2 were distilled
from CaH2 immediately prior to use. Compounds 1a, 3a, and 3b
were prepared as previously reported.8,9 Column chromatography
was carried out on aluminum oxide (neutral, Brockman 1, 150
mesh) from Aldrich Chemical Co., Inc. or silica gel-60 (230-400
mesh) from General Intermediates of Canada or Silicycle. Thin-
layer chromatography (TLC) was done on aluminum sheets coated
with aluminum oxide 60 F254 from EM Separations or plastic sheets
coated with silica gel G UV254 from Macherey-Nagel and visualized
by UV light. IR spectra were done with a Nic-Plan IR Microscope
on films cast from CH2Cl2. For IR data, useful functional groups
and 3-4 of the strongest absorptions are reported including, but
not limited to, C-H, CdC, and Ct C bond stretches. 1H, 13C, and
31P NMR spectra were acquired on a Varian-400 at 27 °C in either
CDCl3 or CD2Cl2. Solvent peaks 7.24, 5.32 for 1H and 77.00, 53.80

Chiral cis-Platinum Acetylide Complexes
Organometallics, Vol. 27, No. 23, 2008 6325
for 13C, respectively, were used as reference and H3PO4 as 31P
reference. For simplicity, the coupling constants of the aryl protons
for para-substituted tolyl groups have been reported as pseudo-
first-order, even though they are second-order (AA′XX′) spin
systems. Coupling constants J are reported as observed. EI-MS (70
eV) were done with a Kratos MS 50 instrument, and ESI-MS with
either a Micromass Zabspec oaTOF or PE Biosystems Mariner TOF
instrument. For mass spectral analyses, low-resolution data are
provided in cases when M+ is not the base peak; otherwise, only
high-resolution data are provided. Elemental analyses were per-
formed by the Microanalytical Service, Department of Chemistry,
University of Alberta. Circular dichroism spectra were recorded at
20.0 °C, from 550 to 220 nm with 330 increments, on an OLIS
DSM 17 CD, Cary-17 Conversion spectrometer/circular dichroism
module, Online Instruments Inc., with a 1 mm (Hellma) cuvette.
UV-vis spectra were acquired with a Varian Cary 400 Scan
spectrometer at room temperature with a 1 cm quartz cuvette. The
same solutions used for CD spectroscopy were used for UV-vis
spectroscopy, and the appropriate dilutions were prepared to result
in UV absorbencies in the range of A ) 0.2-4.0. The CD and
UV-vis spectra were recorded the same day for each sample. To
ensure the data were statistically equivalent, the standard deviation
of three replicates was calculated and any results >10% were
discarded. The raw data of the replicates were then averaged to
produce a single spectrum.18
2JC-P ) 133 Hz (trans), 2JC-P ) 14 Hz (cis)), 109.2 (d, 3JC-P ) 29
Hz (trans)), 40.8 (d, JC-P ) 34 Hz), 37.3-36.4 (m), 36.1, 19.04,
19.02, 17.7-17.3 (m), 14.1, 12.0; 31P{1H} NMR (162 MHz, CDCl3)
1
δ 65.3 (pseudo-t, JP-Pt ) 2134 Hz); ESI-HRMS (ClCH2CH2Cl)
calcd for C40H71P2PtSi2 ([M + H]+) 864.4217, found 864.4220.
cis-(R,R-Me-DUPHOS)Pt(Ct C-p-CH3-C6H4)2 (4e). 1,2-Bis-
[(2R,5R)-2,5-dimethylphospholano]benzene (2e, 8.3 mg, 0.027
mmol) was added to a solution of 1b (26 mg, 0.027 mmol) in dry
CH2Cl2 (10 mL). The mixture was stirred at rt for 16 h. Solvent
removal and purification via column chromatography (alumina,
hexanes) afforded 4e (16 mg, 81%) as a yellow solid: mp 199 °C
(dec); Rf ) 0.44 (CH2Cl2/hexanes, 2:1); UV-vis (CH2Cl2) λmax (ꢀ)
263 (40 900), 325 (16 900) nm; IR (CH2Cl2, cast) 2923, 2108, 1504
cm-1 1H NMR (400 MHz, CDCl3) δ 7.72-7.67 (m, 2H),
;
7.60-7.57 (m, 2H), 7.35 (d, J ) 8.1 Hz, 4H), 7.02 (d, J ) 8.4,
4H), 3.54-3.38 (m, 2H), 2.81-2.71 (m, 2H), 2.40-2.23 (m, 4H),
2.30 (s, 6H), 2.15-2.05 (m, 2H), 1.76-1.65 (m, 2H), 1.54 (d, J )
7.0 Hz, 3H), 1.49 (d, J ) 7.0 Hz, 3H), 0.88 (d, J ) 7.2 Hz, 3H),
0.84 (d, J ) 7.2 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ
143.6 (pseudo-t, JC-P ) 36 Hz), 134.6, 132.8 (pseudo-t, JC-P
)
8.3 Hz), 131.2 (br), 128.3, 125.4, 111.9 (d, 3JC-P ) 35 Hz (trans)),
2
2
106.3 (dd, JC-P ) 143 Hz (trans), JC-P ) 15 Hz (cis)), 40.5 (d,
JC-P ) 34 Hz), 37.5-36.9 (m), 36.3 (br), 21.2, 17.5 (pseudo-t,
JC-P ) 3.5 Hz), 13.9; 31P{1H} NMR (162 MHz, CDCl3) δ 66.4
1
(pseudo-t, JP-Pt ) 2206 Hz); EIMS m/z 731.2 (M+, 70), 501.1
Representative Procedures. cis-(R,R-Me-DUPHOS)Pt(Ct C-
Sii-Pr3)2 (3e). 1,2-Bis[(2R,5R)-2,5-dimethylphospholano]benzene
(2e, 8.9 mg, 0.029 mmol) was added to a solution of 1a (31 mg,
0.029 mmol) in dry CH2Cl2 (5 mL). The mixture was stirred at rt
for 48 h. Solvent removal and purification via gradient column
chromatography (silica gel, CH2Cl2/hexanes (1:2) to CH2Cl2/hexanes
(1:1)) afforded 3e (22 mg, 88%) as a white solid: mp 193-197
°C; Rf ) 0.72 (CH2Cl2/hexanes, 2:1); UV-vis (CH2Cl2) λmax (ꢀ)
([M - 2(Ct C-p-Me-C6H4)]+, 100); HRMS calcd for C36H42P2Pt
(M+) 731.2410, found 731.2419.
Acknowledgment. This work has been generously sup-
ported by the University of Alberta and the Natural Sciences
and Engineering Research Council of Canada (NSERC)
through the Discovery Grant program. The authors thank the
staff, in particular Wayne Moffat, of the Analytical and
Instrumentation Laboratory at the University of Alberta, for
their help with the circular dichroism spectroscopy.
268 (13 600), 301 (11 000) nm; IR (CH2Cl2, cast) 2938, 2860 cm-1
;
1H NMR (400 MHz, CDCl3) δ 7.67-7.63 (m, 2H), 7.56-7.52 (m,
2H), 3.50-3.38 (m, 2H), 2.74-2.61 (m, 2H), 2.36-2.16 (m, 6H),
1.73-1.62 (m, 2H), 1.48 (d, J ) 7.0 Hz, 3H), 1.44 (d, J ) 7.0 Hz,
3H), 1.12 (d, J ) 3.0 Hz, 18H), 1.11 (d, J ) 2.9 Hz, 18H),
1.08-0.99 (m, 6H), 0.86 (d, J ) 7.2 Hz, 3H), 0.83 (d, J ) 7.2 Hz,
Supporting Information Available: Complete experimental
procedures; spectroscopic data for all new compounds; NMR, CD,
and UV-vis spectra of new compounds; crystallographic informa-
tion for 1b and 4e in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
3H); 13C{1H} NMR (100 MHz, CDCl3) δ 143.8 (pseudo-t, JC-P
36 Hz), 132.8 (pseudo-t, JC-P ) 8.2 Hz), 130.9 (br), 128.9 (dd,
)
(18) For a detailed description of the procedure used for the UV-vis
and CD spectroscopic studies, see the Supporting Information.
OM800633H