Platinum(0) complexes of chiral diphosphines: Enantioface-selective binding of trans-stilbene

Article abstract of DOI:10.1021/om971000j

The zerovalent complexes Pt(diphos)(trans-stilbene) (diphos = dppe, dppf, (S,S)-Chiraphos, R-Tol-Binap, (R,R)-Me-Duphos, (S,S)-Diop) were prepared by reduction of the corresponding Pt(diphos)Cl₂ compounds. NMR and crystal structure data show that the trans-stilbene complexes with chiral diphosphines exist as a mixture of diastereomers differing in their binding of the enantiofaces of the prochiral olefin; for R-Tol-Binap, they can be separated by recrystallization. The complexes Pt((R,R)-Me-Duphos)Cl₂ and Pt(diphos)(trans-stilbene) (diphos = dppf, (S,S)-Chiraphos, R-Tol-Binap, (S,S)-Diop) were structurally characterized by X-ray crystallography.

Full text of DOI:10.1021/om971000j

1412
Organometallics 1998, 17, 1412-1419
P la tin u m (0) Com p lexes of Ch ir a l Dip h osp h in es:
En a n tiofa ce-Selective Bin d in g of tr a n s-Stilben e
Denyce K. Wicht, Michael A. Zhuravel, Ronald V. Gregush, and
David S. Glueck*
6128 Burke Laboratory, Department of Chemistry, Dartmouth College,
Hanover, New Hampshire 03755
Ilia A. Guzei, Louise M. Liable-Sands, and Arnold L. Rheingold
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received November 13, 1997
The zerovalent complexes Pt(diphos)(trans-stilbene) (diphos ) dppe, dppf, (S,S)-Chiraphos,
R-Tol-Binap, (R,R)-Me-Duphos, (S,S)-Diop) were prepared by reduction of the corresponding
Pt(diphos)Cl2 compounds. NMR and crystal structure data show that the trans-stilbene
complexes with chiral diphosphines exist as a mixture of diastereomers differing in their
binding of the enantiofaces of the prochiral olefin; for R-Tol-Binap, they can be separated
by recrystallization. The complexes Pt((R,R)-Me-Duphos)Cl2 and Pt(diphos)(trans-stilbene)
(diphos ) dppf, (S,S)-Chiraphos, R-Tol-Binap, (S,S)-Diop) were structurally characterized
by X-ray crystallography.
In tr od u ction
Gladysz and Boone have recently reviewed the lit-
erature on molecular recognition in related π-complexes
of chiral metal moieties.8 The Pt(0) complex Pt(Diop)-
(C2H4) has been used as a chiral derivatizing agent to
assay the enantiomeric excess of racemic mixtures of
olefins and to study enantioface recognition of prochiral
olefins.9 Here, we report investigations of the coordina-
tion of one substrate, trans-stilbene, to a series of related
chiral metal fragments. In contrast, binding of a variety
of structurally related ligands to the same chiral metal
center has often been examined.10
Zerovalent platinum complexes are useful starting
materials for studies of oxidative addition and its role
in catalysis.1 Analogous chiral reagents find applica-
tions in asymmetric synthesis.2 Our interest in platinum-
catalyzed hydrophosphination3 and a possible asym-
metric version of this reaction led us to investigate
sources of the Pt(diphos) fragment (diphos ) bidentate
diphosphine) as catalyst precursors.4 The ethylene
compounds5 PtL2(C2H4) are common reagents, but re-
lated trans-stilbene complexes6 are, in general, easier
to prepare and more robust.7 We report here the
synthesis of a series of Pt(diphos)(trans-stilbene) com-
plexes and NMR and crystallographic studies of chiral
recognition of the trans-stilbene enantiofaces by chiral
Pt(diphos) fragments.
Resu lts a n d Discu ssion
The precursors Pt(diphos)Cl2 were prepared from Pt-
(COD)Cl2 (COD ) 1,5-cyclooctadiene) and the appropri-
ate diphosphine.11 The (R,R)-Me-Duphos and R-Tol-
Binap complexes 1 and 2 are new and were characterized
spectroscopically and by elemental analyses.12 In ad-
(1) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987. (b) Parshall, G. W.;
Ittel, S. D. Homogeneous Catalysis: the Applications and Chemistry
of Catalysis by Soluble Transition Metal Complexes, 2nd ed.; Wiley:
New York, 1992.
(7) (a) For example, the procedure for generation of a variety of PtL2-
(C2H4) complexes (ref 5a) states that they cannot be isolated by
removing the solvent. (b) Lesley, G.; Nguyen, P.; Taylor, N. J .; Marder,
T. B.; Scott, A. J .; Clegg, W.; Norman, N. C. Organometallics 1996,
(2) Noyori, R. Asymmetric Catalysis in Organic Synthesis; Wiley-
Interscience: New York, 1994.
(3) Wicht, D. K.; Kourkine, I. V.; Lew, B. M.; Nthenge, J . M.; Glueck,
D. S. J . Am. Chem. Soc. 1997, 119, 5039-5040.
15, 5137-5154. Reference 9 describes the isolation of ethylene
complexes of Pt(dppe) and dppb (dppe ) Ph2P(CH2)2PPh2, dppb )
Ph2P(CH2)4PPh2), but these were not obtained pure (see p 5139). (c)
Brown, J . M.; Cook, S. J .; Kimber, S. J . J . Organomet. Chem. 1984,
269, C58-C60. Pt(dppb)(C2H4) was prepared by reduction of the
dichloride with NaBH4 in CH2Cl2/EtOH under ethylene, but the dppp
analogue (dppp ) Ph2P(CH2)3PPh2) made in this way was contami-
nated with Pt(dppp)2. (d) Reference 4a states (p 1196) that Pt-
(Chiraphos)(C2H4) could not be prepared by NaBH4 reduction of
Pt(Chiraphos)Cl2 under ethylene.
(4) For related studies, see: (a) Brown, J . M.; Perez-Torrente, J . J .;
Alcock, N. W. Organometallics 1995, 14, 1195-1203. (b) Paganelli, S.;
Matteoli, U.; Scrivanti, A. J . Organomet. Chem. 1990, 397, 119-125.
(5) (a) Head, R. A. Inorg. Synth. 1990, 28, 132-135. (b) Blake, D.
M.; Roundhill, D. M. Inorg. Synth. 1978, 18, 120-125. (c) Camalli, M.;
Caruso, F.; Chaloupka, S.; Leber, E. M.; Rimml, H.; Venanzi, L. M.
Helv. Chim. Acta 1990, 73, 2263-2274. (d) Nagel, U. Chem. Ber. 1982,
115, 1998-1999. (e) Smith, V. C. M.; Aplin, R. T.; Brown, J . M.;
Hursthouse, M. B.; Karalulov, A. I.; Malik, K. M. A.; Cooley, N. A. J .
Am. Chem. Soc. 1994, 116, 5180-5189. (f) Brown, J . M.; Cooley, N. A.
Organometallics 1990, 9, 353-359.
(8) Gladysz, J . A.; Boone, B. J . Angew. Chem., Int. Ed. Engl. 1997,
36, 550-583.
(9) See Scheme 1 for the structure of Diop. (a) Reference 7c (b)
Parker, D.; Taylor, R. J . J . Chem. Soc., Chem. Commun. 1987, 1781-
1783. (c) Parker, D.; Taylor, R. J . Tetrahedron 1988, 44, 2241-2248.
(d) Fulwood, R.; Parker, D.; Ferguson, G.; Kaltner, B. J . Organomet.
Chem. 1991, 419, 269-276.
(6) Some complexes PtL2(trans-stilbene) are known for monodentate
phosphines L. (a) PPh3: Chatt, J .; Shaw, B. L.; Williams, A. A. J . Chem.
Soc. A 1962, 3269-3270. (b) PEt3: Browning, J .; Green, M.; Spencer,
J . L.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1974, 97-101. (c)
PMe3: Green, M.; Spencer, J . L.; Stone, F. G. A.; Welch, A. J . J . Chem.
Soc., Dalton Trans. 1975, 179-184.
(10) See refs 8 and 9 and for a recent example: Quan, R. W.; Li, Z.;
J acobsen, E. N. J . Am. Chem. Soc. 1996, 118, 8156-8157.
S0276-7333(97)01000-5 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/12/1998

Pt(0) Complexes of Chiral Diphosphines
Organometallics, Vol. 17, No. 7, 1998 1413
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1, 4-6, a n d 8
1
4
5
6
8
formula
fw
C
19H30Cl4P2Pt
C52H48FeOP2Pt
1001.78
C46H48OP2Pt
873.97
C66H60OP2Pt
1126.17
C45H44O2P2Pt
873.92
657.26
space group
a, Å
b, Å
P212121
P21/n
I222
P212121
P1h
9.7798(2)
13.5498(2)
18.2175(3)
14.701(9)
17.195(7)
17.739(5)
16.8401(2)
25.4756(2)
37.1463(3)
11.0429(2)
16.4825(3)
28.8459(4)
12.5542(2)
14.2110(2)
14.3244(2)
75.6220(6)
68.8019(7)
70.4527(7)
2221.64(8)
2
c, Å
R, deg
â, deg
94.67(3)
γ, deg
V, Å3
2414.08(5)
4
4469(4)
4
15936.18(12)
16
5250.38(15)
4
Z
cryst color, habit
D(calc), g cm-3
µ(Mo KR), cm-1
temp, K
abs corr
T(max)/T(min)
diffractometer
radiation
R(F), %a
R(wF2), %a
colorless block
1.808
63.91
red block
1.489
35.60
257(2)
yellow plate
1.427
36.34
yellow plate
1.425
27.77
yellow block
1.409
32.68
173(2)
223(2)
213(2)
213(2)
empirical
1.000/0.376
P4/CCD
empirical
1.000/0.420
P4/CCD
Mo KR (λ ) 0.710 73 Å)
3.87
empirical
1.000/0.781
P4/CCD
Siemens P4
P4/CCD
2.53
6.09
6.28
12.53
2.98
6.14
4.68
12.87
10.00
Quantity minimized ) R(wF2) ) ∑[w(Fo - Fc2)2/∑[(wFo2)2]1/2; R ) ∑∆/∑(Fo), ∆ ) |(Fo - Fc)|.
a
2
Sch em e 1a
F igu r e 1. ORTEP diagram of 1‚CH2Cl2, with 30% prob-
ability thermal ellipsoids. The solvent molecule is not
shown. Selected bond lengths (Å): Pt-P(2) 2.2178(13), Pt-
P(1) 2.2183(11), Pt-Cl(1) 2.3828(12), Pt-Cl(2) 2.3881(12).
Selected bond angles (deg): P(2)-Pt-P(1) 87.73(4), P(2)-
Pt-Cl(1) 89.72(5), P(1)-Pt-Cl(1) 177.20(5), P(2)-Pt-Cl-
(2) 177.91(5), P(1)-Pt-Cl(2) 90.21(4), Cl(1)-Pt-Cl(2) 92.34
a
(4).
(i) Reagents: trans-stilbene + 2 equiv of reducing agent;
LiBEt3H for 3-5, NaBH4 for 6, NaBH(OMe)3 for 7 and 8.
dition, the Duphos complex 1 was structurally charac-
terized by X-ray crystallography as a CH2Cl2 solvate.
Data collection and structure refinement are sum-
marized in Table 1. An ORTEP diagram and selected
bond lengths and angles appear in Figure 1, and
additional information is in the Experimental Section
and the Supporting Information. The complex adopts
the expected square-planar structure. The Duphos bite
angle is 87.73(4)°; this small distortion is balanced by
the Cl-Pt-Cl angle of 92.34(4)°. The Pt-Cl bond
lengths (2.383(12) and 2.388(12) Å) are similar to those
for cis-Pt(PMe3)2Cl2 (2.364(8) and 2.388(9) Å),13 consis-
tent with similar trans influences for PMe3 and Duphos.
The Pt(0) trans-stilbene complexes 3-8 (diphos )
dppe (3), dppf (4), (S,S)-Chiraphos (5), R-Tol-Binap (6),
(R,R)-Me-Duphos (7), (S,S)-Diop (8)) were prepared by
reduction of the corresponding dichlorides in the pres-
ence of excess trans-stilbene (Scheme 1). An attempt
to make Pt(dppe)(cis-stilbene) (9) initially gave the
desired complex, according to 31P NMR monitoring of
the reaction mixture, but isomerization occurred on
workup and recrystallization to give a mixture of the
cis- and trans-stilbene complexes 9 and 3. When an
isolated sample of this mixture is redissolved, further
isomerization occurs slowly at room temperature; heat-
ing to 50 °C causes complete conversion of 9 into 3.
(11) See Scheme 1 for ligand structures. Most of these dichlorides
have been reported previously. dppe: Hudson, M. J .; Nyholm, R. S.;
Stiddard, M. H. B. J . Chem. Soc. A 1968, 40-43. dppf: Bandini, A.
L.; Banditelli, G.; Cinellu, M. A.; Sanna, G.; Minghetti, G.; Demartin,
F.; Manassero, M. Inorg. Chem. 1989, 28, 404-410 and ref 1 therein.
Chiraphos: Morandini, F.; Consiglio, G.; Piccolo, O. Inorg. Chim. Acta
1982, 57, 15-19. Diop: Gramlich, V.; Consiglio, G. Helv. Chim. Acta
1979, 62, 1016-1024.
(12) The closely related Pt(S-Binap)Cl2 has been prepared (Kollar,
L.; Sandor, P.; Szalontai, G. J . Mol. Catal. 1991, 67, 191-198) and
(13) Messmer, G. G.; Amma, E. L.; Ibers, J . A. Inorg. Chem. 1967,
6, 725-730.
1
shows J Pt-P ) 3667 Hz.

1414 Organometallics, Vol. 17, No. 7, 1998
Wicht et al.
Ta ble 2. Selected NMR Da ta for th e Com p lexes
P t(d ip h os)(tr a n s-stilben e)a
3
4
5a ,b
6a ,b
7a ,b
8a ,b
δ (1H)b
4.88
4.35
4.93
4.90
63
4.65
4.62
64
60
57.5
d
217
d
14
4.64
4.45
61
4.25
4.15
59
b
2J Pt-H
61
d
60
65
63
59
δ(13C)c
57.5
215
14
54.4
54.6
d
50.3
53.4
230
d
58.5
58.6
206
208
13
c
1J Pt-C
d
c
2J P-C
d
15
16
15
d
16
13
δ(31P)
49.0
3343
24.5
3763
56.4
53.8
3333
3316
27.8
30.0
3546
3490
71.4
66.3
3137
3091
10.6
10.5
3632
3623
1J Pt-P
F igu r e 2. Two possible diastereomers of Pt(diphos)(trans-
stilbene) (diphos ) chiral bidentate diphosphine). The
quadrant diagram (view along the PtP2 plane) illustrates
steric interactions of trans-stilbene with the Pt(diphos)
fragment. Black circles represent steric hindrance due to
substituents of the C2-symmetric diphosphine.
a
In C6D6, except for the 13C spectrum of 4 (CD2Cl2). Chemical
shifts are given in ppm and coupling constants in hertz. For 5-8,
a
refers to the major diastereomer and b to the minor one.
Coordinated stilbene CH. c Coordinated stilbene CH. Not mea-
b
d
sured.
Several related metal-mediated cis-trans isomeriza-
tions of stilbene and its derivatives have been re-
ported.14
coordinated trans-stilbene appear between 4.4 and 4.9
1
ppm in the H NMR spectra. They exhibit coupling to
2
195Pt with J Pt-H of approximately 60 Hz, and the 13C-
The syntheses of the stilbene complexes generally go
in high yield, with lower isolated yields attributable to
the high solubility of some derivatives in organic
solvents. Several reducing agents were assayed, with
those listed in the scheme being most convenient. For
example, complexes 7 and 8 could also be prepared with
LiBEt3H, but the formation of a dark oil after extraction
with toluene made separation and purification of the
products difficult.
The new complexes are yellow solids (4 is red), which
are robust in solution in the absence of air and can be
stored at room temperature as solids under nitrogen for
months. Since trans-stilbene is prochiral, binding dif-
ferent enantiofaces of this olefin in 5-8 gives mixtures
of diastereomers.15 The binding selectivities can be
rationalized on steric grounds with a quadrant diagram
analysis,8 as shown in Figure 2; this is also discussed
below along with structural data obtained from X-ray
crystallography. In most cases, recrystallization gave
samples enriched in one enantiomer, and R-Tol-Binap
derivative 6 could be isolated as a pure diastereomer
(see below).
{1H} NMR signals of the olefinic carbons appear as an
apparent triplet (2J CP ) 13-16 Hz) between 50 and 59
1
ppm with a J Pt-C coupling of approximately 200 Hz.
Spectroscopic monitoring of the syntheses summa-
rized in Scheme 1 provided more information on the
formation of 5-8 and on the observed diastereoselec-
tivity in their binding of trans-stilbene. For example,
treatment of Pt((S,S)-chiraphos)Cl2 with LiBEt3H in
THF gave a solution whose 31P NMR spectrum showed
a 2:1 mixture of diastereomers. However, after extrac-
tion with toluene and one recrystallization, compounds
5a and 5b were obtained in an approximately equal
ratio. Multiple recrystallizations from THF/petroleum
ether result in enrichment (5:1) of complex 5a . The
ratio of 5a to 5b also changes in solution in the absence
of excess trans-stilbene. For example, a sample of
diastereomers 5a and 5b in C6D6 (5:1 ratio) converted
to a 1.5:1 mixture over 2 weeks.
Treatment of Pt(R-Tol-binap)Cl2 (2) with NaBH4 in
EtOH initially gave a dark purple reaction mixture,
which turned brown over ∼12 h while some of the yellow
product 6 precipitated from solution. The 31P NMR
spectrum of the purple solution shows a singlet at 28.8
ppm (1J Pt-P ) 2073 Hz), which is tentatively assigned
to the dihydride Pt(R-Tol-Binap)H2 on the basis of its
small 1J Pt-P coupling.17 In another synthesis, a different
intermediate (δ 27.7, with two sets of Pt satellites, 1J P-Pt
The stilbene complexes were characterized by spec-
troscopy (Table 2), by elemental analyses and mass
spectrometry, and by X-ray crystallography (see below).
The 31P{1H} NMR spectra exhibit singlets with plati-
1
num satellites with J P-Pt values ranging from ca. 3000
to 3700 Hz, similar to those of previously reported Pt-
3
) 3114 and J P-Pt ) 174 Hz), possibly the dinuclear
(0) complexes of ethylene.16 The olefinic protons of
cation18 [Pt2(R-Tol-Binap)2H3]+, was observed. None-
theless, in both cases, after removal of the solvent under
vacuum and extraction with toluene, the 31P NMR
spectrum exhibits a 1.5:1 mixture of diastereomers 6a
and 6b.
(14) For examples of photochemical isomerization, see: (a) Wrighton,
M.; Hammond, G. S.; Gray, H. B. J . Am. Chem. Soc. 1971, 93, 3285-
3287. (b) Sakaki, S.; Okitaka, I.; Ohkubo, K. Inorg. Chem. 1984, 23,
198-203. For thermal processes, see, for example: (c) Manuel, T. A.
J . Org. Chem. 1962, 27, 3941-3945. (d) Castiglione, M.; Giordano, R.;
Sappa, E. J . Organomet. Chem. 1991, 407, 377-389. (e) Todres, Z. V.;
Ionina, E. A.; Pombeiro, A. J . L. J . Organomet. Chem. 1992, 438, C23-
C25. Here, a referee suggested another plausible mechanism for
isomerization, reversible protonation of the Pt complex by catalytic
adventitious acid.
Recrystallization of this mixture from THF or THF/
petroleum ether gives exclusively diastereomer 6a . The
mother liquor is enriched in the minor diastereomer (by
31P NMR), which implies that diastereomer 6a prefer-
(15) For related observations in Ni(0) complexes of chiral diphos-
phinites, see: Casalnuovo, A. L.; RajanBabu, T. V.; Ayers, T. A.;
Warren, T. H. J . Am. Chem. Soc. 1994, 116, 9869-9882.
(17) Schwartz, D. J .; Andersen, R. A. J . Am. Chem. Soc. 1995, 117,
4014-4025.
(18) Knobler, C. B.; Kaesz, H. D.; Minghetti, G.; Bandini, A. L.;
Banditelli, G.; Bonati, F. Inorg. Chem. 1983, 22, 2324-2331.
(16) The P-Pt coupling constants for PtL2(C2H4) complexes where
L
)
PPh3, 1/2dppe, and 1/2dppb are 3721, 3303, and 3524 Hz,
respectively. See ref 7.

Pt(0) Complexes of Chiral Diphosphines
Organometallics, Vol. 17, No. 7, 1998 1415
entially crystallizes from the solution. Pure samples of
6a slowly isomerized in solution to give mixtures of 6a
and 6b over several days. To obtain qualitative mecha-
nistic information on this process, the isomerization of
C6D6 solutions of pure 6a with 0, 1, 5, and 10 equiv of
trans-stilbene was monitored over several days by 31P
NMR. Isomerization occurred most quickly in the tube
with no added stilbene, and increasing the concentration
of stilbene slowed the isomerization. It was not possible
to determine if equilibrium mixtures of 6a and 6b were
obtained due to decomposition after several weeks. No
new signals were observed in the NMR spectra of these
solutions, and the 31P NMR chemical shifts and Pt-P
coupling constants of 6a and 6b were unaffected by
stilbene concentration. These observations suggest that
isomerization of 6 occurs by a dissociative pathway
involving loss of stilbene and binding of the other
enantioface.19
F igu r e 3. ORTEP diagram of 4, with 30% probability
thermal ellipsoids. The THF molecule is not shown.
The (R,R)-Me-Duphos and (S,S)-Diop complexes 7 and
8 were prepared using NaBH(OMe)3 in THF. For 7,
both prior to workup and after one recrystallization from
THF/MeOH, the ratio of the two diastereomers is 3:1
(a :b). As for Chiraphos analogue 5, multiple recrystal-
lizations (petroleum ether, -25 °C) give a sample
enriched in one diastereomer (7:1 ratio). When this
material was dissolved in C6D6, the ratio changed to 3:1
over 1 week. In the case of Diop complex 8, the
diastereomers 8a and 8b exist in approximately equal
ratios (1.2:1) in the reaction mixture prior to workup
and after two recrystallizations from petroleum ether.
This ratio did not change on standing in solution.
From these observations, it appears that the kinetic
diastereomer ratios are not much different from the
apparent thermodynamic ones. We assume that the
diastereomer ratios observed by NMR after days or
weeks represent true equilibrium mixtures, but since
isomerization is slow and since we have not been able
to resolve both diastereomers of a given complex and
allow them to reach “equilibrium” separately, this is not
necessarily true. With this assumption, the observation
in all cases of both diastereomers shows that they are
similar in energy. Diastereomer interconversion occurs
both in the presence and absence of trans-stilbene;
qualitative observations for Tol-Binap complex 6 suggest
that this isomerization is a dissociative process. As
might be expected, the more rigid Tol-Binap and Duphos
complexes are more effective than the relatively flexible
Diop and Chiraphos ones in recognition of trans-stilbene
enantiofaces.
Cr ysta llogr a p h ic Stu d ies. The structures of com-
plexes 4-6 and 8 were determined by X-ray crystal-
lography. Data collection and structure refinement are
summarized in Table 1. ORTEP diagrams are shown
in Figures 3-6, selected bond lengths and angles are
given in Table 3, and additional information appears
in the Experimental Section and the Supporting Infor-
mation. As expected from the solution NMR results,
Chiraphos complex 5 crystallizes as a mixture of dia-
stereomers but resolved R-Tol-Binap compound 6 exists
as a single diastereomer in the solid state. Although
approximately equal amounts of the diastereomers of
F igu r e 4. ORTEP diagrams of the two independent
molecules of 5 in the unit cell, with 30% probability thermal
ellipsoids. The THF molecules are not shown.
Diop complex 8 were observed in solution by NMR, the
crystal studied contained a single diastereomer.
Despite the presence of enantiomerically pure (S,S)-
Diop ligand in compound 8, the Pt complex crystallizes
in the centrosymmetric space group P1h (see Experimen-
tal Section). The packing of the crystal lattice is
apparently determined by the majority of the structure
represented as (stilbene)Pt(Ph2P‚‚‚PPh2). Thus, the
(19) Peng, T.-S.; Gladysz, J . A. J . Am. Chem. Soc. 1992, 114, 4174-
4181.

1416 Organometallics, Vol. 17, No. 7, 1998
Wicht et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in P t(d ip h os)(tr a n s-stilben e) Com p lexesa
4
5
5′
6
8
Pt-P
Pt-C
2.261(3)
2.263(3)
2.272(2) 2.271(2) 2.2806(9) 2.284(2)
2.277(2) 2.274(2) 2.2840(8) 2.290(2)
2.123(11) 2.137(5) 2.118(6) 2.115(4)
2.131(12) 2.139(5) 2.125(6) 2.146(4)
1.47(2)
105.95(12) 87.13(6) 86.55(6) 94.41(3)
40.5(5)
144.7(4)
105.1(4)
109.1(4)
148.7(4)
2.143(6)
2.145(6)
1.459(10)
100.85(6)
C-C
1.438(9) 1.449(10) 1.450(5)
P-Pt-P
C-Pt-C
P-Pt-C
39.3(2) 39.9(3)
39.79(14) 39.8(3)
154.3(2) 156.1(2) 148.81(10) 146.3(2)
115.6(2) 116.6(2) 109.48(11) 106.8(2)
118.3(2) 117.1(2) 116.67(10) 112.8(2)
157.2(2) 156.9(2) 155.83(10) 151.8(2)
(P-Pt-P)- 11.5
(C-Pt-C)
8.1
5.8
8.7
8.9
a
5 and 5′ are diastereomers.
from 1.438(9) to 1.47(2) Å, do not differ significantly.
As expected, these bond distances are longer than the
one in the free olefin (1.341(2) Å at 113K).21 The
C-Pt-C angles in bound stilbene (ranging from 39.3-
(2)° to 40.5(5)°) fall in a narrow range.
F igu r e 5. ORTEP diagram of 6, with 30% probability
thermal ellipsoids. The THF molecule is not shown.
Related ethylene9d (10) and C60 (11)22 complexes of
the Pt(Diop) fragment have been structurally character-
ized previously. These show larger Diop bite angles
than in 8 (105.25(4)°, 109.47(13)°, and 100.85(6)°,
respectively) and similar C-Pt-C angles (38.9(3)°, 42.0-
(4)°, and 39.8(3)°). The Pt-C distances in the fullerene
complex (2.09(2) and 2.12(2) Å) are not significantly
different from those in 8 (2.143(6), 2.145(6) Å), but those
in the ethylene adduct (2.109(5), 2.100(5) Å) are slightly
shorter. The Pt-P bond distances in 8 (2.284(2), 2.290-
(2) Å) are slightly longer than those in 10 (2.261(4),
2.254(1) Å) and 11 (2.262(4), 2.279(4) Å). These differ-
ences are presumably due to a combination of steric and
electronic effects.
The bite angle in Tol-Binap complex 6 (94.41(3)°) is
similar to the average one in Pt(Binap)2 (12; 92°).23 The
Pt-P distances in 6 (2.2806(9) and 2.2840(8) Å) are
shorter than those in 12 (average 2.33 Å); the latter
were previously described as unusually long, perhaps
due to the distortions imposed by the presence of two
chelate rings in 12. The Binap twist angle in 6 (71.5°)
is similar to that in 12 (78°).
F igu r e 6. ORTEP diagram of 8, with 30% probability
thermal ellipsoids. The solvent molecules are not shown.
The conformational flexibility of dppf has been re-
viewed.24 The bite angle observed in 4 (105.95(12)°) is
within the usual range of 93-112°, and the Pt-P bond
lengths (2.261(3) and 2.263(3) Å) are similar to those
in Pt(dppf)Cl2‚0.5(acetone) (2.252(4) and 2.260(4) Å).25
The structure of Chiraphos complex 5 allows direct
comparison of the two diastereomers formed by binding
the different enantiofaces of trans-stilbene. The data
in Table 3 show that the two diastereomers have
virtually identical structures in the solid state. Quali-
tatively, the observed small binding selectivity in solu-
tion may be ascribed to unfavorable steric repulsions
crystallographic symmetry exceeds the molecular sym-
metry. Consequently, the five-membered ring is equally
disordered over two positions corresponding to the (R,R)
and (S,S) configurations in each molecule. As pointed
out by a referee, the structure of a related chiral
organopalladium complex which also crystallized in P1h
shows similar effects and has been described as a
quasiracemate.20
In these complexes, the coordination geometry at
platinum is trigonal and almost planar. The dihedral
angles between the P-Pt-P and the C-Pt-C planes
(Table 3) range from 5.8° to 11.5°. Despite steric and
electronic differences between the diphosphine ligands,
the Pt-P and Pt-C distances are very similar in this
series, ranging from 2.261(3) to 2.290(2) Å and from
2.115(4) to 2.146(4) Å, respectively. Similarly, the C-C
bond lengths in coordinated trans-stilbene, which range
(21) Ogawa, K.; Sano, T.; Yoshimura, S.; Takeuchi, Y.; Toriumi, K.
J . Am. Chem. Soc. 1992, 114, 1041-1051 and references therein.
(22) Bashilov, V. V.; Petrovskii, P. V.; Sokolov, V. I.; Dolgushin, F.
M.; Yanovsky, A. I.; Struchkov, Y. T. Izv. Akad. Nauk, Ser. Khim. 1996,
1268-1274.
(23) Tominaga, H.; Sakai, K.; Tsubomura, T. J . Chem. Soc., Chem.
Commun. 1995, 2273-2274.
(24) Gan, K.-S.; Hor, T. S. A. In Ferrocenes. Homogeneous Catalysis,
Organic Synthesis, Materials Science; Togni, A., Hayashi, T., Eds.;
VCH: Weinheim, Germany, 1995; pp 3-104.
(20) Alcock, N. W.; Hulmes, D. I.; Brown, J . M. J . Chem. Soc., Chem.
Commun. 1995, 395-397. See also: Fraser, C.; Ostrander, R.; Rhein-
gold, A. L.; White, C.; Bosnich, B. Inorg. Chem. 1994, 33, 324-337.
(25) Clemente, D. A.; Pilloni, G.; Corain, B.; Longato, B.; Tiripicchio-
Camellini, M. Inorg. Chim. Acta 1986, 115, L9-L11.

Pt(0) Complexes of Chiral Diphosphines
Organometallics, Vol. 17, No. 7, 1998 1417
approximately 30 °C for 10 min. The solvent was removed in
vacuo, and the resulting solid was washed with 3 5 mL
portions of ether. Recrystallization from CH2Cl2/ether at -25
between the Chiraphos PPh2 groups and the coordinated
stilbene (see Figures 2 and 4). The greater face selec-
tivity seen in Tol-Binap complex 6 is presumably due
to increased steric interactions in this complex and more
efficient transfer of chiral information from the ligand
backbone to the PPh2 groups.2
1
°C yielded 918 mg (92%) of Pt(R-Tol-Binap)Cl2 in 3 crops. H
NMR (CDCl3): δ 7.71-7.64 (m, 4H, Ar), 7.54-7.30 (m, 12H,
Ar), 7.19-7.06 (m, 6H, Ar), 6.71 (d, 2H, Ar), 6.40 (d, 4H, Ar),
2.35 (6H, p-tol Me), 1.95 (6H, p-tol Me). 13C{1H} NMR (CDCl3):
δ 141.2 (Ar), 140.9 (Ar), 138.7 (Ar), 135.6-135.5 (m, Ar),
134.9-134.4 (m, Ar), 133.9 (Ar), 133.0 (Ar), 128.9-128.7 (m,
Ar), 128.4-127.8 (br m, Ar), 127.5 (Ar), 126.6 (Ar), 124.9 (Ar),
123.9 (Ar), 119.4 (Ar), 118.5 (Ar), 21.6 (p-tol Me), 21.3 (p-tol
Me). 31P{1H} NMR (CDCl3): δ 10.0 (1J P-Pt ) 3674). Anal.
Calcd for C48H40P2PtCl2: C, 61.02; H, 4.28. Found: C, 60.93;
H, 4.31.
Con clu sion
A series of platinum(0) trans-stilbene complexes has
been prepared, and the effect of several chiral diphos-
phine ligands on enantioface-selective binding of the
prochiral olefin was probed by NMR and X-ray crystal-
lography. The rigidity of the chiral ligand appears to
play an important role in asymmetric recognition.
Further work with these compounds will focus on
studies of oxidative addition and their use as catalyst
precursors in asymmetric hydrophosphination.
P t(d p p e)(tr a n s-stilben e) (3). A Schlenk tube was charged
with Pt(dppe)Cl2 (2.0 g, 3 mmol) and an excess of trans-stilbene
(815 mg, 4.52 mmol). Addition of THF (50 mL) gave a slurry,
which was treated over 5 min with 6.5 mL of a 1 M solution of
LiBEt3H in THF (6.5 mmol) to give a homogeneous orange
solution after addition was complete. The THF was removed
in vacuo, and the resulting yellow residue was extracted with
4 × 30 mL of toluene. The toluene was removed under
vacuum, and the resulting yellow solid was recrystallized from
THF/petroleum ether at -20 °C to give 1671 mg (72%) of
yellow-orange solid in 4 crops. An analytical sample was
recrystallized twice from THF/petroleum ether to give yellow
crystals. 1H NMR (C6D6): δ 7.69-7.63 (m, 4H, Ar), 7.39-7.29
(m, 6H, Ar), 7.16-6.87 (m, 20H, Ar), 4.90-4.86 (m, 2H, 2J Pt-H
) 61, CHdCH), 2.05-1.96 (m, 4H, CH2). 31P{1H} NMR (C6D6):
δ 49.0 (1J Pt-P ) 3343). IR: 3052, 1595, 1490, 1434, 1214, 1100,
1068, 1027, 963, 876, 815, 753, 693, 522, 494. Anal. Calcd
for C40H36P2Pt: C, 62.08; H, 4.70. Found: C, 61.86; H, 4.93.
P t(d p p e)(cis-stilben e) (9). Attempts to prepare this
complex as for the trans-stilbene analogue (or using NaBH-
(OMe)3) gave a mixture of the cis- and trans-stilbene complexes
as a brown powder. Monitoring of the reaction by 31P NMR
shows that cis-stilbene complex 9 is initially formed and
partially isomerizes to trans-stilbene complex 3 during workup/
recrystallization. Some characteristic resonances of the cis-
Exp er im en ta l Section
Gen er a l Deta ils. Unless otherwise noted, all reactions and
manipulations were performed in dry glassware under a
nitrogen atmosphere at 20 °C in a drybox or using standard
Schlenk techniques. Petroleum ether (bp 38-53 °C), ether,
THF, and toluene were dried and distilled before use from Na/
benzophenone. CH2Cl2 was distilled from CaH2. Methanol
and ethanol were dried over Mg(OMe)2 and Mg(OEt)2, respec-
tively.
NMR spectra were recorded on a Varian 300 MHz spec-
trometer. 1H and 13C NMR chemical shifts are reported
relative to Me4Si and were determined by reference to the
residual 1H or 13C solvent peaks. 31P NMR chemical shifts are
reported relative to H3PO4 (85%), used as an external refer-
ence. Unless otherwise noted, peaks in NMR spectra are
singlets; coupling constants are reported in hertz. Infrared
spectra, recorded as KBr pellets on a Perkin-Elmer 1600 series
FTIR instrument, are reported in cm-1. Elemental analyses
were provided by Schwarzkopf Microanalytical Laboratory.
Mass spectra were done at the University of Illinois, Urbana-
Champaign, IL. Unless otherwise noted, reagents were from
commercial suppliers. Pt(COD)Cl2 was made by the literature
procedure.26 The Pt(diphos)Cl2 compounds were made from
Pt(COD)Cl2 and the diphos ligand in CH2Cl2, as described in
more detail for 1 and 2.
P t[(R,R)-Me-Du p h os]Cl2 (1). A solution of (R,R)-Me-
Duphos (535 mg, 1.75 mmol) in CH2Cl2 (5 mL) was added
dropwise to a stirring slurry of Pt(COD)Cl2 (654 mg, 1.75
mmol) in CH2Cl2 (10 mL) to give a white slurry. In the air,
the solvent was removed under reduced pressure and the
remaining white crystals were washed with Et2O to give Pt-
[(R,R)-Me-Duphos]Cl2 in essentially quantitative yield. The
product was recrystallized from CH2Cl2. 1H NMR (CDCl3): δ
7.67 (3-line pattern, 4H, Ar), 3.55-3.41 (m, 2H, CH), 2.78-
2.65 (m, 2H, CH), 2.45-2.26 (m, 4H, CH2), 2.26-2.06 (m, 2H,
stilbene complex could be differentiated from those of the trans
2
one in the mixture. 1H NMR (C6D6): δ 4.98 (br, 2H, J Pt-H
)
70). 31P{1H} NMR (C6D6): δ 50.9 (1J Pt-P ) 3220).
P t(d p p f)(tr a n s-stilben e) (4). To a solution of Pt(dppf)-
Cl2 (288 mg, 0.35 mmol) in THF (5 mL) was added trans-
stilbene (64 mg, 0.38 mmol) and 710 µL of LiBEt3H (1 M in
THF, 0.710 mmol) to afford a dark yellow solution. The solvent
was removed under vacuum, and the solid residue was
redissolved in toluene and filtered. The solvent was removed
under vacuum, and the product was recrystallized from THF/
petroleum ether to give a dark red solid, 289 mg (89% yield).
X-ray-quality crystals were obtained after several additional
recrystallizations from CH2Cl2/petroleum ether. 1H NMR
(C6D6): δ 7.84-7.83 (m, 4H, Ar), 7.40-7.31 (m, 8H, Ar), 7.19-
2
6.88 (m, 18H, Ar), 4.35 (m, J Pt-H ) 60, 2H, CHdCH), 4.22
(2H, Cp), 4.11 (2H, Cp), 3.84 (2H, Cp), 3.81 (2H, Cp). 13C{1H}
NMR (CD2Cl2): δ 147.4 (quat Ar), 139.6-139.0 (m, Ar), 138.2
(Ar), 137.6 (Ar), 136.6-136.0 (m, Ar), 134.4-134.2 (m, Ar),
133.4-133.2 (m, Ar), 129.5 (Ar), 129.4 (Ar), 129.3 (Ar), 129.0
(Ar), 128.9 (Ar), 128.5 (Ar), 128.0 (m, Ar), 127.7 (br, Ar), 126.8
3
3
CH2), 1.79-1.64 (m, 2H, CH2), 1.43 (dd, J PH ) 19, J HH ) 7,
6H, Me), 0.87 (dd, 3J PH ) 17, 3J HH ) 7, 6H, Me). 13C{1H} NMR
(CDCl3): δ 140.9 (dd, J CP ) 51, J CP ) 26, quat C), 132.6-
1
2
1
2
132.1 (m, Ar), 41.1 (d, J CP ) 39, J C-Pt ) 31, CH), 36.8 (d,
1J CP ) 38, 2J C-Pt ) 31, CH), 36.8 (3J C-Pt ) 33, CH2), 35.8 (broad
2-line pattern with apparent J CP ) 5, CH2), 17.1 (3-line
(Ar), 125.7-125.4 (m, Ar), 122.9 (Ar), 82.8-82.1 (m, Cp), 74.9-
2
74.4 (m, Cp), 71.8 (Cp), 71.4 (Cp), 57.5 (1J Pt-C ) 215, J PC
)
14, CHdCH). 31P{1H} NMR (C6D6): δ 24.5 (1J Pt-P ) 3763).
IR: 3053, 3022, 2924, 1596, 1491, 1431, 1096, 1028, 743, 694.
Anal. Calcd for C48H40P2FePt: C, 62.01; H, 4.34. Found: C,
62.01; H, 4.25.
pattern, J C-Pt ) 34, Me), 13.8 (Me). 31P{1H} NMR (CDCl3):
3
δ 69.4 (1J P-Pt ) 3533). Anal. Calcd for C18H28P2PtCl2: C,
37.77; H, 4.93. Found: C, 37.97; H, 5.03.
P t(R-Tol-Bin a p )Cl2 (2). In the air, to a stirring solution
of Pt(COD)Cl2 (396 mg, 1.06 mmol) dissolved in CH2Cl2 (15
mL) was added R-Tol-Binap (718 mg, 1.06 mmol) dissolved in
CH2Cl2 (5 mL). The pale-yellow solution was heated at
P t ((S,S)-Ch ir a p h os)(tr a n s-st ilben e) (5). To a stirring
slurry of Pt((S,S)-Chiraphos)Cl2 (280 mg, 0.404 mmol) and
trans-stilbene (109 mg, 0.607 mmol) in THF (10 mL) was added
LiBEt3H (849 µL of 1 M THF solution, 0.849 mmol). The
reaction mixture immediately turned dark yellow and was
allowed to stir at room temperature for 5 h. The solvent was
(26) McDermott, J . X.; White, J . F.; Whitesides, G. M. J . Am. Chem.
Soc. 1976, 98, 6521-6528.

1418 Organometallics, Vol. 17, No. 7, 1998
Wicht et al.
removed in vacuo, and the dark yellow residue was extracted
with toluene (20 mL). The toluene solution was filtered, and
the filtrate was concentrated under vacuum to approximately
5 mL. Cooling of this solution to -25 °C overnight gave 180
mg (56%) of a pale yellow product, an approximately equal
mixture of diastereomers. From the mother liquor, the solvent
was removed in vacuo and the resulting residue was dissolved
in a minimum amount of THF. This solution was filtered,
petroleum ether was added, and the solution was cooled to -25
°C to give a second crop (47 mg, 15%; total yield ) 227 mg,
71%). Multiple recrystallizations from THF/petroleum ether
at -25 °C gave crystals suitable for X-ray diffraction. The
NMR spectra are reported as a mixture of diastereomers (a
and b) unless otherwise indicated. 1H NMR (C6D6): δ 7.92-
7.86 (m, 4H, Ar), 7.48-7.18 (m, 20H, Ar), 7.13-6.97 (m, 6H,
6a to 6b was monitored by 31P NMR. After 1 day, traces of
6b were observed. After 3 days, the ratios of 6a :6b were 2:1,
2.5:1, 6:1, and 5:1, respectively. After 1 week, these ratios were
1.4:1, 1.8:1, 4.6:1, and 5:1. After 3 weeks, the ratio was
approximately 2:1 in all four tubes but some decomposition
was evident.
P t((R,R)-Me-Du p h os)(tr a n s-stilben e) (7). To a stirring
slurry of Pt((R,R)-Me-Duphos)Cl2 (310 mg, 0.588 mmol) and
trans-stilbene (116 mg, 0.644 mmol) in THF (10 mL) was added
NaBH(OMe)3 (225 mg, 1.76 mmol) dissolved in THF (5 mL).
The reaction mixture immediately turned yellow, and gas was
evolved. After stirring at room temperature overnight, the
solvent was removed in vacuo and the yellow residue was
extracted with toluene (30 mL) and filtered. The toluene was
removed in vacuo, and the bright yellow solid was dissolved
in a minimum amount of THF. Methanol (30 mL) was added
to the THF solution, and recrystallization at -60 °C gave 200
mg (50%) of a 3:1 (a :b) mixture of diastereomers in three crops.
The NMR spectra are reported as a mixture of diastereomers
unless otherwise indicated. 1H NMR (C6D6): δ 7.39-7.20 (m,
2
2
Ar), 4.93 (m, J Pt-H ) 63, 2H, CHdCH, a ), 4.90 (m, J Pt-H
)
65, 2H, CHdCH, b), 2.51-2.40 (m, 2H, CHMe, a ), 2.34-2.27
3
3
(m, 2H, CHMe, b), 0.76 (dd, J PH ) 11, J HH ) 6, 6H, CHMe,
b), 0.67 (dd, 3J PH ) 12, 3J HH ) 6, 6H, CHMe, a ). 13C{1H} NMR
(C6D6): δ 149.6 (quat Ar), 136.1-135.4 (m, Ar), 133.9-133.4
(m, Ar), 130.8 (Ar), 130.5 (Ar), 130.0 (Ar), 129.3-128.6 (m, Ar),
2
10H, Ar), 6.98-6.84 (m, 4H, Ar), 4.64 (m, J Pt-H ) 61, 2H,
2
CHdCH, a ), 4.45 (m, 2J Pt-H ) 63, 2H, CHdCH, b), 2.69-2.18
(m, 2H, CH), 1.97-1.89 (m, 2H, CH), 1.78-1.69 (m, 2H, CH2),
1.59-1.52 (m, 2H, CH2), 1.48-1.34 (m, 2H, CH2), 1.28 (dd, 3J PH
126.9 (Ar), 123.4 (Ar), 54.6 (apparent t, J CP ) 15, b), 54.4
(apparent t, 2J CP ) 15, a ), 42.7-40.7 (m, CHMe), 18.2 (CHMe,
a ), 17.6 (CHMe, b). 31P{1H} NMR (C6D6): δ 56.4 (1J P-Pt ) 3333,
a ), 53.8 (1J P-Pt ) 3316, b). IR: 3044, 2966, 1595, 1488, 1427,
1211, 1094, 1066, 1022, 744, 688, 633, 533. Low-resolution
FAB MS (3-NBA): m/z 815.1, 802.1 (MH+), 621.0 [(MH -
PhCHdCHPh)+], 565.0, 544.0, 485.9, 408.9, 332.9, 301.9, 183.0,
154.1. High-resolution FAB-MS (3-NBA) m/z: found 802.2335,
calcd for C42H41P2195Pt 802.2331. Anal. Calcd for C42H40P2-
Pt: C, 62.91; H, 5.04. Found: C, 62.14; H, 5.44.
4
) 20, J HH ) 7, 6H, Me, a ), 1.22-1.12 (m, 2H, CH2), 0.58 (dd,
3J PH ) 14, 4J HH ) 7, 6H, Me, b), 0.47 (dd, 3J PH ) 20, 4J HH ) 7,
6H, Me, b), 0.34 (dd, 3J PH ) 14, 4J HH ) 7, 6H, Me, a ). 13C{1H}
NMR (C6D6): δ 150.4-150.2 (m, quat Ar), 148.0-147.1 (m, quat
Ar), 138.1 (quat Ar), 133.5-133.3 (m, Ar), 129.9 (Ar), 129.4
(Ar), 129.2 (Ar), 128.1 (Ar), 127.3 (Ar), 126.5 (Ar), 125.8-125.5
2
(m, Ar), 122.5 (Ar), 53.4 (apparent t, J CP ) 16, CHdCH, b),
2
1
P t(R-Tol-Bin a p )(tr a n s-stilben e) (6). Pt(R-Tol-Binap)Cl2
(313 mg, 0.331 mmol) and trans-stilbene (179 mg, 1.00 mmol)
were dissolved in EtOH (15 mL) and THF (5 mL). Sodium
borohydride (50 mg, 1.33 mmol) was dissolved in EtOH (10
mL) and transferred to the stirring reaction mixture via
cannula. The reaction mixture immediately became dark
purple and was allowed to stir overnight at room temperature.
The solvent was removed in vacuo, and the dark yellow residue
was extracted with toluene (30 mL) and filtered. The toluene
was removed in vacuo, and the yellow solid was dissolved in
THF and filtered. Petroleum ether was added to the THF
solution, and cooling to -25 °C gave 227 mg (65%) of a single
diastereomer (a ) by NMR. 1H NMR (C6D6): δ 8.11-8.04 (m,
50.3 (apparent t, J CP ) 16, J C-Pt ) 230, CHdCH, a ), 40.9
(apparent t, J CP ) 14, CH, b), 39.5 (apparent t, J CP ) 14, CH,
b), 38.4 (apparent t, J CP ) 14, CH, a ), 37.4 (apparent t, J CP
)
14, CH, a ), 37.2 (CH2, b), 36.9 (CH2, a ), 36.7 (CH2, b), 36.6
3
(CH2, a ), 20.3 (apparent t, J CP ) 9, J C-Pt ) 40, Me, a ), 17.1
(apparent t, J CP ) 9, Me, b), 15.4 (Me, b), 15.2 (Me, a ). 31P-
{1H} NMR (C6D6): δ 71.4 (1J P-Pt ) 3137, a ), 66.3 (1J P-Pt ) 3091,
b). IR: 3055, 2922, 2855, 1594, 1488, 1444, 1372, 1322, 1244,
1205, 1155, 1100, 1061, 1022, 994, 916, 816, 750, 694, 644,
622, 527, 500. Low-resolution FAB MS (3-NBA) m/z 682.1
(MH+), 638.1, 547.1, 517.1, 501.1 [(MH - PhCHdCHPh)+],
417.0, 360.9, 334.9, 307.0, 289.0, 180.1, 165.1, 154.1, 136.0,
120.0. High-resolution FAB MS (3-NBA) m/z: found 682.2333,
calcd for C32H41P2195Pt 682.2331. Anal. Calcd for C32H40P2-
Pt: C, 56.37; H, 5.93. Found: C, 56.06; H, 6.08.
4H, Ar), 7.56-7.50 (m, 2H, Ar), 7.29-7.13 (m, 14H, Ar), 6.95-
2
6.65 (m, 14H, Ar), 6.09-6.06 (m, 4H, Ar), 4.65 (m, J Pt-H
)
64, 2H, CHdCH), 2.13 (6H, tol Me), 1.64 (6H, tol Me). 13C-
{1H} NMR (C6D6): δ 149.2 (quat Ar), 148.2 (quat Ar, J C-Pt
P t((S,S)-Diop )(tr a n s-stilben e) (8). To a stirring slurry
of Pt((S,S)-Diop)Cl2 (496 mg, 0.649 mmol) and trans-stilbene
(117 mg, 0.649 mmol) in THF (10 mL) was added NaBH(OMe)3
(194 mg, 1.52 mmol) in THF (5 mL). The reaction mixture
immediately became yellow and homogeneous, and the evolu-
tion of gas was apparent. The solution was allowed to stir at
room temperature for 30 min. The solvent was removed under
vacuum, and the brown residue was extracted with 30 mL of
toluene. The solution was filtered, and the toluene was
removed in vacuo. The light brown residue was washed with
10 mL of petroleum ether, and the resulting brown solution
was refrigerated at -25 °C. The remaining solid was dissolved
in THF and filtered. Petroleum ether was added, and cooling
of this solution overnight at -25 °C gave a dark brown solid
which, by 31P and 1H NMR, was a mixture of Pt((S,S)-Diop)-
(trans-stilbene) and unknown impurities. From the mother
liquor, the solvent was removed under vacuum to give 203 mg
(34%) of the desired product. An additional 81 mg (14%, total
yield ) 48%) was obtained by recrystallization from the
petroleum ether wash at -25 °C. Recrystallization of this
sample from petroleum ether at room temperature gave yellow
crystals. The NMR spectra are reported as a mixture of
diastereomers unless otherwise indicated. 1H NMR (C6D6): δ
7.69-7.62 (m, 2H, Ar), 7.37-7.24 (m, 8H, Ar), 7.17-6.93 (m,
20H, Ar), 4.25 (m, 2J Pt-H ) 59, 2H, CHdCH, b), 4.15 (m, 2J Pt-H
)
48), 140.2 (Ar), 139.4 (Ar), 138.6-138.1 (m, Ar), 137.3 (Ar),
137.1 (Ar), 136.8 (Ar), 135.8-135.6 (m, Ar), 134.8-134.4 (m,
Ar), 133.8 (Ar), 132.7 (Ar), 132.0 (Ar), 126.1 (Ar), 125.7 (Ar),
123.2 (Ar), 57.5 (apparent t, 2J CP ) 14, 1J C-Pt ) 217, CHdCH),
21.6 (tol Me), 21.3 (tol Me). 31P{1H} NMR (C6D6): δ 27.8 (1J P-Pt
) 3546). IR: 3022, 1588, 1494, 1444, 1394, 1305, 1211, 1183,
1094, 1066, 1022, 861, 805, 744, 694, 633, 611, 505, 466, 427.
Low-resolution FAB MS (3-NBA): m/z 1092.3, 1071.1, 1054.2
(MH+), 1040.2, 1026.2, 1010.2, 995.2, 980.2, 873.1 [(MH -
PhCHdCHPh)+], 763.4, 465.1, 307.0, 154.1. High-resolution
FAB MS (3-NBA) m/z: found 1054.3281, calcd for C62H53P2-
195Pt 1054.3270. Anal. Calcd for C62H52P2Pt‚THF: C, 70.37;
H, 5.38. Found: C, 70.05; H, 5.62. The presence of THF was
1
confirmed by H NMR.
Some characteristic resonances of the minor diastereomer
(b) could be differentiated from those of the major one (a ) in
2
the crude product. 1H NMR (C6D6): δ 4.62 (m, J Pt-H ) 60,
2H, CHdCH), 2.09 (6H, p-tol Me), 1.71 (6H, p-tol Me). 31P-
{1H} NMR (C6D6): δ 30.0 (1J P-Pt ) 3490).
Isom er iza tion of 6. Pure samples of diastereomer 6a (∼10
mg, 0.009 mmol) were prepared in C6D6 with 0, 1, 5, and 10
mol equiv of trans-stilbene, respectively. The tubes were
maintained at ambient temperature, and the isomerization of

Pt(0) Complexes of Chiral Diphosphines
Organometallics, Vol. 17, No. 7, 1998 1419
) 59, 2H, CHdCH, a ), 4.10-4.08 (m, 2H, CH, b), 3.98-3.92
(m, 2H, CH, a ), 3.57-3.21 (m, 2H, CH2), 2.33-2.19 (m, 2H,
CH2), 1.19 (6H, Me, b), 1.18 (6H, Me, a ). 13C{1H} NMR (C6D6):
δ 147.6-147.5 (m, quat Ar), 140.0 (apparent t, J CP ) 24, quat
Ar), 138.1 (quat Ar), 137.8 (quat Ar), 137.6 (quat Ar), 137.5
(quat Ar), 134.6-134.3 (m, Ar), 134.0-133.5 (m, Ar), 132.0
(apparent t, J CP ) 7, Ar), 131.5 (apparent t, J CP ) 6, Ar), 130.4
(Ar), 129.4-128.2 (m, Ar), 127.3 (Ar), 126.5-126.0 (m, Ar),
123.6-123.4 (m, Ar), 108.6 (CMe2, a ), 108.4 (CMe2, b), 80.1
(apparent t, J CP ) 8, CH, b), 79.8 (apparent t, J CP ) 8, CH,
All structures were solved using direct methods, completed
by subsequent difference Fourier synthesis, and refined by full-
matrix least-squares procedures. The empirical absorption
corrections for 1, 5, and 8 were applied by using the program
DIFABS.27 The asymmetric units of the structures contain
the following solvate molecules along with one molecule of the
metal complex (two independent molecules of a metal complex
in the case of 5): 1, a dichloromethane molecule; 4, one THF
molecule; 5, one THF molecule in a general position and two
one-half molecules of THF on 2-fold axes; 6, one THF molecule;
8, a complex mixture of hydrocarbons present in petroleum
ether forming what appears to be a continuous hydrocarbon
chain located in channels of the structure. All other non-
hydrogen atoms were refined with anisotropic displacement
coefficients. The hydrogen atoms in the case of the two THF
molecules occupying 2-fold axes in structure 5, in the case of
the chain, and on atoms C(1) and C(3) in structure 8 were
ignored. All assigned hydrogen atoms were treated as ideal-
ized contributions.
1
a ), 58.6 (apparent t, J CP ) 13, J Pt-C ) 208, CHdCH, b), 58.5
(apparent t, J CP ) 13, 1J Pt-C ) 206, CHdCH, a ), 36.9 (apparent
t, J CP ) 13, CH2, a ), 35.4 (apparent t, J CP ) 13, CH2, b), 27.5
(CMe2, a ), 27.4 (CMe2, b). 31P{1H} NMR (C6D6): δ 10.6 (1J P-Pt
) 3632, a ), 10.5 (1J P-Pt ) 3623, diastereomer b). IR (KBr):
3433, 3051, 2983, 2932, 1595, 1489, 1433, 1372, 1243, 1215,
1159, 1098, 1044, 998, 980, 887, 816, 786, 739, 694, 507. Low-
resolution FAB MS (MB): m/z 913.4, 879.2, 863.2, 846.3, 829.2,
756.2, 725.2, 692.2 [(MH - PhCHdCHPh)+], 633.2, 565.1,
531.2, 473.2, 379.1, 302.0, 271.1, 201.1. Anal. Calcd for C45
44O2P2Pt: C, 61.84; H; 5.09. Found: C, 62.46; H, 5.72.
Cr ysta llogr a p h ic Str u ctu r e Deter m in a tion s for 1, 4,
-
All software and sources of the scattering factors are
contained in the SHELXTL (version 5.03) program library (G.
Sheldrick, Siemens XRD, Madison WI).
H
5, 6, a n d 8. The single-crystal X-ray diffraction experiments
were performed on a Siemens P4/CCD diffractometer for 1, 5,
6, and 8 and on a Siemens P4 diffractometer for 4.
Ack n ow led gm en t. We thank Dartmouth College,
the donors of the Petroleum Research Fund, adminis-
tered by the American Chemical Society, the NSF
CAREER Program, the Exxon Education Foundation,
and DuPont for partial support. M.A.Z. acknowledges
GAANN fellowship support from the Department of
Education. The University of Delaware acknowledges
the NSF for their support of the purchase of the CCD-
based diffractometer (grant No. CHE-9628768).
The systematic absences in the diffraction data were
consistent for the reported space groups. For 5, the space
group I222 was chosen based on the combined figure of merit
and the chemically reasonable and computationally stable
results of refinement. For 8, the E-statistics strongly sug-
gested the centrosymmetric space group P1h, which yielded
chemically reasonable and computationally stable results of
refinement. Given the stated enantiomeric purity of the ligand
(Strem, 99.5%), solution and refinement in P1 was also
explored. However, despite considerable dampening and
constraint, the two “independent” molecules were highly
correlated and normally narrowly ranged parameters such as
C-C distances in phenyl rings differed by 0.4 Å. Additionally,
the methyl groups could not be located from difference maps.
In 8, atoms C(2), O(1), and C(6) are equally disordered between
two positions each and were refined isotropically. See the text
for further discussion.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement, atomic coordinates, bond
lengths and angles, anisotropic displacement coefficients, and
H-atom coordinates for 1, 4-6, and 8 (42 pages). Ordering
information is given on any current masthead page.
OM971000J
(27) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.