New chiral complexes of palladium(0) containing P,S- and P,P-bidentate ligands

Article abstract of DOI:10.1021/om970185r

New chiral complexes of Pd(0) containing either the bis(phosphine) (6,6′-dimethoxybiphenyl-2,2′-diyl)bis(3,5-di-tert- butylphenylphospnine) (MeO-BIPHEP, 1) or the phosphine-sulfur chelate (2,3,4,6-tetra-O-acetyl-1-{(2-diphenylphosphino)benzyl)thio}-β-D- g

Full text of DOI:10.1021/om970185r

Organometallics 1997, 16, 3447-3453
3447
New Ch ir a l Com p lexes of P a lla d iu m (0) Con ta in in g P ,S-
a n d P ,P -Bid en ta te Liga n d s
Matthias Tschoerner,† Gerald Trabesinger,† Alberto Albinati,*,‡ and
Paul S. Pregosin*,†
Laboratorium fu¨r Anorganische Chemie, ETH Zentrum, 8092 Zu¨rich, Switzerland, and
Chemical Pharmacy, University of Milan, I-20131 Milan, Italy
Received March 5, 1997X
New chiral complexes of Pd(0) containing either the bis(phosphine) (6,6′-dimethoxybiphe-
nyl-2,2′-diyl)bis(3,5-di-tert-butylphenylphosphine) (MeO-BIPHEP, 1) or the phosphine-sulfur
chelate (2,3,4,6-tetra-O-acetyl-1-{(2-diphenylphosphino)benzyl)thio}-â-D-glucopyranose ((2-
Ph2PC6H4CH2)-S-CHCH(OAc)CH(OAc)CH(OAc)CH(CH2OAc)O, 2) have been prepared, and
the solid-state structure of one of these, Pd(benzoquinone)(2), has been determined. These
Pd(0) complexes reveal interesting solution dynamics, as shown by 2-dimensional exchange
spectroscopy. For the MeO-BIPHEP derivatives, one can obtain useful structural insights
based on the observed restricted rotation around the aryl(3,5-di-tert-butylphenyl) P-C bonds.
In tr od u ction
our research on this reaction, we have studied several
new palladium complexes containing the ligands 1 and
2. The 3,5-di-tert-butylphenyl compound 1 is a member
Complexes of Pd(0) are often invoked and occasionally
directly employed as catalyst precursors in homoge-
neous Heck,1 cross-coupling,2 carbonylation,3 and allylic
alkylation4 reactions. Monodentate tertiary phosphines,
especially PPh3, together with an olefin or acetylene
compound are the most common accompanying ligands
for this oxidation state.5 However, the literature also
contains examples of stable compounds containing
chelating bis(phosphines)6 and diimine7 Pd(0) ligands.
Recently, a bidentate P,N-chelate8 has been shown to
afford a stable Pd(0) complex.
of the MeO-BIPHEP class, reported by Schmid and co-
workers,11 whereas we have prepared the sugar-
phosphine, 2, previously.12 Ligand 2 is interesting in
that the chirality does not reside in the P,S-backbone.
Compound 1 is a promising auxiliary in Pd reactions
as well as in catalytic hydrogenation chemistry using
Ru(II).11,13 Regrettably, when coordinated, 2 suffers
from conformational flexibility in that the six-membered
P,S-chelate ring can exist in two forms. Moreover, the
sulfur atom, which becomes a stereogenic center upon
coordination, can invert readily in solution at ambient
temperature.14 These two factors reduce the effective-
ness of 2 in enantioselective catalysis.
We report here on the preparation and characteriza-
tion of several new Pd(0) complexes based on compounds
1 and 2. The new chiral complexes, 5-9, (Chart 1), have
been prepared using the 1,3-pentenedione, 3, and ben-
zoquinone, 4, and/or the classical dibenzylidene acetone
(dba) as additional stabilizing ligands. The P,S com-
A variety of auxiliaries have proven very successful
in enantioselective allylic alkylation9,10 chemistry. In
† ETH Zu¨rich.
‡ University of Milan.
X Abstract published in Advance ACS Abstracts, J une 15, 1997.
(1) Loiseleur, O.; Meier, P.; Pfaltz, A. Angew. Chem. 1996, 108, 218;
Brown, J . M. Chem. Soc. Rev. 1993, 25.
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(3) Masuyama, Y. Adv. Met.-Org. Chem. 1994, 3 , 255. Grushin, V.
V.; Bensimon, C.; Alper, H. Organometallics 1995, 14, 3259. Grushin,
V. V.; Alper, H. Organometallics 1995, 12, 1890.
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1975, 12, 187.
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W.; Fernandez-Galan, R.; J alon, F. A.; Manzano, B. R.; Rodriguez de
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Chem. 1996, 508, 69.
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Commun. 1995, 1845.
plexes 5 and 6 represent the first examples of isolable
well-characterized Pd(0) compounds containing a sulfur
donor.
(10) (a) Mackenzie, P. B.; Whelan, J .; Bosnich, B. J . Am. Chem. Soc.
1985, 107, 2046. (b) Auburn, P. R.; Mackenzie, P. B.; Bosnich, B. J .
Am. Chem. Soc. 1985, 107, 2033. (c) Andersson, P. G.; Harden, A.;
Tanner, D.; Norrby, P. O. Chem. Eur. J . 1995, 1, 12.
(11) (a) Schmid, R.; Broger, E. A.; Cereghetti, M.; Crameri, Y.;
Foricher, J .; Lalonde, M.; Mueller, R. K.; Scalone, M.; Schoettel, G.;
Zutter, U. Pure Appl. Chem. 1996, 68, 131. (b) Heiser, B.; Broger, E.
A.; Crameri, Y. Tetrahedron: Asymmetry 1991, 2, 51.
S0276-7333(97)00185-4 CCC: $14.00 © 1997 American Chemical Society

3448 Organometallics, Vol. 16, No. 15, 1997
Ch a r t 1. Syn th esis of 5-9
Tschoerner et al.
F igu r e 1. (a) ORTEP plot for 6. (b) Ball and stick plot
showing that one side of the coordination plane is relatively
crowded.
Resu lts a n d Discu ssion
P r ep a r a tion of th e Com p lexes. The new com-
plexes were prepared by dissolving the Pd(0) source,
usually Pd2(dba)3 CHCl3, together with the chiral bi-
dentate ligand and then adding the appropriate olefin.
This reaction is illustrated in Chart 1, and the number-
ing systems used for the ligands are shown in Chart 2.
The sugar-phosphine derivatives 5 and 6 were obtained
in pure form after recrystallization. As these complexes
are relatively soluble, the isolated yields were modest,
ca 40%; however, in situ NMR measurements show that
these reactions with 2 are essentially quantitative. The
MeO-BIPHEP complexes, 7-9, were obtained in ana-
lytically pure form after column chromatography with
yields ranging from 75 to 96%.
Ta ble 1. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) in 6
Pd1-S1
Pd1-P1
Pd1-C2
Pd1-C3
S1-C13
S1-C14
P1-C7
2.354(1)
2.314(1)
2.138(6)
2.138(5)
1.828(5)
1.798(6)
1.838(5)
P1-C111
P1-C121
O1-C1
1.825(6)
1.820(6)
1.227(9)
1.245(8)
1.427(7)
1.33(1)
O2-C4
O3-C14
C5-C6
C2-C3
1.411(9)
S1-Pd1-P1
S1-Pd1-C3
S1-Pd1-C2
P1-Pd1-C3
P1-Pd1-C2
C2-Pd1-C3
93.73(5)
107.4(2)
145.2(2)
158.4(2)
119.9(2)
38.5(2)
Pd1-S1-C13
Pd1-S1-C14
C13-S1-C14
C4-C3-C2
106.4(2)
106.2(2)
103.4(2)
121.2(7)
120.9(6)
C1-C2-C3
benzoquinone complex 6 was determined by X-ray
diffraction methods, and an ORTEP plot of the molecule
is shown in Figure 1a. The immediate coordination
sphere consists of the Pd atom and one double bond of
the quinone, together with the P and S atoms of 2.
The metal-phosphine bond length, Pd-P1 2.314(1)
Å, falls within the literature range for this type of
separation in Pd(0) complexes.17-21 The 2.354(1) Å
X-r a y Diffr a ction Stu d ies. There are still relatively
few solid-state structures on MeO-BIPHEP com-
plexes.11,15-17 Consequently, the structure of the P,S-
(12) Barbaro, P.; Currao, A.; Herrmann, J .; Nesper, R.; Pregosin,
P. S.; Salzmann, R. Organometallics 1996, 15, 1879.
(13) Mezzetti, A.; Tschumper, A.; Consiglio, G. J . Chem. Soc., Dalton
Trans. 1995, 49. Mezzetti, A.; Costella, A.; Del Zotto, P.; Rigo, G.;
Consiglio, G. Gazz. Chim. Ital. 1993, 123, 155.
(14) Abel, E.; Evans, D. G; Koe, J . R.; Sik, V.; Hursthouse, M. B.;
Bates, P. A. J . Chem. Soc., Dalton Trans. 1989, 2315. Abel, E.; Domer,
J . C.; Ellis, D.; Orrell, K. G.; Sik, V.; Hursthouse, M. B.; Mazid, M. H.
J . Chem. Soc., Dalton Trans. 1992, 1073.
(18) Herrmann, W. A; Thiel, W.; Brossmer, C.; Oefele, K.; Prier-
meiler, T. J . Organomet. Chem. 1993, 461, 51.
(15) Schmid, R.; Foricher, J .; Cereghetti, M.; Schonholzer, P. Helv.
Chim. Acta 1991, 74, 370.
(16) Sperrle, M.; Gramlich, V.; Consiglio, G. Organometallics 1996,
15, 5196.
(19) Bashilov, V. V.; Petovskii, P. V.; Sokolov, V. I.; Lindeman, S.
V.; Guzey, I. A.; Stulchkov, Y. T. Organometallics 1993, 12, 991.
(20) Grevin, J .; Kalck, P.; Daran, J . C.; Vaisserman, J .; Bianchini,
C. Inorg. Chem. 1993, 32, 4965.
(17) Bolm, C.; Kaufmann, D.; Gessler, S.; Harms, K. J . Organomet.
Chem. 1995, 502 , 47.
(21) Phillips, I. G.; Ball, R. G.; Cavell, R. G. Inorg. Chem. 1992, 31,
1633.

Chiral Complexes of Palladium(0)
Organometallics, Vol. 16, No. 15, 1997 3449
Ch a r t 2. Nu m ber in g System
Ta ble 2. Exp er im en ta l Da ta for th e X-r a y
Diffr a ction Stu d y of 6
distance for Pd-S1 is routine for Pd-S bond lengths in
complexes of Pd(II),22 suggesting no special interaction
between the sulfur donor and the zero-valent metal. The
two Pd-C bond lengths Pd-C2 and Pd-C3, both at ca.
2.138(6) Å, fall within the normal range. The second
double bond of the quinone is remote from the metal
(>3.5 Å) and, indeed, tilts away from the palladium
atom. There are no unexpected P-C or S-C bond
distances, all being ca. 1.8 Å. At 1.411(9) Å, the length
of the complexed double bond C2-C3 is, as expected,
allowing for some back-bonding from the Pd(0) center
to the olefin. The P-Pd-S angle, at 93.73(5)°, is
somewhat opened but not unusual. From these seem-
ingly normal data, one obtains the impression that
additional Pd(0) complexes with a mixed P,S donor set
should be synthetically accessible. A selection of bond
lengths and bond angles is given in Table 1 and
experimental parameters in Table 2.
formula
C39H39O11 PPdS
mol wt
853.18
data collection T, °C
cryst syst
space group
a, Å
23
monoclinic
P21 (No. 4)
9.1405(5)
b, Å
22.0595(77)
c, Å
10.2021(29)
â, deg
107.64(1)
1960.4(9)
V, Å3
Z
4
F (calcd), g cm-3
1.445
6.128
µ, cm-1
radiation
Mo KR (graphite monochromated
λ ) 0.710 69 Å)
2.5 < θ < 27.0
4086
3170 (|Fo| > 3.0σ(|F|))
0.9998-0.9521
0.029
θ range, deg
no. of indep data coll
no. of obs reflns (no)
transmission coeff
Ra
Perhaps the most interesting feature of the structure
concerns the relative placement of the various organic
fragments of the three donors. As suggested by the
sketch below, one finds the sugar substituent, the axial
P-phenyl, and the remaining six atoms of the benzo-
quinone, all on one side of the metal atom. This aspect
of the structure is illustrated in Figure 1b. This leaves
a
Rw
0.038
GOF
1.171
R ) Σ(|Fo - (1/k)Fc|)/Σ|Fo|; Rw ) [Σw(Fo - (1/k)Fc)2/Σw|Fo| ]1/2
;
a
2
where w ) [σ2(Fo)]-1; σ(Fo) ) [σ2(Fo2) + f4(Fo2)]1/2/2Fo and f ) 0.050.
the sulfur lone pair in a rather open area, in keeping
with Gillespie’s ideas23 on electron pair domains. We
(22) Abel, E.; Evans, D. G; Koe, J . R.; Sik, V.; Hursthouse, M. B.;
Bates, P. A. J . Chem. Soc., Dalton Trans. 1989, 2315. Abel, E.; Domer,
J . C.; Ellis, D.; Orrell, K. G.; Sik, V.; Hursthouse, M. B.; Mazid, M. H.
J . Chem. Soc., Dalton Trans. 1992, 1073. Chivers, T.; Edwards, M.;
Meetsma, A.; van der Grampel, J .; van der Lee, A. Inorg. Chem. 1992,
31, 2156. Capdevila, M.; Clegg, W.; Gonzalez-Duarte, P.; Harris, B.;
Mira, I.; Sola, J .; Taylor, I. C. J . Chem. Soc., Dalton Trans. 1992, 2817.

3450 Organometallics, Vol. 16, No. 15, 1997
Tschoerner et al.
F igu r e 2. Structure of 8.
have noted previously10,24 that in P,S-chelate complexes
there is a tendency to have pseudoaxial substituents on
sulfur, thus leaving the sulfur lone pair in a relatively
open area of the structure.
We have also grown crystals of Pd(dba)(1), 8, and
collected data for this complex. Unfortunately, the
crystal was of poor quality; however, the structure is,
as expected, the immediate coordination sphere consist-
ing of the metal, two P-donors, and one double bond of
the dba (Figure 2), although the data do not warrant a
detailed analysis.25
F igu r e 3. Section of the NOESY spectrum of 5 revealing
the selective exchange (lower left corner) of the olefinic
protons of the dione in 5 (500 MHz, CD2Cl2).
NMR Stu d ies. The Pd(0) P,S complexes, 5 and 6,
each reveal interesting dynamics in solution. Complex
5 exists in two isomeric forms 5a ,b in a ratio of 3.2:1.
The relative position of the sugar moiety is not deter-
mined.
All the proton resonances in 5 are relatively sharp.
Nevertheless, two-dimensional exchange spectroscopy26,27
(Figure 3), shows that there is slow intramolecular
exchange. The exchange spectrum shows that the
olefinic protons pseudotrans to the P donors exchange
selectively with the olefinic protons pseudotrans to the
S donors in the corresponding isomer. This is consistent
F igu r e 4. Section of the NOESY spectrum of 6 revealing
the random exchange of the olefinic protons of the benzo-
quinone (500 MHz, CD2Cl2).
(23) Gillespie, R. J .; Spencer, J . N.; Moog, R. S. J . Chem. Educ. 1996,
73, 622.
(24) Albinati, A.; Eckert, J .; Pregosin, P. S.; Ru¨egger, R.; Salzmann,
R.; Sto¨ssel, C. Organometallics 1997, 16, 579.
(25) The structure was solved, however, the R-factor was unaccept-
ably high. The observed distances and angles were in agreement with
the literature.
(26) Hull, W. E. In Two-dimensional NMR Spectroscopy. Applica-
tions for Chemists and Biochemists; VCH: New York, 1987; p 153.
Ernst, R. R. Chimia 1987 41, 323.
(27) For applications of 2-D exchange spectroscopy, see: (a) Pregosin,
P. S.; Salzmann, R. Coord. Chem. Rev. 1996, 155, 35. (b) Togni, A.;
Burckhardt, U.; Gramlich, V.; Pregosin, P.; Salzmann, R. J . Am. Chem.
Soc. 1996, 118, 1031. (c) Barbaro, P.; Pregosin, P. S.; Salzmann, R.;
Albinati, A.; Kunz, R. W. Organometallics 1995, 14, 5160. (d) Her-
rmann, J .; Pregosin, P. S.; Salzmann, R.; Albinati, A. Organometallics
1995, 14, 3311. (e) Pregosin, P. S.; Salzmann, R.; Togni, A. Organo-
metallics 1995, 14, 842. (f) Breutel, C.; Pregosin, P. S.; Salzmann, R.;
Togni, A. J . Am. Chem. Soc. 1994, 116, 4067.
with a rotation of coordinated 3 without dissociation.
The protons of the dione in both isomers are readily
assigned using 13C,1H-correlation characteristics to-
gether with J (31P,1H) values (trans > cis, see top-left of
Figure 3) and a 31P,1H 2-dimensional correlation.
Complex 6 shows only one 31P signal. All four olefinic
benzoquinone 13C signals for 6 are quite broad, whereas
the analogous proton signals are only slightly broad-
ened. However, it is clear from the exchange spectrum
(Figure 4) that the benzoquinone in 6 dissociates and
then recombines. This conclusion is based on the
presence of exchange cross peaks stemming from traces
of free 4 (not visible in the conventional 1-dimensional
spectrum), as well as the observed lack of selectivity in

Chiral Complexes of Palladium(0)
Organometallics, Vol. 16, No. 15, 1997 3451
Ta ble 3. NMR Da ta for th e Isom er s of
P d (1,3-cyclop en t-4-en ed ion e)(2), 5a
5a (major)
5b (minor)
1H
13C
1H
13C
1
(CdO, trans to S) 200.9 1′
(CdO, trans to S) 201.2
endo
exo
2endo 2.97
2exo 2.46
46.5 2′
46.5 2′
2.97
2.42
46.1
46.1
3
(CdO, trans to P) 199.9 3′
(CdO, trans to P) 199.9
4
5
o-1
m-1
o-2
4.71
4.76
7.43
80.6 4′
72.2 5′
4.70
4.83
7.44
F igu r e 5. 1H tert-butyl region (left) and 31P spectrum of
7 (right).
o-1′
m-1 7.46
o-2′
7.27
7.42
m-2 7.35
7
8
10
6.67
7.29
7.45
132.9 7′
6.73
7.30
7.33
4.00
3.84
4.69
5.43
4.70
5.27
3.63
132.9
8′
10′
12ax 3.67
33.5 12ax
33.5 12eq
81.6 13′
68.0 14′
73.3 15′
16′
′
′
38.7
38.7
12eq 4.24
13
14
15
16
17
18
18
4.70
5.22
5.33
4.91
3.93
3.84
3.99
69.0
73.5
17′
33.5
33.5
31P, 5a 18.2 ppm
31P, 5b 17.6 ppm
a
CD2Cl2, AMX 500, ambient temperature; o ) ortho, m ) meta.
Ta ble 4. Selected 1H NMR Da ta a for
P d (ben zoqu in on e)(2), 6
2
3
4
5
7
8
9
10
5.15
5.26
6.02
6.15
6.73
7.30
7.43
7.42
12eq
12ax
13
14
15
16
17
18
18′
4.22
3.62
4.56
5.23
5.35
5.00
3.93
4.12
3.87
F igu r e 6. Section of the ROESY spectrum of 8 revealing
the four pairs of exchanging ortho protons. The lines
indicate these four selective processes (243 K, 500 MHz,
CD2Cl2).
31P 24.9 ppm
a
b
CD2Cl2, AMX 500, ambient temperature. Ph o-1, 7.37; Ph
temperature. For 7, with its relatively small 1,3-
m-1, 7.46; Ph o-2, 7.37.
the exchange between the four olefinic benzoquinone
protons, i.e., all four are exchanging with each other and
the free benzoquinone. Again, the various coordinated
olefinic protons are recognized using their 3J (31P,1H)
values, the consequent differing multiplicities, and a
31P,1H 2-dimensional correlation. We have no satisfac-
tory explanation for this change of mechanism relative
to 5 . We do note that 4 is slightly larger than 3 and
that in the solid-state structure of 6 (discussed above),
one finds a large number of atoms on one side of the
coordination plane placed fairly close together.
The most pertinent NMR results for 5 and 6 are given
in Tables 3 and 4. From an analysis of the NOESY
spectra for both 5 and 6 it seems that the six-membered
chelate ring conformation is fixed; however, extensive
overlap in the aromatic region prevents a decision as
to the relative position of the stereogenic S center.
The chiral Pd(0) MeO-BIPHEP complexes 7 and 8
exist as single isomers in solution and give simple AX
(or AB) type 31P spectra. We have previously noted28
that coordinated 1 is somewhat unusual in that it often
shows restricted rotation about the P-C bonds associ-
ated with the 3,5-di-tert-butyl aryl groups at ambient
pentenedione, we observe free rotation around these
P-C bonds, as demonstrated by the appearance of the
tert-butyl region (Figure 5). One finds four nonequiva-
lent rings each with two equivalent tert-butyl reso-
nances.29
However, for the dba complex, 8, at ambient temper-
ature, one observes a larger number of aromatic and
tert-butyl signals due to this restricted rotation. The
ROESY spectrum for 8 at 243 K (Figure 6) shows the
eight nonequivalent ortho ring protons which undergo
the expected four selective exchange processes as the
rings slowly rotate (we choose to show these resonances
(29) Close inspection of the aromatic region of 7 reveals two broad
signals, with very similar chemical shifts. One of these broad signals
lies almost completely under a different sharp resonance. We assign
these broad resonances to two nonequivalent ortho protons of one
P-aryl ring, so that one of the four rings is indeed, exhibiting restricted
rotation. Nevertheless, the rotational barriers for 7 are smaller than
those for 8.
(28) Currao, A.; Feiken, N.; Macchioni, A.; Nesper, R.; Pregosin, P.
S.; Trabesinger, G. Helv. Chim. Acta 1996, 79, 1587.

3452 Organometallics, Vol. 16, No. 15, 1997
Tschoerner et al.
We have previously shown28,30 in bis(3,5-di-tert-butyl)
Pd(allyl)(MeO-BIPHEP)+ and RuH(arene)(MeO-BI-
PHEP)+ type complexes that this restricted rotation
around the P-C bonds effectively produces a more rigid
chiral pocket. Further, we have suggested that this
increased rigidity is associated with improved enanti-
oselectivity in several catalytic reactions where the
substrate has substantial bulk.31 We consider that our
observations for 8 represent additional support for this
conclusion.
Although Pd(benzoquinone)(1), 9, was readily pre-
pared (Experimental Section), it was not sufficiently
stable in solution for the length of time necessary to
make the kinds of detailed studies described above.
In summary (a) one can prepare and isolate new
chiral complexes of Pd(0) containing a chelating phos-
phine-sulfur donor, together with an olefin, (b) these
complexes have interesting dynamics, e.g., olefin dis-
sociation or olefin rotation, and (c) the bis(3,5-di-tert-
butyl) MeO-BIPHEP Pd(0) complexes show hindered
rotation around the aryl P-C bonds, in keeping with
previous observations.
F igu r e 7. Section of the NOESY spectrum of 8 revealing
the NOE from the ortho proton of the dba ring to the para
proton of the δ ring (243 K, 500 MHz, CD2Cl2).
Ta ble 5. Selected NMR Da ta a for 7 a n d 8a
7
8
1H
13C
1H
5.03
13C
72.4
2endo
2exo
2.89
2.22
46.4
46.4
2
3
4
5
8
4.40
6.20
7.04 (ca.)
6.20
67.6
124.3
4
5
8
9
10
12
8′
4.30
4.76
6.32
6.76
6.46
3.38
6.32
6.85
6.66
3.50
7.59
73.0
70.1
111.7
128.2
123.7
56.4
112.8
128.2
123.3
56.3
Exp er im en ta l Section
112.6
Gen er a l Con sid er a t ion s. The R(+) and S(-) MeO-
BIPHEP compounds were provided by F. Hoffmann-La Roche
AG, Basel. (2,3,4,6-tetra-O-acetyl-1-{(2-diphenylphosphino)-
benzyl)thio}-â-D-glucopyranose, (2-Ph2PC6H4CH2)-S-CH-
CH(OAc)CH(OAc)CH(OAc)CH(CH2OAc)O, 2, was prepared as
described by us previously.10 All reactions were performed in
an atmosphere of Ar using standard Schlenk techniques. Dry
10
12
8′
9′
6.75
3.38
6.07
6.72
6.08
3.23
8.12, 6.88
7.52
1.16, 1.57
6.88, 6.68
7.15
1.15, 0.95
7.36, 7.06
7.16
1.22, 1.19
8.41, 7.22
7.61
57.5
111.1
9′
10′
12′
o-R
10′
12′
o-R
p-R
t-R
o-â
p-â
t-â
o-γ
p-γ
t-γ
o-δ
p-δ
t-δ
123.4
56.5
132.9
1
and oxygen-free solvents were used. Routine H, 13C, and 31P
t-R
o-â
p-â
t-â
o-γ
p-γ
t-γ
o-δ
p-δ
t-δ
1.34
7.11
7.33
1.21
7.29
7.24
1.19
7.42
7.51
1.35
NMR spectra were recorded with Bruker DPX-250 and 300
MHz spectrometers unless otherwise specified. Chemical
shifts are given in parts per million (ppm), and coupling
constants (J ) are given in Hertz. The 2-dimensional studies
were carried out at 500 MHz for 1H NMR studies. NOESY
and 31P,1H-correlation experiments measurements were car-
ried out as reported previously.27,28 The ROESY spectra for 8
(500 MHz, CD2Cl2, 243 K), were obtained with a 0.4 s spin
lock. The carrier frequency was set in the middle of the proton
spectrum. IR spectra were recorded with a Perkin-Elmer 882
infrared spectrophotometer. Elemental analyses and mass
spectroscopic studies were performed at ETHZ.
131.3
126.3
31.6, 30.8
128.9
125.1
31.5, 31.6
132.5, 126.3
132.2
1.60, 1.01
31.8, 31.4
a
CD2Cl2, DRX 400, ambient temperature; t ) tert-butyl reso-
nance. See Chart 2 for R, â, δ, and γ rings. PA ) 29.3 ppm, 2J (P-
P) ) 18.3 Hz; PB ) 32.6 ppm.
Cr ysta llogr a p h y. A suitable crystal was mounted on a
glass fiber on a CAD4 diffractometer that was used for the
space group determination and for the data collection. Unit
cell dimensions were obtained by a least-squares fit of the 2θ
values of 25 high-order reflections (9.5 e θ e 15.4°). Selected
crystallographic and other relevant data are listed in Table 2
and Supporting Information.
Data were measured with variable scan speed to ensure
constant statistical precision on the collected intensities.
Three standard reflections were used to check the stability of
the crystal and of the experimental conditions and measured
every 90 min; no significant variation was detected. Data were
corrected for Lorentz and polarization factors using the data
reduction programs of the MOLEN crystallographic package.32
An empirical absorption correction was also applied (azimuthal
(Ψ) scans of three reflections having ø > 85°).33 The standard
deviations on intensities were calculated in terms of statistics
alone, while those on Fo were calculated as shown in Table 2.
The structure was solved by a combination of direct and
Fourier methods and refined by full-matrix least squares.
as opposed to the tert-butyl signals as there is less
overlap). Once again,28,30,31 the highest barriers to
rotation are associated with the pseudoaxial P-aryl
groups, with the full sequence being R < δ < â < γ.
Coordination of a larger ligand, such as dba, compresses
the BIPHEP framework, with the squeeze most pro-
nounced between the two pseudoaxial rings and the
biphenyl moiety. Not surprisingly, the pseudoequatorial
BIPHEP ring, δ, closest to the uncoordinated double
bond of dba, is more hindered than its R counterpart
(see fragment above). In support of this, we note the
unexpected NOE between the para proton of the δ-ring
and the ortho protons of one dba ring (Figure 7), thus
confirming that these molecular fragments are in close
contact. Table 5 contains a summary of the NMR
parameters for 7 and 8.
(30) Feiken, N.; Pregosin, P. S.; Trabesinger, G.; Scalone, M.
Organometallics 1997, 16, 537.
(31) Trabesinger, G.; Albinati, A.; Feiken, N.; Kunz, R.; Pregosin,
P. S.; Tschoerner, M. J . Am. Chem. Soc. 1997, submitted for publica-
tion.
(32) MOLEN, Enraf-Nonius Structure Determination Package;
Enraf-Nonius: Delft, The Netherlands, 1990.
(33) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A 1968, 24, 351.

Chiral Complexes of Palladium(0)
Organometallics, Vol. 16, No. 15, 1997 3453
Anisotropic displacement parameters were used for all atoms,
except for the carbon atoms of the phenyl rings. The contribu-
tion of the hydrogen atoms in their calculated positions (C-H
) 0.95 Å, Biso(H) ) 1.3 × Beq(Cbonded) Å2 ) was taken into
account but not refined. As can be expected, the terminal
acetate substituents are undergoing large amplitude motion.
The function minimized was: [∑w(|Fo| - 1/k|Fc|)2]) with w
) [σ2(Fo)]-1. No extinction correction was deemed necessary.
The scattering factors used, corrected for the real and imagi-
nary parts of the anomalous dispersion, were taken from the
literature.34 The handedness of the structure was tested by
refining both enantiomorphs; the coordinates giving the
significantly35 lower Rw factor were used. Upon convergence,
the final Fourier difference map showed no significant peaks.
All calculations were carried out by using the Enraf-Nonius
MOLEN crystallographic programs.32
P d (4-cyclop en ten e-1,3-d ion e)(2), 5. Ligand 2, (64 mg,
100 µmol) and Pd2(dba)3‚CHCl3 (52 mg, 50 µmol) were sus-
pended in ca. 1 mL of acetone. The brown-violet suspension
slowly dissolves to give an orange solution (ca. 120 min).
4-Cyclopentene-1,3-dione, 3, (10 mg, 104 µmol) was added with
stirring. The orange solution changes color within 60 min to
bright yellow. After 24 h of stirring, the solution was filtered
through Celite and evaporated to dryness. The residue was
washed with ether (2 × 1 mL). Recrystallization from acetone/
hexane gave 33 mg (39%) of yellow crystals. Anal. Calcd for
column and pentane/ether 1/1 to 2/1 as eluent (Rf ) 0.4).
Evaporation of the eluent gave 59 mg (95.6%) of the pure
complex as a yellow solid. Anal. Calcd for C75H100O4P2Pd
(1233.98): C, 73.00; H, 8.17. Found: C, 72.8; H, 7.97. Mp:
250-252 °C (dec). FAB-MS: m/e 1234 (M + 1), 1137 (M -
C5H4O2). 31P NMR (CD2Cl2) δ: 29.3 (d, J ) 18 Hz), 32.6 (d, J
) 18 Hz). 1H-NMR (CD2Cl2) δ: 1.18 (s, 18H), 1.21 (s, 18H),
1.34 (s, 18H), 1.35 (s, 18H), 2.22 (d, J ) 20.4 Hz, 1H), 2.87 (d,
J ) 20.4 Hz, 1H), 3.37 (s, 3H), 3.49 (s, 3H), 4.30 (m, 1H), 4.76
(m, 1H), 6.32 (m, 2Har), 6.46 (m, 1Har), 6.66 (m, 1Har), 6.75 (m,
1Har), 6.85 (m, 1Har), 7.1 (m, 2Har), 7.2-7.4. (m, 4Har), 7.44
(m, 2Har), 7.51 (m, 2Har), 7.64-7.67 (m, 2Har). IR (CsI pellet):
υCdO 1708 (s), 1694 (s), 1674 (vs), 1648 (s).
This complex can also be prepared from the usual Pd2(dba)3‚
CHCl3.
P d (d ba )(1), 8. Pd2(dba)3‚CHCl3 (51.7 mg, 50 µmol) and (S)-
(-) 1 (103.1 mg, 100 µmol) were placed in a Schlenk flask.
Upon addition of 5 mL of THF, the dark violet suspension
dissolves to give a brown-orange solution, which was stirred
at 40 °C for 3 h. Filtration of the resulting reaction mixture
was followed by removal of the solvent to afford the crude
product as a dark orange solid. Purification via column
chromatography on 20 g of silica gel using pentane/ether 8.5/
1.5 as eluent led to 102 mg (74.7%) of analytically pure
complex. Anal. Calcd. for C87H110O3P2Pd (1372.19): C, 76.15;
H, 7.84. Found: C, 76.21; H, 7.84. FAB-MS: m/e 1372 (M +
1), 1137 (M - dba). IR (KBr pellet): νCdO 1637 (m).
C
38H39O11PSPd (841.2): C, 54.26; H, 4.67. Found: C, 54.21;
H, 4.53. Mp: 149 °C. FAB-MS: m/e 841 (M + 1), 744 (M +
1 - C5H4O2), 413 (M + 1 - (C5H4O2 + glucopyranosetetraac-
etate)). IR (KBr pellet): υCdO 1753 (vs), 1690 (vs), 1673 (s),
1644 (vs). 31P NMR (CD2Cl2) δ: 18.8 (77% isomer 5a ), 18.3
(23% isomer 5b).
P d (ben zoqu in on e)(1), 9. Pd2(dba)3‚CHCl3 (36 mg, 34.8
µmol) and (S)-1 (71.7 mg, 69.6 µmol) were suspended in 2 mL
of CH2Cl2 and stirred for 16 h. 4 (45 mg, 6 equiv) was then
added to the resulting orange-brown solution. A red-orange
solution was formed within ca. 2 h and then stirred for an
additional 18 h. Workup by filtration and evaporation to
dryness followed by column chromatography using 14 g of
silica gel gave the pure compound. The complex was obtained
as orange-red solid by evaporation of the pentane/ether 2/1
eluent (Rf ) 0.45). Yield: 68 mg (78.4%). Mp: 180 °C (dec).
The ligands dba and excess benzoquinone were eluted with
CH2Cl2. Anal. Calcd for C76H100O4P2Pd (1245.99): C, 73.26;
H, 8.09. Found: C, 73.5; H, 8.24. FAB-MS: m/e 1246 (M +
1), 1137 (M - C6H4O2). 31P NMR (CD2Cl2) δ: 34.8. IR (CsI
pellet): νCdO 1623 (vs).
P d (ben zoqu in on e)(2), 6. Ligand 2, (32.2 mg, 50.4 µmol)
and Pd2(dba)3‚CHCl3 (25.9 mg, 25 µmol) were suspended in
ca. 1 mL of acetone. The brown-violet suspension slowly
dissolves to give an orange solution (ca. 60 min). Benzo-
quinone (6.5 mg, 1.2 equiv) was added to the solution. The
color changes to red-orange, and stirring was continued for
24 h. The solution was filtered through Celite and taken to
dryness. The residue was washed with ether (3 times),
redissolved in acetone, filtered, and reduced to a small volume.
Addition of pentane gave red-orange crystals, which were
collected by filtration. Yield: 17.5 mg (41.0%). Anal. Calcd
for C39H39O11PSPd (853.2): C, 54.9; H, 4.61. Found: C, 54.7;
H, 4.67. FAB-MS: m/e 853 (M + 1), 744 (M + 1 - C6H4O2),
413 (M + 1 - (C6H4O2 + glucopyranosetetraacetate)). IR (KBr
pellet): υCdO 1752 (vs), 1737 (vs), 1632 (s), 1612 (vs), 1574 (s).
31P NMR (CD2Cl2) δ: 23.6.
P d (4-cyclop en ten e-1,3-d ion e)(1), 7. (R)(+)-1 (51.7 mg,
50 µmol) was added to a stirrred suspension of Pd(dba)2 (28.7
mg, 25 µmol) in 2 mL of CH2Cl2. The deep violet suspension
dissolves during 20 h of stirring to afford a brown-orange
solution. Addition of 3 (30 mg, 0.31 mmol) induces a slow color
change to yellow over 18 h. Filtration and evaporation to
dryness gave a yellow powder. This crude product was purified
by column chromatography using 18 g of silica gel in a 10 mm
Ack n ow led gm en t. P.S.P. thanks the Swiss Na-
tional Science Foundation, the ETH Zurich, and F.
Hoffmann-La Roche AG for financial support. We also
thank F. Hoffmann-La Roche AG for a gift of the
BIPHEP ligands as well as J ohnson Matthey for the
loan of precious metals. We especially thank Mr. S.
Leoni and Dr. M. Wo¨rle for the X-ray results on Pd-
(dba)(1).
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
lengths, bond angles, torsion angles, final positional param-
eters, and anisotropic displacement parameters and an ORTEP
plot with a full numbering scheme (10 pages). Ordering
information is given on any current masthead page.
(34) International Tables for X-ray Crystallography; Kynoch: Bir-
mingham England, 1974; Vol. IV.
(35) Hamilton, W. C. Acta Crystallogr. 1965, 17, 502.
OM970185R