Palladium(II) and palladium(0) complexes of BINAP(O) (2-(diphenylphosphino)-2′-(diphenylphosphinyl)-1,1′-binaphthyl)

Article abstract of DOI:10.1021/om020838q

The coordination organopalladium chemistry of 2-(diphenylphosphino)-2′-(diphenylphosphinyl)-1,1′-binaphthyl (BINAP(O)) was found to be totally different from that of other phosphine-phosphine oxide ligands, as well as of BINAP. The reaction of [(MeCN)₂PdCl₂] with BINAP(O) (1 equiv) afforded [(BINAP(O))PdCl₂] (1), in which BINAP(O) is P,O-chelated to Pd in the solid state (X-ray) and in solution (NMR). Treatment of 1 with free BINAP(O) led to the reversible formation of a P,P-bonded nonchelate, [(BINAP(O))₂PdCl₂] (2), which could not be isolated due to the equilibrium being strongly shifted toward 1. Reduction of 1 with LiBH₄ in the presence of BINAP(O) afforded a new zerovalent Pd complex [(BINAP(O))₂Pd] (3), in which both BINAP(O) ligands are P-bonded to Pd and one provides η²-arene coordination via the C=C bond adjacent to the phosphinyl group (X-ray). Oxidative addition of PhI to 3 led cleanly to [(BINAP(O))Pd(Ph)I] (4; Ph trans to O; X-ray) which was also prepared by the reaction of [Pd₂(dba)₃] with BINAPO and PhI. The ultrasound-promoted I/F exchange reaction of [(BINAPO)Pd(Ph)I] with AgF afforded [(BINAP(O))Pd(Ph)F] (5), which was decomposed thermally to produce a mixture of P-F and C-P reductive elimination products.

Full text of DOI:10.1021/om020838q

Organometallics 2003, 22, 555-562
555
P a lla d iu m (II) a n d P a lla d iu m (0) Com p lexes of BINAP (O)
(2-(Dip h en ylp h osp h in o)-2′-(d ip h en ylp h osp h in yl)-
1,1′-bin a p h th yl)
William J . Marshall and Vladimir V. Grushin*
Central Research and Development, E. I. DuPont de Nemours & Co., Inc.,†
Experimental Station, Wilmington, Delaware 19880-0328
Received October 8, 2002
The coordination organopalladium chemistry of 2-(diphenylphosphino)-2′-(diphenylphos-
phinyl)-1,1′-binaphthyl (BINAP(O)) was found to be totally different from that of other
phosphine-phosphine oxide ligands, as well as of BINAP. The reaction of [(MeCN)2PdCl2]
with BINAP(O) (1 equiv) afforded [(BINAP(O))PdCl2] (1), in which BINAP(O) is P,O-chelated
to Pd in the solid state (X-ray) and in solution (NMR). Treatment of 1 with free BINAP(O)
led to the reversible formation of a P,P-bonded nonchelate, [(BINAP(O))2PdCl2] (2), which
could not be isolated due to the equilibrium being strongly shifted toward 1. Reduction of 1
with LiBH4 in the presence of BINAP(O) afforded a new zerovalent Pd complex [(BINAP-
(O))2Pd] (3), in which both BINAP(O) ligands are P-bonded to Pd and one provides η2-arene
coordination via the CdC bond adjacent to the phosphinyl group (X-ray). Oxidative addition
of PhI to 3 led cleanly to [(BINAP(O))Pd(Ph)I] (4; Ph trans to O; X-ray) which was also
prepared by the reaction of [Pd2(dba)3] with BINAPO and PhI. The ultrasound-promoted
I/F exchange reaction of [(BINAPO)Pd(Ph)I] with AgF afforded [(BINAP(O))Pd(Ph)F] (5),
which was decomposed thermally to produce a mixture of P-F and C-P reductive elimination
products.
In tr od u ction
In 1996, Shimizu, Yamamoto, and co-workers re-
ported1 their remarkable observation of chirality rever-
sal depending on the (S)-BINAP to Pd(OAc)2 catalyst
ratio used for the enantioselective elimination reaction
of a 6,6-membered bicyclic allylic carbonate. At a ligand
to Pd ratio of 1, the R product dominated, whereas an
increase in the ratio to 2 resulted in the formation of
mostly the S isomer (eq 1).
generated in equimolar quantities. If an extra 1 equiv
of BINAP is used (i.e. BINAP/Pd(II) ) 2) active catalyst
would be somehow composed of a 1:1:1 blend of Pd(0),
BINAP(O), and more strongly chelating, unreacted
BINAP.
(2) (a) Mason, M. R.; Verkade, J . G. Organometallics 1990, 9, 864;
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A. Organometallics 1992, 11, 3009. (d) Grushin, V. V.; Alper, H.
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A series of additional experiments indicated1 that the
effect was likely due to the facile Pd(II)/P(III) f Pd(0)/
P(V) redox process,2 also reported3 for BINAP (eq 2).
The stoichiometry of reaction 2 shows that at the BINAP
to Pd(II) ratio of 1 the catalyst formed in situ would
derive from BINAP monoxide, BINAP(O), and Pd(0)
† Contribution No. 8359.
(1) Shimizu, I.; Matsumoto, Y.; Shoji, K.; Ono, T.; Satake, A.;
Yamamoto, A. Tetrahedron Lett. 1996, 37, 7115.
(3) Ozawa, F.; Kubo, A.; Hayashi, T. Chem. Lett. 1992, 2177.
10.1021/om020838q CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/31/2002

556 Organometallics, Vol. 22, No. 3, 2003
Marshall and Grushin
Clearly, a 1:1 mixture of BINAP and Pd(OAc)2 can
produce catalytically active Pd(0) complexes of BINAP-
(O) which possess properties that are totally different
from those of Pd(0) BINAP catalysts, even to the extent
of reversal of chirality induced. While the organometallic
and coordination chemistry of BINAP complexes of
palladium is quite well developed,4 very little is known
about their BINAP(O) analogues.5 The Pd BINAP(O)
species generated in situ (eq 2) must have been involved
as intermediates in various catalytic reactions, though
in many cases this fact has not been fully realized. In
this paper we report the synthesis and characterization
of a series of new BINAP(O) complexes of Pd(II) and
Pd(0). These complexes exhibit interesting coordination
modes that differ considerably from those commonly
observed for Pd derivatives of other hemilabile mixed
phosphine-phosphine oxide ligands.
Two sharp singlets at 22.8 and 48.5 ppm were observed
in the 31P NMR spectrum of 1. The strong downfield
shift for the PdO resonance (vs 27.5 ppm for free
BINAP(O)) pointed to PdO-Pd coordination, whereas
the sharpness of the peaks indicated that 1 is inert on
the NMR time scale (20 °C).
Unexpectedly, addition of 1 equiv of (R)-BINAP(O) to
(R)-1 in CH2Cl2 led to a mixture of (R)-1, (R)-BINAP-
(O) (31P NMR: -14.6 and 27.5 ppm), and a new Pd
complex (31P NMR: singlets at 26.3 and 32.7 ppm). On
the basis of the 31P NMR data, the new complex was
formulated as [((R)-BINAP(O))2PdCl2] (2), with only
P-coordination of both BINAP(O) ligands to Pd. Further
experiments with various (R)-1 to (R)-BINAP(O) ratios
and different degrees of dilution revealed that all three
species were in equilibrium (eq 4) which readily estab-
Resu lts a n d Discu ssion
Treatment of [(MeCN)2PdCl2] with 1 equiv of (R)- or
(S)-BINAP(O)6 in toluene or CH2Cl2-benzene under
reflux resulted in quantitative formation of [(BINAP-
(O))PdCl2] (1) (eq 3). A P,O-chelate structure for (S)-1
in the solid state and in solution was established by
X-ray analysis (Figure 1) and NMR data, respectively.7
lished within the time of mixing, while being slow on
the NMR time scale. The formation of 2 is disfavored
by the equilibrium (4), which is strongly shifted toward
(R)-1 and (R)-BINAP(O). Thus, even when a 4-fold
excess of (R)-BINAP(O) was used ([(R)-1] ) 0.8 × 10-2
M; [(R)-BINAP(O)] ) 3.2 × 10-2 M before equilibrium)
the equilibrated mixture exhibited only ca. 40% conver-
sion of the (R)-1 to 2. Integration of the three pairs of
the 31P NMR signals (see the Experimental Section)
(4) For selected reports, see: (a) Ammann, C. J .; Pregosin, P. S.;
Ruegger, H.; Albinati, A.; Lianza, F.; Kunz, R. W. J . Organomet. Chem.
1992, 423, 415. (b) Ozawa, F.; Kubo, A.; Matsumoto, Y.; Hayashi, T.;
Nishioka, E.; Yanagi, K.; Moriguchi, K. Organometallics 1993, 12, 4188.
(c) Pregosin, P. S.; Ruegger, H.; Salzmann, R.; Albinati, A.; Lianza,
F.; Kunz, R. W. Organometallics 1994, 13, 83, 5040. (d) Stang, P. J .;
Olenyuk, B.; Arif, A. M. Organometallics 1995, 14, 5281. (e) Yamagu-
chi, M.; Yabuki, M.; Yamagishi, T.; Sakai, K.; Tsubomura, T. Chem.
Lett. 1996, 241. (f) Wolfe, J . P.; Wagaw, S.; Buchwald, S. L. J . Am.
Chem. Soc. 1996, 118, 7215. (g) Pregosin, P. S.; Salzmann, R. Coord.
Chem. Rev. 1996, 155, 35. (h) Amatore, C.; Broeker, G.; J utand, A.;
Khalil, F. J . Am. Chem. Soc. 1997, 119, 5176. (i) Sodeoka, M.; Tokunoh,
R.; Miyazaki, F.; Hagiwara, E.; Shibasaki, M. Synlett 1997, 463. (j)
Widenhoefer, R. A.; Zhong, H. A.; Buchwald, S. L. J . Am. Chem. Soc.
1997, 119, 6787. (k) Fuss, M.; Siehl, H.-U.; Olenyuk, B.; Stang, P. J .
Organometallics 1999, 18, 758. (l) Cataldo, M.; Nieddu, E.; Gavagnin,
R.; Pinna, F.; Strukul, G. J . Mol. Catal. A 1999, 142, 305. (m) Fujii,
A.; Hagiwara, E.; Sodeoka, M. J . Am. Chem. Soc. 1999, 121, 5450. (n)
Drago, D.; Pregosin, P. S.; Tschoerner, M.; Albinati, A. J . Chem. Soc.,
Dalton Trans. 1999, 2279. (o) Oi, S.; Terada, E.; Ohuchi, K.; Kato, T.;
Tachibana, Y.; Inoue, Y. J . Org. Chem. 1999, 64, 8660. (p) Wolfe, J .
P.; Buchwald, S. L. J . Org. Chem. 2000, 65, 1144. (q) Alcazar-Roman,
L. M.; Hartwig, J . F.; Rheingold, A. L.; Liable-Sands, L. M.; Guzei, I.
A. J . Am. Chem. Soc. 2000, 122, 4618. (r) Pignat, K.; Vallotto, J .; Pinna,
F.; Strukul, G. Organometallics 2000, 19, 5160. (s) Alcazar-Roman, L.
M.; Hartwig, J . F. Organometallics 2002, 21, 491.
allowed for calculation of Keq at 20.7 M-1
.
The reluctance of 1 to form 2 upon addition of BINAP-
(O) was unexpected, given the fact that monoxides of
other bidentate phosphines, such as dppmO, dppeO,
dpppO, dppbO, and dppfcO, are not prone to P,O-
coordination to Pd(II), forming exclusively analogues of
2 upon treatment of Pd(II) chloro derivatives with 2
equiv of the ligand.8,9 Both the rigidity of the BINAP
framework and steric hindrance can provide a rationale
for the favored PdO-Pd coordination and uncommon
position of the equilibrium (4).
A comparison of geometry parameters of (S)-1 (Figure
1) and those reported4b for its BINAP analogue [((R)-
BINAP)PdCl2] reveal much difference between the two.
(5) (a) To the best of our knowledge, only one fully characterized
Pd BINAP(O) complex has been reported, [BINAP(O)PdL], where L )
cyclometalated N,N-dimethyl-(S)-1-(1-naphthyl)ethylamine.5b (b) Glad-
iali, S.; Pulacchini, S.; Fabbri, D.; Manassero, M.; Sansoni, M.
Tetrahedron: Asymmetry 1998, 9, 391.
(6) (a) Grushin, V. V. J . Am. Chem. Soc. 1999, 121, 5831. (b)
Grushin, V. V. Organometallics 2001, 20, 3950. (c) Patent protection:
Grushin, V. V. U.S. Patent 5,919,984, 1999.
(7) For a similar Pt complex, see: Gladiali, S.; Alberico, E.; Pulac-
chini, S.; Kolla`r, L. J . Mol. Catal. A 1999, 143, 155.
(8) Coyle, R. J .; Slovokhotov, Yu. L.; Antipin, M. Yu.; Grushin, V.
V. Polyhedron 1998, 17, 3059.
(9) The platinum analogue of 2, [((S)-BINAP(O))2PtCl2], has been
generated and characterized in solution.7 The isolation and stability
of this Pt complex have not been reported.7

Pd(II) and Pd(0) Complexes of BINAP(O)
Organometallics, Vol. 22, No. 3, 2003 557
F igu r e 2. ORTEP plot of [((R)-BINAP(O))2Pd] ((R)-3), with
thermal ellipsoids drawn to the 50% probability level.
Sch em e 1
F igu r e 1. ORTEP plot of [((S)-BINAP(O)-κ2P,O)PdCl2]
((S)-1), with thermal ellipsoids drawn to the 50% prob-
ability level. Selected bond lengths (Å) and angles (deg):
Pd(1)-O(1), 2.080(2); Pd(1)-P(2), 2.249(1); Pd(1)-Cl(1),
2.268(1); Pd(1)-Cl(2), 2.353(1); P(1)-O(1), 1.517(2); O(1)-
Pd(1)-P(2), 91.16(6); O(1)-Pd(1)-Cl(1), 175.44(6); P(2)-
Pd(1)-Cl(1), 86.98(3); O(1)-Pd(1)-Cl(2), 88.99(6); P(2)-
Pd(1)-Cl(2), 173.15(3); Cl(1)-Pd(1)-Cl(2), 92.36(3).
The molecule of (S)-1 is square planar with the sum of
bond angles at Pd exceeding 359° and the O(1)-Pd-
Cl(1) and P(2)-Pd-Cl(2) angles being 175.44(6) and
173.15(3)°, respectively. In contrast, the geometry around
the metal in [((R)-BINAP)PdCl2] is severely distorted,
with the Cl atoms situated below and above the P2Pd
plane and the sum of coordination angles at Pd being
only 367.3(2)°.4b Thus, formal insertion of an oxygen
atom in one of the Pd-P bonds of [(BINAP)PdCl2]
makes the chelating ligand more flexible, alleviating
steric strain in the coordination sphere and allowing the
molecule to reach the desired planarity. In (S)-1, the
Pd-Cl bond trans to P (2.353(1) Å) is within the
expected range4b and is much longer than the Pd-Cl
bond trans to O (2.268(1) Å), indicating the weaker trans
influence of the phosphynyl ligand.
Due to the apparent, yet not recognized, importance
of BINAP(O) complexes of zerovalent Pd in catalysis (see
above), it was particularly interesting to isolate and
characterize such species, as well as to study their
ability to undergo oxidative addition. Reduction of 1
with excess LiBH4 in the presence of BINAP(O) afforded
an air-sensitive, crystalline reddish brown material
which analyzed as [(BINAP(O))2Pd] (3). Two unresolved
resonances were observed in the 31P NMR spectrum of
3 (benzene-d6) at room temperature, at 22.2 ppm (∆ν1/2
) 50 Hz) and 28.5 ppm (∆ν1/2 ) 500 Hz). Addition of
excess PhI to this NMR sample resulted in a rapid color
change to greenish yellow and concomitant replacement
of the two broad resonances with four 1:1:1:1 sharp
singlets at -13.5, 14.2, 26.5, and 36.7 ppm. The most
upfield and second downfield resonances were from free
BINAP(O), whose presence was also confirmed by TLC.
The other two signals (14.2 and 36.7 ppm) were from
[BINAP(O)Pd(Ph)I] (4), which was eventually isolated
from a similar experiment and fully characterized by
analytical, NMR, and X-ray diffraction data (see below).
Both (R)- and (S)-4 could be more conveniently prepared
by reacting [Pd2(dba)3] with PhI and BINAP(O) (1 equiv/
Pd). All transformations involving the formation of 3
and 4 are shown in Scheme 1.
X-ray analysis of [((R)-BINAP(O)2)2Pd] ((R)-3; 1:1
hexane solvate), revealed its remarkable structure
(Figure 2), in which both BINAP(O) ligands are bonded
to Pd through the P centers, while one of the two is also
π-coordinated to the metal via the aromatic CdC bond
bearing the naphthyl and phosphinyl groups. While
well-characterized η2-arene complexes of Pd(II) are not
uncommon,10-13 their Pd(0) analogues are extremely
rare. Earlier this year, as our work was in progress, a
communication from Buchwald’s group appeared, re-
porting an X-ray structure of a complex of Pd(0) in-
tramolecularly π-coordinated to a phenanthrene moi-
ety.14 To the best of our knowledge, (R)-3 is the only
other structurally characterized η2-arene complex of
zerovalent palladium.
Like complexes of the type P2M(olefin) (M ) Pd(0),
Pt(0)),15,16 (R)-3 is trigonal planar (Y-shaped) with the
P-Pd-P angle being 117.6° and the interplanar angle
between P(1)PdP(3) and C(23)PdC(28) being 142.8°.
Considerable back-donation from the metal is mani-

558 Organometallics, Vol. 22, No. 3, 2003
Marshall and Grushin
fested by the geometry parameters of the coordinated
arene in (R)-3 (Figure 3). The π-coordinated bond
C(23)-C(28) (1.447(4) Å) is longer than the analogous
noncoordinated bond C(67)-C(72) (1.395(4) Å) of the
other BINAP(O) ligand, which is bonded to Pd only
through the P atom (Figures 2 and 3). As a result of
partial rehybridization of C(23) and C(28) toward sp3,
both of the substituents P(2) and C(18) at the π-donating
CdC bond deviate from the mean plane C(23)-C(28)
by 0.62 and 0.64 Å, respectively. In contrast, the
deviations of the ring-forming carbon atoms from the
plane are minor, not exceeding 0.02 Å.
The nonplanarity of a coordinated olefin (Figure 3)
can be quantified by the Ittel-Ibers parameters R, â,
and â′.16 For (R)-3, the parameter R, defined as the angle
between the normal lines to planes C(18)C(28)C(27) and
P(2)C(23)C(24), is calculated at 40.7°. This value is lower
than the 55-61° found15 in a series of Pd(0) complexes
of tetracyanoethylene, a much stronger π-acid. Both the
â and â′ parameters are defined as the other two angles
of the triangle formed by C(23), C(28), and the point of
intersection of the two normals described above. Thus,
the angles â and â′ between C(23)-C(28) and the normal
lines to planes C(18)C(28)C(27) and P(2)C(23)C(24) are
calculated at 66.3 and 73.0°, correspondingly. It was
interesting to compare (R)-3 with the recently reported11a
structure of [(MOP)Pd(allyl)]+, where MOP ) 2-meth-
oxy-2′-(diphenylphosphino)-1,1′-binaphthyl is bound to
Pd via the P atom and the Ar,MeO-disubstituted
aromatic CdC bond. Using the reported11a structural
data for [(MOP)Pd(allyl)]+, we calculated its η2-arene
angle parameters at R ) 31.2, â ) 69.5, and â′ ) 78.8°.
The R angle in [(MOP)Pd(allyl)]+ (a Pd(II) complex;
31.2°) is noticeably more acute than in (R)-3 (a Pd(0)
complex; 40.7°), in accord with much stronger back-
donation expected from zerovalent palladium.
F igu r e 3. ORTEP plot of [((R)-BINAP(O))2Pd] ((R)-3), with
thermal ellipsoids drawn to the 50% probability level,
showing the P,η2-arene coordination of BINAP(O). All
atoms of the second BINAP(O), except for coordinated P,
are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Pd(1)-C(28), 2.160(3); Pd(1)-C(23), 2.228(3); Pd(1)-
P(1), 2.290(1); Pd(1)-P(3), 2.343(1); C(28)-Pd(1)-C(23),
38.47(11); C(28)-Pd(1)-P(1), 84.57(9); C(23)-Pd(1)-P(1),
114.76(9); C(28)-Pd(1)-P(3), 157.86(9); C(23)-Pd(1)-P(3),
122.71(8); P(1)-Pd(1)-P(3), 117.57(3).
The average Pd-C bond distance, 2.19 Å (Pd-C(23)
) 2.228(3) Å and Pd-C(28) ) 2.160(3) Å), is longer than
the values previously determined for Pd(0) olefin com-
plexes, 2.04-2.13 Å.15-19 The Pd-P bond distances of
2.290(1) and 2.343(1) Å for Pd-P(1) and Pd-P(3),
correspondingly, are in the expected range.15 No π-stack-
ing interactions were detected in the structure of (R)-3.
Clearly, the structure of [(BINAP(O))2Pd] is unusual,
being totally different from that of [(BINAP)2Pd], in
which all four P centers are coordinated to the metal.20
It is not surprising, therefore, that reactions catalyzed
by Pd(0) complexes of BINAP may result in a stereo-
chemical outcome that is different from that of analo-
gous reactions conducted in the presence of Pd(0)
catalysts stabilized by BINAP(O) of the same enantio-
meric configuration.1
As mentioned above, the oxidative addition of PhI to
3 resulted in the formation of a 1:1 mixture of free
BINAP(O) and [(BINAP(O))Pd(Ph)I] (4) (Scheme 1).
Only these two products could be observed in the
reaction mixture by 31P NMR spectroscopy (see above).
Therefore, in contrast to [(BINAP(O))PdCl2] (1) (eq 4),
4 does not react with BINAP(O) to give an observable
product. Furthermore, the 31P NMR data indicate that
(10) For examples of some η2- and η4-arene complexes of Pd(II),
see: (a) Ossor, H.; Pfeffer, M.; J astrzebski, J . T. B. H.; Stam, C. H.
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1907.
(13) Soon after preparation of this paper, another paper appeared,
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J .; Patrick, B. O.; J ames, B. R. Organometallics 2002, 21, 4672.
(14) Yin, J .; Rainka, M. P.; Zhang, X.-X.; Buchwald, S. L. J . Am.
Chem. Soc. 2002, 124, 1162.
(17) Benn, R.; Betz, P.; Goddard, R.; J olly, P. W.; Kokel, N.; Kru¨ger,
C.; Topalovic, I. Z. Naturforsch., B 1991, 46, 1395.
(15) Kranenburg, M.; Delis, J . G. P.; Kamer, P. C. J .; van Leeuwen,
P. W. N. M.; Vrieze, K.; Veldman, N.; Spek, A. L.; Goubitz, K.; Fraanje,
J . J . Chem. Soc., Dalton Trans. 1997, 1839 and references therein.
(16) Ittel, S. D.; Ibers, J . A. Adv. Organomet. Chem. 1976, 14, 33.
(18) Schleis, T.; Heinemann, J .; Spaniol, T. P.; Mulhaupt, R.; Okuda,
J . Inorg. Chem. Commun. 1998, 1, 431.
(19) Ellis, D. D.; Spek, A. L. Acta Crystallogr., Sect. C 2001, 57, 235.
(20) For an X-ray structure of [((R)-Tol-BINAP)2Pd], see ref 4q.

Pd(II) and Pd(0) Complexes of BINAP(O)
Organometallics, Vol. 22, No. 3, 2003 559
surprising.21b Being trans to the phosphine, the Pd-I
bond (2.609(1) Å) is slightly longer than the average
value calculated for various reported Pd(II) iodo
complexes (2.597 Å) yet shorter than the Pd-I bond
trans to Ph in [(Ph3P)2Pd(Ph)I].24 In accord with the
strong trans influence of σ-Ph, the Pd-O bond in (R)-4
(2.182(4) Å) is considerably longer than in (S)-1
(2.080(2) Å). In contrast, the Pd-P bond (2.271(2) Å) is
shortened, being trans to the phosphinyl group rather
than a phosphine.24 In general, all trends with the
Pd-O, Pd-P, Pd-C, and Pd-halogen bond distances
of (R)-4 are similar to those previously reported for
the structure of [(dppmO-κ2P,O)Pd(Me)Cl].21a The di-
hedral angle between the Pd coordination plane and the
σ-Ph ring is 79.3°, deviating noticeably from the ideal
value of 90°. This deviation is possibly dictated by the
need to alleviate filled-filled repulsions25 via push-pull
interactions of the negatively charged oxygen with π*
of the σ-aryl through Pd.24
Our longstanding interest in the chemistry of orga-
nopalladium fluoride complexes26,27 prompted us to
attempt I/F exchange on 4 in order to synthesize
[(BINAP(O))Pd(Ph)F]. Treatment of (S)-4 with AgF in
dry benzene under sonication26,27a-e,g cleanly produced
[((S)-BINAP(O))Pd(Ph)F]((S)-5) (eq 5). The 31P NMR
F igu r e 4. ORTEP drawing of [((R)-BINAP(O)-κ2P,O)Pd-
(Ph)I] ((R)-4), with thermal ellipsoids drawn to the 50%
probability level. Selected bond lengths (Å) and angles
(deg): I(1)-Pd(1), 2.609(1); Pd(1)-C(1), 2.011(8); Pd(1)-
O(1), 2.182(4); Pd(1)-P(2), 2.271(2); P(1)-O(1), 1.502(5);
C(1)-Pd(1)-O(1), 173.4(3); C(1)-Pd(1)-P(2), 90.0(2); O(1)-
Pd(1)-P(2), 91.82(14); C(1)-Pd(1)-I(1), 86.5(2); O(1)-
Pd(1)-I(1), 91.53(13); P(2)-Pd(1)-I(1), 176.25(5).
4 exists as a single isomer in solution. Because tertiary
phosphines and σ-aryls are both electron-rich, strongly
trans-influencing ligands, it was proposed that, in the
observed isomer of 4, the σ-phenyl is trans to oxygen
rather than phosphorus of the chelating BINAP(O).21
Indeed, this geometry was confirmed by X-ray analysis
of (R)-4.
The molecule of (R)-4 is square planar, with both the
phosphino and phosphinyl groups coordinated to Pd
and the σ-Ph trans to less electron-donating oxygen
(Figure 4). The planarity of (R)-4 is manifested by the
coordination angles around Pd, varying in the narrow
range 86.5(2)-91.8(2)°. Furthermore, the deviations
of the five atoms from the mean plane defined by
I(1)Pd(1)P(2)O(1)C(1) are minor, being 0.026, 0.059, 0.028,
-0.053, and -0.060 Å, respectively. The Pd-C bond
distance of 2.011(8) Å is within the range of 1.94-2.08
Å for 42 reports of mononuclear σ-phenyl Pd(II) com-
plexes found in the Cambridge Crystallographic Data-
base (CSD version 5.23 of April 2002). Because the
longest reported Pd-Ph bonds (2.04-2.08 Å) are trans
to most strongly trans-influencing phosphine22 or
σ-C23 ligands, the observed geometry of (R)-4 is not
spectrum of (S)-5 exhibited two 1:1 resonances, a singlet
at 40.2 ppm from the coordinated phosphinyl group and
a doublet at 30.5 ppm from the phosphine trans to the
F, as follows27g from the large coupling constant J P-F
)
179.7 Hz (vs 10-20 Hz for cis-J P-F).27a,b,g A doublet at
-215.7 ppm with the same coupling constant of 179.7
Hz was observed in the 19F NMR spectrum of (S)-5. The
(22) Herrmann, W. A.; Brossmer, C.; Priermeier, T.; Ofele, K. J .
Organomet. Chem. 1994, 481, 97. Zhuravel, M. A.; Grewal, N. S.;
Glueck, D. S.; Lam, K.-C.; Rheingold, A. L. Organometallics 2000, 19,
2882. Mann, G.; Baranano, D.; Hartwig, J . F.; Rheingold, A. L. J . Am.
Chem. Soc. 1998, 120, 9205.
(23) Villaneuva, L. A.; Abboud, K. A.; Boncella, J . M. Organome-
tallics 1992, 11, 2963.
(24) Flemming, J . P.; Pilon, M. C.; Borbulevitch, O. Ya.; Antipin,
M. Yu.; Grushin, V. V. Inorg. Chim. Acta 1998, 280, 87.
(25) Caulton, K. G. New J . Chem. 1994, 18, 25.
(21) (a) A similar dppmO complex, [(dppmO-κ2P,O)Pd(Me)Cl], with
the methyl trans to oxygen has been structurally characterized:
Brassat, I.; Englert, U.; Keim, W.; Keitel, D. P.; Killat, S.; Suranna,
G.-P.; Wang, R. Inorg. Chim. Acta 1998, 280, 150. (b) A known
phenomenon recently referred to as transphobia: Vicente, J .; Arcas,
A.; Bautista, D.; J ones, P. G. Organometallics 1997, 16, 2127 (includes
(26) Grushin, V. V. Chem. Eur. J . 2002, 8, 1006.
(27) (a) Fraser, S. L.; Antipin, M. Yu.; Khroustalyov, V. N.; Grushin,
V. V. J . Am. Chem. Soc. 1997, 119, 4769. (b) Grushin, V. V. Angew.
Chem., Int. Ed. 1998, 37, 994. (c) Pilon, M. C.; Grushin, V. V. Organo-
metallics 1998, 17, 1774. (d) Marshall, W. J .; Thorn, D. L.; Grushin,
V. V. Organometallics 1998, 17, 5427. (e) Grushin, V. V. Organome-
tallics 2000, 19, 1888. (f) Roe, D. C.; Marshall, W. J .; Davidson, F.;
Soper, P. D.; Grushin, V. V. Organometallics 2000, 19, 4575. (g)
Grushin, V. V.; Marshall, W. J . Angew. Chem., Int. Ed. 2002, 41, 4476.
a
structurally characterized C,N-cyclometalated dppmO-κ2P,O Pd
complex). Vicente, J .; Abad, J .-A.; Frankland, A. D.; Ram´ırez de
Arellano, M. C. Chem. Eur. J . 1999, 5, 3066. Vicente, J .; Abad, J .-A.;
Hernandez-Mata, F. S.; J ones, P. G. J . Am. Chem. Soc. 2002, 124, 3848.

560 Organometallics, Vol. 22, No. 3, 2003
Marshall and Grushin
geometry of (S)-5 seemed ideally suited for C-F reduc-
tive elimination of PhF from Pd, a key step of the highly
desired, yet not realized, catalytic fluorination of halo-
arenes.26
ferent from those of analogous Pd derivatives of other
phosphine-phosphine oxide ligands and BINAP. The
particularly uncommon [(BINAP(O))2Pd] (3) is a rare
example of a structurally characterized η2-arene Pd(0)
complex, in which the π-bonded aromatic CdC bond is
the one that is most sterically hindered, bearing the
phosphinyl and aryl substituents. The considerable
difference between BINAP and BINAP(O) complexes of
both zerovalent palladium and organopalladium(II)
bears important implications for catalysis. It has been
reported before3 that, under certain conditions, added
BINAP/Pd(II) catalyst is easily and cleanly converted
to BINAP(O) and Pd(0). In the presence of a base, this
process can rapidly occur under very mild conditions,
i.e. minutes at room temperature.6b Upon coming to-
gether, the BINAP(O) and Pd(0) produce catalytically
active BINAP(O) species (such as 3) which, being
structurally very different from BINAP Pd(0) species,
can change the catalytic reaction profile considerably,
up to complete reversal of product chirality.1,28
We have previously demonstrated26,27e,g that the
thermal decomposition of (σ-phenyl)palladium fluoride
complexes stabilized by tertiary phosphines involves
P-F and P-C rather than the needed C-F reductive
elimination. The selectivity observed was thought to be
due, at least in part, to the geometry of those fluorides
trans-[(R3P)2Pd(Ph)F], in which the F and Ph are trans,
while both are cis to the phosphines. On the contrary,
in (S)-5 the F ligand is trans to P and cis to the σ-phenyl
(eq 5), a geometry that one would expect to favor C-F
and suppress P-F reductive elimination. Nonetheless,
the thermal decomposition of (S)-5 did not furnish
fluorobenzene but rather produced a mixture of products
that obviously emerged from C-P and P-F reductive
elimination processes (eq 6).
Exp er im en ta l Section
NMR spectra were obtained with a Bruker Avance DPX 300
spectrometer. Reactions involving Pd(0) complexes and the
Pd(II) fluoride complex were carried out under nitrogen using
glovebox or Schlenk techniques. Both (R)- and (S)-BINAP(O)
were prepared as described in the literature.6 All other
chemicals were purchased from Aldrich and Strem and used
as received. For NMR studies of 3 and 5, deuterated solvents
were dried using standard procedures and stored in a glovebox
over freshly calcined molecular sieves (4 Å). The ultrasound-
promoted synthesis of 5 was carried out with an Aquasonic
50HT ultrasound bath.
[((R)-BINAP (O)-K2P ,O)P d Cl2] ((R)-1). The entire proce-
dure was performed in air. A mixture of (R)-BINAP(O) (205
mg; 0.32 mmol) and [(MeCN)2PdCl2] (83 mg; 0.32 mmol) was
dissolved in warm dichloromethane (5 mL), and this solution
was then evaporated to leave a dark orange oil. Stirring this
oil with benzene (3 mL) under reflux for 30 min produced a
yellow solid which was separated by filtration, recrystallized
from CH2Cl2-ether (twice), and dried under vacuum. The yield
The fluorine-containing products were not isolated
from the complex reaction mixture but rather identified
by their 19F and 31P NMR data, using previously
reported27e assignments (for detailed NMR data, see the
Experimental Section). It is noteworthy that the ease
of thermal decomposition at 115 °C in toluene decreases
noticeably in the order 5 (2 h) > [(Ph3P)2Pd(Ph)F] (16
h)27e > [(Me3P)2Pd(Ph)F] (72 h).27g This order parallels
the apparent lability P(Ph)2O > Ph3P > Me3P on the
metal, which provides additional support to a mecha-
nism that may involve dissociation of a neutral ligand
from Pd prior to reductive elimination.27e Dissociation
of the phosphinyl group from Pd in 5 would result in a
tricoordinate species, from which C-P and P-F reduc-
tive elimination is preferred.
of (R)-1‚1/3CH2Cl2 was 259 mg (96%). Anal. Calcd for C44H32
-
Cl2OP2Pd‚1/3CH2Cl2: C, 63.1; H, 3.9. Found: C, 62.8; H, 3.6.
1H NMR (CD2Cl2, 20 °C): δ 6.1-8.4 (multiplets). 31P NMR
(CD2Cl2, 20 °C): δ 22.8 (s, 1P, PPh2); 48.3 (s, 1P, P(O)Ph2).
[((S)-BINAP (O)-K2P ,O)P d Cl2] ((S)-1). The entire proce-
dure was performed in air. A stirred mixture of [(MeCN)2PdCl2]
(205 mg; 0.79 mmol) and toluene (10 mL) was brought to gentle
boiling. To this mixture was added a solution of (S)-BINAP-
(O) (507 mg; 0.79 mmol) in warm toluene (5 mL). The mixture
was stirred under reflux for 30 min and then cooled to room
temperature. The orange solid was separated by filtration,
recrystallized from CH2Cl2-ether (twice), and dried under
vacuum. The yield of (S)-1‚1/3CH2Cl2 was 620 mg (93%). Anal.
Calcd for C44H32Cl2OP2Pd‚1/3CH2Cl2: C, 63.1; H, 3.9. Found:
C, 63.4; H, 3.7. 1H NMR (CD2Cl2, 20 °C): δ 6.1-8.4 (multi-
plets). 31P NMR (CD2Cl2, 20 °C): δ 22.8 (s, 1P, PPh2); 48.3 (s,
1P, P(O)Ph2).
Rea ction of [((R)-BINAP (O)-K2P ,O)P d Cl2] ((R)-1) w ith
(R)-BINAP (O). A solution of [((R)-BINAP(O)-κ2P,O)PdCl2]
((R)-1: 5.9 mg; 7.2 × 10-3 mmol) and (R)-BINAP(O) (18.5 mg;
2.9 × 10-2 mmol) in CH2Cl2 (0.9 mL) was placed in a standard
5 mm NMR tube and analyzed by 31P NMR at 20 °C (number
of transients 1). The NMR spectrum displayed three pairs of
singlets, from (R)-1 (22.8 and 48.5 ppm), (R)-BINAP(O) (-14.6
and 27.5 ppm), and [((R)-BINAP(O))2PdCl2] (2) (26.3 and 32.7
ppm), in a 1:5.9:0.8 molar ratio. This ratio did not change after
the measurement was repeated in 30 min. On the basis of
Con clu sion
This paper describes a series of new complexes of
Pd(II) and Pd(0) with BINAP(O), a chiral phosphine-
phosphine oxide ligand. These complexes display coor-
dination modes and properties that are markedly dif-
(28) Very recently, it was reported that in some asymmetric Suzuki
cross-coupling reactions, the chirality reversal depending on the Pd-
(OAc)2 to (R)-BINAP ratio might be due to phenomena other than the
formation of BINAP(O) (eq 2). See: Castanet, A.-S.; Colobert, F.;
Broutin, P.-E.; Obringer, M. Tetrahedron: Asymmetry 2002, 13, 659.
these data, Keq was calculated at 20.7 L mol-1
.

Pd(II) and Pd(0) Complexes of BINAP(O)
Organometallics, Vol. 22, No. 3, 2003 561
Ta ble 1. Selected Cr ysta llogr a p h ic Da ta for (S)-1, (R)-3, a n d (R)-4
param
[((S)-BINAP(O))PdCl2] ((S)-1)
44H32Cl2OP2Pd
[((R)-BINAP(O))2Pd] ((R)-3)
[((R)-BINAP(O))Pd(Ph)I] ((R)-4‚C6H14)
empirical formula
fw
crystal size, mm
crystal system
space group
temp, K
C
C88H64O2P4Pd
1383.67
0.10 × 0.04 × 0.03
triclinic
P1
C37.33H34I0.67O0.67P1.33Pd0.67
690.14
0.19 × 0.02 × 0.01
hexagonal
P65
815.94
0.25 × 0.24 × 0.12
monoclinic
P21
173
173
173
a, Å
b, Å
c, Å
11.940(3)
11.711(3)
13.548(3)
11.956(1)
12.809(1)
13.422(1)
63.105(2)
78.267(2)
68.287(2)
1701.5(3)
1
1.350
42
3.40-56.56
none
29.934(6)
29.934(6)
11.858(5)
R, deg
â, deg
108.328(4)
γ, deg
V, Å3
1798.4(7)
2
1.507
9202(5)
9
1.121
Z
calcd density, g cm-3
µ(Mo), cm-1
2θ range, deg
abs cor
79
89
3.16-56.64
SADABS
30 552
8555
2.72-52.72
SADABS
63 593
12 147
no. of rflns collected
no. of unique rflns used
in refinement (I > 4σ(I))
no. of params refined
data to param ratio
R1, %
22 836
15 230
451
18.97
3.5
856
17.79
4.1
552
22.01
5.2
wR2, %
goodness of fit
7.2
1.06
7.0
0.93
12.3
1.03
[((R)-BINAP (O))2P d ] ((R)-3). The entire procedure was
performed under N2. To a mixture of [((R)-BINAP(O)-κ2P,O)-
PdCl2] ((R)-1: 100 mg; 0.12 mmol), (R)-BINAP(O) (80 mg; 0.12
mmol), benzene (10 mL), and water (1.5 mL) was added LiBH4
(20 mg; 0.9 mmol). The mixture was vigorously stirred at room
temperature for 6 h, until all solids had dissolved and a dark
red-brown solution formed. The mixture was evaporated and
the residue carefully dried under vacuum. The dark solid was
extracted first with 7 mL and then with 5 mL of benzene. The
combined extracts were filtered through Celite, reduced in
volume to ca. 3 mL, and treated with hexanes (5 mL, in
portions). After 2 h the red-brown crystals were separated,
washed with hexanes, and dried under vacuum. The yield of
(R)-3 was 145 mg (85%). Anal. Calcd for C88H64O2P4Pd: C,
76.4; H, 4.7. Found: C, 76.1; H, 4.7. 31P NMR (C6D6, 20 °C):
δ 22.2 (br s, 2P, PPh2); 28.5 (br s, 2P, P(O)Ph2).
(a) To a stirred mixture of (S)-BINAP(O) (590 mg; 0.92
mmol), iodobenzene (380 mg; 1.86 mmol), and benzene (15 mL)
was added [Pd2(dba)3] (403 mg; 0.44 mmol). After vigorous
stirring at room temperature for 3 h, the original purple-red
color was gone and much grayish precipitate formed. After
addition of methanol (30 mL) and stirring for 1 h the
precipitate was filtered, washed with methanol, dried, and
redissolved in CH2Cl2. The dichloromethane solution was
filtered through Celite, reduced in volume to ca. 10 mL, and
treated with hexanes (30 mL). After 12 h the pale yellow solid
was filtered, washed with hexanes, and dried under vacuum
to produce 610 mg of the product as tiny yellowish needles.
Evaporation of the benzene-MeOH mother liquors and wash-
ing the residue with MeOH (15 mL) produced an additional
quantity of (S)-4, which was purified by recrystallization from
CH2Cl2-hexanes as described above. The second crop amounted
to 165 mg of the product. The total yield of (S)-4‚1/4CH2Cl2 was
775 mg (91%). Anal. Calcd for C50H37IOP2Pd‚1/4CH2Cl2: C,
[((S)-BINAP (O))2P d ] ((S)-3). Under conditions of the
previous experiment, (S)-3 was prepared in 73% yield (185 mg)
from [((S)-BINAP(O)-κ2P,O)PdCl2] (150 mg), (S)-BINAP(O)
(117 mg), and LiBH4 (30 mg) in a benzene (10 mL)-water (1
mL) biphasic system.
1
62.2; H, 3.9. Found: C, 62.3; H, 3.5. H NMR (CD2Cl2, 20 °C):
δ 6.3-8.4 (multiplets). 31P NMR (CD2Cl2, 20 °C): δ 15.5 (s,
1P, PPh2); 37.8 (s, 1P, P(O)Ph2).
[((R)-BINAP (O)-K2P ,O)P d (P h )I] ((R)-4). The reaction was
carried out under N2. The isolation and purification steps were
performed in air. To a stirred mixture of (R)-BINAP(O) (805
mg; 1.26 mmol), iodobenzene (520 mg; 2.55 mmol), and
methanol (20 mL) was added [Pd2(dba)3] (580 mg; 0.63 mmol).
After vigorous stirring at room temperature for 1 day, the
original purple-red color was gone and a thick grayish slurry
was obtained. The precipitate was filtered, thoroughly washed
with methanol, dried, and redissolved in CH2Cl2. The dichlo-
romethane solution was filtered through a silica gel plug,
which was then washed with CH2Cl2 (TLC control). The
combined dichloromethane solutions were reduced in volume
to ca. 5-10 mL and treated with ether (50 mL). After 12 h
the pale yellow solid was filtered, washed with hexanes, and
dried under vacuum. The yield of (R)-4‚1/4CH2Cl2 was 875 mg
(72%). Anal. Calcd for C50H37IOP2Pd‚1/4CH2Cl2: C, 62.2; H, 3.9.
Found: C, 62.1; H, 3.4. 1H NMR (CD2Cl2, 20 °C): δ 6.3-8.4
(multiplets). 31P NMR (CD2Cl2, 20 °C): δ 15.5 (s, 1P, PPh2);
37.8 (s, 1P, P(O)Ph2).
(b) Iodobenzene (150 mg; 0.74 mmol) was added to a mixture
of [((S)-BINAP(O))2Pd], (S)-3 (150 mg; 0.11 mmol), and benzene
(2 mL). After the mixture was stirred for 2 h, the volatiles
were removed under vacuum, and the residue was stirred with
ethanol (3 mL) for 30 min. The fluffy needles of the product
were separated by filtration, washed with cold (5-10 °C) EtOH
(3 × 1 mL), dried, and recrystallized from CH2Cl2-hexanes.
The yield of (S)-4 was 91 mg (88%). The material was identical
with the sample of (S)-4 prepared using the [Pd2(dba)3] method
(see above).
[((S)-BINAP (O)-K2P ,O)P d (P h )F ] ((S)-5). The synthesis
and isolation were performed under anhydrous conditions.
(a) In a drybox, a standard 5 mm NMR tube was charged
with [((S)-BINAP(O)-κ2P,O)Pd(Ph)I] ((S)-4: 40 mg; 0.04 mmol),
AgF (25 mg; 0.20 mmol), and benzene (1 mL). The tube was
sealed with a rubber septum, brought out, and sonicated with
occasional shaking at 20-40 °C. After 1 h 15 min, 31P NMR
analysis indicated 70% conversion to [((S)-BINAP(O)-κ2P,O)-
Pd(Ph)F] ((S)-5). The sonication was resumed and continued
for an additional 1.5 h, after which the exchange was complete.
31P NMR: δ 30.5 (d, J P-F ) 179.7 Hz, 1P, PPh2); 40.2 (s, 1P,
[((S)-BINAP (O)-K2P ,O)P d (P h )I] ((S)-4). The reactions
were carried out under N2. The isolation and purification steps
were performed in air.

562 Organometallics, Vol. 22, No. 3, 2003
Marshall and Grushin
P(O)Ph2). 19F NMR, δ: -215.7 (d, J P-F ) 179.7 Hz). No other
signals were observed in the NMR spectra.
31P NMR spectroscopy. No fluorobenzene was present in the
sample (19F NMR). On the basis of the NMR data and previous
assignments27e three products were identified. (1) Ph3PF2: 19F
(b) In a drybox, a 25 mL round-bottom Schlenk flask was
charged with [((S)-BINAP(O)-κ2P,O)Pd(Ph)I] ((S)-4: 300 mg;
0.31 mmol), AgF (120 mg; 0.94 mmol), and benzene (8 mL).
The flask was sealed with a rubber septum, brought out, and
sonicated, with stirring, at 20-40 °C for 10 h. 31P NMR
analysis indicated 100% conversion. In drybox, the solution
was filtered through Celite. The solids were extracted with
warm benzene (3 × 3 mL) and filtered through the same Celite
plug. The combined benzene filtrates were reduced in volume
to ca. 5 mL, treated with ether (10 mL), and left at room
temperature overnight. The solid was separated, recrystallized
from hot benzene-hexanes, and dried under vacuum. The
NMR δ -39.6 (d, J P-F ) 666 Hz); 31P NMR δ -56.1 (t, J P-F
)
666 Hz). (2) 1-(2-Ph2(O)PC10H6)-1′-(2′-C10H6PPh2F2): 19F NMR
δ -34.2 (d, J P-F ) 684 Hz); 31P NMR δ -50.4 (t, J P-F ) 684
Hz). (3) 1-(2-Ph2(O)PC10H6)-1′-(2′-C10H6PPh3F): 19F NMR δ 8.2
(d, J P-F ) 658 Hz); 31P NMR δ -65.4 (d, J P-F ) 658 Hz).
Structural formulas of the products are presented in eq 6.
X-r a y Diffr a ction Stu d ies. A Bruker SMART 1K CCD
diffractometer (Mo KR radiation) was used for X-ray analysis
at -100 °C of all three complexes. In all cases, SADABS
correction was applied. The structures were solved by direct
methods and refined by full-matrix least squares on F2. All
non-hydrogen atoms were refined anisotropically, while all of
the hydrogen atoms were idealized using a riding model. A
summary of the crystallographic data is presented in Table 1.
For full details of the X-ray studies, see the Supporting
Information.
yield of (S)-5‚C6H6 was 209 mg (72%). Anal. Calcd for C50H37
-
FOP2Pd‚C6H6: C, 73.2; H, 4.7. Found: C, 73.3; H, 4.3. 1H NMR
(toluene-d8, 20 °C): δ 6.2-9.2 (multiplets). 31P NMR (toluene-
d8, 20 °C): δ 30.5 (d, J P-F ) 179.7 Hz, 1P, PPh2); 40.2 (s, 1P,
P(O)Ph2). 19F NMR (toluene-d8, 20 °C): δ -215.7 (d, J P-F
)
179.7 Hz).
Th er m a l Decom p osition of [((S)-BINAP (O)-K2P ,O)P d -
(P h )F ] ((S)-5). In a drybox, a standard 5 mm NMR tube was
charged with [((S)-BINAP(O)-κ2P,O)Pd(Ph)F] ((S)-5: 40 mg)
and toluene-d8 (0.7 mL), sealed with a rubber septum, brought
out, and heated at 115 °C (oil bath) for 2 h. Palladium metal
formation was observed. The sample was analyzed by 19F and
Su p p or tin g In for m a tion Ava ila ble: Full details of the
X-ray crystallographic studies of (S)-1, (R)-3, and (R)-4. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM020838Q