Rhenium-containing phosphorus donor ligands for palladium-catalyzed suzuki cross-coupling reactions: A new strategy for high-activity systems

Article abstract of DOI:10.1021/om0492956

The chiral racemic methyl complex (n⁵-C₅H ₅)Re(NO)(PPh₃)(CH₃) is converted to the rhenium-containing phosphorus donor ligands (n⁵-C₅H ₅)Re(NO)(PPh₃)((CH₂)_nPR ₂) (n/R = 3a, 0/Ph; 3b, 0/f-Bu; 3c, 0/Me; 5a, 1/Ph; 5b, 1/t-Bu) and (n⁵-C₅H₄PR₂)Re(NO)(PPh ₃)(CH₃) (7; R = a, Ph; b, t-Bu) via standard reactions (3, TfOH/CH₂Cl₂ or HBF₄/chlorobenzene, then PR₂H, then t-BuOK; 5, Ph₃C⁺X^-, then PR₂H, then t-BuOK; 7, n-BuLi, then PR₂Cl). (n ⁵-C₅H₄PR₂)Re(CO)₃ (R = Ph, t-Bu) is prepared from (n⁵-C₅H₅)Re(CO) ₃ analogously to 7. Most of these species are effective ligands for palladium-catalyzed Suzuki couplings. Typical conditions involve toluene solvent, an aryl bromide (1.0 equiv), phenylboronic acid (1.5 equiv), K ₃PO₄ (2.0 equiv), Pd(OAc)₂ (1 mol %), the rhenium/PR₂ species (4 mol %), and 60-100°C. In the cases of 3 and 5, the rhenium/PR₂ species are generated in situ from indefinitely stable conjugate acids [rhenium/PR₂H]⁺ and t-BuOK (2 equiv or 8 mol %). The bulkier and more electron-rich rhenium/P(t-Bu)₂ systems generally give more active catalysts than the rhenium/PPh₂ analogues. Under many conditions, the activities of 3a and 3b approach (but do not exceed) those of the corresponding, organophosphines PPh₃ and P(t-Bu)₃, the latter being a benchmark ligand for Suzuki couplings. Turnover numbers of > 1000 are easily realized. Chloroarenes can be coupled, but at much slower rates and in lower yields. The crystal structures of 5b and 7b are determined. The trigonal phosphorus atoms become increasingly pyramidalized in the series 5b < 5a < 7b.

Full text of DOI:10.1021/om0492956

Organometallics 2005, 24, 245-255
245
Rhenium-Containing Phosphorus Donor Ligands for
Palladium-Catalyzed Suzuki Cross-Coupling Reactions:
A New Strategy for High-Activity Systems
Sandra Eichenseher, Olivier Delacroix,† Klemenz Kromm,‡ Frank Hampel, and
J. A. Gladysz*
Institut fu¨r Organische Chemie, Friedrich-Alexander-Universita¨t Erlangen-Nu¨rnberg,
Henkestraâe 42, 91054 Erlangen, Germany
Received September 9, 2004
The chiral racemic methyl complex (η5-C5H5)Re(NO)(PPh3)(CH3) is converted to the
rhenium-containing phosphorus donor ligands (η5-C5H5)Re(NO)(PPh3)((CH2)nPR2) (n/R )
3a, 0/Ph; 3b, 0/t-Bu; 3c, 0/Me; 5a, 1/Ph; 5b, 1/t-Bu) and (η5-C5H4PR2)Re(NO)(PPh3)(CH3)
(7; R ) a, Ph; b, t-Bu) via standard reactions (3, TfOH/CH2Cl2 or HBF4/chlorobenzene,
then PR2H, then t-BuOK; 5, Ph3C+X-, then PR2H, then t-BuOK; 7, n-BuLi, then PR2Cl).
(η5-C5H4PR2)Re(CO)3 (R ) Ph, t-Bu) is prepared from (η5-C5H5)Re(CO)3 analogously to 7.
Most of these species are effective ligands for palladium-catalyzed Suzuki couplings. Typical
conditions involve toluene solvent, an aryl bromide (1.0 equiv), phenylboronic acid (1.5 equiv),
K3PO4 (2.0 equiv), Pd(OAc)2 (1 mol %), the rhenium/PR2 species (4 mol %), and 60-100 °C.
In the cases of 3 and 5, the rhenium/PR2 species are generated in situ from indefinitely
stable conjugate acids [rhenium/PR2H]+ and t-BuOK (2 equiv or 8 mol %). The bulkier and
more electron-rich rhenium/P(t-Bu)2 systems generally give more active catalysts than the
rhenium/PPh2 analogues. Under many conditions, the activities of 3a and 3b approach (but
do not exceed) those of the corresponding organophosphines PPh3 and P(t-Bu)3, the latter
being a benchmark ligand for Suzuki couplings. Turnover numbers of >1000 are easily
realized. Chloroarenes can be coupled, but at much slower rates and in lower yields. The
crystal structures of 5b and 7b are determined. The trigonal phosphorus atoms become
increasingly pyramidalized in the series 5b < 5a < 7b.
Introduction
been found by substituting phosphines that are bulkier
and/or more electron-rich.2-5 Although there are many
obvious approaches to such phosphines, we sought new
paradigms that were far removed from earlier investi-
gations.
The importance of the Suzuki or Suzuki-Miyaura
cross-coupling of arylboronic acids and aryl halides in
organic synthesis has grown dramatically over the past
decade.1 During this period, there have been intense
efforts to optimize the palladium catalysts commonly
used for these transformations.1-4 Many involve phos-
phine donor ligands, and enhanced activities have often
Thus, we set out to develop new catalysts based upon
monodentate phosphorus donor ligands that feature a
novel and untested design element: an 18-valence-
electron transition metal center R or â to the phosphorus
atom. These “spectator metals” would not directly
participate in the bond-breaking or bond-making steps
of the catalytic cycle. Such coordinatively saturated
LnMPR2 and LnMCH2PR2 species have an extensive
literature. They, and/or nitrogen or sulfur analogues,
have been shown to be much more basic and nucleo-
philic than model compounds without the metal.6-12 As
analyzed elsewhere, this can be attributed to repulsive
interactions between occupied orbitals (metal lone pair/
heteroatom lone pair or M-C bond/heteroatom lone
† Current affiliation: LCMT, UMR CNRS 6507, ENSICAEN, France.
‡ Current affiliation: Dynamit Nobel, Leverkusen, Germany.
(1) (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. (b)
Suzuki, A. J. Organomet. Chem. 1999, 576, 147. (c) Kotha, S.; Lahiri,
K.; Kashinath, D. Tetrahedron 2002, 58, 9633. (d) Miyaura, N. Top.
Curr. Chem. 2002, 219, 11. (e) Miura, M. Angew. Chem., Int. Ed. 2004,
43, 2201; Angew. Chem. 2004, 116, 2251.
(2) (a) Wolfe, J. P.; Singer, R. A.; Yang, B. H.; Buchwald, S. L. J.
Am. Chem. Soc. 1999, 121, 9550. (b) Walker, S. D.; Barder, T. E.;
Martinelli, J. R.; Buchwald, S. L. Angew. Chem., Int. Ed. 2004, 43,
1871; Angew. Chem. 2004, 116, 1907.
(3) (a) Littke, A. F.; Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2000, 122,
4020. (b) Liu, S.-Y.; Choi, M. J.; Fu, G. C. Chem. Commun. 2001, 2408.
(4) This literature is enormous, and only approaches involving bulky
and/or electron-rich phosphorus donor ligands are cited herein. In
addition to refs 2 and 3, see: (a) Zapf, A.; Ehrentraut, A.; Beller, M.
Angew. Chem., Int. Ed. 2000, 39, 4153; Angew. Chem. 2000, 112, 4315.
(b) Clarke, M. L.; Cole-Hamilton, D. J.; Woolins, J. D. J. Chem. Soc.,
Dalton Trans. 2001, 2721. (c) Li, G. Y. J. Org. Chem. 2002, 67, 3643,
and earlier work cited therein. (d) Kataoka, N.; Shelby, Q.; Stambuli,
J. P.; Hartwig, J. F. J. Org. Chem. 2002, 67, 5553. (e) Verkade, J. G.;
Kisanga, P. B. Aldrichim. Acta 2004, 37, 3. (f) Zapf, A.; Jackstell, R.;
Rataboul, F.; Riermeier, T.; Monsees, A.; Fuhrmann, C.; Shaikh, N.;
Dingerdissen, U.; Beller, M. Chem. Commun. 2004, 38. (g) Khanapure,
S. P.; Garvey, D. S. Tetrahedron Lett. 2004, 45, 5283. (h) an der Heiden,
M.; Plenio, H. Chem. Eur. J. 2004, 10, 1789.
(5) Valentine, D. H., Jr.; Hillhouse, J. H. Synthesis 2003, 2437.
(6) Minireview: Delacroix, O.; Gladysz, J. A. Chem. Commun. 2003,
665.
(7) Buhro, W. E.; Zwick, B. D.; Georgiou, S.; Hutchinson, J. P.;
Gladysz, J. A. J. Am. Chem. Soc. 1988, 110, 2427.
(8) (a) Giner Planas, J.; Gladysz, J. A. Inorg. Chem. 2002, 41, 6947.
(b) Giner Planas, J.; Hampel, F.; Gladysz, J. A. Chem. Eur. J. 2005,
11, in press.
(9) Dewey, M. A.; Knight, D. A.; Arif, A.; Gladysz, J. A. Chem. Ber.
1992, 125, 815.
(10) McCormick, F. B.; Gleason, W. B.; Zhao, X.; Heah, P. C.;
Gladysz, J. A. Organometallics 1986, 5, 1778.
10.1021/om0492956 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 12/14/2004

246 Organometallics, Vol. 24, No. 2, 2005
Eichenseher et al.
pair).7,9,11-14 Furthermore, most metal fragments con-
stitute bulky substituents.
Scheme 1. Synthesis of Complexes with
Re(CH2)nPR2 Linkagesa
Accordingly, we set out to probe whether effective
palladium catalysts can be generated from LnMPR2 and
LnMCH2PR2 species, where LnM is the chiral rhenium
fragment (η5-C5H5)Re(NO)(PPh3). Such complexes are
easily synthesized in both racemic and enantiomerically
pure form.7,15 Certain ferrocenyl-PR2 systems are also
very effective ligands for palladium-catalyzed Suzuki
couplings.3b Hence, we also sought to survey related
PR2-substituted cyclopentadienyl complexes. However,
in the case of ferrocene such phosphines are less
electron-rich than the organic analogues PR3.16 As
described in the narrative below, these types of rhe-
nium-containing phosphorus donor ligands often give
highly active palladium-based Suzuki catalysts. A por-
tion of these data have been communicated,17 and
complementary work with ruthenium complexes is
described elsewhere.8
One potential concernsthat the spectator metal frag-
ment might somehow compromise catalyst lifetimes or
stabilitiessmerits note at the outset. However, metal-
containing ligands of all typessnot just the familiar
ferrocenessare playing rapidly increasing roles in ca-
talysis.6 Furthermore, chelating diphosphines of the
formula (η5-C5H4PR2)Re(NO)(PPh3)((CH2)nPR2) (n ) 0,
1), which feature a chiral rhenium fragment in the
backbone, give long-lived rhodium hydrogenation and
hydrosilylation catalysts.18 High enantioselectivities are
obtained, consistent with molecular catalysts. Further-
more, a logical step for future studies would be to exploit
the second, coordinatively saturated metal more directly
in the catalytic cycle, perhaps as a hydrogen-bond or
proton acceptor. Various types of secondary interactions
are being increasingly recognized as key factors in
palladium-based catalysts.2b
a (a) CH2Cl2, TfOH, 0 °C (R ) Ph, t-Bu) or chlorobenzene,
HBF4, -41 °C (R ) Me). (b) PR2H; CH2Cl2, rt (R ) Ph) or
benzene, reflux (R ) t-Bu) or chlorobenzene, -41 °C to rt
-
(R ) Me). (c) t-BuOK, THF, rt. (d) Ph3C+X- (X- ) PF6 or
BF4-), CH2Cl2, -60 °C. (e) PR2H, -60 °C to rt.
Scheme 2. Synthesis of Complexes with
(η5-C5H4PR2)Re Linkagesa
Results
1. Rhenium-Containing Phosphorus Donor Lig-
ands. The rhenium-containing ligands were prepared
as summarized in Schemes 1 and 2. First, the racemic
methyl complex (η5-C5H5)Re(NO)(PPh3)(CH3) (1)19 was
treated with TfOH/CH2Cl2 or HBF4/chlorobenzene. Meth-
ane evolved, and subsequent additions of secondary
phosphines PR2H gave the corresponding adducts [(η5-
C5H5)Re(NO)(PPh3)(PR2H)]+X- (2; R/X- ) a, Ph/TfO-;
b, t-Bu/TfO-; c, Me/BF4-) in 82-56% yields. Next,
a (a) n-BuLi, THF, -78 °C to rt. (b) PR2Cl, THF, -78 °C
to rt.
deprotonations with t-BuOK afforded the phosphido
complexes (η5-C5H5)Re(NO)(PPh3)(PR2) (3; R ) a, Ph,
86%; b, t-Bu, 92%; c, Me). Compounds 2b and 3a,b were
originally reported some time ago,7 as were tosylate and
tetrafluoroborate analogues of 2a.7,18a,20 Whereas 2a-c
are stable for years, 3a-c oxidize quite rapidly to the
corresponding oxides in solvents that are not rigorously
deoxygenated.7
(11) (a) Fulton, J. R.; Sklenak, S.; Bouwkamp, M. W.; Bergman, R.
G. J. Am. Chem. Soc. 2002, 124, 4722. (b) Holland, A. W.; Bergman,
R. G. J. Am. Chem. Soc. 2002, 124, 14684. (c) Fox, D. J.; Bergman, R.
G. Organometallics 2004, 23, 1656.
Next, 1 was treated with Ph3C+X-, which generates
an electrophilic methylidene complex, and secondary
phosphines PR2H were added (Scheme 1, bottom).
Workups gave the phosphonium salts [(η5-C5H5)Re(NO)-
(PPh3)(CH2PR2H)]+X- (4; R/X- ) a, Ph/PF6-; b, t-Bu/
BF4-) in 94-85% yields. Deprotonations with t-BuOK
then afforded the rhenium-containing phosphines (η5-
C5H5)Re(NO)(PPh3)(CH2PR2) (5; R ) a, Ph; b, t-Bu) in
94-76% yields. Complex 5a has been described previ-
ously, as has the tetrafluoroborate analogue of 4a.18a,20
Due to the extra methylene group, 5a,b are much more
(12) Conner, D.; Jayaprakash, K. N.; Gunnoe, T. B.; Boyle, P. D.
Inorg. Chem. 2002, 41, 3042.
(13) Caulton, K. G. New J. Chem. 1994, 18, 25.
(14) For other possible contributing factors, see: Holland, P. L.;
Andersen, R. A.; Bergman, R. G. Comments Inorg. Chem. 1999, 21,
115.
(15) Zwick, B. D.; Dewey, M. A.; Knight, D. A.; Buhro, W. E.; Arif,
A. M.; Gladysz, J. A. Organometallics 1992, 11, 2673.
(16) O’Connor, A. R.; Nataro, C. Organometallics 2004, 23, 615.
(17) Eichenseher, S.; Kromm, K.; Delacroix, O.; Gladysz, J. A. Chem.
Commun. 2002, 1046.
(18) (a) Kromm, K.; Zwick, B. D.; Meyer, O.; Hampel, F.; Gladysz,
J. A. Chem. Eur. J. 2001, 7, 2015. (b) Kromm, K.; Hampel, F.; Gladysz,
J. A. Organometallics 2002, 21, 4264. (c) Kromm, K.; Osburn, P. L.;
Gladysz, J. A. Organometallics 2002, 21, 4275.
(19) Agbossou, F.; O’Connor, E. J.; Garner, C. M.; Quiro´s Me´ndez,
N.; Ferna´ndez, J. M.; Patton, A. T.; Ramsden, J. A.; Gladysz, J. A.
Inorg. Synth. 1992, 29, 211.
(20) To help consolidate a fragmented literature, updated syntheses
and characterization of the previously reported rhenium complexes in
Scheme 1 (and alternative salts for some cations) are provided in the
Supporting Information.

Pd-Catalyzed Suzuki Cross-Coupling Reactions
Organometallics, Vol. 24, No. 2, 2005 247
Table 1. Summary of Crystallographic Data
stable toward oxidation than 3a,b, and show no dete-
rioration after several hours in air.
5b‚t-BuOH‚1.5CH2Cl2
7b
As shown in Scheme 2, 1 was next treated with
n-BuLi to generate the lithiocyclopentadienyl complex
(η5-C5H4Li)Re(NO)(PPh3)(CH3) (6).21 Subsequent addi-
tions of chlorophosphines PR2Cl gave the phosphocy-
clopentadienyl complexes (η5-C5H4PR2)Re(NO)(PPh3)-
(CH3) (7; R ) a, Ph; b, t-Bu) in 60-42% yields. These
were also more stable toward oxidation than 3a,b.
Similar sequences have been executed with other (η5-
C5H5)Re(NO)(PPh3)(X) species.18 The many interesting
NMR properties associated with all of the preceding
compoundsssuch as distinct signals for the diastereo-
topic PR2 or PR2H groups and dynamic behavior arising
from pyramidal inversion at phosphorusshave been
detailed in earlier papers.7,18a,b
We also sought reference compounds for 7 with
somewhat different electronic properties. Accordingly,
(η5-C5H5)Re(CO)3 was similarly converted to the lithio-
cyclopentadienyl complex (η5-C5H4Li)Re(CO)3 (9).22 Sub-
sequent additions of PR2Cl gave the target compounds
(η5-C5H4PR2)Re(CO)3 (10; R ) a, Ph; b, t-Bu) in 98-
30% yields. The tert-butyl-substituted species 10b could
only be isolated in ca. 95% spectroscopic purity, so it
was not tested in catalysis.
2. Structural Data. During the course of the preced-
ing syntheses, single crystals of tert-butyl-substituted
5b were obtained. Since the structures of 3a,b and
nonracemic (S)-5a had been previously determined,7,18a
X-ray data were collected as described in Table 1 and
the Experimental Section. To our surprise, refinement
revealed a solvate of the composition 5b‚t-BuOH‚1.5CH2-
Cl2, with the t-BuOH retained from the deprotonation
of 4b despite an intermediate vacuum-drying step. Two
independent molecules were present in the unit cell,
differing slightly in the ReCH2-PC bond conformations
or torsion angles. One (but not the other) showed
hydrogen bonding from the phosphorus lone pair to a
t-BuOH proton, as depicted in Figure 1 (top). Key
metrical parameters are summarized in Table 2.
The bond lengths and angles about rhenium and the
Re-CH2 bond conformation were similar to those in (S)-
5a. The hydrogen atom in the hydrogen bond could not
be located. However, from the phosphorus-oxygen
separations, 3.744 Å, phosphorus-hydrogen distances
of 2.8-2.9 Å could be estimated. A related type of
hydrogen bond has been found between the cation and
anion of the complex [(η5-C5H5)Re(NO)(PPh3)(P(t-Bu)-
H2)]+Cl-.15 The trivalent phosphorus atoms of the two
independent molecules were similarly pyramidalized, as
reflected by the sums of the bond angles (337.8-338.5°).
As would be expected from their bulky tert-butyl sub-
stituents, they were much less pyramidal (more pla-
narized) than the trivalent phosphorus atom in (S)-5a
(305°). The corresponding values for 3b and 3a, in which
the phosphorus atoms are directly bound to rhenium,
are 332° and 323°.7 Some possible consequences for
catalysis are discussed below.
formula
fw
temperature [K]
wavelength [Å]
cryst syst
space group
a [Å]
C37.50H53Cl3NO2P2Re C32H40NOP2Re
904.30
702.79
173(2)
173(2)
0.71073
0.71073
triclinic
P1h
monoclinic
P21/c
14.2299(1)
15.8221(2)
17.9834(2)
69.791(1)
89.882(1)
87.044(1)
3794.06(7)
4
9.3511(3)
25.5777(4)
13.0351(3)
90
105.2548(9)
90
b [Å]
c [Å]
R [deg]
â [deg]
γ [deg]
V [Å3]
3007.88(13)
4
Z
F
calc [Mg/m3]
1.583
1.552
absorp coeff [mm-1
F(000)
]
3.532
1828
4.171
1408
cryst size [mm3]
θ limit [deg]
0.40 × 0.35 × 0.35
1.21-27.50
-18, 18; -20, 20;
-23, 22
0.20 × 0.20 × 0.20
1.80-27.50
-12, 12; -22, 32;
-16, 16
index ranges (h, k, l)
no. of reflns collected 32 633
no. of indep reflns 17 355
[R(int) ) 0.019]
no. of reflns [I>2σ(I)] 14 128
max. and min.
transmn
12 403
6838
[R(int) ) 0.0214]
5857
0.3711 and
0.3323
0.4892 and
0.4892
no. of data/restraints/ 17 355/27/852
params
6838/0/334
goodness-of-fit on F2
final R indices
[I>2σ(I)]
1.017
1.118
R1 ) 0.0442
wR2 ) 0.1250
R1 ) 0.0577;
wR2 ) 0.1377
2.477 and -1.840
R1 ) 0.0325
wR2 ) 0.0890
R1 ) 0.0407;
wR2 ) 0.0981
1.203 and -1.505
R indices (all data)
largest diff peak and
hole [e‚Å-3
]
mined and is depicted in Figure 1 (bottom). The triva-
lent phosphorus in this complex is much more pyrami-
dal than those in 3b or 5b‚t-BuOH‚1.5CH2Cl2, as
reflected by the sum of the bond angles (315°). The
cyclopentadienyl ligand adopts a conformation that
maximizes the distances between the bulky P(t-Bu)2 and
PPh3 moieties. One tert-butyl group is approximately
anti to the cyclopentadienyl-rhenium bond, as reflected
by C-P-C-C torsion angles of ca. (90° (Table 2). As
would be intuitively expected, the rhenium-carbon σ
bond (2.163(5) Å) was slightly shorter than those in 5b‚
t-BuOH‚1.5CH2Cl2 (2.199(5)-2.209(6) Å) and related
benzyl and secondary alkyl complexes (2.203(8)-2.215-
(4) Å).23
3. Relative Ligand Reactivities in Palladium-
Catalyzed Suzuki Couplings. Experiments were first
conducted under conditions similar to those popularized
by Buchwald,2a using Pd(OAc)2 as the palladium source
(1 mol %), twice this amount (2 mol %) of the rhenium-
containing phosphorus donor ligand, K3PO4 as the
boron-activating base, toluene solvent, and elevated
temperatures. Scouting reactions showed good activities.
However, as noted above, some of the rhenium com-
plexes are easily oxidized. Hence, for operational con-
venience, experiments were conducted with the conju-
gate acids 2a-c or 4a,b, and t-BuOK (2.0 equiv) was
added to effect deprotonation in situ. The similar use
of protonated organophosphines in several palladium-
catalyzed reactions has been reported.24
Crystals of another tert-butyl-substituted species, 7b,
were also obtained. The structure was similarly deter-
(21) (a) Heah, P. C.; Patton, A. T.; Gladysz, J. A. J. Am. Chem. Soc.
1986, 108, 1185. (b) Kowalczyk, J. J.; Arif, A. M.; Gladysz, J. A. Chem.
Ber. 1991, 124, 729.
(22) Casey, C. P.; Czerwinski, C. J.; Hayashi, R. K. Organometallics
1996, 15, 4362, and references therein.
(23) (a) Merrifield, J. H.; Strouse, C. E.; Gladysz, J. A. Organome-
tallics 1982, 1, 1204. (b) Kiel, W. A.; Lin, G.-Y.; Constable, A. G.;
McCormick, F. B.; Strouse, C. E.; Eisenstein, O.; Gladysz, J. A. J. Am.
Chem. Soc. 1982, 104, 4865.

248 Organometallics, Vol. 24, No. 2, 2005
Eichenseher et al.
Table 2. Key Distances [Å], Bond Angles [deg], and Torsion Angles [deg] for 5b‚t-BuOH‚1.5CH2Cl2 and 7b
a
5b‚t-BuOH‚1.5CH2Cl2
7b
Re-N1
1.750(5)/1.758(5)
Re-N1
Re-C1
Re-P1
N1-O1
P2-C11
P2-C50
P2-C60
1.753(4)
2.163(5)
2.3475(11)
1.208(6)
1.829(5)
1.908(6)
1.894(6)
Re-C1
2.199(5)/2.209(6)
2.3582(13)/2.3578(13)
1.216(6)/1.205(7)
1.787(5)/1.787(5)
1.847(6)/1.830(8)
1.846(7)/1.865(8)
3.744/-
Re-P2
N1-O1
P1-C1
P1-C50
P1-C60
P1-O80
N1-Re-C1
N1-Re-P2
C1-Re-P2
O1-N1-Re
C1-P1-C50
C1-P1-C60
C50-P1-C60
N1-Re-C1-P1
P2-Re-C1-P1
C50-P1-C1-Re
C60-P1-C1-Re
100.3(2)/102.2(3)
91.39(15)/90.96(17)
87.05(14)/86.86(15)
175.0(5)/171.9(5)
112.9(3)/112.7(3)
109.2(3)/109.7(3)
115.7(3)/116.1(4)
-73.7(4)/-71.1(4)
-164.6(3)/-161.4(4)
64.1(4)/93.3(5)
N1-Re-C1
95.19(17)
93.08(14)
87.24(12)
177.1(4)
106.0(2)
100.0(2)
108.7(3)
-88.1(5)
79.8(4)
N1-Re-P1
C1-Re-P1
O1-N1-Re
C11-P2-C50
C11-P2-C60
C60-P2-C50
C60-P2-C11-C12
C60-P2-C11-C15
C50-P2-C11-C12
C50-P2-C11-C15
24.8(5)
-167.3(4)
-165.8(3)/-135.7(4)
a The doubled values represent the two independent molecules in the unit cell.
Scheme 3. Standard Screening Conditions for
Suzuki Couplings
employed, so that the amount of bromobenzene con-
sumed and biphenyl formed could be continuously
quantified by gas chromatography. The first set of
experiments was conducted at 100 °C, and the results
with 2a-c and 4a,b are summarized in entries 1-5 of
Table 3. The conversion of bromobenzene is plotted as
a function of time in Figure 2 (top). The yields of
biphenyl were normally very similar, suggesting little
if any homocoupling of phenylboronic acid.
The catalysts derived from the phenyl- and tert-butyl-
substituted RePR2 systems 3a,b are distinctly more
reactive than those derived from methyl-substituted 3c
(less bulky) or the corresponding ReCH2PR2 systems
5a,b (less bulky and electron-rich). Curiously, the rate
with 5b is less than that in the absence of a donor
ligand, and factors that may be in play are analyzed in
the discussion section. Although tert-butyl-substituted
3b gives the most reactive catalyst, coupling was so fast
that the rate could not be distinguished from that of
P(t-Bu)3, the benchmark organophosphine (entry 10).3a
The reactivity of the catalyst with phenyl-substituted
3a also appeared close to that with the organic analogue
PPh3 (entry 9).
To improve the time resolution and allow better
reactivity comparisons, rates with selected ligands were
monitored at 80 °C. These data are summarized in
entries 12-16 of Table 3 and Figure 2 (bottom). Again,
the catalyst derived from 3b appeared close in activity
to that from P(t-Bu)3. However, 3a gave a somewhat
slower catalyst than PPh3. To still better define the
relative reactivities of the 3b/P(t-Bu)3 systems, two
experiments were conducted at 60 °C (Table 3, entries
17, 18). Now it becomes clear that the organophosphine
Figure 1. (top) Partial structure of 5b‚t-BuOH‚1.5CH2-
Cl2 (one of two independent molecules); (bottom) Structure
of 7b.
Thus, as summarized in Scheme 3, the coupling of
bromobenzene and phenylboronic acid was studied
using 1 mol % of Pd(OAc)2 and Pd/Re/t-BuOK mol ratios
of 1:4:8. Phenylboronic acid was used in excess over
bromobenzene (1.5:1), as some homocoupling can occur
under Suzuki conditions.1c,d An internal standard was
(24) Netherton, M. R.; Fu, G. C. Org. Lett. 2001, 3, 4295.

Pd-Catalyzed Suzuki Cross-Coupling Reactions
Organometallics, Vol. 24, No. 2, 2005 249
Table 3. Data for Suzuki Couplings under the Conditions of Scheme 3: Conversion [%] of Bromobenzene
and (in parentheses) Yield [%] of Biphenyl as Determined by GC
time (h)
donor liganda
entry
1
(temp, °C)
0.25
0.5
85
(77)
100
(100)
24
(14)
81
(72)
21
1
2
4
8
24
48
96
168
3a
(100 °C)
3b
(100 °C)
3c
(100 °C)
5a
66
(60)
97
(92)
14
(8)
71
(64)
19
(10)
33
97
(90)
100
(93)
2
3
38
(29)
86
(77)
25
(13)
63
58
(50)
89
(80)
26
(16)
70
84
96
(90)
98
(87)
33
99
100
(96)
(76)
93
(83)
31
(19)
77
(95)
100
(90)
40
4
(100 °C)
5b
5
45
60
(44)
76
(57)
(100 °C)
(12)
49
(24)
83
(80)
100
(98)
(28)
96
(94)
(33)
100
(96)
6
7ab
(100 °C)
7bb
(32)
64
(62)
53
(53)
78
(65)
98
(98)
41
(35)
15
(7)
84
(79)
12
(2)
67
(50)
88
(47)
81
(81)
74
(70)
91
(86)
100
(100)
44
(38)
27
(18)
99
(94)
12
(60)
89
(88)
90
(85)
100
(95)
(69)
95
(95)
96
(96)
(75)
98
(96)
100
(100)
7
(100 °C)
8
10ab
(100 °C)
b
9
PPh3
(100 °C)
P(t-Bu)3
(100 °C)
none
10
11
12
13
14
15
16
17
18
19
20
49
(42)
61
(51)
100
(96)
12
(2)
98
(92)
98
(97)
95
52
55
60
60
61
(55)
64
(55)
66
(59)
(100 °C)
3a
(80 °C)
3b
(45)
84
(50)
93
(53)
98
(54)
100
(98)
(78)
(83)
(89)
(80 °C)
3c
14
(4)
21
(12)
48
(41)
95
(92)
99
(97)
99
(99)
(80 °C)
(2)
85
(81)
96
(95)
74
b
PPh3
100
(92)
100
(97)
100
(97)
96
(80 °C)
P(t-Bu)3
(80 °C)
3b
(87)
21
(8)
79
(60 °C)
P(t-Bu)3
(60 °C)
3b
(rt)
P(t-Bu)3
(rt)
(69)
86
(91)
91
99
100
(98)
11
(77)
11
(81)
11
(87)
11
(93)
11
(97)
11
16
76
80
(0)
(0)
(0)
(0)
(0)
(0)
(0)
99
(69)
99
(75)
99
24
30
41
58
87
97
(97)
(19)
(24)
(34)
(55)
(86)
(99)
(99)
(99)
a Generated in situ from the conjugate acid and t-BuOK unless noted. b This ligand was added directly and not generated from the
conjugate acid.
gives the more reactive catalyst, at least through 86%
conversion. The catalyst derived from 3b remains active
at room temperature (entry 19). However, the conver-
sion plateaus at 11% for a considerable period, suggest-
ing that the initially generated species is not responsible
for most of the catalysis.
The phosphocyclopentadienyl donor ligands in Scheme
2 were tested next. These were used in their unpro-
tonated forms, and data from reactions at 100 °C are
summarized in entries 6-8 of Table 3. Consistent with
the trend for 3a,b, tert-butyl-substituted 7b gave a more
active catalyst than phenyl-substituted 7a. However, as
is readily seen from Figure 2, rates are much slower
than with 3a,b. The rhenium atoms in the donor ligands
10a,b have three good π-accepting ligands, which should
lead to less electron-rich systems than 7a,b. Nonethe-
less, 10a gave a more active catalyst than 7a. Had 10b
been available in pure form and tested, it would likely
have been more reactive yet. Thus, other factors clearly
play roles in the relative rates.
containing electron-withdrawing groups, such as 11, are
generally activated, whereas those containing electron-
donating groups, such as 12-14, are usually deacti-
vated. In all cases, complete conversions and good to
excellent yields were obtained over the course of a few
minutes to hours at 100 °C, as summarized in entries
1-8 of Table 4. Parallel experiments were conducted
with ligands 7a,b, as summarized in entries 9-16.
As seen for bromobenzene, the catalyst derived from
3b was more reactive than that from 3a. Reactions with
aryl bromides 11, 13, and 14 were essentially complete
within 15 min, and 12 within 30 min. In contrast, 3a
required ca. 2 h for the complete conversion of 12 and
13. As expected from Table 3, the catalyst derived from
7b was slower still, requiring 4-8 h for nonactivated
12-14. The catalyst derived from 7a required days for
the complete conversion of the nonactivated substrates.
Entry 8 with 3b and the aryl bromide 14 was repeated
on a 5-fold greater scale. Column chromatography gave
the phenylnaphthalene 18 in 97% yield.
4. Substrate Scope and Other Experiments. The
two most active rhenium-containing ligands from Table
3, 3a,b, were applied to Suzuki couplings of substituted
aryl bromides as shown in Scheme 4. The conditions
were analogous to those in Scheme 3. Substrates
Aryl chlorides are especially desirable substrates for
metal-catalyzed carbon-carbon bond forming reac-
tions.25 However, they are much less reactive than aryl
bromides. Screening experiments with chlorobenzene
and phenylboronic acid were conducted at 100 °C under

250 Organometallics, Vol. 24, No. 2, 2005
Eichenseher et al.
treated with K3PO4 (2.0 equiv) at 100 °C, the charac-
teristic orange-red color of 3b was generated. Entry 2
of Table 3 was repeated with this sample. After 0.5 h,
the conversion and yield were 100% and 99%, virtually
equivalent to the results with t-BuOK. A similar reac-
tion was conducted, but with all components mixed
simultaneously. After 0.5 h, the data were identical.
The effectiveness of the lead ligand 3b was also
screened under Suzuki conditions popularized by Fu.3a
These involved bromobenzene, phenylboronic acid (1.1
equiv), Pd2(dba)3 (1.5 mol %), 3b (3.6 mol %, generated
in situ from 2b and t-BuOK (1:2)), and KF (3.3 equiv).
Although detailed studies were not conducted, 3b gave
a more active catalyst than P(t-Bu)3 at room tempera-
ture. However, P(t-Bu)3 was more reactive in couplings
conducted at 60 °C.
Discussion
The preceding data constitute another in an ongoing
series of examples where bulky and/or electron-rich
phosphorus donor ligands give more active catalysts for
Suzuki or other palladium-catalyzed carbon-carbon
bond forming reactions.4 It is often overlooked that
bulkier phosphorus donor ligands are less pyramidal,
as reflected in the crystal structure of 5b versus 5a and
3b versus 3a. This trend is very pronounced in trialkyl
phosphines (PH3, P(CH3)3, P(t-Bu)3) and results in more
lone pair p character.27 Hence, such species are intrinsi-
cally more basic or electron-rich. In any event, electron-
rich ligands should help to facilitate oxidative addition
steps, which are often rate-determining in catalytic
cycles. Bulkier ligands furthermore promote lower
coordination numbers, which can also facilitate oxida-
tive addition.
However, the basicity-enhancing rhenium moieties in
3a,b do not result in catalytic activities higher than
those of the corresponding organophosphines, at least
for Suzuki couplings of aryl bromides or chlorides under
the Buchwald conditions. Perhaps a non-oxidative-
addition step of the catalytic cycle has become rate
determining, for which the rhenium fragment imparts
unfavorable steric or electronic properties. The lower
activity of the catalyst derived from 7b versus 3b is
consistent with its increased pyramidalization (Figure
1) and inductive effects previously observed with fer-
rocene-substituted PR2 moieties.16 However, the greater
activity of 10a as compared to 7a is curious. Although
we have no quantitative data on their relative basicities,
the latter is almost certainly more electron-rich. Hence,
other factors clearly play roles in the relative reactivi-
ties.
Figure 2. Plots of bromobenzene conversion (Table 3)
under the conditions of Scheme 3: (top) data at 100 °C;
(bottom) data at 80 °C.
conditions analogous to Scheme 3. After 168 h, ligands
3a,b gave conversions of only 5% and 40%, correspond-
ing to yields of 2% and 31%. After 96 h under identical
conditions, PPh3 and P(t-Bu)3 gave conversions of 12%
and 83%, corresponding to yields of 7% and 76%. This
provides another example where P(t-Bu)3 is superior to
3b. For comparison, 3a,b were also tested with the more
activated substrate 4-chloroacetophenone. After 168 h,
conversions were 46% and 88%, and the yields of
4-phenylacetophenone (15) were 28% and 51%.
Under the conditions of Schemes 3 or 4, turnover
numbers cannot exceed 100, which is insufficient for
industrial applications. Thus, entries 7 and 8 of Table
4 were repeated, but with reduced palladium and
rhenium loadings of 0.1 and 0.4 mol %. After 1.0 and
0.5 h, complete conversions and quantitative yields were
again obtained. This establishes that turnover numbers
of g1000 are easily realized.
We originally speculated that ReCH2PR2PdX systems
derived from 5a,b might be shorter-lived or less active
due to possible equilibration with +RedCH2 and
[R2PPdX]- species.17,28 However, we have since found
that 5a is in fact cyclometalated by Pd(OAc)2 to give a
novel palladacycle with rhenium in the backbone.29 This
system has catalytic activity in its own right and will
The boron-activating base K3PO4 is only slightly less
strong than the t-BuOK used to deprotonate the ligand
precursors 2a-c and 4a,b (∆pKa(H2O) ca. 6).26 We
therefore wondered whether the t-BuOK was needed at
all. Accordingly, when a toluene solution of 2b was
(27) Jiao, H.; Le Stang, S.; Soo´s, T.; Meier, R.; Kowski, K.; Radema-
cher, P.; Jafarpour, L.; Hamard, J.-B.; Nolan, S. P.; Gladysz, J. A. J.
Am. Chem. Soc. 2002, 124, 1516, and references therein.
(28) For a similar electrophile-promoted process with a ReCH2S-
(dO)CH3 complex, see: Meyer, O.; Arif, A. M.; Gladysz, J. A. Orga-
nometallics 1995, 14, 1844.
(25) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 2002, 41, 4176;
Angew. Chem. 2002, 114, 4350.
(26) Perrin, D. D. Ionisation Constants of Inorganic Acids and Bases
in Aqueous Solution, 2nd ed.; Pergamon: New York, 1982.

Pd-Catalyzed Suzuki Cross-Coupling Reactions
Organometallics, Vol. 24, No. 2, 2005 251
Scheme 4. Suzuki Reactions of Other Aryl Bromides
Table 4. Data for Suzuki Couplings under the Conditions of Scheme 4: Conversion [%] of Aryl Bromides
and (in parentheses) Yield [%] of Biaryl as Determined by GC
time (h)
entry
1
educt
ligand
3aa
0.25
0.5
1
2
4
8
24
48
96
11
100
(86)
100
(78)
20
(20)
70
2
11
12
12
13
13
14
14
11
11
12
12
13
13
14
14
3ba
3aa
3ba
3aa
3ba
3aa
3ba
7ab
7bb
7ab
7bb
7ab
7bb
7ab
7bb
3
41
(40)
98
(98)
91
(83)
82
97
(92)
100
(100)
(82)
100
(100)
97
4
(70)
81
5
99
(87)
100
(88)
(64)
100
(88)
100
(100)
98
(98)
79
(70)
92
(90)
66
(63)
66
(63)
44
(38)
58
(85)
6
7
8
100
(100)
86
(85)
99
(96)
71
(68)
79
(77)
57
(45)
74
(64)
73
9
94
100
(99)
(90)
100
(96)
76
10
11
12
13
14
15
16
80
(75)
93
(91)
75
(64)
94
(86)
84
(75)
74
(70)
83
(76)
99
(98)
80
(65)
100
(92)
89
86
91
(81)
97
(82)
100
(84)
(71)
86
(85)
69
(58)
83
(75)
79
(77)
100
(98)
84
91
(70)
95
(74)
100
(76)
(67)
(50)
66
(57)
52
(50)
90
95
100
(79)
(63)
55
(55)
(67)
60
(60)
(76)
88
(87)
(76)
99
(79)
100
(97)
(95)
a Generated in situ from the conjugate acid and t-BuOK. b This ligand was used directly and not generated from the conjugate acid.
be described separately. For this reason, we do not place
any special significance on the relative reactivities of
the catalysts from 5a,b. We also considered the pos-
sibility that palladium might somehow catalyze the
scrambling of the bonds to the trivalent phosphorus
atoms in the rhenium complexes, giving PPh3 or P(t-
Bu)3 (and other species). However, when 3b and Pd(OAc)2
were combined in C6D6 (4:1 mol ratio), no P(t-Bu)3 or
other decomposition process was detected by 31P NMR.
Another approach to enhancing catalyst activities is
to achieve a more direct entry into the catalytic cycle.
For example, the phosphorus donor ligand might be
precoordinated to palladium, rendering substitution
steps unnecessary. However, there have been to our
(29) Friedlein, F. K.; Hampel, F.; Gladysz, J. A. Manuscript in
preparation.

252 Organometallics, Vol. 24, No. 2, 2005
Eichenseher et al.
commercial Ph3C+X- can vary, and crystallization from CH2-
Cl2/hexane or CH2Cl2/benzene33 is recommended. All other
materials were obtained from standard sources as summarized
in the Supporting Information and used without purification.
knowledge no spectroscopic investigations of the nature
of the catalyst under Buchwald-type conditions or any
procedure involving Pd(OAc)2. NMR data for Fu-type
catalysts that use Pd2(dba)3 suggest that monophos-
phine adducts LPd play key roles.3a Accordingly, experi-
ments involving preformed MPR2Pd species will be
described in our next paper,8b using metal fragments
that are more electron-rich than the rhenium systems
described herein.
There is also increasing interest in enantioselective
Suzuki couplings that lead to chiral biaryls.30 Since
rhenium-containing phosphorus donor ligands of the
types in Schemes 1 and 2 are easily prepared in
enantiomerically pure form,7,15,18,19 this represents an
attractive possible extension of this work. At the same
time, note that the use of chiral racemic rhenium
complexes in the present study allows for the possibility
of diastereomeric species on the reaction coordinate, e.g.,
whenever at least two such ligands are coordinated to
palladium or are present in a Pdx complex. This poses
another potential complication in interpreting the rela-
tive reactivity data in Tables 3 and 4.
In summary, this study has extended the types of
metal-containing phosphorus donor ligands that can be
employed in metal-catalyzed reactions,6 as well as the
scope of reactions in which rhenium-containing ligands
can be applied. In most cases (but not all), the rhenium-
containing ligands appear to be innocent, in line with
past experience.18 However, there are also fascinating
possibilities for incorporating secondary interactions,
which appear to be important attributes of many highly
active palladium catalysts.2b Future papers will describe
similar experiments that utilize ruthenium-containing
ligands of the type (η5-C5H5)Ru(PR′3)2(PR2).8b These are
considerably more electron-rich than 3a,b, as confirmed
by quantitative basicity measurements. Also, applica-
tions of 3a,b, 5a,b, and 7a,b in additional types of
catalytic reactions will be reported.
[(η5-C5H5)Re(NO)(PPh3)(PPh2H)]+TfO- (2a).34 A Schlenk
flask was charged with 1 (6.145 g, 11.00 mmol)19,35 and dry
degassed CH2Cl2 (100 mL) and cooled to 0 °C. Then TfOH (1.4
mL, 2.4 g, 16 mmol) was slowly added with stirring. After 20
min, the mixture was filtered through a medium frit containing
1 cm of silica gel. The silica gel was eluted with dry CH2Cl2
(50 mL) and then dry CH2Cl2/acetone (95:5 v/v; 50 mL). Solvent
was removed from the eluate via oil pump vacuum. The red
powder was dissolved in dry CH2Cl2 (150 mL), and PPh2H (3.80
mL, 4.09 g, 22.0 mmol) was added with stirring. After 48 h,
the mixture was concentrated in vacuo to ca. 50 mL. Dry ether
(100 mL) was added, and the sample was stored in the freezer
overnight. The precipitate was collected by filtration (medium
frit), washed with dry ether, and dried by oil pump vacuum
to give 2a (7.879 g, 8.965 mmol, 82%) as a yellow powder, mp
125-126 °C. Anal. Calcd (%) for C36H31F3NO4P2ReS (878.85):
C 49.20, H 3.56, N 1.59, S 3.65. Found: C 48.71, H 3.72, N
1.51, S 3.69. IR (thin film, cm-1): ν˜ 1710 (s, NO), 1262 (vs,
1
CF). H NMR (400 MHz, CDCl3): PPh3 and PPh2 at δ 7.49-
7.00 (m, 25H); 7.31 (dd, 1H, 1J(H,P) ) 394.0 Hz, 3J(H,P) )
4.8 Hz, PH), 5.26 (s, 5H, C5H5). 13C{1H} NMR (100.5 MHz,
2
CDCl3): PPh3 at δ 133.0 (d, J(C,P) ) 11.1 Hz, o), 131.7 (d,
3
4J(C,P) ) 2.7 Hz, p), 129.3 (d, J(C,P) ) 11.1 Hz, m); PPhPh′
2
4
at 133.0 (d, J(C,P) ) 10.7 Hz, o), 131.6 (d, J(C,P) ) 2.3 Hz,
p), 131.5 (d, 4J(C,P) ) 2.3 Hz, p′), 131.3 (d, 2J(C,P) ) 10.6 Hz,
3
3
o′), 129.6 (d, J(C,P) ) 11.2 Hz, m), 129.5 (d, J(C,P) ) 11.6
Hz, m′); 120.9 (q, J(C,F) ) 323.7 Hz, CF3), 92.6 (s, C5H5).36
1
31P{1H} NMR (161.8 MHz, CDCl3): δ 12.7 (d, J(P,P) ) 13.3
2
2
Hz, PPh3), -7.8 (d, J(P,P) ) 13.3 Hz, PPh2H).
[(η5-C5H5)Re(NO)(PPh3)(PMe2H)]+BF4- (2c). A Schlenk
flask was charged with 1 (0.5600 g, 1.002 mmol)19,35 and
chlorobenzene (50 mL) and cooled to -41 °C. Then HBF4 (7.3
M in ether; 0.151 mL, 1.10 mmol) was added with stirring.
The flask was immersed in liquid N2, evacuated, and trans-
ferred under vacuum to a glovebox. To the almost thawed
mixture was added cold PMe2H (0.12 g, 2.0 mmol, -32 °C).37
The flask was removed from the glovebox and placed in a cold
bath (-60 °C). An oil pump vacuum was applied. The mixture
was warmed to room temperature and concentrated to ca. 30
mL. The yellow precipitate was collected by filtration, washed
with ether (3 × 10 mL), and dissolved in CH2Cl2. A layer of
ether was added. After 1 day, the supernatant was decanted
and the yellow oil dried by oil pump vacuum to give 2c‚(CH2-
Cl2)0.5 (0.550 g, 0.794 mmol, 79%) as yellow fibers, mp 135 °C.
Anal. Calcd (%) for C25H27BF4NOP2Re‚(CH2Cl2)0.5 (734.92): C
41.68, H 3.84, N 1.91. Found: C 41.69, H 3.79, N 1.71. IR (thin
film, cm-1): ν˜ 1691 (s, NO), 1050 (s, BF). 1H NMR (400 MHz,
CDCl3): δ PPh3 at 7.51-7.50 (m, 9H), 7.29-7.24 (m, 6H); 5.56
Experimental Section
General Procedures. All experiments were carried out
under nitrogen or argon. NMR spectra were recorded on
standard 300-500 MHz FT spectrometers, referenced to a
residual solvent signal (1H: CHCl3, 7.24 ppm; C6D5H, 7.15
ppm; 13C: CDCl3, 77.0 ppm; C6D6, 128.00 ppm) or H3PO4 (31P,
internal capillary, 85%, 0.00 ppm) and recorded at 25-28 °C
unless noted. IR spectra were recorded on an ASI React IR-
1000 spectrometer. Mass spectra were obtained using a
Micromass Zabspec instrument. Gas chromatography was
conducted on a ThermoQuest Trace GC 2000 instrument
(OPTIMA-5-0.25 µm capillary column, 25 m × 0.32 mm).
Elemental analyses were determined with a Carlo Erba
EA1110 CHN instrument (in-house).
Solvents were freshly dried before use, as described in the
Supporting Information. The n-BuLi (≈1.6 M in hexanes,
Acros) was standardized by titration versus N-benzylbenza-
mide (2×),31 PPh2Cl (98%, Acros) was vacuum distilled, chlo-
robenzene (for Suzuki reactions) was distilled, and P(t-Bu)3H+-
BF4- was prepared by a literature procedure.32 The quality of
1
3
(apparent dsext, 1H, J(H,P) ) 381 Hz, J(H,P) ) 6 Hz, PH),
5.51 (s, 5H, C5H5), 1.80/1.53 (2 dd, 18H, 2J(H,P) ) 12 Hz,
4J(H,P) ) 6 Hz, CH3/CH3′), 5.32 (s, 1H, 0.5 CH2Cl2). 13C{1H}
2
NMR (100.5 MHz, CDCl3): δ PPh3 at 133.0 (d, J(C,P) ) 11
1
4
Hz, o), 132.6 (d, J(C,P) ) 56 Hz, i), 131.6 (d, J(C,P) ) 2 Hz,
3
p), 129.3 (d, J(C,P) ) 11 Hz, m); 91.5 (s, C5H4), 53.8 (s, CH2-
Cl2), 13.1 (d, 1J(C,P) ) 39 Hz, CH3), 12.2 (d, 1J(C,P) ) 41 Hz,
(31) Burchat, A. F.; Chong, J. M.; Nielsen, N. J. Organomet. Chem.
1997, 542, 281.
(32) Jia, G.; Morris, R. H. J. Am. Chem. Soc. 1991, 113, 875.
(33) Patton, A. T.; Strouse, C. E.; Knobler, C. B.; Gladysz, J. A. J.
Am. Chem. Soc. 1983, 105, 5804.
(34) Analogous tosylate and tetrafluoroborate salts have been
(30) (a) Cammidge, A. N.; Cre´py, K. V. L. Chem. Commun. 2000,
1723. (b) Yin, J.; Buchwald, S. L. J. Am. Chem. Soc. 2000, 122, 12051.
(c) Castanet, A.-S.; Colobert, F.; Broutin, P.-E.; Obringer, M. Tetrahe-
dron: Asymmetry 2002, 13, 659. (d) Willis, M. C.; Powell, L. H. W.;
Claverie, C. K.; Watson, S. J. Angew. Chem., Int. Ed. 2004, 43, 1249;
Angew. Chem. 2004, 116, 1269. (e) Cammidge, A. N.; Cre´py, K. V. L.
Tetrahedron 2004, 60, 4377.
reported.7,18a
(35) Zhou, Y.; Dewey, M. A.; Gladysz, J. A. Organometallics 1993,
12, 3918.
(36) The ipso PPh3 and PPhPh′ signals were not observed.
(37) Caution: PMe2H is pyrophoric and was stored at -32 °C in a
glovebox. Preparation: (a) Parshall, G. W. Inorg. Synth. 1968, 11, 157.
(b) King, R. B.; Cloyd, J. C., Jr. J. Am. Chem. Soc. 1975, 97, 46.

Pd-Catalyzed Suzuki Cross-Coupling Reactions
Organometallics, Vol. 24, No. 2, 2005 253
C′H3). 31P{1H} NMR (161.8 MHz, CDCl3): δ 13.1 (d, 2J(P,P) )
through a Celite plug (4 × 2 cm, oven dried at 120 °C, cooled
to room temperature under vacuum). The filtrate was concen-
trated to ca. 10 mL and layered with dry pentane (30 mL).
After 3 days, orange prisms had formed. The supernatant was
decanted and the product dried by oil pump vacuum to give
5b (0.338 g, 0.481 mmol, 76%) as orange prisms, mp 172 °C
dec. Anal. Calcd (%) for C32H40NOP2Re (702.83): C 54.69, H
5.74, N 1.99. Found: C 54.53, H 5.80, N 1.89. IR (thin film,
2
16 Hz, PPh3), -62.2 (d, J(P,P) ) 16 Hz, PMe2H). MS (FAB,
3-NBA): m/z (%) 606 (100) [M]+, 544 (8) [M - PMe2H]+.
-
[(η5-C5H5)Re(NO)(PPh3)(CH2PPh2H)]+PF6 (4a).38
A
Schlenk flask was charged with 1 (4.500 g, 8.055 mmol)19,35
and dry CH2Cl2 (200 mL) and cooled to -60 °C. Then
-
Ph3C+PF6 (3.441 g, 8.862 mmol) was added with stirring.
Within 30 min, the orange suspension became a light yellow
solution. Then PPh2H (1.70 mL, 1.83 g, 9.83 mmol) was added
dropwise with stirring. After 10 min, the cold bath was
removed. The solution turned orange and then red. After 1.5
h, the mixture was concentrated to ca. 50 mL by oil pump
vacuum. Dry pentane (150 mL) was added. After 2 h, the
precipitate was collected by filtration, washed with dry pen-
tane (2 × 25 mL), and dried by oil pump vacuum to give 4a
(6.719 g, 7.560 mmol, 94%) as a yellow powder, mp 197-198
°C dec. Anal. Calcd (%) for C36H33F6NOP3Re (888.78): C 48.65,
H 3.74, N 1.58. Found: C 48.52, H 3.86, N 1.52. IR (thin film,
cm-1): ν˜ 1656 (m, NO), 834 (vs, PF6). 1H NMR (400 MHz, CD2-
Cl2): PPh3 and PPh2 at δ 7.87-7.32 (m, 25H); 7.11 (ddd, 1H,
1J(H,P) ) 489.5 Hz, 3J(H,H) ) 12.9 Hz, 3J(H,H′) ) 3.2 Hz,
PH), 4.89 (s, 5H, C5H5), 2.65-2.55 (m, 1H, CHH′), 2.42-2.30
(m, 1H, CHH′). 13C{1H} NMR (100.5 MHz, CD2Cl2): PPh3 at
1
cm-1): ν˜ 1639 (s, NO). H NMR (400 MHz, C6D6): δ PPh3 at
7.57-7.52 (m, 6 H), 7.06-6.96 (m, 9 H); 4.92 (s, 5H, C5H5),
1.91-1.84 (m, 1H, CHH′), 1.68 (dd, 1H, 2J(H,P) ) 15 Hz,
3
3J(H,P) ) 5 Hz, CHH′), 1.50/1.16 (2 d, 18H, J(H,P) ) 10 Hz,
CH3/CH3′). 13C{1H} NMR (100.5 MHz, C6D6): δ PPh3 at 136.7
2
(d, 1J(C,P) ) 51 Hz, i), 133.9 (d, J(C,P) ) 11 Hz, o), 130.1 (s,
p), 128.4 (d, 3J(C,P) ) 11 Hz, m); 91.2 (s, C5H5), 33.3 (d,
1J(C,P) ) 31 Hz, PC), 32.0 (d, 1J(C,P) ) 26 Hz, PC′), 31.3/30.0
2
1
(2d, J(C,P) ) 13 Hz, CH3/CH3′), -25.4 (d, J(C,P) ) 44 Hz,
CH2). 31P{1H} NMR (161.8 MHz, C6D6): δ 52.9 (d, 3J(P,P) ) 7
Hz, P(t-Bu)2), 24.1 (d, 3J(P,P) ) 7 Hz, PPh3). MS (FAB,
3-NBA): m/z (%) 704 (15) [MH]+, 558 (100) [M - P(t-Bu)2]+.
(η5-C5H4PPh2)Re(NO)(PPh3)(CH3) (7a). A Schlenk flask
was charged with 1 (0.300 g, 0.537 mmol)19,35 and dry THF
(15 mL) and cooled to -78 °C. Then n-BuLi (1.6 M in hexanes;
0.36 mL, 0.58 mmol) was added dropwise with stirring. The
orange solution was stirred at -30 °C for 5.5 h and then briefly
warmed to room temperature. The red sample was cooled to
-78 °C, and a solution of PPh2Cl (0.106 mL, 0.130 g, 0.590
mmol) in dry THF (5 mL) was slowly added. The mixture was
allowed to warm to room temperature overnight and filtered
through layered silica/Celite (1.5 cm/1.5 cm) with THF rinses
(4 × 5 mL). The combined filtrates were taken to dryness by
oil pump vacuum. Dry benzene (10 mL) was added. The
mixture was filtered through layered silica/Celite (1.5 cm/1.5
cm) with benzene rinses (5 × 10 mL). The combined filtrates
were concentrated by oil pump vacuum to ca. 2 mL and layered
with dry pentane (60 mL). After 1 day, the precipitate was
collected by filtration (medium frit), washed with dry pentane,
and dried by oil pump vacuum to give 7a (0.240 g, 0.323 mmol,
60%) as an orange powder, mp 205-207 °C dec. Anal. Calcd
(%) for C36H32NOP2Re (742.81): C 58.21, H 4.34, N 1.89.
Found: C 57.01, H 4.38, N 1.90. IR (thin film, cm-1): ν˜ 1629
(s, NO). 1H NMR (400 MHz, C6D6): PPh3 and PPh2 at δ 7.66-
7.50 (m, 10H), 7.20-6.95 (m, 15H); C5H4 at 4.75, 4.67, 4.63,
3.79 (4 br s, 4H); 1.54 (d, 3H, 3J(H,P) ) 6.0 Hz, CH3). 13C{1H}
1
2
δ 134.4 (d, J(C,P) ) 55.5 Hz, i), 133.8 (d, J(C,P) ) 11.1 Hz,
o), 131.4 (d, 4J(C,P) ) 1.9 Hz, p), 129.4 (d, J(C,P) ) 10.2 Hz,
3
m), PPhPh′ at 134.4 (s, p), 132.5 (d, 2J(C,P) ) 10.2 Hz, o), 131.9
(d, 2J(C,P) ) 10.2 Hz, o′), 130.4 (d, 3J(C,P) ) 12.0 Hz, m), 130.1
(d, 3J(C,P) ) 12.0 Hz, m′), 124.6 (d, 1J(C,P) ) 69.4 Hz, i), 122.5
1
1
(d, J(C,P) ) 86.0 Hz, i′); 90.9 (s, C5H5), -35.7 (dd, J(C,P) )
28.7 Hz, J(C,P) ) 3.7 Hz, CH2). 31P{1H} NMR (161.8 MHz,
2
CD2Cl2): δ 29.6 (d, 3J(P,P) ) 10.6 Hz, PPh2H), 21.5 (d,
3J(P,P) ) 11.9 Hz, PPh3), -143.3 (sep, 1J(P,F) ) 708.1 Hz, PF6).
[(η5-C5H5)Re(NO)(PPh3)(CH2P(t-Bu)2H)]+BF4 (4b). A
-
Schlenk flask was charged with 1 (0.632 g, 1.13 mmol)19,35 and
dry CH2Cl2 (30 mL) and cooled to -60 °C. Then Ph3C+BF4
-
(0.448 g, 1.36 mmol) was added with stirring. Within 30 min,
the orange suspension became a light yellow solution. Then
P(t-Bu)2H (0.230 mL, 0.182 g, 1.24 mmol) was added dropwise
with stirring. The solution turned red. The mixture was stirred
for 12 h while the cold bath warmed to room temperature. All
volatiles were removed by oil pump vacuum. The orange
residue was extracted with benzene (10 mL). The extract was
filtered through a syringe filter and added dropwise to vigor-
ously stirred hexanes (100 mL). The beige precipitate was
collected and analogously reprecipitated from CH2Cl2/hexanes
(5/100 mL). The precipitate was collected by filtration, washed
with hexanes (10 mL), and dried by oil pump vacuum to give
4b (0.760 g, 0.961 mmol, 85%) as an orange powder, mp 190-
1
NMR (100.5 MHz, C6D6): PPh3 at δ 136.9 (d, J(C,P) ) 50.9
2
Hz, i), 134.1 (d, J(C,P) ) 11.1 Hz, o), 130.0 (s, p), 128.5 (d,
3J(C,P) ) 6.4 Hz, m); PPhPh′ at δ 138.6 (d, 1J(C,P) ) 66.6 Hz,
i), 138.5 (d, 1J(C,P) ) 64.7 Hz, i′), 134.3 (d, 2J(C,P) ) 10.2 Hz,
o), 133.9 (d, 2J(C,P) ) 6.5 Hz, o′), 130.4 (s, p), 128.8 (d,
192 °C. Anal. Calcd (%) for C32H41BF4NOP2Re (790.64):
C
3
48.61, H 5.23, N 1.77. Found: C 48.68, H 5.17, N 1.65. IR (KBr,
cm-1): ν˜ 1642 (s, NO), 1054 (s, BF). 1H NMR (400 MHz,
CDCl3): PPh3 at δ 7.54-7.42 (m, 7H), 7.42-7.28 (m, 8H); 6.88
(dd, 1H, 1J(H,P) ) 410 Hz, 3J(H,H) ) 11 Hz, PH), 5.24 (s,
5H, C5H5), 1.72/1.46 (2 m, 2H, CHH′), 1.35/1.31 (2 d, 18H,
3J(H,P) ) 10 Hz, CH3/CH3′). 13C{1H} NMR (100.5 MHz,
CDCl3): δ PPh3 at 134.0 (d, 1J(C,P) ) 51.5 Hz, i), 133.3 (d,
2J(C,P) ) 11 Hz, o), 130.9 (s, p), 128.9 (d, 3J(C,P) ) 11 Hz, m);
91.0 (s, C5H5), 33.6 (d, 1J(C,P) ) 33 Hz, PC), 32.3 (d,
1J(C,P) ) 37 Hz, PC′), 28.3 (s, CH3), 27.2 (s, C′H3), -44.1 (d,
1J(C,P) ) 26 Hz, CH2). 31P{1H} NMR (161.8 MHz, CDCl3): δ
3J(C,P) ) 6.4 Hz, m), 128.7 (d, J(C,P) ) 6.5 Hz, m′); C5H4 at
2
1
101.0 (d, J(C,P) ) 3.7 Hz), 100.6 (d, J(C,P) ) 18.5 Hz, CP),
91.0 (s), 87.5 (d, 2J(C,P) ) 4.6 Hz), 86.4 (s); -34.3 (d,
2J(C,P) ) 6.0 Hz, ReCH3). 31P{1H} NMR (161.8 MHz, C6D6):
3
δ 25.2 (d, J(P,P) ) 1.9 Hz, PPh3), -18.0 (s, C5H4PPh2). MS
(FAB, 3-NBA): m/z (%) 759 (52) [MO]+, 743 (64) [M]+, 579
(100).
(η5-C5H4P(t-Bu)2)Re(NO)(PPh3)(CH3) (7b). A Schlenk
flask was charged with 1 (0.300 g, 0.537 mmol)19,35 and dry
THF (15 mL) and cooled to -78 °C. Then n-BuLi (1.6 M in
hexanes; 0.36 mL, 0.58 mmol) was added dropwise with
stirring. The orange solution was stirred at -30 °C for 5.5 h
and then briefly warmed to room temperature. The red sample
was cooled to -78 °C, and a solution of P(t-Bu)2Cl (0.112 mL,
0.107 g, 0.590 mmol) in dry THF (5 mL) was slowly added.
The mixture was allowed to warm to room temperature
overnight, becoming deep red-brown, and was filtered through
layered silica/Celite (2 cm/2 cm) with THF rinses (2 × 10 mL).
The combined filtrates were taken to dryness by oil pump
vacuum. Dry benzene (20 mL) was added. The mixture was
filtered through layered silica/Celite (2 cm/2 cm) with benzene
rinses (4 × 10 mL). The combined filtrates were concentrated
3
3
73.9 (d, J(P,P) ) 23 Hz, P(t-Bu)2), 20.3 (d, J(C,P) ) 23 Hz,
PPh3). MS (FAB, 3-NBA): m/z (%) 704 (80) [M]+, 558 (100)
[M - P(t-Bu)2H]+.
(η5-C5H5)Re(NO)(PPh3)(CH2P(t-Bu)2) (5b). An oven-dried
Schlenk tube was charged with 4b (0.500 g, 0.633 mmol) and
dry THF (25 mL). Then t-BuOK (1.0 M in THF; 0.70 mL, 0.70
mmol) was added with stirring. The orange mixture turned
red. After 1 h, the solvent was removed by oil pump vacuum.
Dry CH2Cl2 (25 mL) was added. The mixture was filtered
(38) An analogous tetrafluoroborate salt has been reported.18a

254 Organometallics, Vol. 24, No. 2, 2005
Eichenseher et al.
by oil pump vacuum to ca. 5 mL and layered with dry pentane
(80 mL). After 1 day, the solvent was decanted, and the residue
dried under oil pump vacuum to give 7b (0.157 g, 0.223 mmol,
42%) as orange blocks, mp 220-221 °C dec. Anal. Calcd (%)
for C32H40NOP2Re (702.83): C 54.69, H 5.74, N 1.99. Found:
C 54.58, H 5.72, N 2.07. IR (thin film, cm-1): ν˜ 1629 (s, NO).
1H NMR (400 MHz, C6D6): PPh3 at δ 7.61-7.56 (m, 6H), 7.05-
6.95 (m, 9H); C5H4 at 5.20, 5.11, 4.99, 3.12 (4 br s, 4H); 1.49
(d, 3H, 3J(H,P) ) 6.1 Hz, CH3), 1.41 (d, 9H, 3J(H,P) ) 11.7
Hz, CH3), 1.20 (d, 9H, 3J(H,P) ) 11.0 Hz, CH′3). 13C{1H} NMR
a light brown powder of ca. 95% spectroscopic purity, mp 227-
230 °C dec. IR (thin film, cm-1): ν˜ 2030 (s, CO), 1922 (vs, CO).
1H NMR (400 MHz, C6D6): δ C5H4 at 4.99 (dd, 2H, 3J(H,H′) )
2.0 Hz, 3J(H,P) ) 4.0 Hz), 4.46 (dd, 2H, 3J(H′,H) ) 2.0 Hz,
4J(H′,P) ) 2.0 Hz); 1.05 (d, 18H, 3J(H,P) ) 11.6 Hz, CH3).
13C{1H} NMR (100.5 MHz, C6D6): δ 194.3 (s, CO), C5H4 at 95.3
(d, J(C,P) ) 15.7 Hz), 84.8 (s), 84.1 (d, J(C,P) ) 15.7 Hz); 32.7
1
2
(d, J(C,P) ) 22.2 Hz, PC), 30.5 (d, J(C,P) ) 13.9 Hz, CH3).
31P{1H} NMR (161.8 MHz, C6D6): δ 27.9 (s, C5H4P(t-Bu)2).
Suzuki Couplings. A (Tables 3, 4). An oven-dried Schlenk
flask was charged with a phosphorus donor ligand (protonated
form unless noted; 0.0179 mmol, 4 mol %) and dry toluene (4
mL). Then t-BuOK (1.0 M in THF; 0.036 mL, 0.036 mmol) was
added with stirring (omitted for ligands used in deprotonated
form). The yellow mixture turned red. After 5 min, Pd(OAc)2
(0.0045 M in toluene; 1.0 mL, 0.0045 mmol, 1 mol %; higher-
turnover experiments: 0.100 mL, 0.000448 mmol, 0.1 mol %),
phenylboronic acid (0.0820 g, 0.673 mmol), K3PO4 (0.1900 g,
0.8950 mmol), an internal standard (tridecane (0.050 mL,
0.038 g, 0.205 mmol), hexadecane (0.060 mL, 0.046 g, 0.204
mmol), or eicosane (0.0577 g, 0.2042 mmol)), and an aryl halide
(0.45 mmol) were added. The red-brown suspension was stirred
at the indicated temperature and monitored by GC until
complete conversion or catalyst deactivation (up to 168 h). The
product was identified by comparison of the GC retention time
to that of an authentic sample. B. An oven-dried Schlenk flask
was charged with a protonated ligand (0.0161 mmol, 3.6 mol
%) and dry THF (4 mL). Then t-BuOK (1.0 M in THF; 0.032
mL, 0.032 mmol) was added with stirring. The yellow mixture
became red. After 5 min, Pd2(dba)3 (0.0062 g, 0.0068 mmol,
1.5 mol %), phenylboronic acid (0.0600 g, 0.492 mmol), KF
(0.0859 g, 1.48 mmol), tridecane (0.050 mL, 0.038 g, 0.205
mmol), and an aryl halide (0.45 mmol) were added. The
suspension was stirred at room temperature or 60 °C and
analyzed as described in procedure A. C (preparative experi-
ment). Complex 2b (0.0752 g, 0.0896 mmol, 4 mol %) and dry
toluene (15 mL), t-BuOK (1.0 M in THF; 0.18 mL, 0.18 mmol,
2.0 equiv/ligand), Pd(OAc)2 (0.0050 g, 0.022 mmol, 1 mol %),
phenylboronic acid (0.4097 g, 3.360 mmol), K3PO4 (0.9510 g,
4.480 mmol), and 6-methoxy-2-bromonaphthalene (0.5311 g,
2.240 mmol) were combined in a procedure analogous to A.
The red-brown suspension was stirred at 100 °C. After 1 h,
the mixture was cooled to room temperature, diluted with
ether (15 mL), and washed with aqueous NaOH (2 N, 5 mL).
The NaOH layer was separated and washed with ether (10
mL). The combined organic layers were washed with brine (10
mL) and dried (MgSO4). The solvents were removed by rotary
evaporation, and the residue was chromatographed (silica gel
column, 17.5 × 3 cm, 9:1 v/v hexanes/ethyl acetate). Solvent
was removed from the product-containing fractions (Rf ) 0.56,
TLC) to give 6-methoxy-2-phenylnaphthalene as a white
mother-of-pearl solid (0.511 g, 2.18 mmol, 97%). The NMR data
closely matched literature values:40 1H NMR (300 MHz,
1
(100.5 MHz, C6D6): PPh3 at δ 137.1 (d, J(C,P) ) 50.9 Hz, i),
2
4
134.0 (d, J(C,P) ) 11.1 Hz, o), 130.0 (s, J(C,P) ) 1.9 Hz, p),
3
1
128.5 (d, J(C,P) ) 10.2 Hz, m); C5H4 at 112.3 (d, J(C,P) )
29.6 Hz, CP), 95.8 (d, 2J(C,P) ) 6.5 Hz), 89.6 (s), 87.4 (s), 82.2
(s); 33.3 (d, 1J(C,P) ) 21.3 Hz, PC), 32.7 (d, 1J(C,P) ) 22.2 Hz,
PC′), 30.8 (d, 2J(C,P) ) 4.6 Hz, CH3), 30.7 (d, 2J(C,P) ) 4.6
Hz, C′H3), -35.0 (d, J(C,P) ) 8.3 Hz, ReCH3). 31P{1H} NMR
2
(161.8 MHz, C6D6): δ 25.6 (s, PPh3), 24.9 (s, C5H4P(t-Bu)2).39
MS (FAB, 3-NBA): m/z (%) 719 (25) [MO]+, 703 (100) [M]+,
646 (60).
(η5-C5H4PPh2)Re(CO)3 (10a). A Schlenk flask was charged
with 8 (0.180 g, 0.537 mmol)19 and dry THF (15 mL) and cooled
to -78 °C. Then n-BuLi (1.6 M in hexanes; 0.36 mL, 0.58
mmol) was added dropwise with stirring. The light yellow
solution was stirred at -30 °C for 5.5 h and then briefly
warmed to room temperature. The sample was cooled to
-78 °C, and a solution of PPh2Cl (0.106 mL, 0.130 g, 0.590
mmol) in dry THF (5 mL) was slowly added. The mixture was
allowed to warm to room temperature overnight and filtered
through layered silica/Celite (2 cm/2 cm) with THF rinses
(4 × 5 mL). The combined filtrates were taken to dryness by
oil pump vacuum. Dry benzene (10 mL) was added. The
mixture was filtered through layered silica/Celite (2 cm/2 cm)
with benzene rinses (3 × 10 mL). The combined filtrates were
concentrated by oil pump vacuum to ca. 5 mL and layered with
dry pentane (60 mL). After 1 day, the precipitate was collected
by filtration (medium frit), washed with dry pentane, and dried
by oil pump vacuum to give 10a (0.273 g, 0.525 mmol, 98%)
as an off-white powder, mp 129-131 °C. Anal. Calcd (%) for
C20H14O3P2Re (519.51): C 46.24, H 2.72. Found: C 46.36, H
2.72. IR (thin film, cm-1): ν˜ 2019 (s, CO), 1922 (s, CO). 1H
NMR (400 MHz, C6D6): PPh2 at δ 7.32-7.28 (m, 4H), 7.07-
7.01 (m, 6H); C5H4 at 4.76 (dd, 2H, 3J(H,H′) ) 2.0 Hz,
3J(H,P) ) 3.6 Hz), 4.42 (dd, 2H, 3J(H′,H) ) 2.0 Hz, 4J(H′,P) )
2.0 Hz). 13C{1H} NMR (100.5 MHz, C6D6): δ 193.6 (s, CO),
1
2
PPh2 at δ 137.6 (d, J(C,P) ) 10.7 Hz, i), 133.6 (d, J(C,P) )
3
19.8 Hz, o), 129.3 (s, p), 128.8 (d, J(C,P) ) 7.6 Hz, m); C5H4
at 96.6 (d, 1J(C,P) ) 21.4 Hz, CP), 92.6 (d, 2J(C,P) ) 13.8 Hz),
85.6 (s). 31P{1H} NMR (161.80 MHz, C6D6): δ -17.1 (s, C5H4-
PPh2).
(η5-C5H4P(t-Bu)2)Re(CO)3 (10b). A Schlenk flask was
charged with 8 (0.180 g, 0.537 mmol)19 and dry THF (15 mL)
and cooled to -78 °C. Then n-BuLi (1.6 M in hexanes; 0.36
mL, 0.58 mmol) was added dropwise with stirring. The
colorless solution was stirred at -30 °C for 5.5 h and then
briefly warmed to room temperature. The light yellow sample
was cooled to -78 °C, and a solution of P(t-Bu)2Cl (0.112 mL,
0.107 g, 0.590 mmol) in dry THF (5 mL) was slowly added.
The mixture was allowed to warm to room temperature
overnight, becoming deep yellow, and was filtered through
layered silica/Celite (2 cm/2 cm) with THF rinses (2 × 10 mL).
The combined filtrates were taken to dryness by oil pump
vacuum. Dry benzene (20 mL) was added. The mixture was
filtered through layered silica/Celite (2 cm/2 cm) with benzene
rinses (4 × 10 mL). The combined filtrates were concentrated
by oil pump vacuum to ca. 5 mL and layered with dry pentane
(80 mL). After several days, the precipitate was collected by
filtration (medium frit), washed with dry pentane, and dried
by oil pump vacuum to give 10b (0.078 g, 0.16 mmol, 30%) as
4
CDCl3): Np and Ph at δ 7.97 (d, J(H,H) ) 1.2 Hz, 1H), 7.79
(m, 2H), 7.71 (m, 3H), 7.46 (m, 2H), 7.35 (m, 1H), 7.17 (m,
2H); 3.93 (s, 3H, OCH3). 13C{1H} NMR (75.5 MHz, CDCl3): Np
and Ph at δ 157.7, 141.2, 136.4, 133.8, 129.7, 129.2, 128.8,
127.2, 127.1, 126.1, 125.6, 119.2, 105.6 (13 s); 55.3 (s, OCH3).
Crystallography. A. A CH2Cl2 solution of 5b that had been
dried under 0.006 Torr for 1 h was layered with hexane. After
3 days, the orange prisms were taken to a Nonius KappaCCD
diffractometer for data collection as outlined in Table 1. Cell
parameters were obtained from 10 frames using a 10° scan
and refined with 16 382 reflections. Lorentz, polarization, and
absorption corrections41 were applied. The space group was
determined from systematic absences and subsequent least-
squares refinement. The structure was solved by direct
methods. The parameters were refined with all data by full-
matrix least-squares on F2 using SHELXL-97.42 Non-hydrogen
(39) Tentative assignment
(40) Zapf, A.; Beller, M. Chem. Eur. J. 2000, 6, 1830.

Pd-Catalyzed Suzuki Cross-Coupling Reactions
Organometallics, Vol. 24, No. 2, 2005 255
atoms were refined with anisotropic thermal parameters. The
hydrogen atoms were fixed in idealized positions using a riding
model. Scattering factors were taken from the literature.43 The
asymmetric unit contained two independent molecules of 5b,
two t-BuOH molecules, and three CH2Cl2 molecules. The
carbon atoms were disordered in two of the CH2Cl2 molecules
and were refined to 55:45 (C70/C70A) and 84:16 (C90/C90A)
occupancies. The chlorine atoms of the other CH2Cl2 molecule
were disordered over six positions (C120-C125) and were
refined with a fixed occupancy of 1/3. B. A benzene solution of
7b was layered with pentane. After 1 day, the orange blocks
were analyzed as described for 5b (cell parameters from 10
frames using a 10° scan; refined with 6330 reflections). The
structure was solved and refined as described for 5b.
Acknowledgment. We thank the Deutsche For-
schungsgemeinschaft (DFG, GL 300/4-1), the von Hum-
boldt Foundation (fellowship to O.D.), and Johnson
Matthey PMC (palladium loan) for support.
(41) (a) “Collect” data collection software, Nonius B.V., 1998. (b)
“Scalepack” data processing software: Otwinowski, Z.; Minor, W.
Methods Enzymol. 1997, 276 (Macromolecular Crystallography, Part
A), 307.
(42) Sheldrick, G. M. SHELX-97, Program for refinement of crystal
structures; University of Go¨ttingen, 1997.
(43) Cromer, D. T.; Waber, J. T. In International Tables for X-ray
Crystallography; Ibers, J. A., Hamilton, W. C., Eds.; Kynoch: Bir-
mingham, England, 1974.
Supporting Information Available: Additional experi-
mental details and preparations of rhenium complexes,20 and
a cif file of crystallographic data. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0492956