Electronic and steric effects on the reductive elimination of diaryl ethers from palladium(II)

Article abstract of DOI:10.1021/om030230x

Arylpalladium aryloxide complexes containing sterically and electronically varied phosphine ligands were prepared, and the rates for reductive elimination of diaryl ethers from these complexes were studied to determine the ligand properties that most strongly accelerate this unusual reaction. Electronic and steric effects were probed by preparing monomeric palladium complexes of the type (L)Pd(Ar)(OAr′), in which L = DPPF (1,1′-bis-diphenylphosphinoferrocene), CF₃-DPPF (1,1′-bis[di(4-(trifluoromethyl)phenyl)phosphino]ferrocene), and D-t-BPF (1,1′-bis(di-tert-butylphosphino)ferrocene) and Ar = electron-deficient and electron-neutral aryl groups. Direct C-O bond-forming reductive elimination to form diaryl ethers in high yield was observed after warming the complexes that contained an electron-deficient aryl group bound to palladium. The rate constant for C-O bond-forming reductive elimination from the CF₃-DPPF-ligand palladium complex was twice that obtained for the analogous DPPF-ligated-complex. Reductive elimination of diaryl ether from the more bulky D-t-BPF complex occurred roughly 100 times faster than from the DPPF complex. Thermolysis of DPPF and CF₃-DPPF complexes containing an electron-neutral aryl group did not form diaryl ether. Thermolysis of (D-t-BPF)Pd(Ph)(OC₆H₄-4-OMe) also did not form diaryl ether and generated the two monophosphines PhP(t-Bu)₂ and FcP(t-Bu)₂ (di-tert-butylphosphinoferrocene). However, heating of a FcP(t-Bu)₂-ligated aryloxide complex containing an electron-neutral, palladium-bound aryl group generated diaryl ether in 10-25% yield. Moreover, heating of this complex in the presence of an excess of P(t-Bu)₃ or Ph₅FcP(t-Bu)₂ or 1 equiv of 2-di-tert-butylphosphino-1,1′-binaphthyl generated diaryl ether in higher, 58-95%, yields. The effect of ligand concentrations on reaction yields implied that exchange of the bulkier ligands with FcP(t-Bu)₂ induced the reductive elimination of diaryl ether.

Full text of DOI:10.1021/om030230x

Organometallics 2003, 22, 2775-2789
2775
Electr on ic a n d Ster ic Effects on th e Red u ctive
Elim in a tion of Dia r yl Eth er s fr om P a lla d iu m (II)
Grace Mann, Quinetta Shelby, Amy H. Roy, and J ohn F. Hartwig*
Department of Chemistry, Yale University, P.O. Box 208107,
New Haven, Connecticut 06520-8107
Received March 27, 2003
Arylpalladium aryloxide complexes containing sterically and electronically varied phos-
phine ligands were prepared, and the rates for reductive elimination of diaryl ethers from
these complexes were studied to determine the ligand properties that most strongly accelerate
this unusual reaction. Electronic and steric effects were probed by preparing monomeric
palladium complexes of the type (L)Pd(Ar)(OAr′), in which L ) DPPF (1,1′-bis-diphenylphos-
phinoferrocene), CF3-DPPF (1,1′-bis[di(4-(trifluoromethyl)phenyl)phosphino]ferrocene), and
D-t-BPF (1,1′-bis(di-tert-butylphosphino)ferrocene) and Ar ) electron-deficient and electron-
neutral aryl groups. Direct C-O bond-forming reductive elimination to form diaryl ethers
in high yield was observed after warming the complexes that contained an electron-deficient
aryl group bound to palladium. The rate constant for C-O bond-forming reductive elimination
from the CF3-DPPF-ligated palladium complex was twice that obtained for the analogous
DPPF-ligated complex. Reductive elimination of diaryl ether from the more bulky D-t-BPF
complex occurred roughly 100 times faster than from the DPPF complex. Thermolysis of
DPPF and CF3-DPPF complexes containing an electron-neutral aryl group did not form diaryl
ether. Thermolysis of (D-t-BPF)Pd(Ph)(OC6H4-4-OMe) also did not form diaryl ether and
generated the two monophosphines PhP(t-Bu)2 and FcP(t-Bu)2 (di-tert-butylphosphinofer-
rocene). However, heating of a FcP(t-Bu)2-ligated aryloxide complex containing an electron-
neutral, palladium-bound aryl group generated diaryl ether in 10-25% yield. Moreover,
heating of this complex in the presence of an excess of P(t-Bu)3 or Ph5FcP(t-Bu)2 or 1 equiv
of 2-di-tert-butylphosphino-1,1′-binaphthyl generated diaryl ether in higher, 58-95%, yields.
The effect of ligand concentrations on reaction yields implied that exchange of the bulkier
ligands with FcP(t-Bu)2 induced the reductive elimination of diaryl ether.
In tr od u ction
thetic method. The reductive elimination of aryl sul-
fides,31-33 arylamines,33-40 and aryl ethers9,33,41-43 is the
product-forming step of these catalytic processes, as
Palladium-mediated cross-coupling that forms an
aromatic carbon-heteroatom bond in amines,1-8 eth-
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* Corresponding author. E-mail: john.hartwig@yale.edu.
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10.1021/om030230x CCC: $25.00 © 2003 American Chemical Society
Publication on Web 05/29/2003

2776 Organometallics, Vol. 22, No. 13, 2003
Mann et al.
by theory;62 it has also been observed by experiment,
but the observed effect has been difficult to interpret
and the magnitude of the effect difficult to measure
when equilibria precede reductive elimination.63 For two
complexes with similar steric properties, the opposite
reaction, oxidative addition, is clearly faster to the com-
plex with the more electron-donating ancillary ligands.64
Because reductive elimination relieves steric hin-
drance, one might expect that a complex with similarly
electron-donating, but sterically more demanding, ancil-
lary ligands would undergo reductive elimination faster
than a complex with less sterically demanding ligands.
Indeed, studies on the rate of reductive elimination of
arene from arylrhodium hydrides65 showed that com-
plexes ligated by tert-butyldimethylphosphine elimi-
nated arene faster than those containing n-butyldi-
methylphosphine. However, the magnitude of this steric
effect on rate was small. Other pertinent studies have
involved simultaneous variation of steric and electronic
properties.66 The effect of sterically hindered ligands on
the rate of stoichiometric carbon-heteroatom bond-form-
ing reductive eliminations is not well documented, but
recent catalytic formation of diaryl ethers suggests that
steric hindrance may promote reductive elimination.10,15,21
The number of donor atoms in a ligand or the number
of coordinated monodentate ligands can also influence
the rate of reductive elimination. Yamamoto62 and
Stille67 showed that reductive elimination to form C-C
bonds occurs from complexes containing bisphosphines
and monophosphines, but that reductive elimination
from three-coordinate monophosphine complexes occurs
Sch em e 1
shown for formation of ethers in Scheme 1. As a result,
fundamental studies have been conducted on these
unusual elementary reactions. These investigations
have shown that increasing electron density on the het-
eroatom and decreasing electron density on the pal-
ladium-bound aryl group leads to increasing reaction
rates.32,34,41 Because alkoxide ligands are less electron-
donating than amide or thiolate ligands, the formation
of aryl ethers by reductive elimination is especially
challenging.
Thus, the palladium-catalyzed formation of eth-
ers10,11,13-15,17-21 occurs in a less general fashion than
the formation of arylamines, and the palladium-
catalyzed formation of diaryl ethers has been particu-
larly challenging.10,11,15,21 Diaryl ethers are substruc-
tures found in many natural products with potential
biological activity. The formation of the diaryl ether unit
is often one of the most difficult steps in the synthesis
of these materials. Thus, new methods for the construc-
tion of diaryl ethers have been actively pursued.16,44-59
On a more fundamental level, the reductive elimination
to form the C-O bond in ethers is an elementary
reaction that has been limited to special cases or to
examples that form ether in low yields.1,9,41-43,60 Thus,
we sought to define the steric and electronic properties
of a phosphine ligand that would create large enough
rate accelerations to observe reductive elimination of
diaryl ethers in a general fashion.
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Reductive Elimination of Diaryl Ethers from Pd(II)
Organometallics, Vol. 22, No. 13, 2003 2777
Sch em e 2
{Pd[P(o-tolyl)3](C6H4-2-Me)(µ-Br)}2. Addition of FcP-
(i-Pr)2 to the dimeric {Pd[P(o-tolyl)3](C6H4-2-Me)(µ-Br)}2
formed the monomeric Pd bromide complex Pd[FcP-
(i-Pr)2]2(C6H4-2-Me)(Br), 4.
The 31P NMR spectra of 2a deserve comment. The 31
P
NMR spectrum of 2a in benzene-d6 contained two
doublets at δ 37.5 and 46.8, which are consistent with
a simple square-planar, cis geometry. The 31P NMR
spectrum of 2a in THF-d8, however, consisted of two
doublets (δ 38.5 and 48.4) and a singlet (δ 22.3). No
signal near that of free D-t-BPF was observed, and the
singlet was not that of the potential decomposition
product Pd(D-t-BPF)n (δ 55.9). Furthermore, the 31P
NMR spectrum of a solution of 2a in CDCl3 displayed
one singlet at δ 21.6. The species that displayed two
doublet resonances was regenerated from this complex
by evaporation of CDCl3 under vacuum and dissolution
of the solid in benzene-d6. Thus, complex 2 displays a
solvent-dependent equilibrium between two arylpalla-
dium complexes.71
The second isomer clearly resulted from dissociation
of halide in the more polar solvent. Conductivity mea-
surements on 1.0 mM solutions of 2a , NBu4Br, and
(PPh3)2Pd[C6H3-2-Me-5-(t-Bu)](Br) in dry, degassed ni-
tromethane gave molar conductances of 70.3, 74.5, and
6.8 Ω-1 cm2 mol-1, respectively. These values are con-
sistent with literature values for 1 mM solutions of 1:1
electrolytes in nitromethane.71 Moreover, the same 31P
NMR resonance was obtained after addition of AgBF4
to 2a in THF. Three-coordinate d8 complexes are com-
monly T-shaped;62,72-76 however, this complex adopts a
square-planar structure with a Pd-Fe interaction. The
structures of the two species in equilibrium are depicted
in eq 1. A related cationic D-t-BPF complex containing
faster than it does from four-coordinate bisphosphine
complexes. The authors’ laboratory has shown that
reductive elimination of amines from arylpalladium
amido complexes occurs from both three-coordinate
monophosphine and four-coordinate bisphosphine com-
plexes and that the elementary step of reductive elimi-
nation is faster from the three-coordinate species.34
Thus, sterically hindered ligands may also promote the
formation of monophosphine three-coordinate complexes
that undergo reductive elimination of diaryl ether faster
than four-coordinate, bisphosphine complexes.
Because catalytic processes are multistep and often
involve changes in catalyst composition and reaction
medium, it is difficult to assess how a single step of a
catalytic process is affected by perturbations of the
catalyst structure. In particular, studies on the overall
catalytic process do not reveal the effect of a structural
perturbation on the portion of a catalytic cycle that
occurs after the turnover-limiting step. To define quan-
titatively the relative effects of ligand steric and elec-
tronic properties on the rates of reductive elimination
of diaryl ethers, we report the thermal chemistry of
isolated arylpalladium aryloxide complexes. Our results
demonstrate that alterations in ligand steric hindrance
and number of donor atoms have a more pronounced
effect on reaction rate than do readily accessible changes
in phosphine electronic properties.
a palladium-bound methyl group and a related cationic
bis-diphenylphosphino omoscene complex have been
reported recently.77,78 The BF4 analogue of 2c was
isolated in pure form after addition of AgBF4 to 2a and
recrystallization from THF.
Resu lts
2. Mon om er ic P a lla d iu m Ar yloxid e Com p lexes
Con ta in in g F er r ocen yl Bisp h osp h in es. The synthe-
A. Syn th esis of Ar ylp a lla d iu m Ha lid e a n d Ar yl-
p a lla d iu m Ar yloxid e Com p lexes. 1. Ar ylp a lla d iu m
Br om id e Com p lexes. The synthesis of arylpalladium
bromide complexes used in this study is shown in
Scheme 2. Complexes of the structure (D-t-BPF)Pd(Ar)-
(Br) (2a , Ar ) C6H4-4-CN; 2b, Ar ) Ph) were obtained
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from the addition of D-t-BPF to a solution of the
68-70
appropriate {Pd[P(o-tolyl)3](Ar)(Br)}2
compound.
The dimeric palladium bromide complex {Pd[FcP-
(t-Bu)2](C6H4-2-Me)(µ-Br)}2 (3) was isolated in pure form
in 31% yield after reaction of FcP(t-Bu)2 (1a ) with
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tallics 1996, 15, 2745-2754.

2778 Organometallics, Vol. 22, No. 13, 2003
Mann et al.
Sch em e 3
Sch em e 5
Sch em e 4
The arylpalladium aryloxide complex (D-t-BPF)Pd(Ph)-
(OC6H4-4-OMe) (10) was isolated in analytically pure
form in 32% yield after reaction of (D-t-BPF)Pd(Ph)(Br)
with the sodium aryloxide in THF solvent.
3. Ar ylp a lla d iu m Ar yloxid e Com p lexes Con ta in -
in g F er r ocen yl Mon op h osp h in es. Dimeric arylpal-
ladium aryloxide complexes {Pd[FcP(t-Bu)2](Ar)(µ-OC6H4-
4-R)}2 (11a , Ar ) C6H4-2-Me, R ) OMe; 11b, Ar ) C6H4-
4-Me, R ) OMe; 11c, Ar ) C6H3-2,4-Me2, R ) O-n-Bu)
were synthesized as shown in Scheme 5. Addition of
sodium aryloxide to the arylpalladium bromide com-
plexes (3a -c) containing ligand 1a , which were formed
in situ by phosphine exchange in THF solvent, formed
the desired aryloxide complexes. Monomeric Pd[FcP-
(i-Pr)2]2(C6H4-2-Me)(OC6H4-4-OMe) (12) was isolated in
43% yield by reaction of [FcP(i-Pr)2]2Pd(Ar)(Br) (4) with
CsOH‚H2O, which gave Pd[FcP(i-Pr)2]2(C6H4-2-Me)(OH)
as a mixture of cis and trans isomers, followed by
addition of p-methoxyphenol.
sis of palladium aryloxide complexes (L)Pd(C6H4-4-CN)-
(OAr), in which L ) DPPF (Ar ) OC6H4-4-OMe, 5a ; Ar
) OC6H4-4-O-n-Bu, 5b; Ar ) OC6H3-3,5-(t-Bu)2, 5c),
CF3-DPPF (Ar ) OC6H4-4-OMe, 6a ; Ar ) OC6H3-3,5-
(t-Bu)2, 6b) or D-t-BPF (Ar ) OC6H6-4-OMe, 7a ; Ar )
OC6H3-3,5-(t-Bu)2, 7b) is summarized in Scheme 3.
Addition of KOAr to a THF solution of (L)Pd(C6H4-4-
CN)(Br) or addition of NaOAr to a THF solution of (L)-
Pd(C6H4-4-CN)(OC6H4-4-CN) formed complexes 5a -6b.
Analytically pure yellow solids were isolated in 56-83%
yields. D-t-BPF-ligated palladium bromide 2a reacted
with NaOC6H4-4-OMe or KOC6H3-3,5-t-Bu2 to give
palladium aryloxide complexes (D-t-BPF)Pd(C6H4-4-
CN)(OC6H4-4-OMe), 7a , and (D-t-BPF)Pd(C6H4-4-CN)-
(OC6H3-3,5-t-Bu2), 7b. The 31P NMR spectra of both 7a
and 7b were, again, unusual. The spectrum in benzene-
d6 contained the expected two doublets (δ 42.1 and 55.4
for 7a ; δ 42.1 and 55.6 for 7b) but the 31P NMR
spectrum of each compound in THF-d8 contained one
singlet near δ 21.8, in addition to the expected two
doublets. Thus, the arylpalladium phenoxide complex
generates the same cationic palladium species, this time
by dissociation of a phenoxide counterion. Consistent
with this assertion, the 31P NMR signal assigned to the
cations generated from 2a , 7a , and 7b are nearly
identical in THF solvent. Nevertheless, the reductive
elimination chemistry of this complex presented below
occurred in the highest yields in nonpolar solvents such
as toluene and THF, in which the compound adopts
predominantly a monomeric square-planar structure,
although a distorted one (vide infra).
4. Syn t h esis of Nick el Ca r b on yl Com p lexes of
th e F er r ocen yl Liga n d s. Nickel carbonyl complexes
containing the ferrocenyl ligands were prepared to allow
comparison of the electronic properties of these lig-
ands to those of ligands on Tolman’s classic scale.80
These complexes were prepared by addition of ligand
to Ni(CO)4 at room temperature. (Caution: Nickel car-
bonyl is highly toxic. It was handled under vacuum on
a Schlenk line in a well-ventilated hood.) The νCO values
for L2Ni(CO)2 complexes in which L2 ) DPPF were 1999
and 1940 cm-1, and the νCO values for L2Ni(CO)2 in
which L2 ) 4-CF3-DPPF were 2010 and 1950 cm-1 81
.
The difference between these νCO values is similar to
the difference in νCO values between complexes of triaryl
and trialkylphosphines, but one should realize this dif-
ference in νCO results from the effect of two phosphine
donor atoms.80 The L2Ni(CO)2 complex with L2 ) DtBPF
did not form, but the binuclear complex {[(CO)3Ni]2-
(D-t-BPF)} with one Ni(CO)3 unit bound to each of
the two phosphorus was isolated. This complex showed
an A1 νCO value of 2055 cm-1, which is nearly identi-
cal to the value of 2056 cm-1 for {(CO)3Ni[P(t-Bu)3]}.80
{Ni(CO)3[FcP(t-Bu)2]} was also prepared, and the A1 νCO
value was an identical 2055 cm-1. Clearly, D-t-BPF and
1a are strongly electron-donating ligands. One might
imagine that the large phosphine substituents of D-t-
BPF and 1a would lengthen the Pd-P bond distance,
but Tolman showed long ago that the A1 νCO value for
LNi(CO)3 is lower when L ) P(t-Bu)3 than when L )
PMe3.82
Palladium aryloxide complexes with an electron-
neutral palladium-bound aryl group were synthesized
as shown in Scheme 4. Addition of DPPF or CF3-DPPF
to a toluene or benzene solution of [(PPh3)Pd(Ph)(µ-
OAr)]2 (Ar ) C6H4OMe, C6H3-3,5-t-Bu), which was
79
formed in situ by protonation of [(PPh3)Pd(Ph)(µ-OH)]2
(79) Grushin, V. V.; Kuznetsov, V. F.; Bensimon, C.; Alper, H.
Organometallics 1995, 14, 3927-3932.
(80) Tolman, C. A. Chem. Rev. 1977, 77, 313-348.
(81) Hamann, B.; Hartwig, J . F. J . Am. Chem. Soc. 1998, 120, 3694-
3703.
with 4-methoxyphenol or 3,5-di-tert-butylphenol, pro-
duced the DPPF and CF3-DPPF arylpalladium arylox-
ides 8a ,b and 9 in 67%, 66%, and 55% isolated yield.

Reductive Elimination of Diaryl Ethers from Pd(II)
Organometallics, Vol. 22, No. 13, 2003 2779
F igu r e 1. ORTEP drawing of (D-t-BPF)Pd(Br)(C6H4-4-CN)
(2a ). Hydrogen atoms and solvent molecule are omitted for
clarity. Thermal ellipsoids are drawn at 30% probability.
F igu r e 2. ORTEP drawing of the cationic portion of [(D-
t-BPF)Pd(C6H4-4-CN)](BF4) (2c). Hydrogen atoms and
solvent molecule are omitted for clarity. Thermal ellipsoids
are drawn at 30% probability.
Ta ble 1. Selected In tr a m olecu la r Bon d Dista n ces
a n d An gles In volvin g th e Non -Hyd r ogen Atom s of
(D-t-BP F )P d (Br )(C6H4-4-CN) (2a )
Bond Distances (Å)
Ta ble 2. Selected In tr a m olecu la r Bon d Dista n ces
a n d An gles In volvin g th e Non -Hyd r ogen Atom s of
[(D-t-BP F )P d (C6H4-4-CN)](BF 4) (2c)
Pd(1)-Br(1)
Pd(1)-P(2)
2.4934(7)
2.492(1)
Pd(1)-P(1)
Pd(1)-C(1)
2.345(1)
2.033(5)
Bond Angles (deg)
Bond Distances (Å)
Br(1)-Pd(1)-P(1) 151.59(4) Br(1)-Pd(1)-P(2)
92.30(4)
104.28(5)
153.3(1)
Pd(1)-P(1)
Pd(1)-Fe(1)
2.3103(12)
2.9988(8)
Pd(1)-P(2)
Pd(1)-C(27)
2.3065(12)
2.001(4)
Br(1)-Pd(1)-C(1)
P(1)-Pd(1)-C(1)
82.2(1)
92.1(1)
P(1)-Pd(1)-P(2)
P(2)-Pd(1)-C(1)
Bond Angles (deg)
80.31(4) Fe(1)-Pd(1)-P(2)
angle between the planes: [P(1)-Pd(1)-P(2)]
and [Br(1)-Pd(1)-C(1)]
35.2
Fe(1)-Pd(1)-P(1)
79.44(4)
159.75(4)
Fe(1)-Pd(1)-C(27) 177.67(12) P(1)-Pd(1)-P(2)
P(1)-Pd(1)-C(27) 100.87(12) P(2)-Pd(1)-C(27) 99.37(12)
5. X-r a y Str u ctu r es of D-t-BP F a n d F cP (t-Bu )2
P a lla d iu m Com p lexes. X-ray structures were ob-
tained of D-t-BPF-ligated bromide 2a , 2c, and 7a and
FcP(t-Bu)2-ligated phenoxide 11b. The structure of
palladium bromide complex 2a is shown in Figure 1.
Crystal data for each structure are included in the
Supporting Information, and selected bond distances
and angles for 2a are provided in Table 1. The geometry
about the metal center is a highly distorted square plane
in which the P1-Pd1-P2 bond angle is a large 104.28-
(5)° and the Br1-Pd1-C1 bond angle a small 82.2(1)°.
The dihedral angle between P1-Pd1-P2 and Br1-
Pd1-C1 planes is 35.20°; this angle shows a large
distortion toward a tetrahedron from an ideal square-
planar geometry in which this angle would be 0°. This
distortion was also shown by the large sum of the four
angles about the Pd center, 370.9°. The Pd1-P1 and
Pd1-P2 bond distances were 2.345(1) and 2.492(1) Å.
The Pd1-P2 bond is one of the longest Pd-P bond
lengths reported.83
The structure of complex 2c, which resulted from
halide dissociation from 2a , is shown in Figure 2.
Selected bond distances and angles for 2c are provided
in Table 2. The formation of a dative Pd-Fe bond
creates a distorted square-planar geometry around Pd
with a P1-Pd1-P2 bond angle of 159.75(4)°. This angle
is slightly larger than the 158.21(2)° P-Pd-P angle in
the analogous cationic palladium methyl complex77 or
the 155.9(1)° angle in a similar dicationic palladium
containing PPh3 instead of the phenyl at palladium.84
The Pd-Fe distance of 2.999(8) Å is significantly shorter
than the 4.4 Å Pd-Fe distance in complex 2a , which
contains no interaction between Fe and the Pd center.
It is also slightly shorter than the 3.0683 Å Pd-Fe
distance in the analogous cationic methyl77 and slightly
longer than the 2.877(2) Å distance in the PPh3-li-
gated dication. To accommodate this short distance, the
Cp(centroid)-Fe-Cp(centroid) angle is only 166.2°.
These P1-Pd-P2 angles, Fe-Pd bond lengths, and Cp
ring distortions are similar to those in related complexes
of metallocenyl phosphine and thiolate ligands with
M-Pd interactions.78,85
The structure of phenoxide 7a is shown in Fig-
ure 3. Selected bond distances and angles are col-
lected in Table 3. This complex displays distortions
similar to those found in the bromide complex 2a .
The P1-Pd1-P2 and O1-Pd1-C1 bond angles were
104.93(3)° and 85.99(10)°. The dihedral angle between
the P1-Pd1-P2 and O1-Pd1-C1 planes was a large
23.92°, and the sum of angles at the Pd center was
365.3°. Again, the Pd-P bond trans to the aryl group
(Pd1-P1, 2.4819(7) Å) was significantly longer than the
other Pd-P bond (Pd1-P2, 2.3051(8) Å).
An ORTEP diagram of 11b is shown in Figure 4.
Selected bond distances and angles are provided in
Table 4. The sum of the four angles about the palladium
(84) Sato, M.; Shigeta, H.; Sekino, M. J . Organomet. Chem. 1993,
458, 199-204.
(85) Seyferth, D.; Hames, B. W.; Rucker, T. G.; Cowie, M.; Dickson,
R. S. Organometallics 1983, 2, 472-474.
(82) Tolman, C. A. J . Am. Chem. Soc. 1970, 92, 2953-2956.
(83) Woo, T. K.; Pioda, G.; Rothlisberger, U.; Togni, A. Organome-
tallics 2000, 19, 2144-2152.

2780 Organometallics, Vol. 22, No. 13, 2003
Mann et al.
atoms.86 The C(ipso)-Pd-O angle was 88.8°, but the
P-Pd-O bond angle was a much larger 102.9°. The
Pd-P distance in 11b was 2.279(3) Å, which is simi-
lar to the 2.288(3) Å distance in analogous dimeric
P(o-tolyl)3-ligated aryl halide complexes68 and to the
2.30-2.32 Å Pd-P distances in typical four-coordinate,
PPh3-ligated Pd(II) complexes.87
B. Ca r bon -Oxygen Bon d -F or m in g Red u ctive
Elim in a tion of Dia r yl Eth er s. 1. Rea ction s of Mon -
om er ic Ar ylp a lla d iu m Ar yloxid e Com p lexes Con -
ta in in g Bisp h osp h in es. Thermolysis of complexes
5a -7b, which contain bidentate phosphines and an
electron-poor aryl group bound to the palladium, and
thermolysis of 8-10, which contain a phenyl group
bound to palladium, were conducted in the presence of
dative ligands, such as PPh3, PhCCPh, D-t-BPF, or
DPPF, to bind the Pd(0) product. The only metal
products observed at the end of all of the thermal
reactions were homoleptic Pd(0) phosphine complexes
or Pd(0) complexes ligated by phosphine and alkyne. In
all cases, reactions of 5a ,c and 6a ,b led to the reductive
elimination of diaryl ethers and the formation of Pd(0)
complexes in good yield (eq 2). Reactions of DPPF-
F igu r e 3. ORTEP drawing of (D-t-BPF)Pd(OC6H4-4-OMe)-
(C6H4-4-CN) (7a ). Hydrogen atoms and solvent molecule
are omitted for clarity. Thermal ellipsoids are drawn at
30% probability.
Ta ble 3. Selected In tr a m olecu la r Bon d Dista n ces
a n d An gles In volvin g th e Non -Hyd r ogen Atom s of
(D-t-BP F )P d (OC6H4-4-OMe)(C6H4-4-CN) (7a )
Bond Distances (Å)
Pd(1)-P(1)
Pd(1)-O(1)
2.4819(7)
2.077(2)
Pd(1)-P(2)
Pd(1)-C(1)
2.3051(8)
2.028(3)
Bond Angles (deg)
P(1)-Pd(1)-P(2)
P(1)-Pd(1)-O(1)
104.93(3) P(2)-Pd(1)-O(1) 163.78(6)
81.00(6)
P(2)-Pd(1)-C(1)
93.36(8)
P(1)-Pd(1)-C(1) 155.24(8) O(1)-Pd(1)-C(1)
85.99(10)
angle between the planes [P(1)-Pd(1)-P(2)]
and [C(1)-Pd(1)-O(1)]
23.92
ligated palladium complex 5a conducted at 110 °C for
5 h in the presence of 2 equiv of added PPh3 formed
diaryl ether in greater than 90% yield, and the same
reaction conducted in the presence of 1-2 equiv of DPPF
formed diaryl ether in 83% yield. CF3-DPPF complexes
6a and 6b reductively eliminated diaryl ether at 110
°C after 5 h in 95% and 62% yield, respectively, in the
presence of 2-3 equiv of PPh3. Reactions in the presence
of PhCCPh and CF3-DPPF formed diaryl ether in
similar yields. Reductive elimination from DPPF-ligated
5a at the lower temperature of 50 °C occurred with a
half-life greater than 60 h.
Reductive elimination of diaryl ether from D-t-BPF-
ligated 7a ,b containing an electron-poor aryl group
bound to the metal (eq 3) occurred at rates that were
F igu r e 4. ORTEP drawing of {Pd[P(C5H4FeC5H5)(t-Bu)2]-
(C6H4-4-Me)(OC6H4-4-OMe)}2 (11b). Hydrogen atoms and
solvent molecule are omitted for clarity. Thermal ellipsoids
are drawn at 50% probability.
Ta ble 4. Selected In tr a m olecu la r Bon d Dista n ces
a n d An gles of {P d [P (C5H4F eC5H5)(t-Bu )2]-
(C6H4-2-Me)(OC6H4-4-OMe)}2 (11b)
Bond Distances (Å)
Pd(1)-P(1)
Pd(1)-O(1)
2.279(3)
2.189(6)
Pd(1)-O(1*)
Pd(1)-C(1)
2.121(6)
1.966(9)
Bond Angles (deg)
faster than those for reductive elimination from its
DPPF analogues. Palladium complexes 7a and 7b were
consumed after 1 h at 50 °C and gave ether in 45% and
57% yield in the presence of 4 equiv of D-t-BPF to
coordinate the Pd(0) product. Thermolysis of 5a -7b in
P(1)-Pd(1)-O(1)
P(1)-Pd(1)-C(1)
O(1)-Pd(1)-C(1)
167.6(2)
93.4(3)
88.8(3)
P(1)-Pd(1)-O(1*)
O(1)-Pd(1)-O(1*)
O(1*)-Pd(1)-C(1)
102.9(2)
76.6(3)
162.8(3)
center was 361.7°, demonstrating the near planarity at
the metal. The Pd-O-Pd-O torsion angle was 33.2°,
and this angle indicates that the central Pd and bridging
oxygen atoms adopt the puckered geometry that is
common for dimeric complexes with bridging hetero-
(86) Aullon, G.; Ujaque, G.; Lledos, A. Inorg. Chem. 1998, 37, 804-
813.
(87) Pierpont, C. G.; Downs, H. H. Inorg. Chem. 1975, 14, 343-
347.

Reductive Elimination of Diaryl Ethers from Pd(II)
Organometallics, Vol. 22, No. 13, 2003 2781
the presence or absence of excess sodium aryloxide
occurred in a similar fashion. Sodium alkoxides had
been suggested to accelerate the formation of alkyl
ethers in previous studies.42
In contrast to these reactions, heating of DPPF and
CF3-DPPF complexes 8a,b and 9, containing an electron-
neutral Pd-bound aryl group, did not produce detectable
amounts of diaryl ether in the presence or absence of a
trap or sodium aryloxide (eq 4). Though quantitative
the generation of the pentaphenylferrocenylphosphine,
which generates catalysts that are active for the forma-
tion of biaryl ethers.21
2. Red u ctive Elim in a tion of Dia r yl Eth er s fr om
P alladiu m Ar yloxide Com plexes Con tain in g Mon o-
p h osp h in es. Thermolysis of FcP(t-Bu)2-ligated arylpal-
ladium aryloxide 11a , which contains an electron-
neutral aryl group, at 70 °C in the presence or absence
of sodium aryloxide, aryl bromide, or ligand 1a gave
diaryl ether in 5-25% yields (eq 6) and Pd[FcP-
rate data on the reactions of 8a ,b and 9 were not
obtained because of the absence of ether product, the
rate of decomposition of these species was similar to the
rate of elimination from 5a -7b. Half-lives for decay of
8b at 100 °C in the presence of 2 equiv of PPh3 or DPPF
were within a factor of 2 of the half-lives for decay of
5c, which contained an electron-poor palladium-bound
aryl group. Complex 8b reacted slightly slower in most
experiments. Thus, the absence of product formed from
complexes with unactivated aryl groups is due partly
to slower reductive elimination and partly to a faster
mode for decomposition other than reductive elimina-
tion. We considered that the similar rate was due to
rate-limiting dissociation of phenoxide as occurs from
10 in polar solvents. Consistent with this hypothesis,
complexes 8b and 5c reacted faster in polar solvents
such as DMF and NMP. However, thermolyses in this
medium formed arene, biaryl compounds, and phenol,
but no ether. Thus, competing decomposition could occur
by dissociation of phenoxide, but diaryl ether does not
appear to form by this path.
(t-Bu)2]2.10 Addition of sodium aryloxide to dimeric
bromide complex 3, followed by heating at 80 °C for 1
h, gave diaryl ether in a similar 22% yield. Thus, dimeric
11a does generate some diaryl ether by reductive
elimination, but this complex is not a true intermediate
in the catalytic process. FcP(t-Bu)2 undergoes arylation
of the unsubstituted cyclopentadienyl ligand to gene-
rate Ph5FcP(t-Bu)2 (1b), which is present in the true
catalyst.21
Thus, heating of FcP(t-Bu)2-ligated 11a in the pres-
ence of 40 equiv of pentaphenylferrocenyl 1b gave diaryl
ether in a higher 66% yield. This result demonstrates
the high reactivity of a complex containing ferrocene
ligand 1b, relative to that containing only 1a , and
further substantiates the intermediacy of arylpalladium
phenoxides ligated by 1b as intermediates in the
recently reported catalytic process. The two homoleptic
and one mixed-ligand palladium(0) complexes were the
metal products. These complexes were prepared inde-
pendently by addition of the two ligands together to
CpPd(allyl) or Pd[P(o-tolyl)3]2, or by mixing of the two
homoleptic Pd(0) complexes containing these ligands.
Reaction of 11b at 40 °C in the presence of 1 equiv of
2-(di-tert-butylphosphino)-1,1′-binaphthyl (1c), which is
a ligand present on catalysts for the formation of diaryl
ethers,15 formed the diaryl ether in 58% yield. Reaction
in the presence of a large excess of 1c (20 equiv),
however, formed the diaryl ether in only 10% yield.
These reactions formed {Pd[FcP(t-Bu)2]2} as the exclu-
sive phosphine-ligated Pd(0) product, along with pal-
ladium black. Thus, ligand 1c is not consumed during
this reaction and acts as a catalyst to induce the
reductive elimination from 11a . The highest yield of
diaryl ether occurred upon warming of o-tolyl complex
11a at 70 °C in the presence of 10 equiv of P(t-Bu)3.
This reaction gave diaryl ether and Pd[P(t-Bu)3]2 in 95%
yield (eq 6). Clearly, the equilibrium for ligand exchange
and the rate of reductive elimination from the resulting
species both influence the yields of reductive elimination
from 11a in the presence of the added ligand.
Even though complexes generated from palladium
precursors of D-t-BPF catalyzed the formation of diaryl
ethers from electron-neutral aryl halides in 40-50%
yield, thermolysis at 110 °C of D-t-BPF complex 10,
which contains an electron-neutral aryl group, produced
no detectable diaryl ether (eq 5). These conditions
consumed 10 completely. Addition of various species
that would be present in the catalytic system (D-t-BPF,
sodium aryloxide, NaBr, aryl halide, DBA), as well as
the addition of PhCCPh or PPh3 to coordinate the
Pd(0) product, had no effect on this reaction. Careful
analysis of all reaction products by GC/MS showed the
formation of aryl alcohol, biaryls, and the monophos-
phines PhP(t-Bu)2 and FcP(t-Bu)2 (1a ) (eq 5). These two
phosphines did not form in detectable amounts during
the high-yield reductive elimination of diaryl ether from
complexes 7a ,b, which contain electron-poor, palladium-
bound aryl groups. However, formation of the ferroce-
nylphosphine from D-t-BPF was the first step toward
In contrast to the high yields of ether formed from
heating of o-tolyl complex 11a in the presence of
P(t-Bu)3, heating of p-tolyl complex 11b formed diaryl
ether in only 25% yield in the presence of P(t-Bu)3.
Moreover heating of 11b in the presence of excess 1a

2782 Organometallics, Vol. 22, No. 13, 2003
Mann et al.
Ta ble 5. Effect of Liga n d Con cen tr a tion on Yield
of Red u ctive Elim in a tion of Dia r yl Eth er fr om
11a a
or 1b did not form ether. Thermolysis of monomeric,
FcP(i-Pr)2-ligated 12 formed Pd[FcP(i-Pr)2]2, but gen-
erated free 4-methoxyphenol as only the product from
the aryloxo group (eq 7). The Pd(0) product was pre-
pared independently by the reaction of FcP(i-Pr)2 with
Cp(allyl)Pd.
[1a ]b
[P(tBu)3]b
[1b]b
[1c]b
yield (%)
15.0
15.0
15.0
95
71
22
74
64
33
58
27
0
0.15
15.
6.7
6.8
7.1
0.070
3.6
0.65
0.65
29.0
0.070
a
b
[11a ] ) 7.0 × 10-3 M. M × 102.
C. Mech a n istic Stu d ies of th e F or m a tion of Di-
a r yl Eth er s. 1. Red u ctive Elim in a tion fr om Mon -
om er ic, Bis-p h osp h in e-Liga ted P a lla d iu m Ar ylox-
id es. The rates of reductive elimination of the high-yield
formation of diaryl ethers from 5c and 6b were mea-
ladium p-methoxyaryloxo complex 11a and 2,4-dimeth-
ylphenylpalladium p-butoxyaryloxo complex 11c was
heated at 75 °C in the presence of 5-7 equiv of added
P(t-Bu)3, 1a , or 1b (eq 8). Each reaction gave all four
1
sured by H NMR spectroscopy in toluene-d8. Kinetic
data were obtained by monitoring the disappearance of
the arylpalladium aryloxo complex in sealed NMR tubes
completely immersed in an oil bath maintained at 105
°C. 1H NMR spectra were obtained periodically at room
temperature.
Reductive elimination from the more electron-poor
CF3-DPPF complex 6b was roughly 2 times faster than
it was from the DPPF complex 5c. Plots of ln[5c] or ln-
[6b] versus time were linear over three half-lives for
reaction in the presence of 4 equiv of diphenylacetylene
and either no added sodium aryloxide or 5 equiv of
added sodium aryloxide. The reductive elimination at
105 °C occurred with a half-life of 7000 s, and the
reaction at 50 °C occurred with a half-life of about 3
days (2.4 × 105 s). In contrast to a previous system,42
the rate constants for reductive elimination from 5c
and 6b at 105 °C in the presence or absence of 5 equiv
of sodium aryloxide were indistinguishable (kobs ) (1.0
( 0.3) × 10-4 s-1 and (1.0 ( 0.3) × 10-4 s-1 for 5c, and
possible diaryl ethers in nearly equal amounts. The
exchange could occur by an associative mechanism or
by a process involving a catalytic amount of phenol, but
these data are at least consistent with reversible
generation of monomeric arylpalladium phenoxide com-
plexes from 11a -c.
Addition of P(t-Bu)3 to 11a appeared to partially
displace ligand 1a , and this equilibrium precluded
simple kinetic studies. Small amounts of free 1a were
observed after addition of P(t-Bu)3. Addition of excess
pentaphenylferrocenyl ligand 1b to 11a did not generate
free ligand 1a . However, reaction of phenoxide 11a in
the presence and absence of excess phosphine 1b at 60
°C occurred at similar rates, even though the yields of
diaryl ether were substantially different.
-4
-4
kobs ) (1.7 ( 0.3) × 10
s-1 versus (2.0 ( 0.3) × 10
s-1 for 6b). The rate constant for reductive elimination
did not depend on the identity or quantity of added
dative ligand and is, therefore, zero order in the reagent
that traps the Pd(0). The rate constants for thermolysis
of DPPF-ligated complex 5c in the presence of 1.6 × 10-2
to 6.7 × 10-2 M DPPF, instead of PhCCPh, were (1.5 (
Thus, we evaluated the yields, instead of rates, for
the formation of diaryl ether in the presence of varying
concentrations of added phosphine, as summarized in
Table 5. The yield of diaryl ether produced from the
reaction between 11a and P(t-Bu)3, 1b, or 1c was
significantly lower in the presence of added FcP(t-Bu)2.
For example, reactions containing a 1:1 ratio of 1a and
P(t-Bu)3 formed diaryl ether in only 22% yield, while
reactions containing a 1:100 ratio of 1a and P(t-Bu)3
formed the ether in 71% yield. Reactions performed with
a 1:1 ratio of 1a and 1b formed diaryl ether in only 30%
yield, while reactions containing a 1:100 ratio formed
diaryl ether in 64% yield.
0.4) × 10-4 s-1
.
D-t-BPF-ligated 7b reacted roughly 2 orders of mag-
nitude faster than the analogous phenylphosphine
complex. Reactions of 7b were first-order in palladium
complex, and the rate constant at 50 °C was (2.8 ( 0.3)
× 10-4 s-1. This rate constant corresponds to a half-life
of 2400 s. Even after considering that the ether is
formed from 7b in only 56% yield, the rate constant for
reaction of 7b indicates that reductive elimination from
this hindered complex occurs at a time scale that is
much shorter than the 2.4 × 105 s half-life for reaction
of the analogous DPPF-ligated complex 5c at the same
temperature.
2. Mech a n ism of Red u ctive Elim in a tion fr om Di-
m er ic, Mon op h osp h in e-Liga t ed P a lla d iu m Ar yl-
oxid es. Mechanistic studies were also conducted on the
high-yield elimination of diaryl ether from 11a in the
presence of added P(t-Bu)3. Crossover experiments were
conducted to probe for reversible cleavage of dimeric 11a
to form monomeric intermediates prior to reductive
elimination. First, a 1:1 mixture of 2-methylphenylpal-
Discu ssion
A. Eva lu a tion of F a ctor s Th a t Con tr ol Red u ctive
Elim in a tion of Dia r yl Eth er . The Pd(II) compounds
described here are the first isolated aryloxide complexes
that undergo reductive elimination of ethers. Organo-
palladium aryloxide complexes have been generated

Reductive Elimination of Diaryl Ethers from Pd(II)
Organometallics, Vol. 22, No. 13, 2003 2783
previously,88-90 but they have not formed ethers. For
example, thermolysis of (Tol-BINAP)Pd(C6H4-4-CN)-
(OC6H4-4-Me) at 60 °C resulted in <5% yield of diaryl
ether,42 and (DMPE)PdMe(OPh) generated products
from phenoxyl radicals, but no ether, after one-electron
oxidation.91 In contrast, thermolysis of arylpalladium
complexes containing the dative ligand DPPF, an elec-
tron-poor palladium-bound aryl group, and the phenox-
ide OC6H4-4-OMe resulted in formation of diaryl ether
in high yield. Thermolysis of the analogous DPPF com-
plexes containing an electron-neutral aryl group bound
to Pd generated biaryl compounds and phenol, but no
ether. These results show that reductive elimination of
diaryl ethers from monomeric arylpalladium aryloxide
complexes with unactivated, Pd-bound aryl groups is a
particularly difficult transformation to observe.
Several possible relationships between ligand proper-
ties and reductive elimination rates and the relative
importance of each perturbation on the rates and yields
for the formation of diaryl ethers were evaluated in the
present study. This work showed that steric hindrance
can dramatically increase the rate of reductive elimina-
tion and that monodentate ligands are so far required
to observe reductive elimination of diaryl ethers from
arylpalladium complexes that lack activating substitu-
ents on the palladium-bound aryl ring.
1. Eva lu a tion of P h osp h in e Liga n d Electr on ic
Effects. Studies to evaluate the importance of phos-
phine electronics on reductive elimination showed that
the CF3-DPPF complex 6a underwent reductive elimi-
nation only 2 times faster than the analogous DPPF
complex 5a . Neither the DPPF- nor CF3-DPPF complex
with a neutral phenyl group bound to the palladium
formed diaryl ether. Thus, conventional electronic ef-
fects on the rate of reductive elimination were observed,
but the magnitude of the rate difference was small. The
difference in electron-donating ability of the two arylphos-
phine ligands in this study certainly does not span the
full range of possible ligand electronic properties, but
modification of aromatic substituents at phosphorus is
unlikely to allow reductive elimination to form diaryl
ether from complexes with unactivated, Pd-bound aryl
groups. Importantly, electron-donating properties of
alkylphosphines should not dramatically retard the rate
for reductive elimination because the difference be-
tween the νCO values in Ni(CO)2 complexes of DPPF and
CF3-DPPF is similar to the difference between the value
for Ni(CO)3L in which L is an arylphosphine and for
Ni(CO)3L in which L is an alkylphosphine.
containing a closely related arylphosphine. The A1 νCO
value of 2055 cm-1 for {[(CO)3Ni]2(D-t-BPF)} showed
that the DtBPF ligand is strongly electron-donating.
Thus, the acceleration of reductive elimination from 7b
due to steric effects clearly exceeds any decelerating
effect due to the strong electron-donating ability of the
ligand.
The importance of steric effects on reductive elimina-
tion of diaryl ether from complexes of monophosphines
was clearly demonstrated by observing reductive elimi-
nation of diaryl ether from FcP(t-Bu)2-ligated complexes,
but no reductive elimination from FcP(i-Pr)2-ligated
complexes. FcP(t-Bu)2 and FcP(i-Pr)2 have similar elec-
tronic properties, but the latter ligand is, of course, less
sterically demanding. The effect of steric hindrance was
also shown by the increased yields of diaryl ether formed
from reaction of FcP(t-Bu)2-ligated 11a after addition
of the more hindered P(t-Bu)3, (Ph5Fc)P(t-Bu)2, or 2-di-
tert-butylphosphino-1,1′-binaphthyl.
3. Effect of Coor d in a tion Nu m ber : Red u ctive
Elim in a tion fr om P h en oxo Com p lexes Con ta in in g
Ster ica lly Hin d er ed Mon op h osp h in es. Previous ki-
netic studies on C-N and C-C bond-forming reductive
elimination have shown that reductive elimination
occurs faster from three-coordinate palladium species
than from four-coordinate species.34,62,67 However, re-
ductive elimination of aryl ethers did not occur from
complexes containing standard monophosphines. Dur-
ing unpublished exploratory studies we found that
thermolysis of the products from addition of alkali
aryloxides to P(o-tolyl)3-ligated arylpalladium halides92
and heating of known triphenylphosphine-ligated pal-
ladium aryloxides produced no ether.89,91 In contrast,
complexes in this study containing particularly hindered
alkylmonophosphines underwent reductive elimination
of diaryl ethers, even when the complex contained
electron-neutral, palladium-bound aryl groups. Thus,
the combination of phosphine steric hindrance and the
generation of three-coordinate complexes allows the
formation of diaryl ethers by C-O bond-forming reduc-
tive elimination.
B. Mech a n ism of th e Red u ctive Elim in a tion of
Dia r yl Eth er . 1. Red u ctive Elim in a tion fr om D-t-
BP F -Liga ted Com p lexes. Kinetic data ruled out a
reductive elimination that is induced by the added
dative ligand and implied that a simple intramolecular
reductive elimination occurs directly from the starting
arylpalladium phenoxide. Reductive elimination of dia-
ryl ether from the D-t-BPF-ligated arylpalladium phe-
noxides 5-7 was first-order in the palladium complex
and zero-order in added ligands. The demanding steric
properties of 7 could lead to partial dissociation of the
chelating ligand. Our kinetic data cannot distinguish
between direct elimination and elimination after dis-
sociation of one phosphorus donor in the coordinated
D-t-BPF. However, dissociation of one phosphorus of
D-t-BPF from D-t-BPF-ligated 10 bearing an electron-
neutral palladium-bound aryl group would generate
nearly the same intermediate that is, presumably,
generated during reaction of dimeric 11a containing the
ferrocenylmonophosphine 1a . Because 11a forms some
diaryl ether but thermolysis of 10 does not, we disfavor
reaction of D-t-BPF-ligated 7 after opening of the
2. Eva lu a tion of Ster ic Effects. In contrast to these
small differences in rate resulting from changes in
electronic properties, large differences in rate were
observed from changes in ligand steric properties. In
particular, thermolysis of D-t-BPF-ligated cyanophenyl
aryloxide 7b formed diaryl ether with a rate that was
two or more orders of magnitude faster than that for
reductive elimination from analogous Pd complexes
(88) Seligson, A. L.; Cowan, R. L.; Trogler, W. C. Inorg. Chem. 1991,
30, 3371-3381.
(89) Kim, Y.-J .; Osakada, K.; Takenada, A.; Yamamoto, A. J . Am.
Chem. Soc. 1990, 112, 1096-1104.
(90) Alsters, P. L.; Baesjou, P. J .; J anssen, M. D.; Kooijman, H.;
Sicherer-Roetman, A.; Spek, A. L.; van Koten, G. Organometallics 1992,
11, 4124-4135.
(91) Seligson, A. L.; Trogler, W. C. J . Am. Chem. Soc. 1992, 114,
7085-7089.
(92) Mann, G.; Hartwig, J . F. Unpublished results.

2784 Organometallics, Vol. 22, No. 13, 2003
Mann et al.
chelating ligand. Generation of a monophosphine com-
plex from 7 by P-C bond cleavage prior to reductive
elimination does not occur. Although cleavage of the
phosphine during thermolysis of 10 was observed, none
of the monophosphines formed by P-C cleavage were
observed during the thermolysis of 7. Thus, the in-
creased steric properties of D-t-BPF appear to promote
elimination by accelerating C-O bond formation di-
rectly from the starting complex 7.
2. Red u ctive Elim in a tion fr om F cP (t-Bu )2 Com -
p lexes. Quantitative rate data that uncovered a de-
tailed mechanistic pathway for reductive elimination
from 11a -c were difficult to obtain. Yet, reductive
elimination of diaryl ether from 11b is clearly induced
by substitution of 1a by the larger phosphine ligand 1b,
P(t-Bu)3, or binaphthyl 1c. Reactions conducted in the
presence of high concentrations of 1b or P(t-Bu)3 formed
diaryl ether in high yields, while reactions conducted
with low concentrations of added ligand formed diaryl
ether in low yields. Moreover, reactions conducted with
1b, 1c, or P(t-Bu)3 along with FcP(t-Bu)2 generated
lower yields of diaryl ether. The presence of FcP(t-Bu)2
in the latter reactions will decrease the concentration
of the ligand substitution product.
Reductive elimination from dimeric 11b most likely
occurs after formation of a monomeric species. Products
from thermolysis of a mixture of 11a and 11c in the
presence or absence of added P(t-Bu)3 suggested that
three-coordinate monomeric arylpalladium phenoxides
were generated reversibly. Moreover, previous studies
on dimeric amides and thiolates32,34,37,93 have shown
clearly that reductive elimination occurs from mono-
meric complexes. Rate constants for reaction of 11a in
the presence and absence of ligand 1b were nearly
identical, even though the yields were significantly
different. These data suggest that the added ligand
intercepts the chemistry of a reactive intermediate
formed from 11a . Although not shown unambiguously,
this intermediate that reacts with the incoming ligand
is likely to be the three-coordinate arylpalladium phe-
noxide or a species that gives rise to this three-
coordinate phenoxide.
C. Rela tion sh ip betw een Ca ta lytic a n d Stoich io-
m etr ic Rea ction s. There is a strong parallel between
complexes that undergo reductive elimination and the
types of palladium complex that catalyze the formation
of diaryl ethers. First, palladium complexes of arylphos-
phines catalyze the formation of diaryl ethers from aryl
halides bearing electron-withdrawing groups, and a
combination of CF3-DPPF and palladium precursors
leads to formation of diaryl ethers with faster rates and
higher yields than a combination of DPPF and pal-
ladium precursors.11 Moreover, complexes of sterically
hindered monodentate ligands are the most efficient at
formation of diaryl ethers.10,15,21 The only bidentate
ligand that has generated a catalyst for the formation
of diaryl ethers from electron-neutral aryl halides has
generated this catalyst by cleavage and reaction with
the aryl halide substrate to form a new hindered
monophosphine.10
ligated arylpalladium phenoxide 11a and the excellent
yields of diaryl ether generated from coupling of aryl
halides with phenoxides in the presence of catalytic
amounts of 1a and Pd(DBA)2 was initially perplexing.
These results clearly ruled out arylpalladium bromide
and phenoxide complexes 3 and 11a , which contain FcP-
(t-Bu)2 ligand 1a , as intermediates in the catalytic
process. However, we have shown that transformation
of the parent ferrocenyl ligand 1a to the perarylated
ferrocenyl ligand 1b under the conditions of the catalytic
reaction generated the true catalyst.21 Reactions cata-
lyzed by complexes of this more hindered ligand 1b
proceeded in higher yields and with faster rates than
those catalyzed by complexes of FcP(t-Bu)2.21 Consistent
with these faster rates and higher yields for the catalytic
system bearing ligand 1b or the di-tert-butylphosphino-
binaphthyl ligand of Buchwald, the rate of reductive
elimination from 11a in the current work was faster and
occurred in high yield when heated in the presence of
excess Ph5FcP(t-Bu)2 or the binaphthyl ligand.
D. Con clu sion s. Variation of electronic properties of
palladium complexes with bidentate phosphines showed
only small effects on the rate of C-O bond-forming
reductive elimination, but changes in steric properties
of the ligand had a dramatic effect. The presence of a
single donor atom on the sterically hindered ligand is
important for generating a three-coordinate arylpalla-
dium phenoxide intermediate that forms diaryl ether
product from complexes with electron-neutral, pal-
ladium-bound aryl groups. The relative size of P(t-Bu)3,
FcP(t-Bu)2, Ph5FcP(t-Bu)2, and 2-(di-tert-butylphosphino)-
1,1′-binaphthyl in the transition state structure is
unclear; simple modeling of Pd(0) complexes showed
that the steric demands of the FcP(t-Bu)2 ligand on the
metal center dramatically change with conformation.
Nevertheless, the results presented here demonstrate
clearly that increased steric hindrance in palladium
complexes with monodentate phosphines increases the
rate of reductive elimination enough to allow new
reaction chemistry.
Previous reactions of aryl halides with phenoxides
were catalyzed by palladium complexes of arylphos-
phines and led to C-C bond formation at the o- or
p-position of the phenoxide.94-96 The reductive elimina-
tion reactions of the isolated phenoxides studied in the
present work form C-O instead of C-C bonds. Presum-
ably the C-C couplings with phenoxides observed
during previous work occur by reductive elimination
after rearrangement of an O-bound phenoxide to a less
stable C-bound form that resembles an enolate. The
steric and electronic properties of the ligands presented
in the current work, therefore, accelerate C-O bond-
forming reductive elimination enough to allow reaction
from the thermodynamically preferred, but less reactive,
O-bound arylpalladium phenoxide complex.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were performed in a
drybox under N2 using solvents that were distilled from
The contrast between the low yields of diaryl ether
generated by reductive elimination from FcP(t-Bu)2-
(94) Hennings, D. D.; Iwasa, S.; Rawal, V. H. J . Org. Chem. 1997,
62, 2-3.
(95) Satoh, T.; Kawamura, Y.; Miura, M.; Nomura, M. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1740-1742.
(93) Louie, J .; Hartwig, J . F. J . Am. Chem. Soc. 1995, 117, 11598-
11599.
(96) Satoh, T.; Inoh, J .-I.; Kawamura, Y.; Kawamura, Y.; Miura, M.;
Nomura, M. Bull. Chem. Soc. J pn 1998, 71, 2239-2246.

Reductive Elimination of Diaryl Ethers from Pd(II)
Organometallics, Vol. 22, No. 13, 2003 2785
sodium/benzophenone ketyl (toluene, benzene, ether, and THF)
or from calcium hydride (methylene chloride) unless otherwise
stated. 1H NMR spectra were obtained on a 300 MHz spec-
trometer and were referenced to residual protiated solvents.
13C NMR spectra were obtained on an AM 500 MHz spectrom-
eter. 31P{1H} NMR spectra were obtained on an Omega 300
MHz spectrometer with shifts reported relative to an external
85% H3PO4 standard, and 19F{1H} NMR spectra were obtained
on an Omega 500 MHz spectrometer with shifts reported
relative to an external CFCl3 standard. GC data were obtained
on an HP 5890 gas chromatograph. GC/MS data were obtained
on a HP 5890 gas chromatograph equipped with an HP5971A
mass spectral analyzer. IR spectra were obtained on a MIDAC
M Series spectrometer. Ligands 1a and 1b were prepared
according to published methods.10,21
{P d [P (C5H4F eC5H5)(t-Bu )2](C6H4-2-Me)(Br )}2 (3). To a
solution of {Pd[P(o-tolyl)3](o-MeC6H4)(Br)}97 (246 mg, 0.211
mmol) in 3 mL of THF was added 199 mg (0.503 mmol) of
P(C5H4FeC5H5)(t-Bu)2 in 2 mL of THF. The solution was stirred
at room temperature for 2 h. The solvent was removed under
vacuum, and the solids were redissolved in pentane. The
resulting suspension was filtered through Celite to give an
orange solution. The pentane was removed under vacuum, and
the resulting orange solid was redissolved in toluene, layered
with pentane, and cooled at -35 °C for 2 days. Orange crystals
1
(78.7 mg, 31% yield) were obtained. H NMR (C6D6, 25 °C): δ
1.36 (d, 13.9 Hz, 18H), 1.44 (d, 13.9 Hz, 18H), 2.10 (s, 6H),
3.72 (s, 2H), 3.77 (s, 2H), 3.82 (s, 2H), 3.86 (s, 2H), 3.97 (s,
10H), 6.75-6.84 (m, 6H), 7.49 (dd, 7.3 Hz, 3.1 Hz, 2H). 31P-
{1H} NMR (C6D6): δ 54.04 (s). Anal. Calcd for C50H68Br2-
Fe2P2Pd2‚C7H8: C, 52.36; H, 5.86. Found: C, 52.11; H, 5.96.
[F cP (i-P r )2]2P d (C6H4-2-Me)(Br ) (4). (C5H4FeC5H5)P(i-Pr)2
(0.130 g, 0.430 mmol) and {Pd[P(o-tolyl)3](C6H4-2-CH3)(Br)}2
(0.100 g, 0.086 mmol) were dissolved in 20 mL of toluene and
stirred for 3 h. Solvent was removed under vacuum. Benzene
(1 mL) and pentane (10 mL) was added to the orange solid to
dissolve free phosphines. The remaining solid was washed with
pentane (3 × 5 mL) and dried under vacuum (0.1048 g, 69%).
1H NMR (C6D6): δ 1.28 (q, 7.1 Hz, 6H, CHMe2), 1.45 (q, 7.9
Hz, 6H, CHMe2), 1.53 (q, 7.5 Hz, 6H, CHMe2), 1.54 (q, 7.1 Hz,
6H, CHMe2), 2.15 (s, 3H, C6H4Me), 2.81 (m, 2H, CHMe2), 3.39
(m, 2H, CHMe2), 3.65 (br s, 2H, C5H4P), 3.81 (br s, 2H, C5H4P),
3.90 (br s, 2H, C5H4P), 4.00 (s, 10H, C5H5), 4.17 (br s, 2H,
C5H4P), 6.57 (d, 7.2 Hz, 1H, C6H4Me), 6.67 (t, 7.10 Hz,
1H, C6H4Me), 6.75 (t, 7.12 Hz, C6H4Me), 7.40 (d, 7.3 Hz, 1H,
C6H4Me). 13C{1H} NMR (C6D6): δ 19.73 (s, CHMe2), 20.03 (s,
CHMe2), 20.54 (s, CHMe2), 21.38 (s, CHMe2), 27.04 (t, 12.2 Hz,
CHMe2), 27.75 (s, C6H4Me), 30.46 (t, 11.6 Hz, CHMe2), 68.60
(t, 3.4 Hz, C5H4P), 69.41 (t, 3.2 Hz, C5H4P), 69.73 (s, C5H5),
73.09 (t, 5.6 Hz, C5H4P), 73.67 (br s, C5H4P), 76.35 (t, 16.1 Hz,
i-C5H4P), 122.51 (s, C6H4Me), 123.09 (s, C6H4Me), 129.45 (s,
C6H4Me), 138.16 (t, 4.9 Hz, C6H4Me), 143.13 (t, 3.8 Hz,
C6H4Me). 31P{1H} NMR (C6D6): δ 23.94 (s). Anal. Calcd
for C39H53BrFe2P2Pd: C, 53.12; H, 6.06. Found: C, 52.91; H,
5.95.
[P d (DP P F )(C6H4-4-CN)(OC6H4-4-OMe)] (5a ). A 100 mL
flask was charged with 484 mg (0.676 mmol) of Pd[P(o-
tolyl)3]2,68 456 mg (0.823 mmol) of DPPF, 197 mg (2.05 mmol)
of Na-O-tBu, and 382 mg (1.52 mmol) of 4-cyanophenyl
trifluoromethylsulfonate in 20 mL of THF. The solution was
stirred overnight in the drybox, and a brownish-yellow solid
precipitated from solution. The precipitate was isolated by
filtration and redissolved in 2 mL of a 1:1 mixture of THF and
benzene. A 1:1 mixture of Et2O and pentane was added to the
resulting brown solution to bring the total volume to 10 mL.
[Pd(DPPF)(C6H4-4-CN)(OC6H4-4-CN)] was precipitated from
this solution and isolated in 80% yield (665 mg). This com-
pound was used without further purification. 1H NMR
(CD2Cl2): δ 3.86 (d, 1.6 Hz, 2H), 4.28 (s, 2H), 4.59 (s, 2H), 4.73
(d, 1.8 Hz, 2H), 6.29 (d, 8.6 Hz, 2H), 6.74 (dd, 8.1 Hz, 1.9 Hz,
2H), 6.90 (d, 8.7 Hz, 2H), 7.13-7.19 (m, 6H), 7.22-7.46 (m,
12H), 7.84 (dd, 9.5 Hz, 7.0 Hz, 4H). 31P{1H} NMR (CD2Cl2): δ
32.40 (d, 30.0 Hz), 13.65 (d, 30.0 Hz).
(D-t-BP F )P d (Br )(C6H4-4-CN) (2a ). D-t-BPF (0.386 g, 0.506
mmol) in 4 mL of THF was added to a solution of {Pd[P(o-
18
tolyl)3](C6H4-4-CN)(Br)}2 in 6 mL of THF. The mixture was
stirred for 1.5 h. The solvent was removed under vacuum. The
yellow solid was dissolved in 4 mL of benzene and 15 mL of
pentane was added to precipitate the product. The yellow solid
was washed with pentane (3 × 5 mL). The solid was redis-
solved in THF, concentrated, layered with pentane, and cooled
to -35 °C. Yellow crystals of product were obtained (0.2288 g,
1
59%). H (C6D6): δ 1.08 (v br d, 10.2 Hz, 18H, Pt-Bu), 1.63 (v
br d, 11.9 Hz, 18H, Pt-Bu), 3.92 (br, s, 4H, C5H4P), 4.13 (br s,
4H, C5H4P), 7.01 (d, 8.2 Hz, 2H, m-C6H4CH), 7.81 (t, 7.5 Hz,
2H, o-C6H4CN). 1H (CDCl3): δ 1.38 (t, 7.6 Hz, 36H, Pt-Bu),
4.33 (t, 1.9 Hz, 4H, C5H4P), 5.68 (t, 1.8 Hz, 4H, C5H4P), 7.41
(d, 8.1 Hz, 2H, C6H4CN), 7.83 (d, 8.3 Hz, 2H, C6H4CN). 1H
(CD3NO2): δ 1.44 (t, 7.5 Hz, 36H, Pt-Bu), 4.46 (t, 2.0 Hz, 4H,
C5H4P), 5.32 (t, 2.0 Hz, 4H, C5H4P), 7.50 (d, 8.0 Hz, 2H,
C6H4CN), 8.08 (d, 8.0 Hz, 2H, C6H4CN). 13C{1H} NMR
(CDCl3): δ 30.71 (s, CMe3), 36.81 (t, 6.8 Hz, CMe3), 53.93
(t, 8.9 Hz, i-C5H4P), 70.91 (t, 3.4 Hz, R-C5H4P), 79.18 (s,
â-C5H4P), 107.09 (s, C6H4CN), 118.92 (s, C6H4CN), 130.24 (s,
m-C6H4CN), 138.648 (t, 3.2 Hz, o-C6H4CN), 154.12 (d, 2.3
Hz, i-C6H4CN). 31P{1H} NMR (C6D6): δ 37.46 (d, 22.2 Hz,
1P), 46.85 (d, 22.2 Hz, 1P). 31P{1H} NMR (CDCl3): δ 21.56
(s). 31P{1H} NMR (CD3NO2): δ 23.36 (s). Anal. Calcd for
C33H48BrFeNP2Pd: C, 51.96; H, 6.34; N, 1.84. Found: C, 52.06;
H, 6.36; N, 1.60.
P d (D-t-BP F )(C6H5)(O-C6H4-4-OMe) (2b). To a solution of
104 mg (0.0921 mmol) of {Pd[P(o-tol)3](C6H5)(Br)}2 in 2 mL
of THF was added 89.6 mg (0.189 mmol) of D-t-BPF in 2 mL
of THF. The solution was stirred for 30 min, over whch time
a clear yellow solution resulted. The solvent was removed
under vacuum, and the resulting yellow solid was redissolved
in ca. 1 mL of benzene. This benzene mixture was then pre-
cipitated from ca. 20 mL of pentane, which yielded a yellow
solid. This yellow solid was filtered through a medium-fritted
funnel and washed twice with pentane. The yellow solid,
presumed to be Pd(D-t-BPF)(C6H5)(O-C6H4-4-OMe), which
displayed a chemical shift at 45.11 (d, 25.7 Hz), 36.4 (d, 25.7
Hz) ppm in the 31P NMR spectrum, was isolated in 74.7% yield
(101.3 mg).
[(D-t-BP F )P d (C6H4-4-CN)](BF 4) (2c). AgBF4 (22 mg, 0.11
mmol) was added to a solution of (D-t-BPF)Pd(Br)(C6H4-4-CN)
(65 mg, 0.085 mmol) in 5 mL of THF. The suspension was
stirred at room temperature for 5 min. The solid was then
filtered from solution, and the solvent was removed under
vacuum. The crude material was recrystallized from THF at
-35 °C. Dark orange crystals were obtained (52.1 mg, 80%
yield). 1H NMR (CD2Cl2): δ 1.38 (t, 8.0 Hz, 36H), 1.81 (m, 4H,
THF), 3.67 (m, 4H, THF), 4.29 (m, 4H), 5.31 (m, 4H), 7.44 (d,
4.0 Hz, 2H), 7.85 (d, 4.0 Hz, 2H). 13C NMR (CD2Cl2): δ 25.95
(THF), 31.06 (t, 3.0 Hz), 37.46 (t, 8.3 Hz), 55.15 (t, 8.2 Hz),
68.12 (THF), 71.54 (t, 3.4 Hz), 78.80, 107.88, 119.53, 131.04,
139.29 (t, 4.2 Hz), 154.01. 31P NMR (CD2Cl2): δ 21.71(s); Anal.
Calcd for C33H48NP2F4BFePd‚THF: C, 52.78; H, 6.72; N, 1.66.
Found: C, 52.66, H, 6.67; N, 1.60.
To a solution containing 0.205 mg (0.232 mmol) of [Pd-
(DPPF)(C6H4-4-CN)(OC6H4-4-CN)] in 5 mL of THF was added
35.9 mg (0.246 mmol) of Na(OC6H4-4-OMe). The solution was
stirred at room temperature for 20 min, after which time a
light brown solution remained. The solution was filtered
through Celite, concentrated under vacuum, and crystallized
by layering the THF solution with pentane at -35 °C. The
product (149 mg, 82%) was obtained as yellow blocks. 1H NMR
(C6D6): δ 3.40 (s, 3H), 3.68 (d, 1.2 Hz, 2H), 3.72 (d, 1.5 Hz,
2H), 3.95 (br s, 2H), 4.48 (d, 1.7 Hz, 2H), 6.54 (d, 1.9 Hz, 1H),
6.57 (d, 2.6 Hz, 1H), 6.66 (s, 4H), 6.71-6.76 (m, 4H), 6.82-
6.89 (m, 2H), 7.06-7.19 (m, 6H), 7.21-7.33 (m, 6H), 8.25 (td,
7.1 Hz, 1.1 Hz, 4H). 31P{1H} NMR (C6D6): δ 31.40 (d, 31 Hz),

2786 Organometallics, Vol. 22, No. 13, 2003
Mann et al.
10.64 (d, 31 Hz). IR (KBr, cm-1): νCN 2216.0. Anal. Calcd for
C48H39FeNO2P2Pd: C, 65.07; H, 4.44. Found: C, 64.76; H, 4.31.
[P d (DP P F )(C6H4-4-CN)(OC6H4-4-O-n -C4H9)] (5b). Fol-
lowing a similar procedure for the synthesis of 5a , 232 mg
(0.264 mmol) of [Pd(DPPF)(C6H4-4-CN)(OC6H4-4-CN)] and 76.7
mg (0.408 mmol) of Na(OC6H4-4-O-n-C4H9) were stirred at
room temperature for 1.5 h in 5 mL of THF. The THF was
removed under vacuum, and the resulting solids were redis-
solved in 25 mL of toluene. After filtering through a medium-
fritted funnel, the solution was concentrated, layered with
pentane, and allowed to crystallize at -35 °C. The product
was isolated in 56% yield (137 mg). 1H NMR (C6D6): δ 0.80 (t,
7.3 Hz, 3H), 1.34 (sextet, 7.3 Hz, 2H), 1.58 (quintet, 8.0 Hz,
2H), 3.68 (m, 4H), 3.72 (d, 2.0 Hz, 2H), 3.96 (br s, 2H), 4.48 (d,
1.4 Hz, 2H), 6.55 (d, 1.9 Hz, 1H), 6.65 (d, 1.9 Hz, 1H), 6.65-
6.76 (m, 8H), 6.83-6.88 (m, 2H), 7.09-7.20 (m, 5H), 7.22-
7.31 (m, 7H), 8.26(dd, 9.7 Hz, 7 Hz, 4H). 31P{1H} NMR (C6D6):
δ 31.39 (d, 30.5 Hz), 10.64 (d, 30.5 Hz). IR (KBr, cm-1): νCN
2219.0. Anal. Calcd for C51H45FeNO2P2Pd: C, 66.00; H, 4.89.
Found: C, 65.93; H, 4.97.
[P d (DP P F )(C6H4-4-CN)(OC6H4-3,5-(t-C4H9)2)] (5c). Into
a vial was placed 233 mg (0.276 mmol) of (DPPF)Pd(C6H4-4-
CN)(Br)42 and 86.8 mg (0.356 mmol) of K(OC6H4-3,5-(t-C4H9)2).
To this was added 10 mL of THF. The solution was stirred at
room temperature for 1.5 h, after which time the solvent was
removed under vacuum. The resulting solids were dissolved
in 100 mL of toluene and filtered through Celite. The toluene
was removed under vacuum, and the remaining solids were
dissolved in THF and crystallized by layering the THF solution
with Et2O at -35 °C. The product was obtained as yellow
flakes in 181.9 mg (68%). 1H NMR (C6D6): δ 1.35 (s, 18H),
3.70 (d, 1.1 Hz, 2H), 3.78 (d, 1.7 Hz, 2H), 3.94 (br s, 2H), 4.52
(d, 1.4 Hz, 2H), 6.55 (dd, 7.8 Hz, 1.7 Hz, 2H), 6.63-6.64 (m,
3H), 6.78 (t, 7 Hz, 4H), 6.85-6.90 (m, 2H), 6.99-7.15 (m, 5H),
8.17-8.23 (m, 4H). 31P{1H} NMR (C6D6): δ 31.12 (d, 30.2 Hz),
11.01 (d, 30.2 Hz). IR (THF, cm-1): νCN 2219.5. Anal. Calcd
for C55H53FeNOP2Pd‚0.5C7H8: C, 69.27; H, 5.66. Found: C,
69.51; H, 5.85.
cm-1): νCN 2222.0. Anal. Calcd for C52H35FeNO2P2Pd: C, 53.93;
H, 3.05. Found: C, 53.59; H, 3.11.
P d [(C6H 4-4-CF 3)2P ((C5H 4)2F e)P (C6H 4-4-CF 3)2](C6H 4-4-
CN)(OC6H4-3,5-(t-C4H9)2 (6b). Following a similar procedure
for the synthesis of 5c, reaction of 90.0 mg (0.0807 mmol) of
(CF3-DPPF)Pd(C6H4-4-CN)(Br) and 30.4 mg (0.125 mmol) of
K(OC6H4-3,5-(t-C4H9)2) provided the product in 53% yield (52.8
mg) after crystallization by layering a toluene solution with
pentane and cooling to -35 °C. 1H NMR (C6D6): δ 1.26 (s,
18H), 3.65-3.67 (m, 2H), 3.70-3.71 (m, 2H), 3.96 (br s, 2H),
4.29-4.31 (m, 2H), 6.45-6.49 (m, 2H), 6.62 (d, 1.2 Hz, 1H),
6.99-7.06 (m, 7H), 7.10-7.15 (m, 5H), 7.27 (d, 7.3 Hz, 4H),
8.02 (dd, 9.4 Hz, 8.1 Hz, 4H). 31P{1H} NMR (C6D6): δ 30.61
(d, 30.9 Hz), 10.43 (d, 30.9 Hz). 19F{1H} NMR (C6D6): δ -63.96
(s), -64.20 (s). IR (THF, cm-1): νCN 2221.9. Anal. Calcd for
C
59H49F12FeNOP2Pd: C, 57.14; H, 3.98. Found: C, 57.37; H,
4.24.
(D-t-BP F )P d (OC6H4-4-OMe)(C6H4-4-CN) (7a ). (D-t-BPF)-
Pd(C6H4-4-CN)(Br), 2 (0.200 g, 0.262 mmol), and NaOC6H4-
4-OMe (0.048 g, 0.330 mmol) were dissolved in THF (5 mL)
and stirred for 1 h. The solution was filtered through Celite
and dried in vacuo. The orange solid was dissolved in toluene,
concentrated, layered with pentane, and cooled to -35 °C.
Orange crystals were obtained (0.0431 g, 20%). 1H NMR
(C6D6): δ 1.11 (d, 13.8 Hz, 18H, CMe3), 1.60 (d, 12.2 Hz, 18H,
CMe3), 3.49 (s, 3H, OMe), 3.94 (br s, 4H, C5H4P), 4.18 (br s,
4H, C5H4P), 6.65 (d, 8.3 Hz, 2H, Ph), 6.80 (d, 8.8 Hz, 2H, Ph)
6.90 (d, 8.0 Hz, 2H, Ph), 7.63 (t, 7.3 Hz, 2H, o-C6H4CN). 31P-
{1H} NMR (C6D6): δ 42.07 (d, 25.9 Hz, 1P), 55.36 (d, 25.9 Hz,
1P). Anal. Calcd for C40H55FeNO2P2Pd‚0.61C7H8: C, 61.67; H,
7.00; N, 1.62. Found: C, 61.40; H, 6.84; N, 1.43.
(D-t-BP F )P d (OC6H 4-3,5-(t-C4H 9)2(C6H 4-4-CN) (7b ). A
sample of 2 (0.100 g, 0.131 mmol) and KOC6H3-3,5-(t-Bu)2
(0.040 g, 0.164 mmol) were dissolved in THF (15 mL) and
stirred for 15 min. The solution was filtered through Celite
and dried in vacuo. The yellow solid was dissolved in toluene,
concentrated, layered with pentane, and cooled to -35 °C.
Yellow feathers were obtained (0.084 g, 72%). 1H NMR
(C6D6): δ 1.15 (d, 14.0 Hz, 18H, Pt-Bu), 1.47 (s, 18H, C6H3t-
Bu), 1.59 (d, 12.2 Hz, 18H, Pt-Bu), 3.95 (br s, 4H, C5H4P), 4.19
(br s, 4H, C5H4P), 6.60 (s, 2H, o-C6H3t-Bu2), 6.82 (s, 1H,
p-C6H3t-Bu2), 6.88 (d, 8.4 Hz, 2H, m-C6H4CN), 7.60 (t, 7.2 Hz,
2H, o-C6H4CN). 31P{1H} NMR (C6D6): δ 42.06 (d, 22.2 Hz, 1P),
55.59 (d, 22.2 Hz, 1P). Anal. Calcd for C47H69FeNOP2Pd: C,
63.55; H, 7.83; N, 1.58. Found: C, 63.80; H, 7.72; N, 1.38.
P d (DP P F )(C6H5)(OC6H4-4-OMe) (8a ). Into a vial was
added 74.7 mg (0.0808 mmol) of {Pd(Ph)(PPh3)(µ-OH)}2,99 21.8
mg (0.176 mmol) of p-methoxyphenol, and 3 mL of benzene.
The solution was stirred at room temperature for 5 min, after
which time 102 mg of DPPF (0.183 mmol) dissolved in 5 mL
of benzene was added to the clear solution. This mixture was
stirred for 10 min to give a yellow solution. This solution was
filtered through Celite, and the solution volume was reduced
to 1 mL under vacuum. The product was precipitated from
this solution by addition of pentane. The product was recrys-
tallized by layering an Et2O solution with pentane at -35 °C
(95.6 mg, 69%). 1H NMR (C6D6): δ 3.39 (s, 3H), 3.71 (d, 1.5
Hz, 2H), 3.81 (d, 1.4 Hz, 2H), 3.96 (br s, 2H), 4.54 (d, 1.5 Hz,
2H), 6.62-6.70 (m, 5H), 6.80 (virtual t, 8 Hz, 5H), 6.86-6.90
(m, 3H), 6.91-7.15 (m, 5H), 7.35-7.48 (m, 7H), 8.33 (td, 8 Hz,
1.2 Hz, 4H). 31P{1H} NMR (THF): δ 31.53 (d, 30.5 Hz), 10.31
(d, 30.5 Hz).
{P d [(C6H4-4-CF 3)2P ((C5H4)2F e)P (C6H4-4-CF 3)2](C6H4-4-
CN)(OC6H4-4-OMe)} (6a ). A vial was charged with 0.1658 g
(0.1398 mmol) of {Pd[P(o-tolyl)3](C6H4-4-CN)(Br)}2,42 0.2483 g
(0.3006 mmol) of CF3-DPPF,98 and 10 mL of THF. This mixture
was stirred at room temperature for 1 h, after which time the
solvent was removed under vacuum. Unreacted CF3-DPPF was
removed by suspending the resulting yellow solid in 20 mL of
pentane and filtering the solution through a medium-fritted
funnel. The yellow precipitate collected was then dissolved in
2 mL of toluene. Pentane (20 mL) was added to the toluene
solution to precipitate the product (CF3-DPPF)Pd(C6H4-4-CN)-
(Br). The yellow powder (0.1956 g, 63%) was washed three
times with pentane and used without further purification.
31P{1H} NMR (C7D8): δ 29.1 (d, 34 Hz), 10.2 (d, 33 Hz).
A vial was charged with 46.0 mg (0.0413 mmol) of
(CF3-DPPF)Pd(C6H4-4-CN)(Br) and 80.0 mg (0.049 mmol) of
K(OC6H4-4-OMe) in 3 mL of THF. The solution was stirred at
room temperature for 10 min, after which time the solvent
was removed under vacuum. The resulting solids were dis-
solved in Et2O and filtered through Celite. The product was
isolated in 66% yield (31.4 mg) after crystallization by layering
1
the Et2O solution with pentane at -35 °C. H NMR (C6D6): δ
3.93 (s, 3H), 3.57-3.58 (m, 2H), 3.68-3.58 (m, 2H), 3.98 (br s,
2H), 4.28-4.30 (m, 2H), 6.44-6.52 (m, 4H), 6.60 (d, 8.8 Hz,
2H), 6.93-7.10 (m, 10H), 7.36 (d, 8.1 Hz, 4H), 8.04 (virtual t,
9 Hz, 4H). 31P{1H} NMR (C7D8): δ 31.14 (d, 33 Hz), 9.85 (d,
33 Hz). 19F{1H} NMR (C7D8): δ -62.75 (s), -63.04 (s). IR (THF,
P d (DP P F )(C6H5)[OC6H4-3,5-(ter t-bu tyl)] (8b). Into a vial
was added 200 mg (0.218 mmol) of {Pd(Ph)(PPh3)(µ-OH)}2,99
111 mg (0.538 mmol) of 3,5-di-tert-butylphenol, and 5 mL of
toluene. The solution was stirred at room temperature for 5
min, after which time 250 mg (0.450 mmol) of DPPF dissolved
in 10 mL of toluene was added to the clear solution. This
mixture was stirred for 10 min to give a yellow solution. This
(97) This ortho-methyl isomer was synthesized by a procedure
similar to the synthesis of the para-methyl isomer, whose preparation
is found in: Paul, F.; Patt, J .; Hartwig, J . F. Organometallics 1995,
14, 3030-3039.
(98) Unruh, J . D.; Christenson, J . R. J . Mol. Catal. 1995, 177, 5373-
5374.
(99) Grushin, V. V.; Alper, H. Organometallics 1993, 12, 1890-1901.

Reductive Elimination of Diaryl Ethers from Pd(II)
Organometallics, Vol. 22, No. 13, 2003 2787
solution was filtered through Celite, and the solution volume
was reduced to 1 mL under vacuum. The product was
precipitated from this solution by addition of pentane. The
solid was filtered, washed with pentane, and dried under
was layered with pentane and cooled to -35 °C. This recrys-
tallization provided 45 mg (40% yield) of orange disks that
contained 0.5 equiv of toluene per dimer by 1H NMR spec-
trometry and were analytically pure. 1H NMR (C7D8, -50
°C): δ 1.05 (br d, 13.7 Hz, 18H), 1.99 (d, 14.2 Hz, 18H), 2.61
(s, 6H), 3.43 (s, 6H), 3.56 (br s, 2H), 3.61 (br s, 2H), 3.69 (br s,
2H), 3.74 (br s, 2H), 3.82 (s, 10H), 4.93 (br d, 7 Hz, 2H), 6.55
(br d, 7 Hz, 2H), 6.7-7.0 (m 8H), 7.60 (br d, 7 Hz, 2H), 7.94
(br d, 7 Hz, 2H). 31P{1H} NMR (C7D8): δ 54.1 (s). Anal. Calcd
for C64H82Fe2O4P2Pd2‚0.5 C7H8: C, 60.15; H, 6.43. Found: C,
60.27; H, 6.77.
1
vacuum to give 272 mg (66%) of product. H NMR (C6D6): δ
1.39 (s, 18H), 3.72 (m, 2H), 3.83 (m, 2H), 3.97 (br s, 2H), 4.60
(m, 2H), 6.60-6.62 (m, 4H), 6.77 (d, 1.6 Hz, 2H), 6.83-6.90
(m, 6H), 7.08-7.16 (m, 6H), 7.46-7.53 (m, 6H), 8.29 (td, 8 Hz,
1.2 Hz, 4H). 31P{1H} NMR (C6D6): δ 31.1 (d, 30.9 Hz), 9.56 (d,
31.4 Hz). Anal. Calcd for C54H54FeOP2Pd: C, 68.75; H, 5.78.
Found: C, 68.51; H, 5.86.
P d [(C6H 4-4-CF 3)2P ((C5H 4)2F e )P (C6H 4-4-CF 3)2](C6H 5)-
(OC6H4-4-OMe) (9). Following a similar procedure for the
synthesis of 8, reaction of 101 mg (0.109 mmol) of {Pd(Ph)-
(PPh3)(µ-OH)}2 and 28.8 mg (0.232 mmol) of p-methoxyphenol
provided the product in 23% yield (55.2 mg) after crystal-
lization from a solution of toluene layered with pentane at
-35 °C. 1H NMR (C6D6): δ 3.39 (s, 3H), 3.62-3.63 (m, 2H),
3.69 (d, 1.7 Hz, 2H), 3.99 (br s, 2H), 4.32-4.34 (m, 2H), 6.55-
6.59 (m, 5H), 6.62-6.65 (m, 3H), 6.93-7.37 (m, 8H), 7.41 (d,
3.1 Hz, 4H), 7.66-7.68 (m, 1H), 8.13 (virtual t, 9 Hz, 4H).
31P{1H} NMR (C6D6): δ 31.13 (d, 30.5 Hz), 8.59 (d, 30.5 Hz).
P d [(t-C4H 9)2P ((C5H 4)2F e))P (t-C4H 9)2](C6H 5)(OC6H 4-4-
OMe) (10). To a solution of 104 mg (0.0921 mmol) of {Pd[P(o-
tolyl)3](C6H5)(Br)}234 in 2 mL of THF was added 89.6 mg (0.189
mmol) of D-t-BPF100 in 2 mL of THF. The reaction was stirred
for 30 min, over which time a clear yellow solution resulted.
The solvent was removed under vacuum, and the resulting
yellow solid was redissolved in ca. 1 mL of benzene. (D-t-BPF)-
Pd(Ph)(Br) was then precipitated from this solution by addition
of ca. 20 mL of pentane. This yellow solid was isolated by
filtration through a medium fritted funnel and was washed
twice with pentane to give 101 mg (75%) of a compound
presumed to be Pd[(t-C4H9)2P((C5H4)2Fe))P(t-C4H9)2](C6H5)(Br).
31P{1H} NMR: δ 45.11 (d, 25.7 Hz), 36.39 (d, 25.7 Hz). To a
solution of 101.3 mg of Pd[(t-C4H9)2P((C5H4)2Fe))P(t-C4H9)2]-
(C6H5)(Br) in 2 mL of THF was added 35.3 mg (0.218 mmol)
of KOC6H4-4-OMe. This mixture was stirred for 1 h. The 31P
NMR spectrum indicated complete conversion of the material
to {Pd[P(C5H4FeC5H5)(t-Bu)2](p-MeC6H4)(Br)}2. The solvent
was then removed under vacuum, and the resulting orange
solid was dissolved in 250 mL of pentane. The pentane solution
was filtered through Celite, and the solvent was removed
under vacuum. Orange crystals (32.4 mg, 30%) were isolated
from a solution of toluene layered with pentane cooled at -35
°C. 1H NMR (C6D6): δ 1.25 (d, 13.3 Hz, 18H), 1.67 (d, 12.0 Hz,
18H), 3.49 (s, 3H), 3.96 (s, 4H), 4.24 (d, 5.4 Hz, 4H), 6.82-
6.96 (m, 7H), 7.75 (virtual t, 7.3 Hz, 2H). 31P{1H} NMR
(C6D6): δ 40.74 (d, 24.4 Hz), 53.07 (d, 24.4 Hz). Anal. Calcd
for C39H56FeO2P2Pd2: C, 59.97; H, 7.23. Found: C, 60.00; H,
7.61.
{P d [P (C 5 H 4 F e C 5 H 5 )(t -B u )2 ](C 6 H 4 -4-M e )(O C 6 H 4 -4-
OMe)}2 (11b). To a solution of {Pd[P(o-tolyl)3](C6H4-4-Me)-
(Br)}268 (80.0 mg, 0.137 mmol) in 2-3 mL of toluene was added
136 mg (0.413 mmol) of P(C5H4FeC5H5)(t-Bu)2. The solution
was stirred for 10 min, over which time the starting palladium
complex dissolved, and 31P NMR spectrometry showed conver-
sion of roughly 80% of the material to {Pd[P(C5H4FeC5H5)(t-
Bu)2](C6H4-4-Me)(Br)}2, 3b. At this time, 40 mg (0.274 mmol)
of NaOC6H4-4-OMe was added, and the resulting suspension
was stirred for 30 min. 31P NMR spectrometry showed com-
plete conversion to {Pd[P(C5H4FeC5H5)(t-Bu)2](C6H4-4-Me)-
(OC6H4-4-OMe)}2. The solids were removed by filtration
through Celite. The filtrate was concentrated to 0.5 mL,
layered with pentane, and cooled at -35 °C overnight. Orange-
red crystals (34 mg, 38% yield) suitable for X-ray diffraction
were obtained and were isolated by removing the solvent using
1
a pipet and washing with pentane. H NMR (C7D8, 25 °C): δ
1.47 (br d, 12.5 Hz, 36H), 2.28 (s, 6H), 3.44 (s, 6H), 3.70 (s,
10H), 3.98 (br s, 4H), 4.10 (br s, 4H), 6.40 (br d, 8.5 Hz, 4H),
6.62 (d, 8.6 Hz, 4H), 6.85 (d, 6.6 Hz, 4H), 7.48 (br d, 7 Hz,
4H). 31P{1H} NMR (C7D8): δ 54.2 (s).
{P d [P (C5H 4F eC5H 5)(t-Bu )2](C6H 3-2,4-(CH3)2)(OC6H 4-4-
O-n -Bu )}2 (11c). Into a vial was added 103 mg (0.0864 mmol)
of {Pd[P(o-tolyl)3](C6H4-2,4-Me2)(Br)}2 and 97.7 mg (0.296
mmol) of FcP(t-Bu)2 in 5 mL of THF. This solution was stirred
for 45 min, after which time the solvent was removed under
vacuum. The remaining solids were dissolved in pentane,
filtered through a medium fritted funnel, and washed with
Et2O. This isolated yellow solid {Pd[P(C5H4FeC5H5)(t-Bu)2]-
(C6H3-2,4-(CH3)2)(Br)}2, 3c, was dissolved in 5 mL of THF, and
81.2 mg (0.432 mmol) of NaO-C6H4-n-Bu was added to the
solution. This mixture was stirred at room temperature for
10 min, and the solvent was removed under vacuum. The
resulting brown solid was dissolved in pentane, and the
solution was filtered through Celite and concentrated. The
product was isolated by crystallization from pentane solution
at -35 °C to give 29% yield (35.2 mg) of product. 1H NMR
(C6D6, 25 °C): δ 0.81 (t, 7.3 Hz, 6H), 1.13 (d, 14.0 Hz, 18H),
1.33-1.37 (m, 4H), 1.49-1.55 (m, 4H), 1.98 (d, 13.7 Hz, 18H),
2.32 (s, 6H), 2.56 (s, 6H), 3.73-3.81 (m, 12H), 3.83 (s, 10H),
6.77-6.84 (m, 12H), 7.55 (br d, 6.6 Hz, 2H). 31P{1H} NMR
(C6D6): δ 53.71 (s).
{P d [P (C 5 H 4 F e C 5 H 5 )(t -B u )2 ](C 6 H 4 -2-M e )(O C 6 H 4 -4-
OMe)}2 (11a ). To a solution of {Pd[P(o-tolyl)3](o-MeC6H4)-
97
[F cP (i-P r )2]2P d (C6H4-2-Me)(OC6H4-4-OMe) (12). Com-
pound 4 (0.050 g, 0.055 mmol) and CsOH‚H2O (0.033 g, 0.200
mmol) were dissolved in THF (5 mL) and stirred 18 h.
HOC6H4-4-OMe in 1 mL of THF was added to the reaction
mixture and stirred for 3 h. Solvent was removed in vacuo.
Product was extracted with toluene (2 × 2 mL), and the
solution was filtered through Celite. The solution was concen-
trated, layered with pentane, and cooled to -35 °C to yield
(Br)}2 (100 mg, 0.171 mmol) in 10 mL of toluene was added
170 mg (0.513 mmol) of P(C5H4FeC5H5)(t-Bu)2. The solution
was stirred for 30 min, over which time the starting palladium
complex dissolved, and 31P NMR spectrometry showed conver-
sion of roughly 80% of the material to {Pd[P(C5H4FeC5H5)(t-
Bu)2](o-MeC6H4)(Br)}2, 3a . At this time, 50 mg (0.342 mmol)
of NaOC6H4-p-OMe was added, and the resulting suspension
was stirred for 30 min. 31P NMR spectrometry showed com-
plete conversion to {Pd[P(C5H4FeC5H5)(t-Bu)2](o-MeC6H4)(O-
p-C6H4OMe)}2. The solids were removed by filtration through
Celite. The filtrate was concentrated to 0.5 mL, layered with
pentane, and cooled at -35 °C overnight. Orange-brown
material (86 mg) was obtained and was isolated by removing
the solvent with a pipet and washing with pentane. This
material was redissolved in toluene, and the toluene solution
1
0.022 g (43%) of product. H NMR (C6D6): δ 1.28 (q, 7.2 Hz,
6H, CHMe2), 1.35 (q, 7.2 Hz, 6H, CHMe2), 1.35 (q, 7.3 Hz, 6H,
CHMe2), 1.49 (q, 7.7 Hz, 6H, CHMe2), 2.39 (m, 2H, CHMe2),
2.42 (s, 3H, C6H4Me), 2.56 (m, 2H, CHMe2), 3.58 (s, 3H, OMe),
3.61 (br s, 2H, C5H4P), 3.89 (br s, 12H, C5H5 and C5H4P), 3.956
(br s, 2H, C5H4P), 4.05 (br s, 2H, C5H4P), 6.75 (d, 7.2 Hz, 1H,
C6H4Me), 6.80 (t, 6.7 Hz, 1H, C6H4Me), 6.88 (t, 6.9 Hz, 1H,
C6H4Me), 6.96 (d, 8.7 Hz, 2H, C6H4OMe), 7.03 (d, 8.9 Hz, 2H,
C6H4OMe), 7.45 (d, 7.2 Hz, 1H, C6H4Me). 13C{1H} NMR
(C6D6): δ 19.24 (s, CHMe2), 19.70 (s, CHMe2), 20.16 (s, CHMe2),
(100) Hamann, B. C.; Hartwig, J . F. J . Am. Chem. Soc. 1998, 120,
7369-7370.

2788 Organometallics, Vol. 22, No. 13, 2003
Mann et al.
21.07 (s, CHMe2), 25.00 (t, 10.8 Hz, CHMe2), 27.78 (t, 10.4 Hz,
CHMe2), 27.83 (s, C6H4Me), 55.90 (s, OMe), 69.06 (t, 3.1 Hz,
C5H4P), 69.48 (t, 4.0 Hz, C5H4P), 69.59 (s, C5H5), 72.91 (t, 4.5
Hz, C5H4P), 73.31 (t, 5.4 Hz, C5H4P), 75.46 (t, 15.0 Hz,
i-C5H4P), 115.17 (s, C6H4OMe), 120.39 (s, C6H4OMe), 122.52
(s, C6H4Me), 123.05 (s, C6H4Me), 128.72 (s, C6H4Me), 138.86
(s, C6H4Me), 143.83 (s, C6H4Me), 148.61 (s, C6H4OMe), 164.82
(s, C6H4OMe)). 31P{1H} NMR (C6D6): δ 20.62 (s).
through Celite, and concentrated under vacuum. Orange
crystals (163.2 mg, 77% yield) suitable for X-ray diffraction
were obtained at -35 °C. H NMR (C6D6): δ 1.52 (t, 6.3 Hz,
36H), 4.14 (br d, 1.3 Hz, 4H), 4.37 (s, 10H), 4.53 (br s, 4H).
13C{1H} NMR (C6D6): δ 31.78 (t, 5.4 Hz), 35.66 (t, 4.2 Hz),
69.22, 70.56, 73.89 (t, 5.9 Hz), 79.51 (t, 6.4 Hz). 31P{1H} NMR
(C6D6): δ 56.35 (s). Anal. Calcd for C36H54Fe2P2Pd: C, 56.38;
H, 7.10. Found: C, 56.46; H, 7.22.
1
Ni[(C6H4-4-CF 3)2P ((C5H4)2F e)P (C6H4-4-CF 3)2](CO)2 (13).
Ni(CO)2(PPh3)2 (0.064 g, 0.100 mmol) and (C6H4-4-CF3)2P-
((C5H4)2Fe)P(C6H4-4-CF3)2 (0.083 g, 0.100 mmol) were dis-
solved in THF (9 mL). After 48 h the reaction mixture was
concentrated, pentane (4 mL) was added, and a precipitate
formed. The yellow solids were washed with ether and dried
under vacuum to give 45.3 mg of product in 48% yield. 1H
NMR (THF-d8): δ 4.18 (virtual quartet, 1.74 Hz, 4H, R-C5H4P),
4.45 (virtual triplet, 1.62 Hz, 4H, â-C5H4P), 7.76 (m, 16H,
C6H4CF3). 31P{1H} NMR (C6D6): δ 26.85 (s). IR (KBr, cm-1):
2010 (s), 1950 (s). Anal. Calcd for C40H24F12FeNiO2P2: C, 51.05;
H, 2.57. Found: C, 50.75; H, 2.76.
{P d [P (C5H4F eC5P h 5)(t-Bu )2]}2. To a solution of 104.6 mg
(0.4968 mmol) of [Pd(Cp)(allyl)] in 5 mL of toluene was added
a solution of 741.5 mg (1.043 mmol) of 1b in 2 mL of toluene.
The solution was stirred at room temperature overnight, and
the formation of a pink solid was observed. The solvent was
evaporated under reduced pressure, and pentane was added
to fully precipitate the product. The pink solid was separated
from the red solution by filtration, washed with pentane and
ether, and then dried under vacuum to obtain 60% yield of
the highly insoluble product. 1H NMR (C6D6): δ 1.16 (t, 6.0
Hz, 36H), 4.42 (br s, 4H), 5.06 (br s, 4H), 6.97-7.30 (m, 50H).
31P{1H} NMR (C6D6): δ 61.1. Anal. Calcd for C96H94Fe2P2Pd:
C, 75.46; H, 6.21. Found: C, 75.20; H, 6.10.
{P d [P (C5H4F eC5H5)(t-Bu )2][P (C5H4F eC5P h 5)(t-Bu )2]. To
a solution of 214.4 mg (0.2796 mmol) of {Pd[P(C5H4FeC5H5)-
(t-Bu)2]}2 in 20 mL of THF was added 426.8 mg of {Pd[P(C5H4-
FeC5Ph5)(t-Bu)2]}2. The suspension was stirred under N2 at
70 °C for 2 h. The resulting red solution was determined to be
a mixture of three compounds, the two starting materials and
the mixed ligand Pd(0) complex in equilibrium ratios. No
further reaction was observed after heating the solution
overnight. The solvent was then evaporated, and ether was
added to precipitate and remove {Pd[P(C5H4FeC5Ph5)(t-Bu)2]}2.
Again, the solvent was evaporated from the ether solution, and
pentane was added to precipitate the desired product as a pink/
red solid. Red crystals were obtained in 4% yield from tol-
uene/pentane upon standing two weeks at -35 °C. 1H NMR
(C6D6): δ 1.40 (d, 12.4 Hz, 18H), 1.44 (d, 12.4 Hz, 18H), 4.15
(t, 1.6 Hz, 2H), 4.29 (s, 5H), 4.34 (br t, 1.6 Hz, 2H), 4.53
(m, 2H), 5.13 (br s, 2H), 7.01-7.02 (m, 15H), 7.43-7.45 (m,
10H). 31P{1H} NMR (C6D6): δ 55.93 (d, 615.9 Hz), 61.97 (d,
615.9 Hz).
(CO)3Ni[(t-Bu )2P ((C5H4)2F e)P (t-Bu )2]Ni(CO)3. Caution:
Ni(CO)4 is highly toxic. This material was used in a well-
ventilated hood by vacuum transfer and syringe techniques.
Ni(CO)4 (20 µL, 0.15 mmol) was added by syringe to a screw-
capped NMR tube containing a Teflon-lined septum and 0.7
mL of a C6D6 solution of DtBPF (18 mg, 0.038 mmol). 31P NMR
spectrometry showed immediate conversion to product. The
solvent was then removed under vacuum from the sample
tube. The tube containing the resulting orange crystalline
residue was brought into the drybox, and the solid was
crystallized from pentane at -35 °C to give 15 mg (52%) of
1
light orange crystals. H NMR (C6D6): δ 4.48 (s, 4H), 4.30 (s,
4H), 1.08 (d, 13.2 Hz, 36 H). 31P NMR δ 65.5 (s); IR (KBr, cm-1
)
νCO 2055 (sharp), 1971 (br). Anal. Calcd for C32H44FeNi2O6P2:
C, 50.58; H, 5.84. Found: C, 50.44; H, 5.73.
(CO)3Ni[(t-Bu )2P (C5H4)F eCp ]. Caution: Ni(CO)4 is highly
toxic. This material was used in a well-ventilated hood by
vacuum transfer and syringe techniques. Ni(CO)4 (20 µL, 0.15
mmol) was added by syringe to a screw-capped NMR tube
containing a Teflon-lined septum and 0.7 mL of a C6D6 solution
of FcP(t-Bu)2 (18 mg, 0.038 mmol). 31P NMR spectrometry
showed immediate conversion to product. The solvent was then
removed under vacuum from the sample tube. The tube
containing the resulting orange crystalline residue was brought
into the drybox, and the solid was crystallized from pentane
at -35 °C to give 12 mg (47%) of light orange crystals. 1H NMR
(C6D6): δ 4.19 (virtual q, 1.5 Hz, 2H), 4.07 (s, 5H), 4.02 (m,
2H), 1.10 (d, 13.2 Hz, 36 H). 31P NMR: δ 65.8 (s). IR (KBr,
Kin etic An a lysis of th e Red u ctive Elim in a tion of 5c
a n d 6b. Into two separate vials were placed 6.2 mg (0.0050
mmol) of 5c, and into two other vials was placed 5.1 mg (0.0053
mmol) of 6b. Into each vial was added 3.5 mg (0.020 mmol) of
diphenylacetylene, 0.7 mg (0.004 mmol) of phenanthrene as
internal standard, and 0.6 mL of toluene-d8. Into one vial
containing 5c and one vial containing 6b was added 5.5 mg
(0.024 mmol) of NaO-3,5-C6H3(tBu)2. The solutions were
transferred to NMR tubes, frozen under N2(l), and flame-
sealed. The entire tubes were simultaneously submerged in
an oil bath maintained at a constant 105 °C. Prior to obtaining
cm-1): νCO 2055 (sharp), 1966 (br). Anal. Calcd for C32H44
-
FeNi2O6P2: C, 53.33; H, 5.75. Found: C, 53.50; H, 5.91.
(F cP -i-P r 2)2P d . (Cp)Pd(allyl) (0.100 g, 0.470 mmol) and
FcP(i-Pr)2 (0.426 g, 1.41 mmol) were dissolved in 15 mL of
benzene. After 3 h, the solvent was evaporated under vacuum
and the orange solids were redissolved in pentane (10 mL).
The solution was filtered through Celite, concentrated, and
cooled to -35 °C to give 108.5 mg of product in 33% yield.
1H NMR (C6D6): δ 1.29 (q, 6.9 Hz, 12H, CHMe2), 1.39 (q, 7.5
Hz, 12H, CHMe2), 1.98 (sept of d, 7.0 Hz and 1.8 Hz, 4H,
CHMe2), 4.12 (br s, 4H, C5H4P), 4.35 (br s, 4H, C5H4P), 4.44
(s, 10H, C5H5). 13C{1H} NMR (C6D6): δ 20.33 (t, 3.2 Hz,
CHMe2), 21.11 (t, 5.4 Hz, CHMe2), 26.02 (t, 9.1 Hz, CHMe2),
69.58 (t, 2.2 Hz, â-C5H4P), 70.56 (s, C5H5), 72.11 (t, 5.3 Hz,
R-C5H4P), 77.13 (t, 11.6 Hz, i-C5H4P). 31P{1H} NMR (C6D6): δ
32.77(s). Anal. Calcd for C32H46Fe2P2Pd: C, 54.07; H, 6.52.
Found: C, 53.85; H, 6.40.
1
periodic H NMR spectra for kinetic analysis, the tubes were
removed from the bath and submerged in ice for at least 5
min.
P h osp h in e Dep en d en ce on th e Red u ctive Elim in a tion
fr om 5c. Into four separate vials were weighed 5c (5.0
mg, 0.0052 mmol) and the appropriate amount of DPPF
(5.3 mg, 0.0096 mmol; 12 mg, 0.022 mmol; 19 mg, 0.033 mmol;
or 22 mg, 0.040 mmol). Phenanthrene (0.8 mg, 0.005 mmol)
was added as internal standard. Into each vial was syringed
0.6 mL of toluene-d8. The solutions were transferred to NMR
tubes, frozen in N2(l), and flame-sealed. The samples were
heated at 105 °C and were monitored periodically by 1H NMR.
Red u ctive Elim in a tion fr om 3, 5a , 5b, 6a , 7b, a n d 11a .
For reactions of compound 3, 3-5 mg of 3, ca. 1.5 mg of sodium
aryloxide, and ca. 2 mg of 1,3,5-trimethoxybenzene as internal
standard were placed into a vial. For experiments with 5a ,
5b, 6a , and 7b, ca. 3 mg of the complex and ca. 1 mg of 1,3,5-
trimethoxybenzene as internal standard were placed into vials.
For experiments with 11a , a vial was charged with 3.3 mg of
11a and ca. 1.7 mg of 1,3,5-trimethoxybenzene as internal
{P d [P (C5H4F eC5H5)(t-Bu )2]}2. To a solution of 392.1 mg
68
(0.5480 mmol) of Pd[P(o-tolyl)3]2 in 5 mL of THF was added
365.9 mg (1.108 mmol) of P(C5H4FeC5H5)(t-Bu)2. The solution
was heated in a sealed vial under N2 at 65 °C for 1 h. The
solvent was then removed under vacuum in the drybox. The
resulting orange solid was redissolved in pentane, filtered

Reductive Elimination of Diaryl Ethers from Pd(II)
Organometallics, Vol. 22, No. 13, 2003 2789
standard. A 1H NMR spectrum was obtained of each mix-
ture in toluene-d8. Into a separate vial was placed the
appropriate amount of either PPh3-d15, PhCCPh, DPPF, D-t-
BPF, CF3-DPPF, FcP(t-Bu)3, or P(t-Bu)3. The NMR sample was
poured into the vial of ligand and was returned to the NMR
sample tube. The mixture was heated at the appropriate
temperature until complete reaction had occurred, as judged
1a , pentaphenyl ligand 1b, or binaphthyl ligand 1c. The NMR
sample was poured into the vial of ligand, and the mixture
was returned to the NMR tube. The resulting solution was
heated at 60 °C until complete reaction had occurred, as
determined by 1H and 31P{1H} NMR spectroscopy. Integration
of the final 1H NMR spectrum and comparison with the initial
spectrum provided the yield of diaryl ether.
by H and 31P NMR spectroscopy. Integration of the final H
NMR spectrum and integration of the product and internal
standard signals in the final gas chromatogram (corrected for
response factors) provided the yields of Pd(0) complex and the
yields of diaryl ether.
Red u ctive Elim in a tion of Dia r yl Eth er fr om 11a :
Rep r esen ta tive P r oced u r e. A vial was charged with 6.0 mg
(0.0046 mmol) of complex 11a . 1,3,5-Trimethoxybenzene (1.8
mg, 0.011 mmol) was added as internal standard, and the
solids were dissolved in 0.6 mL of C6D6. A 1H NMR spectrum
was obtained. Into a separate vial was weighed either ligand
1
1
Ack n ow led gm en t. This work was supported by the
NIH (GM55382). We thank J ohnson-Matthey for a gift
of palladium salts and Merck Research Laboratories for
support.
Su p p or tin g In for m a tion Ava ila ble: Procedures and full
tables of crystallographic data for 2a , 2c, 7a , and 11b.
OM030230X