Mechanistic studies of the palladium-catalyzed amination of aryl halides and the oxidative addition of aryl bromides to Pd(BINAP)2 and Pd(DPPF)2: An unusual case of zero-order kinetic behavior and product inhibition

Article abstract of DOI:10.1021/ja9944599

Mechanistic studies of the amination of aryl bromides catalyzed by palladium complexes containing the chelating phosphines BINAP and DPPF are reported. The coupling of primary alkyl- and arylamines, secondary cyclic alkylamines, and secondary arylalkylamines with bromoarenes in the presence of stoichiometric base and Pd(BINAP)₂ (1a) as catalyst, and the reaction of aniline with 4-Br-C₆H₄-t-Bu in the presence of base catalyzed by Pd(DPPF)₂ (2), were studied. The stoichiometric oxidative additions of PhBr to 1a and to 2 were turnover limiting, and kinetic studies were also conducted on this individual step. The stoichiometric oxidative addition of PhBr to 1a showed an inverse first-order dependence on added ligand when the PhBr concentration was low but depended solely on the rate of chelating ligand dissociation at high [PhBr]. There was no measurable solvent effect. In addition, the rates were indistinguishable in the presence and in the absence of amines and salts that are present in the catalytic amination reactions. Similar qualitative data for the oxidative addition of PhBr to 2 was obtained by ¹H NMR spectroscopy. The observed rate constants for the overall amination reactions catalyzed by 1a were shown to be zero order in aryl halide, amine, base, and added ligand, while they were first order in catalyst. These data indicated that the kinetic behavior of the overall reaction was dictated solely by the rate of ligand dissociation from 1a, as observed for the oxidative addition. When secondary amines were used, deviation from this behavior was observed. This anomalous behavior resulted from decay of catalyst rather than a change in the turnover-limiting step. A catalyst decomposition pathway that involves backbone P-C bond cleavage of the chelating bisphosphine ligands was revealed by the stoichiometric oxidative addition studies. Quantitative rate data were also obtained for reaction of 4-Br-C₆H₄-t-Bu with aniline in the presence of base catalyzed by 2. The observed rate constants were zero order in amine and base, inverse first order in added ligand, and first order in aryl bromide. At low concentration of added ligand, the reaction appeared to be first order in amine. However, this deviation from the expected behavior was due to reversible reaction of the catalyst with product.

Full text of DOI:10.1021/ja9944599

4618
J. Am. Chem. Soc. 2000, 122, 4618-4630
Mechanistic Studies of the Palladium-Catalyzed Amination of Aryl
Halides and the Oxidative Addition of Aryl Bromides to Pd(BINAP)2
and Pd(DPPF)2: An Unusual Case of Zero-Order Kinetic Behavior
and Product Inhibition
Luis M. Alcazar-Roman,† John F. Hartwig,*,† Arnold L. Rheingold,‡
Louise M. Liable-Sands,‡ and Ilia A. Guzei‡
Contribution from the Department of Chemistry, Yale UniVersity, P.O Box 208107,
New HaVen, Connecticut 06520-8107, and Department of Chemistry and Biochemistry,
UniVersity of Delaware, Newark, Delaware 19716
ReceiVed December 21, 1999
Abstract: Mechanistic studies of the amination of aryl bromides catalyzed by palladium complexes containing
the chelating phosphines BINAP and DPPF are reported. The coupling of primary alkyl- and arylamines,
secondary cyclic alkylamines, and secondary arylalkylamines with bromoarenes in the presence of stoichiometric
base and Pd(BINAP)2 (1a) as catalyst, and the reaction of aniline with 4-Br-C6H4-t-Bu in the presence of base
catalyzed by Pd(DPPF)2 (2), were studied. The stoichiometric oxidative additions of PhBr to 1a and to 2 were
turnover limiting, and kinetic studies were also conducted on this individual step. The stoichiometric oxidative
addition of PhBr to 1a showed an inverse first-order dependence on added ligand when the PhBr concentration
was low but depended solely on the rate of chelating ligand dissociation at high [PhBr]. There was no measurable
solvent effect. In addition, the rates were indistinguishable in the presence and in the absence of amines and
salts that are present in the catalytic amination reactions. Similar qualitative data for the oxidative addition of
1
PhBr to 2 was obtained by H NMR spectroscopy. The observed rate constants for the overall amination
reactions catalyzed by 1a were shown to be zero order in aryl halide, amine, base, and added ligand, while
they were first order in catalyst. These data indicated that the kinetic behavior of the overall reaction was
dictated solely by the rate of ligand dissociation from 1a, as observed for the oxidative addition. When secondary
amines were used, deviation from this behavior was observed. This anomalous behavior resulted from decay
of catalyst rather than a change in the turnover-limiting step. A catalyst decomposition pathway that involves
backbone P-C bond cleavage of the chelating bisphosphine ligands was revealed by the stoichiometric oxidative
addition studies. Quantitative rate data were also obtained for reaction of 4-Br-C6H4-t-Bu with aniline in the
presence of base catalyzed by 2. The observed rate constants were zero order in amine and base, inverse first
order in added ligand, and first order in aryl bromide. At low concentration of added ligand, the reaction
appeared to be first order in amine. However, this deviation from the expected behavior was due to reversible
reaction of the catalyst with product.
Introduction
and carbonyl R-arylations.43-46 They also catalyze the recently
developed conversion of aryl halides and sulfonates to amines
and ethers.47,48 Many of these cross-coupling reactions involve
aryl halide or sulfonate electrophiles and are initiated by
Palladium complexes chelated by diphosphine ligands cata-
lyze cross-coupling reactions that form C-C bonds, such as
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† Yale University.
‡ University of Delaware.
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10.1021/ja9944599 CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/02/2000

Unusual Zero-Order Kinetic BehaVior and Product Inhibition
J. Am. Chem. Soc., Vol. 122, No. 19, 2000 4619
oxidative addition of the aryl halide or sulfonate to a Pd(0)
complex that is typically ligated by phosphine ligands.49-53 The
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that form organylpalladium hydrocarbyl, amido, and alkoxo
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complexes by olefin insertion.53 In most cases, the “resting state”
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[1,1′-bis(diphenylphosphino)ferrocene (DPPF) and 2,2′-bis-
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4620 J. Am. Chem. Soc., Vol. 122, No. 19, 2000
Alcazar-Roman et al.
Scheme 1
complex is transformed into the cis arylpalladium amido
complex by base and amine. Reductive elimination forms the
final arylamine product. Because of the absence of mechanistic
data on the initial step and the overall cycle, it is not clear which
steps are reversible, which step is irreversible and turnover
limiting, and whether product coordination can inhibit reaction
rates. Moreover, potential pathways for catalyst decomposition
are unknown. For these reasons, we have conducted a kinetic
study of the catalytic amination of aryl bromides and of the
first step in the catalytic cycle, the oxidative addition of aryl
bromides to Pd(DPPF)2 and Pd(BINAP)2.
We report the identification of bis-BINAP and bis-DPPF Pd-
(0) complexes as the dominant resting state in the catalytic cycle
for the amination of aryl bromides and the identification of free
Pd(chelate) as the intermediate that undergoes oxidative addition
of the aryl halide. The activity of Pd(chelate)2 toward oxidative
addition of aryl halides conflicts with that reported by Ama-
tore.51 Further, our studies on the stability of arylpalladium
halide complexes revealed a pathway for decomposition of
palladium aryl halide complexes containing DPPF and BINAP
as ligand. This decomposition pathway generates monodentate
ligands and could, therefore, have an impact on catalyst
selectivity and activity. Moreover, catalyst decomposition and
product inhibition provide unexpected kinetic behavior with
some amine substrates.
Figure 1. ORTEP drawing of Pd[(R)-Tol-BINAP]2.
cream-colored solid that does not oxidatively add iodobenzene
at room temperature.51 Broadwood-Strong prepared light yellow
Pd(DPPF)2 by displacement of ethylene in (DPPE)Pd(C2H4) by
excess DPPF.74 We generated Pd(DPPF)2 as a yellow powder
by reacting 2 equiv of DPPF with Pd[P(o-Tol)3]2 in benzene.
The same 31P{1H} chemical shift of 7.5 ppm as for the previous
yellow material was observed, but the sample contained two
impurities. One of these was identified as free DPPF, and the
second was assigned the dinuclear structure [(DPPF)Pd]2(µ-
DPPF) (3), due to its doublet and triplet 31P{1H} NMR
resonances in a 2:1 ratio. We were unable to obtain pure bulk
samples of 3, but a single crystal was selected and the structure
was confirmed by X-ray analysis. An ORTEP diagram of 3 is
shown in Figure S1 (Supporting Information). This synthetic
work suggested that the two complexes existed in equilibrium.
This assertion was demonstrated by addition of small amounts
of Pd[P(o-Tol)3]2 to a solution of DPPF in THF. When DPPF
is present in excess amounts, a singlet resonance for coordinated
ligand in 2 was observed. After addition of greater than 0.5
equiv of Pd[P(o-Tol)3]2, doublet and triplet signals due to 3 were
observed. Further addition of Pd[P(o-Tol)3]2 led to increasing
amounts of 3 at the expense of 2.
Identification of the Catalyst Resting State. To determine
the resting state of the palladium catalyst for various amination
reactions, we conducted catalytic reactions with amine and either
bromobenzene or 4-Br-C6H4-t-Bu and sodium tert-butoxide base
in the presence of 10 mol % of catalyst in toluene solvent.
Reactions catalyzed by DPPF-ligated palladium were initiated
by a combination of (DPPF)Pd(4-C6H4-t-Bu)Br (4) and DPPF.
Reactions catalyzed by BINAP-ligated palladium were initiated
by 1a. The only species observed by 31P{1H} NMR spectroscopy
for the reaction of primary amines with bromobenzene catalyzed
by BINAP-ligated palladium was Pd(BINAP)2. Reactions
containing P(o-tolyl)3 as internal standard showed less than 15%
loss of Pd(BINAP)2 at the end of the reaction. The only species
observed by 31P{1H} NMR spectroscopy for reaction of aniline
and 4-Br-C6H4-t-Bu catalyzed by DPPF-ligated palladium at
early reaction times was Pd(0) complex 2. The identity of the
resting state for other reactions was less straightforward and
will be discussed below. These data suggest that oxidative
Results
Synthesis and X-ray Structural Study of (Chelate)2Pd(0)
Complexes. Preliminary experiments in our laboratory suggested
that the resting state of the palladium catalyst was a palladium(0)
complex. Thus, we prepared the homoleptic palladium(0) com-
plexes of DPPF and BINAP. One published synthesis of Pd-
(BINAP)2 (1a) involves reaction of (η-Cp)Pd(η-allyl) and (R)-
BINAP and recrystallization of the product from CH2Cl2 and
ether. We prepared Pd(BINAP)2 in 87% isolated yield by the
addition of 2 equiv of either resolved or racemic BINAP to
Pd[P(o-Tol)3]2 in benzene. Only one 31P{1H} resonance at 27.4
ppm was observed for the product in all cases, indicating that
Pd[(R)-BINAP][(S)-BINAP] is not formed or, less likely, that
its 31P{1H} resonance is indistinguishable from those of Pd-
[(R)-BINAP]2 and Pd[(S)-BINAP)]2. Pd[(R)-Tol-BINAP]2 (1b)
was prepared similarly, and it was isolated in 66.8% yield as
single crystals after the reaction mixture was layered with
pentane. An ORTEP diagram of 1b is provided in Figure 1.
This structure can be described as a distorted tetrahedron. The
two P-Pd-P angles containing phosphorus atoms of the same
(R)-Tol-BINAP ligand are 90.87(9)° and 90.84(9)°. The other
two P-Pd-P angles are 122.79(9)° and 120.31(9)°.
The synthesis of Pd(DPPF)2 (2) was less straightforward.
There are conflicting reports about the preparation of this
compound. Amatore51 and Hor73 reported the borohydride
reduction of (DPPF)PdCl2 in the presence of DPPF to form a
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Polyhedron 1993, 12, 721-729.

Unusual Zero-Order Kinetic BehaVior and Product Inhibition
J. Am. Chem. Soc., Vol. 122, No. 19, 2000 4621
Figure 2. ORTEP drawing of the backbone P-C cleavage product 6.
Scheme 2
Figure 3. Determination of the order in BINAP for the oxidative
addition of PhBr to 1a.
scopically after heating of [(DPPF)Pd(Ph)(Br)] at 130 °C in
toluene-d8 or xylenes for 18 h. In DMA solvent, this reaction
occurred in 6 h at 100 °C. These two reactions constitute an
unusual type of P-C bond cleavage and make it possible that
the palladacyclic materials could be produced during catalytic
reactions in which there is a substantial lifetime of the aryl halide
complex. Although the reaction of the DPPF complex occurred
less rapidly than that of [(BINAP)Pd(Ph)(Br)], this ligand
transformation could be important for reactions involving
[(DPPF)Pd(Ar)(Br)] at high temperatures in polar solvents.
Mechanism of Aryl Halide Oxidative Addition to Pd-
(Chelate)2. Although BINAP-ligated aryl halide complex 5 is
unstable toward backbone cleavage and aryl group exchange,
this instability does not affect the rate of oxidative addition of
aryl halides to Pd(0) 1a. Complex 1a displays a metal-to-ligand
charge-transfer band centered at 520 nm, which gives it its deep
wine red color. Due to the difficulty in isolating pure DPPF
complex 2, the stoichiometric oxidative addition to this material
was studied qualitatively; detailed studies were conducted on
the catalytic cycle as described in a later section.
Rate constants for oxidative addition were obtained at 45 °C
by UV-vis spectroscopy of reactions that contained a concen-
tration of 1a of 2.26 × 10-5 M, concentrations of aryl bromide
between 1.78 × 10-3 and 8.95 × 10-2 M, and concentrations
of BINAP ranging from 3.60 × 10-5 to 2.98 × 10-4 M. A
typical kinetic plot for the decay of 1a is given in Figure S2.
The dependence of the reaction rate constant on [BINAP] was
measured using a constant concentration of [PhBr] equal to 1.78
× 10-3 M. A plot of 1/kobs versus [BINAP] is shown in Figure
3. The dependence of reaction rate on [PhBr] was measured
with a constant 5.40 × 10-4 M concentration of BINAP (Figure
4 and double reciprocal plot in Figure S3). Figure 4 illustrates
that the measured rate constant displays saturation behavior at
high concentrations of [PhBr]. At 1.78 × 10-3 M concentration
of PhBr, reaction rates were within 8% of each other in benzene,
toluene, THF, and 2,5-dimethyl-THF solvent (Table 1). Reac-
tions with structurally diverse ortho-substituted aryl halides were
conducted using a concentration of 8.9 × 10-1 M aryl halide,
which is in the region of the curve in Figure 4 that should display
zero-order behavior in [ArBr]. The values of kobs for reaction
of 2-bromoanisole, 2-bromotoluene, and 2-bromo-p-xylene all
showed rate constants that were within experimental error of
that for the addition of bromobenzene to 1a (Table 2). Rate
constants obtained in the presence of tetradecylamine and Bu4-
NPF6 in THF solvent were indistinguishable from those obtained
addition is turnover limiting. When the convenient mixture of
Pd(OAc)2 and 1-2 equiv of BINAP or DPPF as catalyst was
used, 1a and 2 formed within minutes after addition of amine
and base and heating in the NMR spectrometer probe at 75 °C.
In contrast to observations made on the asymmetric Heck
reaction using BINAP as ligand, there was no detectable
resonance for the monoxide of either BINAP or DPPF.50,75,76
Reactions of (Chelate)2Pd(0) Complexes with Aryl Bro-
mides. The observation of (chelate)2Pd(0) complexes as the
resting state prompted us to study the oxidative addition of aryl
bromides to BINAP complex 1a and DPPF complex 2. The
reaction of 4-bromobenzaldehyde with 1a occurred in 99% yield
as determined by 1H NMR spectroscopy employing an internal
standard. The addition of PhBr to 2 occurred in 89% yield, in
contrast to previous assertions that Pd(DPPF)2 does not react
with aryl halides.51 The oxidative addition of bromobenzene to
1a was less straightforward. Heating 1a in the presence of 5
equiv of PhBr at 65 °C produced (BINAP)Pd(Ph)(Br) (5) at
initial stages of the reaction, but signals due to 5 decayed during
later stages and were replaced by two doublets with a trans JPP
value due to two mutually trans phosphine ligands. The material
corresponding to these signals, complex 6 in Scheme 2 and
Figure 2, contains a coordinated PPh3 and a palladacyclic
structure. Palladacyclic complex 6 displays a small dihedral
angle between the naphthyl groups of 51° and displays severe
deviations from ideal geometry at the metal. The square plane
is distorted into a saddle shape, with each pair of trans
substituents bent out of the plane in opposite directions.
Complex 6 is formed by P-C bond cleavage of the ligand
backbone in (BINAP)Pd(Ph)(Br). The P-C cleavage reaction
was also observed with pure 5 prepared by the reaction of {Pd-
[P(o-Tol)3}(Ph)(µ-Br)}2 (7) with BINAP. The P-C cleavage
process was accelerated in more polar solvents, such as THF
or DMA.
The formation of the analogous product from backbone P-C
bond cleavage of [(DPPF)Pd(Ph)(Br)] was identified spectro-
(75) Grushin, V. V. J. Am. Chem. Soc. 1999, 121, 5831-5832.
(76) Ozawa, F.; Kubo, A.; Matsumoto, Y.; Hayashi, T. Organometallics
1993, 12, 4188-4196.

4622 J. Am. Chem. Soc., Vol. 122, No. 19, 2000
Alcazar-Roman et al.
Table 3. Rate Constants for Reaction of Amines with
Bromobenzene Catalyzed by 1a
amine
kobs (× 10 -5 s-1 mol-1 L)
hexylamine
sec-butylamine
benzylamine
p-anisidine
aniline
3.2
3.1
2.8
3.0
2.3
order rate behavior in [ArBr] for the oxidative addition reaction
at large ratios of [ArBr]/[BINAP] should provide an unusual
kinetic situation for the overall catalytic process. The catalytic
reactions contain a much larger concentration of substrate than
free ligand, creating a system that would show zero-order rate
behavior in aryl bromide, ligand, and all substrates that react
after the turnover-limiting step. Thus, the rate of the catalytic
cycle should depend only on the concentration of catalyst. We
conducted studies on the reaction of aryl halides with primary
alkylamines catalyzed by Pd(BINAP)2 as catalyst to test these
predictions. In addition, we studied the arylation of aniline using
(DPPF)Pd(4-C6H4-t-Bu)Br as catalyst to determine if the
qualitative behavior of aryl bromide oxidative addition to Pd-
(DPPF)2 would be observed in quantitative rate studies on the
catalytic system. Both of these reactions occur in high yield.
Reactions of secondary alkylamines with aryl halides using
either catalyst gave variable yields of N,N-dialkylarylamines.
Thus, we also studied the kinetics of the addition of N-
methylaniline, N-methylpiperazine, piperidine, and morpholine
to phenyl bromide catalyzed by Pd(BINAP)2.
Figure 4. Plot of the observed rate constant vs concentration of PhBr
for the oxidative addition of PhBr by 1a.
Table 1. Solvent Effect on the Oxidative Addition of PhBr to 1a
solvent
kobs (× 10-5 s-1
)
benzene
9.9
7.3
8.1
7.2
THF
toluene
2,5-dimethyl-THF
Table 2. Rate Constants for Oxidative Addition of Different Aryl
Bromides to 1a
aryl bromide
kobs (× 10-4 s-1
)
2-bromoanisole
2-bromo-p-xylene
2-bromotoluene
3.9
4.4
4.0
Kinetic Behavior of Reactions of Primary Amines with
Aryl Halides. When Pd(BINAP)2 was used as catalyst, the
reactions were typically conducted at 60 °C with the soluble
alkoxide base NaOC(Et)3, added BINAP, bromobenzene, and
an internal standard (ferrocene or 1,3,5-trimethoxybenzene) in
benzene-d6. Final concentrations of the reaction components
were 1.25 mM Pd(BINAP)2, 1.25-7.98 mM BINAP, 0.1363-
0.500 M NaOC(Et)3, and 0.800-1.60 M PhBr and 12.6 mM
amine. The reactions were monitored by 1H NMR spectroscopy.
Both decay of amine and appearance of product were monitored
when possible. Monitoring of the reactions of primary amines
by 31P{1H} NMR spectroscopy showed that no appreciable
consumption of catalyst 1a occurred (Figure S4). There was at
most a decrease of 15% of the intensity of the resonance
corresponding to 1a vs internal standard (P[o-Tol]3) during this
reaction.
Linear plots of concentration of starting material vs time were
obtained for reactions of hexylamine, sec-butylamine, benzyl-
amine, p-anisidine, and aniline (Figure S5 for hexylamine).
These data demonstrate that the reactions are zero order in
amine. Moreover, all amines, with the single exception of
aniline, gave reaction rates that were within experimental error
of the rate obtained from hexylamine (Table 3). The rate
obtained when aniline was used under the same reaction
conditions was roughly 75% of the magnitude of the rates
obtained for reactions of other amine substrates. The reaction
was determined to be zero order in [BINAP], [PhBr], and
[NaOC(Et)3] by conducting experiments with the concentration
of reagents in the ranges provided above (Table 4).
in their absence. Reactions run in the presence of NaOtBu
deviated from first-order behavior due to the reaction of the
oxidative addition product (BINAP)Pd(Ph)Br with alkoxide to
re-form Pd(0) and generate arenes, biaryls, and small amounts
of tert-butyl aryl ethers.77 The oxidative addition rate constant
at 60 °C in the saturation region of Figure 4 with [1a] equal to
2.26 × 10-5 M, [BINAP] equal to 5.40 × 10-4 M, and [PhBr]
equal to 8.95 × 10-2 M was 3.4 × 10-3 s-1, which is roughly
an order of magnitude greater than the rate measured at 45 °C
((4.3 ( 0.13) × 10-4 s-1).
Although not measured quantitatively, the oxidative addition
of PhBr to DPPF complex 2 showed a similar inverse
dependence on phosphine concentration and positive rate
dependence on [ArBr]. However, saturation of the observed rate
constant at high [ArBr] was not observed. Even at concentrations
of ArBr as high as 0.1 M, the reaction showed a positive
dependence on [ArBr] and an inverse dependence on [DPPF].
Kinetic Behavior of the Catalytic Reactions. In general,
the kinetic behavior of a catalytic cycle is dictated by the kinetic
behavior of the turnover-limiting stoichiometric reaction if this
reaction lies directly on the catalytic cycle. In this case, the rate
law for the reaction of the resting state of the catalyst with
substrate is identical to that of the catalytic system if the reaction
of the resting state is irreversible. However, several differences
between stoichiometric and catalytic reactions can be observed.
For example, the resting state may not lie on the catalytic cycle,
catalysts can decompose, products can inhibit reactions, and
reaction byproducts or additives can affect the rate of the
turnover-limiting step.
Kinetic Behavior of Reactions of Secondary Amines with
Aryl Halides. Reactions employing the secondary cyclic amines
morpholine, piperidine, and N-methylpiperazine and the reaction
employing the acyclic secondary amine N-methylaniline dis-
played plots of amine concentration versus time that resembled
plots of a reaction that was first order in amine (Figure 5). In
some cases, starting amine remained after long reaction times.
Thus, we sought to determine if the kinetic behavior of the
palladium-catalyzed amination could be simply predicted from
the kinetics of the oxidative addition. In particular, the zero-
(77) Mann, G.; Hartwig, J. F. J. Am. Chem. Soc. 1996, 118, 13109-
13110.

Unusual Zero-Order Kinetic BehaVior and Product Inhibition
J. Am. Chem. Soc., Vol. 122, No. 19, 2000 4623
Table 4. Rate Constants for Reaction of Hexylamine with
Bromobenzene Catalyzed by 1a, as a Fucntion of Bromobenzene,
BINAP, and Base Concentrations
kobs
kobs
kobs
[BINAP] (× 10-5 s-1 [ArBr] (× 10-5 s-1 [NaOR] (× 10-5 s-1
(mM)
mol-1 L)
(M)
mol-1 L)
(M)
mol-1 L)
1.3
2.6
4.0
5.3
6.6
8.0
3.2
3.2
3.1
2.6
3.0
3.1
0.800
1.000
1.200
1.400
1.600
3.2
2.7
2.8
2.7
3.0
0.136
0.200
0.300
0.400
0.500
3.2
3.0
2.9
3.4
2.9
Figure 6. Decay of aniline during its reaction with bromobenzene
catalyzed by 2. [DPPF] ) 2.0 mM (inset) and [DPPF] ) 21.6 mM.
Figure 5. Decay of N-methylaniline during the reaction of N-
methylaniline with bromobenzene catalyzed by 1a.
spectra of the aromatic region contained too many components
to determine unambiguously that this material was present. The
backbone P-C cleavage is one of several decomposition
pathways to form catalytically inactive, homogeneous products.
No black palladium-containing material precipitated.
At first glance, these data suggest a change in resting state to
one that reacts with amine.
To determine if the resting state had indeed changed, we
assessed whether oxidative addition was faster than the steps
that follow it in the catalytic cycle when secondary amine
substrates were used. Reaction of lithium morpholide with a
mixture of 5 and BINAP (Pd/L ratio 1:2) gave N-phenylmor-
pholine rapidly at room temperature in high yield. The reaction
of morpholine and NaOC(Et)3 with 5 and ligand also showed
the rapid formation of N-phenylmorpholine without the forma-
tion of any intermediate with a lifetime long enough to detect
by 31P{1H} NMR spectroscopy. Thus, oxidative addition is
much slower than the reaction of any arylpalladium(II) inter-
mediates with amine or base, and the resting state should be a
Pd(0) complex and not a species that reacts with amine.
These apparently conflicting data were explained by careful
examination of the concentration of Pd(BINAP)2 during the
catalytic reactions. In contrast to results from monitoring the
reactions of primary amines catalyzed by 1a, monitoring of
the reaction between N-methylaniline and bromobenzene by
31P{1H} NMR spectroscopy using P(o-tolyl)3 as an internal
standard revealed that 1a was gradually consumed (Figure S6).
Thus, the reduction of reaction rate with conversion was due to
catalyst decomposition, not to a change in resting state and a
resulting rate dependence on amine.
Kinetic Studies of Reactions Catalyzed by Pd(DPPF)2.
Quantitative rate studies on the reaction of aniline with 4-Br-
C6H4-t-Bu were conducted at 60 °C on samples containing 2.0
mM [(DPPF)Pd(4-C6H4-t-Bu)Br], 4.0-38.9 mM DPPF, 0.800-
3.200 M 4-Br-C6H4-t-Bu, 0.200-0.563 M NaOC(Et)3, and 20
mM aniline. Plots of the concentration of aniline versus time
were not linear, again suggesting the possibility that aniline is
involved in the rate-determining step of the catalytic cycle
(Figure 6, top). In contrast, the decay of amine was linear for
reactions containing concentrations of DPPF ranging from 17.9
to 80.2 mM (Figure 6, bottom). Under these conditions, the rate
of the reaction was first order in aryl halide. The catalytic
reaction showed no saturation of the observed rate constant at
high [ArBr]. The reactions were inverse first order in DPPF in
the concentration ranges indicated above and zero order in the
alkoxide base.
Monitoring of the reaction of aniline with 4-Br-C6H4-t-Bu
by 31P{1H} spectroscopy revealed why the decay of amine
during reactions at low [DPPF] was nonlinear. The catalyst was
gradually converted to the arylpalladium diarylamido complex
(DPPF)Pd(4-C6H4-t-Bu)[N(Ph)(4-C6H4-t-Bu)] (8) and free DPPF,
as determined by 31P{1H} NMR spectroscopy (Figure S7). Aryl-
palladium amido complexes of this class have been isolated and
studied previously.79 Complexes electronically similar to 8
undergo first-order reductive elimination at the higher temper-
ature of 75 °C, with a half-life on the order of 10 min.79 Thus,
This consumption of 1a generated free BINAP and small
amounts of other phosphorus-containing compounds. Addition
of DMPE to the reaction solution to liberate coordinated
arylphosphines generated several new 31P{1H} NMR resonances,
one of which was identical to that of free 2-diphenylphosphino-
1,1′-binaphthyl,78 which would be formed by the backbone
cleavage process described above. Unfortunately, 1H NMR
(78) Uozumi, Y.; Suzuki, N.; Ogiwara, A.; Hayashi, T. Tetrahedron 1994,
50, 4293-4302.
(79) Driver, M. S.; Hartwig, J. F. J. Am. Chem. Soc. 1997, 119, 8232-
8245.

4624 J. Am. Chem. Soc., Vol. 122, No. 19, 2000
Alcazar-Roman et al.
the lifetime of this species in the catalytic system at 60 °C is
similar to that of the DPPF-ligated Pd(0) species, and the
presence of one or the other as a resting state depends on the
concentration of product and the concentration of added DPPF.
Early in the reaction, the concentration of diarylamine and,
therefore, diarylamido complex are low. At high [DPPF], the
rate of oxidative addition becomes slower than reductive
elimination or exchange of the diarylamido ligand with aniline
because of the inverse dependence of the oxidative addition kobs
on [ArBr]. The sole resting state becomes the Pd(0) complex
2, and linear plots of the decay of aniline are observed at high
[DPPF], as was shown in Figure 6.
Scheme 3
Discussion
reductive elimination is likely to be rate determining in
alcohol77,86-89 and azole arylation.64,90 The C-C bond-forming
processes are often run in DMF or other polar solvents. In many
of these reactions, BINAP has been used as a ligand for
enantioselection or simply as an effective supporting ligand.16,22-30
Thus, backbone P-C bond cleavage may lead to a change in
catalyst structure for these processes when a chelating phosphine
is used.
Mechanism of Aryl Halide Oxidative Addition to Pd-
(BINAP)2 and Pd(DPPF)2. Potential mechanisms for the oxida-
tive addition of aryl bromides to Pd(chelate)2 (chelate ) DPPF,
BINAP) are shown in Scheme 3. Path A involves the associative
displacement of an arm of the chelating ligand with aryl
bromide, followed by carbon-halogen bond cleavage by the
18-electron Pd(0) complex containing intact, coordinated aryl
bromide. The rate law in eq 1 for this mechanism predicts a
reaction that is first order in aryl bromide and zero order in
added ligand.
Resting State and (In)stability of ArBr Complexes. Ama-
tore50 and Ozawa76 reported that the reduction of Pd(OAc)2 in
solutions containing triphenylphosphine50 or BINAP76 forms
phosphine oxide and acetic anhydride. We observed no signals
due to the monophosphine oxide of either DPPF or BINAP when
Pd(OAc)2 was used as a catalyst precursor,75 and phosphine-
ligated Pd(0) forms more rapidly in the presence of amine and
base than in their absence. 31P{1H} NMR spectroscopy of
reactions containing less than 2 equiv of ligand per palladium
showed a single phosphine complex as the resting state. In such
cases, a catalytically inactive, but soluble, phosphine-free
palladium complex may exist, or the remaining palladium may
simply precipitate from solution.80
The identity of the resting state depended on the phosphine
ligand and type of amine substrate. Although not all of the
pathways for decomposition of catalysts were determined, the
BINAP-ligated palladium complex was unstable during reactions
of secondary amines. The decomposition of the BINAP-ligated
palladium catalyst is consistent with a lower reactivity of this
catalyst toward secondary amines than toward primary amines.
It is also consistent with the need for higher catalyst loadings
with this class of substrate.48 Similarly, the DPPF-ligated
palladium(0) resting state was partially converted to an unpro-
ductive arylpalladium(II) diarylamido resting state. The observa-
tion of the arylpalladium diarylamido complex 8 is consistent
with the competing formation of triarylamines during the
reaction of anilines with unhindered aryl halides. The accumula-
tion of 8 as resting state occurs because the rate for reductive
elimination of triarylamine from 8 is similar to the qualitatively
determined rate of oxidative addition of bromobenzene to 2.
Irreversible cleavage of the backbone P-C bonds in BINAP
and DPPF ligands is unusual. This cleavage process is more
rapid for (BINAP)Pd(Ph)Br than for (DPPF)Pd(Ph)Br. The
cleavage reaction for both compounds was slower than the
reactions of the arylpalladium halides with primary amines
during catalytic reactions, but it may account for some of the
catalyst decomposition during reactions of secondary amines
catalyzed by BINAP-ligated palladium. Moreover, this cleavage
process may be an important catalyst decomposition pathway
for other palladium-catalyzed processes that involve an aryl-
palladium halide resting state, particularly when polar solvents
are used. For example, olefin insertion is often rate determin-
ing in Heck reactions,81 transmetalation is often rate determining
in Stille or Suzuki reactions,82-85 and transmetalation or
Path A:
k1k2[ArBr]
kobs
)
(1)
k-1 + k2
Path B involves reversible dissociation of an arm of the bis-
phosphine ligand, followed by irreversible associative displace-
ment of the monocoordinated ligand, or irreversible carbon-
halogen bond cleavage by the 16-electron species. The rate law
for path B (eq 2) predicts that kobs will, again, show a zero-
order dependence on free ligand concentration.
Path B:
k1k2[ArBr]
k-1
1
1
kobs
)
)
+
(2)
kobs k1
k-1 + k2[ArBr]
k1k2[ArBr]
Path B may, however, show a dependence of reaction rate on
aryl bromide concentration that varies with [ArBr]. It is possible
that zero-order behavior would be observed at high aryl bromide
concentrations if k2[ArBr] becomes significantly larger than k-1
.
A variant of path B involving reversible coordination of aryl
(82) Farina, V.; Krishnan, B. J. Am. Chem. Soc. 1991, 113, 9585-9595.
(83) Farina, V.; Kapadia, S.; Krishnan, B.; Chenjie, W.; Liebeskind, L.
S. J. Org. Chem. 1994, 59, 5905-5911.
(84) Farina, V. Pure Appl. Chem. 1996, 68, 73-78.
(85) Louie, J.; Hartwig, J. F. J. Am. Chem. Soc. 1995, 117, 11598.
(86) Mann, G.; Hartwig, J. F. Tetrahedron Lett. 1997, 38, 8005.
(87) Mann, G.; Hartwig, J. F. J. Org. Chem. 1997, 62, 5413.
(88) Mann, G.; Incarvito, C.; Rheingold, A. L.; Hartwig, J. F. J. Am.
Chem. Soc. 1999, 121, 3224.
(80) The precipitation of Pd(0) is difficult to observe unambiguously
because of the formation of alkali halide salts during the amination reactions.
“Ligandless” palladium, such as Pd(OAc)2, Pd(DBA)2, or (η-Cp)Pd(η-Allyl),
does not catalyze the aryl halide amination reaction.
(81) van Strijdonck, G. P. F.; Boele, M. D. K.; Kammer, P. C. J.; de
Vries, J. G. V.; van Leeuwen, P. W. N. M. Eur. J. Inorg. Chem. 1999,
1073-1076.
(89) Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.; Sadighi, J.
P.; Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 4369-4378.
(90) Mann, G.; Hartwig, J. F.; Driver, M. S.; Fernandez-Rivas, C. J.
Am. Chem. Soc. 1998, 120, 827.

Unusual Zero-Order Kinetic BehaVior and Product Inhibition
J. Am. Chem. Soc., Vol. 122, No. 19, 2000 4625
bromide will be discussed below. Path C involves the full
dissociation of a chelating ligand and direct oxidative addition
of the aryl bromide to the 14-electron intermediate. The rate
law for path C (eq 3) predicts different reaction orders at
different ratios of aryl bromide to free ligand.
Scheme 4
Path C:
k1k2[ArBr]
k-1[L]
1
1
kobs
)
)
)
+
(3)
kobs k1
k-1[L] + k2[ArBr]
k1k2[ArBr]
k1k2[ArBr]
kobs
) k1
when [ArBr] . [L] (4)
k-1[L] + k2[ArBr]
Depending on the ratio of rate constants k2 and k-1, the reaction
can be first order in aryl bromide and inverse first order in free
ligand when the ratio [ArBr]:[L] is small, but zero order in both
when [ArBr]:[L] is large. When [ArBr] is high, the rate law
simplifies to that shown in eq 4. The unsaturated intermediates
in pathways B and C can exist with solvent directly coordinated
to the Pd(0) species or with no direct interaction of the
intermediate with a discrete solvent molecule.
Scheme 5
Our data rule out paths A and B for the oxidative addition
reactions. Path A is inconsistent with the zero-order rate behavior
at high [ArBr]. Both path A and path B are inconsistent with
the inverse dependence of kobs on ligand concentration. Of paths
A-C, only path C is consistent with a first-order dependence
on [PhBr] at low concentrations, a zero-order dependence on
[PhBr] at high concentrations of aryl bromide, and an inverse
first-order dependence on [BINAP] when the aryl bromide
concentration is low.
We cannot, however, distinguish between path C and the
variant of path B in Scheme 3. This modified mechanism
involves reversible displacement of the ligand by aryl bromide
through a combination of dissociative and associative steps to
generate a Pd(0) complex (BINAP)Pd(ArBr) containing intact
aryl bromide. The rate law in eq 5 for this mechanism, which
contains its two preequilibria, is complex but predicts reaction
orders similar to those in path C.
Our observation that the rate of the oxidative addition is
independent of the identity and coordinating ability of the
solvent suggests that a discrete solvent molecule is not directly
coordinated to the Pd(0) intermediate that adds aryl bromide.
Pd(0) amine complexes are not observed in these reactions.
Although amine may coordinate reversibly to the unsaturated
Pd(0) intermediate, the lack of rate dependence on the presence
or absence of amine demonstrates that an amine complex is
not an intermediate for addition of aryl bromides.
Although we did not obtain quantitative rate data for the
oxidative addition of aryl bromide to DPPF complex 2 because
of the difficulty in isolating pure 2, we did observe a clear
inverse dependence of kobs on the concentration of free DPPF.
Thus, Pd(DPPF)2 also undergoes oxidative addition by a
mechanism involving an intermediate containing a single bis-
phosphine ligand formed by full dissociation of a coordinated
DPPF.
Kinetic Studies of the Reaction of Amines with Aryl
Bromides Catalyzed by Pd(BINAP)2 and Pd(DPPF)2. A
summary of the mechanistic conclusions for the reactions of
primary amines catalyzed by BINAP complex 1a is provided
in Scheme 4, and a summary of our conclusions for reactions
of aniline catalyzed by DPPF-ligated palladium is provided in
Scheme 5. As expected, our data are consistent with the general
mechanism involving oxidative addition of aryl halide, genera-
tion of an amido intermediate from amine and base, and
reductive elimination to form product. However, the zero-order
rates at high ArBr for reactions catalyzed by 1a require that
the reaction scheme be different from that shown in Scheme 6
proposed previously.91,92 The different rate behavior for reactions
Modified Path B:
k1k2k3[ArBr]
kobs
)
k-1k3 + k-1k-2[L] + k2k3[ArBr]
k-1
k-1k-2[L]
1
1
)
+
+
(5)
kobs k1
k1k2[ArBr] k1k2k3[ArBr]
k1k2k3[ArBr]
kobs
)
) k1
k-1k3 + k-1k-2[L] + k2k3[ArBr]
when [ArBr] . [L] (6)
This rate equation simplifies to that in eq 6 if [ArBr] is high, as
does the rate law for path C. These rate equations are similar
because the oxidative addition occurs to an intermediate
coordinated by a single bis-phosphine ligand in both cases. Thus,
our data demonstrate that carbon-halogen bond cleavage occurs
either directly by (BINAP)Pd or after coordination to palladium
and formation of (BINAP)Pd(ArBr), which contains coordinated,
intact aryl bromide. We favor path C over this modified path
B. Saturation of kobs at high [PhBr] requires that the [(κ1-
BINAP)(κ2-BINAP)Pd(0)] coordinates PhBr as a dative ligand
much faster than it recoordinates the arm of the κ1-BINAP. This
requirement seems unreasonable, considering the intermolecu-
larity of the PhBr coordination and the weak donating ability
of PhBr.

4626 J. Am. Chem. Soc., Vol. 122, No. 19, 2000
Alcazar-Roman et al.
Scheme 6
cannot involve free (BINAP)Pd. We suggest that reductive
elimination irreversibly forms a 16-electron amine-ligated
Pd(0), which reacts with BINAP in an associative step to form
1a. The oxidative addition could also occur by formation of an
ArBr complex by modified path B, but we disfavor this reaction
mechanism as discussed above. Scheme 4, therefore, involves
closely related but distinct pathways for oxidative addition of
aryl halide and reductive elimination of amine.
For reactions of aniline with aryl bromides catalyzed by 2,
the saturation of the rate constant for oxidative addition at high
[ArBr] was not observed as it was for reactions of 1a. Thus,
recoordination of DPPF was always faster than oxidative
addition of aryl bromide. A first-order dependence of kobs on
aryl bromide concentration and an inverse first-order dependence
of kobs on ligand concentration were, therefore, observed. The
observation of 2 as the resting state when DPPF was added to
the reaction predicts the same rate behavior for the catalytic
reactions and the stoichiometric oxidative addition. This result
was observed, supporting a catalytic mechanism in which the
combination of ligand dissociation and irreversible cleavage of
the carbon-halogen bond control the rate of the catalytic
process. Considering the similarity in ligand structures, we
suggest that DPPF-ligated 2 catalyzes the arylation of anilines
by the same path as does 1a, but the C-X cleavage step is
never fast enough relative to recoordination of ligand to give
saturation in [ArBr].
of secondary amines catalyzed by 1a and the nonlinear plots
for the decay of amine for reactions catalyzed by 2 require
changes in the catalyst during the reaction.
If the Pd(0) species is the resting state and oxidative addition
of aryl halide is irreversible, then oxidative addition would be
the turnover-limiting step. Our studies on the mechanism of
oxidative addition to 1a showed that ligand dissociation was
irreversible and rate limiting when the ratio of [ArBr]:[L] was
high, as it is in the catalytic reactions. Thus, the rate of the
oxidative addition process and the rate of the catalytic cycle
depend only on the rate of dissociation of BINAP from 1a, as
shown in Scheme 4. In this case, the observed zero-order rate
constant for the catalytic reaction, shown in eq 7, is the product
of the catalyst concentration and the observed rate constant for
the oxidative addition of PhBr to 1a at 60 °C. This calculated
rate constant is within a factor of 3 of the measured rate constant
for the reaction of primary amines with aryl halide catalyzed
by 1a.
Effect of Catalyst Changes during the Aminations. Two
additional sets of unexpected rate data were obtained, one for
reactions of secondary amines with aryl bromides catalyzed by
1a, and one for reactions of anilines with aryl bromides catalyzed
by 2 at low concentrations of added DPPF. These two reactions
underscore the importance of clearly determining the catalyst
resting state when interpreting the kinetic data on a catalytic
system.
k1k2[ArBr][PdL2]
kobs
)
One set of data appeared to show a first-order decay of amine
for the reactions of secondary amines with aryl bromides
catalyzed by 1a. In the absence of data on the resting state, one
might conclude that the reaction rate was first order in amine
and that reactions of secondary amines involved a resting state,
such as an arylpalladium halide complex, that reacts with amine.
Instead, the observation of catalyst decomposition and the
confirmation that all stoichiometric reactions after oxidative
addition are faster than the oxidative addition demonstrated that
the unexpected decay was due to decomposition of the catalyst
(Figure S6) in a reaction that depends only on catalyst
concentration. One catalyst decomposition path is backbone
P-C bond cleavage. The palladium binaphthylmonophosphine
complex that would result is much less active for amination
than the BINAP-palladium complexes.92
k-1[L] + k2[ArBr]
) k1[PdL2] when [ArBr] . [L]
(7)
In the previously proposed mechanism of Scheme 6, 1a does
not lie on the catalytic cycle. It generates the actual catalyst by
a preequilibrium of phosphine dissociation. This mechanism is
inconsistent with the zero-order rate behavior at high [PhBr].
The number of turnovers for each (BINAP)Pd(0) generated
would depend on the relative concentrations of [PhBr] and
[BINAP]. For example, the intermediate (BINAP)Pd(0) would
be more likely to add PhBr to initiate a second turnover when
the ratio of PhBr:BINAP is high; it would be more likely to
re-form the resting state 1a when the ratio of PhBr:BINAP is
low. Kinetic simulations using rate constant information from
the oxidative addition process showed that the rates for reactions
by the mechanism in Scheme 6 would depend on [ArBr] and
[BINAP]. To observe the same rate behavior for the stoichio-
metric oxidative addition and catalytic reactions, the species
involved in the oxidative addition mechanism must be an
intermediate in the catalytic cycle. A single ligand dissociation
event must lead to formation of a single product molecule. Thus,
the mechanisms in Schemes 4 and 5 are consistent with our
data.
The second set of data could also have been interpreted as a
change in turnover-limiting step for the reaction of aniline with
aryl bromides catalyzed by 2. However, this behavior was again
due to a reduction in the concentration of active catalyst. Unlike
the irreversible formation of inactive species during the reactions
of secondary amines catalyzed by 1a, catalyst 2 was reversibly
converted to the arylpalladium diarylamido complex 8 by
reaction with product.
The final unexpected observation is the slightly slower
reaction of aniline with aryl halides catalyzed by 1a than we
observed with other amines. The plots of the decay of amine
with time were linear as expected, but the rate of reaction was
roughly 25% slower than that for reactions of the other amines.
In this case, only 15% decomposition of the catalyst was
observed during the reaction. The observed rate constant was
In the mechanism of Scheme 4, 1a lies on the reaction path
and (BINAP)Pd is an intermediate in the oxidative addition. If
reductive elimination involves this same intermediate, the
process in Scheme 6 would result. Thus, reductive elimination
(91) Hartwig, J. F. Angew. Chem., Int. Ed. 1998, 37, 2046-2067.
(92) Wolfe, J. P.; Buchwald, S. L. J. Org. Chem. 2000, 65, 1144-1157.

Unusual Zero-Order Kinetic BehaVior and Product Inhibition
J. Am. Chem. Soc., Vol. 122, No. 19, 2000 4627
Fourier transform NMR spectrometers. 31P{1H} NMR spectra were
obtained on the Ω 300- and 500-MHz spectrometers operating at the
corresponding frequencies. 1H NMR spectra were recorded relative to
residual protiated solvent. 31P{1H} NMR spectra were recorded in units
of parts per million relative to 85% H3PO4 as external standard. UV-
visible spectra were collected on a Varian Cary 3E spectrophotometer
equipped with a thermostated multicell block.
Unless specified otherwise, all reagents were purchased from
commercial suppliers and used without further purification. Pd-
[P(o-Tol)3]2,100 Pd(DBA)2, (PPh3)2Pd(Ph)Br,101 (DPPF)Pd(Ph)Br,79 and
(DPPF)Pd(4-C6H4-t-Bu)Br100 were prepared using literature procedures,
unless otherwise noted. Protiated solvents were heated to reflux and
distilled from purple solutions containing sodium benzophenone ketyl.
Deuterated solvents were dried similarly but were collected by vacuum
transfer. Dichloromethane and dichloromethane-d2 were dried over CaH2
and distilled or vacuum transferred, respectively.
reproducible and independent of the purity of the aniline used.
We do not have an explanation for this single observation.
Comparison to the Kinetic Behavior of Other Catalytic
Systems. Few transition metal-catalyzed reactions are zero order
in all reagents. This kinetic situation must result from a
unimolecular reaction of the catalyst. Ligand dissociation,
reductive elimination, and intramolecular insertion are examples
of such unimolecular reactions. The previously reported zero-
order reactions include those with turnover-limiting olefin or
CO insertion into M-X bonds, as in certain hydroamination/
cyclization reactions,93,94 Heck reactions,81,95 hydroformyla-
tions,96 and alkyne isomerizations.97,98 Except for cyclizations,
these cases typically involve rate measurements using excess
quantities of a reagent which does display a reaction order; these
reactions are, therefore, pseudo zero order and are different from
the case reported here for reactions catalyzed by 1a that are
zero order in all reagents due to saturation behavior. Lanthanide-
catalyzed hydroamination/cyclization is truly zero order in all
reagents. This observation results from the intramolecularity of
the turnover-limiting insertion reaction. In contrast to organo-
metallic catalysts, many enzymes show zero-order rate behavior.
In these biological systems, zero-order behavior results from
rate-limiting product release.99 One can envision that transition
metal Lewis acid catalysts could also show such rate-limiting
product release.
Preparation of Pd(BINAP)2 (1a). Into a 20-mL screw-capped vial
were weighed Pd[P(o-Tol)3]2 (102.3 mg, 0.143 mmol) and BINAP
(180.1 mg, 0.289 mmol), followed by 3 mL of benzene. The dark red
reaction mixture was filtered through Celite, layered with pentane, and
allowed to stand at room temperature for 5 h. Red crystalline solid
was collected by filtration and dried in vacuo to give 173.7 mg (89.7%)
1
of Pd(BINAP)2. H NMR (500 MHz C6D6): δ 5.87 (t, J ) 7.6 Hz,
8H), 6.18 (t, J ) 7.4 Hz, 4H), 6.84 (app t, J ) 7.7 Hz, 4H), 7.05 (app
t, J ) 7.3 Hz, 4H), 7.14-7.26 (m, 16H), 7.33-7.39 (m, 8H), 7.47
(broad, 8H), 7.82 (broad m, 4H), 8.36 (broad, 8H). 31P{1H} NMR
(C6D6): δ 27.4 (s).
Preparation of Pd((R)-Tol-BINAP)2 (1b). Into a 20-mL screw-
capped vial were weighed Pd[P(o-Tol)3]2 (152 mg, 0.212 mmol) and
(R)-Tol-BINAP (289 mg, 0.439 mmol), followed by 5 mL of benzene.
The dark red reaction mixture was filtered through Celite, layered with
pentane, and allowed to stand at room temperature for 5 h. Dark red
crystals suitable for X-ray diffraction were collected by careful
mechanical removal from the reaction medium (100 mg). An additional
107 mg of microcrystalline solid was collected by filtration and drying
in vacuo of the additional solid left after removal of the large crystals.
These two crops yielded a total of 207 mg (66.8%) of Pd((R)-Tol-
Summary and Conclusions
We have shown that the rate of oxidative addition and the
stability of the catalyst toward decomposition and product
inhibition dictate the kinetic behavior of the catalytic cycle and
that bis-chelate complexes 1a and 2 are likely to lie on the actual
catalytic cycles. We have also shown that results from examining
the catalyst stability by 31P NMR spectroscopy throughout the
reaction explain unexpected deviations from the predicted rate
behavior. Although not all pathways leading to catalyst decom-
position and inactivation have been identified, some of the most
significant ones were detected. For reactions catalyzed by
BINAP-ligated palladium, the thermal instability of the ligand
and the removal of palladium as inactive complexes that do
not contain phosphorus are important pathways for deactivation
of the catalyst. For reactions containing DPPF as ligand, an
additional pathway involving formation of a diarylamido
complex, which is more stable than the monoarylamido
complex, stores the palladium in an unproductive form. These
results demonstrate the importance of carefully determining the
catalyst resting state from data that are independent of the rate
behavior and of obtaining quantitative rate behavior for the
overall catalytic process.
1
BINAP)2. H NMR (500 MHz C6D6): δ 1.52 (s, 12H), 2.11 (s, 12H),
5.77 (d, J ) 8.1 Hz, 8H), 6.82-6.95 (m, 8H), 7.00-7.10 (m, 4H),
7.19 (d, J ) 7.5 Hz, 8H), 7.31 (d, J ) 8.4 Hz, 4H), 7.38 (d, J )
8.0 Hz, 4H), 7.49 (broad, 8H), 8.03 (broad m, 4H), 8.39 (broad, 8H).
31P{1H} NMR (C6D6): δ 24.60 (s). Anal. Calcd for C96H80P4Pd: C,
78.76; H, 5.51 Found: C, 78.60; H, 5.65.
Preparation of Pd(DPPF)2 (2). Into a 20-mL screw-capped vial
were weighed Pd[P(o-Tol)3]2 (101.2 mg, 0.142 mmol) and DPPF (156.5
mg, 0.282 mmol), followed by 5 mL of benzene. The orange-yellow
reaction mixture was filtered through Celite and layered with 10 mL
of pentane. Yellow powder (119.8 mg) was collected by filtration and
dried in vacuo. This material consisted of a mixture of Pd(DPPF)2,
1
[Pd(DPPF)]2(µ-DPPF)], and free DPPF, as determined by 31P and H
1
NMR spectroscopy. H NMR (300 MHz C6D6): δ 4.00 (s, 8H), 4.29
(s, 8H), 6.8-7.05 (m, 24H), 7.78 (broad, 16 H). 31P{1H} NMR
(C6D6): δ 7.73 (s).
Isolation of [Pd(DPPF)]2(µ-DPPF) (3). A freshly prepared batch
of impure Pd(DPPF)2 (40.0 mg, 32.9 µmol) was redissolved in
approximately 15 mL of THF. The resulting solution was cooled to
-34 °C and then layered with approximately 5 mL of ether and returned
to the freezer at -34 °C, where it was left standing for 48 h. Crystals
suitable for X-ray diffraction were collected by decanting the solvent
from the reaction vessel and examining the crystalline material visually.
Preparation of {Pd[P(o-Tol)3](Ph)(µ-Br)}2 (7). Pd[P(o-Tol)3]2
(105.2 mg, 0.147 mmol) was added to a solution of bromobenzene
(114.6 mg, 0.730 mmol) in 25 mL of benzene with stirring. After
reaction at ambient temperature for 30 min, the resulting pale yellow
solution was filtered through a bed of Celite to remove any insoluble
material. The clear yellow solution was allowed to react at room
temperature for an additional 5 h and was then concentrated in vacuo
to 1/10 of the original volume. The resulting suspension was layered
Experimental Section
General Considerations. Unless otherwise noted, all manipulations
were conducted using standard Schlenk techniques or in an inert
1
atmosphere glovebox. H NMR spectra were obtained on Bruker AM
500-MHz, GE QE 300-MHz, GE Ω 500-MHz, or GE Ω 300-MHz
(93) Arredondo, V. M.; McDonald, F. E.; Marks, T. J. J. Am. Chem.
Soc. 1998, 120, 4871-4872.
(94) Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1998, 120, 1757-1771.
(95) Beller, M.; Riermeier, T. H. Eur. J. Inorg. Chem. 1998, 1, 29-35.
(96) Vrieze, K.; Groen, J. H.; Delis, J. G. P.; Elsevier: C. J.; van
Leeuwen, P. W. N. M. New. J. Chem. 1997, 21, 807-813.
(97) Coolen, H. K. A. C.; Nolte, R. J. M.; van Leeuwen, P. W. N. M. J.
Organomet. Chem. 1995, 496, 159-168.
(98) Salomon, R. G.; Salomon, M. F.; Kachinski, J. L. J. Am. Chem.
Soc. 1977, 94, 1043-1054.
(99) Walsh, C. Ezymatic Reaction Mechanisms; W. H. Freeman and
Co.: New York, 1979.
(100) Paul, F.; Patt, J.; Hartwig, J. F. Organometallics 1995, 14, 3030.
(101) Fitton, P.; Johnson, M. P.; McKeon, J. E. J. Chem. Soc., Chem.
Commun. 1968, 6-7.

4628 J. Am. Chem. Soc., Vol. 122, No. 19, 2000
Alcazar-Roman et al.
with ether and allowed to stand at ambient temperature for 5 h to yield
58.5 mg (70.0%) of an insoluble pale yellow powder. Anal. Calcd for
C54H52Pd2Br2P2: C, 57.12; H, 4.62. Found: C, 57.38; H, 4.83.
Preparation of (rac-BINAP)Pd(Ph)(Br) (5). Pd[P(o-Tol)3]2 (1.010
g, 1.41 mmol) was added to a solution of bromobenzene (1.18 g, 7.54
mmol) in 120 mL of benzene with stirring. After reaction at ambient
temperature for 30 min, the resulting pale yellow solution was filtered
through a bed of Celite to remove any insoluble material. The resulting
clear yellow solution was then allowed to react at room temperature
for approximately 5 h. After this time, racemic BINAP (877.8 mg, 1.41
mmol) was added, and the reaction was continued until all solid material
dissolved. The final solution was then concentrated to 1/10 of the
original volume in vacuo and layered with ether. A pale yellow powder
was obtained. After recrystallization by layering a concentrated solution
of the product in CH2Cl2 with ether, 637.9 mg of pale yellow
microcrystals with the formula (BINAP)Pd(Ph)Br‚1/2CH2Cl2 was
reaction order in PhBr, [Pd(BINAP)2] and [BINAP] were held constant
at 2.26 × 10-5 and 1.08 × 10-4 M respectively, and [PhBr] was varied
from 1.78 × 10-3 to 8.95 × 10-2 M. For the determination of the rate
of oxidative addition of ortho-substituted aryl bromides, [Pd(BINAP)2]
and [BINAP] were held constant at 2.26 × 10-5 and 1.08 × 10-4 M,
respectively, and neat aryl bromide was added to the reaction to obtain
an aryl bromide concentration of 8.95 × 10-2 M. For the determination
of solvent and additive effects, the concentrations of Pd(BINAP)2,
BINAP, and PhBr were fixed at 2.29 × 10-5, 1.72 × 10-4, and 1.84 ×
10-3, respectively. Samples were prepared by adding stock solutions
into a 5-mL volumetric flask. Each flask was then filled to the 5-mL
volumetric mark with the appropriate solvent. The resulting solutions
were shaken and transferred (∼3 mL) to quartz cuvettes fitted with an
airtight Teflon valve. The UV-visible spectrometer cell block was
warmed to 45 °C. The absorbance of Pd(BINAP)2 was monitored at
λ ) 519 nm, with a 1-s signal averaging time, and 30 s between
acquisitions over at least three half-lives. Kinetic data were fit to the
expression A519 ) B ekt + c, in which k is the pseudo-first-order rate
1
obtained in 50.0% yield. H NMR (300 MHz, C6D6): δ 5.33 (s, 1H,
CH2Cl2 of crystallization), 6.21 (m, 2H), 6.36 (m, 4H), 6.57 (m, 2H),
6.68-7.32 (m, 16H), 7.48 (app d, 2H), 7.60 (broad, 2H), 7.82 (app t,
2H), 7.98 (app t, 3H), 8.08 (app t, 4H). 31P{1H} NMR: δ 28.21 (d,
JPP ) 39.06 Hz), 11.78 (d, JPP ) 39.07 Hz). Anal. Calcd for
C50H37P2PdBr‚1/2CH2Cl2: C, 65.32; H, 4.12. Found: C, 65.32; H, 4.63.
Thermolysis of (DPPF)Pd(Ph)Br and (BINAP)Pd(Ph)Br. A
solution of (DPPF)Pd(Ph)Br (5.0 mg, 6.1 µmol) or (BINAP)Pd(Ph)Br
(5 mg, 5.6 µmol) in THF, benzene, or toluene was transferred to a
screw-capped NMR tube. The solution of (BINAP)Pd(Ph)Br was heated
at 70 °C for 14 h. The solution of (DPPF)Pd(Ph)Br was heated at 110
°C for 16 h. The reaction was monitored by 31P{1H} or 1H spectroscopy
in the case of (DPPF)Pd(Ph)Br at several intervals before the reaction
was complete. After this time, addition of 2.5 equiv of diphenylmeth-
ylphosphine to the reaction mixture produced a new set of doublets
and a resonance corresponding to that of free PPh3.
Preparation of rac-(PPh3)(Br)Pd[2′-(diphenylphosphino)-2-yl-
(1,1′-binaphthyl)] (6). A 250-mL reaction vessel fused to a Kontes
vacuum adapter was charged with (rac-BINAP)Pd(Ph)Br (1.420 g, 1.60
mmol) and 180 mL of benzene. The solution was heated at 65 °C for
14 h. The reaction was evaporated to dryness, and the residue was
redissolved in 10 mL of benzene. The resulting solution was layered
with pentane, and after several hours, 1.25 g (88.3%) of crystalline
product was isolated by filtration. This material contained half a
molecule of benzene per molecule of product. Crystals suitable for X-ray
diffraction were manually selected from this sample. 1H NMR (C6D6):
δ 6.44 (broad, 1H), 6.51 (m, 1H), 6.79 (m, 2H), 6.86 (m, 8H), 6.9-
6.96 (m, 2H), 7.01-7.25 (m, 10H), 7.36 (dd, J1) 8.49 Hz, J2 ) 7.08
Hz, 1H), 7.44 (dd, J1 )7.39, J2 ) 8.55, 1H), 7.49 (d, broad, 1H), 7.54
(d, broad, 1H), 7.60 (d, broad, 1H), 7.70-7.76 (m, 6H), 8.04 (app t,
J ) 9.21 Hz). 31P{1H} NMR (C6D6): δ 31.3 d, 23.6 d (JPP ) 440 Hz)
(relative peak heights, outer to inner, 35:100). Anal. Calcd for C50H37P2-
PdBr‚1/2C6H6: C, 68.81; H, 4.36. Found: C, 68.47; H, 4.34.
constant kobs
.
Rate Determination of Amination of Bromobenzene with Pri-
mary Amines Using Pd(BINAP)2 as Catalyst. A stock solution
consisting of 3.75 mM Pd(BINAP)2, 3.87 mM BINAP, 408.9 mM
NaOC(Et)3, and an internal standard (ferrocene or 1,3,5-trimethoxy-
benzene) was prepared in benzene-d6 and stored in a -35 °C freezer.
Another stock solution was prepared containing a 4.80 M concentration
of bromobenzene in C6D6. A typical reaction mixture was prepared by
mixing 0.200 mL of the first stock solution with 0.150 mL of the second
and 0.250 mL of C6D6 in a screw-capped NMR tube. Neat reagents
were added to the reaction mixture to obtain higher concentrations of
bromobenzene, ligand, or base. The total volume was maintained
constant at 0.600 mL by appropriately reducing the amount of additional
C6D6 added to the reaction. Amines were injected into the NMR tube
via syringe immediately prior to the initiation of the data acquisition
program. Volumes of amine injected were varied so that initial
oncentration of amine would be 12.6 mM (typically 0.6-1.2 µL).
Amines were used as received without prior drying or degassing, with
the exception of aniline which was used as received and also after
purification by distillation under nitrogen over activated molecular
sieves. Zero-order rate constants were obtained by fitting a linear plot
of the amine starting material concentration versus time to the
expression y ) mx + b, in which m is the zero-order rate constant kobs
.
Rate Determination of Amination of Bromobenzene with Aniline
Using Pd(DPPF)2 as Catalyst. A stock solution consisting of 8.0 mM
(DPPF)Pd(4-C6H4-t-Bu)(Br), 16.0 mM DPPF, 4.800 M 4-bromo-tert-
butylbenzene, and an internal standard (1,3,5-trimethoxybenzene) was
prepared in benzene-d6 and stored in a -35 °C freezer. Another stock
solution was prepared containing 0.800 M NaOC(Et)3 in C6D6. A typical
reaction mixture was prepared by mixing 0.150 mL of the first stock
solution with 0.150 mL of the second, and 0.300 mL of C6D6 in a
screw-capped NMR tube. Neat reagents were added to the reaction
mixture to obtain higher concentrations of bromobenzene, ligand, or
base. The total volume was maintained at 0.600 mL by appropriately
reducing the amount of additional C6D6 added to the reaction. Aniline
was injected into the NMR tube via syringe immediately prior to the
initiation of the data acquisition program. Zero-order rate constants
were obtained by fitting a plot of the amine starting material versus
time to the expression y ) mx + b, where m is the zero-order rate
constant kobs. The initial linear portion of a plot was used whenever
product inhibition prevented the use of the entire time course.
Determination of the Resting State in Reactions Catalyzed by
1a. Pd(BINAP)2 (5.0 mg, 3.7 µmol), 4-bromotoluene (6.3 mg, 37 µmol),
and NaO-t-Bu (4.3 mg, 44 µmol) were dissolved in 0.5 mL of benzene
and transferred to a screw-capped NMR tube. Butylamine (4 µL, 40
µmol) was added via syringe. The tube was then placed into the NMR
spectrometer probe and heated at 75 °C. 31P{1H} NMR spectra were
obtained during the course of the reaction until the bromoarene was
judged completely consumed by GC/MS.
Oxidative Addition of PhBr to Pd(chelate)2 (chelate ) BINAP
or DPPF) and Qualitative Observation of Reaction Orders. Pd-
(chelate)2 (1.8-2.2 µmol), ligand (BINAP or DPPF; 1.8-25 µmol),
and 1,3,5-trimethoxybenzene or ferrocene as internal standard were
dissolved in 0.5 mL of benzene-d6 and transferred to a screw-capped
NMR tube containing a PTFE-lined septum cap. PhBr (1-100 µL,
9-900 µmol) was added via syringe to this solution. An initial 1H NMR
1
spectrum was acquired, and the mixture was heated at 55-85 °C. H
NMR spectroscopic data were collected at various reaction times, and
a yield was determined by comparing the integrals of product resonances
and internal standard in the final spectrum vs those of starting material
and standard in the initial spectrum.
Determination of the Oxidative Addition Rate of PhBr to Pd-
(BINAP)2. Separate stock solutions of Pd(BINAP)2, BINAP, and PhBr
were prepared by dissolving Pd(BINAP)2, BINAP, and PhBr in benzene.
Similar stock solutions were prepared in THF and 2,5-dimethyl-THF.
The stock solutions were stored in at -35 °C in a freezer. For
experiments to determine the reaction order in BINAP, the PhBr
concentration was fixed at 1.78 × 10-3 M, the Pd(BINAP)2 concentra-
Determination of the Resting State in the Amination of Aniline
Catalyzed by Pd(OAc)2 and BINAP. Pd(OAc)2 (0.8 mg, 3.5 µmol),
BINAP (4.6 mg 7.4 µmol), 4-bromotoluene (6.3 mg, from 37 µmol to
48 mmol), and NaO-t-Bu (4.3 mg, 44 µmol) were dissolved in 0.5 mL
-6
tion was either 7.10 × 10
or 3.05 × 10-5 M to obtain reasonable
reaction times, and the concentration of BINAP was varied between
3.60 × 10-5 and 2.98 × 10-4 M. For experiments to determine the

Unusual Zero-Order Kinetic BehaVior and Product Inhibition
J. Am. Chem. Soc., Vol. 122, No. 19, 2000 4629
of benzene and transferred to a screw-capped NMR tube. Butylamine
(4 µL, 40 µmol) was added via syringe. The tube was then placed in
the NMR spectrometer probe and heated at 75 °C. 31P{1H} NMR spectra
were obtained during the course of the reaction, until the bromoarene
was judged completely consumed by GC/MS. Two similar experiments
were performed that contained 2.3 and 1.2 mg of BINAP.
Table 5. Data Collection and Refinement Parameters for X-ray
Structures of Pd((R)-Tol-BINAP)2 (1b) and
(PPh3)(Br)Pd[2-diphenylphosphino-2′-yl-1,1′-binaphthyl)] (6)
1b
6
empirical formula
formula weight
crystal color, habit
crystal system
C108H92P4Pd
1632.30
red plates
C56H43BrP2Pd
964.15
yellow block
Determination of the Resting State in the Amination of Aniline
Catalyzed by 1a. Pd(BINAP)2 (5 mg, 3.7 µmol), BINAP (2.3 mg, 3.7
µmol), bromobenzene (75.3 mg, 48 mmol), NaOC(Et)3 (51.1 mg, 0.369
mmol), and tri-o-tolylphosphine (internal standard, 1.0 mg, 3.3 µmol)
were dissolved in 0.550 mL of benzene-d6 and transferred to a screw-
capped NMR tube. Aniline (3.4 µL, 37 µmol) was added via syringe.
The tube was then placed in the NMR spectrometer probe and heated
at 60 °C. 31P{1H} NMR spectra were obtained during the course of the
monoclinic primitive triclinic
lattice parameters
a ) 16.743(7) Å
b ) 19.458(6) Å
c ) 16.859(5) Å
â ) 119.57(3)°
a ) 12.3757(2) Å
b ) 12.9432(2) Å
c ) 14.5021(2) Å
R ) 83.5768(7)°
â ) 82.1315(4)°
γ ) 77.3824(8)°
2237.43(6) Å3
P1h
1
volume
space group
Z value
4776(3) Å3
P21 (No. 4)
2
reaction until aniline was judged completely consumed by H NMR
spectroscopy.
Determination of the Resting State in the Amination of Second-
ary Amines Catalyzed by 1a. Pd(BINAP)2 (5 mg, 3.7 µmol), BINAP
(2.3 mg, 3.7 µmol), bromobenzene (75.3 mg, 0.480 mmol), and NaOC-
(Et)3 (11.3 mg, 81.7 µmol) were dissolved in 0.550 mL of benzene-d6
and transferred to a screw-capped NMR tube. N-Methylaniline (4.0
µL, 37 µmol) was added via syringe. The tube was then placed in the
NMR spectrometer probe and heated at 60 °C. 31P{1H} NMR spectra
were obtained during the course of the reaction until the N-methylaniline
2
diffractometer
radiation
Enraf-Nonius CAD-4 Siemens P4/CCD
Mo KR
Mo KR
(λ ) 0.710 69 Å)
-90.0 °C
R; Rw
(λ ) 0.710 69 Å)
-75(2) °C
R; Rw
T
residuals
0.053; 0.069
goodness-of-fit indicator 1.64
0.0335; 0.0906
0.985
1
was judged completely consumed by H NMR spectroscopy.
Determination of the Resting State in Reactions Catalyzed by 2.
(DPPF)Pd(4-C6H4-t-Bu)(Br) (5.0 mg 6.1 µmol), DPPF (6.8 mg, 12.2
µmol), 4-bromo-tert-butylbenzene (83.2 µL, 0.480 mmol), NaOC(Et)3
(84.3 mg, 0.610 mmol), and tri-o-tolylphosphine (internal standard 1.0
mg, 3.3 µmol) were dissolved in 0.515 mL of benzene-d6 and transferred
to a screw-capped NMR tube. Aniline (5.6 µL, 61 µmol) was added
via syringe. The tube was then placed in the NMR spectrometer probe
and heated at 60 °C. 31P{1H} NMR spectra were obtained during the
course of the reaction until aniline was judged completely consumed
crystal moving counter background measurements were made by
scanning an additional 25% above and below the scan range. The
counter aperture consisted of a variable horizontal slit with a width
ranging from 2.0 to 2.5 mm and a vertical slit set to 2.0 mm. The
diameter of the incident beam collimator was 0.7 mm, and the crystal-
to-detector distance was 21 cm. For intense reflections, an attenuator
was automatically inserted in front of the detector.
Of the 10,313 reflections which were collected, 9969 were unique
(Rint ) 0.062). The intensities of three representative reflections were
measured after every 60 min of X-ray exposure time. No decay
correction was applied.
1
by H NMR spectroscopy.
Reductive Elimination of N-Phenylmorpholine from (BINAP)-
Pd(Ph)Br (5). A solution of 5 (5.0 mg, 5.6 µmol), BINAP (7.0 mg,
11.3 µmol), and ferrocene (internal standard) in 0.5 mL of benzene-d6
was prepared and transferred to a screw-capped NMR tube containing
The linear absorption coefficient, µ, for Mo-R radiation is 3.1 cm-1
.
Azimuthal scans of several reflections indicated no need for an
absorption correction. The data were corrected for Lorentz and
polarization effects.
1
a septum cap lined with PTFE. A H NMR spectrum was obtained.
This solution was then quickly transferred via syringe to another similar
NMR tube containing lithium morpholide (0.6 mg, 6.5 µmol). The
sample was quickly cooled to 0 °C in an ice bath and transferred to
The structure was solved by direct methods102 and expanded using
Fourier techniques.103 The non-hydrogen atoms were refined anisotro-
pically. Hydrogen atoms were included but not refined. In the case of
methyl group hydrogen atoms, one hydrogen atom was located in the
difference map and included at an idealized distance to set the
orientation of the remaining two hydrogen atoms. Four benzene solvent
molecules were included and refined at 50% occupancy. The final cycle
of full-matrix least-squares refinement104 was based on 6383 observed
reflections (I > 3.00σ(I)) and 1125 variable parameters and converged
(largest parameter shift was 0.02 times its esd) with unweighted and
weighted agreement factors of
1
the NMR spectrometer probe at room temperature. Another H NMR
spectrum was obtained to determine the yield of N-phenylmorpholine.
The same reaction was repeated by adding a solution of morpholine
(1 µL, 11.4 µmol) and NaOC(Et)3 (1.6 mg, 11.4 µmol) in benzene-d6
(0.1 mL) to a similar solution of 5, BINAP, and internal standard. The
experiments were repeated in order to obtain 31P{1H} spectra. In all
cases, greater than 95% yield of N-phenylmorpholine was observed
immediately, and the only detectable palladium species observed by
31P{1H} NMR spectroscopy was 1a.
X-ray Crystal Structure of Pd[(R)-Tol-BINAP]2 (1b). A red
platelike crystal of C108H92P4Pd having approximate dimensions of 0.20
× 0.41 × 0.45 mm3 was mounted on a glass fiber. All measurements
were made on an Enraf-Nonius CAD4 diffractometer with graphite-
monochromated Mo-R radiation. Crystal, data collection, and refinement
parameters are given in Table 5.
Cell constants and an orientation matrix for data collection, obtained
from a least-squares refinement using the setting angles of 25 carefully
centered reflections in the range 10.44 < 2θ < 18.04°, corresponded
to a primitive monoclinic cell with dimensions a ) 16.743(7) Å, b )
19.458(6) Å, c ) 16.859(5) Å, â ) 119.57(3)°, and V ) 4776(3) Å3.
For Z ) 2 and FW ) 1632.30, the calculated density is 1.13 g/cm3.
Based on the systematic absences of 0k0, k ) 2n + 1, packing
considerations, a statistical analysis of intensity distribution, and the
successful solution and refinement of the structure, the space group
was determined to be P21 (No. 4).
R )
||Fo| - |Fc||/ |Fo| ) 0.053
∑
∑
Rw ) [( w(|Fo| - |Fc|)2/ wFo )]1/2 ) 0.069
2
∑
∑
The standard deviation of an observation of unit weight105 was 1.64.
The weighting scheme was based on counting statistics and included a
factor (p ) 0.040) to downweight the intense reflections. Plots of
∑w(|Fo| - |Fc|)2 versus |Fo|, reflection order in data collection, sin
θ/λ, and various classes of indices showed no unusual trends. The
maximum and minimum peaks on the final difference Fourier map
corresponded to 0.65 and -0.51 e-/Å3, respectively.
(102) SIR92: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.;
Giacovazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr. 1994, in
preparation.
(103) DIRDIF94: Beurskens, P. T.; Admiraal, G.; Beurskens, G.;
Bosman, W. P.; de Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-94
program system, Technical Report of the Crystallography Laboratory,
University of Nijmegen, The Netherlands, 1994.
The data were collected at a temperature of -90 ( 1 °C using the
ω-2θ scan technique to a maximum 2θ value of 52.6°. Scans of (0.56
+ 1.14 tan θ)° were made at a speed of 1.5-16.0°/min (in ω). Moving-

4630 J. Am. Chem. Soc., Vol. 122, No. 19, 2000
Alcazar-Roman et al.
Table 7. Selected Bond Distances (Å) and Angles (deg) for
Table 6. Intramolecular Bond Distances (Å) and Angles (deg) for
1b
(PPh3)(Br)Pd[2-diphenylphosphino-2′-yl-1,1′-binaphthyl)] (6)
Pd(1)-P(1)
2.278(2)
Pd(1)-P(3)
2.278(2)
Pd(1)-C(1)
2.010(2) Pd(1)-Br(1)
2.5141(3)
2.3382(6)
156.60(2)
164.27(7)
101.52(2)
Pd(1)-P(1)
2.3079(6) Pd(1)-P(2)
Pd(1)-P(2)
2.2872(13)
127.90(6)
107.80(5)
P(2)-Pd(1)-C(1)
P(2)-Pd(1)-Br(1)
C(1)-Pd(1)-P(1)
C(10)-C(1)-Pd(1)
C(1)-[Br(1)-Pd(1)- 164.77°
P(2) plane]
90.71(7) P(2)-Pd(1)-P(1)
93.22(2) C(1)-Pd(1)-Br(1)
80.02(6) P(1)-Pd(1)-Br(1)
126.9(2) C(2)-C(1)-Pd(1)
P(1)-Pd(1)-P(2)
P(1)-Pd(1)-P(2)
P(1)-Pd(1)-P(3)
124.02(5)
112.8(2)
P(1)-[Br(1)-Pd(1)- -129.34°
P(2) plane]
Neutral atom scattering factors were taken from Cromer and
Waber.106 Anomalous dispersion effects were included in Fcalc
;
the
107
values for ∆f ′ and ∆f ′′ were those of Creagh and McAuley.108 The
values for the mass attenuation coefficients were those of Creagh and
Hubbel.109 All calculations were performed using the teXsan110 crystal-
lographic software package of Molecular Structure Corp.
are consistent for the space groups P1 and P for 3 and P1 and P1h for
6. The E statistics suggested the centrosymmetric option for both, which
yielded chemically reasonable and computationally stable results of
refinement. The structures were solved using direct methods, completed
by subsequent difference Fourier syntheses, and refined by full-matrix,
least-squares procedures. An empirical absorption correction was
applied to the data for both 3 and 6 using the program DIFABS. All
non-hydrogen atoms were refined with anisotropic displacement
coefficients. Hydrogen atoms were treated as idealized contributions.
Three molecules of THF cocrystallized with 3, one of which is
disordered over an inversion center. There is one benzene molecule in
the asymmetric unit of 6. Bond distances and angles for 6 are given in
Table 7. One of the phenyl rings attached to P(1) of 3 possesses very
large thermal ellipsoids in a pattern consistent with positional disorder.
The resolution of the current data did not allow the construction of a
multisite disorder model.
Bond distances and angles for 1b are given in Table 6.
X-ray Crystal Structure of [(DPPF)Pd]2(µ-DPPF) (3) and rac-
(PPh3)(Br)Pd[2′-(diphenylphosphino)-2-yl-(1,1′-binaphthyl)] (6). The
single-crystal X-ray diffraction experiment was performed on a Siemens
P4/CCD diffractometer. Crystal, data collection, and refinement
parameters for 6 are given in Table 5; data for 3 are given in the
Supporting Information. Systematic absences and diffraction symmetry
(104) Least-squares:
Function minimized:
w(|Fo| - |Fc|)2
∑
w ) 4Fo /σ2(Fo ) ) [σ2(Fo) + (pFo/2)2]-1
Fo2 ) S(C - RB)/Lp
2
2
where
All software and sources of the scattering factors are contained in
the SHELXTL (5.03) program library (G. Sheldrick, Siemens XRD,
Madison, WI). The program DIFABS is described by N. Walker and
D. Stuart (Acta Crystallogr. 1983, A39, 158).
σ2(Fo ) ) [S2(C + R2B) + (pFo ) ]/Lp2
2
2 2
and
S ) scan rate, C ) total integrated peak count, R ) ratio of scan time to
background counting time, B ) total background count, Lp ) Lorentz-
polarization factor, and p ) p-factor.
Acknowledgment. We are grateful to the NIH (R29-
GM55382-01-035) for support of this work. The University of
Delaware acknowledges the National Science Foundation (Grant
CHE-9628768) for their support of the purchase of the CCD-
based diffractometer.
(105) Standard deviation of an observation of unit weight:
[Sw(|Fo| - |Fc|)2/(No - Nv)]1/2
where No ) number of observations and Nv ) number of variables.
(106) Cromer, D. T.; Waber, J. T. International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, England, 1974; Vol. IV,
Table 2.2 A.
(107) Ibers, J. A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781.
(108) Creagh, D. C.; McAuley, W. J. In International Tables for Crys-
tallography; Wilson, A. J. C., Ed.; Kluwer Academic Publishers: Boston,
1992; Vol. C, Table 4.2.6.8, pp 219-222.
(109) Creagh, D. C.; Hubbell, J. H. In International Tables for Crystal-
lography; Wilson, A. J. C., Ed.; Kluwer Academic Publishers: Boston, 1992;
Vol. C, Table 4.2.4.3, pp 200-206.
(110) teXsan: Crystal Structure Analysis Package, Molecular Structure
Corporation, 1985, 1992.
Supporting Information Available: Figures S1-S7, tables
of positional parameters and B(eq), U values, intramolecular
distances, intramolecular bond angles, Cartesian coordinates,
and torsion or conformational angles for hydrogen and non-
hydrogen atoms for 1b, 3, and 6 (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
JA9944599