Systematic variation of bidentate ligands used in aryl halide amination. Unexpected effects of steric, electronic, and geometric perturbations

Article abstract of DOI:10.1021/ja9721881

This paper presents effects of varying bidentate phosphine steric properties, electronic properties, and bite angle on product ratios in the amination of aryl bromides. Comparison of the ratios of amine products to dehydrohalogenation products showed that catalysts containing electron rich, modestly hindered phosphines with small bite angles (~-90°) gave the best selectivities. Surprisingly, the arene side product formed from reaction of alkylamines deuterated in the N-H position or deuterated in the position α to the nitrogen showed low levels of deuterium incorporation in many examples. Steric properties and ligand bite angle had the greatest impact on the selectivity for monoarylation versus diarylation of primary amines; ligands with small bite angles gave higher monoarylation-to-diarylation ratios, as did ligands with increased steric bulk. Electron poor or sterically hindered bidentate phosphines reduced the amount of product resulting from aryl exchange of electron rich palladium-bound arenes with those of aryl groups on the phosphine ligands.

Full text of DOI:10.1021/ja9721881

3694
J. Am. Chem. Soc. 1998, 120, 3694-3703
Systematic Variation of Bidentate Ligands Used in Aryl Halide
Amination. Unexpected Effects of Steric, Electronic, and Geometric
Perturbations
Blake C. Hamann and John F. Hartwig*
Contribution from the Department of Chemistry, Yale UniVersity, P.O. Box 208107,
New HaVen, Connecticut 06520-8107
ReceiVed July 1, 1997
Abstract: This paper presents effects of varying bidentate phosphine steric properties, electronic properties,
and bite angle on product ratios in the amination of aryl bromides. Comparisons of the ratios of amine products
to dehydrohalogenation products showed that catalysts containing electron rich, modestly hindered phosphines
with small bite angles (∼90°) gave the best selectivities. Surprisingly, the arene side product formed from
reaction of alkylamines deuterated in the N-H position or deuterated in the position R to the nitrogen showed
low levels of deuterium incorporation in many examples. Steric properties and ligand bite angle had the
greatest impact on the selectivity for monoarylation versus diarylation of primary amines; ligands with small
bite angles gave higher monoarylation-to-diarylation ratios, as did ligands with increased steric bulk. Electron
poor or sterically hindered bidentate phosphines reduced the amount of product resulting from aryl exchange
of electron rich palladium-bound arenes with those of aryl groups on the phosphine ligands.
Introduction
because the selectivity for amination over reduction was en-
hanced by steric bulk.11,13 It was, therefore, remarkable when
a very different class of phosphine ligand, tightly bound che-
lating phosphines such as DPPF (1,1′-bis(diphenylphosphino)-
ferrocene and BINAP (2,2′-bis(diphenylphosphino)-1,1′-binaph-
thyl), were found to be more effective than P(o-tolyl)3 in the
amination chemistry for many amine and aromatic substrates.2,3
A chelating ligand possesses three major characteristics: elec-
tron-donating ability, steric properties, and the P-M-P angle
often called “bite angle”. The effect of these three properties
on the selectivity in hydroformylations,14-16 carbon dioxide
hydrogenation,17 and alkyne hydrosilylation18,19 has been in-
vestigated over the years. However, chelating phosphines are
often used in cross coupling chemistry, and few systematic
studies have been conducted to reveal how all three factors affect
this palladium- and nickel-catalyzed chemistry. Most of the
focus has been placed upon the effect of the bite angle,20 or on
electronic and steric properties of monodentate phosphines.21
In rough terms, chelation inhibits â-hydrogen elimination of
alkyl groups,22,23 and a similar effect appears to control the
selectivity of amido complexes that are intermediates in the
The use of chelating phosphine ligands has greatly improved
the palladium-catalyzed chemistry that forms arylamines from
aryl halides or aryl triflates.1-3 This development is syntheti-
cally important because aromatic amines are fundamental
building blocks in natural products and organic materials,4-6
but classical methods to prepare mixed alkylarylamines can be
tedious, and nucleophilic aromatic substitution of aryl halides
is limited to strongly electron deficient aryl halides or high-
temperature processes involving ill-defined copper reagents.7,8
Originally, palladium complexes containing the labile, steri-
cally encumbered, monodentate triarylphosphine ligands such
as P(o-tolyl)3 were the only catalysts for the intermolecular
amination chemistry involving amines in the presence of tin
amides.9-12 Kinetic studies, along with investigations of the
ligand steric effects on selectivity, showed that P(o-tolyl)3 was
unusually effective because each intermediate in the catalytic
cycle was a highly unsaturated, monophosphine complex and
(1) For a review see: Hartwig, J. F. Synlett 1997, 329-340.
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1718.
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118, 7215-7216.
(13) Hartwig, J. F.; Paul, F. J. Am. Chem. Soc. 1995, 117, 5373-5374.
(14) Unruh, J. D.; Christenson, J. R. J. Mol. Catal. 1982, 14, 19-34.
(15) Kranenburg, M.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Vogt,
D.; Keim, W. J. Chem. Soc., Chem. Commun. 1995, 2177-2178.
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Gavney, J., J. A.; Powell, D. R. J. Am. Chem. Soc. 1992, 114, 5535-5543.
(17) Angermund, K.; Baumann, E. D.; Fornika, R.; Go¨rls, H.; Kessler,
M.; Kru¨ger, C.; Leitner, W.; Lutz, F. Chem. Eur. J. 1997, 3, 755-764.
(18) Hofmann, P.; Meier, C.; Englert, U.; Schmidt, M. U. Chem. Ber.
1992, 125, 353-365.
(4) Buckingham, J. Dictionary of Natural Products, 1st ed.; University
Press: Cambridge, MA, 1994.
(5) Negwer, M. Organic -Chemical Drugs and Their Synonyms (an
international surVey), 7th ed.; Akademie Verlag GmbH: Berlin, 1995.
(6) MacDiarmid, A. G.; Epstein, A. J. In Science and Applications of
Conducting Polymers; Salaneck, W. R., Clark, D. T., Samuelsen, E. J., Eds.;
Adam Hilger: New York, 1991; p 117.
(7) Lindley, J. Tetrahedron 1984, 40, 1433-1456.
(8) Paine, A. J. J. Am. Chem. Soc. 1987, 109, 1496-1502.
(9) Kosugi, M.; Kameyama, M.; Migita, T. Chem. Lett. 1983, 927-928.
(10) Kosugi, M.; Kameyama, M.; Migita, T. Nippon Kagaku Kaishi 1985,
3, 547-551.
(19) Hofmann, P.; Meier, C.; Hiller, W.; Heckel, M.; Riede, J.; Schmidt,
M. U. J. Organomet. Chem. 1995, 490, 51-70.
(20) Brown, J. M.; Guiry, P. J. Inorg. Chim. Acta 1994, 220, 249-259.
(21) Farina, V.; Krishman, B. J. Am. Chem. Soc. 1991, 113, 9585-9595.
(22) Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi, T.;
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(23) Whitesides, G. M.; Gaasch, J. F.; Stedronsky, E. R. J. Am. Chem.
Soc. 1972, 94, 5258-5270.
(11) Louie, J.; Paul, F.; Hartwig, J. F. Organometallics 1996, 15, 2794-
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7902.
S0002-7863(97)02188-4 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/31/1998

Systematic Variation of Bidentate Ligands
J. Am. Chem. Soc., Vol. 120, No. 15, 1998 3695
Scheme 1. General Procedure for Ligand Synthesis
Scheme 2. Model Reactions Studied
Figure 1. Structures of the bidentate phosphine ligands.
amination chemistry. We have recently shown that â-hydrogen
elimination from amido complexes occurs from a 14-electron,
three-coordinate intermediate.24 In contrast, C-N bond-forming
reductive elimination of amines from square planar Pd(II)
complexes can occur from either a four- or three-coordinate
intermediate.25 Thus, chelating ligands provide enhanced
selectivity for reductive elimination over â-hydrogen elimination
in the amination chemistry.
However, not all chelating ligands are equally effective, and
no systematic studies have revealed why one ligand is more
effective than another in the aryl halide amination chemistry.
One might expect that more hindered chelating ligands would
combine the benefits of the hindered P(o-tolyl)3 with the benefits
of chelation. One might also expect that electron poor ligands
would enhance the formation of amination products, since
reductive elimination is accelerated by reducing the electron
density at the metal center.26 Finally, reductive elimination is
typically faster for complexes with chelating ligands containing
large bite angles than it is for complexes with small bite angles.20
Thus, one might expect that increasing the size of the bite angle
created by the chelating phosphine would increase the yields
of amination product.
We have tested these hypotheses in a systematic fashion by
varying DPPF (1,1′-bis(diphenylphosphino)ferrocene). We have
chosen to use this ligand as a parent structure because it is
effective in the amination chemistry, it is simple to modify, and
it has been used in many other transition-metal-catalyzed
reactions. We have prepared ligands that are more hindered,
more electron poor, or more electron rich than DPPF. We have
also prepared bis(diarylphosphino) ligands that produce pal-
ladium complexes with both larger and smaller bite angles. The
results from these studies are unexpected, and show that the
rate for reductive elimination should not be the dominant
consideration when ligands for the next generation amination
catalysts are designed.
2. Selection of Model Reactions and Methods for Analy-
sis. We chose the amination reactions in Scheme 2 for our
studies because these reactions produced mixed secondary
amines in modest yields and would, therefore, reveal both
beneficial and detrimental effects of ligand steric and electronic
perturbations. The reaction between (4-bromobutyl)benzene and
n-butylamine and the reaction between (4-bromobutyl)benzene
and isobutylamine occurred in yields between 55% and 65%
for the parent DPPF ligand. The reaction between 4-bromo-
N,N-dimethylaniline and aniline occurred in 75% yield when
the parent DPPF was used as ligand. Thus, these three reactions
were used for our studies on how ligand properties affect
aminations of aryl halides using both primary alkylamines and
primary arylamines.
The reactions were conducted using a combination of 5 mol
% Pd(dba)2 and 2 equiv of the chelating ligand. However,
similar results were obtained with two other catalyst precursors,
Pd(OAc)2 and Pd[P(o-tolyl)3]2. In addition to the major ami-
nation product, competing products were arene, resulting from
dehydrohalogenation of the aryl halide, and diarylalkylamine
(or triarylamine in the case of aminations involving aniline)
resulting from diarylation of the primary amine. Reactions
involving 4-bromo-N,N-dimethylaniline also showed products
from aryl group exchange between the phosphine and aryl
halide. The relative amounts of the reaction products were
assessed by gas chromatography, correcting for response factors
obtained from isolated materials. Arylamine products were also
isolated in selected cases to ensure that the GC values accurately
corresponded to product distributions in larger scale reactions.
3. Results from Varying Ligand Steric, Electronic, and
Geometric Properties. 3.a. Effect of Steric Perturbations.
The results in Tables 1 and 2 show the effect of varying the
steric bulk of the phosphine ligands on reaction 1 in Scheme 2.
A comparison of DPPF and the o-tolyl version DTPF showed
that the amount of arene product increased by roughly 8-fold
with this increase in ligand size. Similar comparisons of phenyl-
and o-tolylphosphine ligands based on diaryl ether backbones
Results
1. Ligand Preparation. The ligands employed in this study
are shown in Figure 1, along with their abbreviations. Typically,
the ligands were prepared in multigram quantities by dilithiation
of the backbone (Cp2M, diaryl ether, or bromonaphthalene)
followed by quenching with a chlorodiarylphosphine (Scheme
1).14,27,28 Alternatively, some of these ligands were prepared
in small quantities by addition of aryllithium or aryl Grignard
reagents to bis(dichlorophosphino)ferrocene (Scheme 1).29
(24) Hartwig, J. F. J. Am. Chem. Soc. 1996, 118, 7010-7011.
(25) Driver, M. S.; Hartwig, J. F. J. Am. Chem. Soc. 1997, 119, 8232.
(26) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987; pp 324-329.
(27) Hillebrand, S.; Bruckmann, J.; Kru¨ger, C.; Haenel, M. Tetrahedron
Lett. 1995, 36, 75-78.
(28) de Lang, R.-J.; van Soolingen, J.; Verkruijsse, H. D.; Brandsma, L.
Synth. Commun. 1995, 25, 2989-2991.
(29) Nifant’ev, I. E.; Boricenko, A. A.; Manzhukova, L. F.; Nifant’ev,
E. E. Phosphorus, Sulfur, Silicon 1992, 68, 99-106.

3696 J. Am. Chem. Soc., Vol. 120, No. 15, 1998
Hamann and Hartwig
Table 1. Steric Effects on Reaction 1 in Scheme 2 To Give
BuC6H5 1, p-BuC6H4NHBu 2, and (p-BuC6H4)2NBu 3
Table 3. Electronic Effects on Reactions 1 and 4 in Scheme 2 To
Give BuC6H5 1, p-BuC6H4NHBu 2 or 6, and (p-BuC6H4)2NBu 3 or
7
ligand
DPPF
DTPF
DPPDPE
DTPDPE
DPPX
% 1a
% 2a
% 3a
ligand
amine
% 1a
% 2 or 6a
2:3 or 6:7b
4.4 ( 0.2
34 ( 1.0
40 ( 2.5
46 ( 8.0
24 ( 1.2
22 ( 1.5
52 ( 2.5 (46)
36 ( 2.0
11 ( 1.5
25 ( 5.0
47 ( 3.0
35 ( 4.0
22 (1.0
p-MeODPPF n-butyl
p-MeODPPF isobutyl
4.0 ( 0.6 55 ( 1.0
9.1 ( 0.8 68 ( 1.5
4.4 ( 0.2 52 ( 2.5 (46)
9.2 ( 1.5 69 ( 1.0 (42)
5.5 ( 0.5 53 ( 0.5
2.6 ( 0.1
150c
5.8 ( 0.4
3.6 ( 0.9
2.0 ( 0.7
7.0 ( 1.4
7.6 ( 1.8
DPPF
DPPF
n-butyl
isobutyl
n-butyl
2.4 ( 0.1
15 ( 1.8
2.9 ( 0.1
25 ( 8.1
8.8 ( 0.2
14 ( 3.0
p-CF3DPPF
p-CF3DPPF
3,5-CF3DPPF n-butyl 14 ( 2.5
DTPX
isobutyl 17 ( 1.5
49 ( 1.0
49 ( 5.0
40 ( 1.5
a Yields are based on the average of two or more runs. Yields in
parentheses are isolated yields.
DFPF n-butyl 16 ( 1.5
a Yields are based on the average of two or more runs. Yields in
parentheses are isolated yields. b Ratio of monoarylation to diarylation
product. c Diarylation product was less than the GC observation limits.
Table 2. Steric Effects on Aryl Migration for Reaction 2 in
Scheme 2 To Give Me2NPh 4, Me2NC6H4NHPh 5, and a
Diarylamine
ligand
DPPF
% 4a
% 5a
5:Ph2NHb
by known aryl group exchange processes. Palladium-bound
electron rich aryl groups are known to be particularly susceptible
to these exchange processes.30-32 In the case of the diphenyl-
phosphino ligands, diphenylamine would be the diarylamine
product resulting from rearrangement prior to amine formation.
In the case of the di-o-tolylphosphino ligands, (o-tolylphenyl)-
amine would be the product from rearrangement.
Consistent with previous data on palladium-catalyzed Heck
reactions,33 we found that an increase in steric bulk of the
phosphine aryl group led to a significant reduction in the amount
of amine product that results from prior aryl group migration
in reactions catalyzed by complexes containing DPPF and
DTPF. A similar effect of steric properties on aryl group rear-
rangements was observed for reactions catalyzed by DPPDPE
and DTPDPE. However, no significant difference in the amount
of rearrangement was observed for reactions catalyzed by the
two types of ligands based on a xanthene backbone.
0 ( 0.2
69 ( 6.2 (75)
78 ( 7.3
26 ( 6.1
76 ( 5.9
70 ( 1.1
62 ( 4.1
45 ( 14
89 ( 9.6
21 ( 8.4
150d
4.9 ( 0.5
3.9 ( 0.3
DTPF
0.4 ( 0.4
0.4 ( 0.4
1.7 ( 0.3
0 ( 0.2
DPPDPEc)
DTPDPE
DPPX
DTPX
0.5 ( 0.3
a Yields are based on the average of two or more runs. Yields in
parentheses are isolated yields. b The migration product is a tolylphen-
ylamine when o-tolylphosphine derivatives were used. c Reactions only
went to 60% and 55% completion. d Diarylation product was less than
the GC observation limits.
Scheme 3. Equilibrium and Rate Constants Involved in the
Relative Rates for Mono- and Diarylation of Primary
Amines
3.b. Effects of Perturbing Ligand Aryl Group Electronic
Properties. The influence of phosphine aryl group electronic
properties was evaluated by employing ligands that contained
electron-donating and electron-withdrawing groups on the phos-
phine aromatic rings. As stated in the Introduction, one would
expect that electron poor phosphines would accelerate the rate
of reductive elimination and increase the amine:arene ratio. The
effect of perturbing the phosphine aryl group electronic proper-
ties was small, but the observed effect contradicted our expec-
tation that was based on conventional principles.
The reaction of n-butylamine with (4-bromobutyl)benzene
was conducted with a combination of Pd(dba)2 and several
modified DPPF ligands. The results of experiments conducted
with these modified ligands are provided in Table 3. Reactions
conducted with the ligands 3,5-CF3DPPF and DFPF, which
would be less electron rich than DPPF, showed an increase in
arene formation. Altering the phosphine-bound aromatic ring
with a single substituent gave less substantial variation in the
ratios of amination to reduction products. However, reactions
involving p-CF3-modified DPPF did give a slight increase in
the amount of arene product relative to reactions with DPPF,
while reactions conducted with the more electron rich p-MeO-
modified DPPF ligand gave slightly decreased amounts of arene
product.
again showed no enhancement of the amine:arene ratio upon
increasing the ligand steric properties, although the amine:arene
ratio was not altered substantially in these cases.
Selectivity for arylation of the primary alkylamine over
arylation of the alkylarylamine product must rely on the
product’s increased size and/or its decreased basicity. Equi-
librium between the palladium amido complexes as well as the
relative rates of reductive elimination for the primary and
secondary amido complexes will determine the monoarylation
vs diarylation products (Scheme 3). Steric effects are important,
as ligand size was found to have a pronounced effect on the
selectivity for the formation of monoarylamine product over
diarylamine product (Tables 1 and 7). A comparison between
DPPF and DTPF showed almost a 3-fold increase in the
selectivity for formation of secondary alkylarylamine over
tertiary diarylamine when DTPF was used as ligand along with
1.2 equiv of n-butylamine. Similar effects on selectivity were
observed when diphenylphosphino- and di-o-tolylphosphino-
substituted diphenyl ether ligands were employed.
The effect of reducing the phosphine aryl group electron
density had a larger effect on the reactions of isobutylamine
In addition to evaluating ligand steric effects on the amination
of electron neutral aryl bromides with primary alkylamines, we
examined the impact of varying ligand steric properties on the
amination of the electron rich aryl halide 4-bromo-N,N-
dimethylaniline with aniline (reaction 2 in Scheme 2, Table 2).
Electron rich aryl bromides often exchange with the aryl groups
on the phosphine during catalytic and stoichiometric reactions
(30) Kong, K.-C.; Cheng, C.-H. J. Am. Chem. Soc. 1991, 113, 6313-
6315.
(31) Segelstein, B. E.; Butler, T. W.; Chenard, B. L. J. Org. Chem. 1995,
60, 12-13.
(32) Herrmann, W. A.; Broâmer, C.; O¨ fele, K.; Beller, M.; Fischer, H.
J. Organomet. Chem. 1995, 491, C1-C4.
(33) Ziegler, C. B., Jr.; Heck, R. F. J. Org. Chem. 1978, 43, 2941-
2945.

Systematic Variation of Bidentate Ligands
J. Am. Chem. Soc., Vol. 120, No. 15, 1998 3697
Table 4. Electronic Effects on Aryl Migration for Reaction 2 in
Scheme 2 To Give Me2NPh 4, Me2NC6H4NHPh 5, and a
Diarylamine
Table 5. Effect of the Bite Angle on Reaction 1 in Scheme 2 To
Give BuC6H5 1, p-BuC6H4NHBu 2, and (p-BuC6H4)2NBu 3
ligand
bite angle (deg)
% 1a
% 2a
% 3a
ligand
% 4a
% 5a
5:ArPhNHb
DPPN
BINAP
DPPF
DPPR
DPPDPE
DPPX
82b
1.4 ( 1.0 78 ( 3.8
5.7 ( 0.7
92.7,c 85b
99.0c
101c
0.9 ( 0.2 91 ( 2.0 (75) 3.0 ( 0.3
4.4 ( 0.2 52 ( 2.5 (46) 22 ( 1.0
p-MeODPPF
DPPF
p-CF3DPPF
3,5-CF3DPPF
DFPF
0.9 ( 0.9
0 ( 0.2
71 ( 5.7
21 ( 6.5
45 ( 14
88c
69 ( 6.2 (75)
74 ( 3.1
2.0 ( 1.0
0 ( 0.2
36 ( 2.0
40 ( 2.5
24 ( 1.8
12 ( 1.0
11 ( 1.0
47 ( 3.0
5.2 ( 3.4
3.6 ( 0.9
7.0 ( 1.4
101b
67 ( 2.0
65 ( 2.3
27 ( 4.0
150c
109b
2.3 ( 0.4
a Yields are based on the average of two or more runs. Yields in
parentheses are isolated yields. b Aryl group is that of the phosphine
ligand. c These examples had at least one trial where the migration
product was less than GC observation limits.
a Yields are based on the average of two or more runs. Yields in
parentheses are averaged isolated yields. b Calculated values for the
natural bite angle; see refs 15 and 38. c Values from crystallographic
structure determination of the palladium dichloride complexes; see refs
22 and 39-41.
the DPPF ligands than might be expected on the basis of changes
in νCO that resulted from variations in the aryl groups of
monodentate triarylphosphine ligands. For comparison, previous
35
changes in para substituents from Ph to p-CF3C6H4 or from
36
Ph to p-MeOC6H4 on Vaska’s complex [Ir(PPh3)2(CO)Cl],
which contains two phosphine ligands, led to changes in νCO
of roughly 10 wavenumbers. Further, these changes led to
differences in oxidative addition reaction rates that varied by
2-3 orders of magnitude for MeI addition and an order of
magnitude for H2 addition.35
Our data for the DPPF ligands show that substantial changes
in electron density can be detected by νCO for the di-CF3 ligand,
but only small changes were observed for the OMe-substituted
ligand. Thus, these ligands perturb the electron density at the
metal much less than do analogous monodentate ligands, and
the resulting differences in selectivity will, therefore, be sub-
tle. These data also demonstrate that the electronic donating
abilities of BINAP and DPPF are more similar than one might
expect, and that differences in selectivity between DPPF and
BINAP most likely arise from structural, rather than electronic,
differences.
Figure 2. Changes in CO stretching frequency as a function of the
phosphine aryl group and backbone.
3.c. Effect of Altering the Ligand Bite Angle. As noted
in the Introduction, reductive elimination rates are typically
accelerated by increased bite angle. In contrast to this estab-
lished trend, the yields of arylamine were generally higher for
reactions involving ligands with small bite angles (Table 5).
The xanthene-based ligand gave more amination product than
DPPR or the diphenyl ether based-ligand DPPDPE, but this
difference is more likely to originate in the preorganized
structure of this ligand relative to the flexible DPPDPE. A
correlation between ligand bite angles and the amount of
reduction product clearly showed that reducing the size of the
bite angle led to decreasing amounts of reduction products,
particularly for preorganized bidentate ligands such as BINAP
and the naphthalene-based ligand DPPN.37-41
(Table 3). For the reactions involving isobutylamine p-CF3-
DPPF gave a substantially increased amount of arene relative
to the amount of arene in reactions involving DPPF and
p-MeODPPF. This set of results from perturbing the aryl group
electronic properties shows that electron poor ligands do not
provide enhanced rates for reductive elimination relative to
competing processes that form arene.
No trends were observed in monoarylation to diarylation
selectivities as the electronics were perturbed. However,
reactions involving the 3,5-CF3DPPF ligand with butylamine
or p-MeODPPF with isobutylamine did show significant dif-
ferences relative to DPPF. Aryl exchange processes were
affected by the electronic properties of the phosphine aryl group.
During the coupling of the electron rich aryl bromide 4-bromo-
N,N-dimethylaniline with aniline, reactions involving the elec-
tron poor and electron neutral DPPF derivatives gave less amine
resulting from prior aryl group migration than did reactions
involving the more electron rich p-MeODPPF (Table 4).
To understand the extent to which the CF3 and OMe groups
altered the electron density at the metal center and to determine
potential electronic affects of changing the backbone from
ferrocenyl to binaphthyl, we prepared carbonyl complexes
Reducing the size of the bite angle also led to increased
selectivity for monoarylation over diarylation products. For the
(34) Tolman, C. A. Chem. ReV. 1977, 77, 313.
(35) Wilson, M. R.; Liu, H.; Prock, A.; Giering, W. P. Organometallics
1993, 12, 2044.
(36) Lawson, H. J.; Atwood, J. D. J. Am. Chem. Soc. 1989, 111,
6223.
(37) Several ligands that create small bite angles such as bis(diphen-
ylphosphino)ethane, bis(diphenylphosphino)ethylene, and bis(diphenylphos-
phino)benzene, were shown previously to give poor product:arene ratios.
In some cases, the low yields of amination product may be due to ligand
decomposition under the reaction conditions; see refs 2 and 3.
(38) Casey, C. P.; Whiteker, G. T. Isr. J. Chem. 1990, 30, 299-304.
(39) Ozawa, F.; Kubo, A.; Matsumoto, Y.; Hayashi, T.; Nishioka, E.;
Yanagi, K.; Moriguchi, K. Organometallics 1993, 12, 4188-4200.
(40) Hayashi, T.; Ohno, A.; Lu, S.-j.; Matsumoto, Y.; Fukuyo, E.; Yanagi,
K. J. Am. Chem. Soc. 1994, 116, 4221-4226.
containing the different ligands to evaluate changes in νCO
.
Figure 2 shows the νCO values for four Ni(0) complexes that
were prepared by reaction of the modified DPPF ligands with
[Ni(CO)2(PPh3)2]. The electronic properties of monodentate
ligands have been evaluated previously using IR data on [Ni-
(CO)3L] complexes.34 Less change in νCO was observed for
(41) Li, S.; Wei, B.; Low, P. M. N.; Lee, H. K.; Hor, T. S.; Xue, F.;
Mak, T. C. W. J. Chem. Soc., Dalton Trans. 1997, 1289-1293.

3698 J. Am. Chem. Soc., Vol. 120, No. 15, 1998
Hamann and Hartwig
Table 6. Product Ratios for Diarylation Reaction 3 in Scheme 2
To Give BuC6H5 1, p-BuC6H4NHBu 2, and (p-BuC6H4)2NBu 3
Scheme 4. Amount of Arene Formed from â-Hydrogen
Elimination vs Arene from Competing Reactions
ligand
DPPN
% 1a
% 2a
% 3a
3.3 ( 0.1
17 ( 4.0
3.9 ( 0.8
27 ( 1.0
38 ( 1.0
15 ( 1.5
3.7 ( 2.3
3.8 ( 0.5
4.3 ( 0.4
8.7 ( 1.3
3.1 ( 1.0
17 ( 1.0
2.1 ( 2.1
5.4 ( 0.8
5.0 ( 0.6
1.9 ( 1.9
49 ( 0.6
39 ( 11
BINAP
DPPF
DTPF
DPPDPE
DPPX
p-MeODPPF
p-CF3DPPF
106 ( 8.0 (85)
24 ( 4.0
7.5 ( 3.6
63 ( 11
97 ( 8.5
106 ( 15
a Yields are based on the average of two or more runs. Yields in
parentheses are isolated yields.
Table 7. Effect of Amine Sterics: Product Ratios for Reaction 4
of Scheme 2 To Give BuC6H5 1, p-BuC6H4NH-i-Bu 6,
(p-BuC6H4)2-Ni-Bu 7
aryl halides. The reaction of 2-bromotoluene with n-butylamine
gave the monoarylation product in 99% yield for BINAP, 96%
yield for DPPF, 77% yield for DTPF, 50% yield for DPPDPE,
89% yield for DPPX, and 96% yield ((1.0%) for p-MeODPPF
by GC. The product was isolated in 92% yield using DPPF.
These yields are substantially increased over those for reactions
of n-butylamine with (4-bromobutyl)benzene. No diarylation
products were seen in any of these reactions.
ligand
% 1a
% 6a
6 : 7a
DPPN
BINAP
DPPF
DTPF
DPPDPE
DPPX
1.5 ( 0.2
1.0 ( 0.2
9.2 ( 1.5
34 ( 0.3
46 ( 0.9
33 ( 0.4
83 ( 0.9
48 ( 14
91 ( 0.5
150b
69 ( 1.0 (42)
39 ( 1.0
6.5 ( 0.6
40 ( 0.5
15 ( 1.8
80b
2.8 ( 0.3
9.8 ( 1.7
5. Labeling Experiments. The unexpected effects of ligand
properties on amine:arene ratios led us to evaluate whether the
arene was actually formed from competing â-hydride elimina-
tion. Amination reactions between (1,1-dideuterio-3-phenyl-
propyl)amine and (4-bromobutyl)benzene were, therefore, con-
ducted (Scheme 4). Butylbenzene formed from these reactions
was then analyzed by mass spectrometry to determine the
percent deuterium incorporation. The reactions were carried
out under the same conditions as the coupling for butylamine
with (4-bromobutyl)benzene. The reaction of (1,1-dideuterio-
3-phenylpropyl)amine with (4-bromobutyl)benzene was con-
ducted using 10 mol % DPPF, DTPF, DPPDPE, and DPPX
with 5 mol % Pd(dba)2 or Pd[P(o-tolyl)3]2. Results from GC/
MS for reactions using Pd(dba)2 as precursor showed only 37%
deuterium incorporation into the arene for reactions involving
DPPF, 14% for those involving DTPF, 27% for those with
DPPDPE, and 64% for those with DPPX. These numbers
increased slightly to 49%, 22%, 52%, and 73%, respectively,
when Pd[P(o-tolyl)3]2 was used as the catalyst precursor (errors
estimated at (5.0%). Little or no hydrodehalogenation product
occurred from chemistry involving the amine N-H position.
Reaction of N,N-dideuterio-(3-phenylpropyl)amine and (4-
bromobutyl)benzene catalyzed by Pd(dba)2 and any of the four
ligands showed little or no deuterated arene. Reactions
conducted with protiated substrates in toluene-d8 solvent also
showed no deuterium incorporation.
Because the imines that would be produced in reactions
involving primary alkylamines are unstable, it is difficult to
assess the mass balance of aminations using these substrates.
Further, we were concerned that a simple â-hydrogen elimina-
tion and subsequent reductive elimination would appear to be
more complex because proton-transfer processes involving a
palladium hydride intermediate may occur and reduce the
percent deuterium incorporation. Thus, we conducted reactions
with HNPh(CD2Ph) that would produce a stable imine. In this
case we observed an amount of deuterated arene that matched
the amount of imine within experimental error. This result
demonstrates that deuterium is not being lost by proton transfers
involving a hydride intermediate. However, a substantial
amount of undeuterated arene was again observed, and there
was not enough imine byproduct to account for this arene. Thus,
there are pathways other than â-hydrogen elimination and
reductive elimination of arene that lead to dehydrohalogenation
a Yields are based on the average of two or more runs. Yields in
parentheses are isolated yields. b These examples had at least one trial
where the diarylation product was less than the GC observation limits.
aminations involving n-butylamine, the ratio of monoarylation
to diarylation product was highest for BINAP and DPPN. As
this result would predict, ligands with large bite angles such as
DPPF were superior for the one-pot formation of diarylated
amine by reaction of n-butylamine with 2 equiv of aryl bromide
(reaction 3 in Scheme 2, Table 6). It appears that DPPF has a
large enough bite angle to accommodate the formation of tertiary
amine. Yet, the reaction does not suffer from producing large
amounts of reduction product as has been observed with the
ligands that possess larger bite angles.
For the reaction of aniline with 4-bromo-N,N-dimethylaniline,
no trend was observed between the bite angle and the amount
of product resulting from aryl migration.
4. Effect of Substrate Steric Properties. It was not clear
whether increasing the size of the amine would hinder formation
of the geometry required for â-hydrogen elimination while
accelerating the reductive elimination process, as was seen for
reactions involving P(o-tolyl)3,42 or whether increased size of
the amide would facilitate â-hydrogen elimination. In fact, the
opposite effect of that detected previously for P(o-tolyl)3 was
observed with the catalysts containing chelating phosphines. A
modest increase in the size of the amine led to an increase in
the amount of arene, rather than arylamine, product.
Reactions with isobutylamine (reaction 4 in Scheme 2 and
Table 7) catalyzed by Pd-DPPF gave a 2-fold increase in the
amount of arene product relative to analogous reactions with
n-butylamine. A larger increase in arene product was observed
when DTPF was used as ligand. Perhaps more predictably,
increasing the size of the amine substrate led to substantial
improvement in the ratio of monoarylation to diarylation
products for reactions involving both DPPF and DTPF. In fact,
only trace amounts of diarylation product were ever observed
in runs involving DTPF.
In contrast to increased amounts of arene that accompanied
increasing size of the amine, substantially decreased amounts
of arene were observed from reactions involving more hindered
(42) Hartwig, J. F.; Richards, S.; Baran˜ano, D.; Paul, F. J. Am. Chem.
Soc. 1996, 118, 3626-3633.

Systematic Variation of Bidentate Ligands
J. Am. Chem. Soc., Vol. 120, No. 15, 1998 3699
of the aryl halide, and these pathways are most important with
substrates containing unactivated hydrogens R to the nitrogen.
The source of the proton in the arene product is not clear, but
it is evident that much of the arene is formed by a process more
complex than expected.
noted many years ago by Heck.33 These aryl exchanges have
been studied more thoroughly recently.30-32
Effects of Perturbing Ligand Aryl Group Electronic
Properties. In contrast to the expectations that ligand electronic
properties would effect the selectivity of the amination reactions
by accelerating reductive elimination, little effect was observed.
Further, the small trend that was observed was in the opposite
direction of what one would expect. The small difference in
selectivity resulting from variation of the aryl group electronic
properties is explained by a weak transmission of the aryl group
electronic properties to the metal center. The small differences
in νCO values for the L2Ni(CO)2 complexes suggest that the
metal center’s electronic properties are less affected by variation
in the chelating ligand aryl groups than they are by monodentate
triarylphosphine ligands. Although we cannot explain precisely
the unexpected observation that decreasing electron density at
the metal center increases the amount of arene, the labeling study
shows that most of the arene does not arise from â-hydrogen
elimination. It should not be surprising, therefore, that the
observed trends deviate from those predicted by trends in
reaction rates for reductive elimination and â-hydrogen elimina-
tion. In fact, the dehydrohalogenation may occur during the
aryl halide addition step or during formation of the palladium
amido complex, rather than after the palladium amide is
generated.
Discussion
At the outset of this study, our expectation and that of others43
based on knowledge of the relationship between the properties
of a metal complex and rates for reductive elimination and
â-hydrogen elimination was an enhancement in the amount of
amination product vs reduction product with sterically hindered
and electron poor bidentate phosphine ligands. The experi-
mental results of this study have shown the logic behind this
prediction to be flawed at two levels. First, the majority of the
arene in reactions of DPPF and DTPF is not formed by
â-hydrogen elimination. Second, the amount of arene that is
formed from â-hydrogen elimination increases with increasing
size of the bidentate phosphine ligand and with increasing size
of the bite angle. A modest increase in arene is formed by
catalysts with the more weakly donating ligands. Thus, the
effect of ligand properties on the amount of arene formed by
â-hydrogen elimination is the opposite of the simple effects one
would expect from previous studies on the chemistry of alkyl
groups. The details of the steric, electronic, and bite angle
properties and their effects on the reaction selectivities are
discussed in the subsequent sections.
Effects of Perturbing Ligand Aryl Group Steric Proper-
ties. Increased steric bulk in either the ligands or the amine
substrates caused an increase in the amount of reduction product.
First, an increase in size of the rigid, bidentate phosphine ligand
DPPF created by incorporating o-tolyl groups led to a dramatic
increase in the amount of arene formed by reactions other than
â-hydrogen elimination. Second, the amount of arene formed
by â-hydrogen elimination increased rather than decreased, albeit
less dramatically.
Apparently the steric properties of the ligand had two effects
on the catalyst selectivity. First, increased steric effects
accelerated a dehydrohalogenation process that competes with
the amination and more standard dehydrohalogenation by
â-hydrogen elimination. Second, the increasing size of the
ligand had a greater effect on the rate of â-hydrogen elimination
than on the rate of reductive elimination. The second result
may occur because of partial dissociation of the bidentate
phosphine, providing a three-coordinate palladium amide aryl
complex that can readily undergo â-elimination. The steric
effects are not simple, however, since reactions of the sterically
hindered substrate 2-bromotoluene catalyzed by unmodified
DPPF gave little reduction. One might expect the increased
steric bulk of the palladium-bound aryl group to also favor
formation of a three-coordinate palladium species.
Increasing the size of the phosphine ligands gave better
monoarylation to diarylation selectivities. This effect is more
simple to rationalize. Clearly, reaction of a sterically hindered
complex with the larger secondary alkylarylamines is less
favorable than reaction with the corresponding primary amine.
These results also suggest that the higher reactivity of the
primary amines in the amination process is largely due to steric
effects.
The basicity of the phosphine ligands also did not have a
pronounced influence on the monoarylation to diarylation
selectivities of primary amines. This result is consistent with
the conclusion drawn above that steric effects are the dominant
factor that control mono- vs diarylation of primary amines.
The phosphine electronic properties did have significant
influence on the degree of aryl migration observed during the
coupling of the electron rich aryl bromide 4-bromo-N,N-dimeth-
ylaniline with aniline (Scheme 2). Strongly electron donating
phosphines gave larger amounts of rearranged product than did
less donating ligands (Table 4). The equilibrium constant in
these aryl exchange processes favors the placement of more
electron rich aryl groups onto the phosphorus and the more
electron poor aryl groups on the metal, but the exchange is more
facile when electron rich aryl groups are on the starting phos-
phines.30-32 It has been proposed that electron poor phos-
phines undergo reductive elimination with the aryl group to
form phosphonium salts less readily than electron rich phos-
phines (Scheme 5),31 making the aryl exchange process slower
for electron poor phosphines compared to electron rich phos-
phines.
Effects of Altering the Ligand Bite Angle. Increasing
ligand bite angle gave decreased ratios of amine to arene
products, exactly the opposite result that would be expected
considering the known effects of the bite angle on reductive
elimination rates. This result can be explained by two factors.
Again, much of the arene does not result from competing
â-hydrogen elimination and reductive elimination, and so
electronic effects on the rates for reaction of the amido
complexes may not be important. Instead, electronic effects
on the oxidative addition of aryl halide or formation of the amido
complexes are likely to be more important. Second, the
phosphines that provide larger bite angles can partially dissociate
more readily than those with bite angles near 90°, generating
three-coordinate intermediates that can undergo â-hydrogen
elimination. Since a greater proportion of the arene results from
â-hydrogen elimination during reactions involving phosphines
that provide large bite angles than those involving phosphines
that create small bite angles, it is likely that partial phosphine
Aryl group migration was also reduced when DTPF or
DTPDPE was employed instead of DPPF or DPPDPE, respec-
tively. Steric effects on aryl group exchange reactions were
(43) Marcoux, J.-F.; Wagaw, S.; Buchwald, S. L. J. Org. Chem. 1997,
62, 1568-1569.

3700 J. Am. Chem. Soc., Vol. 120, No. 15, 1998
Hamann and Hartwig
Scheme 5. Previously Proposed Pathway for Aryl Group Exchange
dissociation does occur with these ligands. Thus, the increase
in rates for â-hydrogen elimination and competing dehydroha-
logenation processes is greater than the increase in rate for
reductive elimination as a result of increasing the ligand bite
angle.
by a factor of 9, and gave the monoarylamine in 67% yield as
determined by GC analysis.
Ortho substituents on the aryl bromide gave a large increase
in yields mostly because diarylation is inhibited, but also because
aryl halide reduction is minimized. For reactions catalyzed by
a combination of Pd(dba)2 and DPPF, the yield of monoarylated
amine from reaction with o-methylbromobenzene was high.
Although the reduced product toluene could not be detected by
GC techniques, the high yield requires that little reduction
occurred.
Surprisingly, the monoarylation to diarylation selectivities
were highest for ligands with small bite angles. We do not
have a firm explanation for this result. However, this empirical
observation may be useful for future ligand development.
Further, this effect is useful in selecting a ligand for diarylation
of primary amines.44 Because the ligands that generate small
bite angles are selective for monoarylation, they give lower
yields for diarylations than do the ligands that create medium-
sized bite angles. The ligands with larger bite angles (>95°)
seem to accommodate more readily the secondary arylamine
substrates than do those with smaller bite angles, but too large
a bite angle leads to an increase in the amount of arene. Thus,
Pd(dba)2/DPPF is a good compromise in ligand properties for
diarylation of primary amines.
There was a poor correlation between bite angle and the
amount of observed rearrangement product for reaction of the
electron rich arene 4-bromo-N,N-dimethylaniline with aniline.
However, it was clear that BINAP, typically a ligand that gives
clean reaction products, was one of the worst ligands of those
tested and gave many different side products in addition to
diphenylamine formed after aryl group exchange.
In many cases, an alteration of the ligand bite angle requires
a change in the structure of the ligand backbone, which may
lead to potential electronic perturbations. The use of nickel(0)
dicarbonyl complexes to determine the electronic differences
between binaphthyl and ferrocene as backbone in an admittedly
crude fashion showed that the backbone did not substantially
change the metal electronic properties. The two νCO values for
the nickel complexes containing DPPF and BINAP varied by 5
and 0 cm-1, while the νCO values varied by 15 and 27 cm-1
when the aryl substituent was varied from p-MeOC6H4 to 3,5-
CF3C6H3. Thus, the influence of changing the ligand backbone
from binaphthyl to ferrocene on the metal electronic properties
appeared to be minimal.
Effects of Substrate Steric Properties. Monoarylation to
diarylation selectivities are higher for branched, primary aliphatic
amine substrates. A small change in the amine steric properties,
n-butylamine versus isobutylamine, produced an approximately
6-fold increase in monoarylation to diarylation selectivity for
reactions conducted with a combination of Pd(dba)2 and DPPF.
Of course, the use of excess amine also led to improved product
ratios. Reaction of 12 equiv of n-butylamine with (4-bromobu-
tyl)benzene gave a monoaryl:diaryl product ratio that improved
Experimental Section
Unless otherwise specified, all reagents were purchased from
commercial suppliers and used without further purification. THF and
toluene were distilled from sodium-benzophenone ketyl under nitrogen.
The following phosphine ligands were prepared according to literature
procedures: DPPR,45 DPPDPE,46 DPPX,27,46 p-MeO-DPPF,47,48 p-CF3-
DPPF,14 DPPN.49,50
Reactions were set up in an inert atmosphere glovebox. Amines
were added by syringe without degassing. 1H, 13C{1H}, and 31P{1H}
NMR spectra were obtained on a GE QE 300 MHz, GE Ω 300 MHz,
or Brucker AM500 MHz Fourier transform spectrometer. 1H and
13C{1H} NMR spectra were recorded relative to residual protiated
solvent; a positive value of the chemical shift denotes a resonance
downfield from TMS. 31P{1H} NMR spectra were recorded relative
to 85% H3PO4; a positive value of the chemical shift denotes a
resonance downfield from H3PO4. Samples for elemental analysis were
submitted to Robertson Microlit Labs, Inc., Madison, NJ 07940.
Samples for mass spectrum analysis were submitted to The University
of Illinois at Champaign-Urbana, School of Chemical Sciences. GC
analyses were conducted on a Hewlett-Packard 5890 instrument
connected to a 3395 integrator.
1,1′-Bis[bis(2-methylphenyl)phosphino]ferrocene.28,51 Ferrocene
(2.280 g, 12.26 mmol) was mixed with 2.1 equiv of n-butyllithium
(2.66 M in hexanes, 9.68 mL, 25.74 mmol), 2.1 equiv of TMEDA (3.88
mL, 25.74 mmol), and hexane (50 mL) in an oven-dried flask fitted
with a condenser, an addition funnel, and a N2 inlet. The reaction was
heated to reflux for 5 h before being cooled to -40 °C. A solution of
bis(2-methylphenyl)chlorophosphine52 (6.400 g, 25.73 mmol) in THF
(15 mL) was added dropwise to the reaction over 10 min. The reaction
(45) Kalck, P.; Randrianalimanana, C.; Ridmy, M.; Thorez, A.; tom
Dieck, H.; Ehlers, J. New J. Chem. 1988, 12, 679-686.
(46) Kranenburg, M.; van der Burg, Y. E. M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J. Organometallics 1995, 14,
3081-3089.
(47) Unruh, J. D. U.S. Pat. Appl. 822,859, 1977.
(48) Yamaguchi, M.; Kido, Y.; Omata, K.; Hirama, M. Synlett 1995,
1181-1182.
(49) van Soolingen, J.; de Lang, R.-J.; den Besten, R.; Klusener, P. A.
A.; Veldman, N.; Spek, A. L.; Brandsma, L. Synth. Commun. 1995, 25,
1741-1744.
(50) Jackson, R. D.; James, S.; Orpen, A. G.; Pringle, P. G. J. Organomet.
Chem. 1993, 458, C3-C4.
(51) Kumobayashi, H.; Taketomi, H.; Akutagawa, S. Jpn. Kokai Tokkyo
Koho 80 02,627, 80 02,627.
(44) For an application of this diarylation in materials chemistry, see:
Thayumanavan, S.; Barlow, S.; Marder, S. R. Chem. Mater. 1997, 9, 3231-
3235.
(52) Clark, P. W.; Mulraney, B. J. J. Organomet. Chem. 1981, 217, 51-
59.

Systematic Variation of Bidentate Ligands
J. Am. Chem. Soc., Vol. 120, No. 15, 1998 3701
was allowed to warm slowly to room temperature and stir for 12 h.
The crude reaction was concentrated to approximately 20% of its
original volume, and the yellow solids were filtered. The solids were
then washed with 1 M HCl (20 mL), H2O (20 mL), ethanol (20 mL),
and ether (20 mL). The solids were dried under vacuum to give 6.214
g of product in 83% yield. 1H NMR: (CDCl3) δ 7.17-6.96 (m, 16H),
4.25 (br s, 4H), 4.06 (br s, 4H), 2.46 (s, 12H). 13C{1H} NMR: (CDCl3)
δ 141.64 (d, J ) 26.3 Hz), 137.51 (d, J ) 10.6 Hz), 133.29, 129.41
(d, J ) 5.1 Hz), 128.4, 125.50, 76.52, 74.15 (d, J ) 15.1 Hz), 72.13
(d, J ) 3.0 Hz), 21.29 (d, J ) 21.6 Hz). 31P{1H} NMR: (CDCl3) δ
-36.81. Anal. Calcd for C38H36FeP2: C, 74.76; H, 5.94. Found: C,
74.31; H, 6.08.
7.11 (m, 10H), 7.04 (t, J ) 7.5 Hz, 4H), 6.97 (t, J ) 7.4 Hz, 2H),
6.79-6.71 (m, 8H), 2.28 (s, 12 H). 13C{1H} NMR: (CDCl3) δ 159.69
(d, J ) 18.5 Hz), 142.30 (d, J ) 27.4 Hz), 134.61 (d, J ) 13.0 Hz),
134.17, 133.01, 130.08, 129.80 (d, J ) 3.3 Hz), 128.32, 127.41 (d, J
) 15.3 Hz), 125.79, 123.58, 118.01, 21.17 (d, J ) 23.2 Hz). 31P{1H}
NMR: (CDCl3) δ -32.62. Anal. Calcd for C40H36OP2: C, 80.79; H,
6.10. Found: C, 80.52; H, 5.98.
9,9-Dimethyl-4,5-bis[bis(2-methylphenyl)phosphino]xanthene.27
9,9-Dimethylxanthene (0.363 g, 1.726 mmol), 2.5 equiv of n-butyl-
lithium (2.5 M in hexanes, 1.73 mL, 4.32 mmol), and 2.5 equiv of
TMEDA (0.651 mL, 4.32 mmol) were dissolved in heptane (10 mL)
under N2 and heated to reflux for 20 min. The reaction was then cooled
to 0 °C and quenched with a solution of bis(2-methylphenyl)-
chlorophosphine52 (0.816 g, 5.178 mmol) in THF (5 mL) over 10 min.
The reaction was then allowed to stir at room temperature for 12 h.
The reaction was diluted with ethyl acetate and washed with H2O (2×).
The organic layer was then dried with Na2SO4 and concentrated in
vacuo. The product was purified first by flash chromatography through
a short layer of silica using 30% ethyl acetate in hexanes as the eluent.
The partially purified solids were washed with hexanes to give 0.425
g of purified product in 39% yield. 1H NMR: (CDCl3) δ 7.45 (dd, J
) 0.9, 7.8 Hz, 2H), 7.21-7.14 (m, 8H), 7.02-6.94 (m, 6H), 6.71 (d,
J ) 7.7 Hz, 4H), 6.51 (dd, J ) 1.3, 7.5 Hz, 2H), 2.29 (s, 12H), 1.71
(s, 6H). 13C{1H} NMR: (CDCl3) δ 152.90 (apparent t, J ) 9.7 Hz),
142.45 (apparent t, J ) 13.5 Hz), 135.62 (apparent t, J ) 7.2 Hz),
132.62, 132.38, 129.72 (d, J ) 1.9 Hz), 128.09, 126.26, 125.69, 124.29
(d, J ) 8.5 Hz), 124.15 (d, J ) 9.1 Hz), 123.37, 34.47, 31.84, 21.25
(apparent t, J ) 11.5 Hz). 31P{1H} NMR: (CDCl3) δ -31.93. Anal.
Calcd for C43H40OP2: C, 81.37; H, 6.35. Found: C, 81.03; H, 6.27.
Dicarbonyl[bis(diphenylphosphino)ferrocene]nickel(0):54 Bis-
(triphenylphosphine)dicarbonylnickel(0) (64.5 mg, 0.101 mmol) was
mixed with 1 equiv of 1,1′-(diphenylphosphino)ferrocene (55.9 mg,
0.101 mmol) in 10 mL of THF solvent. After 4 h the reaction was
filtered through Celite and concentrated under vacuum to yield a yellow
oil. Ether (10 mL) was added to the oil, and a precipitate formed. The
yellow solids were filtered, washed with ether, and dried under vacuum
to give 53.9 mg of product in 79.9% yield. 1H NMR: (C6D6) δ 7.81
(m, 8H), 7.03 (m, 12H), 4.16 (dt, J ) 1.8, 1.8 Hz, 4H), 3.86 (t, J ) 1.8
Hz, 4H). 31P{1H} NMR: (C6D6) δ 25.91. IR (KBr, cm-1): 1999 (s),
1940 (s).
Dicarbonyl[bis[bis(4-methoxyphenyl)phosphino]ferrocene]nickel-
(0). Bis(triphenylphosphine)dicarbonylnickel(0) (73.3 mg, 0.115 mmol)
was mixed with 1 equiv of 1,1′-bis[bis(4-methoxyphenyl)phosphino]-
ferrocene (77.3 mg, 0.115 mmol) in 10 mL of THF solvent. After 18
h the reaction was diluted with 10 mL of pentane, and a precipitate
formed. The yellow solids were filtered, washed with ether, and dried
under vacuum to give 83.2 mg of product in 91.9% yield. 1H NMR:
(C6D6) δ 7.82 (t, J ) 8.7 Hz, 8H), 6.69 (d, J ) 8.3 Hz, 8H), 4.27 (br
s, 4H), 3.95 (br s, 4H), 3.19 (s, 12H). 31P{1H} NMR: (C6D6) δ 22.29.
IR (KBr, cm-1): 2002 (s), 1938 (s). Anal. Calcd for C40H36-
FeNiP2O6: C, 60.88; H, 4.60. Found: C, 60.88; H, 4.65.
Dicarbonyl[1,1′-Bis[bis(3,5-bis(trifluoromethyl)phenyl)phosphino]-
ferrocene]nickel(0). Bis(triphenylphosphine)dicarbonylnickel(0) (79.9
mg, 0.125 mmol) was mixed with 1 equiv of 1,1′-bis[bis(3,5-bis-
(trifluoromethyl)phenyl)phosphino]ferrocene (137 mg, 0.125 mmol) in
10 mL of THF solvent. After 48 h the reaction was concentrated under
vacuum to give a yellow oil. The product was purified via column
chromatography using 2% ethyl acetate in hexanes as the eluent to
give 61.4 mg of purified product in 40% yield. This complex slowly
underwent disproportionation that yielded bis{1,1′-bis[bis(3,5-bis-
(trifluoromethyl)phenyl)phosphino]ferrocene}nickel(0), which prevented
our obtaining satisfactory elemental analysis data. 1H NMR: (C6D6)
δ 8.21 (d, J ) 9.4 Hz, 8H), 7.64 (s, 4H), 3.89 (dt, J ) 1.8, 1.8 Hz,
4H), 3.71 (br s, 4H). 31P{1H} NMR: (C6D6) δ 29.25. IR (KBr, cm-1):
2017 (s), 1965 (s).
1,1′-Bis[bis[3,5-bis(trifluoromethyl)phenyl]phosphino]ferro-
cene.47 To an oven-dried flask fitted with a N2 inlet were added 8
equiv of 3,5-bis(trifluoromethyl)iodobenzene (2.00 mL, 11.28 mmol)
and 6.0 equiv of TMEDA (1.28 mL, 8.47 mmol) in THF (15 mL). The
solution was cooled to -78 °C, and 6.0 equiv of n-butyllithium (2.5
M in hexanes, 3.38 mL, 8.47 mmol) was added dropwise over 5 min.
The reaction was stirred for 2 h at -78 °C (WARNING: the reaction
may explode if allowed to warm). A solution of 1,1′-bis(dichloro-
phosphino)ferrocene29 (0.547 g, 1.411 mmol) in THF (5 mL) was added
dropwise to the reaction over 10 min. The reaction was stirred at -78
°C for 30 min and then allowed to warm slowly to room temperature,
and stirring was continued for 12 h. Methanol (1 mL) was added to
the reaction; it was then concentrated in vacuo. The black residue was
filtered through Celite using 5% ethyl acetate in hexane as the eluent.
The orange filtrate was concentrated to give the crude product. Purified
product, 0.741 g, was obtained as a yellow powder in 48% yield by
crystallization from hexanes. 1H NMR: (CDCl3) δ 7.89 (s, 4H), 7.69
(d, J ) 6.3 Hz, 8H), 4.44 (dd, J ) 1.6, 1.7 Hz, 4H), 4.01 (m, 4H).
13C{1H} NMR: (CDCl3) δ 140.31 (d, J ) 17.5 Hz), 132.82 (d, J )
21.8 Hz), 132.07 (dq, J ) 6.2, 33.3 Hz), 123.43 (d, J ) 4.0 Hz), 122.93
(q, J ) 273.2 Hz), 73.81, 73.57 (d, J ) 15.6 Hz), 73.26 (br s). 31P-
{1H} NMR: (CDCl3) δ -14.99. Anal. Calcd for C42H20F24FeP2: C,
45.93; H, 1.84. Found: C, 46.24; H, 1.90.
1,1′-Bis[di-2-furylphosphino]ferrocene. Using literature proce-
dures53 6.0 equiv of 2-lithiofuran was prepared in THF (10 mL) and
cooled to -78 °C. A solution of 1,1′-bis(dichlorophosphino)ferrocene29
(0.200 g, 0.516 mmol) in THF (5 mL) was added dropwise to the
reaction over 10 min. The reaction was stirred for 90 min at -78 °C
and allowed to warm to room temperature and stir for an additional 12
h. The reaction was then concentrated in vacuo and dissolved in ether
(100 mL). The ether solution was washed with H2O (30 mL, 3×)
followed by brine. The ether solution was then dried with Na2SO4,
filtered, and concentrated. The product was purified first by flash
chromatography through a short layer of silica using CH2Cl2 as the
eluent followed by crystallization from cyclohexane. The product,
0.224 g, was obtained as orange needles in 84% yield. 1H NMR:
(CDCl3) δ 7.63 (d, J ) 0.9 Hz, 4H), 6.67 (dd, J ) 2.5, 1.9 Hz, 4H),
6.39 (m, 4H), 4.32 (dd, J ) 1.6, 1.8 Hz, 4H), 4.17 (dd, J ) 1.5, 1.8
Hz, 4H). 13C{1H} NMR: (CDCl3) δ 152.05 (d, J ) 8.6 Hz), 146.63,
119.79 (d, J ) 24.5 Hz), 110.46, 74.41 (d, J ) 17.8 Hz), 73.31, 72.20
(d, J ) 3.7 Hz). 31P{1H} NMR: (CDCl3) δ -64.92. Anal. Calcd for
C26H20FeO4P2: C, 60.73; H, 3.92. Found: C, 60.47; H, 3.89.
Bis[2-[bis(2-methylphenyl)phosphino]phenyl] Ether.46 Diphenyl
ether (1.75 mL, 9.58 mmol), 2.2 equiv of n-butyllithium (2.66 M in
hexanes, 7.9 mL, 21.08 mmol), and 2.2 equiv of TMEDA (3.18 mL,
21.08 mmol) were stirred in THF (10 mL) under N2 at room temperature
for 16 h (see ref 27 for an improved lithiation procedure). The reaction
was quenched with a solution of bis(2-methylphenyl)chlorophosphine51
(5.242 g, 21.08 mmol) in THF (5 mL) over 15 min. H2O and ether
were added to the reaction, and the layers were separated. The ether
layer was dried with Na2SO4 and concentrated in vacuo. The residue
was heated in boiling ethanol. Not all of the DTPDPE product
dissolved in the ethanol, but the impurities were soluble. The mixture
was then cooled to 0 °C, and the resulting solids were collected by
filtration and washed with ethanol. The solids were dried under vacuum
to give 2.682 g of product in 47% yield. 1H NMR: (CDCl3) δ 7.27-
Dicarbonyl[2,2′-bis(diphenylphosphino)-1,1′-binaphthyl nickel-
(0). Bis(triphenylphosphine)dicarbonylnickel(0) (112 mg, 0.176 mmol)
was mixed with 1 equiv of 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl
(53) Perri, S. T.; Rice, P.; Moore, H. W. Organic Syntheses; Wiley: New
York, 1993; Collect. Vol. 8, pp 179-182.
(54) Vasapollo, G.; Toniolo, L.; Cavinato, G.; Bigoli, F.; Lanfranchi,
M.; Pellinghelli, M. A. J. Organomet. Chem. 1994, 481, 173-178.

3702 J. Am. Chem. Soc., Vol. 120, No. 15, 1998
Hamann and Hartwig
(109 mg, 0.176 mmol) in 10 mL of THF solvent. After 24 h the yellow
solid was filtered, washed with THF, and dried under vacuum to give
74.2 mg of product in 58% yield. 1H NMR: (THF-d6) δ 8.04 (m,
4H), 7.51-7.20 (m, 18H), 7.00 (t, J ) 8.4 Hz, 2H), 6.84 (d, J ) 8.6
Hz, 2H), 6.54 (t, J ) 7.1 Hz, 2H), 6.45 (t, J ) 7.1 Hz, 4H). 31P{1H}
NMR: (THF-d6) δ 34.36; IR (KBr, cm-1): 1994 (s), 1940 (s).
N-Butyl-2-methylaniline.55,56 A reaction vial was charged with
2-bromotoluene (0.267 g, 1.57 mmol), 1.2 equiv of NaOtBu (0.181 g,
1.88 mmol), 0.05 equiv of Pd(DBA)2 (0.045 g, 0.078 mmol), 0.10 equiv
of DPPF (0.087 g, 0.157 mmol), and 8 mL of toluene under a N2
atmosphere in a drybox. The reaction was capped using a PTFE septum
and removed from the drybox. Butylamine (155 µL, 1.88 mmol) was
added via syringe and the reaction heated to 90 °C for 6 h. The reaction
was cooled to room temperature and filtered through Celite, and the
Celite was washed with ether (20 mL, 3×). Aqueous HCl (20 mL, 1
M) was added to the filtrate and the mixture stirred. An orange
precipitate formed. Both layers were filtered together and then
separated. The organic layer was washed with 1 M HCl (10 mL)
followed by H2O (10 mL). The three aqueous washings were combined
and made basic with NaHCO3. This basic solution was washed with
hexane (20 mL, 3×). The hexane solutions were combined, dried over
Na2SO4, and concentrated in vacuo to give 0.239 g of purified product
in 94% yield. 1H NMR: (CDCl3) δ 7.14 (dd, J ) 8.0, 7.5 Hz, 1H),
7.02 (d, J ) 7.6 Hz, 1H), 6.60-6.70 (m, 2H), 3.44 (br s, 1H), 3.18 (t,
J ) 7.1 Hz, 2H), 2.15 (s, 3H), 1.68 (m, 2H), 1.48 (m, 2H), 1.00 (t, J
) 7.4 Hz, 3H). 13C{1H} NMR: (CDCl3) δ 146.36, 129.94, 127.08,
121.60, 116.55, 109.54, 43.59, 31.69, 20.34, 17.40, 13.90.
N-Butyl-4-butylaniline.57 A reaction vial was charged with (4-
bromobutyl)benzene (0.140 g, 0.657 mmol), 1.2 equiv of NaOtBu
(0.0758 g, 0.789 mmol), 0.05 equiv of Pd(DBA)2 (0.0189 g, 0.0328
mmol), 0.10 equiv of DPPF (0.0360 g, 0.0657 mmol), and 8 mL of
toluene under a N2 atmosphere in a drybox. The reaction was capped
using a PTFE septum and removed from the drybox. Butylamine (78.2
µL, 0.789 mmol) was added via syringe and the reaction heated to 90
°C for 12 h. The reaction was cooled to room temperature and
concentrated in vacuo to give the crude product. The purified product,
0.065 g, was obtained in 48% isolated yield by flash chromatography
using a gradient of 5% diethyl ether in petroleum ether to 10% diethyl
ether in petroleum ether as the eluent. 1H NMR: (CDCl3) δ 7.03 (d,
J ) 8.4 Hz, 2H), 6.59 (d, J ) 8.4 Hz, 2H), 3.45 (br s, 1H), 3.12 (t, J
) 7.1 Hz, 2H), 2.54 (t, J ) 7.6 Hz, 2H), 1.66-1.50 (m, 4H), 1.47-
1.34 (m, 4H), 0.99 (t, J ) 7.3 Hz, 3H), 0.95 (t, J ) 7.3 Hz, 3H). 13C-
{1H} NMR: (CDCl3) δ 146.28, 131.62, 129.03, 112.81, 44.05, 34.68,
34.01, 31.67, 22.30, 20.28, 13.96, 13.89. HRMS calcd for C14H23N
(M+) 205.1830, found 205.1837.
mL of toluene under a N2 atmosphere in a drybox. The reaction was
capped using a PTFE septum and removed from the drybox. Butyl-
amine (51.4 µL, 0.520 mmol) was added via syringe and the reaction
heated to 90 °C for 12 h. The reaction was cooled to room temperature
and concentrated in vacuo to give the crude product. The purified
product, 0.156 g, was obtained in 89% isolated yield, based on
butylamine, by flash chromatography using 5% diethyl ether in hexanes
as the eluent. 1H NMR: (CDCl3) δ 7.12 (d, J ) 8.4 Hz, 4H), 6.90 (d,
J ) 8.4 Hz, 4H), 3.65 (t, J ) 7.5 Hz, 2H), 2.57 (t, J ) 7.5 Hz, 4H),
1.60 (m, 6H), 1.37 (m, 6H), 0.98-0.88 (m, 9H). 13C{1H} NMR:
(CDCl3) δ 146.05, 135.28, 129.02, 120.63, 52.20, 34.88, 33.81, 29.61,
22.42, 20.30, 14.00. HRMS calcd for C24H35N (M+) 337.2769, found
337.2766.
N,N-Dimethyl-N′-phenyl-1,4-benzenediamine.58 A reaction vial
was charged with 4-bromo-N,N-dimethyl aniline (0.165 g, 0.825 mmol),
1.2 equiv of NaOtBu (0.0951 g, 0.990 mmol), 0.05 equiv of Pd(DBA)2
(0.0237 g, 0.0412 mmol), 0.10 equiv of DPPF (0.0457 g, 0.0825 mmol),
and 8 mL of toluene under a N2 atmosphere in a drybox. The reaction
was capped using a PTFE septum and removed from the drybox.
Aniline (90.2 µL, 0.990 mmol) was added via syringe and the reaction
heated to 90 °C for 12 h. The reaction was cooled to room temperature
and concentrated in vacuo to give the crude product. The purified
product, 0.141 g, was obtained in 80% isolated yield by flash
chromatography using a gradient of 5% ethyl acetate in hexanes to
10% ethyl acetate in hexanes as the eluent. 1H NMR: (C6D6) δ 7.13
(dd, J ) 7.3, 8.2 Hz, 2H), 6.98 (d, J ) 8.8 Hz, 2H), 6.81-6.77 (m,
3H), 6.57 (d, J ) 8.9 Hz, 2H), 4.91 (br s, 1H), 2.53 (s, 6H). 13C{1H}
NMR: (C6D6) δ 147.56, 146.78, 132.69, 129.49, 123.82, 118.93,
115.19, 114.19, 40.85.
N-Butyl-2-methylaniline. Procedure for Gas Chromatography
Yields. A stock solution was prepared by dissolving 2-bromotoluene
(0.155 g, 0.908 mmol) and the naphthalene standard (0.0820 g, 0.640
mmol) in toluene (15 mL). A second stock solution was prepared by
dissolving Pd(DBA)2 (26.0 mg, 45.3 µmol) in toluene (7.5 mL). Into
a reaction vial was weighed 0.10 equiv of a bidentate phosphine ligand
(6.1 µmol) and 1.2 equiv of NaOtBu (7.0 mg, 72.6 µmol). To each
reaction vial was added 1.0 mL of the 2-bromotoluene stock solution
followed by 0.5 mL of the Pd(DBA)2 stock solution. The reaction
vials were capped with a PTFE septum and removed from the drybox.
Butylamine (7.2 µL, 72.6 µmol) was added to each vial via syringe,
and the reactions were heated to 90 °C for 12 h before 1.0 µL aliquots
were injected onto the gas chromatograph.
N-Butyl-4-butylaniline. Procedure for Gas Chromatography
Yields. A stock solution was prepared by dissolving (4-bromobutyl)-
benzene (0.164 g, 0.772 mmol) and the naphthalene standard (0.0772
g, 0.602 mmol) in toluene (15 mL). A second stock solution was
prepared by dissolving Pd(DBA)2 (22.1 mg, 38.5 µmol) in toluene (7.5
mL). Into a reaction vial was weighed 0.10 equiv of a bidentate
phosphine ligand (5.1 µmol) and 1.2 equiv of NaOtBu (5.9 mg, 61.6
µmol). To each reaction vial was added 1.0 mL of the (4-bromobutyl)-
benzene stock solution followed by 0.5 mL of the Pd(DBA)2 stock
solution. The reaction vials were capped with a PTFE septum and
removed from the drybox. Butylamine (6.1 µL, 61.6 µmol) was added
to each vial via syringe, and the reactions were heated to 90 °C for 12
h before 1.0 µL aliquots were injected onto the gas chromatograph.
N-Isobutyl-4-n-butylaniline. Procedure for Gas Chromatogra-
phy Yields. A stock solution was prepared by dissolving (4-
bromobutyl)benzene (0.166 g, 0.779 mmol) and the naphthalene
standard (0.0710 g, 0.554 mmol) in toluene (15 mL). A second stock
solution was prepared by dissolving Pd(DBA)2 (22.4 mg, 38.9 µmol)
in toluene (7.5 mL). Into a reaction vial was weighed 0.10 equiv of a
bidentate phosphine ligand (5.2 µmol) and 1.2 equiv of NaOtBu (6.0
mg, 62.2 µmol). To each reaction vial was added 1.0 mL of the (4-
bromobutyl)benzene stock solution followed by 0.5 mL of the Pd-
(DBA)2 stock solution. The reaction vials were capped with a PTFE
septum and removed from the drybox. Isobutylamine (6.2 µL, 62.2
µmol) was added to each vial via syringe, and the reactions were heated
to 90 °C for 12 h before 1.0 µL aliquots were injected onto the gas
chromatograph.
N-Isobutyl-4-n-butylaniline. A reaction vial was charged with (4-
bromobutyl)benzene (0.140 g, 0.657 mmol), 1.2 equiv of NaOtBu
(0.0758 g, 0.789 mmol), 0.05 equiv of Pd(DBA)2 (0.0189 g, 0.0328
mmol), 0.10 equiv of DPPF (0.0360 g, 0.0657 mmol), and 8 mL of
toluene under a N2 atmosphere in a drybox. The reaction was capped
using a PTFE septum and removed from the drybox. Isobutylamine
(78.3 µL, 0.789 mmol) was added via syringe and the reaction heated
to 90 °C for 12 h. The reaction was cooled to room temperature and
concentrated in vacuo to give the crude product. The purified product,
0.056 g, was obtained in 42% isolated yield by flash chromatography
using 5% diethyl ether in petroleum ether as the eluent. 1H NMR:
(CDCl3) δ 7.02 (d, J ) 8.2 Hz, 2H), 6.58 (d, J ) 8.2 Hz, 2H), 3.59 (br
s, 1H), 2.94 (d, J ) 6.8 Hz, 2H), 2.53 (t, J ) 7.5 Hz, 2H), 1.92 (m,
1H), 1.59 (m, 2H), 1.37 (m, 2H), 1.02 (d, J ) 6.6 Hz, 6H), 0.96 (t, J
) 7.3 Hz, 3H). 13C{1H} NMR: (CDCl3) δ 146.39, 131.41, 129.03,
112.67, 52.14, 34.67, 34.02, 27.98, 22.32, 20.48, 13.97. HRMS calcd
for C14H23N (M+) 205.1830, found 205.1827.
N-Butyl-N-(4-butylphenyl)-4-butylaniline. A reaction vial was
charged with (4-bromobutyl)benzene (0.246 g, 1.156 mmol), 1.2 equiv
of NaOtBu (0.133 g, 1.387 mmol), 0.025 equiv of Pd(DBA)2 (0.0166
g, 0.0289 mmol), 0.05 equiv of DPPF (0.0321 g, 0.0578 mmol), and 8
(55) Louie, J.; Driver, M. S.; Hamann, B. C.; Hartwig, J. F. J. Org. Chem.
1997, 62, 1268-1273.
(56) Makoto, O.; Koju, I.; Yusuke, I. J. Inclusion Phenom. 1984, 2, 359-
366.
(58) Barchiesi, E.; Bradamante, S.; Pagani, G. A. J. Chem. Soc., Perkin
Trans. 2 1987, 1091-1096.
(57) Louie, J.; Hartwig, J. F. Tetrahedron Lett. 1995, 36, 3609-3612.

Systematic Variation of Bidentate Ligands
J. Am. Chem. Soc., Vol. 120, No. 15, 1998 3703
N-Butyl-N-(4-butylphenyl)-4-butylaniline. Procedure for Gas
Chromatography Yields. A stock solution was prepared by dissolving
(4-bromobutyl)benzene (0.1104 g, 0.518 mmol) and the naphthalene
standard (0.0375 g, 0.293 mmol) in toluene (10 mL). A second stock
solution was prepared by dissolving Pd(DBA)2 (14.9 mg, 25.9 µmol)
in toluene (5.0 mL). Into a reaction vial was weighed 0.10 equiv of a
bidentate phosphine ligand (5.2 µmol) and 1.2 equiv of NaOtBu (6.0
mg, 62.1 µmol). To each reaction vial was added 1.0 mL of the (4-
bromobutyl)benzene stock solution followed by 0.5 mL of the Pd-
(DBA)2 stock solution. The reaction vials were capped with a PTFE
septum and removed from the drybox. Butylamine (2.3 µL, 23.3 µmol)
was added to each vial via syringe, and the reactions were heated to
90 °C for 12 h before 1.0 µL aliquots were injected onto the gas
chromatograph.
N,N-Dimethyl-N′-phenyl-1,4-benzenediamine. Procedure for Gas
Chromatography Yields. A stock solution was prepared by dissolving
4-bromo-N,N-dimethylaniline (0.165 g, 0.826 mmol) and the naphtha-
lene standard (0.110 g, 0.854 mmol) in toluene (15 mL). A second
stock solution was prepared by dissolving Pd(DBA)2 (23.7 mg, 41.3
µmol) in toluene (7.5 mL). Into a reaction vial was weighed 0.10 equiv
of a bidentate phosphine ligand (5.5 µmol) and 1.2 equiv of NaOtBu
(6.3 mg, 66.0 µmol). To each reaction vial was added 1.0 mL of the
4-bromo-N,N-dimethylaniline stock solution followed by 0.5 mL of
the Pd(DBA)2 stock solution. The reaction vials were capped with a
PTFE septum and removed from the drybox. Aniline (6.0 µL, 66.0
µmol) was added to each vial via syringe, and the reactions were heated
to 90 °C for 12 h before 1.0 µL aliquots were injected onto the gas
chromatograph.
Acknowledgment. We gratefully acknowledge support from
the National Institutes of Health, Boehringer Ingelheim, a
National Science Foundation Young Investigator Award, a
Dreyfus Foundation New Faculty Award, and a Camille Dreyfus
Teacher Scholar Award for support for this work. J.F.H. is a
fellow of the Alfred P. Sloan Foundation. We thank Johnson-
Matthey Alpha/Aesar for donation of palladium chloride. We
also thank K. L. Mason for helpful discussions regarding the
syntheses of ferrocene derivatives.
JA9721881