Investigation of steric and electronic features of 3-iminophosphine-based palladium catalysts for intermolecular hydroamination

Article abstract of DOI:10.1021/om301102w

A series of (3-iminophosphine)allylpalladium triflate complexes with systematic variation of both steric and electronic features was isolated and characterized. The ability of the complexes in this series to catalyze the regioselective hydroamination of 3-methyl-1,2-butadiene with aryl amines to form solely the kinetic product was probed by observing conversion to products via NMR spectroscopy. The previously unstudied 3-iminophosphine ligand composed of a di-tert-butyl phosphine, cyclobutene backbone, and tert-butyl imine provided the most active palladium hydroamination catalyst for this transformation known to date.

Full text of DOI:10.1021/om301102w

Article
pubs.acs.org/Organometallics
Investigation of Steric and Electronic Features of 3‑Iminophosphine-
Based Palladium Catalysts for Intermolecular Hydroamination
Nicholas C. Zingales, Andrew R. Shaffer, and Joseph A. R. Schmidt*
Department of Chemistry, School of Green Chemistry and Engineering, College of Natural Sciences and Mathematics, The
University of Toledo, 2801 W. Bancroft Street MS 602, Toledo, Ohio 43606-3390, United States
S
* Supporting Information
ABSTRACT: A series of (3-iminophosphine)allylpalladium
triflate complexes with systematic variation of both steric and
electronic features was isolated and characterized. The ability
of the complexes in this series to catalyze the regioselective
hydroamination of 3-methyl-1,2-butadiene with aryl amines to
form solely the kinetic product was probed by observing
conversion to products via NMR spectroscopy. The previously
unstudied 3-iminophosphine ligand composed of a di-tert-butyl phosphine, cyclobutene backbone, and tert-butyl imine provided
the most active palladium hydroamination catalyst for this transformation known to date.
include those published by Bertrand,5,23,24 Widenhoefer,25−27
INTRODUCTION
■
Yamamoto,28,29 Toste,30 and Schafer,31,32 as well as our own
Hydroamination is an advantageous method for the preparation
group.3,33 Late transition metal catalyzed intermolecular
of primary, secondary, and tertiary amines due to its 100% atom
hydroamination of substituted allenes yields two possible
economy1 and the wide range of regio-, stereo-, and
regioisomers. Addition of the amino moiety to the substituted
enantioselective metal complexes that are available to catalyze
carbon terminus of a monosubstituted allene yields a new chiral
this transformation.2−10 The hydroamination process is
carbon center and a vinyl-terminated product, which is typically
characterized by the addition of an N−H bond of ammonia
the kinetic product of these reactions (Scheme 1). Addition of
or of a primary or secondary amine across an unsaturated C−C
bond of an alkene, alkyne, or allene. The reaction can take place
Scheme 1. Late Transition Metal Catalyzed Hydroamination
either intermolecularly at a high entropic demand using
of Substituted Allenes
affordable and readily obtained substrates or intramolecularly
with low entropic demand, but requiring less accessible starting
materials. Although hydroamination is slightly exothermic, the
direct [2+2] cycloaddition of an N−H across a C−C
unsaturated bond is orbitally forbidden under thermal
conditions, making a catalytic route for this process a virtual
necessity.2
the amine at the less-substituted carbon atom yields an internal
alkene, commonly the thermodynamic product (Scheme 1).
Regioselective hydroamination of substituted allenes to form
the thermodynamic product is much more common and has
been accomplished previously with aryl amines and a gold
catalyst,25,28 secondary alkylamines and gold24,29 or platinum26
catalysts, ammonia and a gold catalyst,23 and hydrazine with a
gold catalyst.5 Also notable is Toste’s mechanistic study
involving the hydroamination of a symmetrical allene with
methyl carbazate, which demonstrated activation of the allene
as the rate-limiting step and implied that there was no
coordinated amine in the catalytic mechanism.30 Regioselective
intermolecular hydroamination of substituted allenes to form
the kinetic (branched) product, though much rarer, has been
accomplished via a gold(I) N-heterocyclic carbene complex,
The hydroamination of allenes allows for the synthesis of
allylic amines, which can be further transformed using a wide
variety of reactions including hydroboration,11 hydroformyla-
tion,12 alkene metathesis,13 and heterocycle synthesis.2 Allylic
amines also play a major role in the synthesis of pharmaceutical
and natural products.14 Early transition metal complexes have
been shown to catalyze allene hydroamination with addition of
the nitrogen group to the central carbon of the allene and
subsequent tautomerization of the resulting enamine to form an
imine in the case of primary amine substrates, whereas late
transition metal catalysts are known to hydroaminate allenes
with addition of the nitrogen moiety to one of the terminal
carbons, resulting in retention of the allyl group.2 Intra-
molecular hydroamination of allenes leads to nitrogen-
containing heterocycles. Although intramolecular hydroamina-
tion of allenes has been studied briefly,15−22 with a focus on
enantioselective conversion to products, examples of inter-
molecular allene hydroamination are more prevalent and
Received: November 15, 2012
Published: January 8, 2013
© 2013 American Chemical Society
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Figure 1. 3-Iminophosphine (3IP) ligands 1−10.
although substrate scope was limited to the addition of an N-
unsubstituted carbamate,4 as well as with a rhodium(I) Josiphos
complex that was able to add a series of anilines
enantioselectively to the more substituted side of the allene.34
The development of new catalysts capable of producing the
branched product in these reactions would be considerably
advantageous in order to expand upon this limited substrate
scope and to allow a much larger variety of allylic amines to be
synthesized via hydroamination. Also of interest is the
development of more cost-effective metal catalysts, as gold,
platinum, and rhodium are among the most expensive of the
transition metals.
complexes whose designs were based upon the results of the
catalytic screening of the original array of eight complexes.
RESULTS AND DISCUSSION
■
The effectiveness of 3-iminophosphine allylpalladium triflate
complexes as catalysts for the hydroamination of 1,3-dienes,
allenes, and alkynes with primary and secondary amines has
been shown previously.33 These results implied that the steric
and electronic properties of the 3IP supporting ligands have a
significant effect on the rates observed in hydroamination
catalysis. These ligand properties can be governed via
substitution of three tunable domains: the size of the alicyclic
backbone and the substituent groups of the imine and
phosphine moieties. For example, cyclic ketones that vary in
ring size can be reacted with the Vilsmeier−Haack reagent,
various amines can be used for the Schiff base condensation,
and phosphination can be completed with different disub-
stituted lithium phosphides in the synthesis of these ligands
(Scheme 2). Our previous reports detail the synthesis and
isolation of ligands 2,35 4,3 and 5,33 as well as their respective
allyl palladium triflate complexes 2Pd,35 4Pd,3 and 5Pd.33
Synthesized previously in our group were 3-iminophosphine
(3IP) ligands 2,35 4,3 and 533 (Figure 1), as well as their
respective [(3IP)Pd(allyl)]OTf complexes 2Pd,35 4Pd,3 and
5Pd.33 2Pd was shown to hydroaminate phenylacetylene and
1,3-cyclohexadiene in moderate yields,35 whereas 5Pd was
shown to hydroaminate 3-methyl-1,2-butadiene (1,1-dimethyl-
allene) and 2,3-dimethyl-1,3-butadiene with secondary alkyl-
amines regioselectively to form the thermodynamic (linear)
products in moderate to excellent yields.33 The most significant
advance in the development of these catalysts came with the
discovery of 4Pd, which was found to regiospecifically
hydroaminate 1,1-dimethylallene using a variety of aryl amines
(anilines) to form solely the kinetic (branched) products in
good to excellent yields.3 Because the observed catalysis of
these three different ligand frameworks varied dramatically, it
was hypothesized that the specific steric and electronic features
of the ligand were responsible for the greatly varying catalytic
activity. Unfortunately, in the development of our hydro-
amination catalysts (2Pd, 4Pd, and 5Pd), the ligand framework
was not altered in a systematic fashion, but rather involved
changes to two ligand components with each new catalyst
explored. Thus, the catalytic data generated with our three
previously published [(3IP)Pd(allyl)]OTf complexes were
insufficient in determining which alterations to ligand design
were critical in order to optimize catalytic activity. As a means
to address this deficiency, synthesized herein is an array of eight
[(3IP)Pd(allyl)]OTf complexes with systematic variance of the
steric and electronic features of the 3IP ligands. Each palladium
complex was screened for catalytic activity in the hydro-
amination of 1,1-dimethylallene with a selection of seven aryl
amines spanning a wide range of steric and electronic
parameters. Also reported herein is the synthesis of two
additional ligands and their respective [(3IP)Pd(allyl)]OTf
Scheme 2. General Synthesis of [(3IP)Pd(allyl)]OTf
a
Complexes
a
n = 1−4, R′ = tBu or 2,6-dimethylphenyl, R″ = tBu or Ph. (i) 2 equiv
of DMF, 1.6 equiv of POCl3, 0 °C, 4 h then 55 °C, 14 h; 0 °C,
NaHCO3; (ii) 1.3 equiv of H2NR′, pentane, 4 Å molecular sieves, 0
°C; (iii) 1.6 equiv of LiPR″2, Et2O, 3 h, RT.
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Unfortunately, the ligands described in our previous reports
varied two tunable domains with each catalyst improvement.
The synthesis of complexes with systematic variation of the
three tunable domains would allow for correlation of catalytic
activity with each domain involved in ligand construction.
Thus, in the current contribution, we set out to produce a
complete series of 3IP ligands utilizing both backbone ring sizes
(cyclopentenyl and cyclohexenyl), imines (tert-butyl and 2,6-
xylyl), and phosphines (tert-butyl and phenyl) to determine the
impact of each unit on catalytic activity (1−8, Figure 1). Then,
by use of the palladium complexes of these eight ligands in
catalysis, we hoped that an empirical understanding of the
effectiveness of these ligand components would allow for the
rational design of improved hydroamination catalysts.
chloride abstraction (Table 1). The absolute change in ppm for
the 31P NMR signal between free ligands and the target
1
Table 1. Comparison between Selected 31P and H NMR
Resonances of [(3IP)Pd(allyl)]OTf Complexes and Their
Respective Free 3IP Ligands (all values in ppm)
a
b
3IPPd
3IP
a
b
3IPPd
3IP
R′NCH
R′NCH
31P δ
31P δ
Δ31P δ
1H δ
1H δ
Δ1H δ
1
2
13.11
16.90
59.48
61.80
25.20
31.78
71.63
75.37
80.64
55.18
−23.20
−24.70
13.24
36.31
41.60
46.24
48.60
37.80
44.48
51.58
55.39
55.83
43.82
7.88
7.94
7.84
8.06
7.70
7.65
7.65
7.85
8.07
7.94
8.64
8.72
8.82
8.88
9.05
9.09
9.32
9.37
9.37
−0.76
−0.78
−0.98
−0.82
−1.35
−1.44
−1.67
−1.52
−1.30
−0.33
3
4
13.20
5
−12.60
−12.70
20.05
Compounds 1, 3, and 6 were synthesized using procedures
analogous to those for 3-iminophosphines 2,35 4,3 and 5,33
respectively, while ligands 7, 8, 9, and 10 required significant
modifications to the experimental methodology (Scheme 2).
The main change involved the dropwise addition of a dilute
solution of lithium di-tert-butylphosphide in diethyl ether to a
rapidly stirred solution of the selected chloroimine in diethyl
ether at ambient temperature. The attempted use of our
previous synthetic procedures consistently resulted in multiple
unidentifiable phosphorus-containing products that were
inseparable from both the target ligand and the final palladium
complex. Overall, the syntheses of ligands 7−10 were especially
sensitive, requiring the purest of starting materials. Chloro-
aldehyde of high purity was produced via neat reaction of the
cyclic ketone with the Vilsmeier−Haack reagent (Scheme 2),
under a nitrogen atmosphere using degassed reagents. After
reacting for 14 h at 55 °C, the resulting solution was made basic
and extracted with pentane, in contrast to diethyl ether as cited
previously.35 This improved methodology, analogous to that of
Paquette,36 is vital for achieving reaction completion and
ensuring chloroaldehyde purity, as well as improving product
stability at both low and ambient temperatures. Prior to its use,
lithium di-tert-butylphosphide was recrystallized from diethyl
ether and rinsed with pentane to minimize highly reactive
impurities that were found to complicate phosphination of the
various chloroimines, leading to multiple unidentifiable
phosphorus-containing products. Ligand coordination and ion
exchange reactions yielding the final [(3IP)Pd(allyl)]OTf
complexes proceeded analogously to Beck and Schmidt3
(Scheme 2) with only slight workup modifications. Specifically,
the intermediate 3IP allylpalladium chloride complex was
rinsed of excess ligand before treatment with silver triflate
because we have found that byproduct silver chloride is readily
coordinated by excess 3IP ligand. Furthermore, toluene was
excluded from the anion exchange step, as its presence seems to
destabilize the palladium complex, resulting in presumed
palladium(0) byproducts that were not soluble in the readily
available solvents.
6
7
8
19.98
9
24.81
10
11.36
8.27
b
a
3IPPd refers to [(3IP)Pd(allyl)]OTf complex. 3IP refers to
uncoordinated ligand.
[(3IP)Pd(allyl)]OTf complexes (Δ31Pδ) varied greatly depend-
ing on the ligand used. Δ31Pδ was always larger for complexes
with larger backbone size while holding phosphine and imine
substituents constant. Also, in every case complexes with di-tert-
butylphosphino moieties had larger Δ31Pδ values than the
corresponding complexes with diphenylphosphino moieties.
Furthermore, all 31P NMR resonances for complexes and
ligands with di-tert-butylphosphino moieties were located
further downfield than those of the corresponding diphenyl-
phosphino moieties. Keeping imine and phosphine moieties
constant, all complexes with larger backbone sizes displayed
signals that were also located further downfield than those with
smaller backbone sizes. These 31P NMR spectroscopic trends
imply that the phosphorus of the ligand is more tightly bound
to the metal for the larger backbone rings and for the di-tert-
1
butylphosphino complexes. All H NMR resonances for the
imine C−H of the palladium complexes rested at or slightly
below 8 ppm, an upfield shift from that of the free ligands,
which were typically found around 9 ppm. Ligand 10 displayed
a significantly upfield imine proton resonance compared to the
rest of the free ligands. It also showed the smallest change in 1H
NMR resonance (Δ1Hδ) upon coordination to form complex
10Pd, with a mere −0.33 ppm shift (the negative number
denoting an upfield shift from ligand to triflated complex). The
other species shifted from −0.76 to −1.67 ppm upon formation
of the triflate complexes. In general, the upfield shift in the
imine proton resonance can be attributed to reduction in the
carbon−nitrogen double-bond character upon coordination of
the imine lone pair to palladium. A smaller than normal upfield
shift correlates to a smaller loss of double-bond character
consistent with weaker imine nitrogen coordination to
palladium. Thus, it seems that ligand 10 binds less strongly
to the metal center through its imine nitrogen atom than the
other ligands in this series. The trends in the 13C NMR spectra
All of the ligands and palladium complexes described in this
report are diamagnetic, and so an analysis of their NMR
spectroscopic features proves quite insightful. As one would
1
anticipate, substantial differences were noted between H, 13C,
and 31P NMR spectra of the free 3-iminophosphine ligands and
those of the [(3IP)Pd(allyl)]OTf complexes. Further differ-
ences were evident when comparing ligands and their
respective complexes with di-tert-butylphosphino moieties to
those possessing diphenylphosphino moieties. Downfield shifts
in the 31P NMR signals were observed upon coordination of
the ligand to the palladium, with a further downfield shift upon
1
parallel those of the H NMR spectra, as there are significant
changes in the chemical shift of the imine carbon between free
and coordinated ligands. The terminal carbons of the allyl
ligands (cis and trans to phosphorus) were readily differentiated
based upon both the magnitude of the JP−C coupling constant
and their relative chemical shift values. The trans carbon was
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typically located downfield from the cis carbon and displayed a
JP−C coupling constant an order of magnitude larger.
Many of the palladium allyl triflate complexes (1Pd, 2Pd,35
4Pd,3 5Pd,33 8Pd, and 9Pd) were structurally characterized via
X-ray crystallography. In all cases, X-ray quality single crystals
were grown from pentane-layered THF solutions at −25 °C.
Each complex had an outer-sphere triflate anion with
palladium’s coordination sphere occupied by the chelating 3-
3
iminophosphine ligand and a single η-allyl group, producing a
distorted square-planar geometry. Structures of 1Pd (see
Supporting Information; Figure S1) and 5Pd,33 differing only
in the size of the alicyclic backbone, both exhibited disorder in
their allyl ligands to the extent that no discernible comparison
could be made between their bite angles. The series of three
complexes with tert-butyl groups on both nitrogen and
phosphorus, but with variation of the backbone size from five
to seven carbon atoms, varied less dramatically in bite angle and
seemed more dependent on the position of the allyl group
relative to that of the alicyclic backbone. Viewing the molecule
along the P−Pd−N plane, an allyl group pointing in the
direction of the backbone is denoted as cis, while one pointing
in the opposite direction is denoted as trans. Complex 4Pd
exists as the trans isomer, 8Pd exists as the cis isomer (see
Supporting Information; Figure S2), and 9Pd has both the cis
and trans isomers in its asymmetric unit (Figures 2 and 3).
Figure 3. ORTEP diagrams (50% thermal ellipsoids) of cis (top) and
trans (bottom) isomers of 9Pd (side views). Triflate anion, hydrogen
atoms, and tert-butyl groups have been omitted for clarity.
substituent group is more significant in determining the angle
than those of the phosphine. All Pd−N distances varied little,
whereas Pd−P distances were generally shorter for diphenyl-
phosphino moieties (∼2.27 Å) than for di-tert-butylphosphino
moieties (∼2.33 Å), which likely reflects the larger steric bulk of
the tert-butyl groups. Similar disubstituted bidentate phosphine
palladium complexes show similar Pd−P bond distance
patterns.37,38
In our most recent report, compound 4Pd was shown to
readily catalyze the hydroamination of 1,1-dimethylallene with
primary aryl amines (anilines) to form exclusively the kinetic
(terminal alkene) products at room temperature (product A;
Table 2).3 Sterically hindered anilines prevented hydro-
amination in all cases, while halogenated anilines required
heating to a temperature of 70 °C in order to achieve
appreciable conversion to product. In an effort to more fully
understand this reactivity, to improve upon the catalytic
performance of 4Pd, and to test our previously reported
complexes 2Pd35 and 5Pd33 in allene hydroamination, the
complete array of ligands 1−8 and their respective complexes
1Pd−8Pd were synthesized. All eight palladium complexes
were then tested in the hydroamination of 1,1-dimethylallene
with a selection of seven anilines displaying diverse steric and
electronic properties (Table 2). The results generated by
screening these eight palladium complexes were generally
disappointing, as most of these complexes showed no catalytic
turnover for the hydroamination of 1,1-dimethylallene with
anilines. From this array, only our previously reported 4Pd was
found to catalyze this hydroamination effectively. Complex 2Pd
also catalyzed the reaction, albeit with extremely poor
conversions compared to that of 4Pd. Complexes 2Pd and
4Pd are very similar, differing only in the substituent groups of
their phosphine moieties. The phosphine tert-butyl groups of
4Pd seem to play a vital role in its catalytic activity, as
substituting them with phenyl groups in 2Pd virtually
eliminated catalytic activity. Changing the tert-butyl group of
the imine moiety into the quite sterically hindered 2,6-
dimethylphenyl group resulted in complete loss of catalytic
activity in all four complexes containing that substituent (1Pd,
3Pd, 5Pd, 7Pd). Furthermore, increasing the backbone ring
size to a cyclohexene ring also destroyed catalytic activity across
Figure 2. ORTEP diagram (50% thermal ellipsoids) of trans-9Pd (top
view). Triflate anion and hydrogen atoms have been omitted for
clarity. Selected bond lengths (in Å): Pd1−P1 = 2.331(1), Pd1−N1 =
2.098(4), Pd1−C21 = 2.162(5), Pd1−C23 = 2.257(5), P1−C3 =
1.845(5), C1−C2 = 1.472(6), C2−C3 = 1.361(6), N1−C1 =
1.288(6). Bond angles (in deg): P1−Pd1−N1 = 92.1(1), C21−
Pd1−C23 = 66.4(2), N1−Pd1−C21 = 166.8(2), N1−Pd1−C23 =
101.5(2), P1−Pd1−C21 = 100.9(1), P1−Pd1−C23 = 162.5(1), Pd1−
P1−C3 = 109.1(2), P1−C3−C2 = 122.4(4), C1−C2−C3 = 126.2(4),
N1−C1−C2 = 131.7(4), Pd1−N1−C1 = 123.2(3).
Those with the trans relationship had more strained bite angles,
i.e., 4Pd at 92.52(6)o and trans-9Pd at 92.1(1)o, while the cis
complexes 8Pd and cis-9Pd had bite angles of 89.8(2)o and
90.1(1)o, respectively. Again, the cyclopentenyl complex (4Pd)
deviated the most from the ideal 90° bite angle. Complex 2Pd,
which is a hybrid of the two series, has a bite angle of 92.9(5)o,
very close to that of 4Pd, most likely due to its similar trans
configuration. This may also indicate that the imine’s
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Table 2. Conversion to Product A for the [(3IP)Pd(allyl)]OTf-Catalyzed Hydroamination of 1,1-Dimethylallene with Aryl
a
Amines
1Pd
2Pd
3Pd
4Pd
5Pd
6Pd
7Pd
8Pd
9Pd
10Pd
b
aniline
--
--
--
--
--
--
--
--
--
60%
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
--
91%
--
2-methyl aniline
3-methyl aniline
4-methyl aniline
4-tertbutyl aniline
4-fluoro aniline
3-methoxy aniline
--
--
--
--
--
--
--
--
13%
16%
17%
9%
12%
>95%
>95%
88%
6%
--
92%
>95%
>95%
90%
72%
--
c
65%
--
62%
--
6%
a
b
c
1
Conversion was monitored via H NMR spectroscopy. “--” indicates <5%. Reaction at 70 °C.
the series of complexes (see 5Pd−8Pd). Overall, as is so often
noted in catalyst design, a very specific set of features (found in
4Pd) was crucial to achieve catalysis, with minor changes
having a devastating impact on catalytic activity.
palladium catalyst when compared to the other ligands in this
collection. Better electron-donating substituents on the
phosphine and imine moieties grant greater catalytic ability to
these complexes, while larger alicyclic backbone ring sizes
almost completely eliminate catalytic activity. Excellent
regiospecific hydroamination of 1,1-dimethylallene is now
attainable for all but the most sterically hindered anilines.
Further refinement of the 3IP ligand set, including investigation
into the effects of phosphine and imine moieties of even greater
electron-donating character, is ongoing. Additionally, use of
these palladium complexes in other catalytic transformations, as
well as one-pot multistep syntheses, continues to be under
investigation in our laboratory.
Despite the fact that no improved catalysts were discovered
upon screening the array of 1Pd−8Pd, we were convinced that
this method would yield an improved catalyst, and so further
investigation into ligand design was undertaken. The results
observed for complexes 1Pd−8Pd necessitated that further
ligand designs incorporate tert-butyl groups on both the
phosphine and imine moieties of the 3IP ligands. Believing
that the conformational stability of the cyclohexene ring was
the downfall of 8Pd when compared to the less stable
cyclopentene ring of 4Pd, ligand 9 and complex 9Pd (each
bearing a cycloheptenyl ring) were synthesized. Unfortunately,
the conformational effects of the cycloheptene ring of 9Pd did
not grant any greater catalytic performance than that of the
cyclohexene ring. Thus, we explored the opposite approach,
utilizing the smaller and highly strained cyclobutenyl ring,
leading to the synthesis of 10 and 10Pd. The smaller alicyclic
ring size of 10Pd significantly enhanced catalytic activity,
producing the same regiospecific product as 4Pd, but at higher
conversions for virtually every substrate and at lower
temperature for those that had required heating with 4Pd.
Most notably, 10Pd catalyzed the reaction of 4-fluoroaniline
with 1,1-dimethylallene at room temperature to give 90%
conversion, as compared to the 65% conversion at 70 °C when
using 4Pd. Also, the reaction of unsubstituted aniline was also
significantly improved, converting 91% of substrate to product,
a 31% increase over that previously reported.3 Due to the
superior performance of 10Pd compared to all of the other 3IP
complexes investigated thus far, it is clear that the size of the
alicyclic ring is a critical component in the design of
[(3IP)Pd(allyl)]OTf catalysts, with the cyclobutenyl backbone
proving to be preferred over larger ring sizes.
EXPERIMENTAL SECTION
■
General Methods and Instrumentation. Alicyclic α,β-unsatu-
rated β-chloroaldehydes and β-chloroimines were synthesized under
ambient atmospheric conditions. All other manipulations were
performed under an inert N2 atmosphere using standard Schlenk
and drybox techniques. Solvents were predried prior to use; methylene
chloride was passed through two columns of 4 Å molecular sieves and
degassed with nitrogen. Pentane, diethyl ether, and toluene were
passed through columns of activated alumina and 4 Å molecular sieves
and degassed with nitrogen. Tetrahydrofuran was distilled from
sodium metal and degassed with nitrogen. n-Butyllithium (1.6 M in
hexanes), (allyl)palladium(II) chloride dimer, diphenylchlorophos-
phine, di-tert-butylchlorophosphine, lithium aluminum hydride, and
silver triflate were purchased from Strem and used without further
purification. Phosphorus oxychloride, tert-butylamine, 2,6-dimethyl
aniline, and cyclopentanone were purchased from Acros and used
without further purification. Cyclohexanone, 1,1-dimethylallene, and
cycloheptanone were purchased from Alfa Aesar and used without
further purification. Cyclobutanone was purchased from Sigma Aldrich
and used without further purification. Dimethylformamide was
purchased from BDH and stored over 4 Å molecular sieves. Anilines
were purchased from Sigma-Aldrich or another commercial source and
dried over calcium hydride, either neat (liquid anilines) or as solutions
in methylene chloride (solid anilines). Liquid anilines were freeze−
pump−thawed three times and vacuum distilled. Solutions of solid
anilines in methylene chloride were freeze−pump−thawed three times
and filtered, and the methylene chloride was removed via reduced
pressure. CDCl3 was purchased from Cambridge Isotope Laboratories,
vacuum transferred from CaH2, and stored over 4 Å molecular sieves.
Benzene-d6 was also purchased from Cambridge Isotope Laboratories,
vacuum transferred from sodium metal, and stored over 4 Å molecular
sieves. Silica gel (Porosity: 60 Å, particle size: 40−63 μm) was
CONCLUSIONS
■
A collection of 10 [(3IP)Pd(allyl)]OTf complexes was
investigated in the catalytic hydroamination of 1,1-dimethyl-
allene with electronically and sterically diverse aryl amines.
There is a strong correlation between the three tunable ligand
structural domains and the catalytic activity of these complexes.
The ligand composed of di-tert-butyl phosphine, cyclobutenyl
backbone, and tert-butyl imine domains led to the most active
1
purchased from Sorbent Technologies and used as received. H and
13C NMR data were obtained on a 600 MHz Inova or 400 MHz VXRS
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NMR spectrometer at ambient temperature at 599.9 MHz for 1H
through a plug of silica to remove excess aniline. Solvent was
evaporated, yielding the final product.
1
NMR and 150.8 MHz for 13C NMR and 399.95 MHz for H NMR
and 100.56 MHz for 13C NMR, respectively. All 31P NMR spectra
were collected on a 400 MHz VXRS NMR spectrometer at ambient
temperature at 161.90 MHz. All spectra were taken using C6D6 or
3-Iminophosphine Ligands. Unless otherwise noted, all 3-
iminophosphine ligands were prepared via the following methodology.
To a Schlenk tube with attached addition funnel was added degassed
chloroimine (1 equiv) and diethyl ether (15 mL). Lithium di-tert-
butylphosphide (1.6 equiv) was dissolved in diethyl ether (30 mL) in a
separate flask. The lithium phosphide was transferred to the addition
funnel and then added dropwise to the rapidly stirring chloroimine
solution at ambient temperature over a time period of 1 h. The
reaction was allowed to stir for an additional 2 h before concentration
in vacuo to an approximate volume of 10 mL. At this time, pentane
(20 mL) was added to help precipitate excess lithium phosphide. The
supernatant was separated via cannula filtration, solvent removed in
vacuo, and the resulting oil triturated with pentane (2 × 10 mL). The
oil was then extracted into pentane (2 × 20 mL) and passed through a
Celite padded frit. Solvent was again removed in vacuo to yield the
final product.
1
CDCl3 as the NMR solvent. H NMR shifts are given relative to the
residual solvent resonances at 7.16 and 7.26 ppm, respectively, and 13C
NMR shifts are given relative to the residual solvent peak of CDCl3
(77.36 ppm). 31P NMR spectra were externally referenced to 0.00 ppm
with 5% H3PO4 in D2O. IR samples were prepared as Nujol mulls and
taken between KBr plates on a Perkin-Elmer XTL FTIR
spectrophotometer. Melting points were observed on a capillary
melting point (Uni-Melt) apparatus in sealed capillary tubes and are
uncorrected. X-ray structure determinations were performed at the
Ohio Crystallographic Consortium, housed at The University of
Toledo. Elemental analyses were determined by Atlantic Microlab,
Inc., Norcross, GA, or Galbraith Laboratories, Inc., Knoxville, TN,
USA. High-resolution mass spectrometry using electrospray ionization
was performed at the University of Illinois Mass Spectrometry
Laboratory, Urbana, IL, USA. The following compounds were
synthesized as previously reported: LiPPh2,35 LiPtBu2,3 2-chlorocyclo-
pentenecarboxaldehyde,35 2-chlorocyclohexenecarboxaldehyde,33 2-
chlorocyclohexene-1-(2,6-xylyl)imine,33 2-chlorocyclopentene-1-(tert-
butyl)imine,35 2-diphenylphosphinocyclopentene-1-(tert-butyl)imine
(2),35 2-di-tert-butylphosphinocyclopentene-1-(tert-butyl)imine (4),3
2-diphenylphosphinocyclohexene-1-(2,6-xylyl)imine (5),33 [(2-diphe-
nylphosphinocyclopentene-1-(tert-butyl)imine)Pd(allyl)]OTf
(2Pd),35 [(2-di-tert-butylphosphinocyclopentene-1-(tert-butyl)imine)-
Pd(allyl)]OTf (4Pd),3 and [(2-diphenylphosphinocyclohexene-1-(2,6-
xylyl)imine)Pd(allyl)]OTf (5Pd).33
(3-Iminophosphine)allylpalladium Triflate Complexes. Sol-
utions of both ligand (1.05 equiv) and allylpalladium chloride dimer
(0.5 equiv) in dichloromethane (10 mL each) were combined at
ambient temperature and allowed to stir for 14 h. Solvent was removed
in vacuo, and the crude solid was triturated and rinsed with pentane
(10 mL each). The solid was redissolved in methylene chloride (10
mL), added to a slurry of silver triflate (0.65 equiv) in methylene
chloride (10 mL), and stirred in the dark for 14 h. The crude reaction
mixture was then passed through a thick pad of Celite, and solvent
removed in vacuo. The resulting solid was triturated with pentane (10
mL), dissolved in a minimal amount of tetrahydrofuran, layered with
pentane, and cooled to −20 °C to promote crystal growth.
2-Chlorocycloheptenecarboxaldehyde: light yellow liquid
General Procedure for the Catalytic Hydroamination
Screening of Compounds 1Pd−10Pd. All manipulations were
performed under an N2 atmosphere. 3-Methyl-1,2-butadiene (68 mg, 1
mmol) was added to a mixture of amine (0.5 mmol), [(3IP)Pd-
(allyl)]OTf complex (5 mol %), and deuterated benzene (0.8 mL).
1
(6.128 g, 63.18%); H NMR (CDCl3) δ 10.11 (s, 1H), 2.83−2.80
(m, 2H), 2.49−2.47 (m, 2H), 1.80−1.76 (m, 2H), 1.71−1.65 (m, 2H),
1.49−1.43 (m, 2H); 13C{1H} NMR (CDCl3) δ 191.1, 156.6, 138.7,
41.9, 31.8, 25.7, 25.1, 24.9; IR: 3331 (w), 2926 (s), 2854 (s), 2740
(w), 2698 (w), 1737 (s), 1675 (s), 1638 (s), 1607 (s), 1446 (s), 1389
(m), 1373 (m), 1337 (m), 1239 (s), 1218 (s), 1140 (s), 1083 (m),
1062 (s), 1047 (m), 1016 (m), 974 (s), 959 (s), 907 (m), 886 (m),
829 (m), 808 (m), 761 (s), 689 (s) cm−1.
1
Conversion to products was monitored via H NMR spectroscopy.
Hydroamination products formed were reported previously.3
Alicyclic α,β-Unsaturated β-Chloroaldehydes. The following
was performed with degassed reagents and solvents, and an
atmosphere of nitrogen was maintained over the mixture as the
reaction proceeded. Dimethylformamide (9.00 g, 123 mmol) was
cooled to 0 °C. POCl3 (15.00 g, 97 mmol) was then added dropwise
with rapid stirring. Formation of the Vilsmeier−Haack reagent was
allowed to proceed for 4 h, slowly warming to room temperature. The
reagent was again cooled to 0 °C before dropwise addition of the
respective cyclic ketone (61 mmol). After slowly warming to room
temperature, the mixture was heated at 55 °C for 14 h. The crude
reaction mixture was quenched over water at 0 °C to produce the
chloroaldehyde. The mixture was made basic with an excess of sodium
bicarbonate before extracting into pentane (4 × 100 mL). The organic
layer was rinsed with water and brine and dried over magnesium
sulfate for 20 min. The organic layer had ethyl acetate added up to 2%
and was passed through a plug of silica. Solvent was evaporated to
yield the final product as a lightly colored liquid.
Alicyclic α,β-Unsaturated β-Chloroimines. tert-Butyl Imines.
To pentane (20 mL) was added activated 4 Å molecular sieves. This
was cooled to 0 °C before adding freshly prepared chloroaldehyde and
1.3 equivalents of tert-butylamine. The reaction was allowed to
proceed for 14 h, slowly warming to ambient temperature. Magnesium
sulfate was added to the reaction mixture and allowed to stir for 20
min before filtering over Celite. Diethyl ether and excess tert-
butylamine were evaporated, yielding the final product.
2-Chlorocyclobutenecarboxaldehyde: light yellow liquid (1.39
g, 19.3%); 1H NMR (CDCl3) δ 9.69 (s, 1H), 2.85 (t, 3JH−H = 3.6 Hz,
3
2H), 2.65 (t, JH−H = 3.6 Hz, 2H); 13C{1H} NMR (CDCl3) δ 183.8,
143.3, 141.5, 35.4, 25.1; IR 3326 (m), 2978 (s), 2945 (s), 2815 (m),
2717 (w), 1782 (m), 1722 (s), 1673 (s), 1607 (s), 1439 (m), 1417
(m), 1373 (s), 1286 (s), 1210 (s), 1112 (s), 965 (s), 878 (m), 791
(w), 769 (m), 731 (s) cm−1.
2-Chlorocyclopentene-1-(2,6-xylyl)imine: orange-red liquid
(3.563 g, 95.77%); 1H NMR (CDCl3) δ 8.23 (s, 1H), 7.05 (d,
3
3
3JH−H = 7.8 Hz, 2H), 6.94 (t, JH−H = 7.8 Hz, 1H), 2.86 (td, JH−H
=
7.8 Hz, 2JH−H = 2.1 Hz, 1H), 2.85 (td, 3JH−H = 7.8 Hz, 2JH−H = 2.4 Hz,
1H), 2.82 (td, 3JH−H = 7.8 Hz, 2JH−H = 2.1 Hz, 1H), 2.81 (td, 3JH−H
=
7.8 Hz, 2JH−H = 2.4 Hz, 1H), 2.12 (s, 6H), 1.96 (pent, 3JH−H = 7.8 Hz,
2H); 13C{1H} NMR (CDCl3) δ 157.6, 151.4, 141.7, 135.8, 128.2,
127.9, 124.0, 39.9, 30.5, 20.9, 18.6; IR: 3062 (w), 3020 (w), 2957 (s),
2915 (s), 2852 (m), 2727 (w), 2360 (w), 2035 (w), 1918 (w), 1839
(w), 1724 (w), 1656 (m), 1625 (s), 1609 (s), 1593 (s), 1467 (s), 1441
(m), 1378 (m), 1347 (m), 1274 (m), 1247 (m), 1190 (s), 1158 (w),
1090 (m), 1033 (w), 985 (w), 938 (m), 912 (w), 844 (m), 760 (s),
723 (m), 671 (w) cm−1.
2-Chlorocyclohexene-1-(tert-butyl)imine: yellow-orange liquid
1
(1.626 g, 81.30%); H NMR (CDCl3) δ 8.46 (s, 1H), 2.50−2.46 (m,
2H), 2.42−2.38 (m, 2H), 1.77−1.71 (m, 2H), 1.68−1.62 (m, 2H),
1.21 (s, 9H); 13C{1H} NMR (CDCl3) δ 154.2, 138.7, 131.7, 57.4, 35.2,
29.8, 26.0, 23.7, 21.8; IR: 2964 (s), 2932 (s), 2859 (s), 2356 (w), 2324
(w), 1717 (w), 1691 (w), 1623 (m), 1560 (w), 1455 (w), 1434 (w),
1366 (m), 1266 (w), 1240 (w), 1209 (m), 1172 (w), 1135 (w), 1115
(w), 1099 (w), 1072 (w), 1025 (w), 989 (m), 957 (w), 905 (w), 868
(w), 826 (w), 779 (w), 695 (w) cm−1.
2,6-Dimethyl Phenyl Imines. To pentane (20 mL) was added
activated 4 Å molecular sieves. This was cooled to 0 °C before adding
freshly prepared chloroaldehyde and 1.3 equivalents of 2,6-
dimethylaniline. The reaction was stirred for 96 h, slowly warming
to ambient temperature. Magnesium sulfate was added to the reaction
mixture and allowed to stir for 20 min before filtering over Celite.
Diethyl ether was evaporated and the product redissolved in pentane.
Ethyl acetate was added up to 2%, and the product solution was passed
2-Chlorocycloheptene-1-(tert-butyl)imine: light yellow liquid
1
(3.640 g, 50.97%); H NMR (CDCl3) δ 8.37 (s, 1H), 2.74−2.71 (m,
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2H), 2.67−2.64 (m, 2H), 1.77−1.75 (m, 2H), 1.65−1.62 (m, 2H),
1.50−1.47 (m, 2H), 1.21 (s, 9H); 13C{1H} NMR (CDCl3) δ 155.0,
142.8, 137.4, 57.7, 40.7, 32.0, 30.3, 26.9, 26.1, 25.5; IR: 3217 (w), 2968
(s), 2926 (s), 2698 (w), 1737 (w), 1680 (m), 1618 (s), 1446 (s), 1368
(s), 1332 (m), 1280 (m), 1259 (s), 1213 (s), 1140 (m), 1099 (m),
1083 (m), 1062 (m), 1016 (w), 974 (s), 959 (s), 922 (m), 901 (s),
876 (w), 829 (m), 808 (w), 761 (s), 684 (m), 626 (m) cm−1.
2-Chlorocyclobutene-1-(tert-butyl)imine: yellow liquid (0.833
1592 (w), 1462 (s), 1379 (m), 1259 (w), 1197 (w), 1171 (w), 1088
(w), 1016 (w), 844 (w), 803 (w), 761 (w), 720 (w) cm−1; HRMS (m/
z) [M + H]+ calcd for C23H37NP 358.2664, found 358.2656.
2-Di-tert-butylphosphinocyclohexene-1-(tert-butyl)imine
(8): light brown liquid (0.715 g, 71.5%); 1H NMR (CDCl3) δ 9.37 (d,
4JP−H = 10.8 Hz, 1H), 2.58−2.56 (m, 2H), 2.50−2.48 (m, 2H), 1.68−
3
1.59 (m, 4H), 1.20 (d, JP−H = 7.2 Hz, 18H), 1.19 (s, 9H); 13C{1H}
3
2
NMR (CDCl3) δ 159.2 (d, JP−C = 47.1 Hz), 149.5 (d, JP−C = 18.1
1
1
5
g, 40.7%); H NMR (CDCl3) δ 7.94 (s, 1H), 2.74−2.73 (m, 2H),
Hz), 144.1 (d, JP−C = 35.4 Hz), 57.4 (d, JP−C = 1.4 Hz), 32.2 (d,
2.66−2.64 (m, 2H), 1.20 (s, 9H); 13C{1H} NMR (CDCl3): δ 147.4,
141.2, 130.3, 57.9, 34.7, 29.9, 26.0; IR 3196 (w), 2967 (s), 2935 (s),
2869 (m), 1787 (w), 1673 (m), 1646 (s), 1607 (m), 1515 (w), 1466
(m), 1422 (w), 1390 (w), 1362 (s), 1335 (m), 1297 (m), 1259 (s),
1205 (s), 1112 (s), 1096 (m), 1020 (m), 976 (s), 954 (m), 894 (m),
878 (m), 802 (m), 785 (m), 731 (m), 573 (s) cm−1.
3JP−C = 5.0 Hz), 31.4 (d, JP−C = 14.9 Hz), 31.0 (d, JP−C = 15.2 Hz),
2
1
30.4, 27.5 (d, JP−C = 5.0 Hz), 23.5, 22.6; 31P{1H} NMR (CDCl3) δ
2
19.98; IR: 2926 (s), 2854 (s), 1618 (m), 1462 (s), 1363 (s), 1259 (m),
1202 (m), 1171 (m), 1088 (m), 1016 (m), 964 (w), 901 (w), 803
(m), 720 (w) cm−1; HRMS (m/z) [M + H]+ calcd for C19H37NP
310.2664, found 310.2659.
2-Diphenylphosphinocyclopentene-1-(2,6-xylyl)imine (1):
2-Di-tert-butylphosphinocycloheptene-1-(tert-butyl)imine
prepared in a manner analogous to that of Shaffer et al.;35 yellow-
(9): yellow oil (0.540 g, 61.6%); 1H NMR (CDCl3) δ 9.37 (d, 4JP−H
=
1
10.8 Hz, 1H), 2.77−2.71 (m, 4H), 1.78−1.75 (m, 2H), 1.62−1.59 (m,
2H), 1.45−1.43 (m, 2H), 1.20 (s, 9H), 1.18 (d, 3JP−H = 12.0 Hz, 18H);
13C{1H} NMR (CDCl3) δ 159.4 (d, 3JP−C = 48.6 Hz), 157.3 (d, 2JP−C
= 18.3 Hz), 149.6 (d, 1JP−C = 36.8 Hz), 57.4 (d, 5JP−C = 1.4 Hz), 35.5
orange solid (0.618 g, 61.8%); mp 99−100 °C; H NMR (CDCl3) δ
4
3
8.64 (d, JP−H = 3.6 Hz, 1H), 7.38−7.34 (m, 10H), 7.00 (d, JH−H
=
7.8 Hz, 2H), 6.90 (t, 3JH−H = 7.8 Hz, 1H), 3.03−3.00 (m, 2H), 2.46−
2.44 (m, 2H), 2.04 (s, 6H), 1.96 (pseudo pent, JH−H = 7.8 Hz, 3JH−H
3
= 7.2 Hz, 2H); 13C{1H} NMR (CDCl3) δ 159.8 (d, 3JP−C = 22.0 Hz),
153.1 (d, 2JP−C = 21.4 Hz), 151.7, 150.2 (d, 1JP−C = 22.6 Hz), 136.5 (d,
3
1
2
(d, JP−C = 5.6 Hz), 33.4 (d, JP−C = 24.7 Hz), 32.9, 31.4 (d, JP−C
=
15.2 Hz), 30.5, 29.4 (d, JP−C = 6.8 Hz), 28.1, 26.3; 31P{1H} NMR
(CDCl3) δ 24.81; IR: 2916 (s), 2854 (s), 1612 (m), 1462 (s), 1363
(s), 1259 (m), 1213 (m), 1171 (m), 1088 (w), 1016 (m), 959 (w),
876 (w), 808 (m) cm−1; HRMS (m/z) [M + H]+ calcd for C20H39NP
324.2820, found 324.2817.
2
1JP−C = 8.7 Hz), 133.4 (d, JP−C = 19.4 Hz), 129.0, 128.8 (d, JP−C
=
=
2
3
6.9 Hz), 128.2, 127.2, 123.8, 38.1 (d, 3JP−C = 4.4 Hz), 34.0 (d, 2JP−C
5.4 Hz), 22.7 (d, JP−C = 2.0 Hz), 18.5; 31P{1H} NMR (CDCl3) δ
−23.20; IR 2961 (s), 2919 (s), 2857 (s), 2720 (w), 1612 (m), 1586
(w), 1455 (s), 1376 (m), 1298 (w), 1240 (w), 1193 (m), 1156 (w),
1088 (w), 1025 (w), 999 (w), 968 (w), 915 (w), 842 (w), 764 (m),
738 (m), 722 (m), 696 (m) cm−1; HRMS (m/z) [M + H]+ calcd for
C26H27NP 384.1882, found 384.1874.
3
2-Di-tert-butylphosphinocyclobutene-1-(tert-butyl)imine
(10): brown oil (0.365 g, 68.9%); 1H NMR (CDCl3) δ 8.27 (d, 4JP−H
=
3
2.0 Hz, 1H), 2.87−2.86 (m, 4H), 1.20 (s, 9H), 1.19 (d, JP−H = 11.6
3
Hz, 18H); 13C{1H} NMR (CDCl3) δ 159.1 (d, JP−C = 21.6 Hz),
1
2
151.4 (d, JP−C = 39.8 Hz), 151.0 (d, JP−C = 5.3 Hz), 57.7, 33.4 (d,
2-Di-tert-butylphosphinocyclopentene-1-(2,6-xylyl)imine
(3): prepared in a manner analogous to that of Beck et al.;3 deep red
1JP−C = 4.7 Hz), 33.0 (d, JP−C = 16.5 Hz), 30.7 (d, JP−C = 13.3 Hz),
2
2
1
4
30.1, 29.4 (d, JP−C = 11.4 Hz); 31P{1H} NMR (CDCl3) δ 11.36; IR:
3
oil (0.910 g, 75.8%); H NMR (CDCl3) δ 8.82 (d, JP−H = 5.4 Hz,
1H), 7.00 (d, 3JH−H = 7.8 Hz, 2H), 6.89 (t, 3JH−H = 7.8 Hz, 1H), 2.98−
2.95 (m, 2H), 2.88−2.85 (m, 2H), 2.07 (s, 6H), 1.99−1.96 (m, 2H),
2956 (s), 2869 (m), 1628 (w), 1571 (w), 1529 (w), 1472 (m), 1389
(m), 1363 (m), 1259 (s), 1213 (m), 1192 (m), 1176 (m), 1093 (s),
1021 (s), 865 (m), 803 (s), 663 (m) cm−1; HRMS (m/z) [M + H]+
calcd for C17H33NP 282.2351, found 282.2351.
3
1.19 (d, JP−H = 11.4 Hz, 18H); 13C{1H} NMR (CDCl3) δ 161.5 (d,
2
1
3JP−C = 29.9 Hz), 156.2 (d, JP−C = 20.7 Hz), 152.1, 151.9 (d, JP−C
=
=
36.5 Hz), 128.1, 127.1, 123.6, 40.1 (d, 2JP−C = 6.5 Hz), 32.9 (d, 3JP−C
[(2-Diphenylphosphinocyclopentene-1-(2,6-xylyl)imine)Pd-
1
1
2
(allyl)]OTf (1Pd): yellow solid (0.154 g, 92.1%); mp 191 °C dec; H
5.7 Hz), 32.6 (d, JP−C = 19.9 Hz), 31.1 (d, JP−C = 14.3 Hz), 23.9,
18.7; 31P{1H} NMR (CDCl3) δ 13.24; IR: 2945 (s), 2853 (s), 1608
(s), 1466 (s), 1360 (m), 1324 (m), 1254 (m), 1190 (m), 1169 (m),
1084 (m), 1062 (m), 1013 (m), 843 (w), 801 (m), 758 (s), 716 (w)
cm−1; HRMS (m/z) [M + H]+ calcd for C22H35NP 344.2507, found
344.2509.
4
NMR (CDCl3) δ 7.88 (d, JP−H = 2.4 Hz, 1H), 7.58−7.55 (m, 8H),
7.51−7.48 (m, 2H), 7.11−7.05 (m, 3H), 5.81−5.77 (m, 1H), 3.66−
3
3.62 (m, 1H), 3.55−3.50 (m, 1H), 3.49 (d, JH−H = 2.4 Hz, 1H),
3
3.11−3.04 (m, 2H), 2.70 (d, JH−H = 12.0 Hz, 1H), 2.65−2.57 (m,
2H), 2.21 (s, 3H), 2.14−2.08 (m, 2H), 2.10 (s, 3H); 13C{1H} NMR
3
2
(CDCl3) δ 164.4 (d, JP−C = 7.2 Hz), 155.8, 153.0 (d, JP−C = 17.2
2-Diphenylphosphinocyclohexene-1-(tert-butyl)imine (6):
Hz), 137.8 (d, 1JP−C = 32.6 Hz), 133.2 (d, 4JP−C = 13.6 Hz), 132.8 (d,
prepared in a manner analogous to that of Kuchenbeiser et al.;33
4JP−C = 13.1 Hz), 132.4 (d, JP−C = 24.3 Hz), 130.2 (d, JP−C = 10.7
2
3
off-white liquid (0.824 g, 82.4%); 1H NMR (CDCl3) δ 9.09 (d, 4JP−H
=
3
1
Hz), 130.17 (d, JP−C = 10.9 Hz), 129.2, 129.0, 128.6 (d, JP−C = 50.1
3.6 Hz, 1H), 7.38−7.32 (m, 10H), 2.56−2.53 (m, 2H), 1.90−1.88 (m,
1
2
2H), 1.66−1.63 (m, 2H), 1.58−1.56 (m, 2H), 1.13 (s, 9H); 13C{1H}
Hz), 128.2 (d, JP−C = 49.8 Hz), 127.3, 123.9 (d, JP−C = 5.9 Hz),
122.4, 120.2, 87.1 (d, 2JP−C = 28.4 Hz), 55.0 (d, 2JP−C = 3.5 Hz), 39.0
3
2
NMR (CDCl3) δ 156.4 (d, JP−C = 40.2 Hz), 147.6 (d, JP−C = 17.7
Hz), 140.7 (d, 1JP−C = 20.4 Hz), 136.7 (d, 1JP−C = 10.8 Hz), 133.6 (d,
2JP−C = 18.9 Hz), 128.6 (d, 3JP−C = 6.3 Hz), 128.6, 57.7, 30.2 (d, 3JP−C
2
3
(d, JP−C = 11.3 Hz), 36.5, 22.4 (d, JP−C = 5.4 Hz), 18.9, 18.8;
31P{1H} NMR (CDCl3) δ 13.11; IR 2926 (s), 2854 (s), 2719 (w),
2
= 3.6 Hz), 30.1, 27.0 (d, JP−C = 5.8 Hz), 23.7, 22.3; 31P{1H} NMR
2677 (w), 1462 (s), 1379 (s), 1301 (w), 1259 (w), 1218 (w), 1145
(w), 1093 (w), 1031 (w), 969 (w), 798 (w), 720 (w), 637 (w) cm−1.
Anal. Calcd for C30H31F3NO3PPdS: C, 52.99; H, 4.60; N, 2.06. Found:
C, 52.99; H, 4.57; N, 2.17.
(CDCl3) δ −12.70; IR: 3126 (w), 3054 (w), 2962 (s), 2921 (s), 2849
(m), 2664 (w), 2274 (w), 1952 (w), 1885 (w), 1814 (w), 1757 (w),
1618 (s), 1582 (w), 1475 (w), 1448 (w), 1428 (s), 1362 (m), 1326
(w), 1305 (w), 1259 (m), 1202 (s), 1090 (m), 1064 (m), 1023 (m),
961 (w), 900 (w), 843 (w), 802 (m), 740 (s), 694 (s) cm−1; HRMS
(m/z) [M + H]+ calcd for C23H29NP 350.2038, found 350.2043.
2-Di-tert-butylphosphinocyclohexene-1-(2,6-xylyl)imine (7):
bright yellow solid (1.100 g, 91.67%); mp 90−91 °C; 1H NMR
(CDCl3) δ 9.32 (d, 4JP−H = 9.6 Hz, 1H), 7.01 (d, 3JH−H = 7.2 Hz, 2H),
6.89 (t, 3JH−H = 7.2 Hz, 1H), 2.72−2.70 (m, 2H), 2.66 (br s, 2H), 2.08
(s, 6H), 1.79−1.77 (m, 2H), 1.72−1.69 (m, 2H), 1.21 (d, 3JP−H = 11.4
[(2-Di-tert-butylphosphinocyclopentene-1-(2,6-xylyl)imine)-
Pd(allyl)]OTf (3Pd): dark brown solid (0.736 g, 61.5%); mp 131 °C
dec; 1H NMR (CDCl3) δ 7.84 (d, 4JP−H = 1.2 Hz, 1H), 7.14−7.07 (m,
3H), 5.69−5.64 (m, 1H), 4.16 (d, 3JH−H = 6.6 Hz, 1H), 3.58−3.54 (m,
1H), 3.18−3.15 (m, 2H), 3.10−3.08 (m, 1H), 2.95−2.90 (m, 2H),
2.77 (d, 3JH−H = 12.6 Hz, 1H), 2.20 (s, 3H), 2.12−2.07 (m, 2H), 2.09
(s, 3H), 1.44 (d, 3JP−H = 15.6 Hz, 9H), 1.34 (d, 3JP−H = 15.6 Hz, 9H);
3
13C{1H} NMR (CDCl3) δ 164.7 (d, JP−C = 6.2 Hz), 157.5, 153.3 (d,
1
2JP−C = 11.9 Hz), 140.2 (d, JP−C = 15.8 Hz), 129.2, 128.9, 127.3,
3
Hz, 18H); 13C{1H} NMR (CDCl3) δ 164.5 (d, JP−C = 48.9 Hz),
2
1
127.1, 126.9, 121.8 (d, 2JP−C = 5.4 Hz), 88.7 (d, 2JP−C = 26.5 Hz), 53.1
151.9, 149.0 (d, JP−C = 18.6 Hz), 148.4 (d, JP−C = 36.8 Hz), 127.7,
126.9, 123.0, 32.6 (d, 1JP−C = 24.1 Hz), 32.1 (d, JP−C = 5.0 Hz), 31.1
3
(d, 2JP−C = 2.7 Hz), 41.1 (d, 3JP−C = 2.1 Hz), 38.7 (d, 2JP−C = 10.0 Hz),
2
2
1
1
2
(d, JP−C = 15.1 Hz), 26.6 (d, JP−C = 6.5 Hz), 23.1, 22.2, 18.4;
38.6 (d, JP−C = 15.8 Hz), 38.3 (d, JP−C = 16.0 Hz), 31.0 (d, JP−C
=
31P{1H} NMR (CDCl3) δ 20.05; IR: 2926 (s), 2854 (s), 1612 (w),
6.2 Hz), 30.7 (d, JP−C = 6.5 Hz), 24.0 (d, JP−C = 3.6 Hz), 18.8;
2
3
584
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Organometallics
Article
31P{1H} NMR (CDCl3) δ 59.48; IR 2926 (s), 2854 (s), 2719 (w),
cm−1. Anal. Calcd for C24H43F3NO3PPdS: C, 46.49; H, 7.00; N, 2.26.
Found: C, 46.58; H, 7.00; N, 2.27.
1612 (w), 1566 (w), 1457 (s), 1379 (s), 1270 (w), 1140 (w), 1083
(w), 1026 (w), 720 (w), 637 (m) cm−1. Anal. Calcd for
C26H39F3NO3PPdS: C, 48.79; H, 6.14; N, 2.19. Found: C, 48.88; H,
6.07; N, 2.33.
[(2-Di-tert-butylphosphinocyclobutene-1-(tert-butyl)imine)-
1
Pd(allyl)]OTf (10Pd): sticky brown solid (0.415 g, 71.4%); H NMR
4
(CDCl3) δ 7.94 (d, JP−H = 1.8 Hz, 1H), 5.60−5.58 (m, 1H), 5.38−
3
5.35 (m, 1H), 4.19−4.16 (m, 1H), 3.99 (d, JH−H = 6.6 Hz, 1H),
[(2-Diphenylphosphinocyclohexene-1-(tert-butyl)imine)Pd-
3
3
3.13−3.02 (m, 4H), 2.54 (d, JH−H = 12.0 Hz, 1H), 1.42 (d, JP−H
=
(allyl)]OTf (6Pd): light brown solid (0.340 g, 85.1%); mp 160 °C dec;
15.0 Hz, 9H), 1.42 (s, 9H), 1.26 (d, JP−H = 15.0 Hz, 9H); 13C{1H}
NMR (CDCl3) δ 160.3 (d, JP−C = 10.7 Hz), 157.5 (d, JP−C = 3.9
3
4
1H NMR (CDCl3) δ 7.65 (d, JP−H = 3.6 Hz, 1H), 7.51 (br s, 6H),
1
3
7.34−7.33 (m, 4H), 5.77−5.70 (m, 1H), 4.90−4.87 (m, 1H), 3.89−
2
2
3
Hz), 140.5 (d, JP−C = 8.6 Hz), 118.5 (d, JP−C = 5.3 Hz), 92.3 (d,
3.85 (m, 1H), 3.39 (s, 1H), 2.96 (d, JP−H = 10.8 Hz, 1H), 2.56 (s,
2JP−C = 25.6 Hz), 65.1, 45.2, 39.9 (d, 1JP−C = 14.6 Hz), 37.6 (d, 1JP−C
=
2H), 1.85−1.81 (m, 4H), 1.73−1.64 (m, 2H), 1.14 (s, 9H); 13C{1H}
19.2 Hz), 35.3 (d, 3JP−C = 5.3 Hz), 32.1 (d, 2JP−C = 16.6 Hz), 30.6 (d,
3
2
NMR (CDCl3) δ 163.9 (d, JP−C = 11.5 Hz), 148.8 (d, JP−C = 12.2
2JP−C = 5.7 Hz), 30.5, 30.3 (d, JP−C = 4.5 Hz); 31P{1H} NMR
2
4
2
Hz), 133.3, 132.1 (d, JP−C = 31.5 Hz), 129.8 (d, JP−C = 19.6 Hz),
129.3 (d, 1JP−C = 32.9 Hz), 127.8 (d, 1JP−C = 45.7 Hz), 121.0 (d, 2JPC
=
(CDCl3) δ 55.18; IR 2916 (s), 2854 (s), 2719 (m), 2293 (w), 1602
(w), 1457 (s), 1374 (s), 1259 (s), 1151 (m), 1088 (m), 1026 (s), 933
(m), 876 (w), 803 (m), 720 (m), 632 (m) cm−1. Anal. Calcd for
C21H37F3NO3PPdS: C, 43.64; H, 6.45, N, 2.42. Found: C, 43.00; H,
6.26; N, 2.21.
6.5 Hz), 80.7 (d, 2JP−C = 31.1 Hz), 64.3, 56.9 (d, 2JP−C = 4.8 Hz), 31.6
(d, 2JP−C = 9.8 Hz), 30.4, 29.9, 22.5 (d, 3JP−C = 4.5 Hz), 21.5; 31P{1H}
NMR (CDCl3) δ 31.78; IR: 2916 (s), 2854 (s), 2719 (m), 2667 (m),
1628 (w), 1586 (w), 1457 (s), 1379 (s), 1259 (s), 1145 (m), 1099
(m), 1026 (m), 974 (m), 912 (m), 798 (m), 720 (m), 637 (m) cm−1.
Anal. Calcd for C27H33F3NO3PPdS·1/2(C4H8O): C, 51.07; H, 5.47;
N, 2.05. Found: C, 51.14; H, 5.44; N, 2.08.
ASSOCIATED CONTENT
■
S
* Supporting Information
[(2-Di-tert-butylphosphinocyclohexene-1-(2,6-xylyl)imine)-
Pd(allyl)]OTf (7Pd): dark brown solid (0.483 g, 36.5%); mp 155−160
°C dec; 1H NMR (CDCl3) δ 7.65 (s, 1H), 7.15−7.08 (m, 3H), 5.69−
Summary of crystal data, collection parameters, and ORTEP
diagrams for crystal structures of 1Pd, 8Pd, and 9Pd. CIF files
providing additional crystallographic data, including bond
lengths and angles, for compounds 1Pd, 8Pd, and 9Pd. This
material is available free of charge via the Internet at http://
pubs.acs.org.
3
5.64 (m, 1H), 4.13 (d, JH−H = 6.6 Hz, 1H), 3.54−3.50 (m, 1H),
3
3.12−3.09 (m, 1H), 2.89−2.86 (m, 1H), 2.79 (d, JH−H = 12.6 Hz,
1H), 2.75−2.72 (m, 1H), 2.65−2.56 (m, 2H), 2.22 (s, 3H), 2.12 (s,
3H), 1.87−1.81 (m, 4H), 1.49 (d, 3JP−H = 15.6 Hz, 9H), 1.39 (d, 3JP−H
= 15.0 Hz, 9H); 13C{1H} NMR (CDCl3) δ 169.0 (d, 3JP−C = 8.6 Hz),
2
1
158.1, 146.7 (d, JP−C = 7.8 Hz), 139.4 (d, JP−C = 13.1 Hz), 129.4,
2
2
AUTHOR INFORMATION
129.0, 127.3, 127.1, 126.8, 122.0 (d, JP−C = 5.4 Hz), 88.0 (d, JP−C
=
■
26.2 Hz), 55.1 (d, 2JP−C = 3.9 Hz), 39.5 (d, 1JP−C = 13.1 Hz), 38.8 (d,
Corresponding Author
1JP−C = 13.9 Hz), 35.7 (d, JP−C = 8.7 Hz), 32.9 (d, JP−C = 2.9 Hz),
2
3
*E-mail: Joseph.Schmidt@utoledo.edu. Phone: 419-530-1512.
Fax: 419-530-4033.
31.8 (d, 2JP−C = 6.6 Hz), 31.4 (d, 2JP−C = 6.9 Hz), 21.8 (d, 3JP−C = 2.3
Hz), 21.4 (d, JP−C = 1.2 Hz), 18.9; 31P{1H} NMR (CDCl3) δ 71.63;
4
Notes
IR: 2916 (s), 2854 (s), 1618 (w), 1560 (w), 1457 (s), 1379 (s), 1270
(s), 1223 (m), 1140 (m), 1031 (m), 912 (w), 798 (w), 720 (w), 637
(m) cm−1. Anal. Calcd for C27H41F3NO3PPdS: C, 49.58; H, 6.32; N,
2.14. Found: C, 49.58; H, 6.37; N, 2.16.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
[(2-Di-tert-butylphosphinocyclohexene-1-(tert-butyl)imine)-
Pd(allyl)]OTf (8Pd): green-brown solid (0.706 g, 53.0%); mp 105 °C
dec; 1H NMR (CDCl3) δ 7.85 (d, 4JP−H = 3.0 Hz, 1H), 5.64−5.57 (m,
1H), 5.08−5.05 (m, 1H), 3.91 (d, 3JH−H = 7.2 Hz, 1H), 3.79−3.76 (m,
This material is based upon work supported by the National
Science Foundation under CHE-0841611. We would like to
acknowledge Dr. John F. Beck for his early contributions to this
project related to substrate screening for catalysis. We would
also like to thank Dr. Kristin Kirschbaum for her assistance with
X-ray crystallography.
3
1H), 2.82 (d, JH−H = 12.0 Hz, 1H), 2.57−2.56 (m, 4H), 1.78−1.67
(m, 4H), 1.45 (s, 9H), 1.45 (d, 3JP−H = 14.4 Hz, 9H), 1.36 (d, 3JP−H
=
3
14.4 Hz, 9H); 13C{1H} NMR (CDCl3) δ 166.9 (d, JP−C = 9.2 Hz),
149.5 (d, 2JP−C = 9.8 Hz), 132.4 (d, 1JP−C = 12.8 Hz), 119.6 (d, 2JP−C
=
2
1
5.6 Hz), 82.4 (d, JP−C = 26.7 Hz), 65.4, 56.6, 38.6 (d, JP−C = 10.9
Hz), 38.6 (d, 1JP−C = 11.3 Hz), 34.4 (d, 2JP−C = 9.5 Hz), 32.4 (d, 3JP−C
= 2.1 Hz), 31.9 (d, 2JP−C = 6.2 Hz), 31.7 (d, 2JP−C = 6.5 Hz), 30.7, 22.7
REFERENCES
■
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3
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