Electronic role of 3-iminophosphine ligands in palladium-catalyzed intermolecular hydroamination

Article abstract of DOI:10.1021/om500792k

This study of the electronic characteristics of (3-iminophosphine)allylpalladium triflate complexes has yielded catalysts with moderate to high activity for the hydroamination of monosubstituted allenes utilizing a wide range of amines. Herein, a new seri

Full text of DOI:10.1021/om500792k

Article
pubs.acs.org/Organometallics
Electronic Role of 3‑Iminophosphine Ligands in Palladium-Catalyzed
Intermolecular Hydroamination
Hosein Tafazolian, Danielle C. Samblanet, 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 West Bancroft Street, MS 602, Toledo, Ohio 43606-3390, United States
S
* Supporting Information
ABSTRACT: This study of the electronic characteristics of (3-
iminophosphine)allylpalladium triflate complexes has yielded
catalysts with moderate to high activity for the hydroamination of
monosubstituted allenes utilizing a wide range of amines. Herein,
a new series of these catalysts was synthesized by varying the
group on the imine moiety in order to explore the effect of the
electronics of the ligand’s imine on the catalytic activity for
intermolecular hydroamination reactions. Four amine substrates
were examined in the catalytic hydroamination of cyclo-
hexylallene, and apparent first-order rate constants were obtained
by 1H NMR spectroscopy. Kinetic isotope effect studies were also performed in order to support a new proposed catalytic cycle
in the hydroamination of cyclohexylallene with secondary amines using [(3IP)Pd(allyl)]OTf catalysts.
Even simple achiral allylamines have attracted a great deal of
attention recently, with many efforts undertaken to refine the
synthetic methods for this class of compounds.38,39 Allylamines,
in spite of being well-known, still commonly require either
multiple steps and tedious workups or stoichiometric amounts
of organometallic reagents to produce, except in cases where
their production can be effected by catalytic allylic amina-
tion.36,37,40 Beyond their applications in traditional organic
synthesis, allylamines can be used as substrates for alkene
metathesis reactions, adding to their usefulness and versatility.41
Conjugated dienes and allenes are two general substrate classes
that can serve as precursors to allylamines via catalytic
hydroamination.1,42 Hydroamination of conjugated dienes has
been widely investigated, and numerous regioselective and
enantioselective transition-metal catalysts have been devel-
oped.28,42−45 In contrast, examples of intermolecular hydro-
amination of allenes, originally reported in 1992,46 are less
common and few catalysts with high functional group tolerance
for unactivated allenes have been reported.1,19,20,22,47−53
Moreover, due to the limited number of allene hydroamination
reports, few comprehensive mechanistic studies have been
undertaken to date.23,34,54
INTRODUCTION
■
In addition to being 100% atom economical, hydroamination is
a particularly versatile method for the production of new C−N
bonds in N-containing organic frameworks.1 By use of a broad
diversity of unsaturated substrates, a wide range of target
compounds, including amines, enamines, and imines, can be
obtained.2 Over the past two decades, many structurally
modified transition-metal catalysts have proven to be capable
of regio- and enantioselective intra- and intermolecular
hydroamination of C−C unsaturated bonds.3−13 Intramolecular
hydroamination can be utilized in the synthesis of N-
heterocycles, facilitating multistep reactions for production of
biologically active molecules in fewer steps, whereas inter-
molecular hydroamination provides acyclic amines that serve as
common building blocks for pharmaceuticals and organic
syntheses.1,14−16 Intermolecular hydroamination is much more
challenging than intramolecular hydroamination, as the process
is calculated to be only slightly exothermic for many substrates,
and it also suffers from an unfavorable entropic term.17,18 As a
result, efforts to develop useful intermolecular hydroamination
catalysts have recently been a topic of great interest
worldwide.11,19−27 Furthermore, the broad significance of
catalytic hydroamination as a tool in both organic and
organometallic synthesis has made mechanistic studies for
better understanding of the catalytic cycles in these processes a
critical pursuit toward enabling organometallic chemists to
rationally tune catalyst frameworks and consequently achieve
higher catalytic activities and reaction yields.28−35
Over the past few years, our group has focused on the
hydroamination of monosubstituted allenes with primary and
secondary amines catalyzed by allylpalladium complexes
supported by 3-iminophosphine (3IP) ligands.55−59 Recently,
we reported the most active catalyst known for the
intermolecular hydroamination of monosubstituted allenes
with anilines, which also displayed a high functional group
The most significant impact of catalytic hydroamination can
be seen through the reduced cost in making valuable products
such as allylamines, which serve as convenient organic
intermediates in the synthesis of complex molecules.36,37
Received: August 1, 2014
Published: May 13, 2015
© 2015 American Chemical Society
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a
Scheme 1. General Synthetic Route for [(3IP)Pd(allyl)]OTf Complexes
a
Legend: (i) 2 equiv of DMF, 1.2 equiv of POCl3, 0 °C, and then stirring at room temperature for 14 h, 0 °C, NaHCO3; (ii) diethyl ether, 4 Å
molecular sieves, 0 °C; (iii) 1.4 equiv of LiPPh2, diethyl ether, 0 °C, and then warming to room temperature.
tolerance.55 This catalyst operated efficiently at ambient
temperature and provided moderate to high yields of
hydroamination products.55 The hydroamination of allenes
has also been pursued by the Breit group in Germany quite
successfully,23,60 although their catalyst requires the more
expensive rhodium metal center and uses high temperature in
the catalytic process, in contrast to our systems, which function
at ambient temperature.
monosubstituted allenes with primary and secondary amines, as
related to 3-iminophosphine supported palladium catalysts.
RESULTS AND DISCUSSION
■
It is important to understand the catalytic mechanism in order
to improve the activity of 3IP-Pd catalysts. Thus, we set out to
investigate the effect of imine electronics on catalyst activity.
For this purpose, a set of new 3IP ligands (2a−f) was designed,
where the groups on phosphine (phenyl) and alicyclic
backbone (cyclopentene) were kept constant (Scheme 1).
The only variable for these new ligands involved the electronics
of the imine unit, controlled by different substituents (EDG or
EWG) at the para position of a phenyl group attached to the
nitrogen (Table 1). By varying the para substituents in these
In parallel with the current study, we recently reported the
correlation of backbone ring size and phosphorus substituent
on catalytic activity with these allylpalladium 3-iminophosphine
complexes.56 This parallel study helped elucidate the catalytic
effect of σ donation from the phosphorus and ring strain due to
backbone composition. In a summary of these results, tert-butyl
groups on the phosphine resulted in higher yields for
hydroamination than phenyl groups. We deduced that the
stronger electron donation of the tert-butyl groups makes the
trans-allylic carbon more labile and, additionally, the tert-butyl
group carries more steric bulk, potentially affecting various
steps in the catalytic cycle. Most importantly, the increased
steric bulk of the tert-butyl group could assist catalysis by
increasing the rate of reductive elimination of the product
allylamine. In other tests, we found that a smaller backbone ring
size was most suitable for the catalysis, which we attributed to
increased ring strain and decreased bite angle, both of which
promote displacement of the imine from palladium to allow for
coordination of reagent amine. In these prior studies, only tert-
butyl and xylyl groups on the imine unit were tested. Given the
limited set of substituents, we were unable to make any
significant conclusions regarding the steric and electronic
effects of the 3IP imine group, and its correlation to
hydroamination catalytic activity remained ambiguous. Thus,
we set out to determine the effect of electron-withdrawing and
electron-donating imine substituents on the catalytic hydro-
amination, as reported herein. Additionally, related deuterium
kinetic isotope effect experiments are reported. Finally, on the
basis of the results herein and our other recent report,56 we
propose a rational catalytic cycle for the hydroamination of
Table 1. Hammett Constants and Reaction Yields of
[(3IP)Pd(allyl)]OTf Precatalysts
Hammett
constant
(σp)
ligand
Y (para
substituent)
chloroimine (% yield; two precatalyst
(unisolated)
steps)
(% yield)
dimethylamino
methyl
−0.830
−0.170
−0.150
−0.150
0.000
1a
1b
1c
1d
1e
1f
2a (74)
2b (69)
2c (65)
2d (63)
2e (71)
2f (76)
3a (59)
3b (62)
3c (54)
3d (52)
3e (60)
3f (69)
ethyl
isopropyl
hydrogen
chloro
0.227
new catalysts, we were then poised to correlate our
experimental data with Hammett constants,61 as these
empirically derived constants adequately represent the
electron-donating and electron-withdrawing character of
substituents in reactions involving substituted benzene
derivatives. In this fashion, it was feasible to investigate the
effect of imine electronics on catalytic hydroamination with
sterics held constant.
The ligands 2a−f and related catalysts 3a−f were synthesized
using protocols related to those developed previously in our
group:56 first, reaction of the Vilsmeier−Haack reagent with
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cyclopentanone, then Schiff base condensation with a para-
substituted aniline, and finally treatment with lithium
diphenylphosphide to produce each 3IP ligand 2a−f. During
the synthesis of these new 3IP ligands, we observed very poor
stability of the newly synthesized β-chloroimines 1a−f.
Reaction progress in the synthesis of 1a−f was monitored by
1H NMR to result in excellent product formation. Unfortu-
nately, after the reaction workup (involving passage through a
short column of silica gel followed by quick drying over
MgSO4), as the solvent was removed, compounds 1a−f started
to decompose in less than 1 h, even though they were relatively
pure at this point. We also performed the reaction and workup
under a nitrogen atmosphere, but it did not resolve these
decomposition problems. This instability of 1a−f forced us to
characterize them only by NMR spectroscopy and then use
them immediately. Thus, 1a−f were quickly isolated under a
nitrogen atmosphere and treated with lithium diphenylphos-
phide directly to transform them to ligands 2a−f. After
successful isolation, these ligands were coordinated to
commercially available allylpalladium chloride dimer, and a
subsequent salt metathesis with silver triflate yielded the
precatalysts 3a−f.
Several years ago, our group investigated the hemilability of
3IP ligands in noncatalytically active (3IP)PdCl2 complexes.62
These compounds displayed extremely weak coordination by
the imine unit of 3IP and a strong affinity toward coordination
of amines in place of the chelating imine. We have since come
to believe that this hemilability plays a significant role in
hydroamination catalysis and that coordination of the amine
substrate to 3IP palladium complexes is crucial for catalytic
hydroamination. Thus, systematic manipulation of the basicity
of this imine unit should have a marked effect on catalytic
activity. Bearing this in mind, we set out to investigate a series
of catalytic experiments using our new complexes 3a−f. Given
our studies from the past several years,55−59 we decided to
investigate the hydroamination of cyclohexylallene with several
amines (pyrrolidine, piperidine, morpholine, and 1,2,3,4-
tetrahydroisoquinoline) (Scheme 2). This group of substrates
was chosen because we expected slow to moderate catalytic
rates, allowing for more accurate comparison of the effects of
the different imines in these catalysts. That is, if more rapid
substrates were chosen, conversion data would have to be
collected immediately, with greater experimental error as a
result. Since we have previously developed very effective
catalysts for hydroamination of cyclohexylallene with these
amines,57 our goal in the present work was to understand the
effect of imine electronics at the expense of the overall reaction
rate.
Our early experiments revealed that variation of the imine
electronics had a drastic effect on the catalytic activity in these
3IP complexes. Because of our past hemilability experiments,
we initially expected catalysts with less electron donating
substituents at the para position of the imine to show higher
activity in hydroamination, since the resulting imine coordina-
tion to palladium would be weaker, facilitating displacement by
substrate amine and entry into the catalytic cycle. In contrast, it
was observed that upon proceeding from negative values of the
Hammett constant (more electron-donating) to positive ones
(more electron-withdrawing), there is a significant increase in
reaction rate, which reaches a maximum and then subsequently
decreases for the most electron-poor imines. To fully
understand the observed trend and kinetics of these reactions,
1
detailed H NMR studies were undertaken.
Reaction Order of Secondary Amine. Since our initial
experiments revealed 3c to be the most active hydroamination
precatalyst, 3c was utilized in catalytic reaction a to determine
the reaction order in amine. In order to accomplish this,
pyrrolidine was added to a mixture of benzene (0.50 mmol),
C6D6 (800 μL) and 3c (0.025 mmol), followed by addition of
1
cyclohexylallene (0.50 mmol). H NMR spectra were recorded
every 2 min with the temperature preset to 25 °C. Quantities of
0.25, 0.50, and 1.0 mmol of amine were tested in duplicate runs,
and ln[initial rate] was plotted versus ln([pyrrolidine]). The
near-unity slope of this line indicates that the reaction is first
order in amine within experimental error (Figure 1).
a
Scheme 2. Catalytic Hydroamination of Cyclohexylallene
Figure 1. Plot of ln(initial rate) versus ln([pyrrolidine]).
Reaction Order of Allene. In continued efforts to probe
the hydroamination mechanism, we set out to verify that allene
insertion was not involved in the rate-determining step by
comparing the reaction rates of pyrrolidine with 0.5, 1, and 2
equiv of cyclohexylallene. Similar to the case for the
1
experiments above, catalytic reactions were investigated by H
NMR spectroscopy. Pyrrolidine (0.50 mmol) was added to a
mixture of benzene (0.50 mmol), C6D6 (800 μL), and 3c
(0.025 mmol), followed by addition of 0.25, 0.50, and 1.0 mmol
of cyclohexylallene in separate experiments. 1H NMR data were
collected every 2 min with the temperature preset to 25 °C.
The ln[initial rate] values were plotted versus ln-
[cyclohexylallene], giving a slope of 0.0760 (Figure 2),
suggesting that the catalytic reaction is zero order in allene.
a
Catalytic procedure: reactions were carried out at 25 °C in NMR
tubes prepared in a glovebox using benzene-d6 as the solvent (800 μL),
catalyst (0.025 mmol), secondary amine (0.50 mmol), and cyclo-
hexylallene (0.50 mmol), with C6H6 (0.50 mmol) as an internal
standard. Conversion was monitored by 1H NMR spectroscopy.
b
Isolated yields were obtained from the average of six hydroamination
reactions catalyzed by 3a−f for each amine.
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Scheme 3. Coordination of Amine Followed by
Intramolecular Proton Transfer
imines represent a rate-determining step involving displace-
ment of this coordinated imine by the reactant amine, while the
slower reaction rates for the electron-poor imines are consistent
with proton transfer becoming kinetically limiting. This latter
intramolecular proton transfer step would be expected to be
highly dependent on the basicity of the imine fragment of 3IP.
Ultimately, this proton transfer step provides a palladium
intermediate bearing an amido ligand that can readily undergo
reductive elimination in a rapid step, as elegantly demonstrated
by Hartwig and co-workers previously.66−69
In summary, this mechanism involving two consecutive steps
with similarly slow kinetics but opposite correlation with imine
electronic character explains why 3e and 3f, which are carrying
the least electron-donating substituents on the imine unit, do
not provide the most active catalysts. Although they almost
definitely undergo coordination of the amine, their catalysis is
hindered by poor reactivity in the intramolecular deprotonation
step, resulting in poor reaction rates. We also investigated two
catalysts with different substituents but the same Hammett
constant to compare their catalytic activity. Ethyl (3c) and
isopropyl (3d) substituents have identical Hammett constants
(σp). Since the steric bulk of the para substituent should have
little or no impact on catalysis, the same reaction rate for both
was expected (Figure 3). In general, these two catalysts showed
very similar catalytic activity for each substrate, although 3d
gave slightly slower rates in each case, which we attribute to a
more pronounced albeit slow catalyst decomposition observed
with 3d.
Figure 2. Plot of ln(initial rate) versus ln([cyclohexylallene]).
The absence of allene from the rate law is not surprising, as
many previous studies have demonstrated rapid insertion of
olefins into Pd−C and Pd−H bonds with a variety of ligand
sets.63−65
Correlation between Observed Reaction Rates and
Hammett Value. With an understanding of the reaction order
of the catalytic substrates, specifically rate = kobs[amine], we
knew that the secondary amine was involved in the rate-
determining step. A possible mechanism involving coordination
of the amine requires concomitant dissociation of the ligand’s
imine unit and thus, the electronics of the imine unit were
investigated. In order to achieve this, we determined the
observed first-order rate constants (kobs) for all six catalysts with
three of the secondary amines. These were then plotted versus
the Hammett σp values for the imine fragment of each ligand
(Figure 3; see the Supporting Information for the rate constant
determinations).
Following the Hammett study, a deuterium-labeled amine
was used to explore the kinetic isotope effect on the catalysis, as
shown in Figure 4. It was previously shown that kH/kD for
Figure 3. Hammett plot of kobs in hydroamination reactions a, b, and
c.
As had been the case with our initial test reactions, upon
proceeding from electron-donating to electron-withdrawing
substituents, reaction rates increase to a maximum in each case
and then subsequently decrease (Figure 3). Though initially
unexpected, since imines with the largest σp values would be
most amenable to substitution by the substrate amine (EWG
would facilitate imine displacement by the amine), this peak in
catalytic activity versus Hammett constant implied that there
may be two steps in the mechanism with similar rate constants,
with one or the other dominant depending on imine
electronics. We hypothesized that the two relevant steps in
the catalytic cycle involved coordination of reagent amine to
the Pd catalyst, followed by intramolecular deprotonation of
the coordinated amine by the dissociated imine unit of 3IP
(Scheme 3). The reduced reaction rates for the electron-rich
Figure 4. Kinetic isotope effects in the hydroamination of cyclo-
hexylallene with piperidine.
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hydroamination of ethylene with aniline catalyzed by an active
Ru complex at 80 °C was 2.2
resonance at low field (9.62−9.83 ppm) assigned to the HC
N proton of the decoordinated imine moiety. Thus, we assert
that the proton transfer step from amine to imine is often rate
limiting, especially in cases involving the most active 3IP-
palladium complexes, although a rate-limiting internal attack on
the allyl group is also consistent with the experimental data for
this system.
0.1.70 This number was
consistent with earlier studies and was related to N−H(D)
bond activation, since this step was considered to be the rate-
determining step. For catalyst 3c, kH/kD for the reaction shown
in Figure 4 was found to be approximately 5.2. To determine
this value, the ratio of the slopes of ln([piperidine]) versus time
was utilized (Figure 4). The large primary kinetic isotope effect
observed strongly implies that cleavage of the N−H bond is
involved in the rate-determining step of the catalysis, consistent
with the intramolecular proton transfer step involved in the
discussion of Hammett correlation above.
In addition to kinetic rate data, our study on hydroamination
using deuterated piperidine revealed that the deuterium
becomes attached to the central carbon of allene exclusively.
Previous reports involving a Rh(I/III) catalytic system showed
that formation of a vinylic species followed by β-hydride
elimination can shift the labeled proton to the terminal carbon
of monosubstituted allenes, but we see no evidence of such
reactivity using our Pd system.23
CONCLUSIONS
■
On the basis of our previous reports, as well as the Hammett
study and deuterium labeling experiments described in this
paper, we have proposed a new catalytic cycle for our 3IP-
palladium-catalyzed intermolecular hydroamination. The elec-
tronics of the imine unit of the 3IP ligand significantly affect the
catalytic activity observed. More specifically, the electron
density on the nitrogen of the imine is significant in two
ways. First, in the step involving coordination of the substrate
amine, less electron density on the iminic nitrogen is favorable
to make it less basic and thus easier for the free amine to
displace the imine from palladium. On the other hand, in the
next step, more electron density on the iminic nitrogen is
necessary to help in deprotonation of the coordinated amine.
Thus, in every case, these two catalytic steps favor opposite
imine electronic trends, making it critically important for us to
find the optimum imine electronics in this system. Among the
ligands tested so far, this optimum point has correlated to an
ethyl group in the para position of a phenyl group attached to
the imine with a Hammett constant of −0.150. This idea can be
extended to other hydroamination substrates to find the best
imine electronics for the 3IP ligand in order to further optimize
these catalysts. Further studies will include testing of new
substrates and ongoing optimization of the 3IP ligand set, with
the continued goal of developing superior hydroamination
catalysts.
On the basis of our previous studies regarding hemilability of
(3IP)PdCl2 upon treatment with a wide range of amines,62 the
results reported above, and catalytic experiments with high
catalyst loading (see the Supporting Information, S6 and S19),
we propose a new catalytic cycle for hydroamination of allenes
with secondary amines using [(3IP)Pd(allyl)]OTf as the
precatalyst (Scheme 4). In this catalytic cycle, the palladium
Scheme 4. Proposed Catalytic Cycle
EXPERIMENTAL SECTION
■
General Methods and Instrumentation. 2-Chlorocyclopent-1-
enecarbaldehyde,56 lithium diphenylphosphide,71 3-iminophosphine
ligands 2a−f, and [(3IP)Pd(allyl)]OTf complexes 3a−f were prepared
via previously published methodology.58 β-Chloroimines 1a−f were
synthesized under ambient conditions. All further manipulations were
performed under a nitrogen atmosphere using either Schlenk
techniques or a nitrogen-filled glovebox, unless otherwise noted.
Solvents were dried prior to use; methylene chloride was passed
through two columns of 4 Å molecular sieves and degassed with high-
purity nitrogen (99.995%). Pentane, diethyl ether, and toluene were
passed through columns of activated alumina and 4 Å molecular sieves
and degassed with nitrogen. CDCl3 and C6D6 were purchased from
Cambridge Isotope Laboratories and, for air-sensitive usage, dried over
calcium hydride and sodium, respectively, freeze−pump−thawed three
times, vacuum-transferred, and stored over molecular sieves in a
nitrogen-filled glovebox. All other solvents were purchased from either
Fisher or Sigma-Aldrich. n-Butyllithium (1.6 M in hexane), (allyl)-
palladium(II) chloride dimer, diphenylchlorophosphine, lithium
aluminum hydride, and silver triflate were purchased from Strem
and applied without further purification. Phosphorus oxychloride,
pyrrolidine, morpholine, 1,2,3,4-tetrahydroisoquinoline, 4-chloroani-
line, and 4-ethylaniline were purchased from Acros; cyclopentanone
and dimethyl-4-phenylenediamine were supplied by Alfa Aesar.
Piperidine, p-toluidine, and cyclohexylallene were purchased from
Aldrich. Aniline and 4-isopropylaniline were obtained from Fisher
Scientific and Maybridge, respectively. All of the substrates for catalytic
reactions, including cyclohexylallene, pyrrolidine, piperidine, morpho-
line, and 1,2,3,4-tetrahydroisoquinoline, were dried over calcium
hydride, freeze−pump−thawed three times, vacuum-transferred, and
precatalyst, after reaction with the substrate amine, produces a
highly reactive and coordinatively unsaturated Pd(II) hydride
species. Next, allene rapidly inserts into the Pd−H bond to
form a (π-allyl)palladium complex. Subsequently, the hemil-
ability of 3IP plays a role as substrate amine coordinates to the
palladium(II) with displacement of the 3IP imine unit. In the
final steps, proton transfer from the coordinated secondary
amine to the imine unit of the 3IP provides an amido complex
of Pd(II), which then undergoes reductive elimination and
protonation of palladium to complete the catalytic cycle.
Alternatively, it is also possible that in the last step, after
coordination of amine to palladium, an internal attack of the
coordinated amine on the allyl group, followed by reductive
elimination, forms the product. The results produced herein are
incapable of resolving these two mechanisms. Notwithstanding,
the 1H NMR studies during active catalysis (see the Supporting
Information, S19) unequivocally demonstrate monodentate
coordination of the 3IP ligand to the metal center in the
1
catalyst resting state, as evidenced by the appearance of a H
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stored in the glovebox over molecular sieves. All other chemicals were
the production of chloroimine. The mixture was stirred for 2 h, and
then the reaction solution was filtered over Celite to remove LiCl
formed in the reaction. The resulting solution was concentrated under
vacuum and was kept under nitrogen at 21 °C overnight to give the
3IP ligand as a yellow solid. Subsequently, the supernatant was filtered
and the solid residue was placed under vacuum to remove the volatiles.
For ligands 2a and 2e, the solid residue was recrystallized in
concentrated pentane to remove phosphine impurities. Percent yields
for the 3IP ligands 2a−f were calculated on the basis of the mass of
starting chloroaldehyde.
1
used as received without further purification. H and 13C NMR data
were obtained on a 600 MHz Varian Unity Inova, 600 MHz Avance III
Bruker, or 400 MHz Varian VXRS NMR spectrometer at 599.9 MHz
for 1H NMR and 150.8 for 13C NMR with the first two spectrometers
and at 399.95 MHz for 1H NMR and 100.56 MHz for 13C NMR with
the VXRS spectrometer. All 31P NMR data were obtained on the 400
1
MHz VXRS NMR spectrometer at 161.90 MHz. H and 13C NMR
shifts are reported relative to CHCl3 (7.26 ppm) and CDCl3 (77.2
ppm) or C6D5H (7.16 ppm) and C6D6 (128.1 ppm). 31P NMR data
were externally referenced to 0.00 ppm with a 5% solution of H3PO4
in D2O. IR samples were prepared between NaCl plates as Nujol
mulls, and data were collected on a PerkinElmer Spectrum 2 FT-IR
spectrometer. Melting points were determined with a capillary melting
point apparatus (Uni-Melt) in sealed capillary tubes under nitrogen.
Elemental analysis and high-resolution mass spectrometry data were
determined by Atlantic Microlab, Inc., Norcross, GA, USA, and
University of Illinois Mass Spectrometry Laboratory, Urbana, IL, USA,
respectively.
Alicyclic α,β-Unsaturated β-Chloroimines 1a−f. To diethyl
ether (60 mL) was added activated 4 Å molecular sieves, and this
mixture was cooled to 0 °C before addition of chloroaldehyde. The
para-substituted aniline (1.1 equiv) was added slowly, and the mixture
was stirred overnight. Reaction completion was monitored by 1H
NMR spectroscopy. For the chloroimines 1a−d another portion of
para-substituted aniline (0.2 equiv) was added after 12 h. After
reaction completion, the solution was passed through a plug of silica to
remove unreacted aniline, followed by drying over MgSO4 for 30 min
before filtering over Celite. The solution containing chloroimine was
concentrated under vacuum and degassed with nitrogen before use in
the next step. Due to decomposition problems, α,β-unsaturated β-
chloroimines could not be stored. Thus, they were used upon reaction
completion immediately after this quick isolation protocol.
2 - D i p h e n y l p h o s p h i n o c y c l o p e n t e n e - 1 - ( 4 - N , N -
dimethylaminophenyl)imine (2a): yellow solid (2.258 g, 74%); mp
1
4
180−183 °C; H NMR (CDCl3) δ 8.98 (d, JP−H = 4.0 Hz, 1H),
3
3
7.41−7.33 (m, 10H), 7.16 (d, JH−H = 9.0 Hz, 2H), 6.70 (d, JH−H
=
9.0 Hz, 2H), 2.98−2.95 (m, 2H), 2.96 (s, 6H), 2.44−2.40 (m, 2H),
1.93−1.88 (m, 2H); 13C{1H} NMR (CDCl3) δ 154.3 (d, 3JP−C = 21.1
2
1
Hz), 152.9 (d, JP−C = 22.6 Hz), 149.7, 147.3 (d, JP−C = 21.1 Hz),
1
2
141.3, 136.6 (d, JP−C = 7.5 Hz), 133.3 (d, JP−C = 19.6 Hz), 128.7,
128.6 (d, 3JP−C = 6.0 Hz), 122.7, 112.9, 40.9, 37.7 (d, 3JP−C = 3.0 Hz),
34.2 (d, JP−C = 4.5 Hz), 22.8; 31P{1H} NMR (CDCl3) δ −24.20; IR
2
(Nujol) 3049 (m), 2805 (m), 1612 (s), 1579 (s), 1566 (m), 1514 (s),
1477 (s), 1446 (s), 1432 (m), 1358 (s), 1261 (w), 1227 (m), 1204
(w), 1167 (s), 1125 (m), 1093 (m), 1075 (m), 1067 (m), 1027 (w),
998 (w), 948 (m), 820 (s), 795 (w), 746 (m), 702 (m), 697 (m) cm−1;
HRMS m/z calcd for C26H28N2P 399.1990 [M + H]+, found 399.1990.
2-Diphenylphosphinocyclopentene-1-(4-methylphenyl)imine
(2b): yellow solid (1.952 g, 69%); mp 123−126 °C; 1H NMR
(CDCl3) δ 8.94 (d, 4JP−H = 4.2 Hz, 1H), 7.41−7.35 (m, 10H), 7.14 (d,
3
3JH−H = 8.4 Hz, 2H), 7.04 (d, JH−H = 8.4 Hz, 2H), 2.99−2.96 (m,
2H), 2.46−2.44 (m, 2H), 2.35 (s, 3H), 1.96−1.91 (m, 2H); 13C{1H}
3
2
NMR (CDCl3) δ 156.4 (d, JP−C = 22.6 Hz), 153.7 (d, JP−C = 21.1
1
1
Hz), 150.0, 149.8, 136.3 (d, JP−C = 9.1 Hz), 136.0, 133.3 (d, JP−C
=
19.6 Hz), 129.8, 128.8, 128.7 (d, 2JP−C = 7.5 Hz), 121.2, 37.9 (d, 3JP−C
2
3
= 3.0 Hz), 34.1 (d, JP−C = 6.0 Hz), 22.7 (d, JP−C = 1.5 Hz), 21.2;
31P{1H} NMR (CDCl3) δ −24.17; IR (Nujol) 3053 (m), 1663 (w),
1614 (w), 1584 (m), 1570 (m), 1519 (m), 1502 (m), 1433 (s), 1378
(s), 1348 (w), 1325 (w), 1306 (w), 1278 (m), 1260 (m), 1214 (w),
1193 (w), 1179 (w), 1168 (w), 1157 (w), 1090 (m), 1068 (m), 1027
(m), 829 (m), 814 (m), 752 (m), 744 (m), 697 (s) cm−1; HRMS m/z
calcd for C25H25NP 370.1725 [M + H]+, found 370.1723.
2-Chlorocyclopentene-1-(4-N,N-dimethylaminophenyl)imine
(1a): 1H NMR (CDCl3) δ 8.50 (s, 1H), 7.20 (d, 3JH−H = 9.0 Hz, 2H),
6.72 (d, 3JH−H = 9.0 Hz, 2H), 2.97 (s, 6H), 2.82−2.79 (m, 4H), 2.17−
2.04 (m, 2H); 13C{1H} NMR (CDCl3) δ 150.80, 149.65, 141.25,
139.74, 136.38, 122.48, 112.84, 40.78, 39.59, 30.56, 20.93.
2-Chlorocyclopentene-1-(4-methylphenyl)imine (1b): 1H NMR
(CDCl3) δ 8.45 (s, 1H), 7.17 (d, 3JH−H = 8.2 Hz, 2H), 7.07 (d, 3JH−H
=
8.2 Hz, 2H), 2.82−2.75 (m, 4H), 2.35 (s, 3H), 2.12−1.96 (m, 2H);
13C{1H} NMR (CDCl3) δ 154.33, 153.66, 149.67, 141.92, 136.13,
129.74, 120.98, 39.66, 30.43, 21.04, 20.85.
2-Diphenylphosphinocyclopentene-1-(4-ethylphenyl)imine (2c):
pale yellow solid (1.909 g, 65%); mp 123−125 °C; 1H NMR
(CDCl3) δ 8.94 (d, 4JP−H = 4.0 Hz, 1H), 7.42−7.34 (m, 10H), 7.17 (d,
2-Chlorocyclopentene-1-(4-ethylphenyl)imine (1c): 1H NMR
3
3JH−H = 8.0 Hz, 2H), 7.06 (d, JH−H = 8.0 Hz, 2H), 2.99−2.95 (m,
3
2H), 2.64 (q, 3JH−H = 7.6 Hz, 2H), 2.46−2.42 (m, 2H), 1.96−1.89 (m,
(CDCl3) δ 8.46 (s, 1H), 7.20 (d, JH−H = 8.0 Hz, 2H), 7.10 (d,
3
3JH−H = 8.0 Hz, 2H), 2.81−2.78 (m, 4H), 2.66 (q, JH−H = 7.6 Hz,
3
2H), 1.23 (t, JH−H = 7.6 Hz, 3H); 13C{1H} NMR (CDCl3) δ 156.4
2H), 2.09−2.02 (m, 2H), 1.25 (t, 3JH−H = 7.6 Hz, 3H); 13C{1H} NMR
(CDCl3) δ 154.43, 153.71, 142.47, 137.36, 136.21, 128.61, 121.08,
39.72, 30.50, 28.51, 21.16, 20.91.
(d, 3JP−C = 21.1 Hz), 153.7 (d, 2JP−C = 19.6 Hz), 150.0, 149.9 (d, 1JP−C
1
2
= 24.1 Hz), 142.4, 136.4 (d, JP−C = 9.1 Hz), 133.3 (d, JP−C = 18.1
Hz), 128.8, 128.7 (d, 3JP−C = 7.5 Hz), 128.6, 121.3, 37.9 (d, 3JP−C = 4.5
Hz), 34.1 (d, 2JP−C = 4.5 Hz), 28.6, 22.7, 15.8; 31P{1H} NMR (CDCl3)
δ −24.21; IR (Nujol) 3064 (m), 1609 (w), 1581 (w), 1571 (w), 1499
(m), 1477 (m), 1462 (m), 1433 (m), 1415 (w), 1377 (m), 1348 (w),
1261 (s), 1091 (s), 1058 (s), 1021 (s), 953 (w), 939 (w), 862 (m),
835 (m), 800 (s), 754 (m), 702 (m), 662 (w) cm−1; HRMS m/z calcd
for C26H27NP 384.1881 [M + H]+, found 384.1885.
1
2-Chlorocyclopentene-1-(4-isopropylphenyl)imine (1d): H NMR
(CDCl3) δ 8.59 (s, 1H), 7.34 (d, 3JH−H = 8.4 Hz, 2H), 7.24 (d, 3JH−H
=
3
8.4 Hz, 2H), 3.03 (sept, JH−H = 6.8 Hz, 1H), 2.94−2.89 (m, 4H),
3
2.20−2.13 (m, 2H), 1.38 (d, JH−H = 6.8 Hz, 6H); 13C{1H} NMR
(CDCl3) δ 154.47, 150.21, 147.06, 141.78, 136.29, 127.18, 121.08,
39.75, 33.82, 30.54, 24.19, 20.94.
2-Chlorocyclopentene-1-(phenyl)imine (1e): H NMR (CDCl3) δ
1
2-Diphenylphosphinocyclopentene-1-(4-isopropylphenyl)imine
(2d): yellow solid (1.918 g, 63%); mp 124−125 °C; 1H NMR
(CDCl3) δ 8.94 (d, 4JP−H = 4.0 Hz, 1H), 7.41−7.34 (m, 10H), 7.19 (d,
8.44 (s, 1H), 7.35−7.32 (m, 2H), 7.16−7.11 (m, 3H), 2.83−2.75 (m,
4H), 2.08−2.01 (m, 2H); 13C{1H} NMR (CDCl3) δ 155.10, 144.04,
139.30, 138.29, 129.13, 126.12, 121.02, 39.71, 30.43, 20.85.
3
3JH−H = 8.4 Hz, 2H), 7.06 (d, JH−H = 8.4 Hz, 2H), 2.99−2.95 (m,
2-Chlorocyclopentene-1-(4-chlorophenyl)imine (1f): 1H NMR
3
2H), 2.90 (sept, JH−H = 6.8 Hz, 1H), 2.46−2.42 (m, 2H), 1.96−1.89
3
3
(m, 2H), 1.25 (d, JH−H = 6.8 Hz, 6H); 13C{1H} NMR (CDCl3) δ
(CDCl3) δ 8.41 (s, 1H), 7.52 (d, JH−H = 8.4 Hz, 2H), 7.08 (d,
3JH−H = 8.4 Hz, 2H), 2.82−2.74 (m, 4H), 2.13−1.98 (m, 2H);
13C{1H} NMR (CDCl3) δ 155.34, 150.84, 143.08, 136.08, 131.68,
129.26, 122.41, 39.80, 30.43, 20.88.
156.5 (d, 3JP−C = 22.6 Hz), 153.8 (d, 2JP−C = 21.1 Hz), 150.1, 149.9 (d,
1
2
1JP−C = 22.6 Hz), 147.0, 136.4 (d, JP−C = 9.1 Hz), 133.3 (d, JP−C
=
18.1 Hz), 128.8, 128.7 (d, 3JP−C = 7.5 Hz), 127.1, 121.3, 37.9 (d, 3JP−C
2
3-Iminophosphine Ligands 2a−f. All of the manipulations were
performed under nitrogen atmosphere using Schlenk techniques. A
solution of freshly prepared chloroimine (used in situ as a solution in
ether) was degassed and cooled to 0 °C. To this was added LiPPh2 (1
equiv) dissolved in diethyl ether via cannula. The amount of LiPPh2
was calculated on the basis of the mass of the chloroaldehyde used for
= 3.0 Hz), 34.1 (d, JP−C = 4.5 Hz), 33.8, 24.2, 22.7; 31P{1H} NMR
(CDCl3) δ −24.82; IR (Nujol) 3067 (m), 2722 (m), 1896 (w), 1614
(m), 1584 (m), 1577 (m), 1516 (m), 1500 (m), 1476 (s), 1458 (s),
1379 (m), 1362 (m), 1351 (w), 1329 (w), 1296 (w), 1276 (w), 1260
(w), 1211 (m), 1180 (w), 1145 (w), 1110 (w), 1100 (m), 1089 (m),
1081 (m), 1068 (w), 1054 (m), 1026 (m), 1015 (w), 999 (w), 861
1814
DOI: 10.1021/om500792k
Organometallics 2015, 34, 1809−1817

Organometallics
Article
2
2
(w), 834 (m), 746 (s), 699 (s) cm−1; HRMS m/z calcd for C27H29NP
398.2038 [M + H]+, found 398.2036.
= 28.7 Hz), 54.9 (d, JP−C = 4.5 Hz), 38.9 (d, JP−C = 12.1 Hz), 36.1,
22.4 (d, JP−C = 4.5 Hz), 21.1; 31P{1H} NMR (CDCl3) δ 12.83; IR
3
(Nujol) 1641 (w), 1614 (w), 1574 (w), 1503 (m), 1462 (s), 1440
(m), 1377 (m), 1296 (s), 1260 (s), 1156 (m), 1098 (m), 1021 (s), 863
(w), 803 (m), 747 (m), 721 (w), 695 (m) cm−1. Anal. Calcd for
C29H29F3NO3PPdS·3CH2Cl2: C, 41.74; H, 3.83; N, 1.52. Found: C,
42.36; H, 3.98; N, 1.67.
2-Diphenylphosphinocyclopentene-1-(phenyl)imine (2e): yellow
1
solid (1.933 g, 71%); mp 120−122 °C; H NMR (CDCl3) δ 8.93 (d,
4JP−H = 4.0 Hz, 1H), 7.45−7.30 (m, 10H), 7.25−7.08 (m, 5H), 3.02−
2.95 (m, 2H), 2.50−2.42 (m, 2H), 1.98−1.89 (m, 2H); 13C{1H} NMR
3
2
(CDCl3) δ 157.1 (d, JP−C = 21.1 Hz), 153.6 (d, JP−C = 19.6 Hz),
152.4, 150.6 (d, 1JP−C = 22.6 Hz), 136.3 (d, 1JP−C = 7.5 Hz), 133.3 (d,
2JP−C = 19.6 Hz), 129.1, 128.8, 128.7 (d, 3JP−C = 6.0 Hz), 126.1, 121.3,
37.9 (d, 3JP−C = 3.0 Hz), 34.1 (d, 2JP−C = 4.5 Hz), 22.7; 31P{1H} NMR
(CDCl3) δ −24.20; IR (Nujol) 3064 (m), 1602 (m), 1570 (s), 1501
(w), 1483 (m), 1475 (s), 1465 (s), 1431 (s), 1377 (m), 1348 (w),
1328 (w), 1308 (w), 1261 (w), 1177 (w), 1091 (m), 1071 (m), 1023
(w), 760 (m), 745 (s), 699 (s), 684 (m) cm−1; HRMS m/z calcd for
C24H23NP 356.1568 [M + H]+, found 356.1566.
[(2-diphenylphosphinocyclopentene-1-(4-ethylphenyl)imine)Pd-
(allyl)]OTf (3c): yellow solid (522 mg, 54%); mp 88−90 °C; 1H NMR
(CDCl3) δ 8.01 (d, 4JP−H = 2.4 Hz, 1H), 7.62−7.52 (m, 10H), 7.26 (d,
3
3JH−H = 8.4 Hz, 2H), 7.24 (d, JH−H = 8.4 Hz, 2H), 5.83−5.76 (m,
1H), 3.96−3.91 (m, 2H), 3.37 (d, 3JH−H = 5.4 Hz, 1H), 3.08−3.03 (m,
2H), 2.68 (q, 3JH−H = 7.8 Hz, 2H), 2.65−2.60 (m, 3H), 2.11−2.03 (m,
3
2H), 1.24 (t, JH−H = 7.8 Hz, 3H); 13C{1H} NMR (CDCl3) δ 162.7
(d, 3JP−C = 7.5 Hz), 155.7, 153.5 (d, 2JP−C = 18.1 Hz), 144.4, 136.5 (d,
4
4
1JP−C = 33.2 Hz), 133.1 (d, JP−C = 13.6 Hz), 132.8 (d, JP−C = 12.1
2-Diphenylphosphinocyclopentene-1-(4-chlorophenyl)imine (2f):
Hz), 132.0 (d, 2JP−C = 22.6 Hz), 129.8 (d, 3JP−C = 10.6 Hz), 129.1 (d,
1
yellow solid (2.269 g, 76%); mp 132−133 °C; H NMR (CDCl3) δ
1JP−C = 48.3 Hz), 128.7, 128.5 (d, JP−C = 45.3 Hz), 123.0 (d, JP−C
=
=
1
3
4
3
8.86 (d, JP−H = 4.2 Hz, 1H), 7.40−7.35 (m, 10H), 7.28 (d, JH−H
=
6.0 Hz), 122.2, 121.1, 120.1, 89.2 (d, 2JP−C = 28.7 Hz), 54.7 (d, 2JP−C
9.0 Hz, 2H), 7.02 (d, 3JH−H = 9.0 Hz, 2H), 2.96−2.93 (m, 2H), 2.46−
2.44 (m, 2H), 1.95−1.90 (m, 2H); 13C{1H} NMR (CDCl3) δ 157.4
(d, 3JP−C = 21.1 Hz), 153.2 (d, 2JP−C = 19.6 Hz), 151.5 (d, 1JP−C = 22.6
3.0 Hz), 38.9 (d, 2JP−C = 10.6 Hz), 36.1, 28.5, 22.4 (d, 3JP−C = 4.5 Hz),
15.6; 31P{1H} NMR (CDCl3) δ 12.73; IR (Nujol) 2293 (w), 1612
(w), 1574 (w), 1502 (m), 1481 (m), 1461 (s), 1437 (s), 1377 (m),
1260 (s), 1222 (s), 1183 (m), 1146 (s), 1099 (s), 1073 (m), 1029 (s),
998 (m), 963 (w), 841 (w), 802 (w), 751 (m), 696 (m) cm−1. Anal.
Calcd for C30H31F3NO3PPdS: C, 52.99; H, 4.60; N, 2.06. Found: C,
52.45; H, 4.75; N, 2.06.
1
2
Hz), 150.9, 136.1 (d, JP−C = 9.1 Hz), 133.3 (d, JP−C = 18.1 Hz),
3
3
131.6, 129.2, 128.9, 128.7 (d, JP−C = 6.0 Hz), 122.6, 38.1 (d, JP−C
=
4.5 Hz), 34.0 (d, JP−C = 6.0 Hz), 22.7; 31P{1H} NMR (CDCl3) δ
−23.91; IR (Nujol) 3414 (m), 1888 (w), 1602 (s), 1581 (s), 1480 (s),
1466 (m), 1433 (m), 1402 (w), 1377 (w), 1260 (w), 1204 (w), 1100
(m), 1089 (s), 1070 (w), 1026 (w), 1009 (m), 825 (w), 812 (w), 746
(m), 704 (m), 698 (s) cm−1; HRMS m/z calcd for C24H22ClNP
390.1178 [M + H]+, found 390.1174.
2
[(2-diphenylphosphinocyclopentene-1-(4-isopropylphenyl)-
imine)Pd(allyl)]OTf (3d): brown solid (495 mg, 52%); mp 93 °C dec;
4
1H NMR (CDCl3) δ 8.01 (d, JP−H = 2.4 Hz, 1H), 7.66−7.52 (m,
10H), 7.26 (s, 4H), 5.82−5.76 (m, 1H), 3.97−3.91 (m, 2H), 3.37 (d,
[(3IP)Pd(allyl)]OTf Catalysts (3a−f). Solutions of 3-iminophos-
phine ligand (1.1 equiv) and allylpalladium chloride dimer (0.5 equiv)
in dichloromethane were combined at ambient temperature and
stirred overnight. The resulting solution was placed under vacuum to
remove all the volatiles and the residue washed with pentane. The
solid residue was then dissolved in dichloromethane and concentrated
to form a saturated solution, followed by layering with pentane to
induce precipitation. The solution was filtered to yield the catalyst,
which was washed with pentane and dried under vacuum before
transferring into the glovebox. Percent yields for the [(3IP)Pd(allyl)]-
OTf precatalysts were calculated on the basis of the allylpalladium
chloride dimer used.
3
3JH−H = 5.4 Hz, 1H), 3.08−3.02 (m, 2H), 2.94 (sept, JH−H = 6.6 Hz,
3
1H), 2.66 (d, JH−H = 12.0 Hz, 1H), 2.64−2.60 (m, 2H), 2.10−2.03
3
(m, 2H), 1.25 (d, JH−H = 6.6 Hz, 6H); 13C{1H} NMR (CDCl3) δ
3
2
162.8 (d, JP−C = 6.0 Hz), 155.8, 153.5 (d, JP−C = 18.1 Hz), 149.1,
136.5 (d, 1JP−C = 33.2 Hz), 133.1 (d, 4JP−C = 13.6 Hz), 132.7 (d, 4JP−C
2
3
= 15.1 Hz), 132.0 (d, JP−C = 22.6 Hz), 129.8 (d, JP−C = 12.1 Hz),
1
1
129.5 (d, JP−C = 34.0 Hz), 128.8, 128.7 (d, JP−C = 36.9 Hz), 127.3,
123.0 (d, 2JP−C = 4.5 Hz), 121.5, 121.1, 89.2 (d, 2JP−C = 28.7 Hz), 54.7
(d, 2JP−C = 4.5 Hz), 38.9 (d, 2JP−C = 12.1 Hz), 36.1, 33.9, 24.1, 22.4 (d,
3JP−C = 6.0 Hz); 31P{1H} NMR (CDCl3) δ 12.72; IR (Nujol) 1611
(m), 1574 (m), 1501 (m), 1482 (m), 1437 (s), 1378 (m), 1366 (m),
1259 (s), 1222 (s), 1148 (s), 1099 (s), 1028 (s), 999 (s), 922 (w), 863
(m), 838 (m), 801 (s), 749 (m), 696 (m), 635 (s) cm−1. Anal. Calcd
for C31H33F3NO3PPdS·0.5CH2Cl2: C, 51.37; H, 4.65; N, 1.90. Found:
C, 50.99; H, 4.98; N, 1.91.
[ ( 2 - d i p h e n y l p h o s p h i n o c y c l o p e n t e n e - 1 - ( 4 - N , N -
dimethylaminophenyl)imine)Pd(allyl)]OTf (3a): red solid (561 mg,
1
4
59%); mp 91 °C dec; H NMR (CDCl3) δ 7.96 (d, JP−H = 1.8 Hz,
1H), 7.59−7.49 (m, 10H), 7.28 (d, 3JH−H = 9.0 Hz, 2H), 6.78 (b, 2H),
5.87−5.80 (m, 1H), 4.15 (d, 3JH−H = 7.2 Hz, 1H), 3.94 (m, 1H), 3.33
(d, 3JH−H = 5.4 Hz, 1H), 3.06−3.01 (m, 2H), 3.03 (s, 6H), 2.63−2.58
(m, 3H), 2.10−2.01 (m, 2H); 13C{1H} NMR (CDCl3) δ 159.8 (d,
[(2-diphenylphosphinocyclopentene-1-(phenyl)imine)Pd(allyl)]-
1
OTf (3e): brown solid (600 mg, 60%); mp 102−104 °C; H NMR
4
(CDCl3) δ 8.02 (d, JP−H = 2.4 Hz, 1H), 7.60−7.45 (m, 8H), 7.43−
2
4
3JP−C = 7.5 Hz), 153.8 (d, JP−C = 18.1 Hz), 135.2, 133.1 (d, JP−C
=
7.38 (m, 2H), 7.33−7.24 (m, 5H), 5.80−5.74 (m, 1H), 3.91−3.86 (m,
2H), 3.37 (d, 3JH−H = 5.4 Hz, 1H), 3.08−3.03 (m, 2H), 2.66 (d, 3JH−H
= 12.6 Hz, 1H), 2.64−2.59 (m, 2H), 2.10−2.03 (m, 2H); 13C{1H}
14.3 Hz), 132.6 (d, 4JP−C = 13.2 Hz), 132.0 (d, 1JP−C = 31.5 Hz), 130.6
(d, 2JP−C = 11.0 Hz), 129.8 (d, 3JP−C = 11.0 Hz), 129.1 (d, 1JP−C = 49.5
3
2
NMR (CDCl3) δ 163.2 (d, JP−C = 6.0 Hz), 157.8, 153.4 (d, JP−C
=
1
2
Hz), 128.8 (d, JP−C = 47.3 Hz), 123.0 (d, JP−C = 5.5 Hz), 122.8,
122.1, 120.0, 112.6, 89.1 (d, 2JP−C = 28.6 Hz), 54.7 (d, 2JP−C = 3.3 Hz),
18.1 Hz), 136.9 (d, 1JP−C = 33.2 Hz), 133.1 (d, 4JP−C = 13.6 Hz), 132.7
(d, 4JP−C = 13.6 Hz), 132.0 (d, 2JP−C = 22.6 Hz), 129.8 (d, 3JP−C = 12.1
2
3
40.5, 39.0 (d, JP−C = 12.1 Hz), 36.1, 22.8, 22.5 (d, JP−C = 5.5 Hz);
1
1
Hz), 129.5, 128.9 (d, JP−C = 49.8 Hz), 128.4 (d, JP−C = 48.3 Hz),
31P{1H} NMR (CDCl3) δ 13.11; IR (Nujol) 1615 (w), 1576 (w),
2
2
128.0, 123.0 (d, JP−2C = 7.5 Hz), 122.1, 121.1, 119.9, 89.0 (d, JP−C
=
1505 (w), 1463 (m), 1296 (s), 1231 (s), 1167 (s), 1100 (m), 1021 (s),
893 (w), 844 (w), 802 (w), 749 (w), 721 (w), 697 (w), 635 (s) cm−1.
[(2-diphenylphosphinocyclopentene-1-(4-methylphenyl)imine)-
Pd(allyl)]OTf (3b): dark brown solid (610 mg, 62%); mp 98 °C dec;
2
28.7 Hz), 54.8 (d, JP−C = 3.0 Hz), 38.9 (d, JP−C = 10.6 Hz), 36.2,
22.4 (d, 3JP−C = 6.0 Hz); 31P{1H} NMR (CDCl3) δ 12.70; IR (Nujol)
1570 (w), 1482 (w), 1463 (s), 1438 (m), 1377 (m), 1261 (s), 1222
(m), 1148 (m), 1099 (m), 1029 (s), 999 (w), 800 (w), 774 (w), 752
(w), 736 (w), 695 (m) cm−1; Anal. Calcd for C28H27F3NO3PPdS: C,
51.58; H, 4.17; N, 2.15. Found: C, 51.21; H, 4.45; N, 2.32.
4
1H NMR (CDCl3) δ 8.02 (d, JP−H = 2.4 Hz, 1H), 7.62−7.48 (m,
3
3
10H), 7.23 (d, JH−H = 7.8 Hz, 2H), 7.19 (d, JH−H = 7.8 Hz, 2H),
5.80−5.73 (m, 1H), 3.97−3.95 (m, 1H), 3.88−3.84 (m, 1H), 3.40 (d,
3JH−H = 5.4 Hz, 1H), 3.08−2.98 (m, 2H), 2.65−2.58 (m, 2H), 2.46 (d,
3JH−H = 12.0 Hz, 1H), 2.39 (s, 3H), 2.09−2.02 (m, 2H); 13C{1H}
[(2-diphenylphosphinocyclopentene-1-(4-chlorophenyl)imine)-
1
Pd(allyl)]OTf (3f): brown solid (663 mg, 69%); mp 109 °C dec; H
4
NMR (CDCl3) δ 8.02 (d, JP−H = 2.4 Hz, 1H), 7.61−7.51 (m, 10H),
3
7.38 (d, 3JH−H = 9.0 Hz, 2H), 7.34 (d, 3JH−H = 9.0 Hz, 2H), 5.80−5.73
NMR (CDCl3) δ 163.0 (d, JP−C = 7.5 Hz), 155.5, 138.4, 136.5 (d,
4
4
1JP−C = 33.2 Hz), 133.1 (d, JP−C = 13.6 Hz), 132.6 (d, JP−C = 12.1
(m, 1H), 3.95−3.93 (m, 1H), 3.92−3.88 (m, 1H), 3.36 (d, 3JH−H = 4.8
2
2
3
Hz), 131.1 (d, JP−C = 34.7 Hz), 130.9, 130.1 (d, JP−C = 15.1 Hz),
Hz, 1H), 3.09−3.03 (m, 2H), 2.66 (d, JH−H = 12.6 Hz, 1H), 2.63−
129.6 (d, JP−C = 12.1 Hz), 129.3 (1JP−C = 52.8 Hz), 128.6 (1JP−C
=
2.59 (m, 2H), 2.08−2.03 (m, 2H); 13C{1H} NMR (CDCl3) δ 163.8
(d, 3JP−C = 7.5 Hz), 156.2, 153.5 (d, 2JP−C = 16.6 Hz), 137.2 (d, 1JP−C
3
51.3 Hz) 123.0 (d, 2JP−C = 4.5 Hz), 122.7, 121.3, 120.8, 89.2 (d, 2JP−C
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Article
4
4
= 33.2 Hz), 133.6, 133.1 (d, JP−C = 15.1 Hz), 132.8 (d, JP−C = 13.6
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2
3
Hz), 132.0 (d, JP−C = 19.6 Hz), 130.4, 129.8 (d, JP−C = 10.6 Hz),
129.5, 129.0 (d, 1JP−C = 48.3 Hz), 128.4 (d, 1JP−C = 48.3 Hz), 123.0 (d,
3JP−C = 7.5 Hz), 122.8, 121.5, 88.9 (d, 2JP−C = 28.7 Hz), 54.9 (d, 2JP−C
2
3
= 3.0 Hz), 38.9 (d, JP−C = 12.1 Hz), 36.2, 22.4 (d, JP−C = 6.0 Hz);
31P{1H} NMR (CDCl3) δ 12.62; IR (Nujol) 1611 (w), 1575 (w),
1483 (s), 1463 (s), 1438 (s), 1377 (m), 1337 (m), 1315 (m), 1261
(s), 1231 (s), 1208 (s), 1155 (s), 1099 (s), 1029 (s), 1012 (s), 999
(m), 983 (m), 860 (w), 832 (w), 747 (m), 720 (w), 695 (m) cm−1;
Anal. Calcd for C28H26ClF3NO3PPdS·CH2Cl2: C, 45.16; H, 3.66; N,
1.82. Found: C, 44.37; H, 3.69; N, 1.94.
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General Procedure for the Catalytic Hydroamination
Screening of Catalysts 3a−f. All manipulations were performed
in an NMR tube inside a nitrogen-filled glovebox. Cyclohexylallene
(61 mg, 0.50 mmol) was added to a mixture of C6H6 (0.50 mmol as
internal standard), secondary amine (0.50 mmol), [(3IP)Pd(allyl)]-
OTf (0.025 mmol), and deuterated benzene (800 μL). The ratio of
each substrate to hydroamination product was monitored by 1H NMR
spectroscopy. After reaction completion was observed, the volatiles
were removed from the reaction mixture under vacuum. The residue
was washed with pentane/ethyl acetate (90/10 by volume) and passed
through a plug of silica. Solvents were removed, and the colorless
liquid was isolated and characterized as the hydroamination products.
Two of the observed hydroamination products, 1-[(2E)-3-cyclohexyl-
2-propen-1-yl]pyrrolidine,72 and 4-[(2E)-3-cyclohexyl-2-propen-1-yl]-
morpholine,73 were reported previously (isolated yields 81% and 87%,
respectively).
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(E)-2-(3-Cyclohexylallyl)-1,2,3,4-tetrahydroisoquinoline: colorless
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1
liquid; yield 85%; H NMR (C6D6) δ 7.05−7.02 (m, 2H), 6.98 (dd,
3JH−H =5.5 Hz, 4JH−H = 2.2 Hz, 1H), 6.90 (dd, 3JH−H = 6.6 Hz, 4JH−H
=
1.9 Hz, 1H), 5.60−5.59 (m, 2H), 3.55 (s, 1H), 3.03−3.02 (m, 2H),
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2.78 (t, 3JH−H = 5.8 Hz, 3H), 2.58 (t, 3JH−H = 5.8 Hz, 2H), 1.94−1.89
2
3
(m, 1H), 1.73−1.70 (m, 2H), 1.65 (dt, JH−H = 13.2 Hz, JH−H = 3.7
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2
3
Hz, 2H), 1.61−1.57 (m, 1H), 1.19 (tt, JH−H = 12.4 Hz, JH−H = 3.3
Hz, 2H), 1.11−1.05 (m, 3H); 13C{1H} NMR (C6D6) δ 139.8, 135.8,
135.0, 129.0, 126.9, 126.3, 125.8, 125.3, 61.2, 56.4, 50.9, 40.9, 33.4,
29.9, 26.6, 26.4; HRMS m/z calcd for C18H26N 256.2065 [M + H]+,
found 256.2062.
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1
(E)-1-(3-Cyclohexylallyl)piperidine: colorless liquid; yield 88%; H
NMR (C6D6) 5.60 (dt, JH−H = 15.8 Hz, JH−H = 6.2 Hz, 1H), 5.55
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3
3
3
3
3
(dd, JH−H = 15.8 Hz, JH−H = 5.9 Hz, 1H), 2.93 (d, JH−H = 6.2 Hz,
2H), 1.93−1.87 (m, 1H), 1.73−1.55 (m, 11H), 1.20−1.02 (m, 9H);
13C{1H} NMR (C6D6) δ 138.3, 126.5, 58.8, 54.2, 40.9, 33.5, 26.6, 26.5,
25.8, 24.0; HRMS m/z calcd for C14H26N 208.2065 [M + H]+, found
208.2067.
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136, 3200−3207.
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2786−2792.
ASSOCIATED CONTENT
* Supporting Information
Text, tables, and figures giving synthetic procedures for
piperidine-d1, reaction rate plots, and NMR spectra. The
Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/om500792k.
■
S
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5757.
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130, 16562−16571.
AUTHOR INFORMATION
Corresponding Author
*J.A.R.S.: e-mail, Joseph.Schmidt@utoledo.edu; tel, 419-530-
1512; fax, 419-530-4033.
■
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Notes
The authors declare no competing financial interest.
(38) Trost, B. M.; Zhang, T.; Sieber, J. D. Chem. Sci. 2010, 1, 427−
ACKNOWLEDGMENTS
This work was supported by the National Science Foundation
under CHE-0841611.
■
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