A Au(I)-Precatalyst with a Cyclopropenium Counterion: An Unusual Ion Pair

Article abstract of DOI:10.1021/acs.joc.6b00241

The synthesis and X-ray crystal structure of a novel Au(I)-precatalyst applied to intermolecular alkyne hydroamination is reported. Density functional theory (DFT) calculations revealed the cyclopropenium counterion of this Au(I)-precatalyst imparts stabi

Full text of DOI:10.1021/acs.joc.6b00241

Note
pubs.acs.org/joc
A Au(I)-Precatalyst with a Cyclopropenium Counterion: An Unusual
Ion Pair
Roya Mir and Travis Dudding*
Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON, Canada
S
* Supporting Information
ABSTRACT: The synthesis and X-ray crystal structure of a novel Au(I)-precatalyst applied to intermolecular alkyne
hydroamination is reported. Density functional theory (DFT) calculations revealed the cyclopropenium counterion of this Au(I)-
precatalyst imparts stability through H-bonding and other noncovalent interactions.
atalytic processes are vital for the manufacturing of a
myriad of materials this age as witnessed by their use in
closed shell interactions;8 (2) the formation of byproducts that
can cause side reactions;9 (3) the fact that many are relatively
expensive (e.g., AgNTf2)10 or unavailable commercially (e.g.,
Ag[B(C6F5)4])11 in addition to being difficult to prepare; (4)
the ability to act as cocatalyst;12 and (5) their potential to
complicate determination of catalytic active species in a
reaction which often makes optimization of a process
challenging. Accordingly, to offer alternative strategies for
circumventing these impasses and in adding to the works of
Teles,2 Nolan,13 Hammond,14 and others,15 we recently
reported a pnictogen based N-centered strong dicationic
C
pharmaceutical, agrochemical, and polymer based manufactur-
ing sectors. Echoing this truth has been the widespread
advancement of catalytic transition-metal-mediated protocols,
which via judicious selection of an appropriate metal and ligand
combination can enable chemo-, regio-, and/or stereoselecitive
transformations. In this context, Cu(I) and Ag(I) catalysis has
had a historical presence, whereas the use of Au(I) as a catalyst
was overlooked until recently owing to a longstanding
misconception alleging it was catalytically dead.1 Notwithstand-
ing, a pioneering Au(I)-catalyzed alcoholysis of alkynes in 1998
by Teles et al.2 dispelled this presumption and in doing so gave
rise to a virtual catalytic gold rush3 that continues to offer
innovative transformations benefiting from the 5d orbital
expansion and 6s orbital contraction in Au(I) resulting from
relativistic effects.4,5
Driving these efforts has of course been intellectual curiosity
in exploring novel modes of chemical reactivity, while at the
same time the robust nature of Au(I) has expedited matters, as
it ameliorates the meticulous need for excluding water or
oxygen from reactions in many cases.6 Nevertheless, a recurring
shortcoming of Au(I)-catalysis has been the employment of
Au(I) precursors, such as the stable linear dicoordinated LAuCl
(L is a two-electron donor) precatalyst, that require activation
by Ag(I) salts or other additives to access catalytically active
unsaturated monocoordinated [LAu(I)]+ complexes. The
drawbacks of using silver activators include the following: (1)
the formation of gold−silver adducts (e.g., dinuclear gold−
silver catalytic resting states)7 resulting from auro-argentophilic
−
organic Brønsted acid 1+−H+·2BF4 (1) that served as an
activator of a Ph3PAu−Pht (Pht = phthalimido) (2) precatalyst
which generated a cationic gold(I) catalyst employed in alkyne
hydroamination (Scheme 1a).16
Given the success of this strong Brønsted acid/Au(I)
catalytic system for hydroamination we envisioned building
upon this development by synthesizing a Au(Pht)2BACI−H
(6) (BACI = bis(diisopropylamino)cyclopenium) precatalyst
that could serve as an in situ derived source of a highly Lewis
acidic Au(I)-catalyst (Scheme 1b). As for 6, it could be secured
in a retrosynthetic sense from phthalimide (7) and known
[Au(BAC)Cl] (8) (BAC = bis(diisopropylamino)cyclo-
penylidene that in turn would be prepared from a synthetic
route that ideally was shorter than those previously reported.
Received: February 6, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.6b00241
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The Journal of Organic Chemistry
Note
bond orbital (NBO) analysis of 6opt was the donation of oxygen
O(1) (NBO charge = −0.68) lone pair density into an
antibonding σ*-orbital of the cyclopropeniminium C(1)−H(1)
bond (ENBO = 10.06 kcal/mol), which is consistent with a
degree of fractional chemical H-bonding or, that is, charge-
transfer-based “partial covalent” H-bonding. While in the
lexicon of Gilli et al. this same interaction typifies a positive
charge-assisted H-bond.18 To further probe the bonding in 6opt,
a (λ2)ρ vs σ noncovalent interaction (NCI)19 plot was
computed at the B3LYP-D3/LACVP++**//B3LYP/Lan2DZ
level of theory which uncovered the presence of several
stabilizing interactions as seen from the highly localized green
isosurface areas in 6NCI (Figure 2), where λ2 equals the second
Scheme 1. Retrosynthesis of Au(I) Precatalyst 6
With the above factors in mind, the synthesis of precatalyst 6
was carried out by reacting bis(diisopropylamino)cyclo-
propenium chloride (9·Cl−) with readily available chloro-
(dimethylsulfide)gold(I) in the presence of inexpensive and
mild base K2CO3 to yield known 817 (Scheme 2). From a
Figure 2. (a) Computed 6NCI corresponding to the noncovalent
interactions (NCI) in 6opt. (b) Computed 6HOMO corresponding to the
HOMO of 6opt (B3LYP-D3/LACVP++**//B3LYP/Lan2DZ level of
theory).
Scheme 2. Synthesis of Precatalyst Au(Pht)2BACI−H (6)
eigenvalue of the density Hessian, ρ the electron density, and σ
the reduced-density gradient. The origin of these favorable
noncovalent interactions derive from H-bond contacts between
the phthalimido oxygen O(1) and a well-aligned manifold of
partial positive cyclopropenium hydrogens, as well as stabilizing
van der Waals contacts. The HOMO of 6opt corresponding to
6HOMO offered additional insight, as it conformed to an
antibonding interaction between the 5dx,y orbital of Au(I) and
the nitrogen 2p(π)-orbital of the phthalimido ligands, thus
suggesting the phthalimido ligands would be susceptible to
protonalysis (Figure 2).
Having insight into the structure of precatalyst 6 as a proof-
of-concept and based on our interest in group 11 catalyzed
processes (e.g., imino-alkylation and alkyne/alkene hydro-
amination reactions),20 which are an effective stratagem for
preparing nitrogen-containing molecules, we were attracted by
the possibility of applying Au(I)-precatalyst 6 to alkyne
hydroamination reactions.
preparative standpoint, it is notable that our route to 8 is the
shortest to date. Potassium phthalimide in acetone was then
added at 45 °C to afford targeted homoleptic Au(I) complex 6
in 87% yield. Subsequently, single-crystal X-ray quality crystals
were grown by vapor diffusion of ethyl acetate into an
acetonitrile solution of 6. The X-ray structure of 6 unveiled
several interesting features, the most dominant being the
presence of a cyclopropenium that apart from balancing the
overall charge of the complex engaged in a stabilizing H-bond
(C(1)−H(1)···O(1), d = 1.80 Å), Figure 1 (Structure A). To
probe the nature of these interactions, a restricted optimization
at the B3LYP/LanL2DZ level of theory, wherein all of the
heavy atoms were frozen and the hydrogens were left
unconstrained starting from the X-ray coordinates of 6, was
performed to provide 6opt (Figure 1). Revealed from a natural
To this end, using a low precatalyst loading of 6 (0.08 mol
%) and strong Brønsted acid 1+−H+·2BF4 (0.16 mol %), an
−
initial reaction of aniline 4a and alkyne 3a was carried out at 50
°C, which to our delight provided imine 5a in 60% yield (Table
1, entry 1). Notably, the yield of this reaction was
approximately 3-fold greater than that obtained under
analogous conditions with structurally related precatalyst 2.16
Given this promising result a number of different substituted
alkynes and amines were subsequently employed to explore the
substrate scope of this reaction. Accordingly, the resonance
donating and inductively electron-withdrawing 4-bromo
substituted aniline 4b and 2,5-dichloroaniline (4c) provided
increased product yields of 84% and 93%, and notably, the
latter product was obtained in a shorter timespan of 4 h (Table
1, entries 2 and 3). Notwithstanding, the comparative use of 4-
fluoroaniline (4d) having a powerful inductively electron-
withdrawing, less resonance donating, and weakly polarizable
halogen afforded imine 5d in a lower 61% yield. The poor
reactivity in this case is thought to derive in large part from the
Figure 1. (a) X-ray structure of 6 (Structure A) with 50% ellipsoid
probability (see Supporting Information). (b) Computed 6opt
optimized at the B3LYP/LanL2DZ level of theory.
B
DOI: 10.1021/acs.joc.6b00241
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Note
Table 1. Au(I)-Catalyzed Alkyne Hydroamination Using 6
nucleophile
R3
ab
,
entry
R1
R2
R4
R5
time (h)
yield (%)
1
3a
3a
3a
3a
3a
3a
3a
3a
3a
3b
3c
3d
H
4a
4b
4c
4d
4e
4f
H
H
H
H
Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
iPr
H
H
H
24
24
4
5a
5b
5c
5d
5e
5f
60
84
93
61
60
45
48
49
72
95
53
60
2
H
H
Br
H
F
3
H
Cl
H
4
H
24
24
24
24
24
24
24
24
24
5
H
H
C2H5
C4H9
H
6
H
H
7
H
4g
4h
4i
C2H5
Me
iPr
H
5g
5h
5i
8
H
Me
H
9
H
10
11
12
OMe
Me
F
4a
4a
4a
H
5j
H
H
5k
5l
H
H
a
b
1
Yields of isolated products after flash chromatography. Reaction conversion after 48 h was insignificant (<1%) based on H NMR when the
Brønsted acid, metal, or Brønsted acid−metal combination were excluded.
interplay of multipolar C−F interactions (e.g., C−F···H−C, C−
F···H−N, or C−F···Au contacts) and reduced amine basicity
resulting from the 4-F-substituent of 4d (Table 1, entry 4).21
On the other hand, the use of more electron-rich substrates
4-ethyl- and 4-butylaniline (4e and 4f) having inductively
donating para- substituents afforded products in 60% and 45%
yield (Table 1, entries 5 and 6). To probe the effect of alkyl
substituents and sterics on the reaction, 2-ethylaniline (4g) was
next investigated, which provided product 5g in low yield
(Table 1, entry 7). The lower yields obtained in the last three
cases (i.e., entries 5−7), presumably, arose from the ability of
electron-rich anilines to competitively bind gold to generate a
less active and/or nonactive catalyst resting state, which in turn
would reduce the concentration of the activated η2-alkyne and
subsequently diminish the rate of amine addition. Reasoning
from this result the effect of steric inhibition of aniline binding
with the catalyst was studied by subjecting 2,4,6-trimethylani-
line (4h) to the reaction conditions which afforded product 5h
in 49% yield. Notwithstanding, in-keeping with our posit of
Au(I)-deactivation via formation of a catalytically inactive
resting state, the use of more sterically hindered substrate 4i
was then tested, affording an improved reaction yield of 72%
(Table 1, entry 9).
Scheme 3. Computed LUMO of 10 and the Relationship of
10 and 11 at B3LYP/Lan2DZ Level of Theory
0.599 at gold in envisioned 10. Notably, the latter term was
decidedly larger than that computed for often employed Au(I)-
complexes having 1,3-bis(2,4,6-trimethylphenyl)-imidazolium
(IMes) and triphenylphosphine ligands (NBO charges = 0.506
and 0.311 at gold). To gain additional insight into conjectural
Au(I) catalyst 10, the relationship of 10 and 11 was evaluated
(B3LYP/Lan2DZlevel of theory), revealing a strong preference
for 10 vice versa 11 as judged by a 43.0 kcal/mol energy
difference.
As for the catalytic cycle of this reaction, it is open to debate
given the multiple roles; a weak phthalimide might serve
mechanistically, especially in terms of proton shuttling which is
a critical event for ensuring effective rates of protodeauration
leading to catalytic turnover in Au(I) hydroamination reactions.
Moreover, the reaction media of these hydroaminations add a
further dimension of complexity, due to the presence of
multiple ions (e.g., cyclopropeniminium) capable of stabilize
charged intermediates and/or charge buildup, likening it to an
ionic liquid, which would arguably have an impact upon
acidities. Irrespective, working from a well-established basis of
either (1) nucleophilic amine addition to an η2-[LAu(I)]+-
activated alkyne complex occurring in an outer sphere
Markovnikov regioselective manner23 or (2) protodeauration
being the rate-determining steps governing catalytic turnover,
which is well-known to be a rate-limiting step in many gold(I)-
catalyzed hydroaminations,23 the tentative catalytic cycle in
While the actual Au(I) catalyst in these reactions remains
elusive at this time, the work of Alcarazo et al.22 concerning
gold(I) coordinated polycationic cyclopropenium-substituted
phosphines lends a degree of support to the probable existence
of a p-block (group 15) coordinated gold(I) catalyst [Au(I)-
(1)]2+·2BF4 (10) having an electron-deficient imidazoliumyl
−
N-cyclopropenium ligand (Scheme 3). As for the formation of
catalyst 10 it could originate in situ from a domino series of
events initiated by the protolysis of 6 by 1+−H+·2BF4 to
−
generate conjugate base 1+, which would serve as a ligand for
Au(I). Consistent with this prospect and the formation of a
reactive Au(I) catalyst was the B3LYP/Lan2DZ computed
−
LUMO of the parent gold complex of 10 with the 2BF4
Scheme 4 is offered. As depicted, initial 1+−H+·2BF4 (1)
−
counterions removed which conformed predominately to a
Au(I) based 6s orbital. Also suggestive of the high gold(I)
based reactivity was a computed NBO charge assignment of
triggered protonalysis of 6 would generate a putative gold(I)
−
complex Au(1+)2·3BF4 that upon ligand dissociation would
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Note
a 300 MHz spectrometer (1H 300 MHz, 13C 75.5 MHz or 13C 150.9
MHz, 19F 292.4 MHz) in CDCl3, D2O, and CD3CN. The chemical
shifts are reported as δ values (ppm) relative to tetramethylsilane. FT-
IR spectra were obtained with an attenuated total reflectance
spectrophotometer from a neat sample.
Scheme 4. Proposed Catalytic Cycle for Hydroamination
Using Precatalyst 6
2. Procedure for Synthesis of Catalyst [AuCl(BAC)] (7). An
round bottom flask (RBF) was charged with [AuCl(SMe2)] (323.9
mg, 1.1 mmol) and K2CO3 (3.7 mg, 0.027 mmol). Subsequently, a
solution of reported17 cyclopropenium chloride (8·Cl−) (275.4 mg, 1.1
mmol) in acetone (10 mL) was added. It was refluxed for 2 h, after
which acetone was removed and the residue dissolved in acetonitrile.
The resulting suspension was filtered, and removal of solvent under
high vacuum afforded [AuCl(BAC)] (7) as a colorless solid (561.8
mg, 91% yield). The spectroscopic data were in full agreement with
spectral data for an authentic sample.17
1H NMR (CD3CN, 300 MHz) δ = 3.81−3.96 (m, 4H), 1.52−1.54
(d, J = 4.42 Hz, 12H), 1.27−1.29 (d, J = 5.40 Hz, 12H); 13C NMR
(CD3CN, 150.9 MHz) δ = 144.7, 132.0, 55.9, 48.0, 21.2, 20.0.
3. Procedure for Synthesis of Catalyst Au(Pht)2BACI−H (6).
To an RBF charged with 7 (335.5 mg, 0.6 mmol) and potassium
phthalimide (233.4 mg, 1.3 mmol), acetone (4 mL) was added. The
resulting suspension was stirred at 45 °C for 3 h. The reaction mixture
was filtered and washed with a small portion of acetone. Subsequently,
filtrate was concentrated, filtered, washed with water, and dried under
a high vacuum. Recrystallization from acetonitrile/ethyl acetate at
room temperature afforded 6 as a white solid (380 mg, 87% yield). Mp
1
188−192 °C; H NMR (CDCl3, 300 MHz) δ = 9.83 (s, 1H), 7.66−
7.69 (m, 4H), 7.53−7.55 (m, 4H), 4.01−4.10 (pentet, J = 6.75 Hz,
2H), 4.73−3.82 (pentet, J = 6.81 Hz, 2H), 1.36 (dd, J = 19.02, 6.68
Hz, 24H); 13C NMR (CDCl3, 150.9 MHz) δ = 178.3, 136.1, 133.9,
131.9, 121.5, 101.1, 56.4, 49.2, 21.3, 20.9.; IR 3087, 2979, 1668, 1568.
FAB/EI results indicated that the ion pair dissociates to [Au(I)Pht2]−
and BAC under the conditions of MS.
afford gold(I) catalyst 10, which following η2-alkyne coordina-
tion would undergo outer sphere trans-addition of aniline to
afford β-anilinium vinylgold species 12. Thereafter, a
subsequent [1,3]-proton shuttling event mediated by phthali-
mide 7 would then result in protodeauration to give the Au(I)
coordinated enamine 13. Catalytic turnover by dissociation or
more probable direct transfer of the Au(I) catalyst to a free
alkyne concurrent with enamine tautomerization would then
follow to provide imine 5a.
As for the protodeauration step it is too early to
diagnostically confirm how this process occurs; however, one
viable possibility is the involvement of phthalimide 7 (a
seeming byproduct) as mediators of [1,3]-proton transfer via
TS2 which was computed to have a gas-phase free energy of
activation (ΔG‡) of 36.8 kcal/mol, Scheme 4. The role of 7 in
this catalytic cycle is notable, as it presents an added
mechanistic subtlety given its function as a proton shuttle for
protodeauration, which in many Au(I)-catalyzed reactions is a
rate-determining step.24
4. General Procedure for the Gold-Catalyzed Hydroamina-
tion of Alkynes with Anilines. In an RBF, gold precatalyst 6 (3.5
−
mg, 0.005 mmol) and 1+−H+·2BF4 (1) (6.0 mg, 0.011 mmol) were
added. To this mixture were added phenylacetylene (735.3 mg, 7.2
mmol) and 2,5-dichloroaniline (972.12 mg, 6 mmol), and the resulting
mixture was stirred at 50 °C for 4 h. After the reaction mixture cooled
to room temperature, flash chromatography (hexanes to ethyl acetate
= 20:1) provided 5c as a colorless oil (1.4 g, 93% yield).
N-(1-Phenylethylidene)aniline (5a).16 Yellow oil. 1H NMR
(CDCl3, 300 MHz) δ = 8.00−8.03 (m, 2H), 7.50−7.45 (m, 3H),
7.38 (t, J = 8.00 Hz, 2H), 7.10 (t, J = 8.00 Hz, 1H), 6.83 (dd, J = 8.66,
1.40 Hz, 2H), 2.26 (s, 3H).
4-Bromo-N-(1-phenylethylidene)aniline (5b).16 Light yellow oil.
1H NMR (CDCl3, 300 MHz) δ = 7.94−8.00 (m, 2H), 7.45−7.47 (m,
5H), 6.69 (d, J = 8.52 Hz, 2H), 2.24 (s, 3H).
2,5-Dichloro-N-(1-phenylethylidene)aniline (5c).16 Light yellow
1
oil. H NMR (CDCl3, 300 MHz) δ = 8.02 (dd, J = 7.5, 1.5 Hz, 2H),
To recap, a solid, bench-stable, gold precatalyst prepared by a
two-step synthesis was disclosed which as revealed from X-ray
structural data and DFT calculations contains a cyclo-
propenium counterion that stabilizes the complex through H-
bonding and other noncovalent interactions. Experimentally,
this precatalyst was shown to be an in situ source of a
conjectural Au(I)-catalyst that was applied to alkyne hydro-
amination. Lastly, a proposed catalytic cycle and DFT
calculations were provided which revealed a [1,3]-proton
transfer event mediated by a phthalimide originating from the
precatalyst was involved in catalyst turnover.
7.47−7.54 (m, 3H), 7.37 (s, 1H), 7.35 (d, J = 8.4 Hz, 1H), 7.03 (dd, J
= 8.40, 2.70 Hz, 1H), 6.87 (d, J = 2.34 Hz, 1H), 2.25 (s, 3H).
4-Fluoro-N-(1-phenylethylidene)aniline (5d).16 Light yellow solid.
Mp 82−86 °C; 1H NMR (CDCl3, 300 MHz) δ = 7.97−8.00 (m, 2H),
7.37 (t, J = 7.14, 2H), 7.11−7.17 (t, J = 9.81 Hz, 3H), 6.77 (dd, J =
8.59, 4.91 Hz, 2H), 2.26 (s, 3H).
4-Ethyl-N-(1-phenylethylidene)aniline (5e).16 Yellow oil. 1H NMR
(CDCl3, 300 MHz) δ = 7.99−8.01 (m, 2H), 7.47 (dd, J = 7.45, 2.01
Hz, 3H), 7.20 (d, J = 8.24 Hz, 2H), 6.75 (d, J = 8.2 Hz, 2H), 2.64−
2.71 (m, 2H), 2.27 (s, 3H), 1.26−1.31 (m, 3H).
4-Butyl-N-(1-phenylethylidene)aniline (5f).16 Light yellow oil. H
1
NMR (CDCl3, 300 MHz) δ = 7.99−8.02 (m, 2H), 7.47 (dd, J = 5.23,
2.09 Hz, 3H), 7.18 (d, J = 8.37 Hz, 3H), 6.75 (d, J = 8.02 Hz, 2H),
2.63 (t, J = 7.68 Hz, 2H), 2.28 (s, 3H), 1.59−1.69 (m, 2H), 1.34−1.46
(m, 2H), 0.96 (t, J = 7.68 Hz, 3H).
EXPERIMENTAL SECTION
■
1. General Information. Materials were obtained from
commercial suppliers and were used without further purification. All
reactions were performed under an inert atmosphere. Reactions were
monitored by thin layer chromatography (TLC) using TLC silica gel
60 F254. Flash column chromatography was performed over Silicycle
ultrapure silica gel (230−400 mesh). NMR spectra were obtained with
2-Ethyl-N-(1-phenylethylidene)aniline (5g).16 Light yellow oil. H
1
NMR (CDCl3, 300 MHz) δ = 8.04−8.07 m, 1.96, 2H), 7.51 (dd, J =
5.46, 2.18 Hz, 3H), 7.19−7.29 (m, 2H), 7.11 (td, J = 7.42, 1.31 Hz,
1H), 6.68 (dd, J = 7.64, 1.09 Hz, 1H), 2.53 (dd, J = 14.84, 7.86 Hz,
2H), 2.24 (s, 3H), 1.18 (t, 8.08, 3H).
D
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The Journal of Organic Chemistry
Note
2,4,6-Trimethyl-N-(1-phenylethylidene)aniline (5h).16 Yellow oil.
1H NMR (CDCl3, 300 MHz) δ = 8.09 (d, J = 3.39, 2H), 7.53 (dd, J =
5.28, 2.02 Hz, 3H), 6.93 (s, 2H), 2.34 (s, 3H), 2.12 (s, 3H), 2.05 (s,
6H).
(12) Wang, D.; Cai, R.; Sharma, S.; Jirak, J.; Thummanapelli, S. K.;
Akhmedov, N. G.; Zhang, H.; Liu, X.; Petersen, J. L.; Shi, X. J. Am.
Chem. Soc. 2012, 134, 9012.
(13) (a) Gaillard, S.; Bosson, J.; Ramon, R. S.; Nun, P.; Slawin, A. M.
Z.; Nolan, S. P. Chem. - Eur. J. 2010, 16, 13729. (b) Gomez-Suarez, A.;
Oonishi, Y.; Meiries, S.; Nolan, S. P. Organometallics 2013, 32, 1106.
(14) Han, J.; Shimizu, N.; Lu, Z.; Amii, H.; Hammond, G. B.; Xu, B.
Org. Lett. 2014, 16, 3500.
(15) (a) Schmidbaur, H.; Schier, A. Z. Z. Naturforsch., B: J. Chem. Sci.
2011, 66, 329. (b) Duan, H.; Sengupta, S.; Petersen, J. L.; Akhmedov,
N. G.; Shi, X. J. Am. Chem. Soc. 2009, 131, 12100. (c) Mizushima, E.;
Hayashi, T.; Tanaka, M. Org. Lett. 2003, 5, 3349.
(16) Mirabdolbaghi, R.; Dudding, T. Org. Lett. 2015, 17, 1930.
(17) Bidal, Y. D.; Lesieur, M.; Melaimi, M.; Cordes, D. B.; Slawin, A.
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42, 33.
2,6-Diisopropyl-N-(1-phenylethylidene)aniline (5i).25 Yellow solid.
Mp 73−77 °C. 1H NMR (CDCl3, 300 MHz) δ = 8.14−8.18 (m, 2H),
7.58−7.59 (m, 3H), 7.37−7.44 (m, 1H), 7.28 (d, J = 1.7 Hz, 1H), 7.22
(s, 1H), 2.88 (hept, J = 6.85 Hz, 2H), 2.21 (s, 3H), 1.25−1.29 (m,
12H). 13C NMR (CDCl3, 75.5 MHz) δ = 164.8, 146.9, 139.2, 136.1,
132.2, 128.5, 127.2, 123.4, 123.0, 28.3, 23.3, 23.0, 18.1.
N-(1-(4-Methoxyphenyl)ethylidene)aniline (5j).16 Light yellow oil.
1H NMR (CDCl3, 300 MHz) δ = 7.97 (d, J = 9.05, 2H), 7.32−7.38
(m, 2H), 7.06−7.14 (m, 1H), 6.96−7.00 (m, 2H), 6.81 (dd, J =
8.48,1.25 Hz, 2H), 3.89 (s, 3H), 2.23 (s, 3H).
N-(1-(p-Tolyl)ethylidene)aniline (5k).16 Light yellow oil. H NMR
1
(CDCl3, 300 MHz) δ = 7.93 (d, J = 7.72, 2H), 7.39 (t, J = 6.61, 2H),
7.29 (d, J = 7.72, 2H), 7.12 (t, J = 7.40 Hz, 1H), 6.84 (d, J = 7.44, Hz,
2H), 2.43 (s, 3H), 2.23 (s, 3H).
(19) Computed at the B3LYP-D3/LACVP++**//B3LYP/Lan2DZ
level. Using Jaguar at B3LYP-D3/LACVP++** to obtain a single
point, whereas Gaussian 09 was used for the B3LYP/Lan2DZ level of
theory.
(20) Ferraris, D.; Young, B.; Cox, C.; Dudding, T.; Drury, W. J.;
Ryzhkov, L.; Taggi, A. E.; Lectka, T. J. Am. Chem. Soc. 2002, 124, 67.
N-(1-(4-Fluorophenyl)ethylidene)aniline (5l).16 Light yellow oil.
1H NMR (CDCl3, 300 MHz) δ = 7.96−8.00 (m, 2H), 7.32−7.38 (m,
2H), 7.09−7.15 (m, 3H), 6.78 (dd, J = 8.79, 1.42), 2.21 (s, 3H).
ASSOCIATED CONTENT
■
(21) (a) Muller, K.; Faeh, C.; Diederich, F. Science 2007, 317, 1881.
̈
S
* Supporting Information
(b) Scerba, M. T.; Leavitt, C. M.; Diener, M. E.; DeBlase, A. F.;
Guasco, T. L.; Siegler, M. A.; Bair, N.; Johnson, M. A.; Lectka, T. J.
Org. Chem. 2011, 76, 7975.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.6b00241.
(22) Carreras, J.; Gopakumar, G.; Gu, L.; Gimeno, A.; Linowski, P.;
Crystallographic data of 6 (CIF)
Spectroscopic data for all compounds, computational
details for 6, 10, and 11 (PDF)
Petusk
18815.
̌
ova, J.; Thiel, W.; Alcarazo, M. J. Am. Chem. Soc. 2013, 135,
(23) Zhdanko, A.; Maier, M. E. Angew. Chem., Int. Ed. 2014, 53, 7760.
(24) Shu, X.-Z.; Nguyen, S. C.; Oba, Y.; He, F.; Zhang, Q.; Canlas,
C.; Somorjai, G. A.; Alivisatos, A. P.; Toste, D. J. Am. Chem. Soc. 2015,
137, 7083.
(25) Chen, D.; Wang, Y.; Klankermayer, J. Angew. Chem., Int. Ed.
2010, 49, 9475.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: tdudding@brocku.ca.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the Natural Sciences and Engineering
Research Council of Canada (NSERC) for funding of this
research.
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DOI: 10.1021/acs.joc.6b00241
J. Org. Chem. XXXX, XXX, XXX−XXX