Hoveyda-grubbs-type precatalysts with unsymmetrical N-Heterocyclic carbenes as effective catalysts in olefin metathesis

Article abstract of DOI:10.1021/acs.organomet.7b00211

In our search for more-selective olefin metathesis catalysts, a series of Hoveyda-Grubbs-type second-generation complexes bearing unsymmetrical N-heterocyclic carbene (NHC) ligands were synthesized and tested in model reactions. It was found that the N-benzyl substituent in NHC has a positive influence on the selectivity of the newly obtained catalysts in the self-metathesis reaction of α-olefins. As expected, a typical relationship between activity and selectivity with respect to the N-aryl substituent used was observed. Dipp-containing complexes exhibited higher stability at elevated temperature, while Mes-bearing complexes typically gave better yields than their Dipp analogues.

Full text of DOI:10.1021/acs.organomet.7b00211

Article
pubs.acs.org/Organometallics
Hoveyda−Grubbs-Type Precatalysts with Unsymmetrical
N‑Heterocyclic Carbenes as Effective Catalysts in Olefin Metathesis
Paweł Małecki, Katarzyna Gajda, Osman Ablialimov, Maura Malinska, Roman Gajda,
́
Krzysztof Wozniak, Anna Kajetanowicz,* and Karol Grela*
́
̇
Faculty of Chemistry, Biological and Chemical Research Centre,, University of Warsaw, Zwirki i Wigury Street 101, 02-089 Warsaw,
Poland
S
* Supporting Information
ABSTRACT: In our search for more-selective olefin metathesis
catalysts, a series of Hoveyda−Grubbs-type second-generation
complexes bearing unsymmetrical N-heterocyclic carbene (NHC)
ligands were synthesized and tested in model reactions. It was found
that the N-benzyl substituent in NHC has a positive influence on the
selectivity of the newly obtained catalysts in the self-metathesis
reaction of α-olefins. As expected, a typical relationship between
activity and selectivity with respect to the N-aryl substituent used was
observed. Dipp-containing complexes exhibited higher stability at
elevated temperature, while Mes-bearing complexes typically gave
better yields than their Dipp analogues.
In this context, we11 and others12 have relied on the creation
of new olefin metathesis ruthenium catalysts bearing uNHCs
INTRODUCTION
■
N-Heterocyclic carbenes (NHCs) are of great interest in the
chemical community, both in academia and in industry,1 due to
(Figure 1). Complexes of this type, due to the presence in the
proximity of the metal center of substituents of different sizes,
their interesting chemical properties as well as reactivity.
Furthermore, their steric and electronic properties can be easily
modified by the introduction of various substituents in the N or
might stabilize the key intermediates to affect the selectivity of
the reactions.13 Such ruthenium complexes were successfully
utilized in cross-metathesis (CM) reactions to give products
N′ position of imidazoliums and imidazoliniums as well as by
introduction of substituents on the NHC backbone.2 Recently,
interest in the utilization of NHCs as organocatalysts has
grown,3 with applications including condensation reactions,
transesterification, 1,2-addition, or ring-opening reactions;
however, the main focus is directed toward their use as ligands
in transition metal complexes. In the latter case, complexes
bearing unsymmetrical N-heterocyclic carbenes (uNHCs) are
of key importance.4
In recent years, olefin metathesis has been one of the most
extensively studied transformations utilized in the formation of
carbon−carbon double bonds.5 The rapid growth of its
significance is closely related to the introduction into laboratory
practices of second-generation complexes, in which phosphine
ligands have been replaced by NHCs. These types of
compounds exhibit enhanced stability toward oxygen and
moisture, greater functional groups’ tolerance, and often also a
higher reactivity than their first-generation counterparts. The
enormous variety of olefin metathesis catalysts has allowed,
inter alia, (a) introduction of metathesis reactions into
industrial practice,6 (b) control of E/Z selectivity,7 (c)
conversion of biomass into more valuable products,8 and (d)
Figure 1. Selected complexes with unsymmetrical N-heterocyclic
carbenes (uNHCs) and cyclic (alkyl)(amino)carbenes (CAACs).
purification of the products through the utilization of
immobilized complexes9 or those with enlarged mass.10 Despite
these great accomplishments, achieving high selectivity in
certain metathesis reactions remains a challenge.
Received: March 20, 2017
© XXXX American Chemical Society
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a
Scheme 1. Synthetic Pathway to the Synthesis of Unsymmetrical NHC Ligands with Mesityl Ligand
a
Reagents and conditions: (a) N-(2,4,6-trimethylphenyl)-1,2-diaminoethane, HCOOH(cat.) (for 1b and 1c) or PTSA(cat.) (for 1a), MeOH, room
temperature, 24 h; (b) NaBH4, MeOH, −10 °C to room temperature, 2 h; (c) (EtO)3CH, HCl, 90 °C for 12 h then 105 °C for 2 h.
a
Scheme 2. Synthesis of Unsymmetrical Hoveyda−Grubbs-Type Complexes Ru-1−Ru-3
a
Reagents and conditions: (a) potassium tert-amylate, toluene, room temperature, 0.5 h, then Hov I, 65 °C; (b) o-isopropoxystyrene, CuCl, toluene,
65 °C.
a
Scheme 3. Synthesis of Unsymmetrical Hoveyda Complexes Ru-4−Ru-8
a
Reagents and conditions: (a) N-(2,6-diisopropylphenyl)-1,2-diaminoethene, MgSO4, MeOH, room temperature, then NaBH4, MeOH, −10 °C to
room temperature; (b) (EtO)3CH, HCl, 90 °C for 12 h then 105 °C for 2 h; (c) potassium tert-amylate, toluene, room temperature, then Hov I, 65
°C, 0.5 h.
enriched in Z-stereoisomers7 as well as in diastereoselective
ring-rearrangement metathesis (dRRM) to provide predom-
inantly a single diastereoisomer.11 Furthermore, complexes
bearing either uNHC12f or cyclic (alkyl)(amino)carbenes
(CAACs)14 were found to be very stable in the presence of
ethylene and hence produced better results in ethenolysis
reactions. Chiral catalysts containing uNHC ligands allow for
conducting asymmetric ring-opening cross-metathesis (AR-
OCM)12b,c,e as well as asymmetric ring-closing metathesis
(ARCM)12e with moderate to excellent enantioselectivity.
Herein we report on the synthesis and evaluation of the
catalytic performance of seven new Hoveyda−Grubbs-type
metathesis (pre)catalysts bearing N-aryl,N′-benzyl-substituted
uNHCs.
diamines (2a−c), followed by cyclization with triethyl
orthoformate to the corresponding NHC precursors (3a−c,
Scheme 1). The first approach to the synthesis of the
Hoveyda−Grubbs-type complexes was based on the direct
reaction between in situ generated NHC carbenes and Hov I.
Unfortunately, in all cases, the yield of the desired complexes
was low, reaching only about 30% (Scheme 2). Therefore,
previously obtained indenylidene-type complexes11a,15 were
subjected to the reaction with o-isopropoxystyrene, providing
Ru-1, Ru-2, and Ru-3 with good yields of 72, 62, and 74%,
respectively.
The synthesis of complexes Ru-4−Ru-7 was easily
accomplished in three steps, as shown in Scheme 3. The
Hoveyda−Grubbs-type second-generation complexes were
obtained in good yields via a standard procedure in which a
phosphine ligand was exchanged for the corresponding NHC in
Hov I catalysts. When a procedure involving transformation of
indenylidene-type complexes, Ind-1−Ind-3, was applied,
compounds with two NHC ligands were obtained. These
species are a subject of ongoing study.
RESULTS AND DISCUSSION
■
Synthesis of Precatalysts. The synthesis of the Mes-
bearing imidazolium ligand precursors was achieved by
condensation of N-(2,4,6-trimethylphenyl)-1,2-diaminoethane
with aldehydes in the presence of a catalytic amount of formic
acid (for 1b and 1c)15 or p-toluenesulfonic acid (for 1a).11a
The resulting diimines were reduced in situ to corresponding
X-ray Crystallographic Studies. Single crystals of Ru-1,
Ru-2, Ru-3, and Ru-4 catalysts, suitable for X-ray measure-
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ments, were obtained from a mixture of dichloromethane
(DCM)/heptane. To describe differences in conformation
between the investigated compounds, we defined a specific
torsion angle (T1), Cα−Cβ−Cγ−Nδ (see Figure 2). This
angle describes the position of benzyl substituents with respect
to the imidazolinium ring.
Figure 3. Degradation of precatalysts Ru-1−Ru-7 in toluene-d8
1
solution at 50 °C under argon monitored by H NMR spectroscopy.
Catalyst decomposition was determined based on the signal ratio
between ruthenium compounds and internal standard, 1,3,5-
trimethoxybenzene. Lines are visual aid only.
Scheme 4. RCM Reaction of Diethyl Diallylmalonate (6)
Figure 2. Structural overlay of molecules: Ru-1 (gray), Ru-2 (yellow),
Ru-3 (purple), and Ru-4 (green). Hydrogen atoms have been omitted
for clarity.
ylidene) ligand. The structures of all tested complexes are
presented in Figure 4.
Depending on the size and position of the modified benzyl
moieties, access to the metallic center is open or blocked. The
difference between the most blocked substituent (Ru-3, T1 =
−152.7(2)°) and the most accessible one (Ru-1, T1 =
−118.4(2)°) is 34.3(2)°.
Thermal Stability Studies. Prior to the test of the activity
of newly obtained complexes containing N-aryl,N′-benzyl-
substituted NHC ligands, the thermal stability of these catalysts
was examined. For this purpose, each of the ruthenium
compounds was dissolved in deuterated toluene under an argon
atmosphere and heated for 1 month at 50 °C. Degradation of
the reference catalysts, with respect to 1,3,5-trimethoxybenzene
1
utilized as an internal standard, was monitored by H NMR
Figure 4. Complexes used in this study.
spectroscopy.
All new catalysts, as well as the Hov II, exhibited high
stability under applied conditions (Figure 3), as illustrated by
the fact that even the least lasting of them decomposed by only
30% during 1 month (for clarification, the scale covers the
range 70−100%). As expected, complexes bearing a mesityl
moiety were less stable than their 2,6-diisopropylphenyl
analogues. The influence of substituents in the ortho position
of benzyl moiety varied, depending on the aryl substituent in
the imidazolinium ring. When comparing the effects of
substituents on the stability of metal complexes for Ru-1−
Ru-3, one can conclude that the more electron-donating the
substituent is, the more stable the complex is. In the case of the
DIPP series (Ru-4−Ru-7) this trend was not so obvious, since
all complexes exhibited similar stability.
Catalytic Performance Tests: Preliminary Studies. In
order to evaluate the influence of structural modifications on
the activity of the newly synthesized complexes containing
functionalized benzyl substituents on NHCs, the RCM reaction
of a model substrate, diethyl diallylmalonate (6), was
performed (Scheme 4). The results were compared with
those of the benchmark Hov II complex with the standard
SIMes (1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-
Model metathesis reaction of 6 was performed in toluene at
50 °C with 0.1 M concentration of substrate in the presence of
1 mol% of the catalyst (Scheme 4).
In this transformation, all N-Mes-bearing precatalysts
exhibited higher activity than their DIPP analogues (Figure
5). On the other hand, even the best complexes of this series,
namely Ru-2 and Ru-3, were slightly worse than their
commercially available counterpart, Hov II; however, after 10
min they also achieved full conversion. Within each series (for
complexes possessing either NMes- or NDIPP-substituted
imidazolines), ruthenium complexes containing methoxy
(OMe, Ru-2 and Ru-5) and dimethylamino groups (NMe2,
Ru-3 and Ru-6) at the ortho position of the N′-benzyl
substituent gave the best results. This might indicate the impact
of the electronic properties of these electron-donating groups
on the catalytic activity of new complexes, since, in all cases,
their benzyl analogues gave worse results. On the other hand,
the Ru-7, possessing an electron-withdrawing substituent, CF3,
gave a result very similar to that obtained with Ru-6, which may
indicate that steric factors are also pivotal in this case.
In the next step, a more demanding substrate, N-allyl-4-
methyl-N-(2-methylallyl)-benzenesulfonamide (8), was exam-
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Figure 5. Time/conversion plot for the RCM reaction of diethyl diallylmalonate (6).
ined under the conditions previously applied for substrate 6
(toluene, 50 °C, c[8] = 0.1 M, 1 mol% of [Ru], Scheme 5).
complexes in the reactions with more demanding substrates, we
decided to examine their performance on a wider range of
substrates undergoing various types of metathesis reactions
(RCM, ene-yne, CM) and compare the results with their
commercial analogues Hov II and Hov II SIPr.
Scheme 5. RCM Reaction of N-Allyl-4-methyl-N-(2-
methylallyl)benzenesulfonamide (8)
In all cases, the progress of the reaction was monitored by
thin-layer chromatography (TLC) until complete consumption
of the starting material (or one of the substrates, as in the
reaction of allylbenzene (16)). In the RCM (Table 1, entries 1
and 2) and ene-yne reactions (Table 1, entry 3), a general trend
was observed according to which the complexes in which
mesityl was the N-aryl substituent in NHC ligand (Hov II and
Ru-1−Ru-3) reached full conversion faster as well as in higher
yields than their analogues with a more sterically hindered
aromatic “arm” (Hov II SIPr and Ru-4−Ru-7). Moreover, both
symmetrical catalysts were found to be the most active
complexes in their groups; however, prolonging the reaction
time allowed full conversion and high yields also with
unsymmetrical Hoveyda-type compounds. The above observa-
tion is also true for the CM reaction between allylbenzene (16)
and cis-1,4-diacetoxy-but-2-ene (17) (Table 1, entry 4); all
complexes allowed the full conversion of the substrate 16 as
well as high yield of product 18. Furthermore, the E/Z
selectivity of the reaction in the majority of cases was close to
7:1, the only clear deviation from the rule being the reaction
catalyzed by Ru-4 (here E/Z = 3.6:1).
The results obtained for the more crowded substrate 8
exhibited the same trend that was previously observed for
diethyl diallylmalonate (6) (Figure 6). Here again, the
Hoveyda−Grubbs second-generation catalyst gave the best
result; however, complexes Ru-1−Ru-3 containing N-benzyl,
N′-mesityl-substituted NHC ligands were only slightly worse
than the benchmark Hov II, but again better than their
diisopropylphenyl analogues Ru-4−Ru-7. Within the series,
results were also consistent with those obtained previously,
which means that the activity of the complexes increased in that
order of substituents: OMe > NMe2 > H. The only exception
was Ru-7, which was less effective upon reaction of compound
8 with more crowded double bond.
Scope and Limitation Study of uNHC-Bearing Com-
plexes in Metathesis Reactions. Prior to testing the new
Figure 6. Time/conversion plot for the RCM reaction of N-allyl-4-methyl-N-(2-methylallyl)benzenesulfonamide (8).
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a
Table 1. Preparative Metathesis Reactions with Different Ru Complexes
a
b
1
Reaction conditions: c = 0.01 M, toluene (dry, degassed), 50 °C, under argon. Determined by H NMR
Diastereoselective Ring-Rearrangement Metathesis
(dRRM). Owing to Blechert’s previous studies on dRRM of
cyclopentene 19 (Scheme 6), it is known that Grubbs and
Scheme 6. Diastereoselective Ring Rearrangement
Metathesis of Cyclopentene 19
Hoveyda−Grubbs second-generation complexes give better
diastereoselectivity than the corresponding first-generation
complexes (ratios 2:1 and 1:1, respectively), with an almost
quantitative conversion of the substrate.16 Even better
diastereoselectivity (9:1) was obtained with a tetrahydro-
quinoline-based Grubbs-type precatalyst, but at the expense
of conversion.17 Recently we have shown that also complexes
bearing uNHCs as ligands can improve the selectivity toward
the trans diastereoisomer (up to 4.7:1). As the newly obtained
complexes (structures presented in Figure 7) belong to the
same class of compounds as catalysts previously tested by us,11
also in their cases high selectivity toward the trans diastereo-
Figure 7. Complexes previously used in dRRM of cyclopentene 19.
isomer was expected. In this context, their performance in
dRRM of 19 was determined and compared with previous
results, as well as these obtained with commercial Hov II SIPr
(Table 2). As expected, when new complexes with uNHCs in
which a mesityl was the N-aryl substituent (Ru-1−Ru-3) were
utilized, a high selectivity was observed, up to 5:1 for Ru-1 and
4.9:1 for Ru-3. On the other hand, the results obtained for
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high selectivity is observed; however, high catalyst loading is
required to achieve satisfactory yields.22
Table 2. Results of dRRM of Cyclopentene 19 with Different
Ru Complexes
a
The most commonly used solution to decrease the level of
isomerization is addition of quinones23 or metallic mercury to
the reaction mixture.21 Another possible approach is the
utilization of recently developed specialized catalysts bearing
uNHCs which do not result in isomerization of the double
bond.12h,i In the latter case, indenylidene precatalysts bearing
uNHC ligands with an N-cycloalkyl moiety (see Figure 1)
provided the desired product with remarkable 99% selectivity
when used at low loading (50 ppm). What’s more, this excellent
olefin distribution with no isomerization was observed even in
the absence of benzoquinone additives and after 24 h of
reaction. In this context, we tested our new complexes bearing a
substituted benzyl moiety in self-metathesis reaction of 1-
octene (22) and compared them with their symmetrical
analogues Hov II and Hov II SIPr (Scheme 7, Figure 9).
In the examined reaction, the symmetrical Hoveyda−
Grubbs-type complexes were found to be the fastest ones,
reaching full conversion after about 5 min. On the other hand,
they exhibited the worst selectivity. When Hov II was utilized
in the reaction, the desired product, tetradec-7-ene (23),
represented only 25% of the reaction mixture, while the rest
was accounted for by its shorter and longer homologues. An
even worse result was obtained in the presence of Hov II SIPr,
when the reaction mixture consisted of side products with an
85% yield. Reactions went in a much cleaner way when
unsymmetrical complexes were applied, and at the same time
reaction rates were only slightly slower, the full conversion
being reached after 30 min for DIPP-containing NHCs and
after 90 min for their Mes analogues. In the initial stage of the
reaction, mainly the desired product 23 was observed in an
amount of about 80% for each of the tested catalysts, and the
byproducts appeared more slowly. This process was the slowest
for Ru-2, for which it was possible to obtain a selectivity of
about 80% after 2 h of reaction. Based on the advantages
exhibited by the new complexes, in a preparative setup, after the
self-CM metathesis reaction reaches its maximum, a commer-
cial isocyanide scavenger, SnatchCat,24 or a similar fast-acting
quenching agent, can be used to cease any further Ru-catalyzed
metathesis and isomerization events, allowing product 23 to be
obtained in high purity. To confirm the practical applicability of
these catalysts, the self-metathesis reaction of 35 mmol (5.59
mL) of 1-octene (22) was carried out in the presence of 500
ppm of Ru-4. After 10 min, SnatchCat solution (5 equiv) was
added and the reaction flask content was distilled to provide
65% of analytically pure tetradec-7-ene (23) as a mixture of E/
Z isomers (81:19). Isomerization products were not observed.
b
c
entry
Ru complex
conversion [%]
trans:cis dr
1
Hov II
Ru-1
95
94
2:1
5:1
2
3
Ru-2
96
4.1:1
4.9:1
1:1
4
Ru-3
98
5
Hov II SIPr
Ru-4
99
6
98
1.4:1
1.3:1
1.3:1
1.6:1
1:1
7
Ru-5
89
8
Ru-6
98
9
Ru-7
99
10
11
12
13
14
15
16
17
18
19
Gr II17
95
d
Ind II15
>95
>95
>95
>95
95
2:1
Ind-111a
3.8:1
4.7:1
4.5:1
3.6:1
3:1
d
Ind-215
d
Ind-315
d
Ind-411b
d
Ind-511b
62
d
Ind-611b
57
3.4:1
3.1:1
9:1
d
Ind-711b
56
d
d
Ble17
58
a
Reaction conditions: c[19] = 0.02 M, 5 mol% of precatalyst, CDCl3
b
saturated with ethylene, 22 °C, 10 h. Determined by 1H NMR.
c
d
Determined by GC using durene as an internal standard. Structures
of complexes are presented in Figure 7.
complexes with SIPr-substituted imidazoline were clearly
disappointing. Parent Hov II SIPr gave the same result as
Grubbs and Hoveyda−Grubbs first-generation complexes, and
its unsymmetrical analogues were only slightly better. Still, the
most selective Ru complex remained the tetrahydroquinoline-
based Grubbs-type precatalyst (trans:cis dr = 9:1), although at
the expense of conversion (58%).
Self-Metathesis of Linear Olefins. Migration of the
double bond during the metathesis reaction is one of the most
common side reactions which can significantly alter the product
distribution and decrease the yield of the desired product. This
undesired side process is attributed to ruthenium hydrides like
A,18 B,19 and C (Figure 8),20 as well as ruthenium
Figure 8. Examples of ruthenium hydrides active in isomerization of
double bonds. Cy = cyclohexyl, Mes = mesityl.
CONCLUSIONS
■
Seven new Hoveyda−Grubbs-type ruthenium complexes
bearing unsymmetrical N-heterocyclic carbenes were synthe-
sized and fully characterized. Their activity was compared with
that of commercially available symmetrical analogues Hov II
and Hov II SIPr. It was found that unsymmetrical catalysts
used in typical metathesis reactions like RCM of diethyl
diallylmalonate (6), N-allyl-4-methyl-N-(2-methylallyl)-
nanoparticles,21 which can be formed as products of
decomposition of the metathesis catalysts and can act as
isomerization agents. The isomerization of the double bond,
and hence the drop in selectivity of the metathesis reaction, is
observed mainly in the processes catalyzed by the second-
generation complexes. When first-generation catalysts are used,
Scheme 7. Self-Metathesis Reaction of 1-Octene (22) Leading to 7-Tetradecene (23)
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Figure 9. Reaction profiles for self-metathesis reaction of 1-octene (22).
benzenesulfonamide (8), tert-butyl 2-(diallylcarbamoyl)-
pyrrolidine-1-carboxylate (10), and 2-allyl-2-phenylpent-4-ene-
nitrile (12); ene-yne metathesis of (1-(allyloxy)prop-2-yne-1,1-
diyl)dibenzene (14) or allylbenzene (16); and CM of cis-1,4-
diacetoxy-but-2-ene (17) show only a slightly lower activity
than the parents Hov II and Hov II SIPr, which means that
this structural modification has a minimal impact on their
effectiveness as catalysts. As expected, the differences become
more apparent when uNHC-bearing complexes were utilized in
reactions of more demanding substrates. In dRRM reaction of
cyclopentene (19), the new complexes Ru-1, Ru-2, and Ru-3
showed a much higher selectivity than Hov II, but to our great
surprise all SIPr-substituted complexes, including unsym-
metrical ones, gave an equimolar mixture of cis and trans
diastereosomers, which means that they cannot be catalysts of
choice in this transformation. Even greater differences between
catalysts with symmetrical or unsymmetrical NHC ligands were
visible in the self-metathesis reaction of 1-octene (22). For this
transformation, the use of parent Hoveyda−Grubbs complexes
(Hov II or Hov II SIPr) results in the formation of a mixture
of byproducts, composed mainly of shorter and longer
homologues of 23. Importantly, the reaction carried out in
the presence of unsymmetrical Ru compounds resulted in an
almost 80% yield of tetradec-7-ene (23), therefore proving the
better selectivity of the new catalysts in self-CM of α-olefins. It
shall be noted, however, that the Olivier-Bourbigou and
Mauduit’s catalyst, providing selectivities up to 99%, remains
even more advantageous for self-CM of α-olefins.12i
EXPERIMENTAL SECTION
■
General Remarks. All reagents were purchased from Sigma-
Aldrich, Strem, TCI, and Alfa Aesar and used without further
purification. All reactions involving the synthesis of metal complexes
were carried out in oven-dried glassware with magnetic stirring under
an argon atmosphere with anhydrous solvents, using standard Schlenk
techniques. Toluene and diethyl ether were distilled over potassium,
while DMF was distilled over CaH2 under an atmosphere of argon. To
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test the activity of precatalysts, HPLC-grade solvents (Aldrich)
CH2Cl2 and toluene were used as received. Analytical thin-layer
chromatography (TLC) was performed using silica gel 60 F254
precoated plates (0.25 mm thickness) with a fluorescent indicator.
Visualization of TLC plates was performed by UV light with KMnO4.
Flash chromatography was performed using silica gel 60 (230−400
mesh). NMR spectra were recorded on an Agilent 400-MR DD2 400
MHz spectrometer. NMR chemical shifts are reported in ppm and
referred to residual solvent peaks at respectively 7.26 and 77.16 ppm
(dimethylamino)benzaldehyde (1c) (1 g, 6.7 mmol) in MeOH (10
mL), formic acid (2 drops), N-(2,4,6-trimethylphenyl)-1,2-diamino-
ethane (1.19 g, 6.7 mmol), and NaBH4 (1.43 g, 36 mmol) were used.
Purification by silica gel chromatography (c-Hex/EtOAc 3:1, followed
by c-Hex/EtOAc 1:1) yielded 2c as a yellow oil (1.31 g, 63%).15 1H
NMR (500 MHz, CDCl3): δ = 7.28 (dd, JHH = 7.4, 4JHH = 1.7 Hz, 1H,
4
Ar-H), 7.15 (dt, JHH = 7.6, JHH = 1.7 Hz, 1H, Ar-H), 7.06−6.93 (m,
2H, Ar-H), 6.74 (s, 2H, Mes-H), 3.83 (s, 2H, Ar-CH2-N), 2.98−2.95
(m, 2H, N-CH2-CH2), 2.77−2.72 (m, 2H, N-CH2-CH2), 2.62 (s, 6H,
N-Me), 2.19 (s, 6H, Ar-CH3), 2.15 (s, 3H, Ar-CH3) ppm. 13C NMR
(125 MHz, CDCl3): δ = 152.8, 144.0, 134.7, 131.1, 129.7, 129.5,
127.8, 123.4, 119.4, 50.1, 49.7, 48.4, 45.1, 20.7, 18.6 ppm.
for H and 13C in CDCl3, 5.32 and 53.84 ppm for H and 13C in
CD2Cl2, and 2.50 and 39.52 ppm 1H and 13C in DMSO-d6. The
following abbreviations are used in reporting NMR data: s (singlet), d
(doublet), t (triplet), q (quartet), m (multiplet), br (broad). Unless
otherwise stated, all coupling constants (J) are between protons
through three bonds and expressed in Hz. Spectra are reported as
follows: chemical shift (δ, ppm), multiplicity, integration, coupling
constants (Hz). IR spectra were recorded on a PerkinElmer Spectrum
One FTIR spectrometer with a diamond ATR accessory. Wave-
numbers are given in cm−1. GC analyses were performed using a
Clarus 580 chromatograph with durene as an internal standard.
Elemental microanalyses were made using a Vario EL III apparatus.
Melting points were recorded on an OptiMelt SRS apparatus with a
heating rate of 10 °C/min. High-resolution electrospray mass spectra
(ESI-HRMS) were recorded on a Quattro LC triple-quadrupole mass
spectrometer, calibrated with an internal standard solution of sodium
formate or sodium iodide in MeOH.
General Procedure for the Preparation of Diamines. To the
solution of an appropriate aldehyde (1.1 equiv) in methanol was added
MgSO4 (2 equiv) or a catalytic amount of p-toluenesulfonic acid
(PTSA, ca. 5−7 mg) or a catalytic amount of HCOOH and N-aryl-1,2-
diaminoethane (1 equiv). The resulting mixture was stirred for 24 h at
room temperature. Then, to the resulting mixture was added MeOH
(10−30 mL), and the flask was placed in an ice-cooled bath. After that,
NaBH4 (5 equiv) was added portionwise (with 10 min intervals during
30 min) and the mixture was stirred for 2 h at room temperature. The
solvent was evaporated, and the crude mixture was washed with
saturated NaHCO3(aq) solution until the pH became slightly basic.
The product was extracted with EtOAc (3 × 40 mL). Purification of
the crude mixture was accomplished by silica gel chromatography
(cyclohexane/EtOAc). The fractions containing the desired product
were concentrated.
1
1
N1-(2,6-Diisopropylphenyl)-N2-benzyl-1,2-diaminoethane Dihy-
drochloride (4a). Following the general procedure, a solution of
benzaldehyde (1a) (1.59 g, 15 mmol) in MeOH (70 mL), MgSO4
(3.27 g, 27.2 mmol), N-(2,6-diisopropylphenyl)-1,2-diaminoethene (3
g, 13.6 mmol), and NaBH4 (2.57 g, 68 mmol) were used. A precipitate
of N-(2,6-diisopropylphenyl)-1,2-diaminoethene dihydrochloride with
HCl/Et2O instead of column chromatography was used to purified the
product. N1-(2,6-Diisopropylphenyl)-N2-benzyl-1,2-diaminoethane di-
chloride (3.45 g, 11.1 mmol, 82%) was obtained as a white powder,
mp 215−217 °C (dec). 1H NMR (400 MHz, CD3OD): δ = 7.65−7.57
(m, 2H, Ar-H), 7.52−7.44 (m, 4H, Ar-H), 7.43−7.37 (m, 2H, Ar-H),
4.36 (s, 2H, Ar-CH2-N), 3.77−3.60 (m, 4H, N-CH2-CH2), 3.21 (hept,
JHH = 6.8 Hz, 2H, Ar-CH), 1.34 (d, JHH = 6.7 Hz, 12H, CH-CH3)
ppm. 13C NMR (100 MHz, CDCl3): δ = 143.9, 132.0 131.6, 131.3,
130.9, 130.9, 130.4, 127.2, 52.8, 50.0, 44.3, 29.5, 25.1 ppm. IR (film
from CH2Cl2): ν = 2969, 2804, 1582, 1459, 1442, 1340, 984, 814, 800,
742, 699, 683, 578, 521 cm−1. Anal. Calcd for C21H32Cl2N2: C, 65.79;
H, 8.53; N, 7.22; Cl, 18.49. Found: C, 65.80; H, 8.53; N, 7.22; Cl,
18.24.. HRMS (ESI): m/z calcd for C21H30N2: [M+H+] 311.2482,
found 311.2469.
N1-(2,6-Diisopropylphenyl)-N2-(2-methoxybenzyl)-1,2-diamino-
ethane (4b). Following the general procedure, a solution of N-(2,6-
diisopropylphenyl)-1,2-diaminoethene (5 g, 22.7 mmol) in methanol
(100 mL), 2-methoxybenzaldehyde (1a) (3.47 g, 25 mmol),
magnesium sulfate (5.46 g, 45.4 mmol), and sodium borohydride
(4.29 g, 114 mmol) were used. Purification by silica gel
chromatography yielded 4b as a yellow oil (5.8 g, 17.03 mmol,
1
75%). H NMR (400 MHz, CDCl3): δ = 7.36−7.26 (m, 2H, Ar-H),
7.17−7.11 (m, 2H, Ar-H), 7.10−7.05 (m, 1H, Ar-H), 6.98 (td, JHH
=
N1-(2,4,6-Trimethylphenyl)-N2-benzyl-1,2-diaminoethane (2a).
Following the general procedure, a solution of benzaldehyde (1a)
(1.79 g, 12.32 mmol) in MeOH (12 mL), PTSA (ca. 5−7 mg), N-
(2,4,6-trimethylphenyl)-1,2-diaminoethane (2 g, 11.2 mmol), and
NaBH4 (1.70 g, 44.8 mmol) were used. Purification by silica gel
chromatography (cyclohexane/EtOAc 4:1, followed by cyclohexane/
EtOAc, 1:1) yielded 2a as a yellow oil (2.12 g, 71%).11a 1H NMR (400
MHz, CDCl3): δ = 7.38−7.33 (m, 4H, Ar-H), 7.30−7.27 (m, 1H, Ar-
H), 6.83 (s, 2H, Mes-H), 3.86 (s, 2H, Ar-CH2-N), 3.08−3.06 (m, 2H,
N-CH2-CH2), 2.88−2.86 (m, 2H, N-CH2-CH2) 2.29 (s, 6H, Ar-CH3),
2.24 (s, 3H, Ar-CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 143.8,
140.2, 131.2, 129.7, 129.5, 128.6, 128.3, 127.2, 53.9, 49.5, 48.3, 20.7,
18.6 ppm.
7.4, 4JHH = 1.0 Hz, 1H, Ar-H), 6.92 (d, JHH = 7.9 Hz, 1H, Ar-H), 3.90
(s, 2H, Ar-CH2-N), 3.87 (s, 3H, O-CH3), 3.37 (hept, JHH = 6.8 Hz,
2H, Ar-CH), 3.03 (dd, JHH = 6.7, 4.7 Hz, 2H, N-CH2-CH2), 2.90 (dd,
JHH = 6.6, 4.6 Hz, 2H, N-CH2-CH2), 1.27 (d, JHH = 6.9 Hz, 12H, CH-
CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 157.7, 143.7, 142.5,
129.7, 128.6, 128.2, 123.6, 120.5, 110.3, 55.3, 51.3, 49.2, 49.0, 27.6,
24.4 ppm. IR (film from CH2Cl2): ν = 3356, 2959, 2866, 1588, 1491,
1457, 1362, 1239, 1100, 1050, 1030, 934, 750, 575, 530 cm−1. Anal.
Calcd for C22H32N2O: C, 77.60; H, 9.47; N, 8.23. Found: C, 77.54; H,
9.50; N, 8.22. HRMS (ESI): m/z calcd for C22H32N2O: [M+H+]
341.2587, found 341.2600.
N1-(2,6-Diisopropylphenyl)-N2-(2-(dimethylamino)benzyl)-1,2-
diaminoethane (4c). Following the general procedure, a solution of
N-(2,6-diisopropylphenyl)-1,2-diaminoethene (2.43 g, 11 mmol), 2-
(N,N′-dimethylamino)benzaldehyde (1.81 g, 12.1 mmol), magnesium
sulfate (2.65 g, 22 mmol), and sodium borohydride (2.09 g, 55.2
mmol) in methanol was used. Purification by silica gel chromatography
N1-(2,4,6-Trimethylphenyl)-N2-(2-methoxybenzyl)-1,2-diamino-
ethane (2b). Following the general procedure, a solution of 2-
methoxybenzaldehyde (1b) (2 g, 14.4 mmol) in MeOH (10 mL),
formic acid (2 drops), N-(2,4,6-trimethylphenyl)-1,2-diaminoethane
(2.57 g, 14.4 mmol), and NaBH4 (2.87 g, 72 mmol) were used.
Purification by silica gel chromatography (c-Hex/EtOAc 3:1, followed
by cHex/EtOAc 1:1) yielded 2b as a yellow oil (2.65 g, 60%).15 1H
NMR (500 MHz, CDCl3): δ = 7.26−7.22 (m, 2H, Ar-H), 6.91 (dt, JHH
1
yielded 4c as a yellow oil (3.15 g, 8.9 mmol, 81%). H NMR (400
4
MHz, CDCl3): δ = 7.46 (dd, JHH = 7.5, JHH = 1.6 Hz, 1H, Ar-H),
7.31−7.26 (m, 1H, Ar-H), 7.19−7.06 (m, 5H, Ar-H), 3.98 (s, 2H, Ar-
CH2-N), 3.39 (hept, JHH = 6.8 Hz, 2H, Ar-CH), 3.05 (dd, JHH = 6.6,
4.5 Hz, 2H, N-CH2-CH2), 2.93 (dd, JHH = 6.7, 4.4 Hz, 2H, N-CH2-
CH2), 2.75 (s, 6H, N-CH3), 1.28 (d, JHH = 6.9 Hz, 12H, CH-CH3)
ppm. 13C NMR (100 MHz, CDCl3): δ = 152.7, 143.8, 142.4, 134.8,
129.5, 127.7, 123.6, 123.6, 123.3, 119.3, 51.4, 50.0, 49.6, 45.1, 27.7,
24.4 ppm. IR (film from CH2Cl2): ν = 3356, 2959, 2826, 1491, 1448,
1382, 1310, 1255, 1188, 1154, 1112, 1048, 946, 799, 753, 565 cm−1.
Anal. Calcd for C23H35N3: C, 78.14; H, 9.98; N, 11.89. Found: C,
4
= 7.4, JHH = 1.0 Hz, 1H, Ar-H), 6.87−6.85 (m, 1H, Ar-H), 6.80 (s,
2H, Mes-H), 3.83 (s, 2H, Ar-CH2-N), 3.82 (s, 3H, O-CH3), 3.05−3.03
(m, 2H, N-CH2-CH2), 2.8−2.6 (m, 2H, N-CH2-CH2), 2.26 (s, 6H, Ar-
CH3), 2.22 (s, 3H, Ar-CH3) ppm. 13C NMR (125 MHz, CDCl3): δ =
157.8, 143.9, 131.1, 129.9, 129.7, 129.5, 128.4, 120.5, 110.4, 55.4, 49.2,
48.9, 48.3, 20.7, 18.6 ppm.
N1-(2,4,6-Trimethylphenyl)-N2-(2-(dimethylamino)benzyl)-1,2-
diaminoethane (2c). Following the general procedure, a solution of 2-
H
DOI: 10.1021/acs.organomet.7b00211
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
78.03; H, 9.91; N, 11.82. HRMS (ESI): m/z calcd for C23H35N3: [M
+H+] 354.2904, found 354.2910.
°C.15 1H NMR (500 MHz, CDCl3): δ = 9.62 (s, 1H, CH-Imd), 7.52
4
(dd, JHH = 7.4, JHH = 1.7 Hz, 1H, Ar-H), 7.39−7.35 (m, 1H, Ar-H),
N1-(2,6-Diisopropylphenyl)-N2-(2-(trifluoromethyl)benzyl)-1,2-
diaminoethane (4d). Following the general procedure, a solution of
N-(2,6-diisopropylphenyl)-1,2-diaminoethene (2 g, 9.08 mmol) in
methanol (80 mL), 2-(trifluoromethyl)benzaldehyde (1d) (1.77 g,
9.98 mmol), magnesium sulfate (2.19 g, 18.16 mmol), and sodium
borohydride (1.72 g, 45.4 mmol) were used. Purification by silica gel
chromatography yielded 4d as a yellow oil (2.57 g, 6.79 mmol, 75%).
1H NMR (400 MHz, CDCl3): δ = 7.74 (d, JHH = 7.8 Hz, 1H, Ar-H),
6.97 (dt, JHH = 7.5, JHH = 1.1 Hz, 1H, Ar-H), 6.93 (d, JHH = 8.4 Hz,
4
1H, Ar-H), 6.9 (s, 2H, Mes-H), 5.10 (s, 2H, Ar-CH2-N), 4.1 (s, 4H, N-
CH2-CH2), 3.86 (s, 3H, O-CH3), 2.27 (s, 9H, Ar-CH3) ppm. 13C
NMR (125 MHz, CDCl3): δ = 159.5, 158.0, 140.1, 135.3, 131.8, 131.0,
130.8, 129.9, 121.3, 120.9, 110.8, 55.6, 51.1, 48.3, 48.0, 21.0, 17.9 ppm.
N1-(2,4,6-Trimethylphenyl)-N2-(2-(dimethylamino)benzyl)-4,5-di-
hydro-1H-imidazol-3-ium Chloride (3c). Following the general
procedure, from N1-(2,4,6-trimethylphenyl)-N2-(2-dimethylamino)-
benzyl)-1,2-diaminoethane (2c) (1.2 g, 3.85 mmol), triethyl
orthoformate (6.8 mL), and HCl (4 M solution, 2 mL), 3c was
obtained as white crystals (1.1 g, 80%), mp 174−177 °C.15 1H NMR
(500 MHz, CDCl3): δ = 9.96 (s, 1H, CH-Imd), 7.40−7.35 (bs, 1H,
Ar-H), 7.28 (t, JHH = 7.3 Hz, 1H, Ar-H), 7.14−6.99 (bs, 2H, Ar-H),
6.83 (s, 2H, Mes-H), 5.30 (s, 2H, Ar-CH2-N), 4.08−3.81 (m, 4H, N-
CH2-CH2), 2.61 (s, 6H, N-CH3), 2.22 (s, 6H, Ar-CH3), 2.20 (s, 3H,
Ar-CH3) ppm. 13C NMR (125 MHz, CDCl3): δ = 159.7, 153.6, 140.2,
135.2, 130.9, 130.8, 130.1, 130.0, 127.3, 124.5, 120.2, 50.9, 48.6, 48.0,
45.5, 21.0, 18.0 ppm.
7.69 (d, JHH = 8.5 Hz, 1H, Ar-H), 7.58 (t, JHH = 7.8 Hz, 1H, Ar-H),
7.39 (t, JHH = 7.6 Hz, 1H, Ar-H), 7.15−7.11 (m, 2H, Ar-H), 7.10−7.05
(m, 1H, Ar-H), 4.07 (s, 2H, Ar-CH2-N), 3.36 (hept, JHH = 6.8 Hz, 2H,
Ar-CH), 3.04 (dd, JHH = 6.6, 4.0 Hz, 2H, N-CH2-CH2), 2.97 (dd, JHH
= 6.6, 4.0 Hz, 2H, N-CH2-CH2), 1.26 (d, JHH = 6.9 Hz, 12H, CH-
CH3) ppm. 13C NMR (100 MHz, CDCl3) δ = 143.6, 142.5, 139.2 (q,
4
2
4JCF = 1.5 Hz), 132.0 (q, JCF = 1.1 Hz), 130.1, 128.3 (q, JCF = 30.1
Hz), 127.0, 126.0 (q, 3JCF = 5.8 Hz), 124.7 (q, 1JCF = 274.0 Hz), 123.7,
123.6, 51.3, 49.8 (q, JCF = 2.2 Hz), 49.6, 27.7, 24.3 ppm. 19F NMR
4
(376 MHz, CDCl3) δ = −59.64. IR (film from CH2Cl2): ν = 3365,
2961, 2869, 1445, 1311, 1256, 1159, 1115, 1059, 1036, 799, 755, 654
cm−1. Anal. Calcd for C22H29N2F3: C, 69.82; H, 7.72; N, 7.40; F,
15.06. Found: C, 69.81; H, 7.74; N, 7.38; F, 15.13. HRMS (ESI): m/z
calcd for C22H29N2F3: [M+H+] 379.2356, found 379.2368.
General Procedure for the Preparation of Dihydroimid-
azolium Salts with Diisopropylphenyl Substituent. A mixture of
diamine (1 equiv), triethyl orthoformate (10 equiv), and ammonium
chloride (2 equiv) was heated at 120 °C for 4 h under an argon
atmosphere. The reaction mixture was cooled to room temperature,
and precipitate was filtered off, washed with Et2O, and dried in a high
vacuum.
N1-(2,6-Diisopropylphenyl)-N2-(2-nitrobenzyl)-1,2-diamino-
ethane (4e). Following the general procedure, a solution of N-(2,6-
diisopropylphenyl)-1,2-diaminoethene (2.3 g, 11.5 mmol) in methanol
(75 mL), 2-nitrobenzaldehyde (1.74 g, 11.5 mmol), magnesium sulfate
(2.4 g, 23 mmol), and sodium borohydride (1.97 g, 52.2 mmol) were
used. Purification by silica gel chromatography yielded 4d as a yellow
N1-(2,6-Diisopropylphenyl)-N2-benzyl-4,5-dihydro-1H-imid-
azolinium Chloride (5a). Following the general procedure, from N1-
(2,6-diisopropylphenyl)-N2-benzyl-1,2-diaminoethane (4a) (4 g, 12.9
mmol), triethyl orthoformate (19.5 g, 21.9 mL, 129 mmol), and
ammonium chloride (1.38 g, 25.8 mmol), 5a was obtained as a white
1
oil which solidified after standing (3.24 g, 9.1 mmol, 87%). H NMR
(400 MHz, CDCl3): δ = 7.99 (td, JHH = 8.2, 4JHH = 1.3 Hz, 1H, Ar-H),
7.68 (dd, JHH = 7.7, 4JHH = 1.5 Hz, 1H, Ar-H), 7.61 (td, JHH = 7.5, 4JHH
= 1.3 Hz, 1H, Ar-H), 7.47−7.40 (m, 1H, Ar-H), 7.14−7.01 (m, 3H,
Ar-H), 4.13 (s, 2H, Ar-CH2-N), 3.30 (hept, JHH = 6.8 Hz, 2H, Ar-CH),
3.00 (dd, JHH = 6.7, 4.3 Hz, 2H, N-CH2-CH2), 2.91 (dd, JHH = 6.6, 4.3
Hz, 2H, N-CH2-CH2), 1.23 (d, JHH = 6.9 Hz, 12H, CH-CH3) ppm.
13C NMR (100 MHz, CDCl3): δ = 149.2, 143.5, 142.5, 135.9, 133.3,
1
powder (4.1 g, 11.5 mmol, 89%), mp 254 °C. H NMR (400 MHz,
CDCl3): δ = 10.36 (s, 1H, CH-Imd), 7.53−7.47 (m, 2H, Ar-H), 7.44−
7.34 (m, 4H, Ar-H), 7.20 (d, JHH = 7.8 Hz, 2H, Ar-H), 5.30 (s, 2H, Ar-
CH2-N), 4.19−3.94 (m, 4H, N-CH2-CH2), 2.81 (hept, JHH = 6.8 Hz,
2H, Ar-CH), 1.30 (d, JHH = 6.8 Hz, 6H, CH-CH3), 1.23 (d, JHH = 6.8
Hz, 6H, CH-CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 159.7,
146.4, 133.0, 131.1, 130.0, 129.3, 129.1, 129.1, 124.9, 53.1, 52.2, 47.9,
28.9, 25.1, 24.0 ppm. IR (film from CH2Cl2): ν = 2966, 1629, 1459,
1360, 1258, 1234, 1148, 809, 768, 712, 651, 575, 552, 486 cm−1. Anal.
Calcd for C22H29N2Cl: C, 74.03; H, 8.19; N, 7.85; Cl, 9.93. Found: C,
74.01; H, 8.16; N, 7.81; Cl, 9.73. HRMS (ESI): m/z calcd for
C22H28N2: [M+H+] 321.2325, found 321.2327.
131.2, 128.1, 125.0, 123.8, 123.7, 51.4, 50.8, 49.7, 27.7, 24.4 ppm. IR
(film from CH2Cl2): ν = 3348, 2961, 1527, 1440, 1358, 1312, 1251,
1203, 1107, 1054, 916, 860, 806, 774, 752, 734, 707, 614, 43 cm−1.
Anal. Calcd for C21H29N3O2: C, 70.95; H, 8.22; N, 11.82. Found: C,
70.85; H, 8.21; N, 11.66. HRMS (ESI): m/z calcd for C21H29N3O2:
[M+H+] 356.2333, found 356.2340.
General Procedure for the Preparation of Dihydroimid-
azolium Salts with Mesityl Substituent. A mixture of diamine (1
equiv), triethyl orthoformate (10 equiv), and HCl in dioxane (4 M, 2.1
equiv) was heated in an open vessel at 90 °C for 12 h and then at 105
°C for 2 h. Next, the reaction mixture was cooled to room
temperature, and the solvent was evaporated to one-third of its
volume. Again, the mixture was cooled. Subsequent filtration and
washing with cold diethyl ether yielded the pure imidazolium salt as a
white powder.
N1-(2,6-Diisopropylphenyl)-N2-(2-methoxybenzyl)-4,5-dihydro-
1H-imidazolinium Chloride (5b). Following the general procedure,
from N1-(2,6-diisopropylphenyl)-N2-(2-methoxybenzyl)-1,2-diamino-
ethane (4b) (2.47 g, 7.26 mmol), triethyl orthoformate (11 g, 12.3
mL, 72.6 mmol), and ammonium chloride (0.776 g, 14.5 mmol), 5b
was obtained as a white powder (2.4 g, 6.2 mmol, 85%), mp 255−256
1
°C. H NMR (400 MHz, CDCl3): δ = 9.53 (s, 1H, CH-Imd), 7.59
4
(dd, JHH = 7.4, JHH = 1.7 Hz, 1H, Ar-H), 7.43−7.33 (m, 2H, Ar-H),
7.20 (d, JHH = 7.8 Hz, 2H, Ar-H), 6.99 (t, JHH = 7.5 Hz, 1H, Ar-H),
6.92 (d, JHH = 8.2 Hz, 1H, Ar-H), 5.20 (s, 2H, Ar-CH2-N), 4.26−4.15
(m, 2H, N-CH2-CH2), 4.13−4.04 (m, 2H, N-CH2-CH2), 3.85 (s, 3H,
O-CH3), 2.86 (hept, JHH = 6.7 Hz, 2H, Ar-CH), 1.26 (d, JHH = 6.8 Hz,
6H, CH-CH3), 1.22 (d, JHH = 6.8 Hz, 6H, CH-CH3) ppm. 13C NMR
(100 MHz, CDCl3): δ = 159.2, 158.1, 146.7, 132.1, 131.1, 131.0,
130.1, 1254.0, 121.5, 121.1, 111.0, 55.9, 53.4, 48.5, 48.0, 28.9, 25.1,
24.3 ppm. IR (film from CH2Cl2): ν = 2965, 1629, 1459, 1359, 1258,
1233, 808, 767, 712, 650, 574, 485 cm−1. Anal. Calcd for
C23H31N2ClO·0.5H2O: C, 69.77; H, 8.15. Found: C, 69.89; H, 7.98.
HRMS (ESI): m/z calcd. for C23H30N2O: [M+H+] 351.2431, found
351.2436.
N1-(2,4,6-Trimethylphenyl)-N2-benzyl-4,5-dihydro-1H-imidazol-3-
ium Chloride (3a). Following the general procedure, from N1-
(2,4,6trimethylphenyl)-N2-benzyl-1,2-diaminoethane (2a) (1.50 g,
5.03 mmol), triethyl orthoformate (8.5 mL), and HCl (4 M solution,
2.64 mL), 3a was obtained as a white powder (1.26 g, 76%), mp 214−
216 °C.11a 1H NMR (400 MHz, CDCl3): δ = 10.25 (s, 1H, CH-Imd),
7.46−7.44 (m, 2H, Ar-H), 7.36−7.32 (m, 3H, Ar-H), 6.84 (s, 2H,
Mes-H), 5.14 (s, 2H, Ar-CH2-N), 4.01−4.09 (m, 4H, N-CH2-CH2),
2.23 (s, 6H, Ar-CH3), 2.22 (s, 3H, Ar-CH3) ppm. 13C NMR (100
MHz, CDCl3): δ = 159.7, 140.2, 135.1, 133.0, 131.0, 130.8, 129.3,
129.2, 129.1, 52.1, 51.0, 48.1, 21.0, 18.1 ppm.
N1-(2,6-Diisopropylphenyl)-N2-(2-(dimethylamino)benzyl)-4,5-di-
hydro-1H-imidazolinium chloride (5c). Following the general
procedure, from N1-(2,6-Diisopropylphenyl)-N2-(2-(dimethylamino)-
benzyl)-1,2-diaminoethane (4c) (1.5 g, 4.24 mmol), triethyl
orthoformate (6.42 g, 7.21 mL, 42.4 mmol), and ammonium chloride
(0.454 g, 8.49 mmol) 5c was obtained as a white powder (1.4 g, 3.5
N1-(2,4,6-Trimethylphenyl)-N2-(2-methoxybenzyl)-4,5-dihydro-
1H-imidazol-3-ium Chloride (3b). Following the general procedure,
from N1-(2,4,6-trimethylphenyl)-N2-(2-methoxybenzyl)-1,2-diamino-
ethane (2b) (1.50 g, 5.03 mmol), triethyl orthoformate (8.5 mL),
and HCl (4 M solution, 2.64 mL), 3b was obtained as white crystals
(1.31 g, 76%), decomposes without melting in the range of 223−241
I
DOI: 10.1021/acs.organomet.7b00211
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
mmol, 83%), mp 161−162 °C. H NMR (400 MHz, CDCl3): δ =
yielded the product as a microcrystalline solid, which was dried in
vacuo.
10.07 (s, 1H, CH-Imd), 7.49 (dd, JHH = 7.6, 4JHH = 1.6 Hz, 1H, Ar-H),
7.41 (t, JHH = 7.8 Hz, 1H, Ar-H), 7.35 (td, JHH = 7.7, JHH = 1.6 Hz,
4
General Procedure 2 for the Preparation of Hoveyda−
Grubbs Precatalysts. The corresponding imidazonium chloride (1.2
equiv) was dried in preheated Schlenk flask at 60 °C for 2 h under
high vacum. After the sample cooled to room temperature, toluene was
added under an argon atmosphere to obtain 0.02 M final carbene
concentration. To this vigorously stirred suspension was added
potassium tert-pentoxide (1.7 M in toluene, 1.2 equiv), and the
solution was left until it become clear (usually 2 min). The Schlenk
flask was placed in a preheated (65 °C) oil bath, and Hoveyda−
Grubbs first-generation complex (1 equiv) was added at once. The
progress of the reaction was monitored by TLC (cyclohexane/ethyl
acetate 4:1). After full consumption of Hov I catalyst, the reaction
mixture was cooled to room temperature, and the solvent was
evaporated. Purification by silica gel chromatography (cyclohexane/
ethyl acetate 9:1, followed by cyclohexane/ethyl acetate 1:2) and
further recrystallization from a DCM/MeOH mixture (1:5) yielded
the product as a microcrystalline solid, which was dried in vacuo.
Synthesis of Ru-1. Following general procedure 1, 1-isopropoxy-2-
(prop-1-enyl)benzene (115 mg, 0.651 mmol), Ind-1 (300 mg, 0.326
mmol), CuCl (50 mg, 0.5 mmol), and toluene (8 mL) were used.
Purification by the general procedure (vide supra) yielded the product
1H, Ar-H), 7.22 (d, JHH = 7.8 Hz, 2H, Ar-H), 7.19 (d, JHH = 7.9 Hz,
1H, Ar-H), 7.12 (td, JHH = 7.5, 4JHH = 1.0 Hz, 1H, Ar-H), 5.42 (s, 2H,
Ar-CH2-N), 4.09−3.94 (m, 4H, N-CH2-CH2), 2.88 (hept, JHH = 6.7
Hz, 2H, Ar-CH), 2.70 (s, 6H, N-CH3), 1.32 (d, JHH = 6.8 Hz, 6H, CH-
CH3), 1.24 (d, JHH = 6.9 Hz, 6H, CH-CH3) ppm. 13C NMR (100
MHz, CDCl3): δ = 159.6, 153.6, 146.6, 131.1, 131.1, 130.2, 130.2,
127.6, 125.0, 124.6, 120.2, 53.2, 48.7, 48.1, 45.6, 29.0, 25.2, 24.4 ppm.
IR (film from CH2Cl2): ν = 3390, 2959, 1641, 1498, 1452, 1263, 1214,
1102, 1055, 946, 818, 750, 475 cm−1. Anal. Calcd for: C24H34N3Cl: C,
72.06; H, 8.57; N, 10.51; Cl, 8.86. Found: C, 71.93; H, 8.54; N, 10.46;
Cl, 8.71. HRMS (ESI): m/z calcd for C24H33N3: [M+H+] 364.2747,
found 364.2746.
N1-(2,6-Diisopropylphenyl)-N2-(2-(trifluoromethyl)benzyl)-4,5-di-
hydro-1H-imidazolinium Chloride (5d). Following the general
procedure, from N1-(2,6-diisopropylphenyl)-N2-(2-(trifluoromethyl)-
benzyl)-1,2-diaminoethane (4d) (1.35 g, 3.57 mmol), triethyl
orthoformate (5.39 g, 6.06 mL, 35.7 mmol), and ammonium chloride
(0.382 g, 7.13 mmol), 5d was obtained as a white powder (1.5 g, 3.53
mmol, 99%), mp 207−208 °C. 1H NMR (400 MHz, CDCl3): δ = 9.96
(s, 1H, CH-Imd), 7.84 (d, JHH = 7.6 Hz, 1H, Ar-H), 7.64 (d, JHH = 7.8
Hz, 1H, Ar-H), 7.55 (t, JHH = 7.6 Hz, 1H, Ar-H), 7.44 (t, JHH = 7.7 Hz,
1H, Ar-H), 7.33 (t, JHH = 7.8 Hz, 1H, Ar-H), 7.12 (d, JHH = 7.8 Hz,
2H, Ar-H), 5.36 (s, 2H, Ar-CH2-N), 4.17−3.89 (m, 4H, N-CH2-CH2),
2.77 (hept, JHH = 6.5 Hz, 2H, Ar-CH), 1.18 (d, JHH = 6.9 Hz, 6H, CH-
CH3), 1.15 (d, JHH = 6.9 Hz, 6H, CH-CH3) ppm. 13C NMR (100
MHz, CDCl3): δ = 159.5, 146.3, 133.1, 132.4, 131.1, 131.1, 129.8,
129.5, 128.9 (q, 2JCF = 30.5 Hz), 126.5 (q, 3JCF = 5.6 Hz), 124.8, 124.0
1
Ru-1 as a khaki-colored microcrystalline powder (140 mg, 72%). H
NMR (400 MHz, CDCl3): δ = 16.24 (s, 1H, RuCH), 7.72 (d, JHH
6.8 Hz, 2H, Ar-H), 7.53−7.37 (m, 4H, Ar-H), 7.09 (s, 2H, Mes-H),
6.97−6.93 (m, 3H, Ar-H), 5.64 (s, 2H, Ar-CH2-N), 5.18 (sept, JHH
=
=
6.0 Hz, 1H, O-CH), 3.94−3.89 (m, 2H, N-CH2-CH2), 3.66−3.62 (m,
2H, N-CH2-CH2), 2.47 (s, 3H, Ar-CH3), 2.28 (s, 6H, Ar-CH3), 1.75
(d, JHH = 6.0 Hz, 6H) ppm. 13C NMR (100 MHz, CDCl3): δ = 291.6,
209.9, 152.6, 144.1, 138.9, 138.2, 137.8, 136.2, 129.7, 129.4, 128.9,
128.4, 123.6, 122.7, 122.6, 112.9, 75.2, 56.1, 52.0, 47.9, 22.0, 21.3, 18.3
ppm. IR (KBr): ν = 2978, 2920, 1588, 1574, 1485, 1452, 1415, 1325,
1294, 1269, 1235, 1109, 1095, 1034, 934, 841, 750, 702 cm−1. Anal.
Calcd for C29H34Cl2N2ORu (598.57): C, 58.19; H, 5.73; Cl, 11.85; N,
4.68; Found: C, 58.06; H, 5.80; Cl, 11.66; N, 4.48. HRMS (ESI): m/z
calcd for C29H34Cl2N2ORu: [M-Cl]+ 563.1408, found 563.1417.
Synthesis of Ru-2. Following general procedure 1, 1-isopropoxy-2-
(prop-1-enyl)benzene (97.6 mg, 0.522 mmol), Ind-2 (350 mg, 0.368
mmol), CuCl (55.2 mg, 0.552 mmol), and toluene (10 mL) were used.
Purification by the general procedure (vide supra) yielded the product
1
(q, JCF = 273.9 Hz), 53.4, 48.6, 48.2, 28.7, 25.0, 23.9 ppm. IR (film
from CH2Cl2): ν = 2966, 1632, 1459, 1313, 1260, 1235, 1167, 1114,
1058, 1038, 808, 770, 712, 652, 552, 484 cm−1. Anal. Calcd for
C23H28N2ClF3·0.5 H2O: C, 63.66; H, 6.74. Found: C, 63.54; H, 6.71.
HRMS (ESI): m/z calcd for C23H27N2F3: [M+H+] 389.2199, found
389.2211
N1-(2,6-Diisopropylphenyl)-N2-(2-nitrobenzyl)-4,5-dihydro-1H-
imidazolinium Chloride (5e). Following the general procedure, from
N1-(2,6-diisopropylphenyl)-N2-(2-nitrobenzyl)-1,2-diaminoethane
(4e) (1.05 g, 2.95 mmol), triethyl orthoformate (4.47 g, 5.02 mL, 29.5
mmol), and ammonium chloride (0.316 g, 5.91 mmol), 5e was
obtained as a white powder (1.02 g, 2.54 mmol, 86%), mp 236−237
°C. 1H NMR (400 MHz, CDCl3) δ = 9.44 (s, 1H, CH-Imd), 8.36 (dd,
1
Ru-2 as a green microcrystalline powder (144 mg, 62%). H NMR
(400 MHz, CDCl3): δ = 16.32 (s, 1H, RuCH), 7.94 (d, JHH = 8.0
Hz, 1H, Ar-H), 7.53−7.48 (m, 1H, Ar-H), 7.37−7.33 (m, 1H, Ar-H),
7.08−7.05 (m, 3H, Ar-H), 6.97−6.92 (m, 4H, Ar-H), 5.71 (s, 2H, Ar-
CH2-N), 5.18 (sept, 1H, JHH = 6.0, O-CH), 3.92−3.87 (m, 2H, N-
CH2-CH2), 3.90 (s, 3H), 3.75−3.70 (m, 2H, N-CH2-CH2), 2.46 (s,
3H, Ar-CH3), 2.27 (s, 6H, Ar-CH3), 1.76(d, JHH = 6.0 Hz, 6H) ppm.
13C NMR (100 MHz, CDCl3): δ = C 292.4, 209.1, 157.8, 152.5, 144.1,
138.8, 138.2, 129.6, 129.5, 129.4, 122.6, 122.5, 121.2, 112.9, 110.5,
75.1, 55.5, 51.9, 49.0, 47.9, 22.1, 21.3, 18.3 ppm. IR (KBr): ν = 2927,
1589, 1573, 1493, 1483, 1438, 1412, 1384, 1293, 1268, 1245, 1219,
1161, 1114, 1023, 935, 843, 794, 754 cm−1. Anal. Calcd for
C30H36Cl2N2O2Ru: C, 57.32; H, 5.77; Cl, 11.28; N, 4.46; Found: C,
57.12; H, 5.80; Cl, 11.07; N, 4.28. HRMS (ESI): m/z calcd for
C30H36Cl2N2O2Ru: [M-Cl]+ 593.1514, found 593.1504.
4
4
JHH = 7.7, JHH = 1.4 Hz, 1H, Ar-H), 8.08 (dd, JHH = 8.2, JHH = 1.3
Hz, 1H, Ar-H), 7.76 (td, JHH = 7.6, 4JHH = 1.3 Hz, 1H, Ar-H), 7.61 (td,
JHH = 7.9, 4JHH = 1.4 Hz, 1H, Ar-H), 7.41 (t, JHH = 7.8 Hz, 1H, Ar-H),
5.64 (s, 2H, Ar-CH2-N), 4.36 (dd, JHH = 12.4, 9.2 Hz, 2H, N-CH2-
CH2), 4.12 (dd, JHH = 12.5, 9.2 Hz, 2H, N-CH2-CH2), 2.86 (hept, JHH
= 6.8 Hz, 2H, Ar-CH), 1.27 (d, JHH = 6.8 Hz, 6H, CH-CH3), 1.23 (d,
JHH = 6.8 Hz, 6H, CH-CH3) ppm. 13C NMR (100 MHz, CDCl3) δ =
159.6, 148.8, 146.7, 135.1, 134.7, 131.4, 130.8, 129.8, 128.1, 125.4,
125.1, 53.6, 49.1, 49.0, 28.9, 25.2, 24.3 ppm. IR (film from CH2Cl2): ν
= 2967, 1627, 1527, 1456, 1347, 1259, 1215, 858, 796, 760, 708, 664,
483 cm−1. Anal. Calcd for C22H28ClN3O2: C, 65.74; H, 7.02; N, 10.45;
Cl, 8.82. Found: C, 65.52; H, 6.90; N, 10.42; Cl, 8.87. HRMS (ESI):
m/z calcd for C22H27N3O2: [M+H+] 366.2176, found 366.2182.
General Procedure 1 for the Preparation of Hoveyda−
Grubbs Precatalysts. In an oven-dried Schlenk vessel, the
corresponding indenylidene precatalyst (1 equiv) was added at once
to the vigorously stirring solution of 1-isopropoxy-2-(prop-1-enyl)-
benzene (1.5−2 equiv) in toluene, and the reaction vessel was placed
in a preheated (60 °C) oil bath under an atmosphere of argon. Next,
CuCl (1.5 equiv) was added in two portions with 5 min interval. The
progress of the reaction was monitored by TLC (cyclohexane/ethyl
acetate, 4:1). After full consumption of indenylidene precatalyst (ca. 15
min), the reaction mixture was cooled to room temperature, and the
solvent was evaporated. Purification by silica gel chromatography
(cyclohexane/ethyl acetate 9:1, followed by cyclohexane/ethyl acetate
1:2) and further recrystallization from a DCM/MeOH mixture (1:5)
Synthesis of Ru-3. Following general procedure 1, 1-isopropoxy-2-
(prop-1-enyl)benzene (84.1 mg, 0.477 mmol), Ind-3 (230 mg, 0.239
mmol), CuCl (35.8 mg, 0.358 mmol), and toluene (5 mL) were used.
Purification by the general procedure (vide supra) yielded the product
1
Ru-3 as a deep-green microcrystalline solid (114 mg, 74%). H NMR
(400 MHz, CDCl3): δ = 16.30 (s, 1H, RuCH), 7.90 (d, JHH = 8.0
Hz, 1H), 7.53−7.48 (m, 1H), 7.34−3.30 (m, 1H, Ar-H), 7.20−7.16
(m, 2H, Ar-H), 7.10 (s, 2H, Mes-H), 7.95−6.90 (m, 3H, Ar-H), 5.78
(s, 2H, Ar-CH2-N), 5.16 (sept, JHH = 6.0 Hz, 1H, O-CH), 3.96−3.91
(m, 2H, N-CH2-CH2), 3.69−3.64 (m, 2H, N-CH2-CH2), 2.78 (s, 6H),
2.48 (s, 3H, Ar-CH3), 2.30 (s, 6H, Ar-CH3), 1.75 (d, JHH = 6.0 Hz,
6H) ppm. 13C NMR (100 MHz, CDCl3): δ = 291.4, 209.7, 153.2,
152.6, 144.1, 138.9, 138.2, 137.8, 129.9, 129.7, 129.5, 128.4, 123.6,
122.7, 122.6, 119.0, 113.0, 75.0, 52.0, 50.8, 48.0, 45.2, 22.0, 21.4, 18.3
J
DOI: 10.1021/acs.organomet.7b00211
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
ppm. IR (KBr): ν = 3027, 2982, 2916, 2835, 1587, 1573, 1488, 1471,
1450, 1380, 1327, 1310, 1291, 1274, 1236, 1214, 1154, 1110, 1094,
934, 763, 753 cm−1. Anal. Calcd for C31H39Cl2N3ORu: C, 58.03; H,
6.13; Cl, 11.05; N, 6.55. Found: C, 58.04; H, 6.23; Cl, 10.81; N, 6.39.
HRMS (ESI): m/z calcd. for C31H39Cl2N3ORu: [M-Cl]+ 605.1752,
found 605.1743.
1418, 1381, 1268, 1112, 1050, 934, 842, 809, 764, 741, 642, 578 cm−1.
Anal. Calcd for C34H45Cl2N3ORu: C, 59.73; H, 6.63; N, 6.15; Cl,
10.37. Found: C, 59.60; H, 6.53; N, 6.17; Cl, 10.44. HRMS (ESI): m/z
calcd for C34H43N3ORu: [M+2H]2+ 306.6302, found 306.6291.
Synthesis of Ru-7. Following general procedure 2, N1-(2,6-
Diisopropylphenyl)-N2-(2-(trifluoromethyl)benzyl)-4,5-dihydro-1H-
imidazolinium chloride (5d) (170 mg, 0.4 mmol), Hov I (200 mg,
0.333 mmol), potassium tert-pentoxide solution (202 mg, 0.252 mL,
0.4 mmol), and toluene (20 mL) were used. Purification by the general
procedure (vide supra) yielded the product Ru-7 as a green
Synthesis of Ru-4. Following general procedure 2, N1-(2,6-
diisopropylphenyl)-N2-benzyl-4,5-dihydro-1H-imidazolinium chloride
(5a) (138 mg, 0.388 mmol), Hov I (194 mg, 0.323 mmol), potassium
tert-pentoxide solution (196 mg, 0,245 mL, 0.388 mmol), and toluene
(10 mL) were used. Purification by the general procedure (vide supra)
yielded the product Ru-4, as a deep-green microcrystalline solid (159
1
microcrystalline solid (128 mg, 0.181 mmol, 54%). H NMR (400
MHz, CD2Cl2): δ = 16.12 (s, 1H, Ru = CH), 8.20 (d, JHH = 7.8 Hz,
1H, Ar-H), 7.78 (d, JHH = 7.8 Hz, 1H, Ar-H), 7.73 (t, JHH = 7.7 Hz,
1H, Ar-H), 7.65 (t, JHH = 7.8 Hz, 1H, Ar-H), 7.53 (q, JHH = 8.2 Hz,
2H, Ar-H), 7.44 (d, JHH = 7.8 Hz, 2H, Ar-H), 7.00 (d, JHH = 8.4 Hz,
1H, Ar-H), 6.97−6.86 (m, 2H, Ar-H), 5.83 (s, 2H, Ar-CH2-N), 5.16
(hept, JHH = 6.9 Hz, 1H, O-CH), 4.03−3.92 (m, 2H, N-CH2-CH2),
3.77−3.66 (m, 2H, N-CH2-CH2), 3.20 (hept, JHH = 6.7 Hz, 2H, Ar-
CH), 1.71 (d, JHH = 6.2 Hz, 3H), 1.26 (d, JHH = 7.0 Hz, 3H), 0.90 (d,
JHH = 6.6 Hz, 3H) ppm. 13C NMR (100 MHz, CD2Cl2): δ = 288.4,
212.3, 153.2, 148.9, 143.7, 137.8, 135.6, 132.9, 131.0, 130.3, 130.0,
1
mg, 0.248 mmol, 77%). H NMR (400 MHz, CD2Cl2): δ = 16.21 (s,
1H, RuCH), 7.77−7.71 (m, 2H, Ar-H), 7.63 (t, JHH = 7.7 Hz, 1H,
Ar-H), 7.55 (ddd, JHH = 8.3, 7.0, 4JHH = 2.0 Hz, 1H, Ar-H), 7.51−7.44
(m, 2H, Ar-H), 7.44−7.36 (m, 3H, Ar-H), 5.64 (s, 2H, Ar-CH2-N),
5.16 (hept, JHH = 6.1 Hz, 1H, O-CH), 3.97−3.86 (m, 2H, N-CH2-
CH2), 3.71−3.59 (m, 2H, N-CH2-CH2), 3.16 (hept, JHH = 6.8 Hz, 2H,
Ar-CH), 1.73 (d, JHH = 6.2 Hz, 6H), 1.22 (d, JHH = 6.9 Hz, 6H), 0.87
(d, JHH = 6.7 Hz, 6H) ppm. 13C NMR (100 MHz, CD2Cl2): δ = 290.0,
289.9, 211.2, 153.6, 149.5, 144.2, 138.4, 137.3, 130.6, 130.3, 130.1,
129.6, 129.1, 125.8, 123.3, 122.8, 113.8, 75.9, 56.8, 55.8, 48.2, 28.3,
25.8, 24.0, 22.4 ppm. IR (film from CH2Cl2): ν = 2966, 1571, 1441,
1382, 1270, 1218, 1109, 932, 806, 753, 704, 642, 463 cm−1. Anal.
Calcd for C32H40Cl2N2ORu: C, 59.99; H, 6.29; N, 4.37; Cl, 11.07.
Found: C, 59.98; H, 6.54; N, 4.41; Cl, 11.03. HRMS (ESI): m/z calcd.
for C32H39N2OClRu: [M + H]+ 605.1873, found 605.1859.
2
3
128.9 (q, JCF = 30.3 Hz), 128.5, 126.3 (q, JCF = 5.8 Hz), 125.4,
125.1(q, 1JCF = 273.7 Hz), 123.0, 122.5, 113.4, 75.9, 56.0, 52.3 (q, 4JCF
= 3.0 Hz), 48.5, 28.5, 25.9, 24.1, 22.4 ppm. IR (film from CH2Cl2): ν =
2962, 1590, 1450, 1386, 1310, 1224, 1153, 1113, 1057, 1037, 939, 843,
795, 751, 645, 574 cm−1. Anal. Calcd for C33H39Cl2N2F3ORu: C,
55.93; H, 5.55; N, 3.95; Cl, 10.00; F, 8.04. Found: C, 55.85; H, 5.56;
N, 3.95; Cl, 9.83; F, 8.20. HRMS (ESI): m/z calcd for
C33H37F3N2ORu: [M+2H]2+ 319.1028, found 319.1018.
Synthesis of Ru-5. Following general procedure 2, N1-(2,6-
diisopropylphenyl)-N2-(2-methoxybenzyl)-4,5-dihydro-1H-imid-
azolinium chloride (5b) (111 mg, 0.286 mmol), Hov I (143 mg, 0.239
mmol), potassium tert-pentoxide solution (135 mg, 0.168 mL, 0.286
mmol), and toluene (14 mL) were used. Purification by the general
procedure (vide supra) yielded the product Ru-5 as a green
microcrystalline solid (90 mg, 0.134 mmol, 56%). 1H NMR (400
MHz, CD2Cl2): δ = 16.12 (s, 1H, RuCH), 8.20 (d, JHH = 7.8 Hz,
1H, Ar-H), 7.81−7.70 (m, 2H, Ar-H), 7.70−7.61 (m, 1H, Ar-H),
7.59−7.48 (m, 2H, Ar-H), 7.43 (dd, JHH = 7.8, 4JHH = 2.3 Hz, 2H, Ar-
H), 7.00 (d, JHH = 8.5 Hz, 1H, Ar-H), 6.97−6.86 (m, 2H, Ar-H), 5.83
(s, 2H, Ar-CH2-N), 5.16 (hept, JHH = 6.1 Hz, 1H, O-CH), 4.02−3.92
(m, 2H, N-CH2-CH2), 3.78−3.68 (m, 2H, N-CH2-CH2), 3.20 (hept,
Synthesis of Ru-8. Following general procedure 2, N1-(2,6-
diisopropylphenyl)-N2-(2-nitrobenzyl)-4,5-dihydro-1H-imidazolinium
chloride (5e) (120 mg, 0.3 mmol), Hov I (150 mg, 0.25 mmol),
potassium tert-pentoxide solution (151 mg, 0.189 mL, 0.3 mmol), and
toluene (18 mL) were used. Product Ru-8 was not obtained (0 mg,
0%).
Procedure for the Thermal Stability Studies. Solutions of
Hoveyda-type precatalysts Ru-1-Ru-7, Hov II (SIMes), and Hov II′
(SIPr) (12.8 μmol) in toluene (0.6 mL) and a solution of 1,3,5-
trimethoxybenzene (internal standard, 12.8 μmol, 2.15 mg) in toluene
(0.1 mL) were placed in NMR tubes in the air, and the samples were
equilibrated at 50 °C. 1H NMR spectra were measured after
appropriate time intervals, and the rate of the precatalyst’s
decomposition was monitored by the integration of protons of the
internal standard at δ = 6.07 (s, 3H) and the characteristic RuCH
with chemical shifts around 16 ppm.
RCM of Diethyl Diallylmalonate (DEDAM) (6). Stock solution
of DEDAM was prepared in the following manner: 6 (140 mg, 0.583
mmol) was weighed into a volumetric flask (5 mL). The flask was then
filled with dry, degassed toluene. Next, the flask was closed with a
rubber septum and shaken to homogenize the stock solution. This
stock solution (600 μL) was introduced to an NMR tube equipped
with a septum. The sample was equilibrated at 50 °C in the NMR
probe.
Stock solution of precatalyst was prepared in the following manner:
precatalyst (3.5 μmol) was weighed into a volumetric flask (1 mL).
The flask was then closed with a rubber septum, and dry, degassed
toluene (1 mL) was injected. An aliquot of the precatalyst (100 μL, 0.7
μmol) was taken from the stock solution and injected through the
septum into a solution of substrate in an NMR tube. Data points were
collected over an appropriate period of time, using the Varian array
function. The yield of 7 was determined by comparing the ratio of the
integrals of the methylene protons in the starting material, δ = 2.67
(s), with those in the product, δ = 2.98 (s). Yield was calculated
according to the following equation: yield (%) = ([P] × 100%)/([P] +
[S]).
JHH = 6.0 Hz, 2H, Ar-CH), 1.71 (d, JHH = 6.2 Hz, 4H), 1.26 (d, JHH
=
7.1 Hz, 4H), 0.90 (d, JHH = 6.6 Hz, 4H) ppm. 13C NMR (100 MHz,
CD2Cl2): δ = 288.8, 209.9, 158.4, 153.1, 149.1, 143.8, 138.1, 131.3,
130.1, 129.8, 125.3, 124.8, 123.0, 122.4, 121.3, 113.4, 111.0, 75.8, 56.0,
55.7, 54.0, 49.9, 48.3, 28.4, 26.0, 24.1, 22.5 ppm. IR (film from
CH2Cl2): ν = 2964, 1588, 1420, 1291, 1250, 1215, 1114, 1052, 935,
752, 639, 581 cm−1. Anal. Calcd for C33H42Cl2N2O2Ru: C, 59.10; H,
6.31; N, 4.18; Cl, 10.57. Found: C, 59.08; H, 6.12; N, 4.15; Cl, 10.39.
HRMS (ESI): m/z calcd for C33H41ClN2O2Ru: [M + H]+ 635.1979,
found 635.1977.
Synthesis of Ru-6. Following general procedure 2, N1-(2,6-
diisopropylphenyl)-N2-(2-(dimethylamino)benzyl)-4,5-dihydro-1H-
imidazolinium chloride (5c) (166 mg, 0.415 mmol), Hov I (208 mg,
0.346 mmol), potassium tert-pentoxide solution (195 mg, 0.244 mL,
0.415 mmol), and toluene (18 mL) were used. Purification by the
general procedure (vide supra) yielded the product Ru-6 as a dark-
1
green microcrystalline solid (180 mg, 0.263 mmol, 56%). H NMR
(400 MHz, CD2Cl2): δ = 16.22 (s, 1H, RuCH), 7.86 (dd, JHH = 7.6,
4JHH = 1.7 Hz, 1H, Ar-H), 7.64 (t, JHH = 7.7 Hz, 1H, Ar-H), 7.54 (ddd,
4
JHH = 8.7, 6.5, JHH = 2.5 Hz, 1H, Ar-H), 7.43 (s, 1H, Ar-H), 7.41 (s,
1H, Ar-H), 7.37−7.31 (m, 1H, Ar-H), 7.27−7.16 (m, 2H, Ar-H), 6.99
(d, JHH = 8.3 Hz, 1H, Ar-H), 6.96−6.87 (m, 2H, Ar-H), 5.76 (s, 2H,
Ar-CH2-N), 5.15 (hept, JHH = 6.1 Hz, 1H, O-CH), 3.94 (dd, JHH
=
11.0, 8.3 Hz, 2H, N-CH2-CH2), 3.67 (dd, JHH = 10.9, 8.2 Hz, 2H, N-
CH2-CH2), 3.21 (hept, JHH = 6.8 Hz, 2H, Ar-CH), 2.80 (s, 6H), 1.72
(d, JHH = 6.2 Hz, 6H), 1.25 (d, JHH = 6.9 Hz, 6H), 0.90 (d, JHH = 6.7
Hz, 6H) ppm. 13C NMR (100 MHz, CD2Cl2): δ = 288.5, 288.4, 210.5,
153.9, 153.1, 149.1, 143.8, 138.1, 130.6, 130.2, 130.1, 129.8, 128.83,
125.4, 123.8, 123.0, 122.4, 119.6, 113.5, 75.7, 55.8, 51.7, 48.3, 45.4,
28.6, 25.9, 24.2, 22.5 ppm. IR (film from CH2Cl2): ν = 2965, 1589,
RCM of N-Allyl-4-methyl-N-(2-methylallyl)-benzene-
sulfonamide (8). Stock solutions of substrate 8 and corresponding
complexes were prepared analogously to the procedure reported for
DEDAM (6). Dry, degassed, nondeuterated toluene was used as a
solvent, and the reactions were carried out at 50 °C. Data points were
K
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Article
collected over an appropriate period of time, using the Varian array
function. The yield of 9 was determined by comparing the ratio of the
integrals of the methylene protons in the starting material, δ = 1.70 (s)
with those in the product, δ = 1.29 (s). Yield was calculated according
to the equation given in the previous section.
General Procedure for Ene-Yne Metathesis of 14. To the
substrate 14 (200 mg, 0.805 mmol) in DCM (HPLC grade, 7 mL) was
added a solution of precatalyst (2 mol%) in DCM (HPLC grade, 1
mL). The resulting mixture was stirred at 50 °C. Aliquots (25 μL)
were taken every 30 min and added to the solution of ethyl vinyl ether
in DCM (3 M, 300 μL). The samples were shaken, allowed to stand
for 5 min, and then analyzed by GC. After completion of the reaction,
the solvent was evaporated, and the crude product was purified via
column chromatography (cyclohexane/ethyl acetate 39:1) to yield 15.
1H and 13C NMR spectra are in agreement with those previously
reported.25
General Procedure for RCM of 10. To the substrate 10 (196 mg,
0.666 mmol) in toluene (HPLC grade, 5.6 mL) was added a solution
of precatalyst (1 mol%) in toluene (HPLC grade, 1 mL). The resulting
mixture was stirred at 50 °C. Aliquots (25 μL) were taken every 30
min and added to the solution of ethyl vinyl ether in toluene (3 M, 300
μL). The samples were shaken, allowed to stand for 5 min, and then
analyzed by GC. After completion of the reaction, the solvent was
evaporated, and the crude product was purified via column
chromatography (cyclohexane/ethyl acetate 1:1) to yield 11 as a
brownish oil. 1H NMR spectra are in agreement with those previously
reported.26
yield (purity 99%) as a mixture of E/Z isomers (81:19 base on GC
analysis).
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00211.
NMR spectra of diamines, their hydrochlorides (when
obtained), NHCs, and Ru complexes; crystallographic
data and selected bond lengths and angles of [Ru]-1,
[Ru]-2, [Ru]-3, and [Ru]-4(PDF)
Accession Codes
CCDC 1539095−1539098 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: anna.kajetanowicz@gmail.com.
*E-mail: prof.grela@gmail.com.
■
General Procedure for RCM of 12. To the substrate 12 (131 mg,
0.666 mmol) in toluene (HPLC grade, 5.6 mL) was added a solution
of the corresponding precatalyst (0.5 mol%) in toluene (HPLC grade,
1 mL). The resulting mixture was stirred at 50 °C. Aliquots (25 μL)
were taken every 15 min and added to the solution of ethyl vinyl ether
in toluene (3M, 300 μL). The samples were shaken, allowed to stand
for 5 min, and then analyzed by GC. After completion of the reaction,
the solvent was evaporated, and the crude product was purified via
column chromatography (cyclohexane/ethyl acetate 1:1) to yielded 13
ORCID
Roman Gajda: 0000-0002-9742-2941
Krzysztof Wozniak: 0000-0002-0277-294X
́
Karol Grela: 0000-0001-9193-3305
Notes
The authors declare no competing financial interest.
1
as a colorless oil. H and 13C NMR spectra are in agreement with
ACKNOWLEDGMENTS
those previously reported.27
■
The authors are grateful to the National Science Centre
(Poland) for the NCN MAESTRO Grant No. DEC-2012/04/
A/ST5/00594. The study was carried out at the Biological and
Chemical Research Centre, University of Warsaw, established
within the project cofinanced by European Union from the
European Regional Development Fund under the Operational
Programme Innovative Economy, 2007−2013.
General Procedure for CM of 16 with 17. To the substrate 16
(100 mg, 0.829 mmol) and cis-1,4-diacetoxy-2-butene (17) (286 mg,
1.66 mmol) in DCM (HPLC grade, 7 mL) was added a solution of the
precatalyst (2.5 mol%) in DCM (HPLC grade, 1 mL). The resulting
mixture was stirred at 50 °C for 20 h. Next, the solvent was
evaporated, and the crude product was purified via column
chromatography (cyclohexane/ethyl acetate 9:1) to yield 18 as a
1
colorless oil. H and 13C NMR spectra are in agreement with those
previously reported.28
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was added. After 10 h, the ratio of E/Z isomers in the products 20/21
was measured by GC. 1H and 13C NMR spectra are in agreement with
those previously reported.16
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