Expanding the Family of Hoveyda-Grubbs Catalysts Containing Unsymmetrical NHC Ligands

Article abstract of DOI:10.1021/acs.organomet.7b00488

A series of Hoveyda-Grubbs second-generation catalysts containing N-alkyl/N′-aryl N-heterocyclic carbene (NHC) ligands were synthesized and investigated in representative olefin metathesis reactions. Steric perturbations of unsymmetrical NHCs were achieved through modulation of the hindrance of alkyl (neopentyl, neophyl, cyclohexyl) and aryl (2-isopropylphenyl, mesityl) substituents at the nitrogen atoms in combination with different backbone configurations (syn and anti). The NHC substitution patterns strongly influence the stability and reactivity of the corresponding complexes. In general, complexes bearing an anti NHC backbone are more stable and more active than their corresponding syn isomers. In both the series, the presence of bulky, highly branched N-alkyl groups tends to give reduced catalytic differences between syn and anti isomers, whereas the nature of the N′-aryl substituent (2-isopropylphenyl or mesityl) gives rise to different activity and/or selectivity. Of note, an N′-mesityl catalyst with anti backbone was found to be highly competent in the ethenolysis of ethyl oleate, achieving up to 90% selectivity for the formation of terminal olefins.

Full text of DOI:10.1021/acs.organomet.7b00488

Article
pubs.acs.org/Organometallics
Expanding the Family of Hoveyda−Grubbs Catalysts Containing
Unsymmetrical NHC Ligands
Veronica Paradiso, Valerio Bertolasi, Chiara Costabile, Tonino Caruso, Michał Dąbrowski,§
†
‡
†
†
§
,†
Karol Grela, and Fabia Grisi*
†Dipartimento di Chimica e Biologia “Adolfo Zambelli”, Universita
Italy
̀
di Salerno, Via Giovanni Paolo II 132, I-84084 Fisciano, Salerno,
di Ferrara, Via L. Borsari 46, I-44100 Ferrara, Italy
‡
Dipartimento di Chimica and Centro di Strutturistica Diffrattometrica, Universita
̀
§
̇
Biological and Chemical Research Centre, Faculty of Chemistry, University of Warsaw, Zwirki i Wigury 101, 02-089 Warsaw, Poland
*
S Supporting Information
ABSTRACT: A series of Hoveyda−Grubbs second-generation
catalysts containing N-alkyl/N′-aryl N-heterocyclic carbene
(
NHC) ligands were synthesized and investigated in
representative olefin metathesis reactions. Steric perturbations
of unsymmetrical NHCs were achieved through modulation of
the hindrance of alkyl (neopentyl, neophyl, cyclohexyl) and aryl
(
2-isopropylphenyl, mesityl) substituents at the nitrogen atoms
in combination with different backbone configurations (syn and
anti). The NHC substitution patterns strongly influence the
stability and reactivity of the corresponding complexes. In
general, complexes bearing an anti NHC backbone are more
stable and more active than their corresponding syn isomers. In both the series, the presence of bulky, highly branched N-alkyl
groups tends to give reduced catalytic differences between syn and anti isomers, whereas the nature of the N′-aryl substituent (2-
isopropylphenyl or mesityl) gives rise to different activity and/or selectivity. Of note, an N′-mesityl catalyst with anti backbone
was found to be highly competent in the ethenolysis of ethyl oleate, achieving up to 90% selectivity for the formation of terminal
olefins.
INTRODUCTION
investigated by many researchers (e.g., 1−6, Chart 1).
Successful results in specific metathesis applications, such as
■
The past few years have seen significant advances in the
chemistry of olefin metathesis, mostly due to the development
of easily handled, highly efficient NHC-based ruthenium
catalytic systems (second-generation catalysts), which have
1
Chart 1. Selected Examples of Ruthenium Catalysts with
Unsymmetrical NHCs
2
found successful applications in the synthesis of natural
products and pharmaceuticals as well as in the production of
1
,3
fine chemicals and oleochemicals. The catalytic behavior of
this class of ruthenium complexes can be easily modulated
through judicious modification of the stereoelectronic proper-
4
ties of the NHC ligand. For example, the introduction of
substituents on the backbone of symmetrical NHCs with
reduced bulk on the nitrogen atoms has led to the development
of ruthenium complexes with enhanced stability toward
decomposition pathways via C−H activation of N-aryl
substituents and high efficiency in the formation of hindered
5
olefins. On the other hand, the advent of unsymmetrical NHC
(
uNHC) frameworks, whose fascination lies mainly in the
possibility that they offer to strongly differentiate the steric
bulkiness around the metal, have permitted an increase in6
catalyst activity and selectivity in several metathesis processes.
In this view, the catalytic potential of ruthenium complexes
coordinated with uNHCs, especially those presenting one
Received: June 27, 2017
7
aliphatic and one aromatic amino side group, has been
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00488
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Organometallics
Article
6
d,8
9
asymmetric reactions,
synthesis of alternating copolymers,
previously reported catalysts 9b and 10b, presenting the most
significant reactivity difference between syn and anti isomers.
Furthermore, the catalytic potential of all these complexes was
explored in a specific metathesis application such as ethenolysis
of fatty acid esters, whereas the enantioselective ability of chiral
catalysts 12a−c was investigated in model asymmetric ring-
closing metathesis (ARCM) and asymmetric ring-opening
cross-metathesis (AROCM) reactions.
10
selective formation of cyclic oligomers, ethenolysis reac-
7
d,9b
6c,d,11
tions,
Z-selective metathesis transformations, 7
and
have
e,12
diastereoselective ring rearrangement metathesis,
been achieved.
We have recently proposed an additional strategy for tuning
the catalytic properties of this class of complexes, based on the
introduction of substituents on the backbone of unsymmetrical
NHC moieties in a precise stereochemical arrangement (syn or
anti) (7−10, Chart 2). Through this structural modification, as
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Complexes 11a−c
and 12a−c. The new complexes 11a−c and 12a−c were easily
obtained by following the synthetic procedures illustrated in
Chart 2. Ruthenium Catalysts with Backbone-Substituted
uNHCs
13a
Schemes 1 and 2, respectively. Diamines 13, 14, and 17 were
a
Scheme 1. Synthesis of Ruthenium Complexes 11a−c
previously observed for analogous systems bearing symmetrical
5
c−e
NHCs,
ruthenium complexes showing different catalytic
behaviors depending on the NHC backbone configuration (anti
or syn) and on the bulkiness of the N-alkyl substituent (N-
13
cyclohexyl vs N-methyl) were obtained.
To further investigate the effect on catalyst properties of
unsymmetrical NHCs that combine stereogenic centers on the
backbone with differently encumbered N-alkyl/N′-aryl sub-
stituents, we focused our attention on the development of new
Hoveyda−Grubbs type complexes (11a−c and 12a−c, Chart
a
Reaction conditions: (a) meso-1,2-diphenylethylenediamine, 2-iso-
3) with modified N-substituents. In particular, syn and anti
propylbromobenzene (for 13) or 2-bromomesitylene (for 14),
Pd(OAc) , NaOtBu, BINAP, toluene, 100 °C, 12 h; (b) (1)
2
Chart 3. New Ruthenium Catalysts Bearing uNHCs with
Different Backbone Configurations
R(CH ) CCHO (R = Me, Ph) or cyclohexanone, CH Cl , molecular
3
2
2
2
a
sieves, room temperature, 48 h (for 15a) or 5 days (for 15b and 15c),
2) NaBH , CH OH, room temperature, 3.5 h; (c) NH BF ,
(
4
3
4
4
CH(OEt) , 135 °C, 2 h (for 15a and 15c) or 8 h (for 15b); (d)
3
(
CF ) CH COK, HGI, toluene, 65 °C, 2.5 h.
3 2 3
obtained from the commercial meso- or (R,R)-1,2-diphenyle-
thylenediamine by cross-coupling with 2-isopropylbromoben-
zene or 2-bromomesitylene and subsequent reductive amina-
tion of the appropriate aldehyde or ketone (50−79% yields),
whereas diamine 18 was prepared by installing first the
cyclohexyl and then the mesityl group (51% yield) on the
nitrogen atoms of the starting (R,R)-1,2-diphenylethylenedi-
amine. After cyclization of the diamines so obtained in the
presence of triethyl orthoformate and ammonium tetrafluor-
oborate, the resulting NHC salts (71−90% yields) were
deprotonated in situ with (CF ) (CH )COK and reacted
3
2
3
a
with RuCl (CH-o-iPrO-Ph)(PCy ) (HGI) to afford the
Catalysts 11a−c are racemic mixtures (only one of the enantiomers is
2
3
desired complexes 11a−c and 12a−c as air- and moisture-
stable solids, in yields ranging from moderate to good (45−
depicted), while 12a−c are enantiopure.
7
0%). It should be underlined that complexes 11a−c are
NHC backbone substituted complexes possessing an N-
neopentyl or N-neophyl moiety mixed with an N′-2-
isopropylphenyl group (11a,b and 12a,b), as well as the
analogues having N-cyclohexyl/N′-mesityl substituents (11c
and 12c), were prepared and structurally characterized. The
catalytic performances of 11a−c and 12a−c were evaluated in
standard metathesis reactions and compared with those of
racemic mixtures, while 12a−c are enantiopure.
All of the final products were characterized by 1D and 2D
NMR techniques and ESI-FT-ICR analysis.
Crystals suitable for X-ray diffraction analysis were obtained
for complexes 11a,c and 12c, and their crystal structures are
shown in Figure 1. A selection of bond distances and angles is
given in the Table S2 in the Supporting Information.
B
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a
Scheme 2. Synthesis of Ruthenium Complexes 12a−c
The conformations of the substituents at the N1 and N2 of
the NHC rings are controlled by short intramolecular
interactions between the C4−H4 group of the benzylidene
moiety and the centroid of the C20/C25 phenyl ring, as well as
by interactions between the C14−H14 group of the cyclohexyl
substituent and the Ru atom. The C−H···π interactions
between the C4−H4 group and the centroids C of the C20/
C25 phenyl rings are characterized by the following parameters
H4···C(C20/C25) = 2.70 and 2.58 Å and C4−H4···C = 162
and 168°, for 11c and 12c, respectively. Furthermore, the short
C−H···Ru interactions display H14···Ru1 distances of 2.51 and
2
.50 Å and C14−H14···Ru1 angles of 122 and 123° for
complexes 11c and 12c, respectively.
Before investigating the catalytic behavior of the newly
developed complexes, their thermal stability was studied. C D
6
6
solutions (0.01 M) of each complex, prepared under a nitrogen
atmosphere and containing tetrakis(trimethylsilyl)silane as an
internal standard, were heated at 60 °C for 1 month and
1
monitored by H NMR spectroscopy. Stability tests performed
during the first 14 days are illustrated in Figure 2. After 1 week,
syn complexes 11a,b were found to be almost completely
decomposed (only 4% of initial complexes remained), while
their corresponding anti isomers 12a,b exhibited a greater
stability, as they decomposed within 12 and 10 days,
respectively. Moreover, decomposition rates are very similar
for 11a,b but are significantly different for 12a,b, suggesting a
major effect of the N-alkyl substitution on complex stability in
the presence of an anti NHC backbone configuration. This is
observed also for reference complexes 9b and 10b, where the
presence of the N-cyclohexyl group ensures major stability with
respect to catalysts 11a,b and 12a,b, allowing detection, after 14
days, of 32% of 9b and 42% of 10b unaltered. At 1 month, 26%
of anti isomer 10b still persisted, while only 8% of syn 9b
remained. On the other side, the presence of a more bulky N′-
aryl substituent such as a mesityl group resulted in outstanding
stability of the resulting complexes 11c and 12c, which indeed
both showed no decomposition within 1 month, also proving to
be more robust than the classical, commercially available HGII
a
Reaction conditions: (a) (R,R)-1,2-diphenylethylenediamine, 2-
isopropylbromobenzene Pd(OAc) , NaOtBu, BINAP, toluene, 100
2
°
C, 12 h; (a′) (1) (R,R)-1,2-diphenylethylenediamine, cyclohexanone,
CH Cl , molecular sieves, room temperature, 14 h, (2) NaBH ,
2
2
4
CH OH, room temperature, 3.5 h; (b) (1) R(CH ) CCHO (R = Me,
Ph), CH Cl , molecular sieves, room temperature, 14 h (for 19a) or 5
days (for 19b), (2) NaBH , CH OH, room temperature, 3.5 h; (b′) 2-
bromomesitylene, Pd(OAc) , NaOtBu, BINAP, toluene, 100 °C, 48 h;
3
3 2
2
2
4
3
2
(
1
c) NH BF , CH(OEt) , 135 °C, 2 h (for 19a and 20) or 8 h (for
4 4 3
9b); (d) (CF ) CH COK, HGI, toluene, 65 °C, 2.5 h.
3 2 3
In all compounds the Ru center is pentacoordinated and
adopts a distorted-square-pyramidal coordination geometry.
The Cl atoms are trans-oriented in the basal plane and the
carbene C1 atom is in a trans position with respect to the O1
oxygen of the 2-iPrO substituent at the benzylidene ligand,
which is almost coplanar with the NHC ring, being rotated by
only 8.80(8), 11.20(13), and 3.13(8)° for the three complexes
16
17
catalyst bearing a symmetrically aryl substituted NHC.
As reported in the literature, the stability of unsymmetrical
catalysts is associated with the nature of NHC N-
7
f,18
1
1a,c and 12c, respectively.
substituents.
In a recent study on NHC-Al complexes the
19
Compound 11a crystallizes in the centrosymmetric P2 /n
stability was attributed to steric factors, by using topographic
1
20
space group with the NHC phenyl groups in cis positions with
respect to the C2−C3 bond. Accordingly, the crystal contains a
racemic mixture of both the enantiomers having opposite
configurations (SR or RS) at the C2 and C3 asymmetric carbon
atoms. The conformations of the substituents at the N1 and N2
NHC atoms are mainly determined by short intramolecular
interactions: H14b···Ru1 = 2.54 Å and H4···(centroid of C19/
C24 phenyl ring) = 2.40 Å.
Complexes 11c and 12c are isomers with different relative
configurations at the C2 and C3 atoms of NHC group. Both
crystallize in the noncentrosymmetric C2 space group. In 11c
the phenyl groups, bonded to C2 and C3 of the NHC ring, are
in cis positions. Accordingly, the C2 and C3 carbons display
opposite configurations: S and R, respectively. Conversely, in
complex 12c the phenyl groups at C2 and C3 are in trans
positions and the C2 and C3 carbon atoms of NHC display the
same R chirality. The absolute configurations could be
determined reliably from the crystallographic data, using the
maps and %VBur as steric parameters. %VBur is a well-known
parameter, successfully used to quantify the steric hindrance of
NHC ligands by measuring the amount of volume of a sphere
centered on the metal, buried by overlap with atoms of the
ligand. Bulkier ligands occupy a larger amount of that sphere
and present greater %VBur values.
21
To observe if the decomposition of our complexes could be
correlated to the steric NHC encumbrance, topographic maps
(Figure 3) and %VBur of complexes 9b, 10b, 11a−c, and 12a−c
were calculated. Since no X-ray were available for complexes
11b and 12a,b, we used DFT minimum energy optimized
structures for all complexes for topographic maps and %VBur
calculations. %VBur could be sensitive to the conformations of
the N-alkyl group; nevertheless the only complexes that could
present reasonable additional low-energy structures are 11b and
12b bearing N-neophyl substituents, due to the rotation around
the C−C single bond that changes the position of the Ph group.
The only significant degree of freedom for N-cyclohexyl and N-
neopentyl groups lies in rotation around N−C bond, but in
both cases it is difficult to imagine different low-energy
14
calculated Flack parameters of 0.00(2) and −0.03(2) for
complexes 11c and 12c, respectively.
C
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15
Figure 1. ORTEP views of compounds 11a,c and 12c showing the thermal ellipsoids at the 40% probability level.
quadrant (%VBur Max), and the overall %VBur values are
reported.
According to topographic maps, higher steric hindrance is
concentrated on the N-alkyl substituent side, which is always
located far from the alkylidene. 11c and 12c, presenting the
highest %VBur, were also shown to be the most stable
complexes. Nevertheless, according to the data in Table 1 the
complex stability seems more correlated to the %VBur Max value
(
%
representative of the most hindered quadrant). The lower the
VBur Max, the lower the stability shown by the complex. In
order to give a more comprehensive overview, data for complex
HGII from DFT optimization (see the Supporting Informa-
tion) are also reported in Table 1 even if we did not expect a
behavior in line with that of the examined catalysts due to the
different nature of NHC ring substitution. Concerning the
nature of the deactivating species and the mechanisms of
deactivation, it is hard to reach a conclusion. Indeed, although
for symmetrical NHCs bearing N-aryl substituents with low
hindrance decomposition via C−H activation is well
Figure 2. Thermal stability in C D at 60 °C under nitrogen of Ru
6
6
1
complexes 11a−c and 12a−c. Decomposition was monitored by H
NMR spectroscopy using tetrakis(trimethylsilyl)silane as an internal
standard. The lines are intended as a visual aid only.
structures. For the N-neopentyl group, which could adopt
apparently more conformations, the orientation is imposed by
the phenyl groups on the backbone. Minimum energy
structures of 11b and 12b involve a partial π-stacking
interaction between the phenyl substituent on the backbone
and the phenyl of the neophyl group (Figure 4). Different
conformations without π stacking were explored for the last two
complexes. Nevertheless, the best optimized structures present
internal energies increases of 1.6 and 1.8 kcal/mol for 11b and
22
documented, for complexes 9b, 10b, and 11a−c, presenting
a mono-ortho-substituted N-aryl group, a careful check of the
distances between the o-CH bond and Ru suggests no
correlation between these distances and the stability of the
complexes. On the other hand, it is worth noting that
decomposition pathways of olefin metathesis catalysts bearing
NHC ligands with N-alkyl groups are still quite unknown. To
the best of our knowledge, the only examples are related to
cyclometalated ruthenium benzylidene complexes reported by
Grubbs (e.g., 3, Chart 1), formed through a carboxylate-assisted
1
2b, respectively, and did not show dramatic differences in
topographic maps and %V , the phenyl group of neophyl
Bur
being far from the metal center. Topographic maps and
structures of these conformations are reported in the
Supporting Information.
23
C−H activation.
The electrochemical behavior of 9b, 10b, 11a−c, and 12a−c
was also investigated to gain useful information about the
electron-donating properties of the NHC ligand coordinated to
In Table 1, the percentages of undecomposed complex after
days, the values of %VBur representative of the most hindered
3
D
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Figure 3. Topographic steric maps of 9b, 10b, 11a−c, and 12a−c. The iso-contour curves of steric maps are given in Å. The maps were achieved by
starting from minimum energy structures of complexes optimized by DFT calculations. The complexes are oriented according to the complex
scheme of the corresponding map. %VBur representative of each single quadrant is reported for each map.
Table 1. Percentage of Undecomposed Complex after 3
Days, value of the %VBur Representative of the Most
Hindered Quadrant (%VBur Max), and Value of the Overall
%
VBur and for 9b, 10b, 11a−c, and 12a−c
a
b
complex
complex (%)
%VBur Max
%VBur
1
1
1
1
9
1
1a
1b
2b
2a
b
17
18
39.4
39.6
40.4
40.9
41.1
42.2
42.9
41.4
42.1
30.7
30.9
30.5
31.0
31.0
30.5
32.9
31.8
31.5
35
64
68
0b
70
HGII
84
Figure 4. DFT optimized structures of complexes 11b and 12b.
1
1
1c
2c
100
100
2
4
a
the metal. The Ru(II)/Ru(III) redox potentials derived by
cyclic voltammetry are reported in Table 2.
Percentage of undecomposed complex after 3 days in C D at 60 °C
6
6
b
under nitrogen. %V representative of the most hindered quadrant
Bur
The values registered for complexes 9b, 10b, 11c, and 12c
bearing an N-cyclohexyl group are quite similar, varying in a
range of only 3−13 mV, and no clear trend depending on the
NHC backbone configuration and/or the nature of the N′-aryl
substituent was observed. For complexes 11a,b and 12a,c with
a branched N-alkyl substituent, differences in redox potentials
are even less significant (3−8 mV), indicating a negligible role
not only of the N-substitution but also of the relative
(NE or SE in Figure 3 depending on the complex shape).
orientation of substituents on the backbone. On the whole,
electronic properties of uNHCs coordinated to the examined
complexes seem to be influenced very little by the types of
substitution patterns. The lowest redox potential values,
reflecting the highest electron density at the metal center, are
observed for complexes 9b and 12c, characterized by an N-
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Table 2. Redox Potentials of Ruthenium Complexes 9b, 10b,
In the RCM of diethyl diallylmalonate (23, Figure 5A),
catalysts 11a,b and, 12a,b were able to complete cyclization in a
range of 5−8 min, with 12a emerging as the most efficient
system, nearly equaling the best performing catalyst 10b.
However, in contrast to what has been observed for systems
containing a flexible cyclohexyl N-substituent (9b, 10b), the
introduction of bulky, highly branched N-alkyl moieties, such as
neopentyl or neophyl groups, led to strongly reduced
differences between complexes with syn and anti NHC
backbone configuration. Indeed, anti complexes 12a,b showed
activities only slightly higher than those of their syn congeners
1
1a−c, and 12a−c Determined by Cyclic Voltammetry
a
complex
ΔE1/2 (V)
E − E (mV)
a
c
9
1
1
1
1
1
1
1
b
0.947
0.960
0.969
0.978
0.972
0.976
0.961
0.950
73
0b
1a
2a
1b
2b
1c
2c
102
102
112
98
112
98
83
1
1a,b (Table S3 in the Supporting Information).
Increasing the steric hindrance of the N′-aryl substituent
b
HGII
0.860
66
a
2
Redox potentials determined using cyclic voltammetry in CH Cl2
from a 2-isopropyphenyl to a mesityl group (11c, 12c) led to
less efficient catalytic systems that, again, exhibited a significant
discrepancy between catalytic behaviors of anti (98%
conversion in 37 min) and syn (89% conversion in 60 min)
isomers (Table S3 in the Supporting Information). In the RCM
of N-diallyl tosylamine (25, Figure 5B), activities of all the
tested catalytic systems were equal or inferior to those observed
for the malonate derivative 23, which typically is more reluctant
to undergo cyclization reactions, confirming the tendency of
this class of ruthenium catalysts bearing uNHCs to give RCM
under nitrogen. Conditions: 1 mM analyte, 0.1 M NBu PF6 as
4
supporting electrolyte, and 1 mM octamethylferrocene as an internal
b
standard. Scan rate: 100 mV/s. Redox potential reported in the
20
literature is 0.850 V.
cyclohexyl group. In comparison to HGII catalyst, complexes
9
b, 10b, 11a−c, and 12a−c are anodically shifted by 87−118
mV, underlining a lower donor ability of the corresponding
uNHC ligands. This finding was already observed for
ruthenium complexes bearing symmetrical NHCs with phenyl
groups on the backbone. However, we are not able to
unambiguously ascribe the lower donor ability of the examined
uNHCs to the backbone substitution or to the nature of the N-
substituents. Work is in progress to gain more information
about this issue.
13b
nonproductive events with less demanding substrates.
In
both of the RCM reactions, all of the new catalysts emerged as
less active than commercial symmetrical HGII used at 10 times
lower catalyst loading (Table S3).
25
The kinetic profiles for the RCM of 27 and 29 promoted by
catalysts 11a−c and 12a−c are sketched in Figure 6. Anti
catalysts with neopentyl (12a) and neophyl N-substituents
(12b) were able to quantitatively convert 27 in 13 and 10 min,
respectively (Figure 6A), proving to be more efficient than their
syn congeners 11a and 11b. In the RCM of the N-tosyl
derivative 29 (Figure 6B), N-neopentyl catalysts 11a and 12a
showed similar activities (99% conversion within 7 and 5 min,
respectively), whereas N-neophyl catalysts 11b and 12b
disclosed a more marked reactivity difference dependent on
the NHC backbone configuration. Indeed, anti catalyst 12b
quantitatively furnished the cyclic product 30 within 5 min,
while syn isomer 11b required 12 min.
Ring-Closing Metathesis (RCM) Activity Studies. The
catalytic performances of 11a−c and 12a−c were first evaluated
in RCM reactions of malonate and N-tosyl derivatives with
different degrees of steric hindrance. All cyclization reactions
1
were carried out at 60 °C in C D and monitored by H NMR
6
6
spectroscopy. The corresponding kinetic plots are shown in
Figures 5−7, where the conversion−time curves previously
determined for the same ring closures promoted by catalysts 9b
1
3
and 10b are also displayed. Comparisons to commercially
available HGII catalyst are included in the graphs. Further
details, are reported in the Tables S3−S5 in the Supporting
Information.
In both RCM reactions for the formation of cycloolefins 28
and 30, the worst performances were given by N-cyclohexyl/
Figure 5. Kinetic profiles for the RCM of 23 (A) and 25 (B).
F
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Figure 6. Kinetic profiles for the RCM of 27 (A) and 29 (B).
Figure 7. Kinetic profiles for the RCM of 31 (A) and 33 (B).
N′-mesityl catalysts, which, in addition, displayed remarkable
differences in the catalytic activity of the syn and anti isomers.
In addition, for these transformations all of the newly
synthesized catalysts were revealed to be less efficient than
HGII (see Table S4 in the Supporting Information).
were found to exhibit better performances in comparison to
HGII in the RCM of 31 and 33. However, in the ring closure of
33, the catalytic activities of 11b and 12b presenting a bulky
neophyl N-substituent were very similar to that of the
benchmark commercial catalyst (see Table S5 in the
Supporting Information).
For RCM, as well as for other kind of metathesis later
discussed in this paper, an important role could be played by
the two catalyst sides of unsymmetrical complexes, which
would possibly depend on the rate of NHC rotation vs the
metathesis reaction. Nevertheless, to the best of our knowledge,
there have been no studies clarifying the role of NHC
unsymmetrical N-substitution. The hypothesis of NHC
rotation was explored by Collins in asymmetric metathesis
Finally, we compared the catalytic behaviors of 11a−c and
1
(
2a−c in the RCM of sterically demanding diolefins 31 and 33
Figure 7 and Table S5 in the Supporting Information). All of
the catalysts were found to perform better in the RCM of N-
tosyl substrate 33 than in that of malonate substrate 31. In the
RCM of 33, catalyst 12a with a neopentyl N-group behaved like
the best performant 10b possessing an N-cyclohexyl substituent
(
97% conversion), while it appeared less efficient in the
cyclization of 31 (88% vs >97% conversion). The correspond-
ing syn isomer 11a showed lower propensity to effect both
cyclizations of 31 and 33, as also observed for the analoguous
N-cyclohexyl complex 9b.
Moving from neopentyl to neophyl as an N-substituent was
sufficient to render negligible the role of NHC backbone
configuration; indeed 11b and 12b exhibited comparable
catalytic activities. Changing the N′-aromatic moiety from 2-
isopropylphenyl to mesityl dramatically affected the catalytic
behavior, as was clearly shown from an analysis of conversion
plots for both RCM reactions carried out with 11c and 12c. All
of the catalysts having an N′-2-isopropylphenyl substituent
promoted by ruthenium catalysts bearing a chiral C -symmetric
1
ligand, but no definitive conclusion was reached. To address
this issue, further experimental as well as theoretical studies
26
should be undertaken.
Cross-Metathesis (CM) Activity. The catalytic behavior of
newly synthesized catalysts 11a−c and 12a−c was then
examined in the standard cross-metathesis (CM) reaction of
allyl benzene (35) and cis-1,4-diacetoxy-2-butene (36) (Scheme
3). The results are summarized in Table 3 together with the
available data for the same reactions performed with catalysts
9b, 10b, and HGII.
G
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 3. CM of Substrates 35 and 36
Scheme 4. Ethenolysis of Ethyl Oleate (39)
Table 3. CM of 35 and 36 Promoted by Catalysts 11a−c and
1
2a−c
same reaction carried out in the presence of HGII (entry 10)
isolated yield of 37
isolated yield of 38
29a
a
b
b
were added. Moreover, comparison with BerEt
catalyst
Figure 8), bearing a cyclic alkylaminocarbene (CAAC) ligand
entry 9), was included, since ruthenium complexes with
entry catalyst
(%)
E/Z
(%)
E/Z
(
(
1
2
3
4
5
6
7
8
9
9b
72
67
78
80
80
69
50
89
69
2.6
7.6
3.0
7.6
4.2
7.7
3.9
4.4
8.6
23
28
19
11
20
7
5.5
5.7
5.0
6.1
4.5
6.6
5.2
5.8
5.3
10b
11a
12a
11b
12b
11c
12c
HGII
CAAC ligands are the most active catalysts for ethenolysis
29b−f
known to date.
Higher selectivities, yields, and turnover numbers (TONs)
were displayed by catalysts with anti backbone configuration
(
Table 4, entries 4, 6, and 8), which gave better performances
38
11
15
than symmetrical HGII catalyst. Anti catalyst 10b, although it
gave an improved yield and TON with respect to its syn
congener 9b (cf. entries 1 and 2), showed lower selectivity. On
the other hand, catalyst 9b was already found to show a peculiar
behavior, revealing a marked propensity to give nonproductive
a
b
Reactions in CH Cl at 40 °C for 12 h, catalyst 2.5 mol %. E/Z
2
2
1
ratios were determined by H NMR spectroscopy.
13b
metathesis events, which is a desirable feature for targeted
reactions such as ethenolysis. The nature of the N-alkyl group
seems to have a slight effect on the selectivity of ethenolysis
reactions (entries 3−6), while the sterics of the N-aryl
substituent (mesityl versus 2-isopropylphenyl) strongly influ-
ences catalyst activity, as was evident, above all, when catalysts
9b and 10b were compared with catalysts 11c and 12c. Indeed
selectivities, yields, and TONs obtained with the latter catalysts
nearly equal those found for the high-performing BerEt catalyst
(entries 7−9). In particular, 12c showed the same selectivity as
BerEt (83%).
All catalysts were found to be competent in the examined
CM reaction, giving only cross-metathesis (37) and homometa-
thesis (38) products. No byproducts arising from double-bond
isomerization were observed. Replacement of a cyclohexyl
group by a neopentyl or neophyl group as N-substituent proved
to have little effect on the activity and selectivity of the
corresponding catalysts (Table 3, entries 1−6), confirming a
major tendency of complexes with a syn backbone configuration
13
to give lower E/Z ratios in comparison to their anti analogues
that indeed behave like commercial HGII (entry 9). On the
other hand, anti complexes 12a,b with highly branched N-alkyl
groups turned out to be more able than anti complex 10b to
furnish the desired cross-coupling product 37 over the
homocoupling product 38. A peculiar behavior was shown by
catalysts 11c and 12c possessing an N′-mesityl group (entries 7
and 8), for which the relative configuration of phenyls on the
NHC backbone strongly differentiates yields of heterocoupled
product 37 while giving very similar E/Z ratios, underlining
how catalytic efficiency is influenced by a delicate balance
between NHC backbone configuration and steric features of N-
substituents.
Encouraged by this finding, as only a few examples of
ruthenium complexes with NHC ligands were found to be very
efficient in ethenolysis reactions, we tested catalyst 12c at lower
catalyst loadings (Table 4, entries 11−14). Under the same
conditions, the superiority of reference BerEt catalyst, and
more in general of CAAC ruthenium complexes, was already
2
9b−f
demonstrated.
At a catalyst loading of 100 ppm a
selectivity of 86% for ethenolysis products 40 and 41 and a
TON of 4100 were observed (entry 11). When the reaction
time was also reduced (entry 12), 90% selectivity was achieved
and yield (44%) and TON (4400) were slightly improved. At
100 ppm, a lower reaction temperature (40 °C) afforded lower
yield and TON (entry 13), while at a catalyst loading as low as
20 ppm and 50 °C (entry 14), 12c displayed unchanged
selectivity (83%) and the best TON reported so far for N-alkyl/
The increasing interest in industrially relevant cross-meta-
thesis reactions such as ethenolysis of fatty acid monoesters
derived from renewable biomass to produce higher value-added
3
c,d,f,27
products
prompted us to investigate the catalytic
7d
potential of newly developed systems in the ethenolysis of
ethyl oleate (39; Scheme 4 and Table 4). Indeed, ruthenium
complexes bearing unsymmetrical NHCs have already demon-
strated their attractiveness as catalysts for the cross-metathesis
of methyl oleate with ethylene, showing high selectivities for
N-aryl NHC complexes.
Asymmetric Metathesis Reactions. The catalytic per-
30
formances of enantiomerically pure catalysts 12a−c were also
evaluated in asymmetric metathesis transformations and
13b
compared to those of catalyst 10b.
The asymmetric ring-
7
d
ethenolysis products over self-metathesis products.
This feature was attributed to their strong preference to
closing metahesis (ARCM) of achiral trienes 44 and 45
(Scheme 5) and the asymmetric ring-opening cross-metathesis
(AROCM) of meso-norbornene derivative 48 with styrene
(Scheme 6) were chosen as model reactions. The results for
ARCM reactions are reported in Table 5 and compared to
those of catalyst 2a, representing the closest example of
28
propagate as a methylidene species.
As reported in Table 4 (entries 1−12), catalysts 9b, 10b,
1
1a−c, and 12a−c were all compared at 500 ppm catalyst
loading and 10 bar of ethylene (99.9% purity). Data for the
H
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 4. Ethenolysis of Ethyl Oleate (39) with Catalysts 9b, 10b, 11a−c, and 12a−c
a
b
c
d
e
entry
cat.
9b
cat./39 (ppm)
temp (°C)
time (h)
conversion (%)
selectivity (%)
yield (%)
TON
1
2
3
4
5
6
7
8
9
500
500
500
500
500
500
500
500
500
500
100
100
100
20
50
50
50
50
50
50
50
50
50
50
50
50
40
50
3
3
3
3
3
3
3
3
3
3
3
2
3
3
38
63
53
70
53
71
75
81
85
71
48
49
39
18
77
58
60
64
43
57
81
83
83
43
86
90
88
83
29
36
32
45
23
40
61
67
70
30
41
44
34
15
580
720
10b
11a
640
12a
900
11b
12b
11c
460
800
1220
1340
1400
600
12c
BertEt
HGII
12c
1
1
1
1
1
0
1
2
3
4
4100
4400
3400
7500
12c
12c
12c
a
The reactions were run neat using 5.4 mmol of ethyl oleate at 150 psi of ethylene (99.9% purity) with dodecane (150 μL) used as an internal
b
c
standard. Determined by GC analysis. Conversion = 100 − [(final moles of 39) × 100/[initial moles of 39]. Determined by GC analysis.
d
Selectivity = 100(moles of ethenolysis products 40 + 41)/[(moles of 40 + 41) + (2 × (moles of 42 + 43))]. Yield= (conversion × selectivity)/100.
e
TON = yield × (initial moles of 39/moles of catalyst)/100.
Table 5. ARCM of 44 and 45 with 10b, 12a−c, and 2a
b
cat.
(mol %)
time
(h)
yield
(%)
a
c
entry substrate
additive
ee (%)
d
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
44
44
44
44
44
44
44
44
44
44
44
44
44
45
45
45
45
45
45
45
45
10b (2.5)
10b (4.0)
12a (2.5)
12a (4.0)
12b (2.5)
12b (4.0)
12b (4.0)
12c (2.5)
12c (2.5)
12c (4.0)
12c (4.0)
2a (2.5)
none
NaI
2
2
>98
>95
>98
>98
>98
83
19 (S)
52 (S)
16 (S)
43 (S)
18 (S)
47 (S)
43 (S)
7 (R)
7 (R)
24 (S)
24 (S)
82 (S)
48 (S)
42 (S)
-
d
none
NaI
2
2
none
NaI
2
2
Figure 8. Ruthenium complex with a CAAC ligand (Bertrand’s
catalyst).
NaI
20
2
87
none
none
NaI
18
41
2
>98
7
Scheme 5. ARCM of 44 and 45
0
1
2
3
4
5
6
7
8
NaI
25
2
7
e
none
NaI
>95
>95
>95
-
e
2a (4.0)
2
d
d
10b (2.5)
10b (4.0)
12a (2.5)
12a (4.0)
12b (2.5)
12b (4.0)
12c (2.5)
2a (2.5)
none
NaI
3
3
none
NaI
3
>98
-
41 (R)
-
3
none
NaI
3
>95
-
36 (S)
-
enantioselective catalyst with a monodentate C -symmetric
1
8
a
19
3
NHC ligand.
2
0
1
none
none
3
-
-
With regard to the enantioselective desymmetrization of
triene 44 (Table 5), the only discriminating factor for both the
yield and for the enantioselectivity appeared to be the nature of
the N′-aromatic substituent. Indeed, catalysts 12a,b containing
an N′-2-isopropylphenyl group were able to promote the
ARCM of triene 44 in high yields and low enantiomeric
f
2
95
8 (S)
a
Reactions without additive were performed in CH Cl ; reactions with
2
2
b
NaI were carried out in THF. Temperature: 40 °C. Yields based on
c
NMR analysis. Enantiomeric excesses determined by chiral GC.
d
e
f
Taken from ref 13. Reference 8b. Reference 32.
Scheme 6. AROCM of 48 with Styrene
I
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
excesses, as already observed for the parent catalyst 10b
the reaction mixture, except for stilbene derived from the
homometathesis of styrene, and only products having trans
stereochemistry were obtained.
(
entries 1, 3, and 5), whereas complex 12c with an N-mesityl
group gave the cyclic product 46 in only 18% yield and 7% ee
entry 8). Prolonged reaction time led to almost quantitative
(
Low to moderate enantiomeric excesses were registered, and
the highest ee value (43%) was achieved with catalyst 12c,
which also gave a product distribution slightly different from
that of the catalysts 10b and 12a,b (Table 6, entry 4)
suggesting a major propensity of 12c to propagate via a
formation of 46 (entry 9), while it did not improve the
enantiomeric excess. In an effort to enhance enantioselectivity,
as occurred with ARCM reactions promoted by chiral systems
31
based on C -symmetric NHCs, the effect of using an additive
2
28
such as NaI was investigated. A good increase in enantiomeric
excesses was found for both 12a and 12b (entries 4 and 6),
although to a lesser extent than for 10b (entry 2). Moreover,
for 12b the presence of NaI led to a decrease in the formation
of cyclic product 46, and also a longer reaction time resulted in
comparable results in terms of both product yield and
enantioselectivity (entries 6 and 7). The addition of NaI to
methylidene species, as observed in ethenolysis reactions.
CONCLUSION
■
New Hoveyda−-Grubbs catalysts with unsymmetrical NHC
ligands combining differently encumbered N-substituents and
syn or anti phenyl groups on the backbone (11a−c, 12a−c)
have been developed. Their thermal stabilities and their
catalytic behaviors were investigated and compared to those
of analogous complexes with N-cyclohexyl/N′-2-isopropyl-
phenyl groups (9b, 10b) as well as to commercially available
HGII bearing a symmetrical NHC. N′-2-Isopropylphenyl
complexes with an anti backbone (10b, 12a−c) are more
stable than their syn isomers (9b, 11a−c), and the nature of N-
alkyl substitution (neopentyl, neophyl vs cyclohexyl) accounts
for the observed stability order. N′-Mesityl catalysts (11c, 12c)
show outstanding stabilities that can be correlated to their
higher steric bulkiness. In the RCM reactions of less
encumbered substrates, the introduction of bulky, highly
branched N-alkyl groups leads to reduced activity differences
between syn and anti complexes with respect to complexes with
an N-cylohexyl group, whereas the presence of an N′-mesityl
substituent gives rise to lower activities, also correlated to the
nature of the NHC backbone configuration. In all cases,
catalytic performances are inferior to those of HGII catalyst. In
the RCM of more demanding substrates, the N′-2-isopropyl-
phenyl anti catalyst with an N-neopentyl substituent (12a) is
found to be highly efficient, nearly equaling the performance of
an analogous catalyst with an N-cyclohexyl group (10b), while
N′-mesityl catalysts (11c, 12c) show dramatically lower
activities, proving to be less efficient also than HGII that, as
is well-known, is scarcely competent to promote this class of
reactions. On the other hand, catalysts 11c and 12c gave
interesting results in the ethenolysis of ethyl oleate, out-
performing their analogues and HGII. In particular, anti catalyst
1
2c had a deleterious effect on yield and caused inversion of
enantioselectivity (entries 10 and 11).
In analogy with 10b (Table 5, entry 14), catalysts 12a,b
successfully accomplished the most challenging ARCM of 45 to
generate tetrasubstituted olefin 47 in moderate enantiomeric
excesses (entries 16 and 18), while 12c was found to be
inactive. Very likely, the bulkiness of the N′-mesityl group
reduces the active space around the metal, preventing the
approach of the sterically encumbered triene 45.
Attempts to improve reaction enantioselectivity using NaI as
an additive failed (Table 5, entries 15, 17, and 19). As a general
remark, in both ARCM reactions, catalysts 12a−c showed
8a
behaviors quite different from that of catalyst 2a. Indeed, in
the ARCM of 44 they disclosed lower enantiomeric excesses
and opposite response to the addition of NaI with respect to 2a
(
entries 12 and 13). On the other hand, they proved to be
much more enantioselective than 2a in the ARCM of 45 (entry
2
3
2
1).
Concerning the AROCM of cis-5-norbornene-endo-2,3-
dicarboxylic anhydride (48) with styrene (Scheme 6), the
results are summarized in Table 6. It should be noted that
Table 6. AROCM of 48 with Styrene in the Presence of 10b
and 12a−c
a
isolated yield isolated yield isolated yield ee (49)
entry catalyst
of 49 (%)
of 50 (%)
of 51 (%)
(%)
b
1
2
3
4
10b
12a
12b
12c
46
57
45
37
15
11
11
16
10
16
16
13
19
21
43
12c gives up to 90% selectivity for ethenolysis over self-
metathesis products with a TON of 4400 and, at low catalyst
loading (20 ppm), displays 83% selectivity with a TON of
7500, which is the best result reported to date for ethenolysis
reactions promoted by N-alkyl/N′-aryl NHC ruthenium
catalysts. Asymmetric metathesis transformations mediated by
enantiopure anti catalysts 12a−c clearly indicate that the nature
of the N′-aromatic group is the main discriminating factor for
the observed activities and enantioselectivities. The strong
influence of the type of NHC substitution pattern on
metathesis reactions evidenced by this study underlines, once
again, the importance of identifying NHC structural
modifications that can allow the design of improved active
and selective catalysts.
22
a
b
Enantiomeric excess determined by chiral HPLC. Reference 13b.
N,N′-diaryl catalysts, such as those reported by Hoveyda,
33
Grubbs, and Blechert, are the most effective catalysts for
AROCM reactions known up to now. As the NHC architecture
is very different from that of our catalysts, we found more
appropriate to refer results reported with the newly synthesized
catalysts to those obtained by Grubbs with more similar N-
alkyl/N′-aryl NHC ruthenium metathesis catalysts, showing the
34
highest selectivity at 82% ee.
All of the catalysts promoted AROCM of 48 with
1
conversions >98%, as determined by H NMR spectroscopic
EXPERIMENTAL SECTION
General Information. All reactions involving organometallic
compounds were performed under nitrogen using standard Schlenk
■
analysis of crude reaction mixture after 4 h. The desired
product 49 was obtained in 37−57% isolated yields, along with
the side products 50 and 51 (see Table 6), also obtained in
AROCM reactions promoted by Grubbs’ N-alkyl/N′-aryl
1
3a
13b
13a
and glovebox techniques. Diamines 13, 17, and 18, substrates
36
3
5
for metathesis reactions, and 2-methyl-2-phenylpropanaldehyde
3
4
catalysts. Analogously, no other compound was detected in
were prepared according to the literature procedures. Ethyl oleate was
J
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
purchased from Sigma-Aldrich Company and stored on activated
neutral alumina before use. All other reagents were purchased from
Sigma-Aldrich and TCI Chemicals and used without further
purifications. Solvents were dried and distilled before use. Deuterated
temperature, diluted with hexane, and then filtered through a plug of
silica gel with methanol as eluent. The crude yellow oil was purified by
flash column chromatography on silica gel (hexane/ethyl acetate 9/1
to 6/4) to give the desired product as a yellow oil.
1
solvents were degassed under a N flow and stored over activated 4 Å
N -Mesityl-1,2-diphenylethane-1,2-diamine (14). MW = 330.5 g/
2
1
molecular sieves. Flash column chromatography of ligand intermedi-
ates was performed using silica gel 60 (230−400 mesh) from Sigma-
Aldrich, and flash column chromatography of organometallic
compounds was performed, under nitrogen flow, using silica gel 60
mol. Yield: 79%. H NMR (300 MHz, CDCl ): δ 7.29−7.27 (m, 3H,
3
Ar-H); 7.23−7.20 (m, 3H, Ar-H); 7.10−7.07 (m, 2H, Ar-H); 7.02−
6.98 (m, 2H, Ar-H); 6.75 (s, 2H, Ar-H); 4.43 (d, J = 4.9 Hz, 1H, N-
CH-CH-N); 4.35 (d, J = 5.2 Hz, 1H, N-CH-CH-N); 2.21 (s, 3H, Ar-
13
1
(
230−400 mesh) from TSI Cambridge. Analythical thin-layer
CH ); 2.16 (s, 6H, Ar-CH ). C{ H} NMR (75 MHz, CDCl ): δ
3
3
3
chromatography (TLC) was performed using silica gel 60 F254
143.8; 142.8; 139.8; 130.1; 129.7 (overlapped); 128.5; 128.2; 128.1;
precoated plates with a fluorescent indicator. The visualization was
127.8; 127.2; 127.1; 67.7; 60.2; 20.6; 19.3. ESI+MS: m/z 353.2
+
performed using UV light or KMnO . NMR spectra were recorded on
(MNa ).
4
1
1
2
a Bruker Avance 250 spectrometer (250 MHz for H; 62.5 MHz for
C), a Bruker AM 300 spectrometer (300 MHz for H; 75 MHz for
(1R,2R)-N -cyclohexyl-N -mesityl-1,2-diphenylethane-1,2-dia-
mine (20). MW = 412.6 g/mol. Yield: 51%. H NMR (400 MHz,
1
1
3
3
1
1
1
C), a Bruker AVANCE 400 spectrometer (400 MHz for H; 100
CDCl
m, 2H, Ar-H); 6.67 (s, 2H, Ar-H); 4.41 (d, J = 7.2 Hz, 1H, N-CH-
CH-N); 4.21 (d, J = 7.2 Hz, 1H, N-CH-CH-N); 2.33−2.28 (m, 1H,
Cy-H); 2.15 (s, 3H, Ar-CH ); 2.13 (s, 6H, Ar-CH ); 2.01−1.98 (br d,
3
): δ7.20−7.15 (m, 5H, Ar-H); 7.09 (br s, 3H, Ar-H); 7.01−6.99
MHz for 13C; 161.97 MHz for P), and a Bruker ASCEND 600
31
(
1
13
spectrometer (600 MHz for H; 150 MHz for C). NMR samples
were prepared by dissolving about 10 mg of compounds in 0.5 mL of
deuterated solvent. H and C chemical shifts are listed in parts per
3
3
1
13
1
H, Cy-H); 1.67 (br t, 3H, Cy-H); 1.54 (br s, 1H, Cy-H); 1.17−1.10
13 1
million (ppm) downfield from TMS and are referenced from the
(m, 5H, Cy-H). C{ H} NMR (100 MHz, CDCl ) δ: 142.4; 142.3;
3
solvent peaks or TMS. 31P chemical shifts are referenced using H PO4
141.9; 129.8; 128.3; 128.0; 127.9 (overlapped); 127.8; 126.9; 67.1;
3
as external standard. Spectra are reported as follows: chemical shift
65.5; 53.7; 35.0; 32.8; 26.3; 25.2, 24.8, 20.5, 19.6. ESI+MS: m/z 413.9
+
20
D
(ppm), multiplicity, and integration. Multiplicities are abbreviated as
(MH ). [α]
= −45.3° (c = 0.5, CH Cl ).
2 2
follows: singlet (s), doublet (d), triplet (t), multiplet (m), broad (br),
overlapped (o). Elemental analyses for C, H, and N were recorded on
a ThermoFinnigan Flash EA 1112 instrument and were performed
according to standard microanalytical procedures. Electrochemical
measurements were conducted with an AUTOLAB PG STAT 302N
potentiostat. A three-electrode configuration was employed. The
working electrode was a Pt disk (diameter 2 mm), the counter
electrode a Pt bar, and the reference a quasi-reference electrode
General Procedure for the Alkylation of Diamines. A round-
bottom flask was charged with the diamine (1 equiv), the carbonylic
compound (3 equiv of pivalaldehyde for 15a and 19a, 6 equiv of 2-
methyl-2-phenylpropanaldehyde for 15b and 19b, and 7 equiv of
cyclohexanone for 15c) and anhydrous methylene chloride (C = 0.1
M). The reaction mixture was stirred at room temperature over
activated molecular sieves 4 Å for 48 h (15a), 14 h (19a), or 5 days
(15b, 19b, and 15c) and then filtered. Then, the solvent was removed
under reduced pressure and anhydrous MeOH was added (C = 0.1 M)
(
PtQRE)1, calibrated vs octamethylferrocene as internal standard. All
cyclic voltammograms were recorded in dry CH Cl under a nitrogen
followed by portionwise addition of NaBH (4 equiv) under a nitrogen
2
2
4
atmosphere using NBu PF (0.1 M) as supporting electrolyte at a scan
atmosphere. The reaction mixture was stirred for 3.5 h, diluted with
methylene chloride, and extracted with water. The organic layer was
4
6
rate of 100 mV/s. Potentials were referenced against the potential of
octamethylferrocene. ESI-MS measurements of organic compounds
were performed on a Waters Quattro Micro triple quadrupole mass
spectrometer equipped with an electrospray ion source. ESI-FT-ICR
measurements of complexes were performed on a Bruker Solaris XR
instrument. Enantiomeric excesses were determined by chiral GC
dried over anhydrous Na SO , and then the solvent was removed
2 4
under vacuum to afford a yellowish oil which was then purified by flash
column chromatography on silica gel (hexane/ethyl acetate 9/1).
1
2
N -(2-Isopropylphenyl)-N -neopentyl-1,2-diphenylethane-1,2-di-
1
amine (15a). MW = 400.6 g/mol. Yield: 60%. H NMR (300 MHz,
(
Agilent Technologies 6850) or by chiral HPLC (JASCO MD-4015
CDCl ): δ 7.31−7.30 (m, 3H, Ar-H); 7.25−7.23 (m, 3H, Ar-H);
3
Photo diode array detector, PU4180 RMPLC Pump) and were
compared to racemic samples. Ethenolysis mixture composition was
determined by GC (Agilent Technologies 7890A). Optical activity was
determined using a JASCO P2000 polarimeter.
7.19−7.16 (m, 1H, Ar-H); 7.08−7.01 (m, 3H, Ar-H); 6.91 (t, J = 8.0
Hz, J = 7.2 Hz, 1H, Ar-H), 6.68 (t, J = 7.4 Hz, J = 7.4 Hz, 1H, Ar-H);
6.31 (d, J = 8.2 Hz, 1H, Ar-H); 5.42 (br s, 1H, Ar-H); 4.63 (t, J = 4.7
Hz, J = 4.7 Hz, 1H, N-CH-CH-N); 4.15 (d, J = 4.7 Hz, 1H, N-CH-
The DFT calculations were performed with the Gaussian09 set of
CH-N); 3.12−2.99 (m, 1H, Ar-CH-(CH
N-CH -C(CH ); 2.20 (d, J = 11.4 Hz, 1H, N-CH
(d, J = 6.6 Hz, 3H, Ar-CH-(CH ); 1.35 (d, J = 6.8 Hz, 3H, Ar-CH-
(CH ); 0.97 (s, 9H, N-CH -C(CH
CDCl ) δ: 143.9; 140.2; 139.8; 132.2; 128.2; 128.1; 127.9; 127.8;
3
)
); 2.37 (d, J = 11.4 Hz, 1H,
2
3
7
38
programs, using the BP86 functional of Becke and Perdew. The
electronic configuration of the molecular systems was described with
the standard split-valence basis set with a polarization function of
Ahlrichs and co-workers for H, C, N, O, and Cl (SVP keyword in
2
3
)
3
2
-C(CH ); 1.41
)
3 3
)
3 2
13
1
)
) ). C{ H} NMR (75 MHz,
3 3
3
2
2
3
3
9
Gaussian). For Ru we used the small-core, quasi-relativistic
127.4; 127.2; 126.6; 124.8; 116.9; 111.7; 68.7; 62.8; 59.8; 31.8; 27.8;
+
Stuttgart/Dresden effective core potential, with an associated
27.7; 22.5; 22.4. ESI+MS: m/z 401.4 (MH ).
1
2
(
(
8s7p6d)/[6s5p3d] valence basis set contracted according to a
311111/22111/411) scheme (standard SDD keywords in Gaus-
(1R,2R)-N -(2-Isopropylphenyl)-N -neopentyl-1,2-diphenyl-
1
ethane-1,2-diamine (19a). MW = 400.6 g/mol. Yield: 70%. H NMR
40
sian09). The geometry optimizations were performed without
symmetry constraints, and the characterization of the located
stationary points was performed by analytical frequency calculations.
(300 MHz, CD Cl ): δ 7.33−7.22 (m, 10H, Ar-H); 7.15 (dd, J = 7.7
2 2
Hz, J = 1.3 Hz, 1H, Ar-H); 6.83 (dt, J = 7.6 Hz, J = 1.5 Hz, 1H, Ar-H);
6.64 (dt, J = 7.0 Hz, 1H, Ar-H); 6.21 (d, J = 8.1 Hz, 1H, Ar-H); 5.82
(br s, 1H, NH); 4.42 (d, J = 6.9 Hz, 1H, N-CH-CH-N); 3.86 (d, J =
%
VBur was calculated by starting from DFT optimized structures by
choosing the metal as the center of the sphere, selecting atomic Bondi
radii scaled by 1.17 and a radius sphere of 3.5.
Synthesis of 11a−c and 12a−c. General Procedure for the
Arylation of Diamines. Under a nitrogen atmosphere, in a round-
bottom flask equipped with a magnetic stirrer and a condenser, 2,2′-
bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) (0.2 equiv), palla-
dium acetate (0.1 equiv), sodium tert-butoxide (2 equiv), and toluene
6.8 Hz, 1H, N-CH-CH-N); 3.25−3.16 (m, 1H, Ar-CH-(CH
(d, J = 11.3 Hz, 1H,, N-CH -C(CH ); 2.09 (d, J = 11.3 Hz, 1H,, N-
CH -C(CH ); 1.42 (d, J = 6.8 Hz, 3H, Ar-CH-(CH ); 1.38 (d, J =
6.7 Hz, 3H, Ar-CH-(CH ) ); 0.95 (s, 9H, N-CH -C(CH ) ). C{ H}
3 2
) ); 2.28
)
3 3
2
)
3
)
3 2
2
3
1
3
1
3
2
2
3 3
NMR (75 MHz, CD Cl ) δ: 144.7; 142.4; 141.7; 133.2; 128.6; 128.5;
2
2
128.1; 127.5; 127.3; 126.5; 125.0; 117.2; 111.9; 70.4; 64.4; 60.1; 31.8;
+
20
27.8; 27.7; 23.0; 22.4. ESI+MS: m/z 401.4 (MH ). [α]D = +49.1 (c =
(
C = 0.05 M) were introduced. The orange solution was stirred for a
0.5, CH Cl ).
2
2
1
2
few minutes. Then the diamine (1 equiv) and mesityl bromide (1
N -(2-Isopropylphenyl)-N -(2-methyl-2-phenylpropyl)-1,2-diphe-
nylethane-1,2-diamine (15b). MW = 462.7 g/mol. Yield: 73%. H
1
equiv) were added and the reaction mixture was heated to 100 °C for
48 h. After this time the purple mixture was cooled to room
NMR (250 MHz, CDCl ): δ 7.28 (d, J = 4.4 Hz, 4H, Ar-H); 7.21−
3
K
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
7
.20 (m, 4H, Ar-H); 7.09−7.07 (m, 4H, Ar-H);6.86 (d, J = 7.3 Hz, 2H,
130.2; 128.8; 128.0; 127.9; 127.7; 127.6; 127.5; 127.0; 78.1; 75.4; 57.6;
−
Ar-H); 6.82−6.77 (m, 3H, Ar-H); 6.60 (t, J = 7.5 Hz, J = 7.3 Hz, 1H,
Ar-H); 6.19 (d, J = 7.9 Hz, 1H, Ar-H); 5.12 (d, J = 5.1 Hz, 1H, NH);
33.6; 28.7; 28.0; 24.5; 23.8. ESI+MS: m/z 411.5 (M − BF ).
4
[α]2
0
= +313.0 (c = 0.5, CH
Cl
2
).
D
2
4
1
1
.43 (t, J = 5.2 Hz, J = 5.1 Hz, 1H, N-CH-CH-N); 3.99 (d, J = 4.9 Hz,
3-(2-Isopropylphenyl)-1-(2-methyl-2-phenylpropyl)-4,5-diphenyl-
4
5
1
7
,5-dihydro-1H-imidazol-3-ium Tetrafluoroborate (16b). MW =
H N-CH-CH-N); 2.90−2.82 (m, 1H, Ar-CH-(CH ) ); 2.62 (d, J =
3
2
1
60.5 g/mol. Yield: 71%. H NMR (400 MHz, CD Cl ): δ 8.36 (s,
1.3 Hz, 1H, N-CH -CPh(CH ) ); 2.51 (d, J = 11.3 Hz, 1H, N-CH -
2
2
2
3
2
2
H, N-CH-N); 7.41−7.32 (m, 9H, Ar-H); 7.20−7.19 (m, 4H, Ar-H);
CPh(CH ) ); 1.37 (s, 3H, N-CH -CPh(CH ) ); 1.31−1.29 (m, 6H,
N-CH -CPh(CH ) and Ar-CH-(CH ) ); 1.24−1.22 (d, J = 6.8 Hz,
3
2
2
3 2
.00−6.98 (m, 3H, Ar-H); 6.83 (d, J = 6.8 Hz, 3H, Ar-H); 5.73 (d, J =
2
3
2
3 2
13
1
12.4 Hz, 1H, N-CH-CH-N); 4.91 (d, J = 11.6 Hz, 1H, N-CH-CH-N);
3
1
1
2
H, Ar-CH-(CH ) ). C{ H} NMR (100 MHz, CDCl ) δ: 147.7;
3
2
3
4
1
.33 (d, J = 14.4 Hz, 1H, N-CH -CPh(CH ) ); 3.57 (d, J = 14.4 Hz,
43.8; 140.0; 139.7; 132.2; 128.3; 128.1; 128.0; 127.9; 127.7; 127.5;
27.1; 126.5; 126.0; 125.9; 124.7; 116.9; 111.7; 68.4; 62.8; 59.8; 38.9;
7.6; 27.4; 27.0; 22.5; 22.3. ESI+MS: m/z 463.2 (MH ).
2 3 2
H, N-CH -CPh(CH ) ); 3.02−2.92 (m, 1H, Ar-CH-(CH ) ); 1.54
2
3
2
3 2
+
(s, 3H, N-CH -CPh(CH ) ); 1.45 (s, 3H, N-CH -CPh(CH ) ); 1.29−
2
3
2
2
3 2
13 1
1
2
1.27 (m, 6H, Ar-CH-(CH ) ). C{ H} NMR (100 MHz, CD Cl ): δ
(
1R,2R)-N -(2-Isopropylphenyl)-N -(2-methyl-2-phenylpropyl)-
3
2
2
2
1
60.1; 145.4; 145.2; 131.6; 130.9; 130.2; 129.6; 129.5; 129.2; 128.6;
1
7
7
,2-diphenylethane-1,2-diamine (19b). MW = 462.7 g/mol. Yield:
1
127.8; 127.6; 126.4; 73.3; 71.1; 59.1; 39.8; 28.9; 27.7; 25.6; 24.5; 24.1.
9%. H NMR (300 MHz, CDCl ): δ7.32−7.26 (m, 8H, Ar-H); 7.17−
.16 (m 8H, Ar-H); 6.83 (br t, 1H, Ar-H); 6.64 (br t, 1H, Ar-H); 6.14
3
−
ESI+MS: m/z 474.9 (M − BF ).
4
(
4R,5R)-3-(2-Isopropylphenyl)-1-(2-methyl-2-phenylpropyl)-4,5-
(
d, J = 7.6 Hz, 1H, Ar-H); 5.61 (br s, 1H, NH); 4.24 (br s, 1H, N-CH-
diphenyl-4,5-dihydro-1H-imidazol-3-ium Tetrafluoroborate (21b).
CH-N); 3.76 (br d, 1H, N-CH-CH-N); 3.05 (br t, 1H, Ar-CH-
1
MW = 560.5 g/mol. Yield: 90%. H NMR (300 MHz, CDCl ): δ 8.46
3
(
CH ) ); 2.64 (d, J = 10.9 Hz, 1H, N-CH -CPh(CH ) ); 2.48 (d, J =
3 2 2 3 2
(
s, 1H, N-CH-N); 7.50−7.45 (m, 7H, Ar-H); 7.37−7.09 (m, 9H, Ar-
H); 6.97 (d, J = 8.3 Hz, 1H, Ar-H); 6.81 (d, J = 7.6 Hz, 2H, Ar-H);
.00 (d, J = 8.3 Hz, 1H, N-CH-CH-N); 4.60 (d, J = 8.0 Hz, 1H, N-
CH-CH-N); 4.30 (d, J = 14.8 Hz, 1H, N-CH -CPh(CH ) ); 3.55 (d, J
1
0.9 Hz, 1H, N-CH -CPh(CH ) ); 1.41−1.33 (m, 12H, N-CH -
2
3
2
2
13 1
CPh(CH ) and Ar-CH-(CH ) ). C{ H} NMR (75 MHz, CDCl )
3
2
3
2
3
5
δ:147.4; 144.3; 141.8; 141.1; 132.7; 128.4; 128.2; 127.7; 127.3; 127.0;
2
3 2
1
2
26.4; 126.0; 124.7; 116.9; 111.7; 69.7; 64.2; 59.8; 38.8; 27.7; 27.6;
7.1; 22.8; 22.4. ESI+MS: m/z 463.1 (MH ). [α]D = +65.8 (c = 0.5,
+
20
= 14.8 Hz, 1H, N-CH -CPh(CH ) ); 2.67−2.56 (m, 1H, Ar-CH-
2 3 2
(
CH ) ); 1.57 (s, 3H, N-CH -CPh(CH ) ); 1.40 (s, 3H, N-CH -
3
2
2
3
2
2
CH Cl ).
2
2
1
2
CPh(CH
Hz, 3H, Ar-CH-(CH
3
)
2
); 1.15 (d, J = 6.7 Hz, 3H, Ar-CH-(CH
3
)
2
); 0.86 (d, J = 6.9
N -Cyclohexyl-N -mesityl-1,2-diphenylethane-1,2-diamine (15c).
13
1
1
3
)
2
). C{ H} NMR (100 MHz, CD
Cl ): δ
2 2
MW = 412.6 g/mol. Yield: 50%. H NMR (300 MHz, CDCl ): δ
3
1
1
2
58.9; 145.5; 145.2; 134.9; 134.2; 130.9; 130.7; 130.4; 130.3; 129.6;
7.26−7.25 (m, 3H, Ar-H); 7.16−7.13 (m, 3H, Ar-H); 6.93−6.90 (m,
2H, Ar-H); 6.85−6.82 (m, 2H, Ar-H); 6.71 (s, 2H, Ar-H); 4.91 (br s,
1H, NH); 4.49 (br s, 1H, N-CH-CH-N); 4.38 (d, J = 4.5 Hz, 1H, N-
29.3; 127.9; 127.5; 127.4; 127.2; 126.8; 126.5; 73.6; 57.7; 39.6; 28.4;
−
20
D
8.2; 25.9; 24.7; 23.6. ESI+MS: m/z 474.9 (M − BF ). [α]
=
4
+
210.6 (c = 0.5, CH Cl ).
2 2
CH-CH-N); 2.33 (br s, 1H, Cy-H); 2.18 (br s, 9H, Ar-CH ); 1.99 (br
3
1
-Cyclohexyl-3-mesityl-4,5-diphenyl-4,5-dihydro-1H-imidazol-3-
1
s, 1H, Cy-H); 1.71−1.57 (m, 4H, Cy-H); 1.38 (br s, 1H, Cy-H); 1.18−
ium Tetrafluoroborate (16c). MW = 510.4 g/mol. Yield: 79%. H
.13 (m, 5H, Cy-H). 13C{ H} NMR (75 MHz, CDCl ) δ: 142.8;
41.5; 139.7; 129.7; 129.1; 128.4; 128.0; 127.8; 127.5; 127.1; 127.0;
26.9; 66.8; 63.7; 53.2; 35.1; 33.0; 26.3; 25.1; 24.7; 20.5; 19.8. ESI
1
1
1
1
3
NMR (300 MHz, CDCl ): δ 8.45 (s, 1H, N-CH-N); 7.24−7.23 (m,
3
4
(
H, Ar-H); 7.03−6.92 (m, 4H, Ar-H); 6.85−6.72 (m, 4H, Ar-H); 6.61
d, J = 11.8 Hz, 1H, N-CH-CH-N); 5.95 (d, J = 11.8 Hz, 1H, N-CH-
+
+
MS: m/z 413.2 (MH ).
CH-N); 3.63 (t, 1H, Cy-H); 2.48 (s, 3H, Ar-CH ); 2.33−2.20 (s, 3H,
3
General Procedure for the Synthesis of Tetrafluoroborate Salts.
Ar-CH ); 2.17 (s, 3H, Ar-CH ); 1.94−1.77 (m, 3H, Cy-H); 1.63−1.55
3
3
Diamine (1 equiv) and triethyl orthoformate (8 equiv) were
introduced in a flask equipped with a magnetic stirrer and a condenser.
The reaction mixture was stirred at room temperature for a few
minutes. Then ammonium tetrafluoroborate (1.2 equiv) was added
and the solution was heated at 130 °C for 2 h (16a, 21a, 16c, 22) or 8
h (16b, 21b). After that, the condenser was removed in order to
facilitate evaporation of ethanol produced during the reaction. The
crude brownish oil was washed with diethyl ether and purified by flash
column chromatography on silica gel (hexane/ethyl acetate 9/1 to 1/
13
1
(
m, 3H, Cy-H); 1.38−1.21 (m, 3H, Cy-H). C{ H} NMR (100 MHz,
CDCl ) δ: 157.4; 139.4; 135.2; 133.9; 131.9; 131.1; 130.3; 129.9;
3
1
2
29.3; 129.0; 128.9; 128.2; 127.5; 72.6; 67.8; 58.6; 32.3; 31.8; 25.3;
−
5.0; 24.9; 20.9; 19.7; 19.5. ESI+MS: m/z 425.2 (M − BF ).
4
(
4R,5R)-1-Cyclohexyl-3-mesityl-4,5-diphenyl-4,5-dihydro-1H-imi-
dazol-3-ium Tetrafluoroborate (22). MW = 510.4 g/mol. Yield: 75%.
1
H NMR (250 MHz, CDCl ) δ:8.62 (s, 1H, N-CH-N); 7.52−7.32 (m,
3
7
H, Ar-H); 7.18−7.15 (m, 3H, Ar-H); 6.86 (br s, 1H, Ar-H); 6.69 (br
s, 1H, Ar-H); 5.66 (d, J = 8.1 Hz, 1H, N-CH-CH-N); 5.12 (d, J = 7.9
Hz, 1H,, N-CH-CH-N); 3.75−3.66 (br t, 1H, Cy-H); 2.35 (s, 3H, Ar-
1
) to obtain the product as a white solid.
-(2-Isopropylphenyl)-1-neopentyl-4,5-diphenyl-4,5-dihydro-1H-
imidazol-3-ium Tetrafluoroborate (16a). MW = 498.4 g/mol. Yield:
3
CH ); 2.19−2.11 (m, 5H, Cy-H); 1.92−1.84 (m, 1H, Cy-H); 1.75 (s,
3
3
H, Ar-CH ); 1.63 (s, 3H, Ar-CH ); 1.45−1.20 (m, 4H, Cy-H).
3
3
1
8
7
1%. H NMR (400 MHz, CD Cl ): δ 8.70 (s, 1H, N-CH-N); 7.50−
13
1
2
2
C{ H} NMR (100 MHz, CDCl ): δ 156.8; 140.2; 136.3; 134.8;
3
.48 (m, 1H, Ar-H); 7.36−7.35 (m, 2H, Ar-H); 7.25−7.18 (m, 4H, Ar-
1
3
33.7; 130.7; 130.3; 130.2; 129.5; 129.0; 128.6; 127.0; 75.6; 70.4; 58.5;
H); 7.11−6.97 (m, 7H, Ar-H); 6.19 (br t, 1H, N-CH-CH-N); 5.98 (br
t, 1H, N-CH-CH-N); 4.01 (d, J = 14.2 Hz, 1H, N-CH -C(CH ) );
2.3; 31.5; 25.1; 24.8; 21.0; 18.8; 18.0. ESI+MS: m/z 424.5 (M −
−
20
2
3
3
BF ). [α] = +309.8 (c = 0.5, CH Cl ).
4 D 2 2
3
.21−3.11 (m, 2H, N-CH -C(CH ) and Ar-CH-(CH ) ); 1.34−1.29
2
3
3
3
2
General Procedure for the Synthesis of Catalysts. In a glovebox,
potassium hexafluoro-tert-butoxide (1 equiv) was added to a
suspension of tetrafluoroborate salt (1 equiv) in toluene (C = 0.1
M). The reaction mixture was stirred for a few minutes at room
temperature, and then (PCy )Ru(CH-o-OiPrC H )Cl (0.5 equiv)
13 1
(
m, 6H, Ar-CH-(CH ) ); 1.08 (s, 9H, N-CH -C(CH ) ). C{ H}
3 2 2 3 3
NMR (100 MHz, CD Cl ): δ160.6; 145.6; 131.8; 130.9; 130.5; 130.4;
2
2
1
2
29.8; 129.5; 129.4; 128.8; 128.7; 127.9; 127.7; 73.6; 72.2; 58.7; 33.2;
9.0; 27.7; 24.5; 24.1. ESI+MS: m/z 411.4 (M − BF ).
−
4
3
6
4
2
(4R,5R)-3-(2-Isopropylphenyl)-1-neopentyl-4,5-diphenyl-4,5-dihy-
was added. The flask was removed from the glovebox and stirred at 65
dro-1H-imidazol-3-ium Tetrafluoroborate (21a). MW = 498.4 g/
mol. Yield: 90%. H NMR (400 MHz, CD Cl ): δ 8.58 (s, 1H, N-CH-
N); 7.58−7.56 (m, 3H, Ar-H); 7.45−7.34 (m, 7H, Ar-H); 7.27−7.25
°
C for 2.0 h. The reaction mixture was cooled to room temperature
and purified by flash column chromatography on silica gel (hexane/
diethyl ether 5/1 to 1/1).
1
2
2
(
m, 2H, Ar-H); 7.21−7.18 (m, 2H, Ar-H); 5.53 (d, J = 8.0 Hz, 1H, N-
[
3-(2-Isopropylphenyl)-1-neopentyl-4,5-diphenylimidazolidinyl-
CH-CH-N); 5.37 (d, J = 8.0 Hz, 1H, N-CH-CH-N); 3.82 (d, J = 14.9
Hz, 1H, N-CH -C(CH ) ); 3.06 (d, J = 14.9 Hz, 1H, N-CH -
idene]dichloro(2-isopropoxyphenylmethylene)ruthenium (11a).
1
2
3
3
2
MW = 730.8 g/mol. Yield: 45%. H NMR (600 MHz, C D ): δ
6
6
C(CH ) )); 2.96−2.89 (m, 1H, Ar-CH-(CH ) ); 1.23 (d, J = 6.8 Hz,
16.29 (major isomer, s, 1H, RuCH-oOiPrC H ); 16.22 (minor
3
3
3
2
6
4
3
H, Ar-CH-(CH ) ); 1.09 (s, 9H, N-CH -C(CH ) ); 1.02 (d, J = 6.8
isomer, s, 0.3H); (mixed signals of both isomers) 8.96 (d, J = 7.3 Hz,
1H, Ar-H); 7.99 (br s, 1H, Ar-H); 7.94 (br s, 1H, Ar-H); 7.85 (d, J =
6.8 Hz, 1H, Ar-H); 7.20 (d. J = 7.8 Hz, 1H, Ar-H); 7.53−7.50 (m, 3H,
3
2
2
3 3
13
1
Hz, 3H, Ar-CH-(CH ) ). C{ H} NMR (100 MHz, CD Cl ): δ
3
2
2
2
159.3; 145.9; 135.1; 134.7; 131.4; 131.0; 130.9; 130.8; 130.7; 130.3;
L
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Ar-H); 7.37 (br t, 1H, Ar-H); 7.31−7.28 (m, 1H, Ar-H); 7.25−7.23
6.10; N, 3.53. Found: C, 66.70; H, 6.07; N, 3.45. ESI-FT-ICR (11b-
Cl): m/z calcd 757.2499, found 757.2494.
(
br t, 1H, Ar-H); 7.09−7.03 (m, 3H, Ar-H); 6.98 (br s, 3H, Ar-H);
6
.93−6.90 (m, 1H, Ar-H); 6.82−6.65 (m, 5H, Ar-H); 6.48 (d, J = 9.1
[(4R,5R)-3-(2-Isopropylphenyl)-1-(2-methyl-2-phenylpropyl)-4,5-
Hz, 1H, Ar-H); 6.22 (d, J = 7.3 Hz, 1H, Ar-H) (only major isomer
signals are shown below) 5.99 (t, J = 10.0 Hz, 1H, N-CH-CH-N); 5.56
diphenylimidazolidinylidene]dichloro(2-isopropoxyphenyl-
1
methylene)ruthenium (12b). MW = 792.8 g/mol. Yield: 61%. H
NMR (600 MHz, C D ): δ 16.39 (minor isomer, s, 0.1H, RuCH-
(
d, J = 14.6 Hz, 1H, N-CH -(CH ) ); 5.41 (d, J = 10.0 Hz, 1H, N-CH-
6
6
2
3 3
oOiPrC H ); 16.36 (major isomer, s, 1H); (only major isomer signals
CH-N); 4.70 (br s, 1H, O-CH-(CH ) ); 4.13 (d, J = 13.7 Hz, 1H, N-
6
4
3
2
are shown below) 7.50 (d, J = 7.6 Hz, 4H, Ar-H); 7.19−7.15 (m, 5H,
CH -(CH ) ); 3.41 (m, 1H, Ar-CH(CH ) ); 1.77 (s, 6H, O-CH-
2
3
3
3 2
Ar-H); 7.11−7.08 (m, 3H, Ar-H); 7.02−6.98 (m, 3H, Ar-H); 6.91 (d, J
(
CH ) ); 1.24 (s, 9H, N-CH -(CH ) ); 1.18 (br s, 6H, Ar-
3 2 2 3 3
13
1
=
8.1 Hz, 2H, Ar-H); 6.84 (t, J = 7.6 Hz, J = 7.1 Hz, 1H, Ar-H); 6.75
CH(CH ) ). C{ H} NMR (125 MHz, C D ): δ (only major isomer
3
2
6
6
(t, J = 7.6 Hz, 2H, Ar-H); 6.68 (t, J = 7.6 Hz, J = 7.1 Hz, 1H, Ar-H);
signals are shown below) 291.8 (RuCH-oOiPrC H ); 291.2; 216.1;
6
4
6
.50 (d, J = 8.1 Hz, 1H, Ar-H); 5.64 (d, J = 14.2 Hz, 1H, N-CH2-
1
1
1
1
7
5
2
63.7; 163.5; 153.2; 149.1; 148.9; 148.4; 147.3; 144.5; 143.5; 142.4;
41.3; 139.7; 139.2; 138.9; 138.5; 133.8; 133.3; 133.2; 131.2; 130.7;
30.5; 130.4; 130.2; 129.6; 129.4; 129.3; 129.3; 129.0; 128.9; 128.8;
27.7; 128.6; 127.5; 127.2; 127.0; 126.9; 126.8; 126.1; 122.5; 113.2;
8.3; 77.4; 75.5; 75.2; 70.8; 69.8; 68.6; 65.2; 62.5; 62.0; 61.1; 60.2;
9.8; 32.8; 32.7; 31.3; 30.2; 29.4; 29.3; 29.2; 28.8; 27.7; 27.6; 27.3;
5.6; 24.8; 24.5; 24.4; 24.3; 24.2; 23.6; 22.8; 22.2; 22.1. Anal. Calcd for
(
1
CH ) ); 4.79 (d, J = 14.2 Hz, 1H, N-CH -(CH ) ); 4.74−4.71 (m,
3
3
2
3 3
H, O-CH-(CH ) ); 4.70 (d, J = 1.9 Hz, 1H, N-CH-CH-N); 4.60 (d, J
3
2
=
1.9 Hz, 1H, N-CH-CH-N); 3.36−3.31 (m, 1H, Ar-CH(CH ) ); 2.06
3
2
(s, 3H, N-CH -CPh(CH ) ); 1.82 (d, J = 6.2 Hz, 3H, O-CH-(CH ) );
2 3 2 3 2
1
.78 (d, J = 6.2 Hz, 3H, O-CH-(CH ) ); 1.41 (s, 3H, N-CH -
3 2 2
CPh(CH ) ); 1.27 (d, J = 6.6 Hz, 3H, Ar-CH(CH ) ); 0.89 (d, J = 6.6
3
2
3 2
13
1
Hz, 3H, Ar-CH(CH ) ). C{ H} NMR (125 MHz, C D ): δ (only
C H Cl N ORu (730.77): C, 64.10; H, 6.34; N, 3.83. Found: C,
3
2
6
6
39
46
2
2
major isomer signals are shown below) 291.6 (RuCH-oOiPrC H );
6
3.88; H, 6.37; N, 3.71. ESI-FT-ICR (11a-Cl): m/z calcd 695.2342,
6
4
2
1
13.8; 153.6; 148.5; 147.7; 144.7; 139.8; 139.7; 139.5; 133.2; 129.6;
29.5; 129.5; 129.3; 129.2; 127.9; 127.3; 127.1; 126.5; 126.4; 126.2;
found 695.2339.
[
(4R,5R)-3-(2-Isopropylphenyl)-1-neopentyl-4,5-diphenyl-
imidazolidinylidene]dichloro(2-isopropoxyphenylmethylene)-
122.9; 122.6; 113.5; 80.4; 75.5; 72.8; 63.4; 40.0; 32.3; 32.2; 27.9; 27.8;
25.7; 24.9; 24.8; 23.6; 23.4; 22.6; 22.6; 22.5; 22.4. Anal. Calcd for
C H Cl N ORu (792.84): C, 66.66; H, 6.10; N, 3.53. Found: C,
1
ruthenium (12a). MW = 730.8 g/mol. Yield: 70%. H NMR (600
MHz, C D ): δ 16.38 (minor isomer, s, 0.1H, RuCH-oOiPrC H );
6
6
6
4
44 48
2
2
16.38 (major isomer, s, 1H); (only major isomer signals are shown
66.69; H, 6.14; N, 3.44. ESI-FT-ICR (12b-Cl): m/z calcd 757.2499,
below) 7.75 (br s, 2H, Ar-H); 7.56 (d, J = 6.8 Hz, 2H, Ar-H); 7.43 (d.
J = 8.1 Hz, 1H, Ar-H); 7.30 (t, J = 7.5 Hz, J = 7.5 Hz, 2H, Ar-H);
found 757.2505.
[1-Cyclohexyl-3-mesityl-4,5-diphenylimidazolidinylidene]-
dichloro(2-isopropoxyphenylmethylene)ruthenium (11c). MW =
7
.19−7.08 (m, 5H, Ar-H); 7.02−6.98 (m, 3H, Ar-H); 6.67 (t, J = 7.4
Hz, J = 7.4 Hz, 1H, Ar-H); 6.57 (t, J = 7.4 Hz, J = 7.4 Hz, 1H, Ar-H);
.47 (d, J = 8.3 Hz, 1H, Ar-H); 5.42 (d, J = 13.5 Hz, 1H, N-CH2-
CH ) ); 5.26 (d, J = 2.7 Hz, 1H, N-CH-CH-N); 4.86 (d, J = 2.7 Hz,
742.8 g/mol. Yield: 63%. 1H NMR (600 MHz, C
D
): δ 16.56
H ); 16.44 (minor isomer, s,
6 4
6
6
6
(
(major isomer, s, 1H, RuCH-oOiPrC
0.1H); 8.78 (br s, 1H, Ar-H); 7.37 (br s, 1H, Ar-H); 7.15−7.12 (m,
2H, Ar-H); 7.00 (t, J = 7.5 Hz, J = 7.5 Hz, 1H); 6.78 (br s, 1H, Ar-H);
6.70−6.67 (m, 5H, Ar-H); 6.62−6.60 (m, 3H, Ar-H); 6.56 (br s, 1H,
Ar-H); 6.47 (d, J = 8.3 Hz, 1H, Ar-H); 6.27 (br s, 1H, Ar-H); (only
major isomer signals are shown below) 6.04 (d, J = 9.3 Hz, 1H, N-CH-
3
3
1
1
1
H, N-CH-CH-N); 4.71−4.67 (m, 1H, O-CH-(CH ) ); 4.16 (d, J =
3
2
4.8 Hz, 1H, N-CH -(CH ) ); 3.47−3.43 (m, 1H, Ar-CH(CH ) );
2
3
3
3 2
.78 (d, J = 6.0 Hz, 3H, O-CH-(CH ) ); 1.72 (d, J = 6.0 Hz, 3H, O-
3
2
CH-(CH ) ); 1.28 (d, J = 7.0 Hz, 3H, Ar-CH(CH ) ); 1.10 (s, 9H, N-
3
2
3 2
13
1
CH -(CH ) ); 0.97 (d, J = 7.0 Hz, 3H, Ar-CH(CH ) ). C{ H} NMR
CH-N); 5.72 (t t, J = 3.1 Hz, J = 3.4 Hz, 1H, O-CH-(CH ) ); 5.04 (d,
3 2
2
3
3
3 2
(
125 MHz, C D ): δ (only major isomer signals are shown below)
J = 9.0 Hz, 1H, N-CH-CH-N); 4.73−4.68 (m, 1H, Cy-H); 3.07 (d, J =
11.5 Hz, 1H, Cy-H); 2.86 (d, J = 12.4 Hz, 1H, Cy-H); 2.63 (s, 3H, Ar-
6
6
2
1
1
3
1
6
91.7 (RuCH-oOiPrC H ); 214.4; 153.6; 148.5; 144.7; 140.3;
6
4
39.6; 139.4; 133.3; 129.9; 129.7; 129.6; 129.5; 129.4; 129.0; 127.3;
27.2; 127.1; 122.8; 122.6; 113.5; 80.7; 75.4; 73.9; 63.3; 63.2; 33.9;
2.2; 29.8; 28.0; 27.9; 24.9; 24.8; 23.8; 23.7; 23.3; 22.6; 22.6; 22.4;
4.7; 14.5. Anal. Calcd for C H Cl N ORu (730.77): C, 64.10; H,
CH
Cy-H); 1.81 (d, J = 6.1 Hz, 3H, O-CH-(CH
3H, O-CH-(CH ); 1.76−1.73 (m, 1H, Cy-H); 1.67−1.59 (m, 3H,
Cy-H); 1.12−1.06 (m, 1H, Cy-H); 0.97−0.87 (m, 1H, Cy-H).
3
); 2.43 (s, 3H, Ar-CH
3
); 1.95 (s, 3H, Ar-CH
3
); 1.88−1.84 (m, 2H,
)
3 2
); 1.78 (d, J = 6.1 Hz,
)
3 2
39
46
2
2
13
1
.34; N, 3.83. Found: C, 64.12; H, 6.31; N, 3.76. ESI-FT-ICR (12a-
C{ H} NMR (125 MHz, C D ): δ (only major isomer signals are
6 6
Cl): m/z calcd 695.2342, found 695.2344.
shown below) 290.9 (RuCH-oOiPrC H ); 214.0; 152.9; 145.0;
6
4
[
3-(2-Isopropylphenyl)-1-(2-methyl-2-phenylpropyl)-4,5-
139.9; 138.1; 138.0; 137.5; 136.8; 133.1; 130.6; 129.6; 129.5; 129.2;
122.6; 122.5; 113.2; 75.6; 74.9; 64.9; 63.7; 33.7; 33.4; 33.3; 26.8; 26.6;
diphenylimidazolidinylidene]dichloro(2-isopropoxyphenyl-
1
methylene)ruthenium (11b). MW = 792.8 g/mol. Yield: 70%. H
2
2.3; 20.8; 20.8; 20.3; 20.2. Anal. Calcd for C H Cl N ORu
40 46 2 2
NMR (600 MHz, C D ): δ 16.31 (major isomer, s, 1H, RuCH-
6
6
(742.78): C, 64.68; H, 6.24; N, 3.77. Found: C, 64.62; H, 6.27; N,
3.81. ESI-FT-ICR (11c-Cl): m/z calcd 707.2342, found 707.2339.
oOiPrC H ); 16.36 (minor isomer, s, 0.2H); (only major isomer
6
4
signals are shown below) 8.88 (d, J = 8.3 Hz, 1H, Ar-H); 7.50−7.47
[
(4R,5R)-1-Cyclohexyl-3-mesityl-4,5-diphenylimidazol-
(
m, 2H, Ar-H); 7.28−7.23 (m, 1H, Ar-H); 7.18−7.17 (m, 1H, Ar-H);
idinylidene]dichloro(2-isopropoxyphenylmethylene)ruthenium
1
7
1
6
.09−7.03 (m, 3H, Ar-H); 7.01−6.95 (m, 4H, Ar-H); 6.93−6.91 (m,
H, Ar-H); 6.86−6.85 (m, 3H, Ar-H); 6.73−6.67 (m, 1H, Ar-H);
.59−6.56 (m, 5H, Ar-H); 6.50 (d, J = 8.5 Hz, 1H, Ar-H); 6.47−6.44
(12c). MW = 742.8 g/mol. Yield: 54%. H NMR (600 MHz, C D ): δ
6
6
16.44 (s, 1H, RuCH-oOiPrC H ); 7.14−7.08 (m, 6H, Ar-H); 7.05
6
4
(t, J = 7.3 Hz, J = 7.3 Hz, 1H, Ar-H); 7.00−6.94 (m, 5H, Ar-H); 6.78
(br s, 1H, Ar-H); 6.68 (t, J = 7.3 Hz, J = 7.5 Hz 1H, Ar-H); 6.57 (br s,
1H, Ar-H); 6.46 (d, J = 8.2 Hz, 1H, Ar-H); 5.70 (t t, J = 3.1 Hz, J = 3.0
Hz, 1H, Cy-H); 5.48 (d, J = 6.4 Hz, 1H, N-CH-CH-N); 4.78 (d, J =
6.8 Hz, 1H, N-CH-CH-N); 4.71−4.67 (m, 1H, O-CH-(CH ) ); 3.10
(
m, 1H, Ar-H); 5.90 (d, J = 9.7 Hz, 1H, N-CH -(CH ) ); 5.82 (d, J =
2 3 3
13.6 Hz, 1H, N-CH-CH-N); 4.91 (d, J = 9.7 Hz, 1H, N-CH -(CH ) );
2 3 3
4
.80 (d, J = 13.6 Hz, 1H, N-CH-CH-N); 4.75−4.71 (m, 1H, O-CH-
(
CH ) ); 3.42−3.38 (m, 1H, Ar-CH(CH ) ); 2.09 (s, 3H, N-CH -
3
2
3
2
2
3 2
CPh(CH ) ); 1.82−1.80 (m, 6H, O-CH-(CH ) ); 1.45 (s, 3H, N-
CH -CPh(CH ) ); 1.20 (d, J = 7.2 Hz, 3H, Ar-CH(CH ) ); 1.15 (d, J
(d, J = 11.1 Hz, 1H, Cy-H); 2.85 (d, J = 12.4 Hz, 1H, Cy-H); 2.54 (s,
3H, Ar-CH ); 2.07 (s, 3H, Ar-CH ); 1.96−1.88 (m, 2H, Cy-H); 1.79−
3
2
3 2
2
3
2
3
2
3
3
13
1
=
7.2 Hz, 3H, Ar-CH(CH ) ). C{ H} NMR (125 MHz, C D ): δ
1.77 (m, 9H, Ar-CH and O-CH-(CH ) ); 1.63−1.58 (m, 3H Cy-H);
3
2
6
6
3
3 2
13 1
(
mixed signals of both isomers) 292.1; 291.6; 220.6; 215.9; 163.9;
1.00−0.86 (m, 3H Cy-H). C{ H} NMR (125 MHz, C D ): δ 290.2
6
6
1
1
1
1
6
3
2
63.7; 153.6; 149.1; 148.5; 148.3; 144.8; 144.5; 141.7; 139.5; 134.1;
33.4; 133.2; 131.4; 130.5; 130.2; 129.8; 129.7; 129.5; 129.3; 129.1;
29.0; 128.8; 128.0; 127.9; 127.9; 127.7; 127.5; 127.1; 127.0; 126.3;
26.3; 126.2; 122.8; 113.5; 78.6; 77.5; 77.4; 75.8; 75.5; 75.4; 70.2;
9.1; 68.7; 65.2; 62.7; 62.2; 61.2; 60.5; 60.1; 39.6; 39.5; 38.9; 34.0;
2.0; 30.5; 29.1; 29.0; 28.6; 28.5; 27.9; 24.8; 24.6; 24.5; 24.5; 24.4;
2.6; 22.5. Anal. Calcd for C H Cl N ORu (792.84): C, 66.66; H,
(RuCH-oOiPrC H ); 211.8; 153.3; 145.2; 143.3; 141.0; 139.2;
6
4
138.8; 137.5; 130.4; 130.2; 129.7; 129.4; 129.3; 129.3; 129.1; 128.9;
122.8; 122.7; 113.5; 79.3; 75.2; 69.6; 64.2; 34.5; 34.3; 32.3; 32.2; 27.4;
26.9; 26.2; 26.1; 22.7; 22.6; 21.3; 21.2; 21.2; 21.1; 20.0; 19.9; 19.5.
Anal. Calcd for C H Cl N ORu (742.78): C, 64.68; H, 6.24; N, 3.77.
4
0
46
2
2
Found C, 64.57; H, 6.34; N, 3.68. ESI-FT-ICR (12c-Cl): m/z calcd
707.2342, found 707.2362.
44
48
2
2
M
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
General Procedures for RCM Reactions. An NMR tube with a
screw-cap septum top was charged with 0.80 mL of a solution of the
catalyst (1−5%) in C D . After equilibration of the sample at 60 °C in
product. The reaction mixture was filtered on neutral alumina and
injected into the GC system without further purifications.
AROCM of 48 with Styrene (Scheme 6, Table 6). Under a
nitrogen atmosphere, 48 (0.43 mol) and styrene (4.3 mmol) were
simultaneously added to 7.5 mL of a CH Cl solution of the catalyst (3
2 2
6
6
the NMR probe, 0.080 mmol of substrate (0.1 M) was injected into
the tube. Conversions of each substrate were monitored over time by
1
H NMR.
mol %). The reaction mixture was stirred at room temperature for 3 h
and then concentrated and purified via column chromatography
RCM of Diethyl Diallylmalonate (23) (Figure 5A). A 19.3 μL
portion of 23 was injected into a heated NMR tube containing 0.80
mL of catalyst solution (1 mol %). The conversion to 24 was
determined by integrating the methylene protons of the reagent at δ
(
petroleum ether/diethyl ether 1/1) to afford the product as a
transparent oil. About 1.3 mg of the product was dissolved in 2 mL of
hexane/2-propanol 1/1 (HPLC grade purity), filtered using a syringe
filter, and then injected into the HPLC system.
2.84 (dt) and of the product at δ 3.14 (s).
RCM of N-Tosyldiallylamine (25) (Figure 5B). A 17.2 μL portion of
5 was injected into a heated NMR tube containing 0.80 mL of
catalyst solution (1 mol %). The conversion to 26 was determined by
integrating the methylene protons of the reagent at δ 3.71 (d) and of
the product at δ 3.90 (s).
RCM of Diethyl Allylmethallylmalonate (27) (Figure 6A). A 20.5
μL portion of 27 was injected into a heated NMR tube containing 0.80
mL of catalyst solution (1 mol %). The conversion to 28 was
determined by integrating the methylene protons of the reagent at δ
.96(d), 2.93 (s) and of the product at δ 3.18 (m), 3.07 (s).
RCM of N-Tosylallylmethallylamine (29) (Figure 6B). A 19.4 μL
portion of 29 was injected into a heated NMR tube containing 0.80
mL of catalyst solution (1 mol %). The conversion to 30 was
determined by integrating the methylene protons of the reagent at δ
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00488.
2
■
*
S
Experimental procedures, figures giving NMR spectra of
the new complexes, GC and HPLC chromatograms of
ethenolysis reaction mixture, 46, 47, and 49, and
experimental details for complexes 47 and 48 (PDF)
Cartesian coordinates for the optimized structures
2
(XYZ)
3
.70(d), 3.67 (s) and of the product at δ 3.96 (m), 3.82 (s).
RCM of Diethyl Dimethallylmalonate (31) (Figure 7A). A 21.6 μL
Accession Codes
CCDC 1533652−1533654 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.
portion of 31 was injected into a heated NMR tube containing 0.80
mL of catalyst solution (5 mol %). The conversion to 32 was
determined by integrating the methylene protons of the reagent at δ
2.98 (s) and of the product at δ 3.15 (s).
RCM of N-Tosyldimethallylamine (33)(Figure 7B). A 20.2 μL
portion of 33 was injected into a heated NMR tube containing 0.80
mL of catalyst solution (5 mol %). The conversion to 34 was
determined by integrating the methylene protons of the reagent at δ
AUTHOR INFORMATION
Corresponding Author
*E-mail for F.G.: fgrisi@unisa.it.
■
3.69 (s) and of the product at δ 3.90 (s).
CM of Allylbenzene (35) and cis-1,4-Diacetoxy-2-butene
36) (Scheme 3, Table 3). Under a nitrogen atmosphere, 66 μL of 35
(
ORCID
and 160 μL of 36 were added simultaneously to a solution of the
catalyst (2.5 mol %) in dry methylene chloride. The reaction mixture
was refluxed under nitrogen overnight and then purified by column
chromatography with hexane/ethyl acetate 9/1 as eluent. Products 37
and 38 were obtained as transparent oils, and E/Z ratios were
Chiara Costabile: 0000-0001-8538-7125
Fabia Grisi: 0000-0003-3904-9541
Notes
The authors declare no competing financial interest.
1
determined by H NMR.
Ethenolysis of 39 (Scheme 4, Table 4). Under a nitrogen
atmosphere, in an autoclave, 39 (5.4 mmol) and dodecane (150 μL)
were introduced. At this point, a t = 0 sample was prepared. The
autoclave was purged with ethylene three times, and then a toluene
solution of the catalyst (20 to 500 ppm) was added. The autoclave was
purged with ethylene three times and then charged with a pressure of
ACKNOWLEDGMENTS
The authors thank Dr. Patrizia Iannece, Dr. Ivano Immediata,
and Patrizia Oliva for technical assistance. This work was
■
̀
financed by the Ministero dell’Universita e della Ricerca
Scientifica e Tecnologica. Financial support from POR
C A M P A NI A F E S R 2 0 0 7 /2 0 1 3 O . O . 2 . 1 . - C U P
B46D14002660009 “Il potenziamento e la riqualificazione del
sistema delle infrastrutture nel settore dell’istruzione, della
formazione e della ricerca” is gratefully acknowledged. M.D.
and K.G. acknowledge the National Science Centre (Poland)
for the NCN MAESTRO Grant No. DEC-2012/04A/ST5/
150 psi. The reaction mixture was stirred at 50 or 40 °C for 3 or 2 h
and then cooled in an ice bath and quenched with ethyl vinyl ether.
After that, GC samples were prepared in hexane. Samples were stored
at −20 °C until GC analysis.
ARCM of 44 and 45 without Additive (Scheme 5, Table 5).
Under a nitrogen atmosphere, the prochiral triene (0.11 mmol) was
added to 2 mL of a CD Cl solution of the catalyst (2.5 mol %). A
2
2
0
0594.
portion of the reaction mixture was transferred in a NMR tube with a
J. Young valve and heated at 40 °C for 2 h for 44 and for 3 h for 45.
Yields were determined via NMR spectroscopy of the crude product.
The reaction mixture was filtered on neutral alumina and injected into
the GC system without further purifications.
ARCM of 44 and 45 with NaI (Scheme 5, Table 5). Under a
nitrogen atmosphere, NaI (0.055 mmol) was added to 1 mL of a THF-
d8 solution of the catalyst (4.0 mol %). The reaction mixture was
stirred at room temperature for 1 h. Then, the prochiral triene (0.055
mmol) was added and then the mixture was transferred to an NMR
tube with a J. Young valve and heated at 40 °C for 2 h for 44 and for 3
h for 45. Yields were determined via NMR spectroscopy of the crude
REFERENCES
■
(1) (a) Grela, K. Olefin Metathesis: Theory and Practice; Wiley:
Hoboken, NJ, 2014. (b) Grubbs, R. H.; Wenzel, A. G.; O’Leary, D. J.;
Khosravi, E. Handbook of Metathesis, 2nd ed.; Wiley-VCH: Weinheim,
Germany, 2015.
(2) (a) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Synthesis and
Activity of a New Generation of Ruthenium-Based Olefin Metathesis
Catalysts Coordinated with 1,3-Dimesityl-4,5-dihydroimidazol-2-yli-
dene Ligands. Org. Lett. 1999, 1 (6), 953−956. (b) Garber, S. B.;
Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H. Efficient and Recyclable
N
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Monomeric and Dendritic Ru-Based Metathesis Catalysts. J. Am.
Chem. Soc. 2000, 122 (34), 8168−8179. (c) Jafarpour, L.; Schanz, H.
J.; Stevens, E. D.; Nolan, S. P. Indenylidene−Imidazolylidene
Complexes of Ruthenium as Ring-Closing Metathesis Catalysts.
Organometallics 1999, 18 (25), 5416−5419.
Ligands. Organometallics 2006, 25 (1), 25−28. (c) Ledoux, N.;
Allaert, B.; Pattyn, S.; Mierde, H. V.; Vercaemst, C.; Verpoort, F. N,N′-
Dialkyl- and N-Alkyl-N-mesityl-Substituted N-Heterocyclic Carbenes
as Ligands in Grubbs Catalysts. Chem. - Eur. J. 2006, 12 (17), 4654−
4661. (d) Thomas, R. M.; Keitz, B. K.; Champagne, T. M.; Grubbs, R.
H. Highly Selective Ruthenium Metathesis Catalysts for Ethenolysis. J.
Am. Chem. Soc. 2011, 133 (19), 7490−7496. (e) Ablialimov, O.;
(
3) (a) Cossy, J.; Arseniyadis, S.; Meyer, C. Metathesis in Natural
Product Synthesis; Wiley-VCH: Weinheim, Germany, 2010. (b) Nickel,
A.; Ung, T.; Mkrtumyan, G.; Uy, J.; Lee, C.; Stoianova, D.; Papazian,
J.; Wei, W.-H.; Mallari, A.; Schrodi, Y.; Pederson, R. L A. Highly
Efficient Olefin Metathesis Process for the Synthesis of Terminal
Alkenes from Fatty Acid Esters. Top. Catal. 2012, 55 (7), 518−523.
́
́
Kędziorek, M.; Torborg, C.; Malinska, M.; Wozniak, K.; Grela, K. New
Ruthenium(II) Indenylidene Complexes Bearing Unsymmetrical N-
Heterocyclic Carbenes. Organometallics 2012, 31 (21), 7316−7319.
(f) Rouen, M.; Borre, E.; Falivene, L.; Toupet, L.; Berthod, M.;
Cavallo, L.; Olivier-Bourbigou, H.; Mauduit, M. Cycloalkyl-based
unsymmetrical unsaturated (U2)-NHC ligands: flexibility and
dissymmetry in ruthenium-catalysed olefin metathesis. Dalton Trans.
2014, 43 (19), 7044−7049. (g) Yu, B.; Hamad, F. B.; Sels, B.; Van
Hecke, K.; Verpoort, F. Ruthenium indenylidene complexes bearing
N-alkyl/N-mesityl-substituted N-heterocyclic carbene ligands. Dalton
Trans. 2015, 44 (26), 11835−11842.
(
c) Chikkali, S.; Mecking, S. Refining of Plant Oils to Chemicals by
Olefin Metathesis. Angew. Chem., Int. Ed. 2012, 51 (24), 5802−5808.
d) de Espinosa, L. M.; Meier, M. A. R. Olefin Metathesis of
Renewable Platform Chemicals. Top. Organomet. Chem. 2012, 39, 1−
4. (e) Higman, C. S.; Lummiss, J. A. M.; Fogg, D. E. Olefin
(
4
Metathesis at the Dawn of Implementation in Pharmaceutical and
Specialty-Chemicals Manufacturing. Angew. Chem., Int. Ed. 2016, 55
(
11), 3552−3565. (f) Bidange, J.; Fischmeister, C.; Bruneau, C.
(8) (a) Van Veldhuizen, J. J.; Gillingham, D. G.; Garber, S. B.;
Kataoka, O.; Hoveyda, A. H. Chiral Ru-Based Complexes for
Asymmetric Olefin Metathesis: Enhancement of Catalyst Activity
through Steric and Electronic Modifications. J. Am. Chem. Soc. 2003,
125 (41), 12502−12508. (b) Fournier, P.-A.; Collins, S. K. A Highly
Active Chiral Ruthenium-Based Catalyst for Enantioselective Olefin
Metathesis. Organometallics 2007, 26 (12), 2945−2949. (c) Tiede, S.;
Ethenolysis: A Green Catalytic Tool to Cleave Carbon-Carbon
Double Bonds. Chem. - Eur. J. 2016, 22 (35), 12226−12244.
(
́
g) Rouen, M.; Queval, P.; Borre, E.; Falivene, L.; Poater, A.;
́
Berthod, M.; Hugues, F.; Cavallo, L.; Basle, O.; Olivier-Bourbigou, H.;
Mauduit, M. Selective Metathesis of α-Olefins from Bio-Sourced
Fischer−Tropsch Feeds. ACS Catal. 2016, 6 (11), 7970−7976.
(
4) (a) Vougioukalakis, G. C.; Grubbs, R. H. Ruthenium-Based
̈
Berger, A.; Schlesiger, D.; Rost, D.; Luhl, A.; Blechert, S. Highly Active
Heterocyclic Carbene-Coordinated Olefin Metathesis Catalysts. Chem.
Rev. 2010, 110 (3), 1746−1787. (b) Samojlowicz, C.; Bieniek, M.;
Grela, K. Ruthenium-Based Olefin Metathesis Catalysts Bearing N-
Heterocyclic Carbene Ligands. Chem. Rev. 2009, 109 (8), 3708−3742.
Chiral Ruthenium-Based Metathesis Catalysts through a Monosub-
stitution in the N-Heterocyclic Carbene. Angew. Chem., Int. Ed. 2010,
49 (23), 3972−3975. (d) Hartung, J.; Dornan, P. K.; Grubbs, R. H.
Enantioselective Olefin Metathesis with Cyclometalated Ruthenium
Complexes. J. Am. Chem. Soc. 2014, 136 (37), 13029−13037.
(9) (a) Vehlow, K.; Wang, D.; Buchmeiser, M. R.; Blechert, S.
Alternating Copolymerizations Using a Grubbs-Type Initiator with an
Unsymmetrical, Chiral N-Heterocyclic Carbene Ligand. Angew. Chem.,
Int. Ed. 2008, 47 (14), 2615−2618. (b) Engl, P. S.; Fedorov, A.;
Coperet, C.; Togni, A. N-Trifluoromethyl NHC Ligands Provide
Selective Ruthenium Metathesis Catalysts. Organometallics 2016, 35
(6), 887−893.
(
c) Paradiso, V.; Costabile, C.; Grisi, F. NHC backbone configuration
in ruthenium-catalyzed olefin metathesis. Molecules 2016, 21 (1), 117−
36.
5) (a) Chung, C. K.; Grubbs, R. H. Olefin Metathesis Catalyst:
1
(
Stabilization Effect of Backbone Substitutions of N-Heterocyclic
Carbene. Org. Lett. 2008, 10 (13), 2693−2696. (b) Kuhn, K. M.;
Bourg, J.-B.; Chung, C. K.; Virgil, S. C.; Grubbs, R. H. Effects of NHC-
Backbone Substitution on Efficiency in Ruthenium-Based Olefin
Metathesis. J. Am. Chem. Soc. 2009, 131 (14), 5313−5320. (c) Grisi,
F.; Mariconda, A.; Costabile, C.; Bertolasi, V.; Longo, P. Influence of
syn and anti Configurations of NHC Backbone on Ru-Catalyzed
Olefin Metathesis. Organometallics 2009, 28 (17), 4988−4995.
(10) Kavitake, S.; Samantaray, M. K.; Dehn, R.; Deuerlein, S.;
́
Limbach, M.; Schachner, J. A.; Jeanneau, E.; Coperet, C.; Thieuleux, C.
Unsymmetrical Ru-NHC catalysts: a key for the selective tandem Ring
Opening−Ring Closing alkene Metathesis (RO−RCM) of cyclo-
octene. Dalton Trans. 2011, 40 (46), 12443−12446.
(
d) Costabile, C.; Mariconda, A.; Cavallo, L.; Longo, P.; Bertolasi,
V.; Ragone, F.; Grisi, F. The Pivotal Role of Symmetry in the
Ruthenium-Catalyzed Ring-Closing Metathesis of Olefins. Chem. - Eur.
J. 2011, 17 (31), 8618−8629. (e) Perfetto, A.; Costabile, C.; Longo,
P.; Bertolasi, V.; Grisi, F. Probing the Relevance of NHC Ligand
Conformations in the Ru-Catalysed Ring-Closing Metathesis Reaction.
Chem. - Eur. J. 2013, 19 (32), 10492−10496. (f) Borguet, Y.; Zaragoza,
G.; Demonceau, A.; Delaude, L. Ruthenium catalysts bearing a
benzimidazolylidene ligand for the metathetical ring-closure of
tetrasubstituted cycloolefins. Dalton Trans. 2015, 44 (21), 9744−9755.
(11) Herbert, M. B.; Grubbs, R. H. Z-Selective Cross Metathesis with
Ruthenium Catalysts: Synthetic Applications and Mechanistic
Implications. Angew. Chem., Int. Ed. 2015, 54 (17), 5018−5024.
́
́
(12) (a) Ablialimov, O.; Kędziorek, M.; Malinska, M.; Wozniak, K.;
Grela, K. Synthesis, Structure, and Catalytic Activity of New
Ruthenium(II) Indenylidene Complexes Bearing Unsymmetrical N-
Heterocyclic Carbenes. Organometallics 2014, 33 (9), 2160−2171.
(b) Smolen
́ ́ ́
, M.; Kosnik, W.; Loska, R.; Gajda, R.; Malinska, M.;
Wozniak, K.; Grela, K. Synthesis and catalytic activity of ruthenium
́
(
6) (a) Tornatzky, J.; Kannenberg, A.; Blechert, S. New catalysts with
indenylidene complexes bearing unsymmetrical NHC containing a
heteroaromatic moiety. RSC Adv. 2016, 6 (80), 77013−77019.
(13) (a) Paradiso, V.; Bertolasi, V.; Grisi, F. Novel Olefin Metathesis
Ruthenium Catalysts Bearing Backbone Substituted Unsymmetrical
NHC Ligands. Organometallics 2014, 33 (21), 5932−5935. (b) Para-
diso, V.; Bertolasi, V.; Costabile, C.; Grisi, F. Ruthenium olefin
metathesis catalysts featuring unsymmetrical N-heterocyclic carbenes.
Dalton Trans. 2016, 45 (2), 561−571.
unsymmetrical N-heterocyclic carbene ligands. Dalton Trans. 2012, 41
(
27), 8215−8225. (b) Hamad, F. B.; Sun, T.; Xiao, S.; Verpoort, F.
Olefin metathesis ruthenium catalysts bearing unsymmetrical hetero-
cylic carbenes. Coord. Chem. Rev. 2013, 257 (15−16), 2274−2292.
(
c) Shahane, S.; Bruneau, C.; Fischmeister, C. Z Selectivity: Recent
Advances in one of the Current Major Challenges of Olefin
Metathesis. ChemCatChem 2013, 5 (12), 3436−3459. (d) Montgom-
ery, T. P.; Johns, A. M.; Grubbs, R. H. Recent Advancements in
Stereoselective Olefin Metathesis Using Ruthenium Catalysts.
Catalysts 2017, 7 (3), 87−124.
(14) Parsons, S.; Flack, H.; Wagner, T. Use of intensity quotients and
differences in absolute structure refinement. Acta Crystallogr., Sect. B:
Struct. Sci., Cryst. Eng. Mater. 2013, 69, 249−259.
(15) Burnett, M. N.; Johnson, C. K. ORTEP III; Oak Ridge National
Laboratory, Oak Ridge, TN, 1996; Report ORNL-6895.
(
7) Selected examples of N-alkyl/N-aryl NHC-Ru complexes:
(
a) Dinger, M. B.; Nieczypor, P.; Mol, J. C. Adamantyl-Substituted
N-Heterocyclic Carbene Ligands in Second-Generation Grubbs-Type
(16) Dichloro[1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene]
Metathesis Catalysts. Organometallics 2003, 22 (25), 5291−5296.
(2-isopropoxyphenyl methylene)ruthenium(II) (HGII).
(17) Under the employed conditions, after 1 month 100% of 11c and
12c still persisted, while 79% of HGII was undecomposed.
(
b) Vehlow, K.; Maechling, S.; Blechert, S. Ruthenium Metathesis
Catalysts with Saturated Unsymmetrical N-Heterocyclic Carbene
O
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
18) Małecki, P.; Gajda, K.; Ablialimov, O.; Malin
́
́
Commun. 2013, 49, 9491−9493. (e) Marx, V. M.; Sullivan, A. H.;
Melaimi, M.; Virgil, S. C.; Keitz, B. K.; Weinberger, D. S.; Bertrand, G.;
Grubbs, R. H. Cyclic alkyl amino carbene (CAAC) ruthenium
complexes as remarkably active catalysts for ethenolysis. Angew. Chem.,
Int. Ed. 2015, 54 (6), 1919−1923. (f) Gawin, R.; Kozakiewicz, A.;
Wozniak, K.; Kajetanowicz, A.; Grela, K. Hoveyda-Grubbs Type
Precatalysts with Unsymmetrical N-Heterocyclic Carbenes as Effective
Catalysts in Olefin Metathesis. Organometallics 2017, 36 (11), 2153−
2166.
(
19) Wu. M, M.; Gill, A. M.; Yunpeng, L.; Falivene, L.; Yongxin, L.;
́
Gunka, P. A.; Dąbrowski, P.; Skowerski, K. Bis(Cyclic Alkyl Amino
Ganguly, R.; Cavallo, L.; Garcìa, F. Synthesis, structural studies and
ligand influence on the stability of aryl-NHC stabilized trimethylalu-
minium complexes. Dalton Trans. 2015, 44 (34), 15166−15174.
Carbene) Ruthenium Complexes: A Versatile, Highly Efficient Tool
for Olefin Metathesis. Angew. Chem., Int. Ed. 2017, 56 (4), 981−986.
(30) Only enantiopure anti catalysts were tested due to the difficulty
in separating racemic mixtures of syn isomers, although preliminary
studies to evaluate the effect of syn and anti stereochemical
relationships of substituents on the backbone of uNHC have been
undertaken by some of us. See: Paradiso, V.; Menta, S.; Pierini, M.;
Della Sala, G.; Ciogli, A.; Grisi, F. Enantiopure C1-symmetric N-
Heterocyclic Carbene Ligands from desymmetrized meso-1,2-
Diphenylethylenediamine: Application in Ruthenium- Catalyzed
Olefin Metathesis. Catalysts 2016, 6 (11), 177.
(
20) Falivene, L.; Credendino, R.; Poater, A.; Petta, A.; Serra, L.;
Oliva, R.; Scarano, V.; Cavallo, L. SambVca 2. A Web Tool for
Analyzing Catalytic Pockets with Topographic Steric Maps. Organo-
metallics 2016, 35 (13), 2286−2293.
(
21) (a) Dorta, R.; Stevens, E. D.; Scott, N. M.; Costabile, C.;
Cavallo, L.; Hoff, C. D.; Nolan, S. P. Steric and Electronic Properties
of N-Heterocyclic Carbenes (NHC): A Detailed Study on Their
Interaction with Ni(CO) . J. Am. Chem. Soc. 2005, 127 (8), 2485−
4
2495. (b) Cavallo, L.; Correa, A.; Costabile, C.; Jacobsen, H. Steric and
(31) (a) Seiders, T. J.; Ward, D. W.; Grubbs, R. H. Enantioselective
Ruthenium-Catalyzed Ring-Closing Metathesis. Org. Lett. 2001, 3
(20), 3225−3228. (b) Funk, T. W.; Berlin, J. M.; Grubbs, R. H. Highly
Active Chiral Ruthenium Catalysts for Asymmetric Ring-Closing
Olefin Metathesis. J. Am. Chem. Soc. 2006, 128 (6), 1840−1846.
(32) Stenne, B.; Timperio, J.; Savoie, J.; Dudding, T.; Collins, S. K.
Desymmetrizations Forming Tetrasubstituted Olefins Using Enantio-
selective Olefin Metathesis. Org. Lett. 2010, 12 (9), 2032−2035.
(33) (a) Van Veldhuizen, J. J.; Garber, S. B.; Kingsbury, J. S.;
Hoveyda, A. H. A Recyclable Chiral Ru Catalyst for Enantioselective
Olefin Metathesis. Efficient Catalytic Asymmetric Ring-Opening/
Cross Metathesis in Air. J. Am. Chem. Soc. 2002, 124 (18), 4954−4955.
(b) Berlin, J. M.; Goldberg, S. D.; Grubbs, R. H. Highly Active Chiral
Ruthenium Catalysts for Asymmetric Cross- and Ring-Opening Cross-
Metathesis. Angew. Chem., Int. Ed. 2006, 45 (45), 7591−7595.
electronic effects in the bonding of N-heterocyclic ligands to transition
metals. J. Organomet. Chem. 2005, 690 (24−25), 5407−5413.
c) Jacobsen, H.; Correa, A.; Poater, A.; Costabile, C.; Cavallo, L.
(
Understanding the M (NHC) (NHC  N-heterocyclic carbene)
bond. Coord. Chem. Rev. 2009, 253 (21−22), 687−703.
(
22) (a) Hong, S. H.; Chlenov, A.; Day, M. W.; Grubbs, R. H.
Double C-H activation of an N-heterocyclic carbene ligand in a
ruthenium olefin metathesis catalyst. Angew. Chem., Int. Ed. 2007, 46
27), 5148−5151. (b) Mathew, J.; Koga, N.; Suresh, C. H. C-H Bond
(
Activation through σ-Bond Metathesis and Agostic Interactions:
Deactivation Pathway of a Grubbs Second-Generation Catalyst.
Organometallics 2008, 27 (18), 4666−4670.
(
23) Cannon, J. S.; Zou, L.; Liu, P.; Lan, Y.; O’Leary, D. J.; Houk, K.
N.; Grubbs, R. H. Carboxylate-Assisted C(sp3)−H Activation in
Olefin Metathesis-Relevant Ruthenium Complexes. J. Am. Chem. Soc.
̈
(c) Tiede, S.; Berger, A.; Schlesiger, D.; Rost, D.; Luhl, A.; Blechert,
2
014, 136 (18), 6733−6743.
24) Sußner, M.; Plenio, H. π-Face donor properties of N-
heterocyclic carbenes. Chem. Commun. 2005, 43, 5417−5419.
25) Perfetto, A.; Bertolasi, V.; Costabile, C.; Paradiso, V.; Caruso,
S. Highly Active Chiral Ruthenium-Based Metathesis Catalysts
through a Monosubstitution in the N-Heterocyclic Carbene. Angew.
Chem., Int. Ed. 2010, 49 (23), 3972−3975.
(
̈
(
(34) Thomas, R. M.; Grubbs, R. H. Mechanistic Studies of
Enantioselective N-aryl, N-alkyl NHC Ruthenium Metathesis Catalysts
in Asymmetric Ring-Opening Cross-Metathesis. Chem. New Zealand
2011, 75 (2), 65−71.
T.; Longo, P.; Grisi, F. Methyl and Phenyl Substituent Effects on the
Catalytic Behavior of NHC Ruthenium Complexes. RSC Adv. 2016, 6
(
98), 95793−95804.
(
26) Fournier, P.-A.; Savoie, J.; Stenne, B.; Bed
́
ard, M.; Grandbois,
(35) Gatti, M.; Vieille-Petit, L.; Xinjun, L.; Mariz, R.; Drinkel, E.;
Linden, A.; Dorta, R. Impact of NHC Ligand Conformation and
Solvent Concentration on the Ruthenium-Catalyzed Ring-Closing
Metathesis Reaction. J. Am. Chem. Soc. 2009, 131 (27), 9498−9499.
(36) Rodrigues, C. A. B.; Norton de Matos, M.; Guerreiro, B. M. H.;
Gonc a̧ lves, A. M. L.; Romao, C. C.; Afonso, C. A. M. Water as efficient
̃
medium for mild decarbonylation of tertiary aldehydes. Tetrahedron
Lett. 2011, 52 (22), 2803−2807.
(37) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; N.
Kudin, K.; Staroverov, V. N.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi,
J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
Revision A.02; Gaussian, Inc., Wallingford, CT, 2009.
A.; Collins, S. K. Mechanistically Inspired Catalysts for Enantiose-
lective Desymmetrizations by Olefin Metathesis. Chem. - Eur. J. 2008,
1
4 (28), 8690−8695.
27) (a) Mol, J. C. Application of olefin metathesis in oleochemistry:
an example of green chemistry. Green Chem. 2002, 4 (1), 5−13.
b) Spekreijse, J.; Sanders, J. P. M.; Bitter, J. H.; Scott, E. L. The
Future of Ethenolysis in Biobased Chemistry. ChemSusChem 2017, 10
3), 470−482.
28) (a) Stewart, I. C.; Keitz, B. K.; Kuhn, K. M.; Thomas, R. M.;
(
(
(
(
Grubbs, R. H. Nonproductive Events in Ring-Closing Metathesis
Using Ruthenium Catalysts. J. Am. Chem. Soc. 2010, 132 (25), 8534−
8535. (b) Keitz, B. K.; Grubbs, R. H. Probing the Origin of Degenerate
Metathesis Selectivity via Characterization and Dynamics of
Ruthenacyclobutanes Containing Variable NHCs. J. Am. Chem. Soc.
2
(
011, 133 (40), 16277−16284.
29) (a) Anderson, D. R.; Lavallo, V.; O’Leary, D. J.; Bertrand, G.;
Grubbs, R. H. Synthesis and reactivity of olefin metathesis catalysts
bearing cyclic (alkyl)(amino)carbenes. Angew. Chem., Int. Ed. 2007, 46
38), 7262−7265. (b) Anderson, D. R.; Ung, T.; Mkrtumyan, G.;
Bertrand, G.; Grubbs, R. H. Kinetic Selectivity of Olefin Metathesis
(
Catalysts Bearing Cyclic (Alkyl)(Amino)Carbenes. Organometallics
2
008, 27, 563−566. (c) Schrodi, Y.; Ung, T.; Vargas, A.; Mkrtumyan,
G.; Lee, W.-C.; Champagne, T. M.; Pederson, R. L.; Hong, S. H.
Ruthenium Olefin Metathesis Catalysts for the Ethenolysis of
Renewable Feedstocks. Clean: Soil, Air, Water 2008, 36 (8), 669−
(38) (a) Becke, A. D. Density-functional exchange-energy approx-
imation with correct asymptotic behavior. Phys. Rev. A: At., Mol., Opt.
Phys. 1988, 38 (6), 3098−3100. (b) Perdew, J. P. Density-functional
approximation for the correlation energy of the inhomogeneous
electron gas. Phys. Rev. B: Condens. Matter Mater. Phys. 1986, 33 (12),
673. (d) Zhang, J.; Song, S.; Wang, X.; Jiao, J.; Shi, M. Ruthenium-
catalyzed olefin metathesis accelerated by the steric effect of the
backbone substituent in cyclic (alkyl)(amino) carbenes. Chem.
P
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
8
822−8824. (c) Perdew, J. P. Density-functional approximation for the
correlation energy of the inhomogeneous electron gas. Phys. Rev. B:
Condens. Matter Mater. Phys. 1986, 34 (13), 7406−7406. (d) Capo-
bianco, A.; Caruso, T.; Peluso, A. Hole delocalization over adenine
tracts in single stranded DNA oligonucleotides. Phys. Chem. Chem.
Phys. 2015, 17, 4750−4756.
(
39) Schaefer, A.; Horn, H.; Ahlrichs, R. J. Fully optimized contracted
Gaussian basis sets for atoms Li to Kr. J. Chem. Phys. 1992, 97 (4),
571−2577.
40) (a) Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Accuracy
2
(
of energy-adjusted quasirelativistic ab initio pseudopotentials: all-
electron and pseudopotential benchmark calculations for Hg, HgH
and their cations. Mol. Phys. 1993, 78 (5), 1211−1224. (b) Kuechle,
W.; Dolg, M.; Stoll, H.; Preuss, H. J. Energy-adjusted pseudopotentials
for the actinides. Parameter sets and test calculations for thorium and
thorium monoxide. J. Chem. Phys. 1994, 100 (10), 7535−7542.
(
c) Leininger, T.; Nicklass, A.; Stoll, H.; Dolg, M.; Schwerdtfeger, P.
The accuracy of the pseudopotential approximation. II. A comparison
of various core sizes for indium pseudopotentials in calculations for
spectroscopic constants of InH, InF, and InCl. J. Chem. Phys. 1996,
105 (3), 1052−1059.
Q
DOI: 10.1021/acs.organomet.7b00488
Organometallics XXXX, XXX, XXX−XXX