Full Paper
recently discovered high-concentration RCM (HC-RCM).[110] Im-
portantly, under harsh conditions required for the HC-RCM, Ru-
3 was giving much higher selectivity than standard symmetri-
cal NHC bearing Ru-1, yielding the valuable musk macrocycle
in good isolated yield (Scheme 11). As the diene substrate
used in this reaction was prepared entirely from a biosourced
substrate-methyl oleate,[111] it creates also the first example of
use of Ru-3 in the sustainable preparation of a macrocyclic
ketone, (E/Z)-civetone, under high-concentration RCM condi-
tions.[110]
were provided by the EA analytical laboratory at the Institute of
Organic Chemistry, Polish Academy of Sciences (PAS). HRMS were
provided by the Faculty of Chemistry University of Warsaw or ana-
lytical laboratory at the Institute of Organic Chemistry, PAS. NMR
spectra were recorded on an Agilent 400-MR DD2 400 MHz spec-
trometer. NMR chemical shifts are reported in ppm downfield from
solvent residual peak (d=7.26 and 77.16 ppm for 1H and 13C in
1
CDCl3, d=5.32 and 54.00 ppm for H and 13C in CD2Cl2). Data are
reported as follows: chemical shift, multiplicity (s: singlet, d: dou-
blet, t: triplet, q: quartet, qui: quintuplet, m: multiplet), coupling
constant (J in Hz) and integration. Deuterated solvents were pur-
chased from Sigma–Aldrich, stored over molecular sieves used
without further purification (chloroform) or distilled under inert at-
mosphere from CaH2 (dichloromethane). 13C NMR spectra were re-
corded at 100 MHz using broadband proton decoupling and chem-
icals shifts are reported in ppm using residual solvent peaks as a
reference.
Conclusion
An 2-isopropoxybenzylidene ruthenium complex featuring
new uNHC ligand containing phenanthrene N-substituent has
been successfully synthesized from the corresponding azolium
salt. The new complex (Ru-3) has been fully characterized and
tested in a number of metathesis reactions. Ru-3 exhibits the
same initiation rate and activity in the model RCM reactions as
commercially available Hoveyda–Grubbs II-generation complex
(Ru-1), which is in contrast to other uNHC-based Ru catalysts.
Interestingly, it contrasted from Ru-1 by being nonreactive at
low temperature towards some 2-allyl-1,3-diketones, and it is
substantially less prone to double-bond isomerisation in ho-
mometathesis of the a-olefin–1-octene, as well as affords im-
proved yield in the formation of challenging, medium-sized
rings (7,8-membered).
Further details of experimental procedures and characterization
data are presented in the Supporting Information.
[3-Benzyl-1-(10-phenyl-9-phenanthryl)]-2-imidazolidinylide-
ne)dichloro(o-isopropoxyphenylmethylene)ruthenium (Ru-3)
A 50 mL Schlenk flask was charged with 213.4 mg of imidazolidini-
um salt 7 (0.47 mmol, 1.1 equiv) and dried under vacuum in 708C
for 30 min. Next, it was cooled to room temperature and 20 mL of
toluene were added. To the resulted suspension, a solution of
0.3 mL 25% KOtAm was added and after disappearance (ꢁ2–
3 min), 259 mg of Hoveyda I (0.43 mmol, 1 equiv) was added and
the Schlenk flask was inserted into a preheated oil bath (708C).
The reaction was monitored by TLC and after ꢁ20 min (full conver-
sion) the Schlenk flask with the mixture was inserted into an ice
bath. After cooling the mixture below room temperature, n-hexane
was added (1 part for 2 parts of mixture) and the solution was
chromatographed with 0!10!20% EtOAc/n-hexane. A greenish–
brown band was collected and after evaporation, the solid was re-
crystallized from DCM/MeOH affording 230 mg as a brownish-
green microcrystalline solid (72%). 1H NMR (400 MHz, CDCl3) d=
16.60 (s, 1H), 8.92 (d, J=8.3 Hz, 1H), 8.80 (d, J=8.3 Hz, 1H), 8.13
(d, J=8.2 Hz, 1H), 7.79 (dt, J=16.0, 8.1 Hz, 3H), 7.71–7.62 (m, 3H),
7.56 (dt, J=16.7, 7.5 Hz, 3H), 7.44 (t, J=6.6 Hz, 4H), 7.40–7.29 (m,
3H), 6.86 (d, J=8.3 Hz, 1H), 6.64 (t, J=7.5 Hz, 1H), 6.24 (d, J=
7.5 Hz, 1H), 5.81–5.50 (m, 2H), 5.21–5.04 (m, 1H), 3.80 (q, J=11.2,
9.9 Hz, 1H), 3.47–3.33 (m, 2H), 3.10 (q, J=12.8, 11.1 Hz, 1H),
1.75 ppm (d, J=6.1 Hz, 6H); 13C NMR (101 MHz, CDCl3) d=289.8,
210.6, 152.8, 143.4, 138.2, 136.2, 135.9, 135.0, 133.3, 131.8, 130.9,
130.7, 129.8, 129.7, 129.5, 129.3, 129.2, 128.8, 128.5, 128.3, 127.9,
127.9, 127.8, 127.4, 127.1, 125.8, 122.8, 122.5, 122.3, 122.3, 112.8,
75.3, 56.2, 53.0, 47.6, 22.3, 22.2 ppm; IR (diamond tip) n˜ =3059,
2987, 2889, 1587, 1572, 1472, 1436, 1419, 1381, 1263, 1214,
Importantly, Ru-3 was significantly more stable than stan-
dard general-purpose catalyst in the presence of ethylene. As
such, Ru-3 outperformed Ru-1 in the ethenolysis of biorenewa-
ble feedstock, ethyl oleate, and b-caryophyllene, delivering re-
sults comparable or better to the state of the art CAAC-based
Ru-4. The improved selectivity and high robustness of Ru-3 in
ethylene facilitated the first ethenolysis of naturally occurring
caryophyllene affording useful derivatives in outstanding
yields. The above properties seem to be unique and may open
practical applications of this complex.[112]
Finally, Ru-3 gave much better results in high-concentration
RCM (HC-RCM) synthesis of E/Z-civetone, exhibiting outstand-
ing selectivity as compared with Ru-1.[110]
Experimental Section
General information
1110 cmꢀ1
;
M.p. 230.58C, decomposition; HRMS: calcd:
If not noted otherwise, all reactions were carried out under argon
atmosphere in oven dried glassware (overnight, 1358C) with mag-
netic stirring. Commercially available chemicals were used without
further purification. Hoveyda II (Ru-1) catalyst was purchased from
STREM Chemicals. Ru-2 and Ru-4 were synthesized by known pro-
tocols.[32,46] Solvents were purified by Solvent Purification System,
Mbraun MB-SPS-800. Analytical TLC was performed on Merck silica
gel 60 with fluorescent indicator UV254 TLC plates. The flash
column chromatography was performed using Merck silica gel 60
(particle size: 0.040–0.063 mm, 230–400 mesh) typically using n-
hexane/ethyl acetate the eluent system. IR spectra were recorded
on a Perkin–Elmer Spectrum One FTIR spectrometer with diamond
ATR accessory, wave numbers are in cmꢀ1. Elemental Analyses (EA)
(C40H35N2ORu+): 661.1798; found: 661.1795; Difference: d=
0.45 ppm; m.p. 230.58C, decomposition; EA: elemental analysis
calcd (%) for C40H36Cl2N2ORu: C, 65.57; H, 4.95; Cl, 9.68; N, 3.82;
found: C, 65.53; H, 5.06; Cl, 9.66; N, 3.85.
Acknowledgements
We wish to thank the National Science Centre (Poland) for the
NCN MAESTRO Grant No. DEC-2012/04A/ST5/00594. The study
was carried out at the Biological and Chemical Research
Centre, University of Warsaw, established within the project co-
Chem. Eur. J. 2020, 26, 1 – 14
11
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