Synthesis, structure and catalytic study of oxygen chelated ruthenium (II) carbene complex

Article abstract of DOI:10.1016/j.poly.2014.03.034

New oxygen chelated ruthenium carbene complex containing carbonyl oxygen and ether oxygen has been developed. The X-ray structure of the complex showed that the carbonyl oxygen of the amide and the terminal oxygen of the benzylidene ether are both coordinated to the metal to give an octahedral structure. The catalytic activities of this new complex for olefin metathesis reactions were investigated and it exhibited excellent performances for the ring-closing metathesis (RCM) of diethyl diallymalonate at 30 °C and even at 0 °C. The initiation rate of the catalyst was higher than that for the Hoveyda catalyst ((H₂IMes)(Cl)₂Ru = C(H)(C₆H ₄-2-OiPr)) and it was also active for cross metathesis (CM).

Full text of DOI:10.1016/j.poly.2014.03.034

Polyhedron 76 (2014) 51–54
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structure and catalytic study of oxygen chelated ruthenium
(II) carbene complex
b
a
b,
Guiyan Liu a, , Mingbo Shao , Huizhu Zhang , Jianhui Wang
⇑
⇑
a College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Key Laboratory of Inorganic-Organic Hybrid Functional Material
Chemistry (Tianjin Normal University), Ministry of Education, Tianjin Normal University, Tianjin 300387, PR China
b Department of Chemistry, College of Science, Tianjin University, Tianjin 300072, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
New oxygen chelated ruthenium carbene complex containing carbonyl oxygen and ether oxygen has
been developed. The X-ray structure of the complex showed that the carbonyl oxygen of the amide
and the terminal oxygen of the benzylidene ether are both coordinated to the metal to give an octahedral
structure. The catalytic activities of this new complex for olefin metathesis reactions were investigated
and it exhibited excellent performances for the ring-closing metathesis (RCM) of diethyl diallymalonate
at 30 °C and even at 0 °C. The initiation rate of the catalyst was higher than that for the Hoveyda catalyst
((H2IMes)(Cl)2Ru = C(H)(C6H4-2-OiPr)) and it was also active for cross metathesis (CM).
Ó 2014 Elsevier Ltd. All rights reserved.
Received 23 January 2014
Accepted 20 March 2014
Available online 1 April 2014
Keywords:
Ruthenium (II)
N-heterocyclic carbene
Crystal structure
Coordination
Homogeneous catalysis
1. Introduction
standard and challenging substrates. On the basis of these
researches; we herein report a new NHC ruthenium (II) complex
Owing to the advent of highly efficient, well-defined ruthenium
catalysts 1–4 (Chart 1) [1], olefin metathesis has emerged as a
powerful tool for constructing carbon–carbon double bonds [2].
Among these complexes, ruthenium-benzylidene catalyst 4 which
introduced by Hoveyda and coworker bears N-heterocyclic carbene
(NHC) ligand, and exhibits extraordinary activity and stability [1c].
However, compared with Grubbs catalyst 2, it has a slowly initiate
due to the donation of an electron from iPrO to ruthenium cause.
The rate of initiation of chelated complexes is affected by the elec-
tronic and steric effects that act upon the RuÁ Á ÁO coordination. So,
in order to boost the activity of 4, all kinds of changes were done by
researchers [3–7]. For example, in 2006, Bieniek et al. [6d] synthe-
sized complex 5 by functionalizing the aliphatic end groups of the
complexes by attaching an ester group which enhanced the leaving
group properties of the styrenyl ether and in 2011 Bieniek et al.
[6e] synthesized a series of complexes 6 with different substituents
(an ester group, a ketonic group, or a malonic group). All of these
complexes had an additional functional group the coordinated to
the metal center. All these catalysts were found to exhibit higher
activities than that of the unmodified complex 4 in ring-closing
metathesis (RCM) and cross metathesis (CM) reactions for both
in which the leaving group properties of the styrenyl ether of
complex 4 is enhanced by attaching an amide functional group
to the aliphatic end group. The carbonyl oxygen of the amide and
the terminal oxygen of the benzylidene ether are both coordinated
to the metal. In addition to structural study the catalytic activity of
the new complex is explored.
2. Results and discussion
The synthesis of new complex is depicted in Scheme 1. Ester-
substituted styrenyl ether 8 was prepared by reacting commer-
cially available 7 with 2-bromo-propionic acid ethyl ester in the
presence of potassium carbonate. The N,N-dimethyl substituted
carbene ligand amide precursors 9 were obtained by hydrolysis
and acylation of 8. The precursor 9 was then reacted with 2 in
the presence of copper (I) chloride in CH2Cl2 at 40 °C, as described
by Kingsbury and co-workers. [1c]. This resulted in the exchange of
the styrene group to give the desired catalyst 10 in good yield
65.7% as greenish crystalline solids.
Crystals of the new Ru complex 10 was grown by slow
evaporation from CH2Cl2/ethyl acetate. The molecular structure of
the complex is shown in Fig. 1, along with a selection of interatomic
distances and bond angles. The X-ray structure shows that the
arrangements of the ligands around the metal center have charac-
teristics in common with those found in the Grubbs/Hoveyda
⇑
Corresponding authors. Tel.: +86 13642014012; fax: +86 022 23766530 (G. Liu).
Fax: +86 022 27403475 (J. Wang).
E-mail addresses: guiyanliu2013@163.com (G. Liu), wjh@tju.edu.cn (J. Wang).
http://dx.doi.org/10.1016/j.poly.2014.03.034
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

52
G. Liu et al. / Polyhedron 76 (2014) 51–54
Chart 1. Ruthenium metathesis catalysts.
Fig. 2. Catalytic activities of 10, 5a and 4 in the RCM of diallyl diethylmalonate
(CH2Cl2, 1 mol% ruthenium precatalyst): (a) 30 °C, 0.1 M, 30 min; (b) 0 °C, 0.02 M,
6 h, conversions calculated from 1H NMR results.
The catalytic activity of 10 for RCM was tested with diethyl dial-
lylmalonate 11. The relative conversion rates for RCM by 10 under
similar conditions are shown in Fig. 2. At 30 °C, the catalytic activ-
ity of 10 is slightly higher than that of the unmodified 4. All the cat-
alysts, high RCM conversions of 11 (>97%) were achieved after
30 min at 30 °C. In order to clearly compare the efficiencies of
two complexes, they were used in RCM reactions at 0 °C with the
same substrate. The rate of initiation of the amide catalyst 10
was significantly higher than the unmodified 4. The catalytic activ-
ity of 10 has an apparent enhancement. A good conversion is
obtained after 6 h. This is similar to complex 5a.
Scheme 1. Synthesis of oxygen chelated ruthenium (II) carbonyl complex 10.
Further studies showed that catalyst 10 is also active for many
other ring closures of substrates which containing nitrogen, oxy-
gen and sulfur to result in the formation of either five-, six- or
seven-membered rings with di- or tri-substituted double bonds
(see Table 1). The products were obtained in high conversions at
35 °C with low catalyst loading (0.1 mol%). A specific example of
the RCM is the bulky-substituted dienes 23, a more challenging
case. 10 gave good conversions at elevated temperatures (80 °C
in toluene) with high catalyst loading (2.0 mol%) and a longer reac-
tion time (24 h). Furthermore, in order to test the ability of our
complex for the cross metathesis of olefins, 27 and 28 were
selected and produced high yields of 29 when 2.5 mol% of catalyst
was used (Table 1, entry 9).
Fig. 1. Perspective view of the catalyst 10. Ellipsoids are drawn at the 50% probability
level. Selected interatomic distances (Å) and bond angles (deg): Ru(1)–C(1) =
1.972(5), Ru(1)–C(28) = 1.844(5), Ru(1)–O(1) = 2.171(3), Ru(1)–O(2) = 2.355(3),
Ru(1)–Cl(2) = 2.3717(14), Ru(1)–Cl(1) = 2.3918(12), Cl(2)–Ru(1)–Cl(1) = 167.54(4),
C(1)–Ru(1)–O(1) = 172.38(17), C(28)–Ru(1)–O(1) = 81.60(18), C(1)–Ru(1)–Cl(2) =
88.28(15), O(1)–Ru(1)–Cl(1) = 90.69(10).
3. Conclusions
second-generation complex. However, complex 10 additionally has
a weak bonding interaction between the carbonyl oxygen of the
amide group and the ruthenium center (Ru(1)–O(2) = 2.355 Å). This
enhances their stability in air. The interatomic distances Ru(1)–O(1)
for 10 between the ether oxygen and the metal Ru centers is only
2.171(3) Å and is shorter than 4 (2.257 Å) and 5a (2.207 Å) contain-
ing ester groups. In addition, the interatomic distance (Ru(1)–
O(2) = 2.355 Å) between the carbonyl group and the metal center
is also shorter than 5a (2.536 Å).
A new double oxygen (the ether oxygen and the carbonyl oxy-
gen) chelated ruthenium carbene metathesis catalysts was pre-
sented. The coordination of the carbonyl oxygen of the amide
group and the ruthenium center gave additional protection to the
metal center. This enhanced it stability in air and made it easier
to purify with silica gel column chromatography. Interestingly, it
exhibited higher activity and stability than the unmodified 4 in
RCM and CM reactions for wide range substrates which containing
nitrogen, oxygen and sulfur.

G. Liu et al. / Polyhedron 76 (2014) 51–54
53
Table 1
Application of catalyst 10 to different substrates (0.5 M in CH2Cl2 or in toluene).
Entry
1
Diene
Product
Cat. (mol%)
0.1
Conditionsa
0.5 h
Yield (%)c
98
2
3
0.1
0.1
0.5 h
0.5 h
99
99
4
5
6
0.1
0.1
0.1
0.3 h
1.0 h
0.5 h
99
98
98
7
8
2.5
0.1
24.0 hb
0.5 h
95
98
9
2.5
12.0 h
94
a
b
c
Reactions were conducted at 35 °C in CH2Cl2.
In toluene at 80 °C.
Isolated yields after silica gel chromatography. Yields determined by 1H NMR spectroscopy.
(d, J = 6.7 Hz, 1H). 13C NMR (100 MHz, CDCl3) d: 14.1, 18.6, 18.9,
34.4, 61.1, 73.1, 112.1, 115.3, 126.2, 127.1, 127.4, 128.0, 130.8,
137.2, 153.3, 172.4 ppm. IR (KBr) v: 3081, 2983, 2936, 2869, 1755,
1637, 1499, 1375, 1272, 1243, 1137, 1096, 1052, 870, 903,
4. Experiment
4.1. Synthesis of ethyl-2-(4-methyl-2-(prop-1-enyl)phenoxy)
propanoate 8
805 cmÀ1
.
A flask was charged with dry acetone (8 mL), K2CO3 (0.5 g,
3.7 mmol) and 7 (2.5 mmol). The mixture was heated to 50 °C and
alpha bromo ethyl propionate (0.6 g, 3.3 mmol) was slowly added.
Then, the reaction mixtures were stirred for 3 h under reflux. After
cooling to room temperature, the mixtures were filtered and con-
centrated to afford the crude product. The crude product was puri-
fied by silica gel chromatography (pentanes: CH2Cl2 = 1:1).
Colorless oil. Yield: 97.7%. Anal. Calc. for C15H20O3: C, 72.55; H,
8.12. Found: C, 72.51; H, 8.15%. 1H NMR (400 MHz, CDCl3) d
(ppm): 1.27 (t, J = 6.3 Hz, 3H), 1.64 (d, J = 6.5 Hz, 3H), 1.93
(q, J = 6.6 Hz, 3H), 2.29 (s, 3H), 4.22 (q, J = 6.7 Hz, 2H), 4.72
(q, J = 6.3 Hz, 1H), 5.99 (m, 1H), 6.62 (m, 2H), 6.93 (m, 1H), 7.24
4.2. Synthesis of 2-(4-methyl-2-(prop-1-enyl)phenoxy)propanoic acid
9
A flask was charged with 8 (2.1 mmol) and NaOH (6.2 mL,
10.0%). The reaction mixtures were stirred for 5 h under reflux.
After cooling to 0 °C, HCl (6 M) was added until the pH was 3–4.
Stirring was continued for 15 min at 0 °C. The precipitate was then
filtered and washed with water. After drying the desired acids
were obtained. Under N2, the acid (1.2 mmol) was charged with
SOCl2 at 50 mL Schlenk. After the reaction, the mixture was stirred
for 2 h under reflux, and then the SOCl2 was removed. Next 2 mL of

54
G. Liu et al. / Polyhedron 76 (2014) 51–54
dry benzene and dimethylamine (40%, 2.0 eq) were added at 0 °C
under N2. The reaction mixture was stirred at room temperature
for 12 h. The organic layer was removed and the aqueous layer
was extracted with benzene. The organic layers were combined
and washed with saturated salt water, dried over magnesium sul-
fate, filtered and concentrated. Purification by flash column chro-
matography on silica (CH2Cl2) gave the desired product. Light
yellow oil. Yield: 67.7%. Anal. Calc. for C15H21NO2: C, 72.84; H,
8.56; N, 5.66. Found: C, 72.86; H, 8.48; N, 5.55%. 1H NMR
trace amounts of Ru residues. Conversions were estimated by 1H
NMR spectroscopy and obtained by comparing the ratios of the
integrals of the starting materials with those of products. The cat-
alytic activities of ruthenium carbene 10 for a variety of substrates
are shown in Table 1.
Acknowledgements
Financial supports from NSFC (21102102, 21072149, and
20872108) are gratefully acknowledged.
(400 MHz, CDCl3)
d (ppm): 1.65 (d, J = 6.5 Hz, 3H), 1.94 (q,
J = 6.6 Hz, 3H), 2.29 (s, 3H), 2.95 (s, 3H), 3.09 (s, 3H), 4.90 (q,
J = 6.2 Hz, 1H), 6.01 (m, 1H), 6.65 (m, 2H), 6.95 (m, 1H), 7.28 (d,
J = 6.8 Hz, 1H). 13C NMR (100 MHz, CDCl3) d: 17.6, 18.9, 34.4,
36.3, 36.5, 73.9, 112.0, 115.1, 126.1, 127.0, 127.2, 127.8, 130.6,
137.1, 153.1, 172.1 ppm. IR (KBr) v: 3061, 2934, 2933, 1661,
Appendix A. Supplementary data
CCDC 981748 contains the supplementary crystallographic data
for complex 10. This data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
1455, 1444, 1366, 1234, 1110, 1061, 1044, 955, 733 cmÀ1
.
4.3. Preparation of complex 10
To a Schlenk flask charged with Grubbs’ catalyst 2 (0.42 g,
0.50 mmol) and CuCl (0.05 g, 0.50 mmol), compound 9 (0.6 mmol)
in 10 mL dry dichloromethane was added at room temperature
under N2. The resulting mixture was stirred for 40 min at 40 °C.
After being cooled to room temperature, the reaction mixture
was filtered and the clear filtrate was collected. The solvent from
the filtrate was evaporated under vacuum to give a residue. The
residue was purified by silica gel chromatography (CH2Cl2: ethyl
acetate = 2:1 or pentanes: ethyl acetate = 3:2 or1:1) to give the
desired product as a green crystalline solid. Yield: 65.7%. Anal. Calc.
for C34H43Cl2N3O2Ru: C, 58.53; H, 6.21; N, 6.02. Found: C, 58.45; H,
6.21; N, 5.95%. 1H NMR (400 MHz, CDCl3) d (ppm): 1.41 (d,
J = 6.3 Hz, 3H), 2.38 (s, 3H), 2.40 (bs, 6H), 2.52 (bs, 12H), 2.77 (s,
3H), 2.79 (s, 3H), 4.10 (s, 4H), 5.23 (q, J = 6.6, 1H), 6.54 (d,
J = 8.3 Hz, 1H), 6.75 (s, 4H), 7.08 (s, 4H), 7.28 (d, J = 8.4 Hz, 1H),
16.37 (s, 1H). 13C NMR (100 MHz, CDCl3) d: 16.7, 21.4, 27.3, 36.2,
37.0, 51.9, 62.2, 73.4, 112.3, 129.4, 129.3, 129.6, 133.2, 138.3,
145.9, 149.4, 171.4, 210.5, 302.1 ppm. IR (KBr) v: 3033, 2912,
2845, 2735, 1946, 1628, 1475, 1445, 1415, 1233, 1217, 1129,
References
[1] (a) P. Schwab, M.B. France, J.W. Ziller, R.H. Grubbs, Angew. Chem., Int. Ed. 34
(1995) 2039;
(b) P. Schwab, R.H. Grubbs, J.W. Ziller, J. Am. Chem. Soc. 118 (1996) 100;
(c) J.S. Kingsbury, J.P.A. Harrity, P.J. Bonitatebus, A.H. Hoveyda, J. Am. Chem. Soc.
121 (1999) 791;
(d) S. Gessler, S. Randl, S. Blechert, Tetrahedron Lett. 41 (2000) 9973;
(e) M. Scholl, S. Ding, C.W. Lee, R.H. Grubbs, Org. Lett. 1 (1999) 953;
(f) J. Huang, E.D. Stevens, S.P. Nolan, J.L. Petersen, J. Am. Chem. Soc. 121 (1999)
2674;
(g) M. Scholl, T.M. Trnka, J.P. Morgan, R.H. Grubbs, Tetrahedron Lett. 40 (1999)
2247.
[2] (a) R.H. Grubbs, Ed. Handbook of Metathesis, vols. 1–3, Wiley–VCH, Weinheim,
Germany, 2003.;
(b) R.R. Schrock, A.H. Hoveyda, Angew. Chem., Int. Ed. 42 (2003) 4592;
(c) T.M. Trnka, R.H. Grubbs, Acc. Chem. Res. 34 (2001) 18;
(d) A. Furstner, Angew. Chem., Int. Ed. 39 (2000) 3012;
(e) M. Schuster, S. Blechert, Angew. Chem., Int. Ed. 36 (1997) 2037;
(f) D. Astruc, New J. Chem. 29 (2005) 42.
[3] (a) F. Verpoort, J.C. Martins, Eur. J. Org. Chem. (2009) 655;
(b) B. De Clercq, F. Verpoort, Tetrahedron Lett. 43 (2002) 9101;
(c) J.J. Van Veldhuizen, S.B. Garber, J.S. Kingsbury, A.H. Hoveyda, J. Am. Chem.
Soc. 124 (2002) 4954;
(d) J.J. Van Veldhuizen, D.G. Gillingham, S.B. Garber, O. Kataoka, A.H. Hoveyda, J.
Am. Chem. Soc. 125 (2003) 12502;
(e) D.G. Gillingham, A.H. Hoveyda, Angew. Chem., Int. Ed. 46 (2007) 3860.
[4] (a) T.W. Funk, J.M. Berlin, R.H. Grubbs, J. Am. Chem. Soc. 128 (2006) 1840;
(b) J.M. Berlin, S.D. Goldberg, R.H. Grubbs, Angew. Chem., Int. Ed. 45 (2006)
7591;
1103, 853, 571 cmÀ1
4.4. Kinetics study of 10, 5a and 4
Schlenk flask was charged with catalyst (0.02 mmol,
.
A
(c) P.A. Fournier, S.K. Collins, Organometallics 26 (2007) 2945;
(d) T.W. Funk, Org. Lett. 11 (2009) 4998;
(e) B.K. Keitz, K. Endo, P.R. Patel, M.B. Herbert, R.H. Grubbs, J. Am. Chem. Soc.
134 (2012) 693;
(r) B.K. Keitz, A. Fedorov, R.H. Grubbs, J. Am. Chem. Soc. 134 (2012) 2040;
(g) B.K. Keitz, K. Endo, M.B. Herbert, R.H. Grubbs, J. Am. Chem. Soc. 133 (2011)
9686;
1.0 mol%) and CH2Cl2. The sample was equilibrated at 30 °C (or
0 °C) before diethyl diallylmalonate 11 was added via a syringe.
Aliquots were taken from the reaction mixture at the appropriate
times using a syringe and were quenched immediately with
0.1 mol/L PEI in CH2Cl2. The resulting solution was then subjected
to short column chromatography to remove the Ru metal residue
using CH2Cl2 as the eluent. The solvent from the collected solution
was evaporated under vacuum. The conversion yield to substrates
was determined by comparing the ratio of the integrals of the 1H
NMR methylene proton peaks in the starting material with those
in the product. The results are shown in Fig. 2.
(h) K. Endo, R.H. Grubbs, J. Am. Chem. Soc. 133 (2011) 8525.
[5] (a) H. Wakamatsu, S. Blechert, Angew. Chem., Int. Ed. 41 (2002) 2403;
(b) A.M. Dunne, S. Mix, S. Blechert, Tetrahedron Lett. 44 (2003) 2733;
(c) H. Wakamatsu, S. Blechert, Angew. Chem., Int. Ed. 41 (2002) 794.
[6] (a) K. Grela, S. Harutyunyan, A. Michrowska, Angew. Chem., Int. Ed. 41 (2002)
4038;
(b) A. Michrowska, R. Bujok, S. Harutyunyan, V. Sashuk, G. Dolgonos, K. Grela, J.
Am. Chem. Soc. 126 (2004) 9318;
(c) S. Harutyunyan, A. Michrowska, K. Grela, Highly Active Ruthenium
(Pre)catalyst for Metathesis, vol. 3, Wiley–Interscience, New York, 2004, p. 169;
(d) M. Bieniek, R. Bujok, M. Cabaj, N. Lugan, G. Lavigne, D. Arlt, K. Grela, J. Am.
Chem. Soc. 128 (2006) 13652;
4.5. Catalytic study of the ruthenium carbenes 10
´
(e) M. Bieniek, C. Samojłowicz, V. Sashuk, R. Bujok, P. Sledz´, N. Lugan, G.
The general procedure for metathesis reactions with ruthenium
carbenes 10 was performed as follows: a certain amount of ruthe-
nium carbene catalyst 10 (0.0005–0.0125 mmol) and a solution of
the substrate (0.5 mmol) in 1.0 mL dry CH2Cl2 (or toluene) was
mixed in a reaction flask under nitrogen. The reaction mixture
was stirred for 0.3–24 h. At the end of the reaction (monitored
by thin-layer chromatography (TLC)), the catalysts were separated
by silica gel chromatography using CH2Cl2 as the eluent to remove
Lavigne, D. Arlt, K. Grela, Organometallics 30 (2011) 4144.
[7] (a) G.L. Wu, S.L. Cao, J. Chen, Z.L. Chen, Eur. J. Org. Chem. (2012) 6777;
(b) C.D. Varnado Jr., E.L. Rosen, M.S. Collins, V.M. Lynch, C.W. Bielawski, Dalton
Trans. 42 (2013) 13251;
(c) K. Arumugam1, C.D. Varnado Jr., S. Sproules, V.M. Lynch, C.W. Bielawski,
Chem. Eur. J. 19 (2013) 10866.;
(d) J.P. Moerdyk, C.W. Bielawski, Organometallics 30 (2011) 2278;
(e) E.L. Rosen, D.H. Sung, Z. Chen, V.M. Lynch, C.W. Bielawski, Organometallics
29 (2010) 250.