Microwave-assisted synthesis of functionalized Shvo-type complexes

Article abstract of DOI:10.1021/om500335m

A simple and expeditious microwave-assisted procedure for the synthesis of a variety of Shvo-type ruthenium complexes has been developed by reacting Ru₃(CO)₁₂ with variously functionalized tetraarylcyclopentadienones under microwave irradiation in MeOH. Ligand precursors have also been prepared under microwave heating by a bis-aldol condensation of 1,3-diphenylacetone with variously functionalized aromatic diketones. All the reactions were very fast and clean, leading to good yields and purities.

Full text of DOI:10.1021/om500335m

Article
pubs.acs.org/Organometallics
Microwave-Assisted Synthesis of Functionalized Shvo-Type
Complexes
Cristiana Cesari, Letizia Sambri, Stefano Zacchini, Valerio Zanotti, and Rita Mazzoni*
Dipartimento di Chimica Industriale “Toso Montanari”, University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
S
* Supporting Information
ABSTRACT: A simple and expeditious microwave-assisted procedure for the
synthesis of a variety of Shvo-type ruthenium complexes has been developed by
reacting Ru3(CO)12 with variously functionalized tetraarylcyclopentadienones
under microwave irradiation in MeOH. Ligand precursors have also been
prepared under microwave heating by a bis-aldol condensation of 1,3-
diphenylacetone with variously functionalized aromatic diketones. All the
reactions were very fast and clean, leading to good yields and purities.
approaches have been developed since its first synthesis,2a−c,15
but all the reported procedures still require high temperatures
well-known as Shvo-type complexes,1 are precursors of useful
and long reaction times.
INTRODUCTION
■
Hydroxycyclopentadienylruthenium hydride dimer complexes,
Here we report a new rapid, clean, and general method for
the synthesis of variously functionalized Shvo-type complexes,
which takes advantage of microwave heating. Furthermore,
microwave irradiation also provides easier access to the
corresponding tetraarylcyclopentadienone ligands.
and versatile catalysts, successfully applied in a broad variety of
hydrogen-transfer processes such as hydrogenation of carbonyls
and imines and oxidation of alcohols and amines.2 More
recently, applications have been extended to a broader number
of reactions including synthesis of primary amines by using
ammonia,3 biomimetic aerobic oxidation,4 chemoenzymatic
dynamic kinetic resolution of amines,5 N-acylation of hetero-
cycles with aldehydes,6 ammonia−borane dehydrogenation,7
and α,β-deuteration of bioactive amines.8 Furthermore, the
catalyst, supported on silica, has been used in the hydro-
formylation and hydrogenation of propene to butanol,9 and,
combined with Rh complexes, it has been exploited in tandem
reactions, resulting in the isomerization/hydroformylation/
hydrogenation of internal alkenes to yield n-alcohols.10
Promising perspectives are also in the field of green chemistry,
in the transformation of renewable feedstocks,11 including
upgrading of bio-oil by hydrogenation11a and selective
conversion of levulinic and formic acids into γ-valerolactone.12
Stimulated by the possibility to decorate the cyclopentadienyl
of Shvo’s complexes with various functionalities, we inves-
tigated the synthesis of new hydroxypropargyl arylcyclopenta-
dienone ligands. These functionalized tetraarylcyclopentadie-
nones, besides providing a tool for controlling the properties of
the catalyst, are themselves fascinating compounds, with
interesting properties as organogels,13 and useful applications
in material science.14
RESULTS AND DISCUSSION
■
Microwave-Assisted Tetraarylcyclopentadienone Li-
gand Synthesis. Most common synthetic routes to
tetraarylcyclopentadienones involve reaction of diaryl-α-dike-
tones 1 with the diphenylacetone 2, in the presence of KOH or
NaOH, in refluxing EtOH for variable reaction times (2−16 h)
(Scheme 1).13,16
Scheme 1. Examples of Conventional Synthesis of
Tetraarylcyclopentadienones 3
The considerable potential of the Shvo catalyst, which might
be further improved by use of functionalized tetraarylcyclo-
pentadienones, is unfortunately affected by the lack of a simple
and efficient synthetic method. Indeed, different synthetic
Received: March 31, 2014
Published: May 27, 2014
© 2014 American Chemical Society
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a
Table 1. Scope of the Microwave-Assisted Condensation
a
b
Reaction conditions: 1 (1.19 mmol), 2 (1 equiv), NaOH (1 equiv), 0.1 M in EtOH, T = 70 °C, t = 25 min. In parentheses, literature yields (when
c
available) for the classical thermal procedure (80 °C). Reaction performed at room temperature.
Scheme 2. Microwave-Assisted Synthesis of Shvo-Type Complexes 4a−f
In consideration of the fact that microwave irradiation has
proved to be efficient in the acceleration of many organic
reactions, becoming a standard tool in organic synthesis,17 we
have applied this technique for the base-catalyzed bis-aldol
condensation of 1,3-diphenylacetone with α-diketones. As an
initial approach, we investigated benzil (1a, Scheme 1) as
model substrate to study its condensation with 1,3-
diphenylacetone and NaOH, employing EtOH as solvent.
The mixture was stirred and heated in a closed Teflon
microwave reaction vessel. Optimization studies led to the
identification of the best reaction conditions as heating at 70 °C
for 25 min to obtain tetraphenylcyclopentadienone (3a) in 78%
yield. No significant variation has been observed leaving the
mixture under microwave irradiation for a longer time (e.g., 50
min). On the other hand, a shorter reaction time (15 min) did
not give complete conversion of the starting material, leading to
lower yields (55%). Similar results were observed by lowering
the temperature: T = 30 °C, yield = 27%; T = 50 °C, yield =
40%. Finally, yields decrease when performing the reaction at
120 °C (yield = 32%) due to partial decomposition of the
product.
reported in Table 1. We found that the procedure can be
extended to several variously substituted diketones, as micro-
wave irradiation affords yields comparable to the classic reflux
methods, but with much shorter reaction times. Comparisons
with reaction yields reported in the literature are shown in
Table 1. The only exception is the synthesis of 3h (Table 1,
entry 8), which occurs better at room temperature, in that it
typically suffers from thermal oxidative degradation.18
Results evidence that microwave irradiation promotes a
significant acceleration of the reaction. In fact, reaction times,
which typically range from 2 to 16 h in the classic thermal
methods for the preparation of 3b−e, are shortened to 25 min
in the corresponding microwave-assisted procedures.
Like conventional methods,16,19 yields are influenced by the
aryl functionalization (Table 1), and the workup procedure is
particularly convenient when the products are insoluble in
EtOH (3a−c, 3f, 3h), in that it simply consists of a filtration.
Conversely, in the case of soluble products (3d, 3e, 3g)
purification requires column chromatography on silica gel. All
1
the compounds have been characterized by IR, H and 13C
NMR spectroscopy, and comparison with literature data, when
available. For the new compounds 1f, 3f, and 3g complete
characterization is reported in the Experimental Section.
Once the optimized reaction conditions (T = 70 °C and t =
25 min) were established for the unfunctionalized benzil, we
investigated the substrate scope with diketones 1b−h as
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Microwave-Assisted Synthesis of Hydroxycyclopenta-
dienylruthenium Hydride Dimer (Shvo-Type) Com-
plexes. The dinuclear complexes {[3,4-(R-C6H4)2-2,5-Ph2(η5-
C4CO)]2H}Ru2(CO)4(μ-H) [e.g., R = H, OMe, Cl] are
typically prepared by heating Ru3(CO)12 and tetraarylcyclo-
pentadienones in MeOH for 40 h. An alternative two-step
approach involves the synthesis of the precursor 3,4-(R-C6H4)2-
2,5-Ph2(η4-C4CO)Ru(CO)3, which is subsequently trans-
formed to the corresponding dinuclear Shvo-type complex by
a 48 h long reaction in acetone/water in the presence of
Na2CO3. The latter method leads to lower yields and more
difficult purification of the product.
the bridging hydride, at about −18 ppm in CDCl3 (e.g., for 4c:
−18.40), and 13C NMR spectra are consistent with typical
resonances that involve terminal CO (at about 200.20−201.12
ppm) and quaternary carbons of hydroxycyclopentadienyl
ligands (e.g., C1-OH = 154.49−155.63; C2,5 = 101.88−
102.75; C3,4 = 87.78−87.88). Signals of alkyne-containing
substituents in 4d−f present a negligible shift compared with
the corresponding resonances of noncoordinated cyclopenta-
dienones (e.g., for 3d vs 4d the quaternary carbons of the group
−CCC(CH3)2OH resonate at 95.21, 81.79, 65.6313 and
94.93, 81.59, 65.52, respectively), indicating that formation of
the complexes has little influence on the substituents placed on
the five-membered ring. ESI-MS allowed us to identify the
molecular ion of 4c−h (see Experimental Section).
A drawback of the reported methods2,15 is the long reaction
time, which prompted us to explore the potential of microwave
heating in the organometallic synthesis of Shvo-type complexes
4. Indeed, microwave irradiation has been widely used for
transition-metal-catalyzed reactions, but there are few reports
about its application in the syntheses of organometallic20 and
coordination21 compounds. We have found that this technique
impressively reduces the reaction time (from 40 h to 50 min)
required for reacting Ru3(CO)12 with tetraarylcyclopentadie-
nones in methanol (12 mL) (Scheme 2). It is noteworthy that
the syntheses of complexes 4 can be performed with non-
anhydrous solvents in air.
Suitable crystals for X-ray analysis have been obtained for 4b
as its 4b·CH2Cl2 solvate and for the new complex 4c (Figures 1
First we optimized the synthetic procedure for 4a by heating
a mixture of 3 equiv of tetraphenylcyclopentadienone 3a with
Ru3(CO)12 in MeOH (12 mL) in a closed Teflon reaction
vessel at variable temperatures and times. Best reaction
conditions have been found at 110 °C for 50 min, leading to
the complete conversion of Ru3(CO)12 and subsequent
isolation of microcrystalline Shvo’s complex 4a by precipitation,
filtration, and washing with MeOH. Complex 4a was obtained
in about 75% yield.
The substrate scope has been extended to several
tetraarylcyclopentadienones with different R substituents,
leading to yields comparable or higher with respect to classical
methods (Table 2). Yields above 70% have been obtained for
Figure 1. ORTEP drawing of 4b with key atoms labeled. Thermal
ellipsoids are at the 30% probability level. H atoms, apart from H(1)
and H(3), have been omitted for clarity. Selected bond lengths (Å)
and angles (deg): Ru(1)−H(1) 1.68(2); Ru(2)−H(1) 1.68(2);
Ru(1)−Cp(av) 2.256(18); Ru(2)−Cp(av) 2.69(2); Ru(1)−CO(av)
1.886(15); Ru(2)−CO(av) 1.880(16); O(3)−H(3) 1.276(18);
O(53)−H(3) 1.248(18); Ru(1)−H(1)−Ru(2) 149.8(8); O(3)−
H(3)−O(53) 158(7).
Table 2. Scope of the Microwave-Assisted Shvo Complexes’
a
Synthesis
yield
bc
,
and 2). Since structural data for complex 4b have not been
reported previously, its crystallographic structure is herein
reported. The structures of 4b and 4c are very similar to those
previously reported for analogous complexes with respect to
their geometries and bonding parameters, and, therefore, they
will not be discussed any further.1a,15b,d
entry cyclopentadienone
R
product
(%)
1
2
3
4
5
6
3a
3b
3c
3d
3e
3f
H−
MeO−
Br−
4a
4b
4c
4d
4e
4f
75 (67)
73 (70)
72 (62)
24 (22)
23 (25)
74 (72)
(HOMe2C−CC)−
(HOPh2C−CC)−
(C6H11−CC)−
Conclusions. We have developed a very efficient procedure
for the synthesis of variously functionalized tetraarylcyclopen-
tadienones and the corresponding dinuclear ruthenium hydride
Shvo-type complexes based on microwave irradiation. This
class of complexes are of great interest in modern
homogeneous catalytic processes, with promising applications
in biomass conversion into chemicals and biofuel. The new
synthetic procedure, designed to obtain Shvo complexes with
different substituents and functional groups, has been
demonstrated to tolerate various functionalities, avoiding
protection and deprotection steps, with consequent advantages
in terms of atom economy. The reaction needs a relatively low
amount of solvent and, with few exceptions, does not require
long and solvent-consuming purification steps. The most
relevant advantage is reduction of the reaction time, which in
the case of complexes 4 goes from days (40 h) to minutes (50
a
Reaction conditions: Ru3(CO)12 (0.16 mmol), 3 (0.48 mmol),
MeOH (12 mL), T = 110 °C, t = 50 min. In parentheses yields for
the classical thermal procedure in our hands, in agreement with
literature procedures when available (methanol reflux, 40 h). 4h has
b
c
also been obtained by 3h in 15% yield; the poor yield is ascribable to
the instability of 3h at high temperatures.18
complexes 4a, 4b, 4c, and 4f (entries 1−3 and 6 in Table 2),
which can be easily separated by precipitation in methanol,
whereas complexes containing propargyl substituents (4d, 4e)
require separation by column chromatography, leading to lower
yields (22−25%: entries 4 and 5 in Table 2).
FT-IR spectra of compounds 4 show the typical pattern in
the region of CO stretching (e.g., for 4c: ν(CO): 2041, 2010,
1982 cm−1). H NMR spectra exhibit the diagnostic signal of
1
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herein discussed registered a microwave power plot in the range
between 0 and 100 W.
General Procedure for the Microwave-Assisted Synthesis of
Cyclopentadienones 3. Into a 75 mL Teflon vessel with a magnetic
stirrer were placed α-diketone 1 (1.19 mmol), 1,3-diphenylacetone 2
(0.250 g, 1.19 mmol), 12 mL of EtOH, and NaOH (0.0479 g, 1.19
mmol). The vessel was sealed with a lid equipped with a temperature
sensor and placed in the microwave oven. The reaction mixture was
heated for 25 min at 70 °C. The dark purple product was purified by
filtration when solid or by column chromatography. Spectral data for
new compounds are reported.
Tetraphenylcyclopentadienone (3a). Reactants: benzil (1a) (0.250
g, 1.19 mmol), 1,3-diphenylacetone 2 (0.250 g, 1.19 mmol), 12 mL of
EtOH, and NaOH (0.0479 g, 1.19 mmol). The dark purple, crystalline
solid was purified by filtration and washed three times with 5 mL of
EtOH (0.357 g, 78% yield).
3,4-Bis(4-methoxyphenyl)-2,5-diphenylcyclopenta-2,4-dienone
(3b). Reactants: 4,4′-dimethoxybenzil (1b) (0.490 g, 1.81 mmol), 1,3-
diphenylacetone 2 (0.380 g, 1.81 mmol), and NaOH (0.0724 g, 1.81
mmol). The dark purple, crystalline solid was purified by filtration
(0.607 g, 75% yield).
3,4-Bis(4-Bromophenyl)-2,5-diphenylcyclopenta-2,4-dienone
(3c). Reactants: 4,4′-dibromobenzil (1c) (0.452 g, 1.23 mmol), 1,3-
diphenylacetone 2 (0.261 g, 1.23 mmol), and NaOH (0.0492 g, 1.23
mmol). The dark purple, crystalline solid was purified by filtration
(0.471 g, 70% yield).
Figure 2. ORTEP drawing of 4c with key atoms labeled. Thermal
ellipsoids are at the 30% probability level. H atoms, apart from H(1)
and H(3), have been omitted for clarity. Selected bond lengths (Å)
and angles (deg): Ru(1)−H(1) 1.724(13); Ru(1)−Cp(av) 2.264(4);
Ru(1)−CO(av) 1.895(4); O(3)−H(3) 1.2676(19); Ru(1)−H(1)−
Ru(1_1) 140.0(2); O(3)−H(3)−O(3_3) 178(4). Symmetry trans-
formations used to generate equivalent atoms Ru(1_1) and O(53_1):
−x, y, −z+1/2.
min) without affecting the reaction yields. Also the ligand
synthesis takes advantage of a significant reduction of solvent
used and reaction time, which goes from 2 to 16 h under the
classic refluxing method to 25 min under microwave heating.
Functionalization toward novel complexes of type 4 containing
alkyne and −OH groups should be exploited for the
immobilization of Shvo’s catalysts on a solid support by
means of “click” or “coupling” reactions. In principle, catalyst
heterogenization should make recovery and recycling of the
catalyst easier for industrial applications.
3,4-Bis(4-(3-hydroxy-3-methylbut-1-ynyl)phenyl)-2,5-diphenylcy-
clopenta-2,4-dienone (3d). Reactants: 4,4′-bis(2-methyl-3-butin-2-
ol)benzil (1d) (0.307 g, 0.820 mmol), 1,3-diphenylacetone 2 (0.172 g,
0.820 mmol), and NaOH (0.0328 g, 0.820 mmol). The dark purple
solid was purified by chromatography on silica gel (CH2Cl2/ethyl
acetate, 95/5) (0.261 g, 58% yield).
3,4-Bis(4-(3-hydroxy-3,3-diphenylprop-1-ynyl)phenyl)-2,5-
diphenylcyclopenta-2,4-dienone (3e). Reactants: 4,4′-bis(2-phenyl-3-
butin-2-ol)benzil (1e) (0.761 g, 1.22 mmol), 1,3-diphenylacetone 2
(0.262 g, 1.22 mmol), and NaOH (0.0490 g, 1.22 mmol). The dark
purple solid was purified by chromatography on silica gel (CH2Cl2)
(0.320 g, 33% yield).
Synthesis of 4,4′-Bis(cyclohexylethynyl)benzil (1f). 4,4′-Dibromo-
benzil (1b) (0.500 g, 1.22 mmol) and cyclohexylacetylene (0.385 mL,
2.99 mmol) were dissolved in 50 mL of THF in a two-neck round-
bottom flask under nitrogen atmosphere. Dichlorobis-
(triphenylphosphine)palladium(II) (0.168 g, 0.240 mmol), CuI
(0.0473 g, 0.251 mmol), and Et3N (5 mL) were added, and the
mixture was stirred for 1 h at room temperature. Then the solvent was
removed under vacuum, and the crude was purified by chromatog-
raphy on silica gel (petroleum ether/Et2O, 95:5), giving the desired
EXPERIMENTAL SECTION
■
Materials and Procedures. Solvents: THF was dried and distilled
under nitrogen prior to use. Ethanol (EtOH), methanol (MeOH),
dichloromethane (CH2Cl2), ethyl acetate, diethyl ether, petroleum
ether, referring to the fraction of bp 60−80 °C, CDCl3 (Sigma-
Aldrich), and reagents 1,3-diphenylacetone, benzil, NaOH, 4,4′-
dimethoxybenzil, 2-chloro-3′,4′-dimethoxybenzil, 9,10-phenanthrene-
quinone, 2-methyl-3-butin-2-ol, 1,1-diphenyl-2-propyn-2-ol, triethyl-
amine (Et3N), 2,3-butanedione, 2,3-pentanedione, 1-phenyl-1,2-
propanedione (Sigma-Aldrich), 4,4′-dibromobenzil (Alfa Aesar),
dichlorobis(triphenylphosphine)palladium(II), copper iodide (CuI),
and triruthenium dodecacarbonil (Ru3(CO)12) (Strem) have been
used as purchased. 4,4′-Bis(2-methyl-3-butin-2-ol)benzil and 4,4′-
bis(2-phenyl-3-butin-2-ol)benzil have been prepared as previously
reported.13 The prepared derivatives were characterized by spectro-
product 4,4′-bis(cyclohexylethynyl)benzil (1f) (0.478 g, 82% yields) as
1
a pale yellow solid. H NMR (399.9 MHz, CDCl3): δ 7.79 (d, JH,H
=
8.7, 4H, CHaryl), 7.49 (d, JH,H = 8.7, 4H, CHaryl), 2.60−2.45 (m, 2H),
1.85−1.55 (m, 8H), 1.55−1.15 (m, 12H). 13C{1H} NMR (100.6
MHz, CDCl3): δ 193.8 (CO), 132.0 (CH), 131.4 (C), 131.2 (C),
129.7 (CH), 100.0 (C), 80.1 (C), 32.4 (CH2), 29.8 (CH), 25.8 (CH2),
24.8 (CH2). IR (CH2Cl2): ν(CO) 1673 cm−1. GC-MS: 423 (M +
1). Anal. Calcd (%) for C30H30O2: C, 85.27; H, 7.16. Found: C, 85.23;
H 7.18.
1
scopic methods. H and 13C NMR were measured at rt with a 399.9
and 100.6 MHz NMR spectrometer; chemical shifts were referenced
internally to residual solvent peaks for 1H (CDCl3: 7.26 ppm) and 13
C
NMR (CDCl3: 77.00 ppm); infrared spectra were recorded at 298 K
with an FT-IR spectrophotometer. ESI-MS spectra were recorded with
samples dissolved in MeOH or CH3CN.
3,4-Bis[4-(cyclohexylethynyl)phenyl]-2,5-diphenylcyclopenta-2,4-
dienone (3f). Reactants: 4,4′-bis(cyclohexylethynyl)benzil (1f) (0.100
g, 0.240 mmol), 1,3-diphenylacetone 2 (0.0494 g, 0.240 mmol), and
NaOH (0.0096 mg, 0.240 mmol). The dark purple solid was purified
General Procedure for Microwave Experiments. Microwave
reactions were carried out in a “high-throughput rotor” microwave
oven using Teflon vessels equipped with a temperature sensor and
pressure control. The instrument power has been set at a maximum of
600 W. The instrument has been programmed in order to reach the
reaction temperature within 5 min and to maintain it for the required
reaction time. Thereafter the irradiation was stopped and the sample
cooled to room temperature. All the experiments have been followed
by temperature and pressure control while the power of pulsed
microwave irradiation is automatically modulated by the instrument in
order to follow the desired temperature program. All the experiments
1
by filtration (0.0330 g, 23% yield). H NMR (399.9 MHz, CDCl3): δ
7.20−7.10 (m, 14H, CHaryl), 6.76 (d, JH,H = 8.7, 4H, CHaryl), 2.55−
2.45 (m, 2H), 1.85−1.60 (m, 8H), 1.55−1.20 (m, 12H). 13C{1H}
NMR (100.6 MHz, CDCl3): δ 199.9 (CO), 153.6 (C), 132.0 (C),
131.3 (CH), 130.5 (C), 130.1 (CH), 129.3 (CH), 128.1 (CH), 127.6
(CH), 125.5 (C), 124.3 (C), 96.1 (C), 80.3 (C), 32.6 (CH2), 29.7
(CH), 25.9 (CH2), 24.9 (CH2). IR (CH2Cl2): ν(CO) 1712 cm−1.
GC-MS: 598 (M + 1). Anal. Calcd for C45H40O: C, 90.56; H, 6.76.
Found: C, 90.50; H, 6.75.
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3-(2-Chlorophenyl)-4-(3,4-dimethoxyphenyl)-2,5-diphenylcyclo-
penta-2,4-dienone (3g). Reactants: 2-chloro-3′,4′-dimethoxybenzil
(1g) (0.366 g, 1.19 mmol), 1,3-diphenylacetone 2 (0.250 g, 1.19
mmol), and NaOH (0.0479 g, 1.19 mmol). The dark purple solid was
purified by chromatography on silica gel (CH2Cl2/petroleum ether,
(CH2Cl2): ν(CO) 2040; 2011; 1981 cm−1. ESI-MS (m/z) (−):
1413 [M − H]−. Anal. Calcd (%) for C82H66O10Ru2: C, 69.59; H, 4.67.
Found: C, 69.69; H, 4.65.
The same reaction was performed under classic heating conditions
(methanol, 80 °C, 40 h), leading to a yield of 4d of 22%.
1
{[3,4-(4-CCC(Ph)2OH-C6H4)2-2,5-Ph2(η5-C4CO)]2H}Ru2(CO)4(μ-H)
(4e). Reactants: 3,4-bis(4-(3-hydroxy-3,3-diphenylprop-1-ynyl)-
phenyl)-2,5-diphenylcyclopenta-2,4-dienone (3e) (0.382 g, 0.48
mmol), Ru3(CO)12 (0.100 g, 0.16 mmol), and methanol (12 mL).
The complex {[3,4-(4-CCC(Ph)2OH-C6H4)2-2,5-Ph2(η5-
C4CO)]2H}Ru2(CO)4(μ-H) (4e), soluble in MeOH, was purified by
column chromatography on silica gel (eluent: CH2Cl2/EtOAc, 95:5)
(0.105 g, 23% yield). 1H NMR (399.9 MHz, CDCl3): δ (ppm) 8.08−
6.72 (m, 76H, CHaryl); −18.42 (s, 1H, RuHRu); OH variable. 13C{1H}
NMR (100.6 MHz, CDCl3): δ 201.32 (CO); 155.63 (C1-OH, Cp);
144.82 (Cipso, −(Ph)2OH) 133.30−126.02 (CHaryl and Cqaryl); 102.75
(C2,5; Cp); 94.22 (−CCC(CH3)2OH); 87.88 (C3,4; Cp); 86.92
(−CCC(Ph)2OH); 74.85 (−CCC(Ph)2OH). IR (CH2Cl2):
ν(CO) 2039; 2010; 1981 cm−1. ESI-MS (m/z) (−): 1909 [M −
H]−. Anal. Calcd (%) for C122H82O10Ru2: C, 76.65; H, 4.29. Found: C,
76.58; H, 4.32. The same reaction was performed under a classic
heating method (methanol, 80 °C, 40 h), leading to a yield of 4e of
25%.
9:1) (0.142 g, 25% yield). H NMR (399.9 MHz, CDCl3): δ 7.30−
7.00 (m, 17H, CHaryl), 3.71 (s, 3H, OMe), 3.30 (s, 3H, OMe).
13C{1H} NMR (100.6 MHz, CDCl3): δ 200.0 (CO), 154.4 (C),
152.3 (C), 149.3 (C), 148.0 (C), 134.1 (C), 133.7 (C), 131.1 (C),
130.6 (C), 130.3 (CH), 130.2 (CH), 129.8 (CH), 129.7 (CH), 129.3
(CH), 128.13 (CH), 128.09 (CH), 127.9 (C), 127.8 (CH), 127.4
(CH), 126.9 (CH), 125.4 (C), 123.6 (C), 122.4 (CH), 112.0 (CH),
110.5 (CH), 55.7 (CH3), 55.4 (CH3). IR (CH2Cl2): ν(CO) 1713
cm−1. GC-MS: 480 (M + 1). Anal. Calcd for C31H23ClO3: C, 77.74; H,
4.84. Found: C, 77.82; H, 4.85.
1,3-Diphenyl-2H-cyclopenta[l]phenanthrene-2-one (3h). Reac-
tants: 9,10-phenanthrenequinone (1h) (0.248 g, 1.19 mmol), 1,3-
diphenylacetone 2 (0.250 g, 1.19 mmol), and NaOH (0.0479 g, 1.19
mmol). The dark green, crystalline solid (0.0909 g, 20% yield) was
purified by filtration.
General Procedure for the Microwave-Assisted Synthesis of
Shvo-Type Complexes {[3,4-(R-C6H4)2-2,5-Ph2(η5-C4CO)]2H}-
Ru2(CO)4(μ-H) 4. Into a 75 mL Teflon vessel with a magnetic stirrer
were placed tetraarylcyclopentadienone 3 (3 equiv), Ru3(CO)12 (1
equiv), and methanol (12 mL). The vessel was sealed with a lid
equipped with a temperature sensor and placed in the microwave
oven. The reaction mixture was heated for 50 min at 110 °C.
{[2,3,4,5-Ph4(η5-C4CO)]2H}Ru2(CO)4(μ-H) (4a). Reactants: tetraphe-
nylcyclopentadienone (0.180 g, 0.48 mmol), Ru3(CO)12 (0.100 g, 0.16
mmol), and methanol (12 mL). The complex 4a was purified by
filtration (0.260 g, 75% yield). The purity of the product was verified
{[3,4-(4-(C6H11-CC)-C6H4)2-2,5-Ph2(η5-C4CO)]2H}Ru2(CO)4(μ-H)
(4f). Reactants: 3,4-bis[4-(cyclohexylethynyl)phenyl]-2,5-diphenylcy-
clopenta-2,4-dienone (3f) (0.287 g, 0.48 mmol), Ru3(CO)12 (0.100g,
0.16 mmol), and methanol (12 mL). The complex {[3,4-(4-(C6H11-
CC)-C6H4)2-2,5-Ph2(η5-C4CO)]2H}Ru2(CO)4(μ-H) (4f) was pu-
rified by filtration (0.268 g, 74% yield). 1H NMR (399.9 MHz,
CDCl3): δ (ppm) 7.41−6.82 (m, 36H, CHaryl); 2.52−1.05 (m, 44H,
cyclohexane), −18.46 (s, 1H, RuHRu); OH variable. 13C{1H} NMR
(100.6 MHz, CDCl3): δ 201.04 (CO); 155.11 (C1-OH, Cp); 132.0−
124.3 (CHaryl and Cqaryl), 102.63 (C2,5; Cp); 95.7, 81.0 (−CC−),
88.01 (C3,4; Cp); 33.0 (CH2), 29.7 (CH), 26.0 (CH2), 24.9 (CH2). IR
(CH2Cl2): ν(CO) 2037; 2019; 1976 cm−1. ESI-MS (m/z) (+): 1511
[M + H]+. Anal. Calcd (%) for C94H82O6Ru2: C, 74.70; H, 5.43.
Found: C, 74.77; H, 5.38. The same reaction was performed under a
classic heating method (methanol, 80 °C, 40 h), leading to a yield of 4f
of 72%.
1
by comparison of H and 13C NMR and IR spectra with literature
data.15 The same reaction was performed with a classic heating
method (methanol, 80 °C, 40 h), leading to a yield of 67%.
{[3,4-(OMe-C6H4)2-2,5-Ph2(η5-C4CO)]2H}Ru2(CO)4(μ-H) (4b). Reac-
tants: 3,4-bis(4-methoxyphenyl)-2,5-diphenylcyclopenta-2,4-dienone
(3b) (0.213 g, 0.48 mmol), Ru3(CO)12 (0.100 g, 0.16 mmol), and
methanol (12 mL). The complex 4b was purified by filtration (0.211 g,
73% yield). The purity of the product was verified by comparison of
1H and 13C NMR and IR spectra with literature data.15 Suitable
{[3,4-Phenanthren-2,5-Ph2(η5-C4CO)]2H}Ru2(CO)4(μ-H) (4h). Reac-
tants: 1,3-diphenyl-2H-cyclopenta[l]phenanthren-2-one (3h) (0.183 g,
0.48 mmol), Ru3(CO)12 (0.100 g, 0.16 mmol), and methanol (12 mL).
crystals of 4b were obtained by precipitation from MeOH. The same
reaction was performed under a classic heating method (methanol, 80
°C, 40 h), leading to a yield of 70%.
1
The complex 4c was purified by filtration (0.039 g, 15% yield). H
{[3,4-(Br-C6H4)2-2,5-Ph2(η5-C4CO)]2H}Ru2(CO)4(μ-H) (4c). Reac-
tants: 3,4-bis(4-bromophenyl)-2,5-diphenylcyclopenta-2,4-dienone
(3c) (0.260 g, 0.48 mmol), Ru3(CO)12 (0.100 g, 0.16 mmol), and
methanol (12 mL). The complex 4c was purified by filtration (0.242 g,
72% yield). Suitable crystals of 4c were obtained by precipitation from
MeOH. 1H NMR (399.9 MHz, CDCl3): δ 7.45−6.85 (m, 36H,
CHaryl), 3.43 (s, 1H, OH), −18.40 (s, 1H, RuHRu). 13C{1H} NMR
(100.6 MHz, CDCl3): δ 200.20 (CO), 154.49 (C1-OH, Cp), 130.96−
127.13 (Cqaryl and CHaryl), 101.88 (C2,5; Cp), 87.84 (C3,4; Cp). IR
(CH2Cl2): ν(CO) 2041, 2010, 1982 cm−1. ESI-MS (CH3OH, m/z):
1399 [M + H]+, 1421 [M + Na]+. Anal. Calcd (%) for
C62H38Br4O6Ru2: C, 53.22 ; H, 2.78. Found: C, 53.34; H, 2.76. The
same reaction was performed under a classic heating method
(methanol, 80 °C, 40 h), leading to a yield of 4c of 62%.
NMR (399.9 MHz, CDCl3): δ 8.83−7.17 (m, 36H, CHaryl), −19.68 (s,
1H, RuHRu), OH variable. IR (CH2Cl2): ν(CO) 2037, 2008, 1981
cm−1. ESI-MS (CH3OH, m/z): 1083 [M + H]+. Anal. Calcd (%) for
C62H38O6Ru2: C, 68.76; H, 3.51. Found: C, 68.88; H, 3.49.
X-ray Crystallography. Crystal data and collection details for 4b·
CH2Cl2 and 4c are reported in Table S1 in the Supporting
Information. The diffraction experiments were carried out on a
diffractometer equipped with a CCD detector using Mo Kα radiation.
Data were corrected for Lorentz polarization and absorption effects
(empirical absorption correction SADABS).22 Structures were solved
by direct methods and refined by full-matrix least-squares based on all
data using F2.23 All hydrogen atoms were fixed at calculated positions
and refined by a riding model, except H(1) and H(3) in both
structures, which were located in the Fourier map and refined
isotropically using the 1.2-fold Uiso value of the parent atoms. All non-
hydrogen atoms were refined with anisotropic displacement
parameters.
4b·CH2Cl2. The asymmetric unit of the unit cell contains one 4b
complex and one CH2Cl2 molecule (all located on general positions).
The CH2Cl2 molecule is disordered over three independent positions,
and, therefore, it has been split and refined isotropically using one
occupancy parameter per disordered group; the sum of the site
occupation factors of the three images has been restrained to unit
(SUMP 1.0 0.001 1.0 2 1.0 3 1.0 4 line in SHELXL). Some C and O
atoms of 4b have been restrained to isotropic behavior (ISOR line in
SHELXL, s.u. 0.01). The Ru(1)−H(1) and Ru(2)−H(1) distances
have been restrained to be similar (SADI line in SHELXL, s.u. 0.01);
{[3,4-(4-CCC(CH3)2OH-C6H4)2-2,5-Ph2(η5-C4CO)]2H}Ru2(CO)4(μ-
H) (4d). Reactants: 3,4-bis(4-(3-hydroxy-3-methylbut-1-ynyl)phenyl)-
2,5-diphenylcyclopenta-2,4-dienone (3d) (0.263 g, 0.48 mmol),
Ru3(CO)12 (0.100 g, 0.16 mmol), and methanol (12 mL). The
complex {[3,4-(4-CCC(CH3)2OH-C6H4)2-2,5-Ph2(η5-C4CO)]2H}-
Ru2(CO)4(μ-H) (4d), soluble in MeOH, was purified by column
chromatography on silica gel (eluent: CH2Cl2/EtOAc, 95:5) (0,081 g,
1
24% yield). H NMR (399.9 MHz, CDCl3): δ 7.62−6.89 (m, 36H,
CHaryl); 1.55 (s, 24H, CH3); −18.38 (s, 1H, RuHRu); OH variable.
13C{1H} NMR (100.6 MHz, CDCl3): δ 201.12 (CO); 155.52 (C1-
OH, Cp); 131.81−126.75 (CHaryl and Cqaryl); 102.48 (C2,5; Cp);
94.93 (−CCC(CH3)2OH); 87.78 (C3,4; Cp); 81.59 (−CCC-
(CH3)2OH); 65.52 (−CCC(CH3)2OH); 31.37 (CH3). IR
2818
dx.doi.org/10.1021/om500335m | Organometallics 2014, 33, 2814−2819

Organometallics
Article
the same restraint has been applied also to the O(3)−H(3) and
O(53)−H(3) distances. The three images of CH2Cl2 have been
restrained to have similar geometries (SAME line in SHELXL, s.u.
0.02) and similar U parameters (SIMU line in SHELXL, s.u. 0.02).
Restraints to bond distances were applied as follows (s.u. 0.02): 1.75 Å
for C−Clin CH2Cl2.
4c. The asymmetric unit of the unit cell contains half of a complex
molecule located on a 2-fold axis passing through H(1) and H(3).
CCDC reference numbers 990832−990833 contain the supple-
mentary crystallographic data for this paper.
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ASSOCIATED CONTENT
* Supporting Information
Crystallographic data in CIF and PDF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
M.; Anson, C. E.; List, E. J. W.; Mullen, K. Angew. Chem., Int. Ed. 2008,
̈
47, 8292. (b) Liang, Y.; Schwab, M. G.; Zhi, L.; Mugnaioli, E.; Kolb,
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̈
AUTHOR INFORMATION
Corresponding Author
*Tel: +39-0512093700. E-mail: rita.mazzoni@unibo.it.
Notes
T.; Ding, J.; Wang, L.; Baumgarten, M.; Zhou, G.; Mullen, K. J. Am.
̈
■
Chem. Soc. 2009, 131, 14329. (d) Zhi, L.; Wu, J.; Mullen, K. Org. Lett.
̈
2005, 7, 5761. (e) Bauer, R.; Liu, D.; Heyen, A. V.; Schryver, F. D.;
Feyter, S. D.; Mullen, K. Macromolecules 2007, 40, 4753.
̈
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2004, 69, 9191. (b) Casey, C. P.; Singer, S.; Powell, D. R.; Hayashi, R.
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Salant, E.; Shvo, Y. J. Organomet. Chem. 1996, 514, 97. (d) Thalen, L.
K.; Zhao, D.; Sortais, J. B.; Paetzold, J.; Hoben, C.; Backwall, J. E.
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors thank the Ministero dell’Universita
(MIUR) (project: “Designing metal containing molecular
fragments for advanced chemical applications”. The University
of Bologna is acknowledged for financial support through the
FARB Project “Catalytic transformation of biomass-derived
materials into high added-value chemicals”, 2014-2015.
■
̀
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