The effect of the oxidation state of molybdenum complexes on the catalytic transformation of terminal alkynes: Cyclotrimerization vs. polymerization

Article abstract of DOI:10.1016/j.jorganchem.2012.05.044

Reactions of monosubstituted alkynes (PhC≡CH, ^tBuC≡ CH, ⁿBuC≡CH, HOCH₂C≡CH, HO(CH ₃)₂CC≡CH) in the presence of molybdenum(0) and molybdenum(II) carbonyl complexes (Mo(CO)₆/hv, [Mo(CO) ₄(pip)₂] (pip = piperidine), [Mo(CO)₄(pip) ₂]/SnCl₄, [Rpip]₂[{(μ-Cl)Mo(μ-Cl) (SnCl₃)(CO)₃}₂] (R = C₃H ₅, H)) lead to the formation of cyclotrimerization and polymerization products, which were characterized by chromatography (GC-MS, GPC) and by ¹H and ¹³C NMR spectroscopy. The effect of the oxidation state of the molybdenum catalyst on the transformation of the terminal alkynes was observed: cyclotrimerization vs. polymerization. Only molybdenum(II) complexes lead to the formation of polyenic polymers. Moreover, reaction of prop-2-yn-1-ol initiated by [Mo(CO)₄(pip)₂] in dichloromethane leads to the formation of oligomers containing the vinylidene unit. Mechanistic NMR studies show that η²-alkyne complex formation is the principal feature of all transformations of alkynes catalyzed by molybdenum complexes.

Full text of DOI:10.1016/j.jorganchem.2012.05.044

Journal of Organometallic Chemistry 716 (2012) 70e78
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
The effect of the oxidation state of molybdenum complexes on the catalytic
transformation of terminal alkynes: Cyclotrimerization vs. polymerization
*
ꢀ
ꢀ
Izabela Czelusniak, Paulina Kocie˛cka, Teresa Szymanska-Buzar
Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
Reactions of monosubstituted alkynes (PhChCH, tBuChCH, nBuChCH, HOCH2ChCH,
HO(CH3)2CChCH) in the presence of molybdenum(0) and molybdenum(II) carbonyl complexes
Article history:
Received 25 April 2012
Received in revised form
23 May 2012
(Mo(CO)6/hv, [Mo(CO)4(pip)2] (pip ¼ piperidine), [Mo(CO)4(pip)2]/SnCl4, [Rpip]2[{(
m-Cl)Mo(m-Cl)
(SnCl3)(CO)3}2] (R ¼ C3H5, H)) lead to the formation of cyclotrimerization and polymerization products,
which were characterized by chromatography (GCeMS, GPC) and by 1H and 13C NMR spectroscopy. The
effect of the oxidation state of the molybdenum catalyst on the transformation of the terminal alkynes
was observed: cyclotrimerization vs. polymerization. Only molybdenum(II) complexes lead to the
formation of polyenic polymers. Moreover, reaction of prop-2-yn-1-ol initiated by [Mo(CO)4(pip)2] in
dichloromethane leads to the formation of oligomers containing the vinylidene unit. Mechanistic NMR
Accepted 30 May 2012
Keywords:
Molybdenum catalysts
Alkynes
Alkynols
studies show that
alkynes catalyzed by molybdenum complexes.
h
2-alkyne complex formation is the principal feature of all transformations of
Cyclotrimerization
Polymerization
NMR
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
contain pyrazole (Hpz) or 1-Me-imidazole (1-Me-im) ligands,
cyclotrimerize alkynes like ethyl propiolate (EtOOCChCH) and
dimethyl acetylenedicarboxylate (MeOOCChCCOOMe) to give
cyclotrimerization and co-cyclotrimerization reaction products
under mild conditions. The latter complexes are also active in the
cyclotrimerization of HChCPh and HChCCMe¼CH2 [11]. More-
over, the Mo(CO)6/4-chlorophenol system has been used in the
synthesis of alkyne-bridged polymers by the acyclic diyne
metathesis (ADIM) of dipropynylated benzenes [12], while alkyne
cross-metathesis (ACM) as well as ring-closing alkyne metathesis
(RCAM) have been carried out in the Mo(CO)6/2-fluorophenol
system [13].
It has also been established that the polymerization of
monosubstituted alkynes such as phenylacetylene, 1-chloro-2-
phenylacetylene, 2-trimethylsilylphenylacetylene, 2-trifluorome
thylphenylacetylene, and tert-butylacetylene can be carried out
during the photolysis of Mo(CO)6 or W(CO)6 in carbon tetrachloride
or other halogenated alkanes [14e16].
The [2þ2þ2] cyclotrimerization of alkynes represents an
important strategy for the synthesis of benzene derivatives
(Scheme 1), which are useful starting materials for further trans-
formation and building blocks in organic synthesis [1,2]. The
transition-metal-catalyzed cyclotrimerization of alkynes was
discovered by Reppe and Schweckendick in 1948 [3]. Since then,
various metal complexes have been used as catalysts selectively
providing two isomers (1,3,5 or 1,2,4) of polysubstituted benzene
derivatives [4e7]. In some cases, the transition-metal-catalyzed
cyclotrimerization of terminal alkynes is accompanied by poly-
merization leading to the formation of polyenic polymers, or vice
versa, polymerization is accompanied by cyclotrimerization
(Scheme 2) [7e10].
Molybdenum complexes, especially those in a low oxidation
state, are frequently used as catalysts for the cyclotrimerization of
alkynes. Molybdenum (0) complexes such as Mo(CO)6 and its
derivatives: [Mo(CO)3(Hpz)3] and [Mo(CO)3(1-Me-im)3], which
In the course of a search for catalytically active species formed in
the photochemical reaction of M(CO)6 (M ¼ Mo, W) and alkynes,
the
[M(CO)5(
of the
2-alkyne ligand to an
h
2-coordination of alkyne to the metal center of the
h
2-alkyne)] complex and the subsequent rearrangement
1-vinylidene ligand can be observed
* Corresponding author. Faculty of Chemistry, University of Wroc1aw, ul. F. Joliot-
Curie 14, 50-383 Wroc1aw, Poland. Tel.: þ48 71 375 7221; fax: þ48 71 328 2348.
h
h
by low-temperature matrix studies [17,18]. This transformation
may well be the initiation step in the polymerization reaction of
ꢀ
E-mail address: teresa.szymanska-buzar@chem.uni.wroc.pl (T. Szymanska-
Buzar).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.05.044

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I. Czelusniak et al. / Journal of Organometallic Chemistry 716 (2012) 70e78
71
[Mo(CO)4(pip)2] (2) [36,37] was prepared in the photochemical
reaction of Mo(CO)6 and pip in n-hexane. The molybdenum(II)
complex [(C3H5)pip]2[{(m-Cl)Mo(m-Cl)(SnCl3)(CO)3}2] (3a) was
synthesized in reaction of [Mo(CO)4(pip)2] (2) and SnCl4 in
dichloromethane in accordance with a previously reported proce-
dure [38]. A small modification of this procedure in the form of
a shorter reaction time (2 h) of [Mo(CO)4(pip)2] (2) and SnCl4 leads
R
R
R
[M]
HC CR
[M]
+
R
+
+
R
R
Scheme 1. [2þ2þ2] cyclotrimerization of alkynes catalyzed by transition-metal
to the formation of an ionic complex of molybdenum(II), [{(m-Cl)
complexes [M].
Mo(m
-Cl)(SnCl3)(CO)3}2]2- (3b), containing two piperidinium
cations [Hpip]þ as the counter ions. Anal. Calcd for
C16H24Cl10Mo2N2O6 (1124.2): C, 17.09; H, 2.15; N, 2.49. Found: C,
17.70; H, 2.51; N, 2.94.
R
n
Mo(CO)6/PhOH/I2
H
HC CR
+
R3
C=C
Photochemical reactions were carried out under an atmosphere
of nitrogen in a glass reactor with a quartz window. The photolysis
source was an HBO 200 W medium-pressure Hg lamp.
(
)
Scheme 2. Cyclotrimerization vs. polymerization of terminal alkynes in a catalytic
system containing Mo(CO)6, phenol, and iodine [8].
IR spectra were measured with a Nicolet-400 FT-IR instrument
in solution, and with a Bruker IFS66 as Nujol mulls or KBr pellets.
1H, 13C NMR, and two-dimensional 1He1H COSY, 1He13C HMQC,
and 1He13C HMBC NMR spectra were recorded with a Bruker
Avance III 600 MHz (1H, 600.15 MHz; 13C, 150.91 MHz) and a Bruker
Avance 500 MHz (1H, 500.13 MHz; 13C, 125.76 MHz) instruments.
All proton and carbon chemical shifts were referenced to the
residual proton signal for 1H NMR (7.24 CDCl3, 3.60 C4D8O, 3.35
CD3OD, and 1.40 C6D12) or the natural abundant carbon signal of
the solvent for 13C NMR (77.0 CDCl3, 66.0 C4D8O, 49.0 CD3OD, and
26.4 C6D12).
Analyses of the reaction products were performed on a Hewlett-
Packard GCeMS system containing an HP590II gas chromatograph
equipped with a HP-5MS column and an HP5971A mass detector.
Mass spectra were measured by electron impact with an ionizing
energy of 70 eV and on an apex-Ultra mass spectrometer using the
ESI method. The organometallic compounds were analyzed on
MicrOTOF-Q Bruker using the ESI method.
terminal alkynes in the presence of molybdenum(0) and tung-
sten(0) complexes [19,20].
In reaction with oxidants such as Cl2, Br2, I2, CCl4, GeCl4, or SnCl4,
molybdenum(0) carbonyl complexes are transformed to seven-
coordinate molybdenum(II) complexes [21e23]. These molybde-
num(II) complexes readily react with diphenylacetylene in
dichloromethane solution at room temperature to give alkyne
complexes, but in reaction with terminal alkynes they initiate
polymerization and cyclotrimerization reactions [24e27]. As
a result of the above-referenced studies, a plausible mechanism for
the initiation of alkyne polymerization by molybdenum(II) and
tungsten(II) was postulated [28]. It is very probable that an alkyli-
dene ligand initiating the growth of a linear polyenic polymer chain
is formed as a result of the rearrangement of the metallacycle
formed with three or four molecules of alkyne. The simultaneous
formation of cyclotrimerization products of alkynes fits this
mechanism very well. It is very interesting that in reaction of
Gel permeation chromatography (GPC) data were obtained using
a Viscotek GPC max equipped with a Viscotek VE 3580 refractive
[MoI2(CO)(NCMe)(
1,2,4-trimethyl-3,5,6-triphenylbenzene was isolated [29], but the
h
2-MeChCPh)2] with P(OiPr)3, the cyclotrimer
index detector and 2 ꢀ 300 mm Shodex GPC 6
mm KF-802.5 columns
for tetrahydrofuran (THF) solutions (10 mg/cm3) of polymers. THF
was used as the eluent at a flow rate of 1.0 cm3/min at 30 ꢁC. Poly-
styrene standards were used for calibration.
molybdenum(II) complex, [MoCl(
cally converts PhChCPh to
h
3-C3H5)(CO)2(NCMe)2], catalyti-
mixture of E,E-1,2,3,4-
a
tetraphenylbutadiene and hexaphenylbenzene [30].
Thermogravimetric analyses (TGA) of polymers were conducted
under a nitrogen atmosphere at a heating rate of 5 ꢁC/min in the
temperature range 30e600 ꢁC with a Perkin Elmer TMA-7 thermal
analyzer.
However, in contrast to alkyl- and aryl-substituted acetylenes,
the cyclotrimerization and polymerization of hydroxyacetylenes
have been studied less extensively [31e35], which is probably due
to the deactivation of the catalyst by the polar hydroxy group. For
that reason, it seems interesting to investigate the catalytic activity
of molybdenum complexes in the oligomerization of terminal
alkynes containing different substituents.
2.1. Photochemical reactions of 1 and alkynes
A hexane, toluene, or tetrahydrofurane solution (20 cm3) of 1
(0.11 g, 0.42 mmol) and the alkyne tBuChCH or HOCH2ChCH
(ca. 0.2 cm3) in a 1:5 molar ratio was stirred and irradiated at room
temperature for 1e2 h. The reaction course was investigated by
following the IR spectra in solution. All volatile components were
then evaporated under reduced pressure at room temperature, and
the residue was analyzed by the GCeMS method and NMR spec-
troscopy, which revealed the conversion of the alkyne to the
In this paper, we describe the formation and identification by
NMR spectroscopy of the cyclotrimerization and polymerization
products formed in reactions of monosubstituted alkynes
t
(PhChCH, BuChCH, nBuChCH, HOCH2ChCH, HO(CH3)2CChCH)
catalyzed by molybdenum complexes at room temperature. The
effect of the oxidation state of the molybdenum atom on the
selectivity of the alkyne reaction is investigated.
cyclotrimerization products and their
(see Table 1 and Section 2.7.)
h
6-arene complexes
2. Experimental
All reactions were performed using standard Schlenk tech-
niques under an atmosphere of nitrogen and with substrates and
solvents freshly distilled from calcium hydride. Mo(CO)6 (1)
(Sigma-Aldrich) was used as received. Tert-butylacetylene (Sigma-
Aldrich), 1-hexyne (Fluka), fenylacetylene (ABCR) were distilled
from calcium hydride. Prop-2-yn-1-ol (Sigma-Aldrich) was dried
with molecular sieves (4A) and distilled. 2-methylbut-3-yn-2-ol
(99% Fluka) was used as received. The piperidine (pip) complex
2.2. Reaction of prop-2-yn-1-ol in the presence of [Mo(CO)5(THF)]
2.2.1. Reaction in a round-bottomed flask
The [Mo(CO)5(THF)] complex, synthesized in photochemical
reaction of 1 (0.11 g, 0.42 mmol) in tetrahydrofurane (20 cm3), was
isolated by the evaporation of the solvent and then dissolved in
dichloromethane (15 cm3). To this solution, prop-2-yn-1-ol
(0.55 cm3, 10.4 mmol) was added. The mixture was stirred for 1 h

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72
Table 1
Cyclotrimerization reactions of monosubstituted alkynes in the presence of molybdenum complexes [Mo(CO)6] (1), [Mo(CO)4(pip)2] (2), [Rpip]2[{(
m-Cl)
Mo( -Cl)(SnCl3)(CO)3}2] (3).
m
a
Alkyne
Catalytic system
Conversion
Selectivity
of cyclotrimerization
Molar ratio of 1,2,4:1,3,5
substituted benzenes
HOCH2ChCH
HOCH2ChCH
HOCH2ChCH
HOCMe2ChCH
tBuChCH
1/hv
[Mo(CO)5(THF)]
3
3
1/hv
2/SnCl4
3
2/SnCl4
2/SnCl4
3
100b
5c
64
99
100
98
9
100
99
1
100
98
5
71:29
64:36
84:16
83:17
88:12
0:100
0:100
36:64
48:52
50:50
92
50d
100
100
100
100
100
tBuChCH
tBuChCH
nBuChCH
PhChCH
PhChCH
a
After 24 h of reaction time in CH2Cl2 at room temperature, unless stated otherwise.
b
c
2 h in toluene.
1 h in CH2Cl2
2 h in hexane
d
at room temperature. All volatile components were then evapo-
rated under reduced pressure at room temperature, and the residue
was analyzed by NMR spectroscopy and GCeMS. In the GCeMS
spectrum, two signals were observed at retention times (r.t.) of
6.5 min (Mþ ¼ 170) and 7.5 min (Mþ ¼ 168). These signals were
assigned to tri(hydroxymethyl)hexatriene and tri(hydroxymethyl)
benzene, respectively.
Tri(hydroxymethyl)hexatriene: GCeMS: C9H14O3, Mr ¼ 170.21,
r.t. 6.5 min, m/z (relative intensity): 170 (Mþ, 6),133 (12), 98 (18), 84
(100), 63 (14), 49 (4).
84 (100), 69 (22), 56 (9), 41 (13); C6H8O2, Mr ¼ 112.13, r.t. 8.5 min
(0.1%), m/z (relative intensity): 112 (Mþ, 100), 95 (3), 84 (6); 67 (4),
56 (6), 41 (8); C6H8O2, Mr ¼ 112.13, r.t. 8.6 min (0.2%), m/z (relative
intensity): 112 (Mþ, 100), 98 (3), 84 (8); 67 (2), 56 (5), 41 (5);
C15H20O5, Mr ¼ 280.32, r.t. 8.9 min (92%), m/z (relative intensity):
264 (Mþ, ꢂ16, 0.2), 180 (3), 166 (3), 152 (24), 136 (3), 122 (3), 112
(13), 98 (100), 84 (16); 67 (4), 55 (10), 41 (11); C9H12O3, Mr ¼ 168.19,
r.t. 10.7 min (0.2%), m/z (relative intensity): 168 (Mþ, 75), 140 (42),
112 (12), 100(12), 98 (42), 84 (100); 67 (18), 59 (43), 41 (30).
Analysis by NMR spectroscopy (1H, 13C, DEPT, 1He1H COSY,
1He13C HMQC, and 1He13C HMBC) revealed the formation as the
major product (92% yield by NMR) of two compounds: a and b,
containing vinylidene units and existing in a ratio of 2:1 (a:b).
Another compound (c) was identified by NMR analysis (4%) as
containing the hydroxymethylvinyl unit, CH¼CH(CH2OH). These
oily compounds were separated from other products by extraction
to hexane.
Tri(hydroxymethyl)benzene: GCeMS: C9H12O3, Mr ¼ 168.19, r.t.
7.5 min, m/z (relative intensity): 168 (Mþ, 99),131 (83),117 (100), 96
(67), 84 (38), 61 (46), 47 (11).
2.2.2. Reaction in the NMR tube
The course of reaction of the [Mo(CO)5(THF)] complex with
prop-2-yn-1-ol was followed by 1H NMR spectroscopy. In accor-
dance with the general procedure for NMR experiments,
[Mo(CO)5(THF)] (0.05 g, 0.04 mmol) was dissolved in CDCl3
(0.7 cm3) and transferred to the NMR tube. To this solution, prop-2-
yn-1-ol (0.05 cm3, 1.0 mmol) was added. The tube was periodically
monitored by 1H NMR spectroscopy over the desired length of time
in the temperature range from ꢂ20 to 25 ꢁC. The coordination of
prop-2-yn-1-ol to the molybdenum atom was suggested by a signal
at 9.74 ppm observed as a triplet with a coupling constant
4JHeH ¼ 1.9 Hz, which correlated in the COSY NMR spectrum with
a CH2 signal at 2.81 ppm.
(a) 1H NMR (
d, CDCl3, 600.15 MHz): 4.91 (s, 1H, H2C), 4.73 (s, 1H,
2
H2C), 4.65 (s, 1H, CH), 4.36 (d, JHeH ¼ 12.7 Hz, 1H, H2C), 4.10
2
2
(d, JHeH ¼ 12.7 Hz, 1H, H2C), 2.96 (dd, JHeH ¼ 11.0 Hz,
3JHeH ¼ 6.9 Hz,1H, H2C), 2.91 (t, 3JHeH ¼ 7.4 Hz,1H, HC), 2.38 (m,
2
H2C), 2.34 (d, JHeH ¼ 11.0 Hz, H2C), 2.00 (m, 1H, H2C), 1.86 (m,
1H, H2C), 1.71 (m, H2C), 1.57 (m, H2C), 1.43 (m, H2C). 13C{1H}
NMR (d, CDCl3, 150.91 MHz): 141.2 (1C, C), 111.7 (1C, H2C), 81.3
(1C, CH), 68.8 (1C, CH2), 64.7 (1C, CH), 56.3 (CH2), 54.4 (CH2),
47.8 (CH2), 30.3 (CH2), 25.7 (CH2), 18.6 (CH2).
(b) 1H NMR (
d, CDCl3, 600.15 MHz): 4.98 (s, 1H, H2C), 4.81 (s, 1H,
H2C), 4.44 (s, 1H, CH), 4.22 (d, 2JHeH ¼ 12.1 Hz, 1H, H2C), 4.14 (d,
3
2JHeH ¼ 12.1 Hz, 1H, H2C), 3.36 (t, JHeH ¼ 6.9 Hz, 1H, HC), 2.98
2.3. Reaction of alkynes in the presence of 2
2
3
(dd, JHeH ¼ 11.0 Hz, JHeH ¼ 6.9 Hz, 1H, H2C), 2.54 (m, H2C),
2.42 (m, H2C), 2.38 (m, H2C), 2.28 (m, H2C), 2.26 (m, H2C), 2.00
(m, 1H, H2C), 1.86 (m, 1H, H2C), 1.71 (m, H2C), 1.50 (m, H2C), 1.43
A dichloromethane solution (20 cm3) of 2 (0.076 g, 0.2 mmol)
t
and an alkyne: BuChCH, HOCH2ChCH or HO(CH3)2CChCH (ca.
0.3e0.6 cm3), in a 1:25 molar ratio, was stirred at room tempera-
ture for 24 h. All volatile components were then evaporated under
reduced pressure at room temperature, and the residue was
analyzed by NMR spectroscopy and the GCeMS method.
(m, H2C). 13C{1H} NMR (
d, CDCl3, 150.91 MHz): 141.3 (1C, C),
109.4 (1C, H2C), 89.2 (1C, CH), 72.7 (1C, CH2), 61.8 (1C, CH), 55.9
(CH2), 54.5 (CH2), 47.9 (CH2), 30.6 (CH2), 25.4 (CH2), 19.2 (CH2).
3
(c) 1H NMR (
d
, CDCl3, 600.15 MHz): 6.23 (d, JHeH ¼ 14.6 Hz, 1H,
3
3
HC), 5.81 (dt, JHeH ¼ 14.6 Hz, JHeH ¼ 5.7 Hz, 1H, HC), 4.18
t
(d, JHeH ¼ 5.7 Hz, 1H, H2C). 13C{1H} NMR
(
d,
CDCl3,
3
2.3.1. Reaction of BuChCH in the presence of 2
tBuChCH was recovered essentially unchanged after reaction in
the presence of 2.
150.91 MHz): 135.5 (1C, HC), 132.5 (1C, HC), 63.0 (1C, CH2).
2.3.3. ProductsofHO(CH3)2CChCHtransformationin the presence of 2
Analysis by NMR spectroscopy revealed the formation of
compound (a) (ca. 5%) containing the vinyl unit eCH¼CH2, and
2.3.2. Products of HOCH2ChCH transformation in the presence of 2
Analysis of the reaction products by GCeMS showed five signals
which appeared with increasing retention times: C6H8O2,
Mr ¼ 112.13, r.t. 7.6 min (7.5%), m/z (relative intensity): 112 (Mþ, 14),
compound (b) (ca. 95%) containing the piperidinium cation: (a)
1H NMR
(
d,
CDCl3, 500.13 MHz): 5.84 (dd, JHeH ¼ 17.5 Hz,
3

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73
3
3JHeH ¼ 10.7 Hz, 1H, HC), 5.05 (d, JHeH ¼ 17.5 Hz, 1H, H2C), 4.82
formation of compounds containing the olefin bond. Analysis of the
brown solid by NMR in C4D8O revealed the formation of 1,3,5-
tri(hydroxymethyl)benzene and 1,2,4-tri(hydroxymethyl)benzene
in the molar ratio of 1:5 (see Section 2.7). The brown solid residue
insoluble in any organic solvent was analyzed by IR spectroscopy. IR
(d, JHeH ¼ 10.7 Hz, 1H, H2C). 13C{1H} NMR (
d, CDCl3, 125.76 MHz):
3
145.6 (1C, HC), 110.0 (1C, H2C); (b) 1H NMR (
d, CDCl3, 500.13 MHz):
8.53 (s, 2H, NH2), 3.02 (s, 4H, H2C),1.73 (s, 4H, H2C),1.45 (s, 2H, H2C).
, CDCl3, 125.76 MHz): 44.6 (2C, H2C), 22.0 (2C, H2C),
21.8 (1C, H2C). Analysis of the reaction products by the ESI-MS
method showed the anion [C30H38Mo2O14
Supplementary Data for the experimental and calculated spectra).
13C{1H} NMR (
d
(KBr pellet, n
, cmꢂ1 (relative intensity)): 3180 (vs), 2950 (s), 2870
ꢂ
]
(Mꢂ ¼ 814.5) (see
(m), 1715 (w), 1616 (m), 1574 (s), 1471 (w), 1454 (s), 1473 (w), 1406
(m), 1028 (s), 983 (m), 860 (w), 832 (w), 747 (w), 541 (w), 427 (w).
2.4. Reaction of alkynes in the presence of 2 and SnCl4
2.5.4. Characterization of HOC(CH3)2ChCH transformation
products
A dichloromethane solution (15 cm3) of 2 (0.02 g, 0.053 mmol),
In the reaction of 2-methylbut-3-yn-2-ol initiated by 3a or
3b, the formation of a brown solid was observed. The solid was
isolated from a dark solution and both fractions were analyzed
by NMR spectroscopy, which revealed the formation of 1,3,5-
tri(2-hydroxyizopropyl)benzene and 1,2,4-tri(2-hydroxyizopropyl)
benzene in the molar ratio of 1:5 (see Section 2.7). In the 1H NMR
spectrum measured in CDCl3 solution, in addition to cyclotrimer
signals, several proton signals were observed in the range
SnCl4 (0.012 cm3, 0.11 mmol), and an alkyne: PhChCH, BuChCH,
t
nBuChCH (ca. 0.2e0.3 cm3), in a 1:2:50 molar ratio, was stirred at
room temperature for 24 h. All volatile components were then
evaporated under reduced pressure at room temperature, and the
residue was analyzed by the GCeMS method and NMR spectros-
copy, which revealed a ca. 100% conversion of the alkyne and the
formation of cyclotrimers as the major products (see Table 1 and
Section 2.7.).
d
8e5 ppm. The latter signals correlated with carbon signals in the
range 130e110 ppm, which suggested the formation of
d
2.5. Transformation of alkynes in the presence of 3a or 3b
compounds containing the olefin bond. Analysis of the latter
solution by GCeMS showed the presence of dimers (C10H16O2,
Mr ¼ 168.2) and cyclotrimers (C15H24O3, Mr ¼ 252.3) as well as their
hydrogenation products (C10H18O2, Mr ¼ 170.2, C15H26O3,
Mr ¼ 254.4). Analysis by the ESI-MS method revealed the formation
of new molybdenum complexes identified as anions Mꢂ: 291
(C9H7MoO5), 319 (C10H7MoO6), 515 (C25H39MoO5), 571
(C13H14MoO6Sn) (see Supplementary Data for the experimental and
calculated MS spectra). The brown insoluble solid was analyzed by
A
dichloromethane solution (15 cm3) of 3a (0.057 g,
0.048 mmol) or 3b (0.054 g, 0.048 mmol) and an alkyne: PhChCH,
tBuChCH, HOCH2ChCH or HO(CH3)2CChCH (ca. 0.2e0.3 cm3), in
a 1:50 molar ratio, was stirred at room temperature for 24 h. All
volatile components were then evaporated under reduced pressure
at room temperature, and the residue was analyzed by the GCeMS
method and NMR spectroscopy, which revealed the formation of
polymerization and cyclotrimerization products (see Section 2.7.).
IR spectroscopy. IR (KBr pellet, n
, cmꢂ1 (relative intensity)): 3185
(vs), 3112 (s), 2964 (m), 2872 (w), 1611 (m), 1575 (s), 1473 (w), 1455
(s), 1406 (m), 1389 (w), 1279 (w), 1015 (w), 984 (w), 941 (w), 901
(w), 858 (w), 744 (s), 539 (w), 426 (w).
2.5.1. Characterization of poly(tBuChCH) (poly-tBA)
A white powder of poly-tBA synthesized in reaction initiated by
the molybdenum(II) complex 3a was purified by crystallization
from tetrahydrofurane/methanol solution and next investigated by
the GPC, TGA, NMR, and IR methods. The polymer yield was 99%.
GPC analysis: Mn 127,251, Mw 147,368, Mw/Mn 1.16. TGA analysis:
a one-step degradation process with the onset decomposition
2.6. NMR and GCeMS characterization of cyclotrimerization
products of alkynes
1,3,5-triphenylbenzene (1,3,5-TPB) [39,40]: 1H NMR (
500.13 MHz): 7.77 (s, 3H, HC-Bz), 7.68 (d, JHeH ¼ 7.5 Hz, 6H, HCo-
d, CDCl3,
3
temperature at ca. 256 ꢁC. 1H NMR (
(sharp, cis-CH), 6.0 (broad, trans-CH), 1.20 (tBu). 13C{1H} NMR
, C4D8O, 125.76 MHz): 145.9 (CtBu), 129.4 (CH), 39.3, (CMe3), 32.2
(Me). IR (KBr pellet,
, cmꢂ1 (relative intensity)): 2956 (vs), 2868 (s),
d
, C4D8O, 125.76 MHz): 6.28
3
3
Ph), 7.47 (t, JHeH ¼ 7.5 Hz, 6H, HCm-Ph), 7.38 (t, JHeH ¼ 7.5 Hz, 3H,
(d
HCp-Ph). 13C NMR (
d, CDCl3, 125.76 MHz): 142.3, 141.1 (3C, Ci-Ph and
n
3C, C-Bz), 128.8 (d, 1JCeH ¼ 160 Hz, 6C, HCm-Ph), 127.5 (3C, HCp-Ph),
1
1
1479 (s), 1391 (m), 1360 (s), 1260 (w), 1199 (m), 1022 (w), 932 (w),
898 (w), 559 (w).
127.4 (d, JCeH ¼ 159 Hz, 6C, HCo-Ph), 125.2 (d, JCeH ¼ 158 Hz, 3C,
HC-Bz). GCeMS: C24H18, Mr ¼ 306.4, r.t. 12.7 min, m/z (relative
intensity): 306 (Mþ, 100).
2.5.2. Characterization of poly(PhChCH) (poly-PA)
1,2,4-triphenylbenzene (1,2,4-TPB) [39,40]: 1H NMR (
d, CDCl3,
Ochre amorphous poly-PA separated by an excess of methanol
from dichloromethane solution of the reaction mixture was
investigated by the GPC, TGA, NMR, and IR methods. The polymer
yield was 95%. GPC analysis: Mn 2418, Mw 4235, Mw/Mn 1.75. TGA
analysis: a one-step degradation process with the onset decom-
500.13 MHz): 7.67 (dd, 3JHeH ¼ 7.8 Hz, 4JHeH ¼ 1.2 Hz, 1H, HC(5)-Bz),
4
3
7.66 (d, JHeH ¼ 1.2 Hz, 1H, HC(3)-Bz), 7.49 (d, JHeH ¼ 7.8 Hz,
3
1H, HC(6)-Bz), 7.43 (t, JHeH ¼ 7.5 Hz, 2H, HCm-Ph), 7.36
(t, 3JHeH ¼ 7.5 Hz, 1H, HCp-Ph), 7.22 (d, 3JHeH ¼ 7.5 Hz, 4H, HCo-Ph),
7.21 (d, 3JHeH ¼ 7.5 Hz, 2H, HCo-Ph), 7.21 (t, 3JHeH ¼ 7.5 Hz, 2H, HCp-
3
position temperature at ca. 200 ꢁC. 1H NMR (
d
, CDCl3, 500.13 MHz);
a broad signal in the range 7.5e5.5 with three maximums at 6.93,
6.62, and 5.83 ppm. 13C{1H} NMR (
, CDCl3, 125.76 MHz); a broad
signal in the range 130e124 ppm with a maximum at 127.7 ppm. IR
(KBr pellet,
, cmꢂ1 (relative intensity)): 3054 (m), 3025 (m), 2956
Ph), 7.18 (t, JHeH ¼ 7.5 Hz, 4H, HCm-Ph). 13C{1H} NMR (
d, CDCl3,
125.76 MHz): 141.5,141.1,141.0,140.6,140.4,139.6 (3C, Ci-Ph and 3C,
C-Bz), 131.1 (1C, HC(6)-Bz), 130.0 (2C, HCm-Ph), 129.9 (2C, HCm-Ph),
129.4 (1C, HC(3)-Bz), 128.8 (2C, HCm-Ph), 128.0 (2C, HCo-Ph), 127.9
(2C, HCo-Ph), 127.4 (1C, HCp-Ph), 127.1 (2C, HCo-Ph), 126.6 (1C, HCp-
d
n
(w), 2925 (w), 1597 (s), 1575 (w), 1492 (s), 1473 (w), 1444 (s), 1410
(w), 1261 (m), 1074 (m), 1029 (m), 755 (vs), 696 (vs).
Ph), 126.5 (1C, HCp-Ph), 126.1 (1C, HC(5)-Bz). GCeMS: C24H18
,
Mr ¼ 306.4, r.t. 11.4 min, m/z (relative intensity): 306 (Mþ, 100).
1,3,5-tri-t-butylbenzene (1,3,5-TtBB) [28]: 1H NMR (
d, CDCl3,
2.5.3. Characterization of HOCH2ChCH transformation products
The formation of a brown solid was observed from the begin-
ning of the reaction of prop-2-yn-1-ol in the presence of 3a or 3b.
Analysis of the solution by NMR in CDCl3 revealed several proton
500.13 MHz): 7.23 (s, 3H, HC-Bz), 1.31 (s, 27H, CH3-tBu). 13C{1H}
NMR (d, CDCl3, 125.76 MHz): 149.9 (3C, C-Bz), 119.4 (3C, HC-Bz),
35.0 (3C, C-tBu), 31.6 (9C, CH3-tBu). GCeMS: C18H30, Mr ¼ 246.43,
r.t. 6.8 min, m/z (relative intensity): 246 (Mþ, 11), 231 (Mþ, ꢂCH3,
100).
signals of very low intensity in the range d 8e5 ppm, suggesting the

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I. Czelusniak et al. / Journal of Organometallic Chemistry 716 (2012) 70e78
74
1,2,4-tri-t-butylbenzene (1,2,4-TtBB): 1H NMR
(
d
,
C6D12
,
3. Results and discussion
500.13 MHz): 7.57 (d, 4JHeH ¼ 2.3 Hz, 1H, HC(3)-Bz), 7.41
3
3
(d, JHeH ¼ 8.4 Hz, 1H, HC(6)-Bz), 7.02 (dd, JHeH ¼ 8.4 Hz,
4JHeH ¼ 2.3 Hz, 1H, HC(5)-Bz), ca. 1.3 (s, 27H, CH3-tBu). 13C{1H} NMR
3.1. Reactions of alkynes in the presence of molybdenum(0)
complexes 1 and 2
(d, C6D12, 125.76 MHz): 128.8 (1C, HC(6)-Bz), 126.2 (1C, HC(3)-Bz),
121.9 (1C, HC(5)-Bz), 35.7 (3C, C-tBu), 31.6 (9C, CH3-tBu).
3.1.1. Photochemical reactions of 1 with alkynes
1,3,5-tri-n-butylbenzene (1,3,5-TnBB): 1H NMR
(
d
,
CDCl3,
Broad-band photolysis of n-hexane solution of 1 (Chart 1) in the
presence of tBuChCH (1:5) gives rise initially to the substitution of
one CO group by the alkyne and the formation of the pentacarbonyl
complex [Mo(CO)5(tBuChCH)], as inferred from IR spectra con-
taining three v(CO) absorption bands at 2077 (w), 1950 (vs), and
1937 (s) cmꢂ1, characteristic of a molecule with C4v local symmetry
[41,42]. Prolonged irradiation causes these bands to disappear.
Investigations of the reaction products by 1H NMR allowed us to
detect very low-intensity proton signals at ca. 10 ppm (Fig. 1),
3
500.13 MHz): 6.79 (s, 3H, HC-Bz), 2.57 (t, JHeH ¼ 7.7 Hz, 6H,
CH2-nBu), 1.61 (tt, 3JHeH ¼ 7.7 Hz, 6H, CH2-nBu), 1.36
3
3
(qt, JHeH ¼ 7.5 Hz, 6H, CH2-nBu), 0.93 (t, JHeH ¼ 7.4 Hz, 9H,
CH3-nBu). 13C{1H} NMR (
d, CDCl3, 125.76 MHz): 142.7 (3C, C-Bz),
125.8 (3C, HC-Bz), 35.7 (3C, CH2-nBu), 33.8 (3C, CH2-nBu), 22.5 (3C,
CH2-nBu), 14.0 (3C, CH3-nBu). GCeMS: C18H30, Mr ¼ 246.43, r.t.
8.4 min, m/z (relative intensity): 246 (Mþ, 32), 203 (Mþ, ꢂC3H7, 33),
161 (Mþ, ꢂC6H13, 100), 147 (Mþ, ꢂC7H15, 11), 105 (Mþ, ꢂC10H21, 14).
1,2,4-tri-n-butylbenzene (1,2,4-TnBB): 1H NMR
(
d
,
CDCl3,
which can be assigned to an h
2-coordinated alkyne ligand, and
3
500.13 MHz): 7.02 (d, JHeH ¼ 7.6 Hz, 1H, HC(6)-Bz), 6.92 (d,
more intense proton signals in the range 7.5e7.2 assigned to 1,3,5
4JHeH ¼ 1.9 Hz, 1H, HC(3)-Bz), 6.90 (dd, 3JHeH ¼ 7.6 Hz,
and 1,2,4-TtBB formed in the molar ratio of 1:7 (Fig. 2, Tables 1 and
4JHeH ¼ 1.9 Hz, 1H, HC(5)-Bz), 2.57 (t, JHeH ¼ 7.7 Hz, 6H, CH2-nBu),
2). The cyclotrimers that were formed are very good h
6-arene
3
1.61 (tt, JHeH ¼ 7.7 Hz, 6H, CH2-nBu), 1.36 (qt, JHeH ¼ 7.5 Hz, 6H,
ligands which can coordinate to the coordinatively unsaturated
molybdenum(0) species Mo(CO)3 generated in the photochemical
3
3
CH2-nBu), 0.93 (t, JHeH ¼ 7.4 Hz, 9H, CH3-nBu). 13C{1H} NMR
3
(d
, CDCl3, 125.76 MHz): 140.3, 140.1, 137.6 (3C, C-Bz), 129.7 (1C,
reaction of 1. The h
6-coordination of 1,3,5 and 1,2,4-TtBB to the
HC(6)-Bz), 129.2 (1C, HC(5)-Bz), 125.7 (1C, HC(3)-Bz), 35.7 (3C,
CH2-nBu), 33.8 (3C, CH2-nBu), 22.5 (3C, CH2-nBu),14.0 (3C, CH3-nBu).
GCeMS: C18H30, Mr ¼ 246.43, r.t. 8.5 min, m/z (relative intensity):
246 (Mþ, 33), 204 (Mþ, ꢂC3H7, 100), 161 (Mþ, ꢂC6H13, 23), 147
(Mþ, ꢂC7H15, 43), 105 (Mþ, ꢂC10H21, 31).
molybdenum atom was detected by proton signals in the range
5.9e5.5 ppm (Fig. 2) and carbon signals in the range 96e85. The
formation of similar
h
6-arene complexes had previously been
observed in photochemical reaction of W(CO)6 and propyne [41].
Hydroxysubstituted acetylenes are not soluble in an alkane
solution. For that reason, tetrahydrofurane (THF) or toluene were
used as solvents in photochemical reaction of 1 and HOCH2ChCH.
However, monitoring the photochemical reaction of 1 and prop-2-
yn-1-ol in THF solution by IR spectroscopy allowed us to detect
1,3,5-tri(hydroxymethyl)benzene (1,3,5-T(HOCH2)B): 1H NMR
(d
, C4D8O, 500.13 MHz): 7.20 (s, 3H, HC-Bz), 4.57 (s, 6H, H2C). 13C
{1H} NMR (
d, C4D8O, 125.76 MHz): 142.0 (3C, C-Bz), 122.5 (3C, HC-
Bz), 63.6 (3C, H2C). GCeMS: (see Section 2.3.1.).
1,2,4-tri(hydroxymethyl)benzene (1,2,4-T(HOCH2)B): 1H NMR
the formation of
[Mo(CO)5(THF)], which was observed by IR spectra due to three
v(CO) absorption bands at 2078 (w), 1940 (vs), and 1893 (s) cmꢂ1
a
fairly stable pentacarbonyl complex,
(d, C4D8O, 500.13 MHz): 7.37 (s, 1H, HC(3)-Bz), 7.31 (d,
3JHeH ¼ 7.6 Hz, 1H, HC(6)-Bz), 7.21 (d, 3JHeH ¼ 7.6 Hz, 1H, HC(5)-Bz),
.
4.64, 4.62, 4.56 (s, 6H, H2C). 13C{1H} NMR (
d, C4D8O, 125.76 MHz):
Thus, the v(CO) absorption bands of the alkyne pentacarbonyl
complex [Mo(CO)5(HOCH2ChCH)] were not detected. Presumably,
they were overlapped by more intense bands of the tetrahy-
drofurane complex. Investigations of the isolated reaction products
by NMR showed only low (ca. 10%) conversion of prop-2-yn-1-ol.
Better results were obtained when the previously synthesized
complex [Mo(CO)5(THF)] dissolved in dichloromethane solution
was used as an initiator for this reaction. In this reaction, 1H NMR
141.2, 139.4, 138.1 (3C, C-Bz), 127.1 (1C, HC(6)-Bz), 125.6 (1C, HC(3)-
Bz), 124.4, (1C, HC(5)-Bz), 63.3, 62.0, 61.7 (3C, H2C). GCeMS: (see
Section 2.3.1.).
1,3,5-tri(2-hydroxyizopropyl)benzene (1,3,5-T(HOCMe2)B): 1H
NMR (
d
, CDCl3, 500.13 MHz): 7.14 (s, 3H, HC-Bz), ca. 1.3 (s, 18H, CH3).
13C{1H} NMR (
d
, CDCl3, 125.76 MHz): 140.5 (3C, C-Bz),117.8 (3C, HC-
Bz). GCeMS: C15H24O3, Mr ¼ 252.35, r.t. 7.7 min, m/z (relative
intensity): 252 (Mþ, 0.2), 198 (Mþ, ꢂ3H2O, 100), 183 (9), 143 (12),
128 (13), 115 (11), 77(9), 63 (2), 41 (6).
spectroscopy made it possible to detect the
h
2-coordination of the
1,2,4-tri(2-hydroxyizopropyl)benzene (1,2,4-T(HOCMe2)B): 1H
O
C
O
NMR (
d
, CDCl3, 500.13 MHz): 7.47 (d, 4JHeH ¼ 1.5 Hz, 1H, HC(3)-Bz),
O
O
C
O
C
C
N
N
3
4
C
7.36 (dd, JHeH ¼ 7.8 Hz, JHeH ¼ 1.5 Hz, 1H, HC(5)-Bz), 7.02
3
(d, JHeH ¼ 7.8 Hz, 1H, HC(6)-Bz), ca. 1.3 (s, 18H, CH3). 13C{1H} NMR
Mo
Mo
C
C
(d, CDCl3, 125.76 MHz): 143.7, 143.2, 141.4 (3C, C-Bz), 125.0 (1C,
C
O
O
O
C
O
C
O
HC(5)-Bz), 120.8 (1C, HC(3)-Bz), 120.5 (1C, HC(6)-Bz), GC-MS:
C15H24O3, Mr ¼ 252.35, r.t. 6.9 min, m/z (relative intensity): 252
(Mþ, 0.02), 216 (Mþ, ꢂ2CH3, 2), 201 (Mþ, ꢂ3OH, 100), 183 (7), 155
(3), 128 (4), 115 (4), 91(2), 51(1), 43 (8).
2
1
Cl
2-
Cl
6-arene)] complexes
Cl
2.7. NMR characterization of [Mo(CO)3(
[Mo(CO)3(
6-1,3,5-TtBB)]: 1H NMR (
h
O
Sn
Cl
C
O
Cl
Cl
C
O
C
h
d, C6D12, 500.13 MHz): 5.67
Mo
Mo
(s, 3H, HC-Bz), ca. 1.3 (s, 27H, CH3-tBu). 13C{1H} NMR (
d, C6D12
,
C
C
O
125.76 MHz): 95.1 (3C, HC-Bz), 35.0 (3C, C-tBu), 31.6 (9C, CH3-tBu).
O
C
Cl
Cl
Sn
6-1,2,4-TtBB)]
(
d
,
C6D12
,
500.13 MHz): 5.93
O
Cl
[Mo(CO)3(
h
(d, 4JHeH ¼ 1.9 Hz, 1H, HC(3)-Bz), 5.65 (d, 3JHeH ¼ 7.2 Hz, 1H, HC(6)-
Cl
3
4
3
Bz), 5.52 (dd, JHeH ¼ 7.2 Hz, JHeH ¼ 1.9 Hz, 1H, HC(5)-Bz), ca. 1.31
(s, 27H, CH3-tBu). 13C{1H} NMR (
d, C6D12, 125.76 MHz): 94.8 (1C,
Chart 1. Schematic view of the molybdenum complexes 1, 2 and 3. An ionic complex
3a contains two allyl piperidinum cations {C3H5pip]þ but 3b contains two piperidinum
cations [Hpip]þ as the counter ions.
HC(3)-Bz), 94.1 (1C, HC(6)-Bz), 90.5 (1C, HC(5)-Bz), 35.7 (3C, C-tBu),
31.6 (9C, CH3-tBu).

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I. Czelusniak et al. / Journal of Organometallic Chemistry 716 (2012) 70e78
75
Table 2
A
B
PhC CH
tBuC CH
Chemical shift (d, ppm) of aromatic protons in NMR spectra (CDCl3) of 1,3,5 and 1,2,4
substituted benzenes obtained in reactions of monosubstituted alkynes RChCH.
R
R
R
R
R
R
R
C
D
nBuC CH
H(2,4,6)
H(3)
H(5)
H(6)
Ph
7.77
7.23
6.79
7.29
7.14
7.66
7.57
6.92
7.37
7.47
7.67
7.02
6.90
7.30
7.36
7.49
7.41
7.02
7.34
7.02
tBu
nBu
CH2OH
CMe2OH
HOCH2C CH
13.2
12.4
11.6
10.8
10.0
(ppm)
2), observed in this reaction by 1H NMR spectroscopy in a 1:1.8
molar ratio. In the GCeMS spectrum, two signals were detected,
one for Mþ ¼ 168 (cyclotrimers) and the other one for Mþ ¼ 170,
thus different by the mass of two hydrogen atoms. This can suggest
that during this catalytic reaction, the cyclotrimerization products
are formed through a molybdenacycloheptatriene intermediate
species (Scheme 4), from which triene may be released in reaction
with the source of the hydrogen atom. This is not surprising for
a reaction of prop-2-yn-1-ol, containing an active hydrogen at the
OH group, which can be oxidatively added to a molybdenum(0)
center. The oxidative addition of the HꢂO bond of phenols to
molybdenum(0) in 1 was suggested by McCullough and Schrock for
the formation of the first reported homogenous system for the
metathesis of alkynes involving 1 as the catalyst precursor [43]. In
all the prop-2-yn-1-ol reactions carried out in the presence of
molybdenum(0) complexes, two equally intense olefin proton
Fig. 1. Selected region of the 1H NMR spectrum showing signals indicating 2-coor-
h
dination of terminal alkynes to the molybdenum center observed in the reaction of: (A)
PhChCH and 2/SnCl4, (B) tBuChCH and 2/SnCl4, (C) nBuChCH and 2/SnCl4, (D)
HOCH2ChCH and [Mo(CO)5THF].
ChC bond of prop-2-yn-1-ol to the molybdenum atom. This
coordination was indicated by two proton signals, one observed as
a triplet (3JHeH ¼ 1.9 Hz) at dH ¼ 9.74 ppm and another observed as
a
twice-as-intense doublet (3JHeH ¼ 1.9 Hz) at dH ¼ 2.81 ppm
(Fig. 1). In this reaction, prop-2-yn-1-ol was transformed to cyclo-
trimers: 1,3,5-T(HOCH2)B and 1,2,4-T(HOCH2)B (Fig. 3, Tables 1 and
A
d
d
c
signals at
d
6.23 (d, 3JHeH ¼ 14.5 Hz) and
d
5.81 (dt, 3JHeH ¼ 14.5 Hz,
3JHeH ¼ 5.7 Hz) were detected in 1H NMR spectra. In COSY NMR
c
a
b
d
a
spectra, the latter signals are correlated, but the signal at
d
d
5.81correlates with the twice-as-intense proton signal at
4.18 ppm. In HMQC spectra, these three proton signals correlate
with the 13C carbon signals at
135.5, 132.5, and 63.0 ppm,
b
d
respectively. Thus, the NMR spectra suggested the formation of
species containing the hydroxymethylvinyl eCH¼CH(CH2OH)
fragment. Such a fragment may include di(hydroxymethyl)buta-
diene (hexa-2,4-diene-1,6-diol) or tri(hydroxymethyl)hexatriene.
The formation of the latter compound was proved by the GCeMS
7.60
7.30
7.20
7.10
7.00
7.50
7.40
CH2OH
CH2OH
HOH2C
d
d
c
b
s
B
a
a
d
d
HOH2C
CH2OH
d
CH2OH
a
d
c
b
c
CH2O
Mo(CO)3
Mo(CO)3
b
*
d
b+d
a
c
5.88
5.80
5.72
(ppm)
5.64
5.56
5.48
5.96
7.1/6 /
7.32 7.24
7.40
4.8
(ppm)
4.4
3.6
4.0
Fig. 2. (A) Partial 1H NMR spectrum (500 MHz, CDCl3) showing signals of ca. 1:7
mixture of 1,3,5-TtBB and 1,2,4-TtBB formed in photochemical reaction of tBuChCH in
the presence of 1. (B) Partial 1H NMR spectrum showing signals of 1,3,5-TtBB and 1,2,4-
Fig. 3. Partial 1H NMR spectrum (500 MHz, C4H8O) showing signals of ca. 1:5 mixture
of 1,3,5-T(HOCH2)B and 1,2,4-T(HOCH2)B formed in reaction of HOCH2ChCH in the
presence of 3b. The proton signal denoted by s is due to C4H8O.
TtBB 6-coordinated to molybdenum center.
h

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I. Czelusniak et al. / Journal of Organometallic Chemistry 716 (2012) 70e78
76
method. We observed correlation between the amount of cyclo-
trimers and the latter species; increasing amounts of this species
lowered the amounts of cyclotrimers. Another species containing
respectively. This NMR analysis as well as the very good solubility of
these oligomers in hexane suggests their formation pathway
through the addition of the polar HꢂO bond of one alkynol mole-
cule to the triple bond of another one. The first step of this reaction
and the formation of vinylidene dimers of prop-2-yn-1-ol is shown
in Scheme 3. However, repeated attempts to resolve the structure of
the final product by NMR analysis failed. The structure of this
compound needs additional studies.
It must be noted that the formation of the vinylidene dimer (A)
(Scheme 3) has been recently proposed as the first step in the
reaction of prop-2-yn-1-ol in the presence of a tetracarbonyl
complex of platinum leading to the formation of a formal tetramer
the hydroxymethylvinyl unit was detected by two equally intense
3
olefin proton signals at
d
6.33 (d, JHeH ¼ 16.5 Hz) and
d 5.91
3
3
(dt, JHeH ¼ 16.5 Hz, JHeH ¼ 5.4 Hz). These two signals may be
assignable to the dimer HOCH2ChCeCH¼CH(CH2OH). However,
a very low concentration of that species in the reaction products did
not make it possible to obtain 13C NMR spectra and interpret it fully.
The highest conversion and selectivity of the cyclotrimerization
reaction of prop-2-yn-1-ol were detected by NMR in photochemical
reaction carried out in toluene solution (Table 1).
of
prop-2-yn-1-ol
(2,5-dimethyl-2,5-bis(2-propynoxy)-1,4-
3.1.2. Reactions of alkynes in the presence of 2
dioxane) [44]. The addition of the HꢂO bond of alcohols to the
triple bond of alkynes has also been observed in their reactions
catalyzed by gold complexes [45].
In the process of studying reactions of alkynes with 2 (Chart 1),
we observed a relatively fast reaction of hydroxysubstituted
alkynes, while alkyl derivatives were almost non-reactive. Thus, in
The very fast reaction of HO(CH3)2CChCH in the presence of 2 in
dichloromethane solution led to the formation of a brown precip-
itate which was very slightly soluble in CDCl3 and could not be
analyzed by the NMR method. Analysis of compounds soluble in
CDCl3 by NMR spectroscopy revealed the formation of a compound
(ca. 5%) containing a vinyl unit, CH¼CH2, and another one (ca. 95%),
containing piperidinium cation (Hpipþ) [38]. Analysis of the reac-
tion products ꢂby the ESI-MS method showed the anion
t
contrast to BuChCH, HOCH2ChCH reacted very smoothly in the
presence of complex 2, and during the first few minutes of the
reaction the complete decay of n(CO) bands of 2 at 2013 (w), 1887
(vs), 1868 (m), and 1819 (w) cmꢂ1 was observed by IR spectra.
GCeMS analysis of the crude reaction products suggested the
formation of oligomers of prop-2-yn-1-ol, such as dimers (7.8%),
trimers (0.2%), and pentamers (92%). However, in the mass spec-
trum of the pentamer, it was impossible to detect the parent
molecular ion (C15H20O5, Mþ ¼ 280); only a very low-intensity peak
for mass 264 (Mþ, ꢂ16) was observed. The most intense peak in this
spectrum was that for mass 98 (C5H6O2).
[C30H38Mo2O14
]
(Mꢂ ¼ 814.5), which may contain a partially
hydrogenated tetramer of 2-methylbut-3-yn-2-ol coordinated to
two molybdenumpentacarbonyl units ([Mo2(CO)10(C5H8O)4H6]).
This suggests fairly good agreement obtained between the exper-
imental and the calculated mass spectrum (see Supplementary
Data). However, the structure of this compound needs additional
studies.
Studies of the crude reaction product by NMR spectroscopy
allowed us to detect two similar compounds formed in a 2:1 molar
ratio, which can be described as compounds a and b, both con-
taining the vinylidene unit, like the two dimers A and B presented
in Scheme 3 (see Supplementary Data for the NMR spectra). The
3.1.3. Reactions of alkynes in the presence of 2 and SnCl4 (1:2)
Reactions of alkyl- or aryl-substituted alkynes (tBuChCH,
nBuChCH, and PhChCH) in dichloromethane solution containing
the piperidine complex 2 are very slow and after 24 h do not give
expected products of alkyne transformation. However, if SnCl4 was
first added to a solution containing complex 2 (ca. 1:2 molar ratio)
and then alkynes were added, the decay of the molybdenum
complex could be observed by IR spectroscopy, and the conversion
of alkynes (PhChCH, tBuChCH, nBuChCH) reached 100% after 24 h
reaction at room temperature. GCeMS and NMR analyses showed
that the alkyne is transformed with high selectivity (ca. 100%) to
cyclotrimerization products (Tables 1 and 2, Figs. 2 and 4). More-
over, analysis of the reaction products by 1H NMR spectroscopy
methylidene protons of a were detected at
Both proton signals correlate with a carbon signal at
the HMQC NMR spectrum. Similar correlation was observed
between the methylidene proton signals at 4.98 and 4.81 ppm
d
4.91 and 4.73 ppm.
d
111.7 ppm in
d
and the carbon signal 109.4 ppm of b. Two protons of the methy-
lene unit bounded to the tertiary carbon of the vinylidene unit are
diastereotopic and were detected as doublets (2JHeH ¼ 12.7 Hz) at
d
4.36 and 4.10 ppm for a and at d 4.22 and 4.14 ppm
(2JHeH ¼ 12.1 Hz) for b. In the 1He13C HMQC NMR spectra, the
correlation between the methylene proton signals at
d 4.36 and
4.10 ppm with carbon signals at
4.22 and 4.14 ppm with carbon signals at
Two tertiary carbons of the vinylidene unit of a and b were detected
at 141.2 and 141.3 ppm, respectively. Their assignment was
d
68.8 for a and proton signals at
d
d
72.7 for b was detected.
revealed the
h
2-coordination of the alkyne to the molybdenum
d
atom detected due to 1H proton signals at ca. 10 ppm (Fig. 1). In
reactions of all of the investigated alkynes, several signals with
different but very low intensities compared with the simulta-
neously observed proton signals of cyclotrimers were observed in
possible due to the observed correlation in the HMBC NMR spec-
trum, in which the latter carbon signals correlated with the above-
discussed methylidene and methylene proton signals as well as
t
with the methine proton signal at
d
2.91 (a) and 3.36 ppm (b); both
this range. Only in reaction of BuChCH was the concentration of
signals were observed as pseudo triplets with JHeH ¼ 7.5 and 6.9 Hz,
the h C
2-alkyne complex high enough for the measurement of the 13
{1H} NMR spectrum. The 1He13C HMQC NMR spectra allowed us to
detect the correlation of proton signals at 10.15 and 10.27 ppm with
carbon signals at 157.7 and 168.6 ppm, respectively. The values of
chemical shifts of these carbon atoms are characteristic for
complexes in which the alkyne coordinates as a two-electron donor
[46e49]. This experiment showed an important role of SnCl4 as an
activator of the molybdenum(0) complex 2. The activation of 2 by
SnCl4 results first of all from its Lewis acid properties, which made
it possible to remove the piperidine ligand from the coordination
sphere of the molybdenum center and to create the possibility of
coordinating and activating the alkyne. Two alkynes coordinated to
a molybdenum center can be transformed through oxidative
coupling to molybdacyclopentadiene and next to a cyclotrimer. The
H
C
O
H
C
O
H
H
H
O
H
H
OH
H
H
C C
C C
H
C
C
C
C C
H
CH
H
H
H
(B)
(A)
Scheme 3. Proposed structure for two vinylidene dimers (A) and (B) formed in reac-
tion of prop-2-yn-1-ol in the presence of 2.

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I. Czelusniak et al. / Journal of Organometallic Chemistry 716 (2012) 70e78
77
precipitation of a white solid was observed. The solid, isolated
after 24 h of reaction time, was shown by GPC analysis to be
a high-molecular-weight polymer (Mn 127251, Mw 147368) with
a low polydyspersity index (PDI ¼ Mw/Mn 1.16). TGA analysis of
poly(tbutylacetylene) (poly-tBA) showed a one-step degradation
process with the onset decomposition temperature at ca. 256 ꢁC.
Such high thermal stability of poly(tBA) was observed for the first
time. As reported previously by Masuda et al. [51], the thermal
degradation of poly-tBA started at ca. 200 ꢁC. This may be the effect
of the polymer structure. Analysis of poly-tBA by NMR spectroscopy
showed the exclusively cis configuration of the polymer units. This
was indicated by one sharp signal at 6.28 ppm in the 1H NMR
spectrum and one signal of three equivalent methyl groups at ca.
32 ppm in the 13C{1H} NMR spectrum (Fig. 5) [28,52,53]. Although
the preferred cis configuration of poly-tBA had been observed
before, the cis polymer content was never so high.
In the reaction of PhChCH in the presence of catalytic amounts
of 3a or 3b, the formation of orange polyphenylacetylene (poly-PA)
was observed. The number-average molecular weight of this
polymer (Mn 2418) is much more smaller than that of poly-tBA, but
the PDI is higher, at 1.75, than that for poly-tBA. The thermal
degradation of poly-PA started at ca. 200 ꢁC, that is at a lower
temperature than for poly-tBA. This may be the effect of the poly-
mer structure. The broad signal in the range 7.5e5.5 with three
maximums at 6.93, 6.62, and 5.83 ppm in the 1H NMR spectrum
and a broad signal in the range 130e124 ppm with a maximum at
127.7 ppm in the 13C{1H} NMR spectrum suggest no regular struc-
ture of the polymer units of poly-PA [52].
When HOCH2ChCH was added to the solution of the molybde-
num(II) complex 3b in dichloromethane, the spontaneous precipi-
tation of a brown solid was observed. Analysis of the soluble
compounds by NMR spectroscopy showed a 64% conversion of
alkynol and the formation of cyclotrimers with 98% selectivity
(1,3,5-T(HOCH2)B and 1,2,4-T(HOCH2)B in the 1:5 molar ratio). The
remaining products included unidentified compounds containing
olefin bonds. Among them, compounds containing the hydrox-
ymethylvinyl unit eCH¼CH(CH2OH) (see Section 3.1.1.) were
detected. Analysis of the brown solid by NMR spectroscopy or GPC
was impossible because of its poor solubility in organic solvents, but
its IR spectrum showed bands characteristic for the simultaneously
formed piperidinium cation of the ionic compound [Hpip]2[SnCl6]
[54] dominating and obscuring polymer bands. The formation of
a brown solid was also observed in the analogous reaction of
HO(CH3)2CChCH and 3b. Analysis of the latter solid by NMR spec-
troscopy or GPC was impossible due to its poor solubility. Analysis of
s
A
*
*
*
*
7.50 7.40
(ppm)
7.10
7.60
7.30 7.20
7.70
7.80
*
*
B
Ph
Ph
Ph
Ph
*
Ph
Ph
*
* *
141
139
131
137 135 133
(ppm)
129 127 125
Fig. 4. (A) Partial 1H NMR spectrum and (B) 13C{1H} NMR spectrum showing signals of
ca. 1:1 mixture of 1,3,5-TPB and 1,2,4-TPB. Carbon signals of 1,3,5-TPB are denoted by
an asterisk (*) and CDCl3 by s.
h
2-coordination of alkyne in the molybdenum complex appears to
be the principal feature of all reactions of alkynes catalyzed by
molybdenum complexes. Another role of tin tetrachloride is to
oxidize molybdenum(0) to molybdenum(II) [38]. This process is
always accompanied by the decarbonylation of molybdenum(0)
carbonyls [23]. The in situ generated coordinatively unsaturated
molybdenum(II) species interacts with alkynes to give a bisalkyne
complex which can be transformed in the presence of an excess of
alkyne to give cyclotrimers. However, at a molar ratio of SnCl4/2
higher than 2, the simultaneous formation of the recently described
stannylation product of alkyne by SnCl4 (chlorovinyltin tri-
chlorides) (Scheme 4) [50] was observed. Thus, tin tetrachloride
reacts with the molybdenum(0) complex 2 as well as with alkynes.
In summary, we can say that complex 2 initiates the cyclo-
trimerization reaction only after activation by SnCl4. The activation
process of 2 may be effected by the formation of the very reactive
s
binuclear molybdenum(II) complex
3 [38]. A similar effect
(an increase in catalytic activity) had been observed before when
iodine was added as oxidant to a catalytic system containing
a molybdenum(0) complex [8].
a
c
d
CH
C
b
a
a
C
CH3
H3C
a
CH3
3.2. Reactions of alkynes in the presence of the molybdenum(II)
complexes 3a and 3b
t
When BuChCH was added to the solution of the molybdenu-
m(II) complex 3a (Chart 1) in dichloromethane, the spontaneous
b
c
d
R
H
SnCl3
SnCl
+
H
C C
R
C C
4
CH2Cl2, r.t.
Cl
120
100
80
90
(ppm)
50
130
110
70 60
40 30
150 140
R = Ph, tBu, nBu, HOCH2
Fig. 5. (a) 13C{1H} NMR spectrum (125.76 MHz, C4D8O) showing signals of poly-t-
Scheme 4. Stannylation of terminal alkynes by SnCl4 [50].
butylacetylene. The carbon signal denoted by s is due to C4D8O.

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I. Czelusniak et al. / Journal of Organometallic Chemistry 716 (2012) 70e78
78
the soluble compounds by NMR spectroscopy showed the formation
of 1,3,5-T(HOCMe2)B and 1,2,4-T(HOCMe2)B in the 1:5 molar ratio.
ESI-MS analysis of the solution revealed the formation of several
molybdenum compounds identified as anions containing alkynol as
References
[1] S. Saito, Y. Yamamoto, Chem. Rev. 100 (2000) 2901e2915.
[2] S. Kotha, E. Brahmachary, K. Lahiri, Eur. J. Org. Chem. (2005) 4741e4767.
[3] W. Reppe, W.J. Schweckendick, Justus Liebigs Ann. Chem. 560 (1948)
104e116.
[4] B.R. Galan, T. Rovis, Angew. Chem. Int. Ed. 48 (2009) 2830e2834.
[5] X. Bu, Z. Zhang, X. Zhou, Organometallics 29 (2010) 3530e3534.
[6] M.J. Calhorda, P.J. Costa, K.A. Kirchner, Inorg. Chim. Acta 374 (2011) 24e35.
[7] E. Farnetti, S. Filipuzzi, Inorg. Chim. Acta 363 (2010) 467e473.
[8] H.C.M. Vosloo, J.A.K. du Plessis, J. Mol. Catal. 65 (1991) 51e54.
[9] H.C.M. Vosloo, J.A.K. du Plessis, J. Mol. Catal. 79 (1993) 7e12.
[10] H.C.M. Vosloo, J.A.K. du Plessis, J. Mol. Catal. 133 (1998) 205e211.
[11] G.A. Ardizzoia, S. Brenna, G. LaMonica, A. Maspero, N. Masciocchi,
J. Organomet. Chem. 649 (2002) 173e180.
a
neutral or anion ligand: Mꢂ 291 [Mo(CO)4(C5H7O)]ꢂ, 319
[Mo(CO)5(C5H7O)]ꢂ,
515
[Mo(C5H8O)4(C5H7O)]ꢂ,
571
[Mo(C5H7O)2(SnCl3)(CO)3]ꢂ. These results confirm the ability of
HO(CH3)2CChCH to coordinate to the molybdenum center as an
anion that is otherwise like the h
2-coordination of the ChC triple
bond, identified here by NMR spectroscopy.
4. Conclusions
[12] U.H.F. Bunz, Acc. Chem. Res. 34 (2001) 998e1010.
[13] V. Sashuk, J. Ignatowska, K. Grela, J. Org. Chem. 69 (2004) 7748e7751.
[14] T. Masuda, Y. Kuwane, T. Higashimura, J. Polym. Sci.: Polym. Chem. Ed. 20
(1982) 1043e1050.
In summary, we have described an efficient and stereoselective
method for the synthesis of substituted benzenes by simple
procedures, under mild reaction conditions, and in good yield.
The cyclotrimerization products formed in reaction of mono-
substituted alkynes (PhChCH, tBuChCH, nBuChCH, HOCH2ChCH,
HO(CH3)2CChCH) have been characterized by 1H and 13C NMR
spectroscopy. It should be noted that benzene derivatives con-
taining the polar functional group OH were obtained for the first
time. It is very well known that the polar hydroxyl group has great
utility for further transformation and as a building block in organic
synthesis. Molybdenum(II) complexes (3a and 3b) formed in
reaction of the molybdenum(0) complex 2 and tin tetrachloride
appeared particularly effective as catalysts for alkynol cyclo-
[15] K. Tamura, T. Masuda, T. Higashimura, Polym. Bull. 32 (1994) 289e296.
[16] K. Tamura, Y. Misumi, T. Masuda, Chem. Commun. (1996) 373e374.
ꢀ
[17] T. Szymanska-Buzar, A.J. Downs, T.M. Greene, A.S. Marshall, J. Organomet.
Chem. 495 (1995) 149e161.
ꢀ
[18] T. Szymanska-Buzar, A.J. Downs, T.M. Greene, A.S. Marshall, J. Organomet.
Chem. 495 (1995) 163e175.
[19] S.J. London, P.M. Shulman, G.I. Geoffroy, J. Am. Chem. Soc. 107 (1985)
6739e6740.
ꢀ
[20] T. Szymanska-Buzar, J. Mol. Catal 93 (1994) 137e147.
[21] P.K. Baker, Adv. Organomet. Chem. 40 (1996) 45e115.
[22] P.K. Baker, Chem. Soc. Rev. 27 (1998) 125e131.
ꢀ
[23] T. Szymanska-Buzar, Coord. Chem. Rev. 249 (2005) 2195e2202.
ꢀ
[24] T. Szymanska-Buzar, J. Mol. Catal. A: Chem. 123 (1997) 113e122.
ꢀ
ꢀ
[25] T. Szymanska-Buzar, T. G1owiak, I. Czelusniak, Inorg. Chem. Commun 4 (2001)
183e186.
ꢀ
[26] T. Szymanska-Buzar, T. G1owiak, J. Organomet. Chem. 575 (1999) 98e107.
t
trimerization. However, the reaction of BuChCH and PhChCH in
the presence of a molybdenum(II) complex leads to the selective
formation of well-characterized polymers.
ꢀ
[27] T. Szymanska-Buzar, T. G1owiak, J. Organomet. Chem. 585 (1999) 215e224.
ꢀ
ꢀ
[28] T. Szymanska-Buzar, I. Czelusniak, J. Mol. Catal. A: Chem. 160 (2000)
133e144.
[29] P.K. Baker, M.G.B. Drew, D.S. Evans, A.W. Johans, M.M. Meehan, J. Chem. Soc.
Dalton Trans. (1999) 2541e2550.
The selectivity of alkyne oligomerization reactions depends on
the oxidation state of the molybdenum atom of the catalyst. Thus,
reactions of monosubstituted alkynes in dichloromethane solution
and in the presence of the molybdenum(0) complex 2 never yields
benzene derivatives without the addition of SnCl4 as an activator.
When SnCl4 was added, benzene derivatives were obtained in good
yields (ca. 100%). In the presence of complex 2, prop-2-yn-1-ol
transforms to a cyclic oligomer containing a vinylidene unit, which
suggests the addition of an HꢂO bond to the triple ChC bond of
alkynol.
[30] J.W. Goodyear, C.W. Hemingway, R.W. Harrington, M.R. Wiseman, B.J. Bridson,
J. Organomet. Chem. 664 (2002) 176e181.
ꢀ
[31] I. Czelusniak, J. Handzlik, J. Organomet. Chem. 694 (2009) 1427e1434.
[32] X. Zhan, M. Yang, H. Sun, Catal. Lett. 70 (2000) 79e82.
[33] Y.-S. Gal, J. Macromol, Sci.-Pure Appl. Chem. A32 (1995) 61e72.
[34] Y.-S. Gal, J. Macromol, Sci.-Pure Appl. Chem. A31 (1994) 1177e1191.
[35] I. Yamaguchi, K. Osakada, T. Yamamoto, Inorg. Chim. Acta 220 (1994) 35e40.
[36] D.J. Darensbourg, R.L. Kump, Inorg. Chem. 17 (1978) 2680e2682.
[37] M. Ardon, G. Hogarth, D.T.W. Oscroft, J. Organomet. Chem. 689 (2004)
2429e2435.
ꢀ
[38] M. Zyder, A. Kochel, T. Szymanska-Buzar, J. Organomet. Chem. 694 (2009)
4196e4203.
It should be noted that regardless of the oxidation state of
molybdenum and the substituents present at the triple bond of
[39] A.M. Cianciusi, A. Furlani, A. La Ginestra, M.V. Russo, G. Pàlyi, A. Vizi-Orsz,
Polymer 31 (1990) 1568e1573.
alkynes, the h
2-coordination of alkynes to the molybdenum center
[40] J. Ejfler, M. Koby1ka, M. Hojniak, P. Sobota, J. Mol. Catal. A: Chem. 224 (2004)
93e96.
was observed by the NMR method at the initiating step of the
reaction.
It is noteworthy that all molybdenum-mediated alkyne reac-
tions take place under very mild conditions.
ꢀ
[41] T. Szymanska-Buzar, K. Kern, J. Organomet. Chem. 622 (2001) 74e83.
[42] F.-W. Grevels, J. Jacke, R. Goddard, C.W. Lehmann, S. Özkar, S. Saldamli,
Organometallics 24 (2005) 4613e4623.
[43] L.G. McCullough, R.R. Schrock, J. Am. Chem. Soc. 106 (1984) 4067e4068.
[44] L. Weber, M. Barlmeyer, J.-M. Quasdorff, H.L. Sievers, H.-G. Stammler,
B. Neumann, Organometallics 18 (1999) 2497e2504.
[45] J.H. Teles, S. Brode, M. Chabanas, Angew. Chem. Int. Ed. 37 (1998) 1415e1418.
[46] J.L. Templeton, B.C. Ward, J. Am. Chem. Soc. 102 (1980) 3288e3290.
[47] R.S. Herrick, J.L. Templeton, Organometallics 1 (1982) 842e851.
Acknowledgments
[48] P.B. Winston, S.J.N. Burgmayer, J.L. Templeton, Organometallics
2 (1983)
We acknowledge Dr J. Skonieczny for measurements of NMR
spectra, M. Hojniak for GS-MS analyses, and M. Jon for ESI-MS
analyses.
167e169.
[49] P.B. Winston, S.J.N. Burgmayer, T.L. Toneker, J.L. Templeton, Organometallics 5
(1986) 1707e1715.
ꢀ
ꢀ
[50] I. Czelusniak, M. Jachimowska, T. Szymanska-Buzar, J. Organomet. Chem. 696
(2011) 3023e3028.
[51] T. Masuda, B.Z. Tang, T. Higashimura, H. Yamaoka, Macromolecules 18 (1985)
2369e2373.
Appendix A. Supplementary data
[52] M. Leclerc, R.E. Prud’homme, A. Soum, M. Fontanille, J. Polym. Sci.: Polym.
Phys. Ed. 23 (1985) 2031e2041.
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.jorganchem.2012.
05.044. These data include MOL files and InChiKeys of the most
important compounds described in this article.
[53] T. Masuda, H. Izumikawa, Y. Misumi, T. Higashimura, Macromolecules 29
(1996) 1167e1171.
ꢀ
[54] A. Malinowska, A. Kochel, T. Szymanska-Buzar, J. Organomet. Chem. 692
(2007) 3994e3999.