Synthesis and characterization of Cp2Zr(C9H9O)2: A new zirconocene derivative catalyzed acetylation of 2-naphtol and benzyl alcohol

Article abstract of DOI:10.1007/s13738-014-0508-5

The new zirconocene compound, Cp₂Zr(C₉H₉O)₂, was successfully prepared from the reaction of zirconocene dichloride with 1-indanol in 1:2 molar ratio in dry chloroform at the presence of triethylamine (Et₃

Full text of DOI:10.1007/s13738-014-0508-5

J IRAN CHEM SOC (2015) 12:513–517
DOI 10.1007/s13738-014-0508-5
ORIGINAL PAPER
Synthesis and characterization of Cp2Zr(C9H9O)2: a new
zirconocene derivative catalyzed acetylation of 2‑naphtol
and benzyl alcohol
Abbas Tarassoli · Hadi Mohmedi‑Kartalaee
Received: 17 April 2014 / Accepted: 16 July 2014 / Published online: 2 August 2014
© Iranian Chemical Society 2014
Abstract The new zirconocene compound, Cp2Zr(C9H9O)2,
was successfully prepared from the reaction of zirconocene
dichloride with 1-indanol in 1:2 molar ratio in dry chloro-
form at the presence of triethylamine (Et3N) and in an inert
atmosphere. This compound was characterized by (1H and
13C) NMR, elemental analysis, FT-IR, UV–Vis, TGA and
mass spectrum data. The catalytic activity of the synthesized
compound for the acetylation of 2-naphtol and benzyl alcohol
with acetic anhydride as an acetylating reagent in the solvent
free conditions was also investigated. The Cp2Zr(C9H9O)2 as
a catalyst affords an efficient and simple method for the acet-
ylation of 2-naphtol and benzyl alcohol.
zirconium and an oxygen donor ligand with industrial and
biological applications [17–21]. Although a number of alco-
hols are widely used in the synthesis of zirconocene com-
pounds, 1-indanol is also a good intermediate in the synthe-
sis of fine chemicals and a readily available material, has not
been reported as a starting material. Among zirconium com-
pounds, zirconocene dichloride is a suitable source of zir-
conocene moieties and we have previously investigated the
reaction of zirconocene dichloride with (PhNH)2P(O)H [22]
and reported two new zirconium complexes [23].
In continuing our research on the ligands containing OH
active sites toward organotin(IV) and phosphorous com-
pounds [24, 25], we have now employed 1-indanol as a com-
pound having OH group to investigate its interaction toward
zirconocene dichloride. In this view, the new synthesized
compound, Cp2Zr(C9H9O)2 is reported here. This compound
has been characterized by FT-IR, multinuclear (1H and 13C)
NMR, UV–Vis spectroscopy, TGA, elemental analysis and
mass spectrometry. The acetylation is known to be an impor-
tant process and highly useful reaction in the synthetic medi-
cine intermediate as well as biologically active compounds.
Besides zirconocene compounds are reported to be used as
catalyst for acetylating of alcohols [26–28]. Therefore in this
article we report the use of a new zirconocene compound as an
efficient catalyst for acetylation of 2-naphtol and benzyl alco-
hol with acetic anhydride as an acetylating agent. Our results
are reported below.
Keywords Zirconocene dichloride · 1-Indanol ·
Acetylation · 2-Naphtol · Benzyl alcohol · Catalytic activity
Introduction
The chemistry of compounds containing zirconocene moie-
ties has been of great interest for many years and also has
recently attracted considerable attention [1–7]. Such organo-
metallic compounds have been used for investigating their
applications either as metal-based anticancer drugs [8, 9]
or as catalyst [10–12]. Furthermore, these compounds have
found numerous applications as reagents in organic synthesis
in order to prepare electronic materials, agrochemicals and
pharmaceuticals [13–16]. In order to prepare a suitable cata-
lyst of this kind, a ligand is needed which could bind to the
zirconium atom at the center of zirconocene moieties. Most
of zirconium catalysts derived from a compound containing
Experimental
Materials and instrumentation
A. Tarassoli (*) · H. Mohmedi-Kartalaee
Department of Chemistry, College of Science,
Shahid Chamran University, Ahvaz, Iran
e-mail: tarassoli@scu.ac.ir; tarasoli@yahoo.com
All the experiments were performed under inert condi-
tions in N2 atmosphere. The solvents and Et3N were
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purchased from Acros, Germany and zirconocene dichlo-
ride, 1-indanol, 2-naphtol, benzyl alcohol and acetic anhy-
dride were purchased from Merck Company. IR spectra
were recorded as KBr disc from 4,000 to 400 cm−1 by a
Bomen FT-IR spectrophotometer. Multinuclear (1H and
13C) NMR was recorded by a Bruker Avance 400 MHz: 1H
NMR (400.13 MHz) and 13C NMR (100.61 MHz) in CDCl3
with TMS as an external reference. The elemental analyses
were performed by COSTECH ECS. The mass spectrum of
the synthesized compound was obtained on a 5975C/7890S
spectrometer. UV–Vis spectrum of the new compound
was recorded with a double beam GBC model Cintra 101
spectrophotometer in DMSO. Thermogravimetric analysis
(TGA) was performed on a STA503 instrument.
(Cp carbons), 124.9 (aromatic carbons of 1-indanol, 35.8,
8.6 and 29.8(1-indanol carbons). Ms: m/z 51, 64, 77, 90,
91, 92, 94, 96, 107, 115, 133 and 224. UV–Vis (λmax, nm)
253, 255, 264 and 273.
Acetylation of 2-naphtol and benzyl alcohol
by Cp2Zr(C9H9–O)2 as a catalyst
In a solvent free condition, 2-naphtol (0.360 g, 2.5 mmol)
was let to react with acetic anhydride (0.24 ml, 2.5 mmol)
in the presence of Cp2Zr(C9H9–O)2 (0.014 g, 0.03 mmol)
as a catalyst for 8 h at room temperature under stirring. The
reaction was monitored by means of TLC and after comple-
tion of the reaction; 2-naphthyl acetate was isolated as pure
product (0.425 g, 92 % yield). The product was character-
ized by FT-IR spectroscopy. This reaction was also carried
out at the same conditions in the absence of catalyst and the
yield was 63 % (Table 1).
In a similar manner benzyl alcohol (0.26 ml,
2.5 mmol) was let to react with acetic anhydride
(0.24 ml, 2.5 mmol) in the presence of Cp2Zr(C9H9–O)2
(0.014 g, 0.03 mmol) and the reaction was monitored by
TLC. The benzyl acetate was isolated as pure product
(0.439 g, 95 % yield) and characterized by FT-IR spec-
troscopy. This reaction was also carried out at the same
conditions in the absence of catalyst and the yield was
66 % (Table 1).
Synthesis of Cp2Zr(C9H9O)2
1-indanol (0.026 g, 0.20 mmol) was dissolved in 20 ml of
dry CHCl3. Then Et3N (0.03 ml, 0.20 mmol) as a base, was
added and stirred for 30 min in an ice bath. Zirconocene
dichloride (0.030 g, 0.10 mmol) in 15 ml of dry CHCl3
was added dropwise to the mixture, which was then stirred
for 60 min in the ice bath. After removing the ice bath, the
reaction mixture was stirred for 4 h at reflux temperature
under nitrogen in the 45–50 °C. Then the reaction mixture
was let to stir for another 1 h at room temperature for com-
pletion. After filtration, the remaining CHCl3 was removed
on a rotary evaporator and the resulting white solid product
was washed with diethyl ether and dried under vacuum.
Yield 78 %, m.p. 250 °C (dec.), Anal. Calcd. for
C28H28O2Zr (%): C, 68.98; H, 5.74; Found (%): C, 68.82;
H, 5.65. IR (KBr, cm−1): υ(C=C), 1,425; υ(C–H), 3,077;
Results and discussion
The reaction of zirconocene dichloride with 1-indanol was
carried out in a 1:2 molar ratio. The procedure and pro-
posed structure are shown in Scheme 1. It seems that the
1
υ(C–O), 1,356; υ(Zr–O), 830. H NMR (δ, ppm, CDCl3):
1.31 (t, 4H), 3.00 (q, 4H) and 5.16 (t, 2H) of 1-indanol pro-
tons, 7.14 (S, 8H, aromatic protons of 1-indanol), 7.35 (S,
10H, Cp protons). 13C{1H} NMR (δ, ppm, CDCl3): 45.8
+ 2 Et3N
Cp2Zr(C 9H9O)2
Cp2ZrCl2 + 2C9H9OH
- 2 Et3NHCl
Table 1 Comparison of the results obtained for the acetylation of
2-naphtol and benzyl alcohol under: (a) new catalyst and (b) catalyst
free
Entry Substrate
Product
Yield
(%)*
a
b
1
92 63
OH
OAc
O
Zr
O
2
95 66
OH
OAc
Scheme 1 The synthesis procedure and the proposed structure for
the new catalyst Cp2Zr(C9H9O)2
* The isolated yields are based on the starting substrates
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J IRAN CHEM SOC (2015) 12:513–517
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high Lewis acidity of the zirconocenium moiety generated
from zirconocene dichloride causes zirconium metal to
become susceptible to bind to oxygen atom of 1-indanol
and hence facilitates the formation of Cp2Zr(C9H9–O)2.
The synthesized compound was characterized by FT-IR,
multinuclear (1H and 13C) NMR, elemental analysis, TGA
and UV–Vis, as well as mass spectrometry. Attempts to
growing single crystal suitable for X-ray crystallography
were unsuccessful.
1H NMR spectra
1
The signal due to OH proton is disappeared in the H
NMR spectrum of the synthesized compound in CDCl3.
The signals at δ 1.31–1.34, 3.00–3.05 and 5.16–5.20 ppm
are assigned to the protons of methylene part of 1-indanol.
The Cp protons are seen at δ 7.35–7.37 ppm and the proton
signals of the aromatic part of 1-indanol are appeared at δ
7.14–7.18 ppm.
IR spectra
13C NMR spectra
The IR spectrum of 1-indanol as a free ligand showed a
wide absorption band centered at 3,234 cm−1 typical of
O–H bond. This band is disappeared in the synthesized
compound indicating the formation of Zr–O bond. How-
ever, the absorption bands at 1,356, 1,426, 3,077 and
829 cm−1 are seen in the new compound which belong
to C–O, (C=C)aromatic, (C–H)aromatic and Zr–O bonds,
respectively.
In the 13C NMR spectrum of this compound in CDCl3, the
Cp carbon signals are seen at δ 45.8 ppm. The carbon atom
of 1-indanol attached to the zirconocene through oxygen,
gives rise to a resonance at 35.8 ppm. Six separate carbon sig-
nals are observed in the range of δ 124.9–128.9 ppm for the
aromatic part of 1-indanol in the 13C NMR spectrum of this
compound. Finally, the signals due to the protons of methyl-
ene part of 1-indanol are appeared at δ 8.6 and 29.8 ppm.
Fig. 1 The mass spectrum of Cp2Zr(C9H9O)2
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The UV–Vis spectrum of Cp2Zr(C9H9O)2
lines at m/z 64, 51 and 77 are related to the cyclopentadi-
enyl ring and the two fragments resulting from the decom-
position of the 1-indanol ligand, respectively.
Four absorption bands are observed for this compound in
UV–Vis spectrum. These are corresponding to σ → σ*,
π → π*, n → σ* and n → π* which appear at λmax/nm
231, 253, 263 and 271, respectively. These absorption
bands are shifted toward longer wavelengths and are seen
at 233, 255, 276 and 283 nm, respectively in the new com-
pound due to the Zr–O bonds formation.
Therogravimetric analysis (TGA ) of Cp2Zr(C9H9–O)2
The new compound was heated at a rate of 10 °C/min from
ambient temperature to 900 °C. Fig. 2 shows the TGA
curve for Cp2Zr(C9H9–O)2. The first weight loss of 1.8 %
from 100 to 112 °C may be attributed to the water and vola-
tile materials. The compound is stable up to 205 °C after
which a rapid weight loss of 25.2 % at about 205 °C was
occurred which belongs to the elimination of a 1-indanol
moiety. The TGA curve also indicates a rapid loss of a large
mass about 40.9 % at 278 °C which is due to the elimina-
tion of the second 1-indanol. This is followed by weight
losses of 52.8 and 62.8 % at 310 and 521 °C, respectively
which could be assigned to the masses of two cyclopenta-
dienyl rings.
The mass spectrum of Cp2Zr(C9H9O)2
The mass spectrum for the new compound (Fig. 1) is con-
sistent with the proposed structure which suggested on
basis of FT-IR, multinuclear NMR and elemental analy-
sis data. The spectrum shows peaks at m/z 224, 133, 115,
107, 90, 91, 92, 94, 96, 77, 64 and 51. The peak at m/z 224
belongs to Zr(C9H9O) moiety. The peak at m/z 133 is cor-
responding to C9H9O fragment. The peaks at m/z 115 and
107 are related to C9H7 and Zr–O fragments, respectively.
The peaks at m/z 90, 91, 92, 94 and 96 are attributable to
zirconium isotopes 90Zr40, 91Zr40, 92Zr40, 94Zr40 and 96Zr40
with naturally relative abundance of 54.46, 11.23, 17.11,
17.40 and 2.80 %, respectively. As is generally the case for
zirconium compounds, the presence of the isotopic pattern
for Zr atom in this spectrum is a strong reason for the exist-
ence of zirconium atom in this compound. Finally the mass
The study of catalytic activity of Cp2Zr(C9H9–O)2
In order to examine the catalytic activity of Cp2Zr(C9H9–
O)2, 2-naphtol and benzyl alcohol were acetylated by
acetyl anhydride in the presence of this new compound as
a catalyst. It was found that a trace of this catalyst is able
to promote the acetylation process toward a high yields in
Fig. 2 Thermogravimetric analysis (TGA) curve for Cp2Zr(C9H9O)2
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Acknowledgments The authors wish to thank the Shahid Cham-
ran University, Research Council for financial support of this project
(Grant 1393).
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