Tetrahydropyranylation of alcohols and phenols catalyzed by a new multi-wall carbon nanotubes-bound tin(IV) porphyrin

Article abstract of DOI:10.1007/s13738-017-1067-3

Abstract: In the present study, tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran (DHP) using tetrakis(p-aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate, [Sn^IV(TNH₂PP)(OTf)₂], and tetrakis(p-aminophenyl)porphyrinatotin(IV) tetrafluoroborate, [Sn^IV(TNH₂PP)(BF₄)₂], supported on multi-wall carbon nanotubes as new catalytic systems is investigated. These new catalysts, [Sn^IV(TNH₂PP)(OTf)₂@MWCNT] and [Sn^IV(TNH₂PP)(BF₄)₂@MWCNT], were characterized using elemental analysis, FT-IR spectroscopic techniques, scanning electron microscopy and diffuse reflectance UV–Vis spectroscopic methods. In these catalytic systems, an optimization on the amounts of catalysts and amount of DHP was done in the tetrahydropyranylation of alcohols and phenols with DHP and the best outcomes were received in the presence of 0.01?mmol (40?mg) of [Sn^IV(TNH₂PP)(OTf)₂@MWCNT] and [Sn^IV(TNH₂PP)(BF₄)₂@MWCNT] with 2?mmol of DHP. Efficiency and reusability are two important features of these new heterogenized catalysts for tetrahydropyranylation of primary, secondary and tertiary alcohols as well as phenols at room temperature. These catalysts were recovered several times with no loss on their initial activity, which indicates their high reusability and stability. Graphical Abstract: In the present study, tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran (DHP) using tetrakis(p-aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate, [Sn^IV(TNH₂PP)(OTf)₂], and tetrakis(p-aminophenyl)porphyrinatotin(IV) tetrafluoroborate, [Sn^IV(TNH₂PP)(BF₄)₂], supported on multi-wall carbon nanotubes as new catalytic systems is investigated. These new catalysts, [Sn^IV(TNH₂PP)(OTf)₂@MWCNT] and [Sn^IV(TNH₂PP)(BF₄)₂@MWCNT], were characterized using elemental analysis, FT-IR spectroscopic techniques, scanning electron microscopy and diffuse reflectance UV–Vis spectroscopic methods. In these catalytic systems, an optimization on the amounts of catalysts and amount of DHP was done in the tetrahydropyranylation of alcohols and phenols with DHP and the best outcomes were received in the presence of 0.01?mmol (40?mg) of [Sn^IV(TNH₂PP)(OTf)₂@MWCNT] and [Sn^IV(TNH₂PP)(BF₄)₂@MWCNT] with 2?mmol of DHP. Efficiency and reusability are two important features of these new heterogenized catalysts for tetrahydropyranylation of primary, secondary and tertiary alcohols as well as phenols at room temperature. These catalysts were recovered several times with no loss on their initial activity, which indicates their high reusability and stability. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s13738-017-1067-3

J IRAN CHEM SOC
DOI 10.1007/s13738-017-1067-3
ORIGINAL PAPER
Tetrahydropyranylation of alcohols and phenols catalyzed by a
new multi‑wall carbon nanotubes‑bound tin(IV) porphyrin
Shadab Gharaati1 · Hadi Kargar1 · Ali Mohammad Falahati1
Received: 18 June 2016 / Accepted: 20 January 2017
© Iranian Chemical Society 2017
Abstract In the present study, tetrahydropyranylation of
alcohols and phenols with 3,4-dihydro-2H-pyran (DHP)
using tetrakis(p-aminophenyl)porphyrinatotin(IV) tri-
Introduction
A heterogeneous catalyst can be simply separated from
reaction media, and environmental concerns together with
economic considerations make this recovery necessary and
convenient [1–3]. Also in extreme operating conditions,
heterogeneous catalysts are typically more tolerant than
their homogeneous analogues. Since purchasing or prepar-
ing transition-metal complexes could be often expensive,
several advantages are accessible by immobilizing them on
a support. Heterogeneous catalysts do not contaminate the
product solution and can be recycled and also can increase
selectivity [4].
Attention and interest in nanoscience and nanotechnol-
ogy has extremely raised the level of research on carbona-
ceous materials, such as fullerenes and carbon nanotubes
(CNT). Carbon nanotubes (CNTs) have made a lot of
attractions in the synthesis, characterization and applica-
tions and due to their unique structural, mechanical and
electronic properties, and many studies have been done
on these compounds [5–8]. CNTs can be used as catalysts
support because of their insoluble attribute in the most sol-
vents. For example, Pt nanoparticles supported on CNTs
have been used for methanol oxidation [9], palladium nan-
oparticles supported on CNTs for semi-hydrogenation of
phenyl acetylene [10], chiral vanadyl salen complex sup-
ported on single-wall CNTs for enantioselective cyanosi-
lylation of aldehydes [11, 12] and manganese(III) porphy-
rin supported on MWCNTs for epoxidation of alkenes with
NaIO4 [13].
fluoromethanesulfonate,
tetrakis(p-aminophenyl)porphyrinatotin(IV)
[SnIV(TNH2PP)(OTf)2],
and
tetrafluor-
oborate, [SnIV(TNH2PP)(BF4)2], supported on multi-wall
carbon nanotubes as new catalytic systems is investigated.
These new catalysts, [SnIV(TNH2PP)(OTf)2@MWCNT]
and [SnIV(TNH2PP)(BF4)2@MWCNT], were characterized
using elemental analysis, FT-IR spectroscopic techniques,
scanning electron microscopy and diffuse reflectance UV–
Vis spectroscopic methods. In these catalytic systems, an
optimization on the amounts of catalysts and amount of
DHP was done in the tetrahydropyranylation of alcohols
and phenols with DHP and the best outcomes were received
in the presence of 0.01 mmol (40 mg) of [SnIV(TNH2PP)
(OTf)2@MWCNT] and [SnIV(TNH2PP)(BF4)2@MWCNT]
with 2 mmol of DHP. Efficiency and reusability are two
important features of these new heterogenized catalysts for
tetrahydropyranylation of primary, secondary and tertiary
alcohols as well as phenols at room temperature. These
catalysts were recovered several times with no loss on their
initial activity, which indicates their high reusability and
stability.
Keywords Nanostructures · Heterogeneous catalysis ·
Supported catalysts · Lewis acids · Hydroxyl compounds ·
Tetrahydropyranyl ether
During the term of different transformations in a syn-
thetic sequence, the protection of hydroxy functional
groups is often mandatory mainly in the synthesis of fine
chemicals and natural products [14–25]. Among them,
tetrahydropyranylation has been known as one of the
* Shadab Gharaati
shadabgharaati@gmail.com
1
Department of Chemistry, Payame Noor University, P.O.
Box 19395-4697, Tehran, Islamic Republic of Iran
1 3

J IRAN CHEM SOC
IV(TNH2PP)(OTf)
[Sn
or
2@MWCNT]
most frequently used solutions to protect hydroxyl groups
in synthetic organic chemistry, in particular natural prod-
uct chemistry, because of its easy installation, general
stability to most nonacidic reagents, and easy removal
under mild acidic conditions [26–28].
A variety of catalysts including protonic and Lewis
acid catalysts such as p-toluene sulfonic acid (PTSA)
[29], bis[trimethylsilyl]sulfate [30], (CH3)3SiI [31],
CuCl2 [32], DDQ [33], Ru(CH3)3(triphos)](OTf)2 [34],
I2 [35], AlCl3·6H2O [36], In(OTf)3 [37], ZrCl4 [38],
K5CoW12O40·3H2O [39], ionic liquids [40], Bu4N+Br3−
[41], and LiOTf [42], K-10 clay [43], alumina impreg-
nated with ZnCl2 [44], silica chloride [45], AlCl3@PS
[46], silica-based sulfonic acid [47, 48], H6P2W18O62
[49], PdCl2(CH3CN)2 [50], vanadyl(IV) acetate [51] and
[SnIV(TPP)(OTf)2] [52] have been developed for tetrahy-
dropyranylation of alcohols and phenols.
IV
(BF )
[Sn
(TNH2PP)
2@MWCNT]
4
R
+
OH
+ NH3
THF
O
O
RO
Scheme 1 Tetrahydropyranylation of alcohols and phenols
with DHP catalyzed by [SnIV(TNH2PP)(OTf)2@MWCNT] or
[SnIV(TNH2PP)(BF4)2@MWCNT]
Experimental
Chemical materials were prepared from Merck or Fluka
chemical companies. MWCNTs (containing –COOH
groups, purity 96%) were bought from Shenzen NTP Fac-
tory (China). FT-IR spectra were taken with potassium
bromide pellets in the range 400–4000 cm−1 with a Nico-
let Impact 400D spectrometer. Scanning electron micro-
graphs (SEMs) of catalysts were done on a Philips XL 30
SEM instrument. Gas chromatography experiments (GC)
were done with a Shimadzu GC-16A instrument using a
2-m column packed with silicon DC-200 or Carbowax
20 m. In the GC experiments, n-decane was applied as an
internal standard. Inductively coupled plasma (ICP) anal-
yses were performed on an ICP-Spectrociros CCD instru-
ment. The diffuse reflectance ultraviolet–visible spectrum
was performed by solid UV–Vis on Shimadzu model 265
In order to solve some problems of these catalysts like
long time of reactions, drastic reaction conditions or tire-
some workups and moisture sensitive or expensive of
these catalysts, improving previous procedures and intro-
duction of new methods are still mandatory.
Electron-deficient metalloporphyrins have been used
as mild Lewis acids catalysts [53–56]. The applications of
chromium and iron porphyrins in organic synthesis have
been reported by Suda group. Suda group used Cr(tpp)
Cl for regioselective [3] rearrangement of aliphatic allyl
vinyl ethers, and for Claisen rearrangement of simple ali-
phatic allyl vinyl ethers, Fe(tpp)OTf for rearrangement of
α,β-epoxy ketones into 1,2-diketones and Cr(tpp)OTf for
highly regio- and stereoselective rearrangement of epox-
ides to aldehydes [57–60]. Also some applications of tin
porphyrins have been reported by Tangestaninejad and
Moghadam groups as mild Lewis acids catalysts in dif-
ferent organic reactions [61–66].
1
spectrophotometer. H NMR spectra were recorded on a
Bruker-Avance AQS 400 MHz spectrometer. Tetra(4-ami-
nophenyl)porphyrin was provided and metallated accord-
ing to the literature [75, 76].
Chlorination of MWCNT‑COOH
The MWCNT-COOH (1 g) and SOCl2 (10 mL) were
mixed and refluxed for 1 h. Then, the reaction mixture
was cooled and the SOCl2 was evaporated. The resulting
precipitate was supposed to be the chlorinated multi-wall
carbon nanotubes, MWCNT-COCl, and applied without
more purification [77].
Lately, we have reported the applications of tin(IV)
tetraphenylporphyrinatotrifluoromethanesulfonate
[52,
67–70], tin(IV)tetraphenylporphyrinato tetraflouroborate
[71] and tetrakis(p-aminophenyl)porphyrinatotin(IV)
trifluoromethanesulfonate supported on chloromethyl-
ated polystyrene [72–74] as mild Lewis acids catalysts in
organic transformations.
Supporting of [SnIV(TNH2PP)Cl2] on chlorinated
MWCNTs [SnIV(TNH2PP)Cl2@MWCNT]
In this paper, we report the preparation, charac-
terization and investigation of catalytic activities of
tetrakis(p-aminophenyl)porphyrinatotin(IV)
trifluo-
romethanesulfonate, [SnIV(TNH2PP)(OTf)2], and of
tetrakis(p-aminophenyl)porphyrinatotin(IV) tetrafluor-
oborate, [SnIV(TNH2PP)(BF4)2], supported on multi-
wall carbon nanotubes in the tetrahydropyranylation
of alcohols and phenols with 3,4-dihydro-2H-pyran
(Scheme 1).
Chlorinated MWCNTs (5 g) and triethylamine (3 mL)
were mixed with a solution of [SnIV(TNH2PP)Cl2] (1 g)
in DMF (50 mL) and refluxed for 72 h. Finally, the mix-
ture was cooled and the catalysts were filtered off and
washed completely with toluene, methanol and ether and
as last step, it was dried in vacuum for several hours.
1 3

J IRAN CHEM SOC
Conversion of [SnIV(TNH2PP)Cl2@MWCNT]
to [SnIV(TNH2PP)(OTf)2@MWCNT]
covalent attachment of [SnIV(TNH2PP)Cl2] to chlorin-
ated MWCNTs through an amide linkage. Afterward, the
chlorines were substituted with OTf or BF4 by the reac-
tion of [SnIV(TNH2PP)(Cl)2@MWCNT] with NaOTf or
NaBF4, respectively. These groups increased the electron
deficiency of tin (IV).
NaOTf (1 g) was added to a suspension of [SnIV(TNH2PP)
Cl2@MWCNT] (2 g) in THF (50 mL) and stirred at 60 °C
for 1 h. Finally, the catalyst was filtered and washed with
acetonitrile.
The characterizations of these catalysts were done
by elemental analysis, SEM, FT-IR and UV–Vis spec-
troscopic methods. The nitrogen content of catalyst was
measured which was 2% (2.01 mmol/g). According to
this measure, the amount of porphyrin linked to MWCNT
was calculated as 0.25 mmol/g. The evidence for con-
nection of tin(IV) porphyrin on the multi-wall carbon
nanotubes was got from FT-IR spectra of [SnIV(TNH2PP)
Cl2] (Fig. 1a), [SnIV(TNH2PP)Cl2@MWCNT] (Fig. 1b),
[SnIV(TNH2PP)(OTf)2@MWCNT] (Fig. 1c) and also,
[SnIV(TNH2PP)(BF4)2@MWCNT] (Fig. 1d). The
bands at 1655 and 3427 cm−1 in the FT-IR spectrum of
[SnIV(TNH2PP)Cl2@MWCNT] and [SnIV(TNH2PP)
(OTf)2@MWCNT] and the bands at 1662 and 3426 cm−1
in the FT-IR spectrum of [SnIV(TNH2PP)(BF4)2@
MWCNT] are attributed to C=O and –NH stretching
bands of amide, respectively. These bands that are not
presented in the homogeneous [SnIV(TNH2PP)Cl2] indi-
cate on attachment of porphyrin on the MWCNT.
Conversion of [SnIV(TNH2PP)Cl2@MWCNT]
to [SnIV(TNH2PP)(BF4)2@MWCNT]
NaBF4 (1 g) was added to a suspension of [SnIV(TNH2PP)
Cl2@MWCNT] (2 g) in THF (50 mL) and stirred at 60 °C
for 1 h. Eventually, the catalyst was filtered and washed
with acetonitrile.
General procedure for tetrahydropyranylation
of alcohol and phenols catalyzed by [SnIV(TNH2PP)
(OTf)2@MWCNT] and [SnIV(TNH2PP)(BF4)2@
MWCNT]
A mixture of alcohol or phenol (1 mmol), [SnIV(TNH2PP)
(OTf)2@MWCNT] (40 mg, 0.01 mmol) or [SnIV(TNH2PP)
(BF4)2@MWCNT] (40 mg, 0.01 mmol) and DHP (2 mmol
per OH group) in THF (0.5 mL) was prepared and stirred
at room temperature for an proper time. The flow of reac-
tion was monitored by GC. At the end of reaction, Et2O
(10 mL) was added and the catalyst was filtered. Afterward,
the filtrates were concentrated under reduced pressure to
afford the crude product.
In addition, the bands at 3453 cm−1 in the FT-IR spec-
trum of [SnIV(TNH2PP)Cl2@MWCNT], at 3353 cm−1
in the FT-IR spectrum of [SnIV(TNH2PP)(OTf)2@
MWCNT] and at 3351 cm−1 in the FT-IR spectrum
of [SnIV(TNH2PP)(BF4)2@MWCNT] are attributed to
stretching vibrations of N–H primary amine. The bands
at 1623 cm−1 in the FT-IR spectrum of [SnIV(TNH2PP)
Cl2@MWCNT], at 1622 cm−1 in the FT-IR spectrum of
[SnIV(TNH2PP)(OTf)2@MWCNT] and at 1621 cm−1 in
the FT-IR spectrum of [SnIV(TNH2PP)(BF4)2@MWCNT]
are attributed to bending vibrations of N–H primary
amine which are not presented in the FT-IR spectrum of
the chlorinated-MWCNT.
Catalyst reusability
As mentioned above, the reusability of catalysts was inves-
tigated through multiple sequential tetrahydropyranylation
of benzyl alcohol. At final step of each reaction, the cata-
lysts were separated from the reaction mixture by simple
filtration and washed thoroughly with Et2O and finally was
dried carefully in order to be used in the next run.
Also conversion of [SnIV(TNH2PP)Cl2@MWCNT] to
[SnIV(TNH2PP)(OTf)2@MWCNT] is because of the pres-
ence of bands at 1282 and 1173 cm−1 that relate to stretch-
ing vibrations of C–F and S=O bands, respectively.
Results and discussion
The FT-IR spectrum of [SnIV(TNH2PP)(BF4)2@
MWCNT] shows three bands at 1005, 1085 and 1171 cm−1
corresponding to B–F stretching bands, respectively.
These peaks signify the conversion of [SnIV(TNH2PP)
Cl2@MWCNT] combination to [SnIV(TNH2PP)(BF4)2@
MWCNT] combination.
Preparation and characterization of the catalysts
[SnIV(TNH2PP)(OTf)2@MWCNT] and [SnIV(TNH2PP)
(BF4)2@MWCNT]
Scheme 2 shows the preparation route for tin porphyrin
catalysts supported on MWCNT. The preparation of tin
porphyrin [SnIV(TNH2PP)(Cl)2@MWCNT] was done by
The UV–Vis spectroscopy of complex [SnIV(TNH2PP)
(OTf)2] showed absorption peaks at 430 (Soret band),
1 3

J IRAN CHEM SOC
NH2
Cl
N
N
N
COCl
H2N
+
NH2
Sn
Cl
N
NH2
NH2
Cl
N
o
N
N
Sn
Cl
NH2
CHN
N
NH2
NaOTf
60o
1
h
C
,
NH2
OTf
NaBF4
60o
1
h
C
,
NH2
N
N
N
o
CHN
Sn
NH2
N
OTf
BF4
N
N
N
o
CHN
Sn
NH
N
BF4
NH2
NH2
Scheme 2 Preparation route for [SnIV(TNH2PP)(OTf)2@MWCNT] or [SnIV(TNH2PP)(BF4)2@MWCNT
1 3

J IRAN CHEM SOC
Fig. 2 UV–Vis spectrum of:
a
heterogeneous [SnIV(TNH2PP)
(OTf)2@MWCNT] and b heterogeneous [SnIV(TNH2PP)(BF4)2@
MWCNT]
Additionally, the UV–Vis spectroscopy of complex
[SnIV(TNH2PP)(BF4)2] showed absorption peaks at 421
(Soret band), 562 and 618 nm (Q bands). The diffuse
reflectance of [SnIV(TNH2PP)(BF4)2@MWCNT] is sim-
ilar to the spectrum of peer solution with only a slight
shift on a Soret band at 424 nm and Q bands at 554 and
620 nm (Fig. 2b).
The SEM images of these catalysts indicate that the
nanotubes are aggregated and have kept their nanotube
properties (Fig. 3).
Fig. 1 FT-IR spectrum of: a [SnIV(TNH2PP)Cl2]; b [SnIV(TNH2PP)
Cl2@MWCNT];
c
[SnIV(TNH2PP)(OTf)2@MWCNT] and
d
[SnIV(TNH2PP)(BF4)2@MWCNT]
Tetrahydropyranylation of alcohols and phenols
catalyzed by [SnIV(TNH2PP)(OTf)2@MWCNT]
and [SnIV(TNH2PP)(BF4)2@MWCNT]
562 and 620 nm (Q bands). The diffuse reflectance of the
[SnIV(TNH2PP)(OTf)2@MWCNT] is similar to the spec-
trum of peer solution with only a slight shift on a Soret
band at 434 nm and Q bands at 574 and 625 nm, which
clearly signify the presence of metalloporphyrin on the
MWCNT (Fig. 2a).
First, an optimization on the various reaction parameters
such as amount of catalysts, kind of solvent and amount
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J IRAN CHEM SOC
Through the tetrahydropyranylation of benzyl alcohol
with DHP in the presence of 1 mol% of [SnIV(TNH2PP)
Cl2@MWCNT] catalyst at room temperature, the impact
of OTf and BF4 groups on the electron deficiency of tin
(IV) porphyrin was shown. The outcome showed that after
10 min the amount of the relevant THP-ether in the pres-
ence of [SnIV(TNH2PP)Cl2@MWCNT] was 18%, pro-
vided after 4 min the reaction was done completely in the
presence of [SnIV(TNH2PP)(OTf)2@MWCNT] and also
after 5 min in the presence of [SnIV(TNH2PP)(BF4)2@
MWCNT].
[SnIV(TNH2PP)(OTf)2@MWCNT] and [SnIV(TNH2PP)
(BF4)2@MWCNT] were found as efficient catalysts for
tetrahydropyranylation of different alcohols and phenols.
Through an optimized condition and at room tempera-
ture, primary, secondary and tertiary alcohols including
aromatic and aliphatic were transformed completely to
their corresponding tetrahydropyranyl ethers in excel-
lent yield (Table 2). In the case of aromatic alcohols, the
natures of substituents have no significant effect on the
tetrahydropyranylation yield.
Investigation on the selectivity of this method was per-
formed through binary mixtures of primary, secondary
and tertiary alcohols and phenols (Tables 3, 4). The out-
comes confirmed that for both heterogeneous catalysts, in
the presence of secondary or tertiary alcohols or phenols,
primary alcohols were quickly converted to their corre-
sponding silyl ethers.
Fig. 3 SEM image of: a [SnIV(TNH2PP)(OTf)2@MWCNT] and b
[SnIV(TNH2PP)(BF4)2@MWCNT]
The use of homogeneous [SnIV(TPP)(OTf)2] in the tet-
rahydropyranylation of alcohols and phenols was reported
in our previous works [52]. In the presence of 1 mol%
of the catalyst, the reaction durations were 3–6 min and
the product yields were 60–97%. In comparison with
its homogeneous peer and in the presence of 1 mol%
of [SnIV(TNH2PP)(OTf)2@MWCNT], the relevant
of DHP was done in the tetrahydropyranylation of ben-
zyl alcohol with DHP. In this process, the best outcomes
were received in the presence of [SnIV(TNH2PP)(OTf)2@
MWCNT] and [SnIV(TNH2PP)(BF4)2@MWCNT], 1 mol%
(40 mg) of each catalyst with 2 mmol of DHP in THF as
solvent (Table 1).
Table 1 Optimization of reaction conditions in the tetrahydropyranylation of benzyl alcohol with tin porphyrins
Entry
Catalyst amount (mmol, mg)
DHP (mmol)
Solvent
[SnIV(TNH2PP)(OTf)2@
MWCNT]
[SnIV(TNH2PP)(OTf)2@
MWCNT]
Time (mmol)
Yield (%)a
Time (mmol)
Yield (%)a
1
2
20 (0.005)
30 (0.0075)
40 (0.01)
50 (0.0125)
40 (0.01)
40 (0.01)
40 (0.01)
40 (0.01)
40 (0.01)
40 (0.01)
2
THF
4
4
4
4
4
4
4
4
4
4
48
82
5
5
5
5
5
5
5
5
5
5
43
71
2
THF
3
2
THF
100
100
81
100
100
78
4
2
THF
5
2
CH3CN
CH2Cl2
CHCl3
n-Hexane
THF
6
2
52
47
7
2
39
36
8
2
14
10
9
1
48
41
10
1.5
THF
77
77
a
GC yield
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J IRAN CHEM SOC
Table 2 Tetrahydropyranylation of alcohols and phenols with DHP catalyzed by tin(IV) porphyrins at room temperature
Entry Hydroxy compound THP ether
[SnIV(TNH2PP)(OTf)2@MWCNT]
[SnIV(TNH2PP)(BF4)2@MWCNT]
Time
(min)
Yield (%)a TOF (h-1)
Time
(min)
Yield (%)a TOF (h-1)
CH2OH
1
CH2OTHP
4
3
100
100
100
100
5
4
100
100
100
100
CH2CH2OH
2
CH2CH2OTHP
CH2CH2CH2OTHP
CH2CH2CH2OH
3
3
5
7
4
4
100
98
100
98
4
6
8
5
5
100
96
100
98
Cl
CH2OH Cl
CH2OTHP
CH2OTHP
4
5
6
8
O2N
CH2OH O2N
80
80
80
80
MeO
CH2OH
CH2OTHP
MeO
100
100
100
100
100
100
100
100
CH2OTHP
CH2OH
OMe
OMe
CH2OH
CH2OTHP
9
4
100
100
5
100
100
Me
Me
OTHP
OH
10
11
4
4
100
100
100
100
5
5
100
100
100
100
OTHP
OH
OTHP
OH
12
4
94
94
5
94
94
OH
OTHP
13
14
6
6
96
93
96
93
6
6
95
90
96
93
CH3
CH3
H
H3C
C
CH3
3C
C
CH3
OTHP
OTHP
OH
OH
15
16
6
4
93
93
6
5
91
93
OTHP
OH
100
100
100
100
OH
Cl
OTHP
Cl
17
18
5
7
100
78
100
78
6
8
98
77
100
78
O2N
H 3C
OH
O2N
OTHP
OH H3C
OTHP
19
20
4
5
98
97
98
97
5
5
97
95
98
97
OH
OTHP
Reaction conditions: hydroxy compound (1 mmol), DHP (2 mmol), catalyst (1 mol%), THF (0.5 mL)
a
GC yield
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J IRAN CHEM SOC
Table 3 Selective
Row ROH
THP ether
Time (min)
Yield (%) a
83
tetrahydropyranylation of
alcohols and phenols catalyzed
by [SnIV(TNH2PP)(OTf)2@
MWCNT] in tetrahydrofuran
CH2OH
OH
CH2OTHP
OTHP
1
4
4
22
87
CH2OTHP
CH2OH
2
Me
OH
Me
OTHP
Me
Me
21
90
CH2OH
CH2OTHP
4
4
3
4
41
95
OTHP
OH
Reaction conditions for a
binary mixture: 1 mmol of
each alcohol or phenol, DHP
(2mmol), catalyst (1 mol%),
THF (0.5 mL)
CH2OH
OH
CH2OTHP
OTHP
15
a
GC yield
Yield (%) a
80
Table 4 Selective
Row ROH
THP ether
Time (min)
5
tetrahydropyranylation of
alcohols and phenols catalyzed
by [SnIV(TNH2PP)(BF4)2@
MWCNT] in tetrahydrofuran
CH2OH
CH2OTHP
OTHP
OH
1
26
77
CH2OTHP
CH2OH
2
5
Me
OH
Me
OTHP
Me
Me
23
92
CH2OH
CH2OTHP
5
5
3
4
34
91
OTHP
OH
Reaction conditions for a
binary mixture: 1 mmol of
each alcohol or phenol, DHP (2
mmol), catalyst (1 mol%), THF
(0.5 mL)
CH2OH
OH
CH2OTHP
OTHP
21
a
GC yield
Table 5 Reusability
Run [SnIV(TNH2PP)(OTf)2@MWCNT]
[SnIV(TNH2PP)(OTf)2@MWCNT]
of tin porphyrins in the
tetrahydropyranylation of
benzyl alcohol with DHP
THP-ether (%)a Time (min) Sn leached (%)b THP-ether (%)a Time (min) Sn leached (%)b
1
2
3
4
5
6
100
100
100
100
100
100
4
4
4
4
4
4
0
0
0
0
0
0
100
100
100
100
100
100
5
5
5
5
5
5
0
0
0
0
0
0
Reaction conditions: benzyl alcohol (1 mmol), DHP (2 mmol), catalyst (1 mol%), THF (0.5 mL)
a
GC yield
b
Determined by ICP
1 3

J IRAN CHEM SOC
tetrahydropyranylation of benzyl alcohol with DHP. After
performing each reaction, the catalyst was filtered and
washed thoroughly with acetonitrile and diethyl ether,
respectively, and finally was dried in order to be reused in
fresh benzyl alcohol and DHP. These heterogeneous cata-
lysts were reused six times consecutively with no detecta-
ble catalyst leaching or a considerable loss of their activi-
ties (Table 5). After each run, the filtrates were used in
order to measure the leaching of catalyst and no Sn was
detected in the filtrates by ICP. Using diffuse reflectance
UV–Vis spectrophotometery, the nature of recovered cat-
alyst was investigated and no change was detected in the
DR UV–Vis spectrum of the catalyst which confirms the
stability and robustness of catalyst (Fig. 4).
Conclusion
In conclusion, the construction and characterization
of [SnIV(TNH2PP)(OTf)2] and [SnIV(TNH2PP)(BF4)2]
immobilized on multi-wall carbon nanotubes were per-
formed for the first time. In order to investigate their
catalytic activities, these new heterogenized catalysts
were used for tetrahydropyranylation of primary, second-
ary and tertiary alcohols and phenols with DHP at room
temperature. Short reaction times, excellent yields, easy
work-up and reusability and stability of the catalyst are
significant advantages of this method.
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Fig. 4 DR UV–Vis spectrum of recovered:
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[SnIV(TNH2PP)
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1 3