Novel peripherally and non-peripherally hydrobenzoin substituted optically active phthalocyanines: Synthesis, characterization, aggregation, electrochemical properties and catalytic applications

Article abstract of DOI:10.1016/j.poly.2018.06.053

The novel optically active two zinc(II)phthalocyanines and two cobalt(II)phthalocyanines with four chiral hydrobenzoin moieties at the non-peripheral (4 and 5) and peripheral positions (6 and 7) of the phthalocyanine ring have been synthesized. The structures of the synthesized compounds are characterized by ¹H NMR, IR, UV–Vis, circular dichroism (CD) and MALDI-TOF MS spectral data. The comparative studies of the spectral, aggregation properties, voltammetry and catalytic applications of novel zinc(II) and cobalt(II)phthalocyanines, tetra-substituted with hydrobenzoin at peripheral and non-peripheral positions, were investigated. All synthesized phthalocyanines are highly soluble in most common organic solvents. In the enantioselective addition of diethylzinc to aldehydes, the best catalytic activity was obtained with 3-methoxybenzaldehyde in the presence of non-peripherally hydrobenzoin substituted zinc(II)phthalocyanine 4 and afforded the corresponding chiral secondary alcohol with the yield of 38% and the enantiomeric excess of 33%. In the oxidation of benzyl alcohol, the highest conversion of benzyl alcohol to benzaldehyde was obtained with non-peripherally substituted cobalt(II)phthalocyanine 5 as 91% with the highest selectivity of 83%.

Full text of DOI:10.1016/j.poly.2018.06.053

Accepted Manuscript
Novel peripherally and non-peripherally hydrobenzoin substituted optically ac-
tive phthalocyanines: Synthesis, characterization, aggregation, electrochemical
properties and catalytic applications
Yaşar Gök, Halil Zeki Gök, Mustafa Kemal Yılmaz, Murat Farsak, İlker Ümit
Karayiğit
PII:
S0277-5387(18)30384-X
https://doi.org/10.1016/j.poly.2018.06.053
POLY 13262
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
25 May 2018
28 June 2018
30 June 2018
Please cite this article as: Y. Gök, H.Z. Gök, M.K. Yılmaz, M. Farsak, I.U. Karayiğit, Novel peripherally and non-
peripherally hydrobenzoin substituted optically active phthalocyanines: Synthesis, characterization, aggregation,
electrochemical properties and catalytic applications, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.
2018.06.053
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Novel peripherally and non-peripherally hydrobenzoin substituted
optically active phthalocyanines: Synthesis, characterization,
aggregation, electrochemical properties and catalytic applications
Yaşar Gök a,, Halil Zeki Göka, , Mustafa Kemal Yılmaz b, Murat Farsak c, İlker Ümit Karayiğitd
a
Department of Biomedical Engineering, Faculty of Technology, Mehmet Akif Ersoy University, 15030,
Bucak/Burdur, Turkey.
b
Department of Chemistry, Faculty of Arts and Sciences, Mersin University, 33343, Mersin, Turkey
c
Department of Food Technology, Applied Science School Of Kadirli, Osmaniye Korkut Ata University, 80000,
Osmaniye, Turkey
d
Department of Chemistry, Faculty of Arts and Sciences, Osmaniye Korkut Ata University, 80000, Osmaniye, Turkey
Abstract
The novel optically active two zinc(II) phthalocyanines and two cobalt(II) phthalocyanines
with four chiral hydrobenzoin moieties at the non-peripheral (4 and 5) and peripheral positions
(6 and 7) of the phthalocyanine ring have been synthesized. The structures of the synthesized
1
compounds are characterized by H NMR, IR, UV-Vis, Circular Dichroism (CD) and MALDI-
TOF MS spectral data. The comparative studies of the spectral, aggregation properties,
voltammetry and catalytic applications of novel zinc(II) and cobalt(II) phthalocyanines, tetra-
substituted with hydrobenzoin at peripheral and non-peripheral positions, were investigated. All
synthesized phthalocyanines are highly soluble in most common organic solvents. In the
enantioselective addition of diethylzinc to aldehydes, the best catalytic activity was obtained with
Corresponding author. Tel.: e-mail: yasar_gok@yahoo.com
 Corresponding author. Tel.: + 90 (248)-3259900-6267; fax: +90 (248)-325 9900; e-mail: halilzekigok@gmail.com,
1

3-methoxybenzaldehyde in the presence of non-peripherally hydrobenzoin substituted zinc(II)
phthalocyanine 4 and afforded the corresponding chiral secondary alcohol with the yield of 38%
and the enantiomeric excess of 33%. In the oxidation of benzyl alcohol, the highest conversion of
benzyl alcohol to benzaldehyde was obtained with non-peripherally substituted cobalt(II)
phthalocyanine 5 as 91% with the highest selectivity of 83%.
Keywords: Optically active phthalocyanine; Catalysis; Electrochemistry; C2-symmetric; Chiral
diol
1. Introduction
Phthalocyanines (Pcs) and their metal complexes are one of the most studied functional
molecular materials in the literature due to their high thermal and chemical stability along with
their unique properties such as strong UV-Vis light absorption, high molar absorption
coefficients, and electron transfer abilities [1, 2]. A goal of research on the chemistry of
phthalocyanines is to achieve control over the structure of synthetic molecules in order to
improve their application capabilities in scientific and technological areas. For these purposes, by
adding various substituents to the non-peripheral and peripheral positions of the benzene rings,
numerous Pcs have been prepared with almost all metal ions in the periodic table [3-9].
Optically active compounds are ubiquitous and play a fundamental role in life, especially in
the area of pharmaceutical and agricultural industries [10]. The design and synthesis of new
optically active compounds is one of the most important goals in modern chemistry [11]. In spite
of large academic interest, the first optically active phthalocyanines were reported in 1993 and
since then, limited number of reports have explored in the synthesis of phthalocyanine bearing
optically active groups [12]. Most of studies have concentrated on combining chiral binaphthol
2

groups with a phthalocyanine core and most of chiral substituents have been attached to the 
positions of the phthalocyanine ring [13-16]. Studies on combining different chiral groups with a
phthalocyanine core are still limited and spectral properties of these molecules are unknown.
Although phthalocyanines have a wide range of applications, they have not received
attention for the usage in enantioselective reactions yet, which is one of the most studied areas in
chemistry [17]. Enantioselective diethyl zinc addition to aldehydes is one of the most studied
catalytic reactions in the field of asymmetric catalysis. The alkylation of aldehydes with
organometallic reagents in the presence of a catalytic amount of a chiral molecule gives a new C-
C bond in an enantioselective manner [18]. Enantioselective addition of organozinc reagents to
aldehydes gives optically active pure secondary alcohols [16, 17]. These alcohols are both key
compounds in the preparation of pharmaceuticals and agrochemicals and important intermediates
in the synthesis of many substrates such as esters, amides, and ethers [19].
Selective oxidation of benzyl alcohol to benzaldehyde is an important organic transformation
as well as the alkylation of aldehydes in organic chemistry. Benzaldehyde is a very valuable
chemical which has widespread applications in perfumery, dyestuff and agrochemical industries
[20, 21]. Normally, benzyl alcohol can be traditionally oxidized to benzaldehyde with various
stoichiometric inorganic oxidants such as chromium reagents (pyridinium chlorochromate or
dipyridine chromium(IV) oxide) and permanganates. Unfortunately, the use of these reagents is
limited since they are relatively expensive, generates equal amounts of metal waste, or requires
large excess of reagent be used. Therefore, the selective oxidation of benzyl alcohol using
different types of oxidants such as hydrogen peroxide, tert-butylhydroperoxide or 3-
chloroperbenzoic acid has been proposed to replace the present oxidation processes that use
stoichiometric quantities of inorganic oxidants. Besides that, synthesis of new efficient and
effective catalysts for selective catalytic oxidation of benzyl alcohol to benzaldehyde is still
demanding for the industrial applications.
3

In this study, we report, for the first time, the synthesis, characterization, aggregation and
electrochemical properties of peripheral and non-peripheral chiral C2-symmetric diol substituted
phthalocyanine complexes, and investigation of their catalytic efficiency in the enantioselective
addition of diethylzinc to aldehydes and the oxidation of benzyl alcohol. It is noteworthy that
there has been no example of optically active phthalocyanines used in the enantioselective
diethylzinc addition to aldehydes so far to the best of our knowledge.
2. Experimental
2.1. Materials and Equipment
(1R,2R)-1,2-diphenylethane-1,2-diol 1 was prepared according to the literature [22]. 3-
nitrophthalonitrile and 4-nitrophthalonitrile were synthesized following the procedure given in
the published paper [23]. All reagents and solvents were reagent grade quality and were obtained
from commercial suppliers. All solvents were dried and purified as described by Perrin and
Armarego [24]. Column chromatography was carried out on silica gel (Merck, Kieselgel 60, 400-
630 mesh).
FTIR spectra were measured on a Perkin Elmer Spectrum 65 spectrometer using KBr pellets.
1H and 13C NMR spectra were recorded on a Varian Mercury 400 MHz spectrometer using
CDCl3 and THF-d8 (99.9%). Mass spectra were measured on a Micromass Quatro LC/ULTIMA
LC-MS/MS and a Bruker Daltonics MALDI-TOF spectrometer. Optical spectra were recorded in
the UV-Vis region with a PG-T80+ spectrophotometer using 1 cm path length cuvettes at room
temperature. Circular dichroism (CD) measurements were performed with a JASCO J-810
spectropolarimeter. Optical rotations were measured with a Rudolph Autopol-I series
polarimeter. GC separations were performed on Shimadzu GC-2010 Plus. Cyclic voltammetry
4

and square wave voltammetry measurements were performed with the three-electrode technique
using a Gamry (Interface 1000) Electrochemical Analyzer under computer control. Elemental
analyses were obtained with a LECO Elemental Analyser (CHNS 0932) spectrophotometer.
Melting points were determined with an electrothermal apparatus and are reported uncorrected.
2.2. Synthesis
2.2.1. 3-((1R,2R)-2-hydroxy-1,2-diphenylethoxy)phthalonitrile (2, Scheme 1)
(1R,2R)-1,2-diphenylethane-1,2-diol 1 (1.5 g, 7.0 mmol) and 22.5 mL of DMSO were placed
in two-neck flask under a nitrogen atmosphere at room temperature. To this reaction mixture was
added 3-nitrophthalonitrile (1.2 g; 7.0 mmol) and stirred for 15 min under inert atmosphere.
Finely ground anhydrous K2CO3 (0.97 g; 7.0 mmol) was then added to the resulting mixture at
room temperature. The reaction was monitored by thin layer chromatography and completed in 2
h. The reaction mixture was poured into water-ice (1:3 v/v) resulting in the formation of light-
yellow precipitate and then extracted with dichloromethane. The combined organic layer was
dried over anhydrous Na2SO4 and the solvent was evaporated under reduced pressure to give a
crude product that was purified by silica gel chromatography. The elution was carried out with
dichloromethane–ethylacetate (95:5). The product was obtained as a white solid. Yield: 1.55 g,
o
(65%); mp: 128-130 C. Found: C, 77.34; H, 4.58; N, 8.19%; molecular formula C22H16N2O2
requires C, 77.63; H, 4.74; N, 8.23%. + 237.67 (c = 1, CHCl3); retention time 15.93
min, Chiral ART Amylose-C, 30:70 n-hexane-iPrOH, flow rate of 0.5 mL/min, 254 nm, t = 40
oC; IR (KBr disc) vmax/cm-1: 3500 (OH), 3064, 3033, 2910, 2232 (CN), 1734, 1579, 1462, 1285,
1
1043, 793, 764, 701; H-NMR (400 MHz, CDCl3, ppm) : 7.43 (t, J = 8.3 Hz, H), 7.29 (dd, J =
7.8 Hz, J = 0.8 Hz, H), 7.25-7.20 (m, 6H), 7.11 (m, 2H), 7.05 (m, 3H), 5.27 (d, J = 7.5 Hz, H),
5

5.10 (d, J = 7.5 Hz, H), 3.09 (br, OH); 13C-NMR (100 MHz, CDCl3, ppm) : 160.3, 137.9, 135.0,
134.3, 128.9, 128.7, 128.4, 128.2, 127.3, 127.1, 121.1, 125.7, 119.0, 117.0, 115.2, 113.1, 105.8,
87.4, 77.9; MS (ESIˉ) MS calculated [M+Cl]- for C22H16N2O2Cl: 375.1 found: 375.2
2.2.2. 4-((1R,2R)-2-hydroxy-1,2-diphenylethoxy)phthalonitrile (3, Scheme 1)
Synthesis of 3 was performed by following the procedure for 2 by using 4-nitrophthalonitrile
(0.89 g, 4.67 mmol), 1 (1 g, 4.67 mmol) and K2CO3 (0.64 g, 4.67 mmol). Yield: 0.81 g, (51%);
o
mp: 59-60 C. Found: C, 76.89; H, 4.56; N, 7.96%; molecular formula C22H16N2O2 requires C,
77.63; H, 4.74; N, 8.23%. +9.99 (c = 1, CHCl3); retention time 17.49 min, Chiral ART
o
Amylose-C, 30:70 n-hexane-iPrOH, flow rate of 0.5 mL/min, 254 nm, t = 40 C; IR (KBr disc)
vmax/cm-1: 3472 (OH), 3063, 3034, 2909, 2231 (CN), 1730, 1596, 1562, 1492, 1315, 1291, 1250,
1
11998, 1007, 838, 764, 699; H-NMR (400 MHz, CDCl3, ppm) : 7.59 (d, J = 8.8 Hz, H), 7.26-
7.24 (m, 7H), 7.16 (dd, J = 8.8 Hz, J = 2.5 Hz, H), 7.10 (dd, J = 7.8 Hz, J =1.25 Hz, 2H), 7.01
(dd, J = 7.8 Hz, J =1.25 Hz, 2H), 5.21 (d, J = 7.3 Hz, H), 5.01 (d, J = 7.3 Hz, H), 2.35 (br, OH);
13C-NMR (100 MHz, CDCl3, ppm) : 160.9, 138.0, 135.1, 134.9, 129.0, 128.8, 128.5, 128.3,
127.2, 127.0, 121.1, 120.7, 117.4, 115.4, 115.0, 107.9, 86.5, 78.1; MS (ESI-) MS calculated
[M+Cl]- for C22H16N2O2Cl: 375.1 found: 375.2
2.2.3. 1(4), 8(11), 15(18), 22(25)-Tetrakis-{(1R,2R)-2-hydroxy-1,2-diphenylethoxy}
phthalocyaninato zinc(II) (4)
3-((1R,2R)-2-hydroxy-1,2-diphenylethoxy)phthalonitrile 2 (0.2 g; 0.59 mmol) was reacted
with anhydrous Zn(CH3CO2)2 (0.055 g; 0.29 mmol) in n-pentanol (2.5 mL) at 140 °C for 24 h in
a Schlenk tube under nitrogen in order to obtain zinc(II) phthalocyanines 4. At the end of this
6

period, the reaction mixture was cooled to room temperature. Solvent of the reaction mixture was
evaporated under reduced pressure to give a crude product. The crude product was purified by
chromatography over silica gel column with a solvent mixture hexane-diethyl ether (7:3)
followed by methanol and chloroform solvents as eluents. The yield was 0.025 g (10%). mp: 222-
223 °C. Found: C, 74.59; H, 4.57; N, 7.92%; molecular formula C88H64N8O8Zn requires C,
74.07; H, 4.52; N, 7.85%. IR (KBr disc) νmax/cm-1: 3451, 3271 (OH), 3064, 3034, 2923, 1767,
1
1723, 1609, 1560, 1482, 1455, 1382, 1275, 1155, 1055, 749, 701. H-NMR (400 MHz, d8-THF,
ppm) : 10.1-8.83 (m, 12H), 7.88-6.95 (m, 40H), 6.01-5.40 (m, 8H); UV-Vis (DMF): max, nm
(log ): 322 (4.71), 634 (4.60), 704 (5.31); MS (MALDI-TOF) (m/z): calculated [M+H]+ for
C88H65N8O8Zn: 1425.7 found: 1425.7.
2.2.4. 1(4), 8(11), 15(18), 22(25)-Tetrakis-{(1R,2R)-2-hydroxy-1,2-diphenylethoxy}
phthalocyaninato cobalt(II) (5)
Synthesis of 5 was performed by following the procedure for 4. Except CoCl2 instead of
Zn(CH3CO2)2 was employed. The amounts of all the reagents were the same except for CoCl2
(0.035 g). The crude product was purified by chromatography over silica gel column with a
solvent mixture hexane-diethyl ether (5:5) followed by chloroform-methanol (98:2) solvent
system as eluents. The yield was 0.43 g (21%). mp: 221-222 °C. Found: C, 74.26; H, 4.40; N,
7.61%; molecular formula C88H64N8O8Co requires C, 74.71; H, 4.54; N, 7.89%. IR (KBr disc)
νmax/cm-1: 3342 (OH), 3061, 3031, 2925, 1721, 1608, 1483, 1458, 1271, 1029, 757, 699; UV-Vis
(DMF): max, nm (log ): 304 (4.54), 634 (4.18), 700 (4.72); MS (MALDI-TOF) (m/z): calculated
[M]+ for C88H64N8O8Co: 1419.4 found: 1419.4.
7

2.2.5. 2(3), 9(10), 16(17), 23(24)-Tetrakis-{(1R,2R)-2-hydroxy-1,2-diphenylethoxy}
phthalocyaninato zinc(II) (6)
Synthesis of 6 was performed by following the procedure for 4. Except 4-((1R,2R)-2-
hydroxy-1,2-diphenylethoxy)phthalonitrile
3
instead of 3-((1R,2R)-2-hydroxy-1,2-
diphenylethoxy)phthalonitrile 2 was employed. The amounts of all the reagents were the same.
The crude product was purified by chromatography over silica gel column with methanol
followed by chloroform as the eluting solvents. The yield was 0.056 g (22%). mp: > 300 °C.
Found: C, 73.77; H, 4.42; N, 7.81%; molecular formula C88H64N8O8Zn requires C, 74.07; H,
4.52; N, 7.85%. IR (KBr disc) νmax/cm-1: 3419 (OH), 3029, 2924, 1715, 1608, 1485, 1452, 1398,
1
1335, 1277, 1225, 1092, 1046, 766, 746, 698; H-NMR (400 MHz, d8-THF, ppm) : 9.13 (m,
6H), 8.86 (m, 6H), 7.50-6.89 (m, 40H), 5.88 (m, 4H), 5.29 (m, 4H); UV-Vis (DMF): max, nm
(log ): 354 (5.03), 614(4.67), 684 (5.35); MS (MALDI-TOF) (m/z): calculated [M+2H]+ for
C88H66N8O8Zn: 1426.4 found: 1426.4.
2.2.6. 2(3), 9(10), 16(17), 23(24)-Tetrakis-{(1R,2R)-2-hydroxy-1,2-diphenylethoxy}
phthalocyaninato cobalt(II) (7)
Synthesis of 7 was performed by following the procedure for 4. Except 4-((1R,2R)-2-
hydroxy-1,2-diphenylethoxy)phthalonitrile 3 (0.4 g; 1.18 mmol) and CoCl2 (0.075 g; 0.58
mmol) instead of 3-((1R,2R)-2-hydroxy-1,2-diphenylethoxy)phthalonitrile (2) and
Zn(CH3CO2)2 respectively were employed. The crude product was purified by chromatography
over silica gel column with a mixture hexane-diethyl ether (3:7) followed by chloroform-
methanol (99:1) as the eluting solvents. The yield was 0.093 g (22%). mp: 297-298 °C. Found: C,
74.99; H, 4.64; N, 7.78%; molecular formula C88H64N8O8Co requires C, 74.71; H, 4.54; N,
8

7.89%. IR (KBr disc) νmax/cm-1: 3552, 3436 (OH), 3062, 3033, 2903, 1709, 1612, 1524, 1477,
1411, 1343, 1275, 1230, 1137, 1064, 1013, 751, 699; UV-Vis (DMF): max, nm (log ): 330
(5.31), 670 (5.43); MS (MALDI-TOF) (m/z): calculated [M]+ for C88H64N8O8Co: 1419.4 found:
1419.4.
2.2.7. General procedure for the oxidation of benzyl alcohol with cobalt(II) phthalocyanines 5
and 7
A schlenk tube containing magnetic stir bar was charged with benzyl alcohol, catalyst and
solvent. The schlenk tube was capped with a rubber septum and was purified with bubbling
nitrogen gas to remove the oxygen for ten minutes. The oxidant was then added and the reaction
mixture was stirred for the desired time. All the products and conversion of benzyl alcohol were
determined by gas chromatography analysis. The catalytic reactions were monitored by GC-FID
chromatograph equipped with a 30 m × 0.25 m × 0.25 m capillary column (Rxi-5ms, 95%
diphenyl, 95% dimethyl polysiloxane) by comparison standards (benzaldehyde, benzoic acid and
1,4-benzoquinone).
2.2.8. General procedure for the enantioselective diethylzinc addition to aromatic aldehydes
Under an argon atmosphere, chiral ligand (0.1 mmol) was dissolved in dry solvent, Ti(OiPr)4
(0.94 mmol) was added and stirred for 1 h for the Ti-mediated reactions. Et2Zn (2 mmol, 1 M in
hexane) was added, and the resulting yellow solution was stirred for 20 min at rt. Aldehyde (1
mmol) was then added dropwise in 10 min. and the reaction was stirred for another 24 h at room
temperature. After quenching with 1 mL saturated NH4Cl solution, 25 mL of H2O was added and
then extracted with CH2Cl2 (3 × 25 mL). The combined organic phases were dried over Na2SO4
9

and evaporated in vacuo. The crude product was purified by flash chromatography to give the
corresponding alcohol. Enantiomeric excesses were determined by GC analysis with chiral HP-
CHIRAL-B20 column.
3. Result and Discussion
3.1. Synthesis and Characterization
(1R,2R)-1,2-diphenylethane-1,2-diol substituted chiral phthalonitriles 2-3 and their optically
active phthalocyanine derivatives 4-7 were synthesized according to the route shown in Scheme
1.
The reaction of 3-nitrophthalonitrile or 4-nitrophthalonitrile with (1R,2R)-1,2-
diphenylethane-1,2-diol (1) in the presence of potassium carbonate as the base in DMSO gave the
desired products 3-((1R,2R)-2-hydroxy-1,2-diphenylethoxy)phthalonitrile 2 and 4-((1R,2R)-2-
hydroxy-1,2-diphenylethoxy)phthalonitrile 3 with moderate yields, respectively. In the IR
spectrum of 2 and 3, the presence of an intense CN stretching band at 2232 and 2231 cm-1, the
disappearance of the strong NO2 stretching vibrations at 1350 and 1550 cm-1 [25], the appearance
of an OH stretching vibration at 3500 and 3472 cm-1, respectively, confirmed the formation of
compounds 2 and 3. The IR spectrum of 3 is very similar to that of 2, but with small shifts in
1
wavenumbers. To determine the exact structure of 2 and 3, the H NMR spectrum was acquired
in CDCl3. The presence of significant resonance of OH group as broad singlet at  = 3.09 for 2
and 2.35 for 3 ppm is agreement with the proposed structures. The aliphatic CH protons were
observed as two doublets at  = 5.27, 5.10 ppm for 2 and 5.21, 5.01 ppm for 3 with a coupling
constant of J = 7.5 and 7.3 Hz, respectively. The other sets of protons were appeared between
about 7.6-7.0 ppm as expected. The 13C NMR spectrum of the same compounds clearly indicated
10

the expected carbon resonances. The nitrile carbons were observed at  = 115.2, 113.1 ppm for 2
and 115.4, 115.0 ppm for 3. The carbon resonances concerning hydroxyl-connected CH and the
oxygen connected CH at  = 87.4, 77.9 ppm for 2 and 86.5, 78.1 ppm for 3 are in good agreement
with the proposed structures. In addition to the elemental analysis results, the molecular ion peak
at m/z = 375.2 [M+Cl]- in the ES/MS mass spectra of both 2 and 3 also confirms the proposed
structures.
The zinc(II) phthalocyanines 4 and 6 were synthesized directly by cyclotetramerization of
the phthalonitrile compounds 2 and 3 in the presence of the anhydrous metal salt Zn(CH3CO2)2 in
a Schlenk system in n-pentanol, respectively. The blue green phthalocyanines were isolated by
column chromatography on silicagel. In the IR spectrum of 4 and 6, the disappearance of the
sharp CN vibration at around 2230 cm-1 and appearance of new resonance at 1609 for 4 and
1608 cm-1 for 6 corresponding to C=N vibration in phthalocyanine core of 4 and 6 confirmed
cyclotetramerization of the phthalonitrile derivatives. The vibration for the OH group was
1
observed at 3451 for 4 and 3419 cm-1for 6. In the H NMR spectrum of 4 and 6, the aromatic
protons appeared at  = 10.1-8.83 (m, 12H), 7.88-6.95 (m, 40H) ppm for 4 and 9.13 (m, 6H), 8.86
(m, 6H), 7.50-6.89 (m, 40H) ppm for 6. The aliphatic CH protons were observed at  = 6.01-5.40
(m, 8H) ppm for 4 and 5.88 (m, 4H), 5.29 (m, 4H) ppm for 6. The molecular ion peaks at m/z:
1425.7 [M+H]+ for 4 and 1426.4 [M+2H]+ for 6 were easily identified. These results confirm that
the complexes have been synthesized successfully.
Cobalt(II) phthalocyanines 5 and 7 were obtained from dicyano derivative 2 and 3 and the
anhydrous metal salt Co(CH3CO2)2 in a Schlenk system in n-pentanol at 140 °C for 24 h,
respectively. The disappearance of the strong CN stretching vibration in the IR spectra of 2 and
3 can be taken as a clear evidence for the formation of phthalocyanine complexes 5 and 7. The
rest of the IR spectra of the cobalt(II) phthalocyanines 5 and 7 are very similar to that of zinc(II)
phthalocyanines 4 and 6. The 1H NMR spectra of cobalt(II) phthalocyanines 5 and 7 could not be
11

acquired due to the paramagnetic cobalt(II) center. In the mass spectra of 5 and 7, the presence of
molecular ion peaks at m/z = 1419.4 [M]+ for both 5 and 7 confirmed the proposed structures.
3.2. UV-Vis and CD absorption spectra
The UV-Vis absorption spectra of metallophthalocyanines 4-7 in THF are shown in Fig. 1
The phthalocyanines show typical electronic spectra with two absorption bands. One of them is in
UV region at about 300-500 nm (B band) and the other one is in the visible region at 600-800 nm
(Q band) [1]. Metal complexes of substituted and unsubstituted phthalocyanines with D4h
symmetry show an intense single Q band in the visible region [26]. Zinc(II) phthloyanines 4 and
6 shows characteristic absorptions in the Q band region at 704 and 680 nm without splitting, with
weaker absorptions at 634 and 612 nm and in the B band region at 320 and 350 nm, respectively.
Cobalt(II) phthalocyanines 5 and 7 exhibit the characteristic absorption in the Q band region at
694 and 668 nm with weaker absorptions at 628 and 604 nm and in the B band region at 372 and
338 nm, respectively. It is well known that α substitution of benzene rings in the phthalocyanine
skeleton results in red shifting of the spectra in metallophthalocyanines [27, 28]. This is due to
the electron density enhancement caused by the substitution at the non-peripheral position in the
case of 4 and 5.
The aggregation behaviors of phthalocyanine complexes 4-7 were investigated in different
solvents such as diethyl ether, DMF, THF, CH2Cl2, CHCl3 (Fig. 2. for complex 5 and 7, see
Supplementary info S-Fig. 1. for complex 4, S-Fig. 2. for complex 6). The cobalt(II)
phthalocyanines 5 and 7 show solvent-dependent spectra. The broadening of the Q band in the
UV-Vis spectra of 5 and 7 in diethyl ether, dichloromethane and chloroform can be attributed to
the monomeric and oligomeric phthalocyanine species for 5 and 7. Changes in the solvent from
diethylether to DMF (thereby raising the dielectric constant of the medium) moved the monomer-
12

dimer equilibrium toward higher monomer ratios. It has been shown that the tendency of the
phthalocyanine to dimerize is greater in solvents of low dielectric constant [29]. Zinc(II)
phthalocyanine complexes 4 and 6 did not show aggregation in these solvents.
The aggregation behaviors of phthalocyanine complexes 4-7 were also investigated at
different concentrations in THF and DMF. The Beer-Lambert law was obeyed for phthalocyanine
complexes 4-7 in THF and DMF from concentrations between 10 x 10-6 and 2 x 10-6 mol dm-3.
As the concentration increased, the intensity of the absorption of the Q band also increased, and
there were no new bands shifted to the higher energy region due to the presence of aggregated
species for all phthalocyanines (Fig. 3. for 4, Supplementary info S-Fig. 3. for CoPc 5, S-Fig. 4.
for ZnPc 6 and S-Fig. 5. for CoPc 7).
Non-peripherally substituted phthalocyanines 4 and 5 and peripherally substituted
phthalocyanines 6 and 7 have four chiral hydrobenzoin substituents. Because of these chiral
substituents, they are expected to have circular dichroism (CD) activity. The CD spectra of these
chiral phthalocyanines were recorded in THF at room temperature. Fig. 4. shows the CD
spectrum of 4 in range 300-800 nm (See supplementary info S-Fig. 6. for the CD spectra of
complexes 5-7). The CD spectra of 4-7 have negative CD signal over the entire spectrum with the
intense Q and B bands corresponding to the electronic absorption spectra of the phthalocyanines.
It is known that negative CD signal is observed in the CD spectra of right-handed conformer,
while positive CD signal is observed in the CD spectra of left-handed conformer [12, 30]. In the
case of all synthesized phthalocyanines 4-7, the appearance of the negative CD signal in the B
and Q band absorption spectra of 4-7 indicates that all compounds are right-handed. This also
proves that due to the existence of the chiral (1R,2R)-1,2-diphenylethane-1,2-diol group at
peripheral and non-peripheral positions of the phthalocyanine complexes 4-7, the effective chiral
information transfer to the phthalocyanines at the molecular level [31].
13

3.2. Electrochemical Measurements
Glassy carbon electrode (0.071 cm2 surface area), a platinum plate (0.5 cm2 surface area) and
an Ag/AgCl electrode were used as the working, counter and the reference electrodes,
respectively. Cyclic voltammograms were obtained at different scan rates at room temperature.
Square wave voltammograms were studied with pulse size of 100 mV and frequency of 25 Hz.
The electrochemical analyses were done in DCM / TBAPF4 containing 0.50 mM solution of
phthalocyanine complexes 4-7. The data of the voltammetry analyses are given in Table.1. Non-
peripheral substituent causes the steric effect on the structure. So, these substituents may impose
some conformational stress on phthalocyanine complexes 4 and 5. According to the given redox
couples in Table 1, the peripheral substituent slightly shifted the potentials more negative.
Electrochemical properties of non-peripherally substituted phthalocyanines complexes 4 and 5
were slightly different from peripherally substituted phthalocyanines complexes 6 and 7 [32, 33].
The cyclic voltammogram (CV) shown in Fig. 5a was obtained with glassy carbon electrode
at various scan rates (250, 100, 75, 50, 25 mV s-1) in DCM/ TBAPF4 electrolyte containing 0.50
mM solution of zinc(II) phthalocyanine 4 (See supplementary info S-Fig. 7-9. for the cyclic
voltammogram (CV) of complexes 5-7). Peak current densities of each molecule increased with
increasing scan rate. In order to be able to decide that a redox reaction is reversible, it is
necessary to follow the steps given below.
 The voltage separation between the current peaks (ΔE) should be equal to 59/n
mV,
 Peak potential should not change with scan rate,
 The ratio of anodic and cathodic peak currents should be equal to 1,
 Peak currents must be proportional to the square root of the scan rate.
The reaction is not reversible if one of these conditions is not met.
14

Hereby, potentials became more positive both anodic and cathodic directions at 100 and 250
mV s-1 scan rates. The potential shifts at higher scan rates are indicated that redox reactions have
quasi-reversible systems. In the backward scan, formed species in the oxidation reactions in the
forward scan, were reduced.
The reversibility of the complex was also checked with the square wave voltammogram
(SWV) given in Fig.5b. Peak current ratios and symmetry of the peaks of a redox couple were
used to characterize reversibility or irreversibility of a redox process. Voltammograms were
analyzed using different parameters, which were half wave peak potential (E1/2), peak to peak
potential separation (∆Ep), the difference between the first oxidation and first reduction
processes(∆E1/2). Ipa/Ipc ratios for reduction and Ipc / Ipa for oxidation reactions.
Fig. 5c shows the dependence of cathodic and anodic peak current densities on the square
root of the scan rate (I -
). The linear curves indicate that the oxidation reactions are
processing with diffusion control at the glassy carbon electrode in DCM / TBAPF4 electrolyte
containing 1.00 mM solution of zinc(II) phthalocyanine 4.
The difference between the first anodic peak to first cathodic peak is directly refers to the
HOMO-LUMO gap of complex. A large HOMO-LUMO gap implies high kinetic stability and
low chemical reactivity because it is energetically unfavorable to add electrons to a high-lying
LUMO, to extract electrons from a low-lying HOMO, and so to form the activated complex of
any potential reaction [34]. When compared with the complexes, it is seen that the non-peripheral
and peripheral substituents of phthalocyanine complexes 4 and 6 influence the band gap, but it
did not cause any change at phthalocyanine complexes 5 and 7. Since zinc redox is an inactive as
central metal, the redox reactions of the structures are directly affected by the positions of the
hydrobenzoin groups at phthalocyanine skeleton. It can be seen that the band gaps of the zinc(II)
phthalocyanine complexes 4 and 6 varied according to the position of hydrobenzoin substituted to
the benzene rings of phthalocyanine . However, since cobalt redox is an active center, the change
15

in the position of the hydrobenzoin substituents in the case of phthalocyanine complexes 5 and 7
did not directly affect the redox reactions and the band gap did not change.
3.3. Catalytic Studies
3.3.2. Enantioselective diethyl zinc addition to aromatic aldehydes
Enantioselective induction of optically active novel phthalonitriles 2 and 3, and their zinc(II)
phthalocanine derivatives 4 and 6 were investigated in the addition of diethylzinc to aromatic
aldehydes (Table 2). This reaction is a known method for the formation of carbon–carbon bonds.
Reactions were carried out using 2 equiv. of diethylzinc (1M solution in hexane) at room
temperature for 24 h in the presence of 0.1 equiv. of the developed ligands in various solvents.
We started with 2-methoxybenzaldehyde as test substrate in order to examine the efficiency of
the chiral ligands. 2-Methoxybenzaldehyde gives the corresponding secondary alcohol with poor
enantioselectivities and yields in both dichloromethane and toluene catalyzed by phthalonitrile 2
(Table 2, entries 1 and 2). Titanium mediated reactions are reported to give more efficient and
selective results [35-37]. Considering these literature data, we also explored the reactivity and
selectivity of the addition of diethylzinc to aromatic aldehydes in the presence of titanium
isopropoxide as additive. Addition of the titanium species did not make any sense in catalytic
activity with chiral ligand 2 (Table 2, entry 3). When the reaction was performed under the
catalysis of 3 in both solvents, we observed parallel outcome (Table 2, entries 4-6). While Zn-Pc
4 showed some enantioselective induction, disappointed results were obtained with Zn-Pc-6
(Table 2, entries 7-10). The reactions were then carried out with another test substrate having an
electron-releasing substituent on the phenyl ring, 3-methoxybenzaldehyde under the catalysis of
all synthesized ligands (Table 2, entries 11-22). Although we obtained some conversions, we
16

could not observe any enantioselectivity except using Zn-Pc 4 as catalyst. It is noteworthy that
Zn-Pc 4 catalyzed the reaction and led to increase in both enantioselectivity and yield (Table 2,
entry 17). The electronic nature of the substituent on the phenyl ring was also investigated. Thus,
using aldehyde with electron-withdrawing chlorine at the 3-position gave some conversion but
any enantioselectivity under the catalysis of all chiral ligands exception of Zn-Pc 4 (Table 2,
entries 23-33). Using benzaldehyde gave unsatisfactory results (Table 2, entries 34-43). No
enantioselective induction was observed on the ethylation of sterically hindered 1-
naphthaldehyde using phthalonitriles 2 and 3 and Zn-Pc 6. Remarkably, moderate yield and
enantioselectivity were observed when using Zn-Pc 4 (Table 2, entry 50). Adding an extra metal
Ti (IV) led to a slight decrease in both the enantioselectivity and yield (Table 2, entry 51).
3.3.2. Oxidation of benzyl alcohol with cobalt(II) phthalocyanines 5 and 7
The catalytic activities of cobalt(II) phthalocyanines 5 and 7 were explored for the oxidation
of benzyl alcohol. Benzyl alcohol can be turned into various organic compounds in oxidation
reactions. In this work, three fragments (benzaldehyde as major product, benzoquinone and
benzoic acid as minor products) were determined due to the attack by catalytically active species
(Scheme 2) [21].
Initially, to examine the catalytic activity of cobalt(II) phthalocyanines 5 and 7, the oxidation
of benzyl alcohol was carried out under two different temperatures (25 and 80°C) in two different
solvents (dimethyl formamide (DMF) and acetonitrile (ACN)) with several oxidants (tert-butyl
hydroperoxide (TBHP), m-chloroperoxybenzoic acid (m-CPBA), and hydrogen peroxide
(H2O2)). The molar ratio of benzyl alcohol, oxidant and catalyst 5 was 115/300/1 and reaction
time was (12 hours for 25 °C and 5 hours for 80 °C) kept constant. The results are presented in
Table 3. Although the oxidation of benzyl alcohol to the benzaldehyde was found to be very slow
17

at room temperature in acetonitrile with TBHP (Table 3, entry 6) and m-CPBA (Table 3, entry 8)
as an oxidant almost full conversion was obtained in DMF when using m-CPBA as an oxidant,
but the benzaldehyde selectivity of the products was poor (20%) (Table 3, entry 3). Besides that,
in the presence of H2O2 as an oxidant, the catalyst 5 showed only 8% conversion in DMF (Table
3, entry 5) even when the temperature is raised to 80 °C. On the other hand, the best
benzaldehyde selectivity (91%) was achieved with TBHP as an oxidant in acetonitrile solvent but
in relatively low conversion (22%) at 80 °C (Table 3, entry 7) with catalyst 5. These studies
showed that high temperature was needed to get best benzaldehyde selectivity for the oxidation
of benzyl alcohol. Therefore, the efficiency of the catalyst 7 was studied at 80 °C with the same
oxidants in DMF and ACN solvents. According to the results on Table 3, catalyst 7 was showed
best selectivity (89%, entry 14) with TBHP in acetonitrile as in the catalyst 5. In the presence of
m-CPBA as oxidant, the catalyst activity and selectivity are moderate in both DMF (Table 3,
entry 12) and ACN (Table 3, entry 15) solvents and also the use of H2O2 as oxidant in ACN very
poor benzaldehyde selectivity (15%, Table 3, entry 16) was obtained. Based on the results, TBHP
in ACN solvent medium was the most efficient oxidant source to oxidation of benzyl alcohol to
benzaldehyde for our catalytic system. The influence of cation and bromine anion to the
oxidation of benzyl alcohol was also investigated with different additives in the presence of
catalyst 5 (Table 3, Entry 17-19). While using any additive gave 22% conversion (entry 7), the
addition of KBr and (Bu)4NBr leads to a substantial increase in conversion of benzyl alcohol to
46% and 64%, respectively (Table 3, entry 17 and 19). However, the benzyl alcohol conversion is
increased up to 94% with 82% selectivity when N-Bromosuccinimide (NBS) used as an additive
(Table 3, entry 18). For comparison, a blank experiment was carried out under the optimized
conditions without catalyst and we did not observe benzaldehyde in the reaction mixture (Table
3, entry 20).
18

To extend catalytic applications of catalyst 5 and 7, the effect of oxidant amount for the
benzyl alcohol oxidation was studied by varying the oxidant to catalyst ratio from 100/1 to 900/1
at 80 °C (Table 4, Fig. 6). For both catalysts 5 and 7, the conversion of benzyl alcohol was
completed for the oxidation process with increasing oxidant to catalyst molar ratio but the
selectivity for benzaldehyde did decrease when greater than 300/1 oxidant/catalyst ratio was
used. The higher oxidant ratio presumably affects coordination the cobalt ion and leads to the
generation of inactive intermediate species [38-42]. Besides, the formation of benzoic acid in
small yields when oxidant to catalyst ratio of 300/1.
The effect of substrate/catalyst ratio on the performance of the oxidation reactions using
catalyst 5 and 7 was then examined (Table 5, Fig. 7). The reaction rate and conversion normally
depended on the amounts of CoPc catalyst used. At a substrate to catalyst ratio of 300:1 the
oxidation of benzyl alcohol can be carried out to 65% (91% benzaldehyde selectivity) and 87%
(81% benzaldehyde selectivity) conversion with catalyst 5 and 7, respectively. On further
increasing the substrates/catalyst ratio, the catalytic activity decreases to such extent that for the
oxidation of benzyl alcohol in 5h.
So far, many of cobalt(II) phthalocyanine catalysts have been reported for oxidation of
benzyl alcohol. A few related studies among these are summarized in the following lines. Çakır et
al. have synthesized and characterized (2-{2-[3-(diethylamino)phenoxy]ethoxy}ethoxy)
substituted Co(II) phthalocyanine and investigated their catalytic activity for benzyl alcohol
oxidation. They found that TBHP is the best oxidant in acetonitrile at 70°C with high total
conversion (89%) and 78% selectivity [43]. Aktaş and coworkers reported the selective oxidation
of benzyl alcohol to benzaldehyde with Co(II) phthalocyanine complex which has halogenated (-
CF3) substituent. This study showed that higher temperature (90°C) and 600/1:substrate/catalyst
ratio was needed to reach an optimum conversion of benzyl alcohol to benzaldehyde in the
presence of TBHP as an oxidant. They also reported that a small amount of benzyl benzoate was
19

formed as by-product during the oxidation reactions [44]. In another report, Saka et al. prepared
2-(2-(4-allyl-2-methoxyphenoxy)ethoxy)ethoxyphthalonitrile and then its new peripherally tetra
substituted Co(II) complex to investigate in benzyl alcohol oxidation. Based on benzyl alcohol,
91% total conversion and 82.4% benzaldehyde selectivity was obtained at 90°C for 3 hours when
400/800/1 substrate/oxidant/catalyst ratio was used [45]. In this work, we achieved the high
conversion (up to 91%) and selectivity (up to 84%) at 80°C with our peripheral and non-
peripheral diol substituted phthalocyanine Co(II) complexes.
4. Conclusion
In the present study, four novel peripherally and non-peripherally hydrobenzoin substituted
optically active phthalocyanine derivatives were synthesized. The structural characterization was
1
done by a combination of H NMR, IR, UV-Vis and MS spectral data. All phthalocyanines are
highly soluble in common organic solvents. The Q-band of non-peripherally substituted
phthalocyanine complexes 4 and 5 was red-shifted relative to that of peripherally substituted
phthalocyanine complexes 6 and 7. The negative CD signals for all phthalocyanines at the CD
spectra of 4-7 prove that the chiral information from the hydrobenzoin substituent at α and β-
position of the phthalocyanine skeleton transferred to phthalocyanines 4-7 at molecular level. The
solvent and concentration effects on the aggregation properties of the phthalocyanines were
determined. The metallophthalocyanines demonstrated no aggregation behavior in DMF and THF
from concentrations between 10 x 10-6 and 2 x 10-6 mol dm-3. Enantioselective catalytic activity of
optically active phthalonitriles 2 and 3, and their zinc(II) phthalocyanines 4 and 6 was evaluated in
diethylzinc addition to aldehydes. The enantioselective addition of diethylzinc to 3-
methoxybenzaldehyde in the presence of non-peripherally hydrobenzoin substituted zinc(II)
phthalocyanine 4 gave the corresponding chiral secondary alcohol with the yield of 38% and the
20

enantiomeric excess of 33%. The catalytic activity of cobalt(II) phthalocyanines 5 and 7 was
investigated in the oxidation of benzyl alcohol by using different oxidants. The highest conversion
of benzyl alcohol to benzaldehyde was obtained with non-peripherally substituted cobalt(II)
phthalocyanine 5 as 91% with the highest selectivity of 83%. These results showed that the
functional phthalocyanines derived from C2-symmetric diols can be interesting in enantioselective
catalytic systems and the oxidation of benzyl alcohol. Further study in this direction is currently in
progress and the results will be reported in due course.
Acknowledgements
This study was supported by the Scientific & Technological Research Council of Turkey
(TUBITAK) (Project No: MAG-115R015). Yunus Kılıç (Department of Chemistry, Osmaniye
Korkut Ata University) is gratefully acknowledged for his assistance. The authors would like to
thank to Prof. Dr. Gülfeza Kardaş (Department of Chemistry, Çukurova University) for her help.
Appendix A. Supplementary data
Supplementary data related to this article can be found at:
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24

Figure captions:
Scheme 1. Synthetic pathway of phthalonitriles and zinc(II) and cobalt(II) phthalocyanine
derivatives. Reagents and conditions: (i) DMSO, K2CO3, rt; (ii) Zn(CH3COO)2, n-pentanol,
DBU, 140 °C, (iii) CoCl2, n-pentanol, DBU, 140 °C,
Scheme 2. Oxidation of benzyl alcohol using cobalt(II) phthalocyanines 5 and 7 as catalysts
Fig. 1. UV–Vis spectra of zinc(II) phthalocyanines (4 and 6), and cobalt(II) phthalocyanines (5
and 7) in THF (Concentration: 210-6 M)
Fig. 2. UV–Vis spectra of cobalt(II) phthalocyanine 5 and 7 in different solvents (Concentration:
1010-6 M)
Fig.3. Aggregation properties of zinc(II) phthalocyanine 4 at different concentrations
(Concentration: 210-6, 410-6, 810-6, 1010-6 M). Inset: Beer-Lambert plot.
Fig.4. (a) CD and (b) electronic spectra of zinc(II) phthalocyanine 4 in THF (concentration:
1010-6 M)
Fig. 5. (a) Effect of the various scan rates (250, 100, 75, 50, 25 mV s-1) on electrooxidation of
0.50 mM solution of 4 in DCM/TBAPF4 electrolyte at the glassy carbon electrode at 298 K. (b)
Square wave voltammetry at 100 mV s-1 scan rate. (c) Dependence of anodic peak current
densities during the forward and backward scan on the square roots of scan rate.
25

Table 1. Voltammetric data of the phthalocyanines. All voltammetric data were given versus
Ag/AgCl
Table 2. Enantioselective addition of diethlyzinc to various aldehydes catalyzed by chiral
phthalonitriles (2, 3)a and zinc(II) phthalociyanines (4, 6)b.
Table 3. The effect of temperature, solvent and oxidant on benzyl alcohol oxidation with
cobalt(II) phthalocyanines 5 and 7a
Table 4. Amount of oxidant effect on benzyl alcohol oxidation with cobalt(II) phthalocyanines 5
and 7a
Table 5. The effect of substrate/catalyst ratio on benzyl alcohol oxidation with cobalt(II)
phthalocyanines 5 and 7a
26

Table 1. Voltammetric data of the phthalocyanines. All voltammetric data were given versus
Ag/AgCl
Redox
a
c
d
Molecule
ZnPc (4)
Mechanism
E1/2
∆Ep(mV)b
Ipa/Ipc
∆E1/2
processes
R1
ZnIIPc-4/ZnIIPc-3
ZnIIPc-1/ZnIIPc0
ZnIIPc-5/ZnIIPc-4
ZnIIPc-2/ZnIIPc-1
CoIIPc-2/CoIPc-2
CoIIIPc-2/CoIIPc-2
CoIPc-3/CoIPc-2
ZnIIPc-2/ZnIIPc-1
ZnIIPc-1/ZnIIPc0
ZnIIPc-4/ZnIIPc-3
ZnIIPc-5/ZnIIPc-4
CoIIPc-2/CoIPc-2
CoIIIPc-2/CoIIPc-2
CoIIPc-2/CoIIPc-1
CoIPc-3/CoIPc-2
-0.77
0.65
23
0
1.05
0.44
0.82
-
1.42
O1
-1.17
-0.37
-0.10
0.57
10
-
R2
O2
25
80
9
1.64
0.50
0.77
1.17
0.45
0.93
0.86
0.62
0.44
1.00
0.76
R1
0.67
1.17
CoPc (5)
ZnPc (6)
O1
-1.16
-0.69
0.48
R2
51
24
4
R1
O1
R2
-0.96
-1.31
-0.21
0.46
---
---
R3
5
45
45
246
20
R1
0.67
O1
CoPc (7)
R2
-0.62
-1.30
R3
aThe potential at the half-diffusion current ((iinitial + ipeak)/2 is E1/2 at 0.100 V s−1 scan rate.
bΔEp = Epa − Epc.
cIp,a/Ip,c for reduction,Ip,c/Ip,afor oxidation processes.
d∆E1/2= E1/2(first oxidation)- E1/2(first reduction)
27

Table 2. Enantioselective addition of diethlyzinc to various aldehydes catalyzed by chiral
phthalonitriles (2, 3)a and zinc(II) phthalocyanines (4, 6)b.
Entry Aldehydes
1
Ligand
Solvent
Dichloromethane
Toluene
Toluene
Dichloromethane
Toluene
Yield (%)c
ee (%)d,e
7 (R)
11 (R)
5 (R)
9 (R)
11 (R)
rac
17 (R)
10 (R)
rac
21
28
20
28
36
30
34
25
36
15
2
2
2
3
3
3
4
4
6
6
2
3f
4
5
6f
7
Toluene
Dichloromethane
Dichloromethane
Dichloromethane
Dichloromethane
8f
9
10f
rac
11
Dichloromethane
Toluene
Toluene
Dichloromethane
Toluene
Toluene
Dichloromethane
Toluene
Dichloromethane
Dichloromethane
Dichloromethane
Dichloromethane
17
20
10
10
15
10
38
28
36
20
24
15
rac
rac
rac
rac
rac
2
2
2
3
3
3
4
4
4
4
6
6
12
13f
14
15
16f
17
rac
33 (R)
rac
30 (R)
rac
18
19g
20f
21
rac
rac
22 f
23
Dichloromethane
Toluene
Toluene
Dichloromethane
Toluene
30
28
10
14
25
10
37
25
23
10
rac
rac
rac
rac
rac
2
2
2
3
3
3
4
4
6
6
24
25 f
26
27
28f
29
Toluene
rac
Dichloromethane
Dichloromethane
Dichloromethane
Dichloromethane
26 (R)
15 (R)
rac
30f
32
33f
rac
34
35
36f
37
38
39f
40
41f
42
43f
Dichloromethane
Toluene
Toluene
Dichloromethane
Toluene
18
25
10
10
15
15
20
15
12
10
rac
rac
rac
rac
5 (R)
rac
rac
rac
rac
rac
2
2
2
3
3
3
4
4
6
6
Toluene
Dichloromethane
Dichloromethane
Dichloromethane
Dichloromethane
44
45
46f
47
48
49f
50
51f
52
53f
Dichloromethane
Toluene
Toluene
Dichloromethane
Toluene
Dichloromethane
Dichloromethane
Dichloromethane
Dichloromethane
Dichloromethane
10
12
10
30
15
25
66
50
28
20
rac
rac
rac
rac
rac
2
2
2
3
3
3
4
4
6
6
rac
26 (R)
20 (R)
rac
rac
28

a Reaction conditions: 1 equiv. aldehyde, 2 equiv. Et2Zn, 10 mol% ligand, rt, 24 h. b 2.5 mol% 4. c Isolated yield.
d Determined by GC analysis with chiral HP-CHIRAL-20B. e Determined by comprasion of optical rotations with the
literature. f Reaction with 0.94 equiv. Ti(OiPr)4. g 5 mol% 4.
29