1108
Published on the web September 11, 2010
Subphthalocyanines Having Axial Substituent with Direct B-C Bond:
General Preparation and Physical Properties
Yasuhiro Yamasaki* and Tomohiro Mori
Department of New Business, Orient Chemical Industries Co., Ltd.,
8-1 Sanra-Higashi-Machi, Neyagawa, Osaka 572-8581
(Received July 20, 2010; CL-100640; E-mail: y_yamasaki@orientchemical.com)
R1
A novel synthetic methodology and the characterization of
R2
B
CN
R2
subphthalocyanines (SubPcs) having an axial substituent with a
direct boron-carbon bond are reported. The SubPcs are found
to be more light- and/or heat resistant than analogs with a
heteroatom between boron and carbon, thereby making SubPcs
suitable for application to functional dyestuff in display devices.
N
N
R1
BX
1
N
3
2
N
N
R1
CN
N
3
R1
Scheme 1. Reported synthesis of SubPcB-R.
Subphthalocyanines (SubPcs) are homologs of tetraazapor-
phyrins as well as phthalocyanines, well-known warped 18³-
electron aromatic systems consisting of three diiminoisoindole
rings capable of coordinating with boron as the core.1,2
Compared to those of phthalocyanines, the Q-band absorptions
of SubPcs are in a relatively small region of around 500 to
600 nm; further, the solubility of SubPcs in some organic
solvents is considerably better than that of phthalocyanines.1,2
Because of these characteristics, SubPcs are attracting consid-
erable attention for application as functional optical dyes for
recording media and neon-cutting filters in plasma displays.3
However, the stability of SubPcs against light and/or heat is
considerably less than that of a conventional material because of
the strain deformation caused by the size of the coordinated
boron atom and the constrained electron distribution around the
boron atom.
R1
X
CN
CN
N
N
i)
R1
N
3
BX3
B
N
N
R1
N
2
R1
R1
R2
N
N
ii)
R1
N
B
N
iii)
N
N
3
R1
Scheme 2. Synthetic procedure for 3: i) xylene, reflux; ii) R2-
MgX¤/THF, ¹10- ¹15 °C; iii) mesitylene, rt.
Many analogs of SubPcs with peripheral and/or axial
substituents, including subazaporphyrins,4 subnaphthalocya-
nines,1,2 and ®-oxo subphthalocyanine dimers1,2,5 have been
synthesized, and from the study of these derivatives, it has been
found that the peripheral substituents affect the Q-band
absorption, but the axial ones do not. Further, while both
generally improve solubility, they are still insufficiently stable
for practical thin-film applications.
SubPcB-OH is generally synthesized from phthalonitrile
with boron trihalide and a subsequent hydrolysis reaction. In
order to synthesize the derivatives with an axial substituent,
because the central boron is ligated by an axial OH, this OH is
usually modified to ether or ester as an axial substituent.1a,6 This
axial element, i.e., oxygen directly linking to boron, may cause
the low stability of SubPcs.
We think that the direct bond between boron and carbon of
the axial substituent should be sufficiently strong to improve the
stability of the entire molecule. The only reported method to
synthesize SubPcs with an axial substituent with a direct boron-
carbon bond is the reaction of phthalonitrile with triphenyl- or
tributylboron or dialkylboron bromide 1 in extremely low yields
(R = Ph or Bu; the yields are below 1%).7 The reported method
is depicted in Scheme 1. However, this method requires a
stoichiometric amount of a strong base such as 1,8-diazabi-
cyclo[5.4.0]undec-7-ene (DBU) together with expensive boron
reagents 1 at a high temperature but result in extremely low
yields. Further, it is difficult to make this type of boron reagent
with various alkyl or aryl groups.
We have succeeded in the syntheses of SubPcs with an axial
substituent and a B-C direct bond (SubPcB-R 3) in considerably
better yields and report here the general synthetic technique
together with the properties of the resulting derivatives.8
The synthetic procedure is illustrated in Scheme 2. The
reaction of haloboron SubPcs 2, prepared by a previously
described method,6 with an excess of the Grignard reagent in
mesitylene afforded 3 in moderate yields of 10% to 40%. Other
carbanions, such as alkyllithium reagents at a low temperature,
did not provide the expected products but resulted in complex
mixtures.
Either alkyl or aryl chloride/bromide could be employed as
the Grignard reagent, and after completion of the reaction, the
reaction mixture was subjected to a typical aqueous workup and
condensation using a rotary evaporator. The obtained purple
solid was purified by column chromatography eluting with a
mixed solvent of ethyl acetate and toluene. By using this novel
methodology, we can directly introduce various substituents on
boron.
The results of the reaction are summarized in Table 1. It can
be seen that the axial substituents do not affect the -max value of
the Q-band absorption, but the peripheral alkylsulfanyl groups
resulted in approximately 20-nm-longer shifts.
Chem. Lett. 2010, 39, 1108-1109
© 2010 The Chemical Society of Japan