Tetrahedron Letters
Connecting BINOL and terpyridine: the electronic effects of the linkage
Zeng Huang , Xi Chen , Jing Zhang , Xiao-Qi Yu , Lin Pu b,
a
a
a
a,
⇑
⇑
a
Department of Chemistry, Key Laboratory of Green Chemistry and Technology (Ministry of Education), Sichuan University, Chengdu 610064, China
Department of Chemistry, University of Virginia, Charlottesville, VA 22904-4319, USA
b
a r t i c l e i n f o
a b s t r a c t
0
Article history:
1,1 -Bi-2-naphthol and terpyridine are covalently connected either directly or through different linkers. It
Received 14 July 2011
Revised 10 August 2011
Accepted 11 August 2011
Available online 19 August 2011
is found that in contrast to the directly connected one, when the saturated methyleneoxy linker is used,
there is inefficient electronic communication between the BINOL and terpyridine units and the fluores-
cence of the BINOL unit cannot be completely quenched by the coordination of terpyridine unit with a
2
+
Cu ion. However, a phenylene linker allows an efficient electronic communication between the BINOL
2+
and terpyridine units and the fluorescence of the BINOL is almost completely quenched upon Cu coor-
dination. The interaction of these compounds with valinol is studied and large fluorescence enhance-
ments are observed for those with efficient electronic communication between the BINOL and
terpyridine units.
Keywords:
BINOL
Terpyridine
Fluorescence
Valinol
Ó 2011 Elsevier Ltd. All rights reserved.
0
1
,1 -Bi-2-naphthol (BINOL) represents a class of chiral mole-
BINOL and terpyridine units has great effects on their electronic
properties.
cules that has found broad applications in asymmetric catalysis,
molecular recognition and materials. In the meantime, multipyri-
1
dine-based ligands such as terpyridine have been used extensively
as metal coordinating ligands. Recently, we and others have cova-
O
2
O
Cl
Cu Cl
N
N
N
N
N
N
N
lently linked BINOL and terpyridine together to build new materi-
N
O
als for various applications.3 For example, we have prepared the
,4
Ru
O
N
N
BINOL-terpyridine compound (R)-1 and found that this compound
i
in combination with ZnEt
2
and Ti(O Pr)
4
is a highly enantioselec-
OH
OH
OH
OH
OH
OH
tive catalyst for the asymmetric reaction of methyl propiolate with
3
a
aromatic aldehydes to generate c-hydroxy-a,b-acetylenic esters.
(R
)-1
(
R
)-2
(R)-3
When terpyridine unit of (R)-1 is coordinated to a Ru(II) metal cen-
ter, the resulting complex (R)-2 is a multi-task catalyst for the tan-
dem oxidation of benzylic alcohols to aldehydes and asymmetric
alkylzinc addition to generate chiral alcohols.3 We also studied
the application of the Cu(II) complex (R)-3 in chiral discrimination.
This complex forms a gel in chloroform upon sonication which
exhibits enantioselective gel collapsing in the presence of chiral
b
We first introduced a saturated methyleneoxy linker between
the BINOL and terpyridine units of (R)-1. As shown in Scheme 1,
from the reaction of (R)-4 with 5 in the presence of K
pound (R)-6 was obtained. The MOM groups of (R)-6 were removed
by treatment with CF CO H to give the BINOL-terpyridine com-
pound (R)-7. The UV spectrum of (R)-7 shows kmax ) = 230
5
2
CO
3
, com-
3
c
amino alcohols. The solution of (R)-3 also shows enantioselective
fluorescent responses toward phenylglycinol. These discoveries
demonstrate that joining the BINOL and terpyrdine units together
can afford them new and promising properties for diverse applica-
tions. In (R)-1, the BINOL and terpyridine units are directly con-
nected. We have also prepared compounds that contain two
different types of linkers between BINOL and terpyridine. Herein,
we report the synthesis and study of these compounds and their
Cu(II) complexes. It is found that the type of linkers between the
3
2
(e
4
4
3
(9.09 ꢀ 10 ), 277 (2.9 ꢀ 10 ), 323 (6.6 ꢀ 10 ) nm. Its fluorescence
spectrum gives emission at k = 371 nm. Treatment of (R)-7 with
2
CuCl gave the corresponding Cu(II) complex (R)-8.
The conversion from (R)-7 to (R)-8 was investigated by using UV
and fluorescence spectroscopic methods. As shown by the UV spec-
tra in Figure 1a, titration of a solution of (R)-7 with CuCl led to a
2
decrease in absorption at k = 230 nm and an increase at
k = 323 nm. These changes are similar to those observed for the
2
(Fig. 2a). However, the change at
k = 277 nm for (R)-7 is small when treated with Cu which is quite
3
c
reaction of (R)-1 with CuCl
2
+
⇑
2
+
different from (R)-1. Upon interaction with Cu , (R)-1 exhibited