Spectral Assignments and Reference Data
Received: 26 July 2008
Revised: 14 October 2008
Accepted: 18 October 2008
Published online in Wiley Interscience: 28 November 2008
Complete assignments of NMR data of salens
and their cobalt (III) complexes
Yoonkyung Woo,a Dongsoo Kohb and Yoongho Lima∗
Salens, derived from 1,2-ethylenediamine and salicylaldehydes, have been widely used as ligands for metal complexes which
have been showing enormous potential in chemical properties of asymmetric catalysts as well as biological properties such as
anticancer agents. Almost all of the salen–metal complexes with their corresponding metal (II)-complexes show the evidences
of chelation of two oxygens in salens. However, several metal (II) complexes, especially cobalt (II) complexes, could not show
NMR spectra due to their paramagnetism. Recently, it has been reported that one of the cobalt (III) complexes was used for
NMR spectroscopy to evaluate its stereoselectivity as a catalyst. Even though many salen ligands are known, their NMR data
are not assigned completely. It was possible that modification in northern part of salen with 2-hydroxyphenyl group afforded
another oxygen chelation site in salen ligand. Here we report that synthesis and full NMR assignment of new salen ligands,
which form meso 1,2-bis(2-hydroxyphenyl)ethylenediamine) and their cobalt (III) complexes. The assignments of 1H and 13
C
c
NMR data obtained in this experiment can help us to predict the NMR data of other salen ligands. Copyright ꢀ 2008 John Wiley
& Sons, Ltd.
Keywords: NMR; 1H NMR; 13C NMR; 2D NMR; salen; cobalt(III) complex
Introduction
the DEPT spectrum. The most upfield shifted 13C peak at 70.2 ppm
should be C7, which was connected directly to the 1H peak at
5.51 ppm in the HMQC spectrum. In addition, C7 was long-range
coupled to the 1H peaks at 7.30 and 8.35 ppm where the latter was
Salen is a chelating ligand that bridges a metal ion with two
nitrogenandtwooxygenatoms. Itresemblesahemegroup, which
functions to facilitate oxygen transport. Unlike a heme group,
however, salen can be easily derived from ethylene diamine and
salicylic aldehyde, and it acts as a catalyst.[1] Salen–metal complex
catalyzes epoxidation, epoxide ring opening, Diels-Alder reaction,
and so on.[2] Furthermore, a cobalt–salen complex can prevent
cells from undergoing proliferation because of its damage on
DNA. As a result, it can act as an antitumor agent. Especially,
it shows activities against breast cancer and prostate cancer. It
is known that the substituents of methoxyl or hydroxyl groups
on 1,2-diarylethane moiety can increase the selectivity for tumor
cell lines.[3] In order to obtain novel cobalt(III)–salen complex, we
synthesized four complexes with 1,2-diarylethane moiety, which
contains hydroxyl groups on A-ring and C-ring as shown in Fig. 1.
The derivatives containing three different substituents on B-ring
andD-ringwereprepared.Becausesalenligandswithoutcobalt(III)
have a mirror plane symmetry, they show severe overlapped
1H NMR data. In cobalt(III)–salen complexes, the mirror plane
symmetryisbrokensothatsevereoverlappingoftheir1HNMRdata
can be distinguished. Until now, X-ray crystallographic structures
of cobalt–salen complexes and their partial NMR data have been
reported, but there is no complete assignment.[4] In this paper, we
report the complete NMR data of eight novel salen compounds
with or without cobalt(III).
1
the most downfield shifted H peak of compound 1. Therefore,
the 1H peak at 8.35 ppm was assigned to be H8, which was directly
attached to the 13C peak at 165.1 ppm. Furthermore, there are two
possible protons that can be long-range coupled with C7, H2, and
H5. As a result, the 1H peak at 7.31 ppm can be assigned H2 or H5.
These two protons could be distinguished in the data of H7–H4
TOCSY but not in the NMR data of compound 1. Therefore, they
weredeterminedonthebasisoftheinterpretationoftheNMRdata
of compound 3. According to the COSY spectrum of compound 3,
the order of four protons such as H2, H3, H4, and H5 was decided.
5
In the TOCSY spectrum, J correlation between H4 and H7 was
observed. From the COSY and TOCSY spectra H2 and H5 were
determined, which were 6.76 and 7.31 ppm respectively. The 13C
peak at 155.2 ppm was long-range coupled with H3, H5, and H7,
so that it was assigned C1. Since one of the quaternary carbons,
the peak at 126.2 ppm, showed a long-ranged coupling with H4,
it was assigned C6. In the HMBC spectrum, H8 was long-range
coupled to two 13C peaks at 118.7 and 131.7 ppm. Because the
former was quaternary carbon and the latter was methine carbon,
1
which were determined to be C9 and C14, respectively. The H
peak at 7.25 ppm was directly attached to C14, so that it was H14.
∗
Correspondence to: Yoongho Lim, Division of Bioscience and Biotechnology,
Konkuk University, Hwayang-Dong 1, Kwangjin-Ku, Seoul, Korea 143-701.
E-mail: yoongho@konkuk.ac.kr
Results and Discussion
According to the 13C NMR spectral analysis, the spectrum of
compound 1 showed 14 peaks. As compounds 1–4 were
synthesized on meso form, they had to possess reflection
symmetry. In addition, ten methine carbons were observed in
a
Division of Bioscience and Biotechnology, RCD, BMIC, RCTC, Konkuk University,
Seoul, Korea 143-701
b
Department of Applied Chemistry, Dongduk Women’s University, Seoul, Korea
136-714
c
Magn. Reson. Chem. 2009, 47, 184–189
Copyright ꢀ 2008 John Wiley & Sons, Ltd.