FULL PAPER
DOI: 10.1002/ejoc.201400120
Synthesis and Selected Reactivity Studies of a Dissymmetric
(Phosphinoylmethylpyridine N-Oxide) Methylamine Platform
Sabrina Ouizem,
[a]
Sylvie L. Pailloux,
[a]
Alisha D. Ray,
[a]
Eileen N. Duesler,
[a]
Diane A. Dickie,
[a]
Robert T. Paine,*
[a]
and Benjamin P. Hay
[b]
Keywords: N ligands / Chelates / Ligand design / Lanthanides / Nitrogen oxides
Efficient syntheses for the precursor molecules, 2-{6-[((di-
phenylphosphoryl)methyl)pyridin-2-yl]methyl}isoindoline-
1,3-dione (2), 2-[(1,3-dioxoisoindolin-2-yl)methyl]-6-[(di-
phenylphosphoryl)methyl]pyridine 1-oxide (3), and their 6-
[bis(2-(trifluoromethyl)phenyl)phosphoryl]methyl analogues
are reported along with their transformations into the dis-
symmetric ligands, [(6-(aminomethyl)pyridin-2-yl)methyl]di-
phenylphosphine oxide (4), 2-(aminomethyl)-6-[(diphenyl-
phosphoryl)methyl]pyridine 1-oxide (5) and 2-(aminometh-
yl)-6-{[bis(2-(trifluoromethyl)phenyl)phosphoryl]methyl}-
pyridine 1-oxide ( 5-F). Selected reactivity of the amino-
methyl substituent of 4 and 5, as well as complexation reac-
Introduction
Organic chelating ligands have been employed for many
years as critical enabling components in metal ion analyti-
cal detection schemes and solvent extraction-based separa-
tion processes. In particular, there has been much interest
given to the development of robust chelating ligands for the
separation of chemically similar f-block ions present in
highly acidic aqueous nuclear process solutions.
[1]
In ad-
dition, renewed interest in the reclamation of rare-earth
ions from low-grade ores and recycle materials
[2]
has also
stimulated parallel growth in the design and synthesis of
selective chelating ligands for this application. As part of
efforts to more fully describe factors that control ligand
chelate interactions on f-block element ions, we have pre-
viously described syntheses for multidonor site molecules
based upon pyridine and pyridine N-oxide platforms decor-
ated with phosphine oxide
[3]
and amide
[4]
functional groups.
In the former class of compounds, this included representa-
tives illustrated by A–E (Figure 1). Examples of A and C
were found to produce strong bidentate O
N
O
P
binding con-
[a] Department of Chemistry and Chemical Biology, University of
New Mexico,
Albuquerque, NM 87131, USA
E-mail: rtpaine@unm.edu
www.unm.edu/~rtpaine/
[b] Chemical Sciences Division, Oak Ridge National Laboratory,
P. O. Box 2008, Oak Ridge, Tennessee, 37831, USA
E-mail: haybp@ornl.gov
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201400120.
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Org. Chem. 2014, 3132–3148 3132
tions of several of the compounds with lanthanide(III) ions
are described. Molecular structures of three uniquely dif-
ferent complexes, {Pr{2-[HC(O)N(H)CH
2
]-6-[Ph
2
P(O)CH
2
]-
C
5
H
3
NO}(NO
3
)
3
(MeOH)}
2
, {Eu{2-[(Me
2
N)
2
CN(H
+
)CH
2
]-6-
[Ph
2
P(O)CH
2
]C
5
H
3
N(H)
+
}(NO
3
)
4
(OMe)} and {Er{2-[(C
8
H
4
O
2
)-
NCH
2
]-6-[Ph
2
P(O)CH
2
]C
5
H
3
N(O)}(NO
3
)
3
(MeOH)}·(CH
3
)
2
-
CO, have been determined by single-crystal X-ray diffrac-
tion methods. The observed and computationally modeled
structures that employ bidentate and tridentate ligand/metal
interactions are compared. These results suggest further
ligand modifications that should provide improved solvent
extraction reagents.
ditions with lanthanide (Ln) ions, whereas E was observed
to form tridentate O
N
O
P
O
P
interactions. Unexpectedly, in
the presence of two or more equivalents of ligand, these
neutral molecules were observed to partially or totally dis-
place charge-compensating anions, for example nitrate,
from the inner coordination sphere of the Ln
III
cations. Ex-
amination of the solvent extraction behavior of these com-
pounds revealed that examples of C and E display particu-
larly favorable performance including increasing extraction
efficiency with increasing nitric acid concentration up to ca.
1 .
[5]
This led to interest in possible applications for these
ligands in advanced separation schemes wherein the ligands
would be incorporated into an ionic liquid solvent or onto
a solid support. However, before such systems can be devel-
oped and evaluated, it is necessary to explore reaction
chemistry for the platforms that will facilitate these efforts.
Figure 1. Generalized structures for ligand types A–E.