Inorg. Chem. 2003, 42, 255−257
NMR Evaluation of the Configurational Stability of Cu(I) Complexes
Vale´rie Desvergnes-Breuil,† Virginie Hebbe,† Christiane Dietrich-Buchecker,‡
,‡
,†
Jean-Pierre Sauvage,* and Je´roˆme Lacour*
De´partement de Chimie Organique, UniVersite´ de Gene`Ve, quai Ernest-Ansermet 30,
CH-1211 Gene`Ve 4, Switzerland, and Laboratoire de Chimie Organo-Mine´rale, UMR CNRS no.
7513, Faculte´ de Chimie, Institut Le Bel, UniVersite´ Louis Pasteur, 4, rue Blaise-Pascal,
67070 Strasbourg-Cedex, France
Received August 30, 2002
Association of chiral [CuL2]+ complexes (L ) 2-R-phen, 6-R-bpy,
and 2-iminopyridine) with TRISPHAT (tris(tetrachlorobenzene-
diolato)phosphate(V)) anion leads to NMR enantiodifferentiation,
which can be used to determine the kinetics of racemization of
the complexes.
1,10-Phenanthrolines (phen, 1), 2,2′-bipyridines (bpy, 2),
and 2-iminopyridines (3) have been widely used as ligands
for Cu(I). The derived pseudotetrahedral complexes are
Figure 1. Stereodynamics among diastereoisomeric [CuL2][∆-4] ion pairs.
sensitive to oxidation, and bulky substituents are usually
introduced in positions adjacent to the N-coordinating atoms
to provide steric inhibition to the geometric reorganization
that occurs upon oxidation. The ligands can be unsym-
metrical, always in case of compounds 3, and their com-
plexation to a copper(I) atom results in the formation of chiral
[CuL2]+ adducts (Figure 1).1,2 VT-NMR evaluation of the
configurational stability of these complexes was previously
reported using ligands that evidenced nonequivalent signals
upon complex formation.3,4 Herein, we present another
method based on the use of a chiral counterion as the source
of NMR differentiation. Simple bpy, phen, and iminopyridine
ligands can be used, and the configurational stability of their
chiral adducts is compared.
As mentioned, unsymmetrical 2-R-phen, 6-R-bpy, and
2-iminopyridine ligands form chiral bis(diimine)copper(I)
complexes (Figure 1),5 of which the configurational stability
can be evaluated by NMR using ligands containing enan-
tiotopic groups.3,4,6 Upon complex formation, these substit-
uents become diastereotopic, and separated NMR signals are
observed when the stereodynamics are slow on the NMR
time scale. The determination of the racemization barriers
is then performed by VT-NMR (∆G‡ ∼ 58-64 kJ‚mol-1 in
CDCl3).7
Unfortunately, this efficient method cannot be applied to
complexes made of ligands deprived of enantiotopic sub-
stituents. For these substrates, it occurred to us that a chiral
counterion could be the source of NMR differentiation. The
association of chiral cationic [CuL2]+ complexes with
* Authors to whom correspondence should be addressed. E-mail:
Jerome.Lacour@chiorg.unige.ch (J.L.); sauvage@chimie.u-strasbg.fr
(J.-P.S.).
† Universite´ de Gene`ve.
(5) James, B. R.; Williams, R. J. J. Chem. Soc. 1961, 2007-2019. Mu¨ller,
E.; Piguet, C.; Bernardinelli, G.; Williams, A. F. Inorg. Chem. 1988,
27, 849-855. Grosshenny, V.; Ziessel, R. J. Chem. Soc., Dalton Trans.
1993, 817-819. Bardwell, D. A.; Thompson, A.; Jeffery, J. C.; Tilley,
E. E. M.; Ward, M. D. J. Chem. Soc., Dalton Trans. 1995, 835-841.
Bonnefous, C.; Bellec, N.; Thummel, R. P. Chem. Commun. 1999,
1243-1244. Meyer, M.; Albrecht-Gary, A. M.; Dietrich-Buchecker,
C. O.; Sauvage, J. P. Inorg. Chem. 1999, 38, 2279-2287. Riesgo, E.
C.; Hu, Y. Z.; Bouvier, F.; Thummel, R. P.; Scaltrito, D. V.; Meyer,
G. J. Inorg. Chem. 2001, 40, 3413-3422.
‡ Universite´ Louis Pasteur.
(1) Von Zelewsky, A. Stereochemistry of Coordination Compounds; John
Wiley & Sons: Chichester, U.K., 1996.
(2) (a) Mitchell, D. K.; Sauvage, J. P. Angew. Chem., Int. Ed. Engl. 1988,
27, 930-931. (b) Chambron, J. C.; Mitchell, D. K.; Sauvage, J. P. J.
Am. Chem. Soc. 1992, 114, 4625-4631. (c) Kaida, Y.; Okamoto, Y.;
Chambron, J. C.; Mitchell, D. K.; Sauvage, J. P. Tetrahedron Lett.
1993, 34, 1019-1022. (d) Riesgo, E. C.; Credi, A.; De Cola, L.;
Thummel, R. P. Inorg. Chem. 1998, 37, 2145-2149.
(3) Van Stein, G. C.; Van Koten, G.; Brevard, C. J. Organomet. Chem.
1982, 226, C27-C30. Van Stein, G. C.; Van Koten, G.; Debok, B.;
Taylor, L. C.; Vrieze, K.; Brevard, C. Inorg. Chim. Acta 1984, 89,
29-39.
(6) R and S correspond to ΛB and ∆B configurations in the oriented-skew-
lines reference system, respectively.
(7) The relationship ∆G‡ ) RTc(22.96 + ln(Tc/x(∆ν2 + 6J2)) was used
to determine the activation energy, ∆G‡, from the coalescence
temperature, Tc (K), the frequency separation of the peaks, ∆ν (Hz),
and the coupling constant between the nuclei, J (Hz).
(4) Riesgo, E.; Hu, Y. Z.; Bouvier, F.; Thummel, R. P. Inorg. Chem. 2001,
40, 2541-2546.
10.1021/ic0259890 CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/31/2002
Inorganic Chemistry, Vol. 42, No. 2, 2003 255