The first β-diketiminate-Ag(l) complexes. Macrocyclic dinuclear and tetranuclear Ag(l)-complexes and linear coordination polymer Ag(l)-complex

Article abstract of DOI:10.1021/ic0501014

Reactions of Ag(l) and a series of β-diketiminate ligands have been investigated to demonstrate that unique macrocyclic dinuclear and tetranuclear Ag(l)-complexes and a linear coordination polymer Ag(l)-complex as well as oxidative C-C coupling dimer products of the ligands were obtained depending on the substituents on the carbon framework of β-diketiminate ligands.

Full text of DOI:10.1021/ic0501014

Inorg. Chem. 2005, 44, 3010−3012
The First
â-Diketiminate−Ag(I) Complexes. Macrocyclic Dinuclear and
Tetranuclear Ag(I)-Complexes and Linear Coordination Polymer
Ag(I)-Complex
Chizu Shimokawa and Shinobu Itoh*
Department of Chemistry, Graduate School of Science, Osaka City UniVersity, 3-3-138 Sugimoto,
Sumiyoshi-ku, Osaka 558-8585, Japan
Received January 22, 2005
Scheme 1
Reactions of Ag(I) and a series of
â-diketiminate ligands have
been investigated to demonstrate that unique macrocyclic dinuclear
and tetranuclear Ag(I)-complexes and a linear coordination polymer
Ag(I)-complex as well as oxidative C
of the ligands were obtained depending on the substituents on
the carbon framework of -diketiminate ligands.
−C coupling dimer products
â
â-Diketiminate derivatives function as essentially mono-
anionic didentate ligands, which have been widely adopted
for the syntheses of transition metal, main group element,
and lanthanide complexes.1 In most cases, â-diketiminate
ligands are adapted to take a closed conformation (type-A),
affording a six-membered metallacyclic ring as a minimum
structural unit of the complexes (Scheme 1). However,
â-diketiminatometal complexes with an open conformation
(type-B) are very rare.1-5
easily obtained by the condensation reaction between acety-
lacetone and 2,6-diisopropylaniline.1,7 Thus, the reaction of
L1- and Ag(I) was first examined. Treatment of L1H with
an equimolar amount of AgPF6 in the presence of triethyl-
amine in methanol at room temperature under anaerobic and
dark conditions resulted in precipitation of silver metal Ag-
(0) and organic materials. From the mixture was isolated an
organic product in a 58% yield, the structure of which was
determined as a dimer of the original ligand (L1)2 (Scheme
2).8 One-electron oxidation of L1- by Ag(I) may occur to
give a radical species L1• and Ag(0), the former of which is
converted into the dimer product (L1)2 by CR-CR radical
coupling and following proton migration from the R-carbon
to the nitrogen atom (imine-to-enamine isomerization, see
Scheme 2).
We herein report our investigation of the reactions of Ag-
(I) and a series of â-diketiminate ligands (L1- - L5-;
deprotonated forms of L1H - L5H, Scheme 1) which found
that the ligands behave quite differently toward the metal
ion depending on the substituents on the carbon framework
(R1 and R2). It should be noted that nothing is known about
coordination chemistry of silver in â-diketiminate ligand
systems.1,6 Thus, the present study provides the first examples
of â-diketiminate-silver(I) complex.
L1- (R1 ) H, R2 ) Me) is one of the most popular
â-diketiminate ligands so far investigated, since it can be
* Author to whom correspondence should be addressed. E-mail:
shinobu@sci.osaka-cu.ac.jp.
A similar CR-CR coupling reaction took place in the same
treatment of L2H and AgPF6 to give (L2)2 in a 79% yield
(Scheme 3). In this case, imine-to-enamine isomerization
does not occur, since there is no proton on the R-carbon of
L2H. Figure 1 shows the crystal structure of (L2)2 that
unambiguously confirms the CR-CR bond formation reac-
tion.9 The bond lengths of N-Câ (1.251(1) Å), CR-Câ
(1) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031-3065.
(2) Clegg, W.; Coles, S. J.; Cope, E. K.; Mair, F. S. Angew. Chem., Int.
Ed. 1998, 37, 796-798.
(3) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G. Organo-
metallics 2001, 20, 1190-1194.
(4) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S.; Sablong, R. Chem.
Commun. 2002, 1920-1921.
(5) Hitchcock, P. B.; Lappert, M. F.; Wei, X.-H. J. Organomet. Chem.
2004, 689, 1342-1349.
(7) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514-1516.
(8) Details of the experimental procedures and the analytical data of the
products are presented in Supporting Information.
(6) Silver(I)-complexes of closely related triazapentadienyl ligands with
fluorinated alkyl substituents were reported recently. Dias, H. V. R.;
Singh, S. Inorg. Chem. 2004, 43, 7396-7402.
3010 Inorganic Chemistry, Vol. 44, No. 9, 2005
10.1021/ic0501014 CCC: $30.25
© 2005 American Chemical Society
Published on Web 04/05/2005

COMMUNICATION
Scheme 2
Figure 1. ORTEP drawing of (L2)2 with 50% probability thermal-
ellipsoids. Hydrogen atoms are omitted for clarity.
Scheme 3
(1.530(1) Å), and CR-CR (1.578(2) Å) also confirm the
structure of (L2)2 indicated in Scheme 3. Occurrence of such
a CR-CR coupling reaction with â-diketiminate ligands
carrying alkyl substituent(s) on the carbon framework may
be a reason for the lack of â-diketiminate-silver coordination
chemistry.
Notably, the same treatment of AgPF6 with L3H carrying
no substituent on the carbon framework (R1 ) R2 ) H)10
gave a dinuclear Ag(I)-complex [AgI2(L3-)2](CH2Cl2)2 in
96% as shown in Figure 2. In this complex, â-diketiminate
ligand L3- exhibits the open conformation (type-B), acting
as a didentate bridging ligand to afford the 12-membered
macrocyclic compound as shown in Figure 2a. The silver(I)
ion exhibits two-coordinate nearly linear structure (bond
angle of N-Ag-N is 173°), and the distance between the
two Ag(I) ions is about 5.0 Å. The 12-membered macrocyclic
ring is perfectly flat and the aromatic ring of 2,6-diisopro-
pylphenyl substituent is almost perpendicular to the macro-
cyclic plane (Figure 2b). In the cases of L1- and L2-, such
a linear conformation of Ag(I) may not be stable due to steric
repulsion between the ligand substituents (R1, R2, and Ar),
thus causing the oxidative degradation (CR-CR coupling)
reaction.
Figure 2. ORTEP drawings [(a) top view and (b) a side view] of
[AgI2(L3-)2](CH2Cl2)2 with 50% probability thermal-ellipsoids. Hydrogen
atoms and the solvent molecules (CH2Cl2) in the crystal lattice are omitted
for clarity.
ring. The silver(I) ions also exhibit a two-coordinate structure,
but the N-Ag-N angles of 154-158° are smaller than that
in the dinuclear Ag(I)-complex (173°). The molecule exhibits
a saddle-shape structure, in which one molecule of CH2Cl2
is entrapped in the cavity (Figure 3b). There seems to be
hydrogen-bonding interaction between the hydrogen atoms
of CH2Cl2 and the nitrogen atoms of -CN groups, but the
distance between the carbon atom of the incorporated CH2-
Cl2 molecule and the nitrogen atom of -CN (4.97 Å) seems
to be too long for the formation of hydrogen-bonding
interaction.
More interestingly, the treatment of AgPF6 with cyano-
ligand L4H11 gave a much larger macrocyclic tetranuclear
Ag(I)-complex shown in Figure 3 in 84% yield.12 As in the
case of the dinuclear Ag(I)-complex (Figure 2), the ligand
is adapted to take the open conformation and acts as a
didentate bridging ligand, producing the large 24-membered
(9) Crystallographic data as well as the selected bond lengths and angles
are presented in Supporting Information.
(10) Cheng, M.; Moore, D. R.; Reczek, J. J.; Chamberlain, B. M.;
Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 8738-
8749.
(11) Shimokawa, C.; Yokota, S.; Tachi, Y.; Nishiwaki, N.; Ariga, M.; Itoh,
S. Inorg. Chem. 2003, 42, 8395-8405.
(12) Multinuclear Ag(I) macrocyclic complexes with a two-coordinate linear
coordination geometry have also been reported in other ligand systems.
(a) Munakata, M.; Wu, L. P.; Kuroda-Sowa, T. In AdVances in
Inorganic Chemistry; Sykes, A. G., Ed.; Academic Press: San Diego,
CA, 1999; Vol. 46, pp 173-303. (b) Gimeno, M. C.; Laguna, A. In
ComprehensiVe Coordination Chemistry II; Fenton, D. E., Ed.;
Elsevier: Amsterdam, 2004; Vol. 6, pp 911-1145.
On the other hand, another electron-deficient nitro-ligand
L5H afforded a totally different â-diketiminatosilver(I)
complex as shown in Figure 4a (72% isolated yield). The
product was a coordination polymer Ag(I)-complex with L5-
exhibiting the closed conformation (type-A), where the
neutral [AgI(L5-)] units associate with each other to form a
head-to-tail (Ag-to-NO2) linear polymer chain. The Ag(I)
Inorganic Chemistry, Vol. 44, No. 9, 2005 3011

COMMUNICATION
Figure4. (a)ORTEPdrawingofthepolymercomplex{[AgI(L5-)](CH2Cl2)}n
with 50% probability thermal-ellipsoids. Hydrogen atoms and CH2Cl2
molecules are omitted for clarity. Schematic drawings of the monomer unit
alignment of (b) the silver(I)-polymer complex and (c) the copper(I)-
polymer complex.
Figure 3. ORTEP drawings [(a) front view and (b) a side view] of
[AgI4(L4-)4(CH2Cl2)] with 50% probability thermal-ellipsoids. Hydrogen
atoms in (a), and hydrogen atoms except those on CH2Cl2 and Ar groups
in (b), are omitted for clarity.
coupling reaction. This may be a reason for the lack of
coordination chemistry in the â-diketiminate-silver system.
Less hindered â-diketiminate ligand L3-, on the other hand,
provided the dinuclear silver(I) complex [AgI2(L3-)2] with
the open conformation of the supporting ligand. The Ag(I)
oxidation state may be stabilized in the linear coordination
geometry, prohibiting the one-electron oxidation of ligand
by Ag(I). The â-diketiminate ligands involving a strong
electron-withdrawing group such as -CN in L4- and -NO2
in L5- can also stabilize the silver(I) oxidation state to give
a unique macrocyclic tetranuclear Ag(I)-complex with the
open conformation (type-B) and the linear polymer-Ag(I)-
complex with a trigonal planar geometry supported by the
ligand with the closed conformation (type-A). Thus, control
of the oxidation state of silver by the ligand is very important
for the development of â-diketiminato-silver complexes.
ion exhibits a distorted trigonal planar structure and the nitro
group acts as a monodentate ligand to link the monomer
units.
We previously reported a linear copper(I)-polymer com-
plex supported by a similar R-nitro â-diketiminate ligand
(Ar ) mesityl).13 The coordination geometry of the metal
center of the Ag(I)-polymer complex is fairly close to that
of the Cu(I)-polymer complex, but the alignment of
monomer units is largely different between the two systems.
Namely, in the copper(I)-system, the six-membered chelate
rings of all the monomer units are parallel to each other,
making a flat wall of the one-dimensional polymer chain
(Figure 4c), whereas the chelate ring of the silver(I)-complex
is perpendicular to that of the neighboring monomer units
as illustrated in Figure 4b. Thus, the copper(I)-polymer
complex exhibits a dark purple color probably due to an
extended d-pπ interaction through the Cu-NO2 linkage,13
but such an extended conjugative interaction is absent in the
silver system due to the perpendicular monomer alignment.
Thus, the color of the Ag(I)-polymer complex is yellow.
In summary, unique behavior of â-diketiminate ligands
has been found in the reaction with AgPF6. With the ordinary
alkyl substituted ligands (L1- and L2-), one-electron oxida-
tion of the ligand occurred to induce the CR-CR radical
Acknowledgment. This work was financially supported
in part by Grants-in-Aid for Scientific Research (15350105)
from the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
Supporting Information Available: Details of the experimental
procedures and analytical data of the products (pdf), and X-ray
structural determination and details of the crystallographic data
(CIF). This material is available free of charge via the Internet at
http://pubs.acs.org.
(13) Yokota, S.; Tachi, Y.; Nishiwaki, N.; Ariga, M.; Itoh, S. Inorg. Chem.
2001, 40, 5316-5317.
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