ISMSC 2007 - Università degli Studi di Pavia

Molecular inclusion of organometallic sandwich complexes within hybrid
cavitand-resorcin[4]arene receptors
María Ángeles Sarmentero, a Guzmán Gil, a Pablo Ballester a,b .
a Institute of Chemical Research of Catalonia (ICIQ), Avda. Països Catalans 16, 43007
Tarragona, Spain. b ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain.
The confinement of guests within molecular vessels modifies their chemical behaviour. While
included, guests can undergo reactions with significant rate enhancement and improved product
selectivity.[1] On the other hand, the inclusion of redox-active guests, generally tends to slow
down the kinetics of heterogeneous electron transfer reactions.[2] The complete encapsulation
of cobaltocenium cations in non polar solvents has been achieved, mainly through cation-
interactions, using non-covalent dimeric and hexameric capsules [3].
In this communication we describe the efficiency of simple and neutral hybrid cavitandresorcin[4]arene
hosts for the molecular inclusion of positively charge organometallic sandwich
complexes. The complexation process has been studied by 1 H-NMR and cyclic voltammetry
techniques in organic solvents.
The obtained results point out that the aromatic cavities present in the vase conformation of
these receptors are electronically rich and capable of including organometallic sandwich cations
by offering CH- and - interactions. Furthermore, the receptors show a remarkable size and
charge selectivity in the molecular inclusion of the redox active guests.
R 2 HN
R 2 HN
H 4
H 3
O
H 9
O
H1
H 5
Co
R 2 HN
H7
NHR 2
O O
H10 R 1
H2 R 1
R 1 H6 R 1 =CH2CH3
R 1
H8 OH HO
Ru
O
H 9
O
R 2 =H;
R 2 =COCH2CH3;
NHR 2
NHR 2
PSB 55
[1] a) D. Fiedler, D. H. Leung, R. G. Bergman and K. N. Raymond, Acc. Chem. Res., 2005, 38,
349-358, b) M. Fujita, M. Tominaga, A. Hori and B. Therrien, Acc. Chem. Res., 2005, 38,
369-378.
[2] C. M. Cardona, S. Mendoza and A. E. Kaifer, Chem. Soc. Rev., 2000, 29, 37-42.
[3] a) D. Ajami, M. P. Schramm, A. Volonterio and J. Rebek, Jr., Angew. Chem. Int. Ed., 2007,
46, 242-244. b) I. Philip and A. E. Kaifer, J. Org. Chem., 2005, 70, 1558-1564.
PSB 56
Subcomponent Exchanges in Self-Assembled Metallo-Organic Structures
David Schultz, Jonathan R. Nitschke
Department of Organic Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211
Geneva 4, Switzerland
Using the principles of dynamic self-assembly we can build structures that are held together by
two kinds of reversible bonds, covalent (C=N) and coordinative (NM) bonds, giving the
possibility for dynamic sorting and substitution to occur.
Selectivity imposed by metal ions was used to simplify dynamic combinatorial libraries of ligand
subcomponents. We have shown that two different copper(I) complexes may self-assemble
quantitatively from a common pool of subcomponents in each other’s presence.[1]
Simultaneous templating involving the cooperative action of Cu I and Fe II allowed us to simplify
an even more complex mixture of compounds.[2]
Substitution of ligand subcomponents in such metallo-organic complexes is ruled by several
factors that can be used to quantitatively and selectively transform one structure into another.
The difference in pKA between the protonated amines was found to drive substitution by
favoring the displacement of the protonated form of the weaker acid and the incorporation of the
deprotonated form of the stronger acid.[4]
Another way to drive subcomponent substitution is provided by the substituent electronic
effects. We have shown the existence of a linear free energy relationship connecting the
electron-donating character of an anilines’ para-substituent, as measured by the Hammett para
parameter, to that aniline’s ability to compete with unsubstituted aniline to form imines.[3]
These results allowed us to design the three-step transformation of a series of copper
containing structures shown below. Electronic effects combined with the chelate effect allowed
each step to proceed in predictably high yield. One interest of this experiment is that the
topology of the product is changed at each step.
O
N
N Cu
N
N
+
O
NH 2
N N
Cu
N N
+
NMe 2
NMe 2
O O
NH2 N N
Cu
N N
+
N
N Cu
N
N
+
99.5%
NH2 97%
H2N NH2 93%
NMe2 N
N Cu
N
N
+
[1] David Schultz and Jonathan R. Nitschke, Proc. Natl. Acad. Sci. USA 2005, 102, 11191-
11195
[2] David Schultz and Jonathan R. Nitschke, Angew. Chem. Int. Ed. 2006, 45, 2453-2456
[3] David Schultz and Jonathan R. Nitschke, J. Am. Chem. Soc. 2006, 128, 9887-9892
[4] David Schultz and Jonathan R. Nitschke, Chem. Eur. J. 2007, in press.
O
O