Subgroup
Members (Left to Right):
(Back Row) Chris Oliveri, Abdel Sumrein, You Moon Jeon, Mike Wiester
(Front Row) Junpei Kuwabara, Jungseok Heo, Hyojong Yoo, Pirmin Ulmann
Inorganic Macrocycles Synthesized
Via the Weak-Link Approach
Our subgroup has developed a new and versatile strategy for preparing
large supramolecular, organometallic ring and cage structures in extraordinarily
high yield (>95%). The method takes advantage of hemilabile ligands that
contain both strong and weak binding moieties that coordinate to metal centers
to organize themselves into condensed structures that consist of thermodynamically
stable 5 or 6 membered rings. The weaker bonds are then broken through the introduction
of small ligating molecules such as CO or CH3CN which
open the condensed ring system into the desired ring structure. This general
approach is applicable to a variety of metals and ligands that have been designed
to take advantage of the hemilabile interactions. Some of the small molecules
can be removed, allowing further chemistry to occur at the unsaturated metal
centers.
By exposing the condensed macrocycles, shown below, to a variety of conditions,
we have successfully synthesized large macrocyclic ring structures in high yields
and used these structures as shape selective recognition elements. Our subgroup
focuses on: (1) developing and extending this synthetic strategy to new ligands
and metal centers, (2) using these ring structures to make unusual molecules
with well-defined geometric shapes such as molecular cylinders, and (3) investigating
the host-guest chemistry and catalytic properties of these fascinating complexes.
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Three-Dimensional Architectures
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We begin with "simple" metal and ligand precursors. These starting materials are either purchased or synthesized in a few high yielding steps from commercially available materials. Thus far, we have used rhodium (I), copper (I), palladium (II) , ruthenium (II), iridium (I), zinc (II), and chromium (III) metal centers, but in principle, the approach will work for any transition metal Upon addition of the ligands to the metals, binuclear intermediates are synthesized. These intermediates contain (1) strong metal-phosphorus bonds, (2) weak ether- , thioether- , amine- , or arene-metal bonds, and (3) thermodynamically stable 5- and 6-membered rings. Depending on the weak-link moieties incorporated into the ligand , either "bow-tie" or"slipped" condensed macrocyclic intermediates are generated. The weak-links incorporated into the closed macrocycles can be selectively displaced through the addition of ancillary ( L ) ligands that bind more strongly to the metal center than the weak-links to yield open cationic or neutral macrocycles.
The weak link approach has been extended from simple two-dimensional rings to more complex three-dimensional architectures. Some examples of these molecules are displayed on the left. In addition to utilizing monodentate ligands to open our structures, bidentate ligands can be employed to yield these more complex architectures. For example, three-tiered "stuffed" macrocycles containing guest molecules spanning the two macrocyclic metal centers are constructed by reacting small bifunctional aromatic molecules with the condensed or open structures to break their weak links. Molecular cylinders containing ligands bound between the metal sites of two macrocycles can be synthesized when bifunctional aromatic molecules that are larger than the cavity diameter are added to the condensed structures. Another example of a three-dimensional structure is the molecular prism. By using two equivalents of a trifunctional ligand and three metal centers, a prism with a large cavity can be synthesized. |
It is the flexibility of the ligands and the coordinative unsaturation or lability of the metal centers generated in the complexes formed via the weak-link approach that, in part, differentiates this approach from other approaches in the field of supramolecular architectures. For a review of this and other supramolecular syntheses see our review in Angewandte Chemie International Edition.
To see some of the structures that we have generated visit the
Macrocycle Crystal Structure Library
Or back to the
Weak-Link References
Farrell, J. R.; Mirkin, C. A.; Liable-Sands, L. M.; Rheingold, A. L. "A Strategy for Preparing Molecular Cylinders with Synthetically Programmable Structural Parameters," J. Am. Chem. Soc., 1998, 120, 11834-11835.
Farrell, J. R.; Mirkin, C. A.; Guzei, I. A.; Liable-Sands, L. M.; Rheingold, A. L. "The Weak-Link Approach to the Synthesis of Inorganic Macrocycles," Angew. Chem., Int. Ed., 1998, 37, 465-467.
Farrell, J. R.; Eisenberg, A. H.; Mirkin, C. A.; Guzei, I. A.; Liable-Sands, L. M.; Incarvito, C. D; Rheingold, A. L.; Stern, C. L.; "Templated Formation of Binuclear Macrocycles Via Hemilabile Ligands," Organometallics, 1999, 18, 4856-4868.
Holliday, B. J.; Farrell, J. R.; Mirkin, C. A.; Lam, K.-C.; Rheingold, A. L. "Metal-Directed Assembly of Triple-Layered Fluorescent Metallocyclophanes," J. Am. Chem. Soc., 1999, 121, 6316-6317.
Dixon, F. M.; Eisenberg, A. H.; Farrell, J. R.; Mirkin, C. A.; Liable-Sands, L. M.; Rheingold, A. L.; “Neutral Macrocycles via Halide-Induced Ring Opening of Binuclear Condensed Intermediates” Inorg. Chem., 2000, 39, 3432-3433.
Holliday, B. J.; Mirkin C. A. "Strategies for the Construction of Supramolecular Compounds through Coordination Chemistry," Angew. Chem., Int. Ed., 2001, 40, 2022-2043.
Liu, X.; Eisenberg, A. H.; Stern, C. L.; Mirkin, C. A. "Flexible Redox-Active Binuclear Macrocycles Formed via the Weak-Link Approach and Novel Hemilabile Ligands with N, N,N',N'-Tetramethyl-1,4-pheylenediamine Units," Inorg. Chem., 2001, 40, 2940-2941.
Eisenberg, A. H.; Dixon, F. M.; Mirkin, C. A.; Stern, C. L.; Incarvito, C. D.; Rheingold, A. L. "Binuclear Palladium Macrocycles Synthesized via the Weak-Link Approach," Organometallics, 2001, 20, 2052-2058.
Holliday, B. J.; Jeon, Y.-M.; Mirkin, C. A.; Stern, C. L.; Incarvito, C. D.; Zakharov, L. N.; Sommer, R. D.; Rheingold, A. L. "Probing the Mechanistic and Energetic Basis for the Weak-Link Approach to Supramolecular Coordination Complexes," Organometallics, 2002, 21(26), 5713-5725.
Ovchinnikov, M. V.; Holliday, B. J.; Mirkin, C. A. "Three-Fold Symmetric Trimetallic Macrocycles Formed via he Weak-Link Approach," Proc. Natl. Acad. Sci., 2002, 99, 4927-4931.
Dixon, F. M.; Farrell, J. R.; Doan, P. E.; Williamson, A.; Weinberger, D. A.; Mirkin, C. A.; Stern, C.; Incarvito, C. D.; Liable-Sands, L. M.; Zakharov, L. N.; Rheingold, A. L. "Rational Design of a Novel Mononuclear Rhodium(II) Complex," Organometallics, 2002, 21, 3091-3093.
Gianneschi, N. C.; Mirkin, C. A.; Zakharov, L. N.; Rheingold, A. L. "A Tetranuclear Heterobimetallic Square Formed from the Cooperative Ligand Binding Properties of Square Planar and Tetrahedral Metal Centers," Inorg. Chem., 2002, 41, 5326-5328.
Eisenberg, A. H.; Mirkin, C.A. “Stepwise Formation of Heterobimetallic Macrocycles Synthesized Via the Weak-Link Approach,” J. Am. Chem. Soc. 2003, 125, 2836-2837.
Masar III, M. S.; Ovchinnikov, M.V.; Mirkin, C.A. “Fine-Tuning the “Weak-Link” Approach: Effect of Ligand Electron Density on the Formation of RhI and IrI Metallomacrocycles,” Inorg. Chem. 2003, 42, 6851-6858.
Holliday, B.J.; Arnold, F.P.; Mirkin, C.A. “The Weak-Link Approach: Quantum Chemical Studies of the Key Binuclear Synthetic Intermediates,” J. Phys. Chem. A 2003, 107, 2737-2742.
Dixon, F. M.; Masar III, M. S.; Doan, P. E.; Farrell, J. R.; Arnold Jr., F.P.; Mirkin, C.A.; Incarvito, C, D.; Zakharov, L. N.; Rheingold, A.L. “Rh(II) and Rh(I) Two-Legged Piano-Stool Complexes: Structure, Reactivity, and Electronic Properties,” Inorg. Chem. 2003, 42, 3245-3255.
Masar III, M. S.; Mirkin, C.A.; Stern, C. L.; Zakharov, L. V.; Rheingold, A.L. “Binuclear Copper(I) Macrocycles Synthesized via the Weak Link Approach,” Inorg. Chem. 2004, 43, 4693-4701.
Brown, A. M.; Ovchinnikov, M. V.; Stern, C. L.; Mirkin, C.A. “Halide-Induced Supramolecular Ligand Rearrangement,” J. Am. Chem. Soc. 2004, 126, 14316-14317.
Ovchinnikov, M. V.; Brown, A. M.; Liu, X.; Mirkin, C.A.; Zakharov, L. N.; Rheingold, A.L. “Heteroligated Metallomacrocycles Generated via the Weak-Link Approach,” Inorg. Chem. 2004, 43, 8233-8235.
Gianneschi, N. C.; Cho, S.; Nguyen, S. T.; Mirkin, C.A. “Reversibly Addressing an Allosteric Catalyst In Situ: Catalytic Molecular Tweezers,” Angew. Chem. Int. Ed. 2004, 43, 5503-5507.
Oh, M.; Stern, C. L.; Mirkin, C.A. “Coordination Polymers with Macrocyclic Cages and Pockets within their Backbones,” Chem. Commun. 2004, 23, 2684-2685.
Khoshbin, M. S.; Ovchinnikov, M.V.; Mirkin, C.A.; Zakharov, L. V.; Rheingold, A.L. “Binuclear Ruthenium Macrocycles Formed via the Weak Link Approach,” Inorg. Chem. 2004, 43, ASAP.
