Weak-link Approach Research Articles

Fine-Tuning the Weak-Link Approach: Effect of Ligand Electron Density on the Formation of Rhodium(I) and Iridium(I) Metallomacrocycles

Fine-Tuning the Weak-Link Approach: Effect of Ligand Electron Density on the Formation of Rhodium(I) and Iridium(I) Metallomacrocycles

Fine-tuning the weak-link approach: effect of ligand electron density on the formation of rhodium(I) and iridium(I) metallomacrocycles.

A novel bis(phosphinoalkyl-thioether)arene ligand with a fluorinated aryl group (1,4-(Ph(2)PCH(2)CH(2)S)(2)C(6)F(4)) has been synthesized. This ligand has been used to prepare symmetric bimetallic structures with Rh(I) and Ir(I) metal centers in high yield. Unlike their nonfluorinated counterparts, these complexes can be opened into large macrocyclic structures through straightforward ligand (i.e., carbon monoxide, nitriles, and isocyanides) substitution reactions at the metal-thioether linkage. In addition, the symmetric bimetallic structures have been shown to react with appropriately sized bifunctional aromatic molecules to form three-tiered host-guest structures.

A supramolecular approach to an allosteric catalyst.

The design and synthesis of a novel, supramolecular allosteric catalyst system, assembled via the weak-link approach, is presented. The catalyst contains two structural Rh(I) centers in thioether- and phosphine-rich hemilabile pockets, and two functional Cr(III) centers bound within salen-based moieties. The catalytic properties of the supramolecular catalyst are compared to those of a Cr(III)-salen monomeric analogue in the context of the asymmetric ring opening of cyclohexene oxide by TMSN3. Allosteric control is afforded via reactions that occur at distal sites which open the macrocyclic cavity and facilitate the catalytic reaction. Kinetic data show a significant rate increase upon opening of the catalyst's flexible macrocyclic cavity and enhanced selectivity and reactivity with respect to the monomeric Cr(III)-salen analogue. The work presented represents a new approach to the construction of abiotic allosteric catalysts.

Stepwise formation of heterobimetallic macrocycles synthesized via the weak-link approach.

A new dissymmetric bis-hemilabile ligand with strong binding phosphorus moieties, weak binding thioether moieties, and weaker binding ether moieties has been synthesized to construct heterobimetallic Rh(I)- and Pd(II)-containing macrocycles. The metals are placed in either the phosphorus/thioether or the phosphorus/ether coordination pocket of the dissymmetric ligand by taking advantage of the stepwise synthetic control offered by the weak-link approach. The weak bonds of these isomeric intermediates are systematically broken through ligand substitution reactions to cleanly and selectively generate a variety of open, macrocyclic architectures.

Probing the Mechanistic and Energetic Basis for the Weak-Link Approach to Supramolecular Coordination Complexes

Through the Weak-Link Synthetic Approach, the unsymmetric hemilabile ligand, 1,4-bis(2-diphenylphosphinoethoxy)naphthalene (7), has been used to prepare binuclear Rh(I) macrocycles in a two-step fashion. The intermediate structure, [(μ2,η1:η4:η1-(1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene))2Rh2][BF4]2 (8), and several macrocyclic complexes, [(μ2-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)2Rh2(CH3CN)4][BF4]2 (9), [(μ2-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)2Rh2(CO)6][BF4]2 (10), and [(μ2-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)2(CO)2Rh2(CH3CN)2][BF4]2 (11), are reported herein. Additionally, the mononuclear Rh(I) complexes, [(η1:η4:η1-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)Rh][BF4] (12) and [(η1:η1-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)(CO)Rh(CH3CN)][BF4] (13), were isolated and fully characterized. Single-crystal X-ray diffraction structures of 8, 9 (cis-, anti-), 11, and 12 were determined. 2-D solution NMR studies and the solid-state crystal structures of 8 ...

Threefold symmetric trimetallic macrocycles formed via the Weak-Link Approach.

The synthesis and characterization of a new threefold symmetric hemilabile phosphino-alkylthioether ligand are described. This ligand can be used in combination with Rh(I) and Ir(I) precursor complexes to prepare 40-membered macrocyles with threefold symmetry via the Weak-Link Approach. Synthesis and characterization of two such structures are reported along with a single crystal x-ray diffraction analysis of one of the key intermediates in the case of Rh(I). This is a demonstration of the viability of the Weak-Link Approach for preparing structures other than bimetallic macrocycles and suggests that it could be generalized for a wide range of higher symmetry structures through appropriate hemilabile ligand design.

Flexible redox-active binuclear macrocycles formed via the weak-link approach and novel hemilabile ligands with N,N,N',N'-tetramethyl-1,4-phenylenediamine units.

A method that utilizes the “weak-link synthetic approach” to binuclear macrocycles and a hemilabile ligand derived from Wurster's reagent (N,N,N‘,N‘-tetramethyl-1,4-phenylenediamine (TMPD)) to prep...

Binuclear Palladium Macrocycles Synthesized via the Weak-Link Approach

The “weak-link approach” to metallomacrocycle synthesis has been employed to synthesize a series of Pd(II) macrocycles in high yield. Although this approach has been used to construct several Rh(I) complexes with a variety of ligands, the generality of this methodology with respect to transition metals has not been demonstrated. When added to [Pd(NCCH3)4][BF4]2, the phosphinoalkyl ether or thioether ligands produce “condensed intermediates”, [(μ-(1,4-(PPh2CH2CH2X)2−Y)2Pd2)][BF4]4 (4, X = O, Y = 2,3,5,6-((CH3)4C6); 5, X = O, Y = C6H4; 6, X = S, Y = C6H4), containing strong P−Pd bonds and weaker O−Pd or S−Pd bonds. The weak bonds of these intermediates can be quantitatively broken through simple ligand substitution reactions to generate the macrocyclic structures [(μ-(1,4-(PPh2CH2CH2X)2−Y)2(Z)4Pd2)][BF4]n (7, X = O, Y = 2,3,5,6-((CH3)4C6), Z = CH3CN, n = 4; 8, X = O, Y = C6H4, Z = CH3CN, n = 4; 9, X = O, Y = 2,3,5,6-((CH3)4C6), Z = CN, n = 0; 10, X = O, Y = C6H4, Z = CN, n = 0; 11, X = S, Y = C6H4, Z = CN, n = 0), in quantitative yields. The extension of this approach to Pd(II) should provide new pathways for modifying the binding and catalytic capabilities of these complexes. Solid-state structures as determined by single-crystal X-ray diffraction studies are presented for compounds 6, 8, and 9.

Weak-link approach builds organometallic macrocycles

Weak-link approach builds organometallic macrocycles

The Weak-Link Approach to the Synthesis of Inorganic Macrocycles.

Homobimetallic macrocycles are prepared from flexible ligands in high yield by means of a new and general synthetic strategy called the "weak-link approach" [Eq. (a)]. Small aromatic molecules can be aligned inside the cage based on their interactions with the two Rh centers of the macrocycle.

The Weak-Link Approach to the Synthesis of Inorganic Macrocycles

The Weak-Link Approach to the Synthesis of Inorganic Macrocycles