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A new class of homoligated palladium(II) weak-link approach (WLA) complexes bearing hemilabile N-heterocyclic carbene (NHC)–thioether ligands is reported that, unlike previous tweezer-like WLA complexes, expand and contract in a linear fashion when switching between configurational states. These complexes can be chemically switched between a trans open state and a trans closed state via the addition or subsequent extraction of Cl–. These bis(NHC) complexes also display unusual isomerization behavior. For example, an NMR spectroscopic investigation into the solution-state configuration of the open complex reveals the presence of interconverting syn,trans and anti,trans isomers, and a kinetic study shows that the barrier is large enough to isolate, store, and study the anti,trans isomer at room temperature. Notably, the linker length between the NHC and thioether moieties can be tailored with additional −CH2– groups, which affords considerable control over the geometric changes imposed by switching. Therefo...

The anionic hemilabile phosphinothioether ligand, [1-(Ph2PCH2CH2S)-closo-1-CB11H11 ](-), which is functionalized with an anionic icosahedral monocarbaborane anion, was synthesized in three steps from [HNMe3][closo-CB11H12]. The ligand was used to synthesize a family of zwitterionic Weak-Link Approach (WLA) complexes that contain platinum(II), palladium(II), and rhodium(I). These complexes were characterized using multinuclear NMR spectroscopy, high-resolution mass spectrometry, and single-crystal X-ray diffraction analyses. Although the C-bound [closo-CB11H11](-) anion behaves as an electron-withdrawing moiety, hemilabile phosphinothioether ligands that are based on this unit are strongly chelating, as determined via the measurement of the chloride association constant. The chelating strength is comparable to that of hemilabile ligands that are functionalized with the very electron-rich B-bound closo-1,7-C2B10H11 moiety, thus demonstrating the use of charge to influence ligand coordination strength. The anionic Rh(I) WLA complex that is synthesized using this ligand can act as the noncoordinating anion of a regular cationic Rh(I) WLA complex. Thus, an unprecedented type of salt, in which the anion and cation are mutually isostructural and isoelectronic WLA complexes, has been synthesized and characterized crystallographically.

A series of d(8) transition-metal (Pt(II) and Pd(II)) coordination complexes incorporating phosphine-functionalized aminoazobenzene derivatives as hemilabile phosphino-amine (P,N) ligands were synthesized and studied as model weak-link approach (WLA) photoresponsive constructs. The optical and photochemical properties of these complexes were found to be highly influenced by various tunable parameters in WLA systems, which include type of metal, coordination mode, type of ancillary ligand, solvent, and outer-sphere counteranions. In dichloromethane, reversible chelation and partial displacement of the P,N coordinating moieties allow for toggling between aminoazobenzene- or pseudostilbene- and azobenzene-type derivatives. The reversible switching between electronic states of azobenzene can be controlled through either addition or extraction of chloride counterions and is readily visualized in the separation between π-π* and n-π* bands in the complexes' electronic spectra. In acetonitrile solution, the WLA variables inherent to semiopen complexes have a significant impact on the half-lives of the corresponding cis isomers, allowing one to tune their half-lives from 20 to 21000 s, while maintaining photoisomerization behaviors with visible light. Therefore, one can significantly increase the thermal stability of a cis-aminoazobenzene derivative to the extent that single crystals for X-ray diffraction analysis can be grown for the first time, uncovering an unprecedented edge-to-face arrangement of the phenyl rings in the cis isomer. Overall, the azobenzene-functionalized model complexes shed light on the design parameters relevant for photocontrolled WLA molecular switches, as well as offer new ways of tuning the properties of azobenzene-based, photoresponsive materials.

An allosterically regulated, asymmetric receptor featuring a binding cavity large enough to accommodate three-dimensional pharmaceutical guest molecules as opposed to planar, rigid aromatics, was synthesized via the Weak-Link Approach. This architecture is capable of switching between an expanded, flexible “open” configuration and a collapsed, rigid “closed” one. The structure of the molecular receptor can be completely modulated in situ through the use of simple ionic effectors, which reversibly control the coordination state of the Pt(II) metal hinges to open and close the molecular receptor. The substantial change in binding cavity size and electrostatic charge between the two configurations is used to explore the capture and release of two guest molecules, dextromethorphan and β-estradiol, which are widely found as pollutants in groundwater.

Tröger's base, a chiral molecule with a rigid 90 degrees backbone, has been incorporated into a novel hemilabile phosphinoalkyl thioether ligand. Using the Weak Link Approach, this ligand has been reacted with Cu(CH3CN)4PF6 and [Rh(COE)2Cl]x (COE = cyclooctene) to form metallomacrocycles. Upon reaction of the ligand with Cu(I), which prefers a tetrahedral coordination geometry, a bimetallic macrocycle was formed. Alternatively, owing to the steric restrictions imposed by the 90 degrees backbone of the ligand and the square-planar geometry of Rh(I), when the ligand was reacted with [Rh(COE)2Cl]x, the formation of bimetallic closed macrocycles was not observed, and instead a mixture of tri- and tetrametallic closed macrocycles is formed. Introducing pyridine to the Cu(I) complex causes the weak thioether-Cu bonds to break, generating a large bimetallic open macrocycle. Upon reaction of the mixture of Rh(I) metallomacrocycles with CO and Cl-, the cyclic structure of these complexes becomes flexible enough that the dimeric bimetallic macrocycle forms, along with tri- and tetrameric open complexes. The mixture of differently sized Rh(I) macrocyclic complexes has been analyzed using gel permeation chromatography, and the tetramer has been characterized by a single-crystal X-ray diffraction study. These are the first examples of metallomacrocycles containing a Tröger's base derivative.

The weak-link approach has been employed to synthesize a series of bimetallic Cu(I) macrocycles in high yield. Addition of phosphinoalkylether or -thioether ligands to [Cu(MeCN)4]PF6 produces "condensed" intermediates, [mu-(1,4-(PPh2CH2CH2X)2Y)2Cu2][PF6]2 (X = S, O; Y = C6H4, C6F4), containing strong P-Cu bonds and weaker O-Cu or S-Cu bonds. The weak bonds of these intermediates can be cleaved through ligand substitution reactions to generate macrocyclic structures, [mu-(1,4-(PPh2CH2CH2X)2Y)2(Z)nCu2][PF6]2 (X = S, O; Y = C6H4, C6F4; Z = pyridine, acetonitrile, diimines, isocyanide) in nearly quantitative yields. The incorporation of tetrahedral Cu(I) metal centers into these macrocycles provides a pathway to complexes that differ from analogous d8 square planar macrocycles generated via this approach in their increased air stability, small molecule reactivity, and ability to form multiple structural isomers. Solid-state structures, as determined by single-crystal X-ray diffraction studies, are presented for condensed intermediates and an open macrocycle

A series of new bis-1,4-phosphinoethoxyaryl hemilabile ligands of the form (1,4-(Ph2PCH2CH2O)2-arene), where the nature and substituent pattern of the central arene ring have been systematically va...

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 ...

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, ...

A new approach to synthesizing binuclear metallomacrocycles is reported. This approach utilizes flexible bisphosphine alkyl−aryl ether hemilabile ligands which complex Rh(I) to form “condensed” mac...

Employment of a weak-link approach to the synthesis of Cu(II) metallacycle [Cu2(C8H18N4O2)2(C2H8N2)2] · 4Cl (2) from [Cu(C8H18N4O2)(Cl)]Cl · 2H2O (1) under very mild reaction conditions was achieved in high yield using a flexible hemilabile multidentate ligand, 4,7-diazadecanediamide.

Air-stable, heteroligated platinum(II) weak-link approach (WLA) tweezer and triple-layer complexes that possess P,X-Aryl hemilabile ligands (P^ = Ph2PCH2CH2-, X = chalcoethers or amines) have been synthesized via the halide-induced ligand rearrangement (HILR) reaction, using a one-pot, partial chloride-abstraction method. The approach is general and works with a variety of phosphine-based hemilabile ligands; when a P,S-Ph ligand is used as the relatively strongly chelating ligand, heteroligated complexes are formed cleanly when an ether- (P,O-Ph), amine- (P,N-Ph2), or fluorinated thioether-based (P,S-C6F4H) hemilabile ligand is used as the weakly chelating counterpart. The HILR reaction has also been used to synthesize bisplatinum(II) macrocycles free of oligomeric material without having to resort to the high-dilution conditions typical for macrocycle synthesis. This approach is complementary to the traditional WLA to the synthesis of macrocyclic complexes which typically proceeds via fully closed, chloride-free intermediates. The structures of the complexes may be toggled between semiopen (with only one chelating ligand) and fully closed (with both ligands chelating) via the abstraction and addition of chloride.

Sequential reaction of two different hemilabile ligands (Ph(2)PCH(2)CH(2)X)(2)Ar (X = S, Ar = C(6)H(4) or C(6)(CH(3))(4); X = NCH(3), Ar = C(6)H(4); X = O, Ar = 9,10-C(14)H(8)) with a Rh(I) metal center resulted in the formation of heteroligated metallomacrocycles in high yield. The specific reaction conditions for each pair of hemilabile ligands are discussed. The solid-state structure of [[1,4-(Ph(2)PCH(2)CH(2)S)(2)C(6)H(4)]-[1,4-(Ph(2)PCH(2)CH(2)S)(2)C(6)(CH(3))(4)]Rh(2)](BF(4))(2), as determined by X-ray crystallography, is presented.

The "weak-link approach" for the synthesis of metallomacrocycles has been used to synthesize a series of novel Ru(II) macrocycles in high yield. RuCl 2 (PPh 3 ) 3 has been reacted with two different phosphino-alkyl-ether hemilabile ligands, 1,4-(PPh 2 (CH 2 ) 2 O) 2 C 6 H 4 and 1,4-(PPh 2 (CH 2 ) 2 OCH 2 ) 2 C 6 H 4 . The hemilabile bidentate ligand coordinates to Ru(II) centers through both the P and O atoms to form bimetallic "condensed intermediates". The weak Ru-O bonds have been selectively cleaved with CO, 1,2-diaminopropane, and pyridine to yield large open macrocycles. This is the first example of the weak-link approach employed to synthesize macrocycles with Ru, and metal centers in general that have more than four coordination sites.

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.

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.

Herein we demonstrate a stepwise synthesis of heteroligated PtII Weak-Link Approach complexes with hemilabile N-heterocyclic carbene–thioether (NHC,S) and phosphino-thioether (P,S) ligands. These complexes, with both tweezer and triple-layer geometries, can be toggled between open, semiopen, and condensed states through the abstraction or introduction of Cl−. All species were fully characterized by multinuclear NMR spectroscopy and, in many cases, by single-crystal X-ray diffraction studies. Because the condensed tweezer and triple-layer species exhibit dynamic behavior at room temperature, the tweezer complex was studied by variable temperature NMR spectroscopy, revealing two species at low temperatures thought to be diastereomers resulting from thioether inversion. The relevant thermodynamic parameters for this exchange were determined. Competition experiments were performed to probe the lability of the P,S ligand, and the ligand scrambling that occurs in WLA systems with entirely P,S ligands was not observed in these NHC,S/P,S heteroligated complexes. In contrast to the halide-induced ligand rearrangement reaction, in which heteroligated complexes form when the electron donating abilities of the “weak links” are different, the stepwise assembly strategy described here does not require different electron-donating abilities of the “weak links”, as it makes use of a non-labile N-heterocyclic carbene–metal interaction instead.

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...