Untitled

Abstract

Metal ion coordination chemistry is well suited to dynamic combinatorial chemistry approaches. [1±3] Diverse metal ion complex libraries can be created simply by mixing a labile metal ion with different ligands. [4] If ligand exchange is rapid, these metal ion complexes form the equilibrating components of a dynamic library. The equilibrium between complexes may be shifted upon addition of molecular targets. For example, small molecule or biopolymer targets perturb the equilibrium between metal ion complexes to increase the concentration of the metal ion complex that best binds the target. [5±7] We previously reported on dynamic combinatorial libraries of metal ion Schiff-base complexes of limited diversity. [8] Our selection protocol utilizes extraction of metal ion complex libraries from aqueous into organic solvent. In this method, the organic solvent is the ultimate target and complexes with the greatest stability and solubility in organic solvent versus aqueous solution are selected. [9] Here we present studies using acylhydrazone ligand libraries and show that these libraries lead to improvements in efficiency and selectivity of metal ion extraction in comparison to single ligand systems.Acylhydrazone ligands (Scheme 1) were chosen to explore the possibility of forming a double-orthogonal library [4] by exchange at metal±ligand (MÀL) and C¼N bonds. [10±13] Initial studies were carried out to establish the feasibility of using these exchange processes. Zn II extracts into chloroform from a buffered aqueous solution in the presence of two equivalents of acylhydrazone ligand 1 (Table 1, Scheme 1). The predominant complex that extracts into chloroform is the neutral complex [Zn(1 À ) 2 ] as determined by comparison of 1 H NMR and mass spectral data to that of an authentic sample. After two hours, the extent of extraction of Zn II from a water/chloroform mixture containing 0.0500 mm [Zn(1 À ) 2 ] is identical within experimental error to a second experiment containing 0.0500 mm Zn(NO 3 ) 2 and 0.100 mm 1, confirming that our system is at equilibrium. Addition of a different acylhydrazone ligand (13) to either of the solutions above followed by stirring for 2 h increases the amount ZUSCHRIFTEN 4270

Behavior of a Dynamic Covalent Library Driven by Combined Pd(II) and Biphasic Effectors for Metal Transport between Phases

“…This last point lays the foundations for a genuine paradigm shift in the liquid-liquid extraction of metals through the adaptive in situ construction of an extractant molecule. [17][18][19] However, the effect of a cation in biphasic systems is not as straightforward because of four main reasons: (1) Components and constituents are distributed in the two phases; therefore, they can access two media with different physical properties. It has already been reported with an acetonitrile/water mixture that a phase separation can induce a redistribution of a DCL, promoting the formation of lipophilic and hydrophilic constituents (respectively in the organic phase and water), antagonistic amphiphilic constituents being consumed.…”

“…Thus, their dynamic covalent behavior has been exploited in the design of DCLs in numerous studies. [12][13][14][16][17][18][29][30][31] In previous work, [17] a [1×2] acylhydrazone-based DCL has been developed and investigated with copper(II) nitrate in water/chloroform biphasic system. It was shown that the addition of Cu(II) triggered a covalent redistribution of the DCL as well as the partial extraction of copper into the organic phase.…”

“…The move to two‐phase environments holds out the prospect of various developments not only in the fundamental understanding of DCL behavior in a complex fluid environment, but also in the development of applications such as adaptive liquid‐liquid separation. This last point lays the foundations for a genuine paradigm shift in the liquid‐liquid extraction of metals through the adaptive in situ construction of an extractant molecule [17–19] . However, the effect of a cation in biphasic systems is not as straightforward because of four main reasons: (1) Components and constituents are distributed in the two phases; therefore, they can access two media with different physical properties.…”

“…Moreover, their formation is reversible and they can undergo reversible transhydrazination reaction. Thus, their dynamic covalent behavior has been exploited in the design of DCLs in numerous studies [12–14,16–18,29–31] …”