Cryptate ligands

Ca can be complexed by crown ethers and cryptate ligands and ia this form can be transported across natural and artificial membranes. 

The subject molecules are obtained as dinuclear copper complexes with the octa-aza cryptate ligands L1 and L2 shown in Scheme 1. 

A system related to OBISDIEN is the cryptate ligand OBISTREN... 

Bz C,lmn benzyl cryptate ligand with /-, m-, and w-membered rings (also Imn crypt)... 

As with amide hydrolysis reactions, extensive mechanistic studies of metal-mediated phosphate monoester hydrolysis reactions have been performed using exchange inert mononuclear Co(III) complexes.9,188-202 To date, only a few zinc complexes that promote phosphate monoester hydrolysis have been reported. A binuclear zinc complex supported by a macrocyclic cryptate ligand (Fig. 36)... 

Fig. 2. Structures of some cryptate ligands (stability constants of their complexes...

Fig. 26) (230). This led to a Mn11 complex having a square prismatic geometry. The second complex is composed of a cryptate ligand that yields a complex with a cubic symmetry (Fig. 27) (231). The third structure is built up from two tetradentate tripodal amine ligands about the Mn I ions (Fig. 26) (232). 

Preliminary kinetic results on cation exchange in cryptates [ligand (21)] show some correlation with thermodynamic parameters, but only go a small way towards the complete elucidation of the mechanism. Metal replacement in complexes of macrocyclic ligands is also illustrated by studies of several metalloporphyrins. ... 

The synthesis of phosphorus analogues of cryptate ligands such as (5.392) seems not unlikely in the near future. Like the multidentate nitrogen ligands, they may be expected to stabilise certain ions by encapsulation. Diphosphate crown ethers such as (5.393) have already been reported. These compounds are fairly easy to make (5.394). 

An octadentate cryptate ligand (Scheme 23a) is well suited for a cubic coordination sphere, as illustrated in Scheme 23(b). However, even such an apparently well-preorganized donor set can be twisted to less obvious geometries, such as the one adopted in 10-coordinate complexes shown in Scheme 23(c). Tentacular octadentate... 

Sepulchrate complexes of other metal ions have been prepared. Thus [Pt(IV)(sep)] has been isolated and can be reduced to give a long-lived platinum(III) transient in aqueous solution. Photophysics of [Cr(III)-(sep)] have also been reported. In a study of the Eu(III)/(II) couple using the related cryptate ligand system, reductions of [Eu(2.2.1)] and [Eu(2.2.2)] by and Cr " are slow enough to be monitored polarographi-cally. Self-exchange rates of 10M" s 4 x 10 s and 5x... 

The approach cannot ordinarily yield ABA copolymers because poly(oxyethylene)oxy anions are unable to activate most vinyl monomers for sequential polymerization. However, in the presence of a strong base complexed with crown ether or cryptate ligands, POE chains with NHCH2Ph or OH end groups become sufficiently nucleophilic to initiate the polymerization of methyl and t-butyl methacrylates giving triblock polymers with central POE segments. ... 

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