Linker ligands

Fluoroarene-Cr(CO)2L complexes 33p [L = CO, PPh3, P(OPh)3, P(pyrrolyl)3, P(pyrolyl)2 (NMeBn)], where L is a potential linker ligand for solid-phase synthesis, have been evaluated with regard to the rates of nucleophilic substitution by amines [35]. The preparative and kinetic results indicate that SNAr reactions on tris(pyrrolyl)phosphine-modified fluoroar-enechromium complexes proceed rapidly and with high efficiency, and are thus appropriate for the development of solid-phase versions for use in combinatorial synthesis (Scheme 18). 

The short peptide linker ligand is specifically designed to be cleaved by the target enzyme in order to enable enzyme detection. Dissociation of the aggregates... 

A second strategy investigated by Stang et al. [79,83] is the use of a C2h diaza-bisheterocycle as linker ligand, such as 2,6-diazaanthracene (DAA) 43 and 2,6-diazaanthracene-9,10-dione (DAAD) 44, as opposed to the D2d or D2h symmetrical ligands commonly used in molecular squares. 

Another approach in preparing porous materials is to combine two types of linker ligands within the same structure. Thus, bimetallic tetracarboxylate units M2(02CR)4... 

Fig. 12 Combination of different metal (Cu or Zn ) with different size of linker ligands L (a-d) to result in 3D MOF with open channels almig the c axis...

Owing to the different size of linker ligands a-d, the resulting frameworks possessed open channels of varied sizes from 4.3 X 4.8 to 10.8 x 10.8 A. Polymerization of styrene was performed using 9a-d and lOb-d as hosts at 70°C. Since styrene has a slightly larger dimension than the channels in 9d and lOd, as expected, no conversion was observed when these two frameworks were used (Table 3). Most importantly, the molecular weight distribution (i.e., polydispersity index Mw/Mn) of polystyrenes produced within the nanochannels was narrower than... 

Figure 3.20 The formation of both (a) an M4L4 molecular square and (b) an M3L3 molecular triangle using semi-protected vertices and a flexible linker ligand.

Covalent PSM this involves eovalent modification of a linker ligand and is the most well-developed type of PSM in MOF chemistry. 

Inorganic PSM this involves a modification of the secondary building units (SBUs), which form the nodes of the MOF network, and includes substitution of the metal centers or linker ligands. 

PSM can also be used to transform the connectivity in a MOF, by joining together two linker ligands. For example. Stock and coworkers showed... 

Dative PSM involves the postsynthetic coordination of a metal center to one of the linker ligands. Examples of dative PSM reactions are summarized in Table 2. 

Benzene-1,4-dicarboxylic acid (H2bdc) is one of the most commonly utilized ligands in MOF chemistry, being the linker ligand for MOF-5. Deprotonated carboxylic acids or carboxylates are hard donors and are... 

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