Janus-type units

The best way to limit or prevent the tendency to chelation toward a single metal center is the use ofligands similar to Janus-type poly-NHCs (see Section 2.3), in which the carbene units point to opposite directions. In this regard, several reports deal with the ligand l,2,4-triazol-3,5-diylidene (ditz. Fig. 14) already described in Section... 

Complementary dendritic hexamers based on a central scaffold made up of linked pentaerythritol and tri(hydroxymethyl)amino methane units have been found to also exhibit liquid-crystalline properties. This star-shaped scaffold was used to create supermolecules containing two different hemispheres, referred to thereafter as Janus supermolecular Hquid crystals (Fig. 76) [323,324]. One of the hemisphere contains three cyanobiphenyl end-groups, whereas the other lobe consists of three chiral phenyl benzoate mesogenic moieties laterally attached. The type of mesophase observed (N ... 

A recent molecular design, Janus liquid-crystalline molecular materials in the form of segmented structures that contain two different types of mesogenic units has recently been reported [108,109]. Janus materials favor different types of mesophase structure, grafted onto the same scaffold, to create giant molecules that contain different hemispheres ( Janus refers to materials with two faces, such as lluorocarbon/hydrocarbon or hydro-philic/hydrophobic, etc., for example Janus amphiphilic dendrimers have been reported [110-114]). 

Most recently. Fan s group [66] readily synthesized a series of chiral diphosphane-functionahzed Janus dendrimers (up to 16 BNIAP units, 39) by using liquid-phase organic synthesis with the third-generation Frechet-type polyether dendron as the soluble support. The ruthenium complexes of these dendritic ligands were... 

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