Silane-based dendrimers

Scheme 5. Silane-based dendrimers containing at the periphery metal-silicon o-bonds.

Scheme 6. van Koten s construction of a silane-based dendrimer functionalized at the periphery with arylnickel(ll) catalytically active sites. 

Scheme 8.8. Silane-based dendrimers have been used for scaffolding of ferrocenyl units described as noninteracting redox centers.

Employment of silane protective groups has facilitated the preparation of polyester-based dendrimers. 

More efficient OLEDs have been reported for phosphorescent tris-cyclometalated homoleptic Ir(III) complex Ir(TPSppy)3 (TPSppy = 2 — (4 -(triphenylsilyl)biphenyl-3-yl)pyridine) with a silane-based dendritic substituent (Fig. 32) [133]. This dendrimer has shown high luminescence efficiency both in solution (0p = 0.63) and in film (0p = 0.74). A polymer-based triplet OLED with this Ir(III) doped emitter exhibits a remarkable efficiency of 32.8cdA maximal brightness of... 

Siloxanes, prepared in 1989 as representatives of silicon-based dendritic molecules ( silicodendrimers ), were the first dendrimers to contain heteroatoms other than the usual ones (N, O, S, halogens) [68]. As with the phosphodendri-mers (Section 4.1.10), their readily modifiable architecture and their pronounced thermostability hold promise of applications, for example, in the form of carbo-silanes as liquid-crystalline materials and catalyst supports. They can be subdivided into a number of basic types and their properties are presented below with the aid of characteristic representatives ... 

Repetitive silicon-based transformations were then employed for dendritic construction. Palladium-catalyzed silane hydroxylation of the core 71 afforded triol 73, which was then treated with three equivalents of monochloropolysiloxane 72 to generate the hexa-hydrido, first generation dendrimer 74. Further application of the Pd-mediated hydroxylation, followed by attachment of monochloro-monomer 72, led to the second (75) and third (76) generation polysiloxane cascades. 

This approach has also been employed for synthesis of highly enan-tiomerically enriched cychc silanes with sihcon-centered chirahty [141]. Zhang et al. [142] prepared second-generation dendrimers based on polyhedral silsesquioxane cores with up to 72 terminal groups at their surface (Scheme 13). 

A new divergent synthesis of tribranched phosphorus-containing dendrimers and their metal-containing counterparts was recently proposed [7]. It is based on the acid-base hydrolysis of aminosilanes with derivatives containing OH groups. The preparation involved the reaction of a bifunctionalized silane such... 

Knapen JWJ, Van der Made AW, de Wilde JC, van Leeuwen PWNM, Wijkens P, Grove DM, van Koten G. Homogeneous catalysts based on silane dendrimers functionalized with arylnickel (II) complexes. Nature 1994 372 659-663. 

P. Wijkens, D.M. Grove, G. Van Koten et al. - Homogeneous Catalysts Based on Silane Dendrimers Functionalized with Arylnickel (II) complexes. 

Irrespective of these differences, both approaches have proved to be extremely successful for the preparation of dendritic macromolecules. By the use of either the divergent or convergent growth approaches a number of different groups have prepared dendrimers based on a wide variety of functional groups i.e. dendritic poly(amides) (5), poly(etherketones) (6), poly(amines) (7), poly(phenylenes) (8), poly(silanes) (9), poly(phosphonium salts) (10), poly(esters) (11), poly(phenylacetylenes) (12), poly(alkanes) (13), etc. Interesting variations on this theme have been the preparation of optically active dendrimers (14), dendritic poly(radicals) (15), and dendrimers based on co-ordination chemistry with... 

Another system based on electrostatic interactions has been reported by van Koten and coworkers [36]. A core-shell dendrimer with a cationic tetra[bis(benzyIammonium)aryl]silane core has been used as a template for the... 

---