Dendritic Carbosilanes Containing Silicon-Bonded 1-[C6H2(CH2NMe2)2-3,5-Li-4] or 1-[C6H3(CH2NMe2)-4-Li-3] Mono- and Bis(amino)aryllithium End Groups: Structure of {[CH2SiMe2C6H3(CH2NMe2)-4-Li-3]2}2

The fixation of bis(2-pyridylimino)isoindolato (BPI) ligands to dendritic carbosilanes

Bis(2-pyridylimino)isoindolato (BPI) ligands, containing an alkynyl linker unit which allows their fixation to carbosilane dendrimers and dendrons, were synthesized by reaction of 4-nitrophthalodinitrile with 4-butynol giving the phthalodinitrile derivative containing the linker. These were subsequently reacted with two molar equivalents of 2-amino-4-methylpyridine and 2-amino-4-(t)butylpyridine yielding the respective BPI protioligands 2a and 2b. Lithiation with LDA and reaction with Si-Cl or Si-OTf (OTf=triflate) end groups in core or peripheral positions of dendritic carbosilanes gave the endodendrally and expdendrally functionalized dendrimers. Among these the first and second generation dendrimers [G-1](8-exo)-4-[C[triple bond, length as m-dash]CCH2CH2O]-10-MeBPI (8), [G-1]12-exo-4-[C[triple bond, length as m-dash]CCH2CH2O]-10-MeBPI (9) and [G-2](16-exo)-4-[C[triple bond, length as m-dash]CCH2CH2O]-10-MeBPI (10) were synthesized and fully characterized. The functional dendrimers were metallated by reaction with [(PhCN)2PdCl2] in dichloromethane to give the corresponding pallada-dendrimers.

New mono- and tricyclopalladated dendritic systems with encapsulated catalytic sites

The preparation of a series of new macrocyclic carbodiazasilane molecules functionalized with the monoanionic [2,6-(CH2NMe2)2C6H3](-)[triple bond]N,C,N-pincer ligand has been accomplished. Palladation of these systems was possible through oxidative addition with [Pd(dba)2] affording exclusive formation of the meso diastereoisomer. The X-ray crystal structures of these novel ligands and of the palladium(II) complex 10 were determined and confirmed the stereochemistry of the organopalladium cage. Attachment of the para-OH functionalized carbodiazasilane macrocycle 16 to a central core led to the formation of the dendritic structure 18 which was palladated to afford the novel multimetallic dendritic system with encapsulated catalytic sites 1. This cyclopalladated carbosilane dendrimer (1) as well as the mononuclear organopalladium cage 10 can be conveniently converted into active Lewis acid catalysts for the aldol condensation reaction. The catalytic data showed higher reaction rates for the dendritic structure than for the corresponding mononuclear systems.

Polycationic (mixed) core-shell dendrimers for binding and delivery of inorganic/organic substrates

The convergent synthesis of a series of polycationic aryl ether dendrimers has been accomplished by a convenient procedure involving quantitative quaternarization of aryl(poly)amine core molecules. The series has been expanded to the preparation of the first polycationic, mixed core-shell dendrimer. All these dendrimers consist of an apolar core with a peripheral ionic layer which is surrounded by a less polar layer of dendritic wedges. These cationic, macromolecular species have been investigated for their ability to form assemblies with (anionic) guest molecules. The results obtained from UV/Vis and NMR spectroscopies, and MALDI-TOF-MS demonstrate that all the cationic sites throughout the dendrimer core are involved in ion pair formation with anionic guests giving predefined guest/host ratios up to 24. The large NMR spectroscopic shifts of resonances correlated with the groupings located in the core of the dendrimers, together with the relaxation time data indicate that the anionic guests are associated with the cationic core of these dendrimers. The X-ray molecular structure of the octacationic, tetra-arylsilane model derivative [Si(C6H3[CH2NMe3](2)-3,5)4]8+. 8I- shows that the iodide counterions are primarily located near the polycationic sphere. The new polycationic dendrimers have been investigated for their catalytic phase-transfer behavior and substrate delivery over a nanofiltration membrane.

Synthesis of periphery-functionalized dendritic molecules using polylithiated dendrimers as starting material

A general method for the functionalization of Si-Cl terminated carbosilane dendritic molecules via organolithium or organomagnesium reagents is described. Quantitative exchange of the bromine atoms of 4-bromophenyl-functionalized dendrimers affords polylithiated species that are valuable starting materials for further functionalization, e.g., into pyridyl alcohols. The latter were successfully applied as catalyst precursors in a ruthenium-mediated ring-closure metathesis reaction.