Convergent and Divergent Noncovalent Synthesis of Metallodendrimers

Abstract

A new building block is constructed with one pyridine and two kinetically inert complexed Pd(II) ions, for the controlled assembly of metallodendrimers following either a convergent or a divergent route. The double pincer ligand 8 was cyclopalladated with Pd[CH3CN]4(BF4)2 and subsequently converted into the neutral bis-palladium chloride complex 3. The pyridine moiety of 3, that is covalently attached to the spacer bridging the two pincer complexes, coordinates to activated palladium centers. Via a combination of pyridine- (3) and cyano-based (2) building blocks, dendrons up to generation three were assembled and characterized with 1H NMR and FT-IR spectroscopy and MALDI-TOF mass spectrometry. These dendrons can coordinate through a cyano ligand to an activated nucleus 1 forming convergently assembled metallodendrimers. Alternatively, building blocks 3 were used in the divergent assembly of more stable metallodendrimers, because of the stronger coordination of pyridine compared to cyano ligands. The formation of metallodendrimers is evidenced by IR and 1H NMR spectroscopy and electro spray and MALDI-TOF mass spectrometry.

Surface-Confined Metallodendrimers: Isolated Nanosize Molecules

“…The 1 H NMR spectra of both MG 1 and MG 2 clearly reflected the coordination of the pyridine ligands with a shift of the a-pyridine protons from d 8.54 to d 8.30, similar to the previously reported metallodendrimer synthesis. [14] The successful formation of the dendritic assemblies was further confirmed by the presence of the molecular peaks minus a BF 4…”

“…The pincer ligand was introduced by reaction of 2 with 3 [13] in the presence of a base. Ligand 4 was subsequently treated with two equivalents of [Pd(CH 3 [14] was added (Scheme 2). This complex coordinates to the palladium center through the pyridine moiety.…”

“…The number of dendrimers on the surface increased with time and seems to level off (Figure 2 To achieve insight into the specificity of the binding of the dendrimer two control experiments were performed with slightly modified compounds, that is, a second generation dendrimer without sulfide chain (G 2,py ) [14] and with a dendrimer in which the sulfide chain is replaced by an alkyl chain (MG 2,C22 ). These compounds do not bind to the substrate at all (Figure 1 b), which strongly indicates that MG 1 and MG 2 bind to the gold substrate through the sulfide moiety (Figure 3).…”

Radiolabeled Dendrimers as Potential PET Agents for Molecular Imaging of Tumor Angiogenesis

“…They can be used as biomimetic catalysts, drug carriers, gene delivery and can also be used in boron neutron capture therapy [27][28][29][30]. The dendrimers are considered potentially advantageous due to their numerous surface functional groups, relatively low immunogenicity and also their size, which is very close to various important biological polymers.…”

Plastic- and liquid-crystalline architectures from dendritic receptor molecules

“…Many convergent and divergent synthetic routes have been developed, in which the convergent approach especially is successful in achieving a high purity and monodispersity of the macromolecules (6,7). Recent alternative approaches involve the coupling of the generations of the dendrimer by metal coordination, to give ''metallodendrimers'' (8,9). The spherical shape of dendrimers is thought to exist in solution, but little is known about their shape in the solid state, although this physical parameter is undoubtedly of great influence on their unique physical properties.…”