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.