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Amphiphilic Dendrimers with Heteroleptic Bis([2,2′: 6′,2″]terpyridine)‐Ruthenium(II) Cores
Author(s) -
Joester Derk,
Gramlich Volker,
Diederich François
Publication year - 2004
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200490262
Subject(s) - chemistry , terpyridine , dendrimer , ruthenium , ligand (biochemistry) , amphiphile , pyridine , sonogashira coupling , steric effects , combinatorial chemistry , stereochemistry , polymer chemistry , crystallography , medicinal chemistry , copolymer , organic chemistry , palladium , metal , biochemistry , polymer , receptor , catalysis
A new series of dendrimers was assembled through formation of homo‐ and heteroleptic Ru II complexes with [2,2′: 6′,2″]terpyridine ligands bearing hydrophilic and hydrophobic dendrons, with the aim to develop amphiphilic vectors for potential use in gene delivery ( Scheme 1 ). The synthesis started with the preparation of the 4′‐(3,5‐dihalo‐4‐methoxyphenyl)‐[2,2′: 6′,2″]terpyridine ligands 1a , b via the Kröhnke pyridine synthesis ( Scheme 2 ), followed by attachment of dendrons 10a – 10f ( Fig. 2 ) by Sonogashira cross‐coupling to give the dendritic ligands 11 – 16 ( Schemes 3 and 4 ). Ligands were subsequently introduced into the coordination sphere of Ru III to give the stable intermediates [Ru( 11 )Cl 3 ] ( 24 ; Scheme 7 ) and [Ru( 14 )Cl 3 ] ( 27 ; Scheme 8 ). These were transformed under reductive conditions into the heteroleptic complexes [Ru( 11 )( 13 )](PF 6 ) 2 ( 25 ) and [Ru( 13 )( 14 )](PF 6 ) 2 ( 29 ). Removal of the ( tert ‐butoxy)carbonyl (Boc) protecting groups in 25 and 29 then gave the desired amphiphilic dendrimers 26 ( Scheme 7 ) and 30 ( Scheme 8 ) with branchings of generations 0 and 1. Complex formation was analyzed by high‐resolution matrix‐assisted laser‐desorption‐ionization Fourier ‐transform ion‐cyclotron‐resonance mass spectrometry (HR‐MALDI‐FT‐ICR‐MS), which provided spectra featuring unique fragment‐ion series and perfectly resolved isotope distribution patterns ( Figs. 4 and 5 ). The preparation of homo‐ and heteroleptic complexes with terpyridine ligands bearing generation‐2 dendrons failed due to steric hindrance by the bulky wedges.