Bis-'pincer'-cyclopalladates 1 and 2 containing an ethynediyl-or a butadiynediyl-bridge have been synthesized, characterized and used as precatalysts in the Heck reaction.
The published data on the synthesis, structure, proper-The published data on the synthesis, structure, properties and applications of dendrimers containing conjugated ties and applications of dendrimers containing conjugated p p-sys--systems, transition metal complexes and organometallic compounds tems, transition metal complexes and organometallic compounds are surveyed and systematised. The bibliography includes 83 are surveyed and systematised. The bibliography includes 83 references references. .
During the last decade there has been increasing interest in the development of new dendritic materials, 1 including organometallic dendrimers 2 and dendrimers containing conjugated π-systems. 3 These materials have a wide variety of applications, such as homogeneous catalysts, 2j-m organometallic sensors 2n or materials possessing electronic and optical properties. 2q,r In our research to construct nano-sized multimetallic materials based on tridentate 'pincer' type ligands, we are interested in rigid nano-size materials based on a hydrocarbon skeleton because they are potential homogeneous catalysts (the so-called cartwheel catalysts) which are expected to be suitable for separation from the reaction mixture by nanomembrane filtration. 4 The syntheses of new conjugated dendritic materials containing PCP-type ligands (Fig. 1) are reported here. These ligand systems are suitable for incorporation of transition-metals, giving rigid highly conjugated organometallic compounds.Compounds 1 and 2 were synthesized from 1,3,5-tribromobenzene and hexabromobenzene, respectively. The aryl bromides were converted into phosphine oxides 4 and 5 via 3-and 6-fold Sonogashira coupling reactions with 3,5-bis[(diphenylphosphinoxide)methyl]phenylacetylene (3) (Scheme 1). 5 The cross-coupling reactions were performed in THF at reflux for 100 (for 4) and 300 h (for 5) affording, after purification, 4 6 and 5 7 in 66 and 25% yield, respectively. Unfortunately, we also observed the formation * Corresponding authors.
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