title: Dendritic ruthenium porphyrins: a new class of highly selective catalysts for alkene epoxidation and cyclopropanation.
abstract: Attachment of Fréchet-type poly(benzyl ether) dendrons [G-n] to carbonylruthenium(II) meso-tetraphenylporphyrin (5) using covalent etheric bonds forms a series of dendritic ruthenium(II) porphyrins 5-[G-n](m) (m=4, n=1, 2; m=8, n=0-2). The attachment was realized by treating the carbonylruthenium(II) complex of 5,10,15,20- tetrakis(4'-hydroxyphenyl)porphyrin or 5,10,15,20-tetrakis(3',5'-dihydroxyphenyl)porphyrin with [G-n]OSO(2)Me in refluxing dry acetone in the presence of potassium carbonate and [18]crown-6. Complexes 5-[G-n](m) were characterized by UV/Vis, IR, and NMR spectroscopy and mass spectrometry. All of the dendritic ruthenium porphyrins are highly selective catalysts for epoxidation of alkenes with 2,6-dichloropyridine N-oxide (Cl(2)pyNO). The chemo- or diastereoselectivity increases with the generation number of the dendron and the number of dendrons attached to 5, and complex 5-[G-2](8) exhibits remarkable selectivity or turnover number in catalyzing the Cl(2)pyNO epoxidation of a variety of alkene substrates including styrene, trans-/cis-stilbene, 2,2-dimethylchromene, cyclooctene, and unsaturated steroids such as cholesteryl esters and estratetraene derivative. The cyclopropanation of styrene and its para-substituted derivatives with ethyl diazoacetate catalyzed by 5-[G-2](8) is highly trans selective.
authors.affiliation: Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong Pokfulam Road, Hong Kong, China.
authors.forename: Jun-Long
authors.initials: JL
authors.lastname: Zhang
authors.forename: Hai-Bing
authors.initials: HB
authors.lastname: Zhou
authors.forename: Jie-Sheng
authors.initials: JS
authors.lastname: Huang
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Che
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D004852:Epoxy Compounds / Q000737:chemistry*; D008665:Metalloporphyrins / Q000138:chemical synthesis* / Q000737:chemistry*; D015394:Molecular Structure; D017975:Ruthenium Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D004852:Epoxy Compounds; D008665:Metalloporphyrins; D017975:Ruthenium Compounds