title: Steric control of organic transformation by a dendrimer cage: organocobalt dendrimer porphyrins as novel coenzyme B(12) mimics.
abstract: Cobalt(II) complexes of poly(aryl ester) dendrimer porphyrins (m-[Gn]TPP)Co(II) and (p-[Gn]TPP)Co(II) (n = 0-3) underwent AIBN-initiated alkylation (AIBN = 2,2'-azobis(isobutyronitrile)) at the metal center with propargyl alcohol in CDCl(3) at 60 degrees C, where the dendritic substituents did not affect the overall conversion rate but selectivity of the alkylation. With the largest (m-[G3]TPP)Co(II), a single organocobalt(III) species (Co(III)-C(=CH(2))CH(2)OH, 4) was selectively formed in 91% yield, due to a steric protection of 4 by the large dendrimer cage from the access of another molecule of cobalt porphyrin species. In contrast, with other cobalt(II) porphyrins, isomerized compounds such as Co(III)-C(CH(3))=CHOH (5) and Co(III)-CH(CH(3))CHO (6) were formed in addition to 4. A stereochemical investigation with (m-[G3]TPP)Co(II) using AIBN-d(12), in place of nondeuterated AIBN, demonstrated that the alkylation (cobalt(III) hydride addition to propargyl alcohol) is selective to a trans adduct. Results also indicated that this addition step does not involve external activation of propargyl alcohol.
authors.affiliation: JST ERATO Nanospace Project, National Museum of Emerging Science and Innovation Building, 2-41 Aomi, Koto-ku, Tokyo 135-0064, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Uyemura
authors.forename: Takuzo
authors.initials: T
authors.lastname: Aida
mesh_terms: D000478:Alkylation; D000480:Alkynes / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry*; D003038:Cobamides / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D018716:Molecular Mimicry; D019906:Nuclear Magnetic Resonance, Biomolecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D020005:Propanols / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013237:Stereoisomerism
chemical_list: D000480:Alkynes; D003038:Cobamides; D009942:Organometallic Compounds; D011166:Porphyrins; D020005:Propanols; D003035:Cobalt; C028255:propargyl alcohol; C000913:cobamamide