Bridged (β-alkoxyalkyl)CoIII(salen) complexes by intramolecular alkoxycobaltation of unactivated alkenes: new models for coenzyme B12

Addition of Sn–OiPr across a C═C Bond: Unusual Insertion of an Alkene into a Main-Group-Metal–Alkoxide Bond

“…The Wacker process and oxymercuration are well-known examples that involve addition of metal (Pd or Hg) and oxygen across CC bonds. Insertion of alkenes into metal–oxygen bonds has been reported also for other transition metals, such as Ir, Rh, Pt, and Au, − as well as cobalt porphyrin systems . In spite of these many examples, we found only one report for a main-group metal: addition of Ge–ONR 2 across a CC bond, which proceeded via stabilized Ge­(III) and TEMPO radicals …”

“…Insertion of alkenes into metal−oxygen bonds has been reported also for other transition metals, such as Ir, Rh, Pt, and Au, 3−6 as well as cobalt porphyrin systems. 7 In spite of these many examples, we found only one report for a maingroup metal: addition of Ge−ONR 2 across a CC bond, which proceeded via stabilized Ge(III) and TEMPO radicals. 8 Considering the importance of alkene oxygenation, we were interested if other metal−oxygen bonds are capable of adding across CC bonds.…”

Photolytic and thermal properties of a new series of intramolecular bridged alkyl cobaloxime complexes

“…Thus the recombination reaction between Co II -complex and carboncenter radical is easier to proceed as compared to the nonbridged complexes. 5,[15][16][17][18] (b). In our bridged alkylcobaloximes, the observed photolyic rate constants increase with decreasing pK a values of the L ligands, i.e.…”

“…In 1980 the first kinds of bridged organocobalt(III) complexes were synthesized and the products of 1,2-rearrangement reaction from photolysis were characterized by Rétey et al 13,14 However, in the past years only a few of cobaloximes, Cosalen and Cocosta complexes with bridged structures have been reported. [15][16][17][18][19][20] It is well recognized that the necessary step in the coenzyme B 12 dependent enzymatic reactions is homolytic cleavage of the Co-C bond, generating a Co(II) species and a 5-deoxyadenosyl radical. Like the above enzyme reactions, photolysis or thermolysis of the 5-adenosylocobalamin and its analogues leads to homolytic cleavage of the Co-C bond.…”

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“…Complex 131 is proposed as a simple model for co-enzyme B 12 . 56 Buta-1,3-diene, C-2-bonded to an enantiomerically pure Co(III) salen complex derived from cyclohexane-1,2-diamine (132) undergoes Diels-Alder reaction with dimethyl fumarate with extremely high diastereofacial selectivity. After reductive cleavage with NaBH 4 , the cyclohexene 133 is obtained in > 98% ee.…”