Intramolecularly alkylated salen complexes: new models for coenzyme B12 with a cobalt-to-ligand carbon bridge

Abstract

The synthesis of Hzsalen (2.2'-[ethane-I ,2-diylbis(nitrilomethylidyne)]diphenol} derived models 1 for coenzyme B,, with a carbon bridge between the ligand and cobalt has been accomplished by condensation of salicylaldehyde and o-substituted 1,2-diamines 8 followed by complexation with Co", reduction to Co' complexes, and intramolecular alkylation. The structures of intramolecularly alkylated Co(salen) complexes with a bridge of three, 1 b, and of four methylene groups, Ic, have been investigated by N M R spectroscopy and determined by X-ray crystallography.

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

“…10 The exact geometry of complex 9 was not determined; however, in view of the results mentioned above, a structure with a chair- 20) is considered most likely. Its 1 H NMR spectrum displays a specific highfield signal at Ϫ0.46 ppm, similar to the signal at Ϫ0.49 ppm reported for an (alkyl)-Co(salen) complex with a trimethylene bridge, 6 and assigned unambiguously by NOE experiments to the pseudo-equatorial β-proton of the bridge [H(18)] which is antiperiplanar with respect to cobalt. Oxidation of cobalt() complex 6e in methanol follows a somewhat different course.…”

“…4 This accords with the finding that distances from Co to the putative radical centres on the substrate or substrate analogues in crystal structures of methylmalonyl-CoA mutase range from 6 to 7 Å. 5 We are interested in the formation and subsequent cleavage of the cobalt-carbon bond in model complexes 6 for B 12 in which an alkenyl substituent is attached to the equatorial ligand and thus forced to stay in close proximity to the cobalt centre during reactions. The reaction of cobalt species with unactivated alkenes is very unusual in the chemistry of B 12 and structural models thereof.…”

“…For 6a-c, bond formation between Co() and the internal sp 2 -carbon would lead to a Co III (salen) derivative with a two-carbon bridge which is too strained to exist as a stable compound. 6 Application of intramolecular alkoxycobaltation to prepare a bridged [ -(2-hydroxy)ethoxyalkyl]Co III (salen) complex: a simple model of coenzyme B 12 with a built-in substrate B 12 -Model complexes to which a substrate (or model thereof) is connected, can be used to test for the possible occurrence of cobalt-substrate interactions in coenzyme B 12 -dependent enzymatic rearrangements. In that vein, intramolecular alkoxycobaltation was used to prepare a bridged Co III (salen) complex with a built-in glycol unit positioned in such a way that, after homolysis of the Co-C bond, a 1,5-H shift could initiate a 1,2radical rearrangement.…”

Structure determination of two metal-organic complexes from high-resolution synchrotron powder diffraction data

“…Tetrahydrofurfurylbromide was prepared according to a published procedure (Smith, 1955). (Tetrahydrofurfuryl)Co(3-mesalen) was synthesized by using the procedure for (n-butyl)Co(salen) (van Arkel et al, 1993).…”

Cobalt (III) Complexes as Novel Matrix Metalloproteinase-9 Inhibitors

“…The synthesis of 3 started with 6-heptenoic acid. Addition of iodine azide, prepared in situ from sodium azide and iodine monochloride, 15 followed by subsequent azide addition produced 11 in a 87% yield. Compound 11 was coupled with 4-biphenyl methylamine (16) using a peptide coupling agent to give 12 in a 96% yield.…”