Carbohydrates tagged with the CCo3(CO)9 cluster †

Two synthetic routes, the direct reaction of a carbohydrate with +COCCo3(CO)9, or the reaction of Co2(CO)8 with 1,1,1-tribromomethyl sugar derivatives have been used to prepare [AcOglc = tetra-O-acetyl-D-glucopyranose, Co3 = CCo3(CO)9] 1-β-AcOglc-N-(CO)-Co3,, 2-β-AcOglc-N-(CO)-Co3,, 1-α- (16) and 1-β-AcOglc-OCH2Co3, 1-α-BnOglc-O-(CO)Co3 and 1-α- and 1-β-AcOmaltose-OCH2Co3. An unusual oxazoline cluster was isolated from the reaction with 2-aminoglucose. An X-ray structure confirmed the structure and absolute configuration of 16. Deprotection of 1-β-AcOglc-OCH2Co3 on ion exchange resin gave water soluble 1-β-glc-OCH2Co3; higher yields of water soluble complexes were obtained by direct reaction of deprotected trihalomethyl derivatives with Co2(CO)8. Dppm complexes of the OCH2Co3 glucose derivatives were also prepared. Reaction of +COCCo3(CO)9 with methyl-α-D-glucopyranoside gave the series 1-MeOglc-3-Co3, 1-MeOglc-3,6-(Co3)2, 1-MeOglc-2,3,6-(Co3)3 and 1-MeOglc-3,4,6-(Co3)3, structurally characterised by 2-D 1H and 13C NMR. The carbohydrate-cluster complexes show reversible redox activity in organic and aqueous media.