Organotransition metal modified sugars

Preparation and characterization of rhenium(I) compounds with amino ester derivatized diimine ligands. Investigations of luminescence. Crystal structures of Re(CO)3Cl(pyca-β-Ala-OEt) and Re(CO)3Cl(pyca-l-Asp(OMe)-OMe)

“…The unequal populations observed in our work may be attributed to the fact that Re(CO) 5 Cl is achiral and Table 3 Selected bond lengths (Å ) and bond angles (°) for 2 and 5 2 5…”

“…They were easily purified giving air-stable, bright orange, crystalline compounds in 47-86% yield. Initial attempts at synthesis were employed using readily prepared Re(CO) 5 Br. It was found that the bromide ligand undergoes partial metathesis with the chloride from the amino acid ester hydrochloride salts in refluxing methanol.…”

“…It was found that the bromide ligand undergoes partial metathesis with the chloride from the amino acid ester hydrochloride salts in refluxing methanol. Re(CO) 5 Br was abandoned as a reagent in favor of Re(CO) 5 Cl ending the problem.…”

“…Good yields were obtained for the compounds when prepared without NEt 3 , presumably because attachment of the diimine to the metal drives the equilibrium between the diimine and the aldehyde and amine to the right. Also, it was recently reported that condensation reactions between amines and pyridine aldehydes or pyridine ketones were accelerated by the presence of Re(CO) 5 Cl. This acceleration occurs because the aldehyde or ketone is bound as a bidentate ligand (bound through the pyridine nitrogen and the carbonyl oxygen), which is rapidly attacked by primary amines yielding the diimine [26].…”

“…Various biological classes of compounds have been examined including steroids [2,3], sugars [4,5], nucleobases [6,7], and receptor molecules [8]. The diverse properties available to organometallic compounds, including paramagnetism [9], the infrared spectra of metal carbonyls [10], photoinduced electron transfer [11], and c-emission [12] or b-emission [13] from radioactive nuclei, provide hope that novel bioconjugates could be used as biomarkers or for therapeutic purposes.…”