Molecular studies of organometallic carbohydrates and related compounds.

Armishaw, Olga Anne

Abstract

The molecular conformations of novel organometallic compounds by single crystal X-ray diffraction have been elucidated. Results have been correlated with spectroscopic data from both the solid and solution state. Five stannylated carbohydrates were studied (three pyranose and two furanose compounds). l,2;3,4-di-O-isopropylidene-6-O-triphenylstannylmethyl-alpha-D-galactopyranose shows the tin in a distorted tetrahedral environment and the pyranose ring in a twist-boat conformation. Only slight changes in conformation between the solid and solution state were observed. l,6-anhydro-3,4-O-isopropylidene-2-O- [(triphenylstannyl)methyl]-beta-D-galactopyranose shows tetrahedral geometry about the tin atom and the pyanose ring has a 1C4 conformation. The tin atom in bis [6-O-(l,2:3,4-di-O-isopropylidene- alpha-D-galactopyranosyl)methyl] phenyltin iodide is pentacoordinated in the solid state as a result of one of the sugar moieties acting as a C,O bidentate ligand. There is no evidence of this chelation occuring in solution. The two furanose tin carbohydrates, 6-deoxy-1,2-O- isopropylidene-6-(triphenylstannyl)-a-D-glucofuranose and (S)-Sn-(5-deoxy- l,2-O-isopropylidene-5-C-diiodophenyl-a-D-xylofuranose both show twist conformations for the ftiranose rings. However, the tin centres are somewhat different, with the triphenylstannyl possessing distorted tetrahedral geometry whereas the diiodo compound has trigonal bipyramidal tin geometry as a result of chelate formation. The tin centre in the diodo compound is chiral and can be designated (S). Methyl 4,6-O-benzylidene-3-deoxy-3-diphenylarsino-alpha-D-altropyranoside and methyl 4,6-O-benzylidene-3-deoxy-3-C-diphenylphosphinyl-alpha-D-altropyranoside are analogues and methyl 4,6-O-benzylidene-2-deoxy-2-diphenylphosphinyl-alpha-D-altropyranoside is a structural isomer of the latter. All compounds show the pyranose ring in the 4C1 conformation. 5-Deoxy-5-C-diphenylarsino-l,2-O- isopropylidene-3-O-p-tosyl-alpha-D-xylofuranose exhibits a furanose ring conformation of 3T2 in solution but an O4 envelope in the solid state. The arsenic atom in both carbohydrates lies in a pyramidal arrangement. Of the five non-metallated carbohydrates studied, three possess furanose rings. The furanose rings in l,2-O-isopropylidene-5-(p-toluenesulphonyl)-alpha-D-xylofiiranose and methyl 2,3-O-isopropylidene-5,6-bis-O-methylsulphonyl-alpha-D-mannofuranoside adopt the envelope conformation in the solid state. The furanose ring in methyl-2,3-O-isopropylidene-5-O-p-tosyl-beta-D-ribofuranoside adopts a flattened half-chair conformation. The two other non-metallated carbohydrates, phenyl 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranoside and 4,6-0- ethylidene-2,3-di-O-methanesulphonyl-alpha-D-glucopyranosyl chloride both possess pyranose rings with a 4C1 conformation. Conformational mobility has been examined by molecular graphics for two of the non-metallated carbohydrates: 1,2-O-isopropylidene-5-(p-toluenesulphonyl)-alpha-D-xylofuranose and phenyl 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranoside. By varying the conformations of the molecules, lower energy structures were found and geometrical comparisons made with the original X-ray data.

Citation

ARMISHAW, O.A. 1997. Molecular studies of organometallic carbohydrates and related compounds. Robert Gordon University, PhD thesis. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-2807283

• Thesis Type: Thesis
• Deposit Date: May 12, 2025
• Publicly Available Date: May 12, 2025
• DOI: https://doi.org/10.48526/rgu-wt-2807283
• Public URL: https://rgu-repository.worktribe.com/output/2807283
• Award Date: Aug 31, 1997