Hypervalent chalcogen compounds

Department of Material Science and Chemistry, Faculty of Systems Engineering, Wakayama University, 930 Sakaedani, Wakayama 640-8510, Japan 

The main purpose of this chapter is to review the development of hypervalent chalcogen chemistry after the book of Chemistry of Hypervalent Compounds edited by Akiba (1999).5 Although several types of compounds may belong to hypervalent ions or molecules by the definition,3a such hypervalent chalcogen compounds (E = S, Se, and Te) will be mainly discussed here that contain CT-type linear bonds.15 

What is the region of bond distances for hypervalent bonds of chalcogens Bond orders of hypervalent 3c-4e are typically around 0.5. A bond distance with a bond order of 0.5 is predicted to be 0.18 A longer than that with a bond order of 1.0.16 

The O-S-X 3c-4e type interactions are summarized by Kucsman and Kapovits.17 They concluded that the SO distance of 1.65-2.25 A belonged to the hypervalent region, with a covalent S-O single bond region of 1.56-1.65 A and an S -O nonbonded interaction region of 2.03-3.25 A, where 3.25 At corresponds to the sum of van der Waals radii of S and O. du Mont et al. proposed that the Se-I distance of 2.60-3.00 A was the typical 3c-4e region, with a predominantly covalent region of less than 2.60 A and a secondary bond 

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Many optically active hypervalent chalcogen compounds, particularly sulfur compounds, have been synthesized and proposed as important key intermediates in various reactions of the chalcogen compounds.46 Since the synthesis of spirosulfurane by Kapovits and Kalman,47 many optically active spir-osulfuranes were isolated in the last decade. Spirosulfurane 28 was separated into enantiomers by kinetic resolution using a chiral host molecule and found to be optically stable by Drabowicz and Martin.48 Spirosulfurane 29 was separated into enantiomers by chromatographic method by Allenmark and Claeson, and characterized by chiroptical methods.49 Optically active... 

TBP are four-coordinated, whereas MC are three. Therefore, the bulkiness around E will be more severe for TBP than for MC. The increased bulkiness around E prefers MC to TBP.21b e Namely, it is possible to prepare hypervalent chalcogen compounds other than those predicted from the general rule based on x, by modulating electronic and/or steric conditions around chalcogens in organic chalcogen compounds. 

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