Chalcogen compounds

The stabihty of organic chalcogen compounds decreases mosdy ia the order sulfur > selenium > tellurium. 

Vibrational spectra of transition metal chalcogen compounds. K, H. Schmidt and A. Muller, Coord. Chem. Rev., 1974,14,115-179 (326). 

A plethora of stoichiometries and structural types are found for the chalcogen compounds of the Group 5 metals. Phases approximating to the composition MX have the NiAs-type structure, whereas the MX2 compounds have layer structures related to M0S2, Cdl2, or CdCl2 types. Sometimes complex layer sequences occur in which the 6-coordinate metal atom is alternatively octahedral and trigonal prismatic. 

Figure 1 Nomenclature of phosphorus-chalcogen compounds (names in brackets refer to the anionic deprotonatedform). R = alkyl, aryl E — S, Se, Te...

The least studied of these two cycles are the tetra-chalcogen compounds [P(E)(EH)(/i-NR)]2 for which only the sulfur analogue (E = S) 37 has been reported. It can be prepared as its ammonium salt from reaction of di-thiophosphonic acid chloride betaine (py.PS2Cl py = pyridine) and one equivalent of primary amine in the presence of NEt3 (Equation 54).66,67... 

Recent Developments in Binary Halogen-Chalcogen Compounds, Polyanions and Polycations... 

Similar to S2C12 or Se2Cl2, which react with [Ti(C5H5)2S5] and [Ti(C5H5)2Se5] to produce cyclic seven-membered chalcogen compounds (S7, l,2-Se2S5, and... 

Synthesis and Stereochemistry of Optically Active Chalcogen Compounds... 

In this chapter, recent development on the synthesis and stereochemistry of optically active chalcogen compounds over the last 10 years will be described, focusing mainly on chiral selenium and tellurium compounds. 

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... 

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... 

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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