Instability heteroatom compounds

Phosphacyclobutene P-oxides 64 are produced by the reaction of titanacyclobutenes with dichlorophenylphosphine <07CEJ4077>. The large instability of heterophosphete compounds 65, composed of a four-membered unsaturated ring with a pentavalent phosphorus atom and a heteroatom, has been identified and characterised by first-principle molecular orbital computations, at several levels of theory showing that strong electron-... 

Cyclic compounds containing two S, Se, or Te atoms may display transannular or intramolecular interactions between the two heteroatoms depending on their positions. If a cation radical is generated on one of the heteroatoms, the second heteroatom can interact to stabilize the cation radical, resulting in the formation of a three-electron-bonded cation radical which further oxidizes to give a dication. Such systems joined by two positively charged heteroatoms have attracted considerable interest. The studies in this field have been hampered by the difficulty of their preparation and further by their instability. 

However, there are some noticeable problems concerning the availability of P-based macrocycles. In contrast with the common heteroatoms such as O and N the inversion barrier of P(III) is higher. So compounds containing two or more phosphorus atoms are usually obtained as a mixture of stereomers, which require separation in order to obtain the individual macrocycles. Another problem is the known instability of phosphines (the most intriguing class of ligands) to oxidation. 

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