Hypervalent- and hypovalent phosphorus (III) compounds based on diazaphosphapentalenes: New types of bonding interaction, positional isomerism, and conjugated associates

GRAPHICAL ABSTRACT

ABSTRACT

3a,6a-Diaza-1,4-diphosphapentalene (DDP) displays extraordinary properties compared to the usual azaphospholes. It possesses a much higher coordination activity with metal ions, which is caused by a novel type of complexation. The heteroaromatic 10π-electron system provides two electrons for P → M bond formation, whereas the phosphorus lone pairs are not involved in the coordination. Interaction of DDP with its 1,4-dichloro-derivative results in formation of extended conjugated associates with intermolecular interactions combining π-stacking and N-P-hypervalent bonding between neighboring blocks. DDP reacts with halocarbons to give addition products to one or to both phosphorus atoms depending on substrate. Adducts of DDP with carbenes and their heavier analogs (R₂E:) show two types of coordination: with planar or pyramidal geometry of the E element. A new family of hypervalent phosphorus compounds derived from 3,5-dimethyl-1-phenyl-1H-pyrazole have been synthesized. The main feature of these compounds is the quite short N–P bond lengths, which are close to normal N–P single bonds. Solutions of phenylpyrazole-based compounds containing hypervalent phosphorus reveal a mixture of positional isomers, which are in equilibrium.

KEYWORDS:

• Diazaphospholes
• heteropentalenes
• low-coordinate phosphorus
• hypervalent phosphorus compound

Funding

This work was supported by the Russian Science Foundation, grant no. 14-13-01015.