58 / 2023-08-15 04:56:10

Cationic Complexes of 3a,6a-Diaza-1,4-diphosphapentalenes

diazadiphosphapentalenes; phosphenium cations; diazaphospholes

New Technologies in Phosphorus Chemistry > 1) New reagents and methods in organophosphorus Chemistry

Among all known organophosphorus heterocycles, 3a,6a-diaza-1,4-diphosphapentalenes (DDP) are distinguished by their high p-donor ability and form charge transfer complexes with organic p-acceptors [1]. A study of the coordination activity of DDPs showed that these heterocycles cannot only function as p-donors, but can also act themselves as p-acceptors at the deficiency of electron density.

The reactions of 1,4-dichloro-3a,6a-diaza-1,4-diphosphapentalenes (DDPCl₂) with 1 equiv. of trimethylsilyl triflate (TMSOTf) lead to replacement of one chlorine atom with the triflate group, thus giving cationic diazadiphosphapentalenes [ClDDP]⁺[TfO]⁻. In the presence of 2 equiv. of TMSOTf and 2 equiv. of 4-dimethylaminopyridine (DMAP), the DDP dication (1) stabilized by two DMAP molecules, is formed [2]. The DMAP molecules are located on one side of the DDP skeleton and lie in parallel planes.

The same reaction of DDPCl₂ with TMSOTf in the presence of free DDP lead to an unusual class of a two-deck dicationic DDPs (2), whose structure is determined by the balance between the interdeck 18πe aromaticity and the covalent P-P bonding [3]. The total energy of the dication [(DDP)₂]²⁺ as a function of the P∙∙∙P separation has a minimum at the P-P distance of 2.85 Å. This distance corresponds to the highest aromaticity index in the interdeck space (NICS(1.0) = -20.72). The energy of interdeck interactions is estimated at 10–15 kcal/mol.



Reference

[1] N. Zolotareva, et al, ChemPlusChem, 2023, 88(2), e202200438.

[2] V. V. Sushev, et al, Rus. J. Coord. Chem., 2023, 49, 218.

[3] V. Sushev, et al, Eur. J. Inorg. Chem. 2023, e202300252.

This work was supported by the Russian Science Foundation (Grant 19-13-00400-P).