Preparation, Structural Analysis, and Reactivity Studies of Phosphenium Dications

This work expands on the recent synthesis
and reactivity of the
two-coordinate P­(III)-containing dication [((Ph3P)2C)­P­(NiPr2)]2+ (3a2+). Two additional dications of general
formula [((RPh2P)2C)­P­(NR′2)]2+ (3b2+, R = 1/2
(CH2)3, R′ = iPr; 3c2+, R = Ph, R′ = Cy) have been prepared.
Solution and solid-state 31P NMR isotropic shifts for this
dication class were observed around 360 ppm. Except for [3a]­[SbF6]2, the 31P CP/MAS NMR spectra
reveal a high degree of structural disorder around the dicationic
site in the solid state. Surprisingly, the synthesis of dication 3a2+ was only possible in the presence
of AlCl4–, SbF6–, and substituted tetraarylborates, while the use of ClO4–, OTf–, BF4–, PF6–, and BPh4– resulted in complex product mixtures. Single-crystal X-ray analysis
of dications 3a2+ and 3c2+ suggested a 4π allyl-like structure
for the central CPN fragment, and this has been supported through
detailed theoretical investigations. Initial reactivity studies between
dications 3a2+/3c2+ and PMe3 show an equilibrium
between the free dication and the target adduct. Furthermore, 3a2+ has been shown to be capable
of O–H bond activation using water and methanol and polymerizes
THF when it is dissolved in this solvent.