Geometrically constrained phosphenium cations

Geometrically constrained P(III) species have been shown to react with small molecules,
e.g. NH3, H2O, ROH, and HBPin.1 In an attempt to prepare a more reactive analogue of
these species we designed their cationic version. Herein we show the first geometrically
constrained phosphenium cation (GCPC) (1) and its reactivity with small molecules
(H2O, ROH, R2NH and NH3) (Scheme 1; top).2 To prepare a more reactive GCPC we
attempted to substitute the pyridine central donor to a carbene one, i.e. OCO-type ligand
(2). However, all the attempts to insert P atom into OCO ligand in which the central donor
is the saturated carbene resulted in imidazolinium ring opening and rearrangement of
rings, leading to three distinct products (3, 4 and 5) (Scheme 1; bottom). 3, 4 and 5 are
interesting compounds in their own right and currently under investigation in our lab.