Aspects of Phosphaallene Chemistry: Heat-Induced Formation of 1,2-Dihydrophosphetes by Intramolecular Nucleophilic Aromatic Substitution and Photochemical Generation of Tricyclic Phosphiranes

3H-Phosphaallenes are accessible
on a new and facile route and
show a fascinating chemical behavior. The thermally induced rearrangement
of Mes*PCC­(H)­R′ (R′ = tBu, Ad) afforded by C–H activation, isobutene elimination,
and C–C and P–H bond formation bicyclic 1-benzo-dihydrophosphetes
(2) with PC3 heterocycles. DFT calculations
suggest a mechanism with intramolecular nucleophilic aromatic substitution
and replacement of an alkyl group by the nucleophilic α-C atom
of the phosphaallene. These bicycles formed W­(CO)5 complexes
(3) or afforded 1,2-dihydrophosphetes with P-bound alkenyl
groups by catalyst-free hydrophosphination of alkynes (4 and 5). The resulting bulky phosphines formed complexes
with IrCp*Cl2, RuCl2, AuCl, or CuO3SCF3. The Ru atom is coordinated by the P atom and a phenyl
group. Irradiation of TripPCC­(H)tBu led by the insertion of the central C atom of the PCC
group into the α-C–H bond of an iPr substituent and by C–C
and P–C bond formation to a new isomer of phosphaallenes, 10, which features a strained PC2 heterocycle.
It formed adducts with M­(CO)5 (M = Cr, Mo, W) and AuCl
and reacted with SO2Cl2 by cleavage of one of
the phosphirane P–C bonds to yield PC4 or PC5 heterocycles. Hydrolysis yielded a PC5 compound
with a P­(O)Cl group.