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.

3H-Phosphaallenes Revisited: Facile Synthesis by Hydroalumination of Alkynylphosphines and β-Elimination, Stability and Trapping of Transient Species by Coordination to Transition Metal Atoms

A facile method for the efficient synthesis of 3H-phosphaallenes, R-P=C=C(H)-R', is presented, which comprises treatment of dialkynylphosphines with dialkylaluminium hydrides (hydroalumination) and elimination of aluminium alkynides from intermediate alkenyl-alkynylphosphines. The stability of the phosphaallenes depends on steric shielding by the substituents at phosphorus (aryl or CH(SiMe₃ )₂ groups). Only supermesityl compounds are persistent at room temperature in solution. This simple method starting with easily accessible dialkynylphosphines and commercially available aluminium hydrides (HAlEt₂ , HAliBu₂ ) allows the generation of transient species, which were trapped by coordination to transition metals. The η¹ -coordination via a P-W bond was observed for tungsten, while the side-on coordination via the P=C bond resulted with platinum. Decomposition of the mesityl derivative yielded an unprecedented product, which may be formed by 1,3-H shift to the P atom, hydrophosphination of the P=C bond of a second phosphaallene and formation of a P-P bond.

Hydroalumination of alkynyl-aminophosphines as a promising tool for the synthesis of unusual phosphines: P–N bond activation, a transient phosphaallene, a zwitterionic AlP2C2heterocycle and a masked Al/P-based frustrated Lewis pair

Hydroalumination of alkynyl-aminophosphines afforded an AlP₂C₂heterocycleviaP–N bond activation and a transient phosphaallene.

Alkynyl functionalized Al/P-based frustrated Lewis pairs – aluminium alkynide elimination and evidence for the formation of 3H-phosphaallenes [R-PCC(H)-tBu]

Hydroalumination of dialkynylphosphines by H-Al[CH(SiMe₃)₂]₂afforded alkenyl–alkynyl phosphines which eliminate dialkylaluminium alkynides spontaneously to form phosphaallenes, aryl-PCC(H)-^tBu.