On Phosphatitanacycles

Titanocene‐phosphinidene and diphosphanediide (or diphosphene) complexes Cp 2 Ti(PMe 3 )P Mes Ter and Cp 2 Ti(P 2 Ar 2 ) (Ar=Tipp, Dipp) undergo formal [2 + 2] or [3 + 2] cycloaddition reactions with terminal alkynes, respectively, to give the corresponding 4‐ and 5‐membered phosphatitanacycles. Cp 2 Ti(PMe 3 )P Mes Ter is shown to react selectively with aryl‐substituted and aliphatic terminal alkynes to give stable phosphatitanacyclobutene species, while the reactivity of Cp 2 Ti(P 2 Ar 2 ) is restricted to aryl‐substituted terminal alkynes featuring strong electron‐withdrawing substituents in para ‐position. These metallacycles were investigated spectroscopically and crystallographically.