Effect of phosphane ligands in the nucleophilic additions at iridium allenylidene complexes

Abstract

The reactivity of allenylidene complexes towards nucleophilic additions has been deeply investigated in ruthenium complexes, however, studies involving iridium complexes are scarce. Thus, several acetonitrile complexes have been synthesized as precursors for the in situ nucleophilic additions of phosphanes and amines at non-isolated allenylidene complexes of formula [IrCp*Cl(=C=C=CPh₂)(L)]PF₆ (L = PMe₃, P(OMe)_3, PPh₂(OMe), PPh₂Me, PCy₃, P(3,5-C₆H₃(CF₃)₂)₃). Therefore, addition of phosphanes as nucleophiles provided different ratios of the allenyl [IrCp*Cl{C(PR₃)=C=CPh₂}(L)]PF₆ (4·R) and alkynyl complexes [IrCp*Cl{C≡C–CPh₂(PR₃)}(L)]PF₆ (5·R) (R = Ph, OMe, Me) depending on the phosphane used as nucleophile and the one bonded to the metal center. The regioselectivity mainly arose from steric demand instead of the electronic effect of the phosphanes. The addition of amines led, in most cases, to the first substituted aminocarbene complexes [IrCp*Cl{=C(NRR')–CH=CPh₂}(L)]PF₆ (R = H, R' = Et (6); R = R' = Et (7)) with the {IrCp*Cl(PR₃)⁺} fragment; however, using a bulky phosphane such as PCy₃, formation of a second product was observed, probably an iridanaphthalene derivative [IrCp*{κ²C,C-{=C(NRR')–CH=CPh₂}(PCy₃)]PF₆ (R = H, R' = Et (8); R = R' = Et (9)).