Reactivity of Octahedral η¹-Allenyl Iridium toward Hard Nucleophiles

Abstract

A labile octahedral (η 1 -allenyl)iridium complex, ( OC -6-42)-Ir(Cl)(PPh 3 ) 2 (OTf)(CO)(η 1 -CHCCH 2 ) ( 2a ), undergoes regioselective addition with water or alcohol at the allenyl central carbon to generate the (η 3 -2-hydroxyallyl) and (η 3 -2-alkoxyallyl)iridium complexes {Ir(Cl)-(PPh 3 ) 2 (CO)[η 3 -CH 2 C(OR)CH 2 ]}(OTf) (R = H ( 3 ), Me ( 4a ), Et ( 4b )), respectively. The complex 3 and the η 3 -oxa-TMM species Ir(Cl)(PPh 3 ) 2 (CO)[η 3 -CH 2 C(O)CH 2 ] ( 5 ) constitutes a conjugate acid−base pair. Hydrolysis of the η 3 -alkoxyallyl complexes yields 3, which further transforms into the carbon-bound iridium enolate ( OC -6-52)-{Ir(Cl)(PPh 3 ) 2 (OH 2 )(CO)[η 1 -CH 2 C(O)CH 3 ]}(OTf) ( 6 ). The reaction of 2a with ammonia results in the substitution of NH 3 for the triflate ligand instead of hydroamination to the allenyl ligand. The construction of the C−N bond, however, is alternatively achieved by replacing the alkoxy group in 4a or 4b with the amino group, leading to the formation of the N-protonated and N-alkylated η 3 -aza-TMM iridium {Ir(Cl)(PPh 3 ) 2 (CO)[η 3 -CH 2 C(NR 2 )CH 2 ]}(OTf) (R = H ( 7a ), Et ( 7b )).