New iridacyclohexadienes and iridabenzenes by [2+2+1] cyclotrimerization of alkynes and facile interconversion between iridacyclohexadienes and iridabenzenes

Iridabenzenes Ir=CHCH=CHCH=C(CH2R)](CH3CN)2(PPh3)2]2+ (R=Ph 4 a, R=p-C6H4CH3 4 b) are obtained from the reactions of H+ with iridacyclohexadienes Ir-CH=CHCH=CHC(=CH-p-C6H4R')](CO)(PPh3)2]+ (R'=H 3 a, R'=CH3 3 b), which are prepared from 2+2+1] cyclotrimerization of alkynes in the reactions of Ir(CH3CN)(CO)(PPh3)2]+ with HCtriple chemical bond]CH and HCtriple chemical bond]CR. Iridabenzenes 4 react with CO and CH3CN in the presence of NEt3 to give iridacyclohexadienes Ir-CH=CHCH=CHC(=CHR)](CO)2(PPh3)2]+ (6) and Ir-CH=CHCH=CHC(=CHR)](CH3CN)2(PPh3)2]+ (7), respectively. Iridacyclohexadienes 6 and 7 also convert to iridabenzenes 4 by the reactions with H+ in the presence of CH3CN. Alkynyl iridacyclohexadienes Ir-CH=CHCH=CHC(=CH-p-C6H4R')](-Ctriple chemical bond]CH)(PPh3)2] (8) undergo a cleavage of Ctriple chemical bond]C bond by H+/H2O to produce Ir-CH=CHCH=CHC(=CH-p-C6H4R')](-CH3)(CO)(PPh3)2] (10) via facile inter-conversion between iridacyclohexadienes and iridabenzenes.