New Iridacyclohexadienes and Iridabenzenes by [2+2+1] Cyclotrimerization of Alkynes and Facile Interconversion between Iridacyclohexadienes and Iridabenzenes

Iridabenzenes [I r{CHCHCHCHC (CH 2 R)}(CH 3 CN) 2 (PPh 3 ) 2 ] 2+ (R=Ph 4 a , R= p ‐C 6 H 4 CH 3 4 b ) are obtained from the reactions of H + with iridacyclohexadienes [I r{‐‐CHCHCHCHC (CH‐ p ‐C 6 H 4 R′)}(CO)(PPh 3 ) 2 ] + (R′=H 3 a , R′=CH 3 3 b ), which are prepared from [2+2+1] cyclotrimerization of alkynes in the reactions of [Ir(CH 3 CN)(CO)(PPh 3 ) 2 ] + with HCCH and HCCR. Iridabenzenes 4 react with CO and CH 3 CN in the presence of NEt 3 to give iridacyclohexadienes [I r{‐‐CHCHCHCHC (CHR)}(CO) 2 (PPh 3 ) 2 ] + ( 6 ) and [I r{‐‐CHCHCHCHC (CHR)}(CH 3 CN) 2 (PPh 3 ) 2 ] + ( 7 ), respectively. Iridacyclohexadienes 6 and 7 also convert to iridabenzenes 4 by the reactions with H + in the presence of CH 3 CN. Alkynyl iridacyclohexadienes [I r{‐‐CHCHCHCHC (CH‐ p ‐C 6 H 4 R′)}(CCH)(PPh 3 ) 2 ] ( 8 ) undergo a cleavage of CC bond by H + /H 2 O to produce [I r{‐‐CHCHCHCHC (CH‐ p ‐C 6 H 4 R′)}(CH 3 )(CO)(PPh 3 ) 2 ] ( 10 ) via facile inter‐conversion between iridacyclohexadienes and iridabenzenes.