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 HC[triple chemical bond]CH and HC[triple 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')](-C[triple chemical bond]CH)(PPh3)2] (8) undergo a cleavage of C[triple 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.

Stable alkynyl complexes of iridium(III) (L(n)Ir-triple bond-R) that are prepared from the reactions of terminal alkynes readily undergo the intramolecular C-C bond-forming reactions between the alkynyl and adjacent hydrocarbyl ligands to yield conjugated olefins. These reactions are initiated by electrophiles (H(+), Me(+)) that attack the beta carbon of the alkynyl ligand to increase the electrophilicity of the alpha carbon of the alkynyl ligand. The C-C bond is then formed between the alpha carbons of the alkynyl and adjacent hydrocarbyl ligands.

Reactions of the iridacyclopentadienes (2a) and (2b) with RC⋮CH (R = C6H5, p-C6H4CH3) give linear conjugated dienynes (RC⋮CCHCHCHCH2 (3) and (5)) and benzene derivatives (RC6H5 (4) and RC6H3C6H8 (6, 6-aryl-1,2,3,4-tetrahydronaphthalene)). Linear conjugated dienynes 3 and 5 are exclusively obtained from the reactions of alkynyl iridacyclopentadienes (7) and (8) (R = C6H5 (a), p-C6H4CH3 (b), cyclohex-1-enyl (c)) with HOTf, respectively. The di- and trinuclear alkynyl iridacyclopentadienes (9a), (9b), and (10) (L3 = (CO)(PPh3)2) react with HOTf to produce the extended and conjugated dienynes p-C6H4(C⋮CCHCHCHCH2)2 (11), (12), and m,m-C6H3(C⋮CCHCHCHCH2)3 (13), respectively, in high yields. Iridacyclohexadienes (17, R‘ = H (a), CH3 (b)) are obtained from the reactions of 7 with HBF4 through a C−C bond-forming reaction between the α-carbons of alkynyl and 1,3-butadiene-1,4-diyl ligands. Plausible reaction pathways are suggested for the C−C bond-forming reaction between RC⋮CH and 1,3-butadiene-1,4-diyl ligands of iridacyclopentadienes to produce linear dienynes.

Reactions of cis-dihydrido complex [Ir(H) 2 (NCCH 3 ) 2 (PPh 3 ) 2 ] + (1) with HCtCH and RCt CH (R ) C 6 H 5 , p-C 6 H 4 CH 3 , cyclohex-1-enyl, C(CH 3 )dCH 2 , C(CH 3 ) 3 ) produce cross-conjugated hexatrienes (RCHdC(CHdCH 2 ) 2 , R-HEX) and octatetraenes (H 2 CdCH-CRdCH-C(-CHd CH 2 )dCHR, R 2 -OCT). Two molecules of HCtCH are inserted into Ir-H bonds of 1 to give cis-bis (ethenyl) from which R-HEX-d 1 are obtained in the presence of a base. Di-and trinuclear alkynyl-bis(alkenyl) complexes [L 5 Ir-CtCp-C 6 H 4 -CtC-IrL 5 ] (7, L 5 ) (-CHdCH 2 ) 2 (CO)(PPh 3 ) 2 ) and [L 5 Ir-CtC-m,m-C 6 H 3 -(CtC-IrL 5 ) 2 ] (8, L 5 ) (-CHdCH 2 ) 2 (CO)(PPh 3 ) 2 ) react with H + to produce extended cross-conjugated olefins, p-C 6 H 4 -(HEX) 2 and m,m-C 6 H 3 -(HEX) 3 , respectively, in high yields. Plausible reaction pathways involve alkenyl-vinylidene complexes that undergo the C-C bond formation reaction between the two hydrocarbyl ligands to produce the cross-conjugated olefins.

Iridabenzenes are produced by an unusual C-C coupling between the R-carbon of the alkynyl ligand and the δ-carbon of the neighboring 1,3-butadienyl ligand upon protonation of the β-carbon of the alkynyl ligand.