Synthesis and Reactivity toward Alkynes of 2-Formyl- and 2-Acetylarylpalladium(II) (Aryl = Phenyl and 5-Nitrophenyl) Complexes. Formation of Indenols and Indenones

The imine C 6 H 4 (CH N n Bu)(NO 2 )-4 reacts with palladium acetate to give the cyclopalladated [Pd 2 {κ 2 -C,N-C 6 H 3 (CH N n Bu)-2-(NO 2 )-5} 2 (μ 2 -OAc) 2 ] ( 1 ). This complex is hydrolyzed in the presence of bromide and 2,2‘-bipyridine (bpy) or PPh 3, affording the ortho -formylaryl complexes [Pd{C 6 H 3 (CHO)-2-(NO 2 )-5}Br(bpy)] ( 2 ) or trans -[Pd{C 6 H 3 (CHO)-2-(NO 2 )-5}Br(PPh 3 ) 2 ] ( 3 ), respectively. Complex 2 reacts with pyridine (py) or PPh 3 in the presence of Tl(TfO) (TfO = CF 3 SO 3 ), giving the cationic species [Pd{C 6 H 3 (CHO)-2-(NO 2 )-5}(py)(bpy)](TfO) ( 4 ) or [Pd{C 6 H 3 (CHO)-2-(NO 2 )-5}(bpy)(PPh 3 )](TfO) ( 5 ), respectively. Similarly, the compounds [Pd{C 6 H 4 C(O)X-2}Br(bpy)] [X = H ( 6 ), Me ( 7 )] react with py and Tl(TfO) to give [Pd{C 6 H 4 C(O)X-2}(py)(bpy)](TfO) [X = H ( 8 ), Me ( 9 )]. The reactions of the neutral complex 2 or 6 with Tl(TfO) and the alkynes PhC⋮CPh, EtC⋮CEt, or MeC⋮CPh at room temperature result in the formation of 2,3-R,R‘-5-X-1 H -inden-1-ol [X = NO 2, R = R‘ = Ph ( 10a ), Et ( 10b ), R = Ph, R‘ = Me ( 10c ); X = H, R = R‘ = Ph ( 11a ), Et ( 11b ), R = Ph, R‘ = Me ( 11c )]. By contrast, the reactions of the cationic complex 4 or 8 with the same alkynes at 90 °C for a long period of time give 2,3-R,R‘-5-X-inden-1-ones [X = NO 2, R = R‘ = Ph ( 12a ), Et ( 12b ), R = Ph, R‘ = Me ( 12c ); X = H, R = R‘ = Ph ( 13a ), Et ( 13b ), R = Ph, R‘ = Me ( 13c )]. This contrasting behavior is discussed and compared with the result of the reaction of the 2-acetylarylpalladium(II) complex 7 with the same alkynes which renders 2,3-R,R‘-1-methyl-1 H -inden-1-ol [R = R‘ = Ph ( 14a ), Et ( 14b ), R = Ph, R‘ = Me ( 14c )]. Complex 9 reacts with MeC⋮CPh to give 14c .