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 C6H4(CH=(NBu)-Bu-n)(NO2)-4 reacts with palladium acetate to give the cyclopalladated [Pd-2{kappa(2)-C,N-C6H3(CH=(NBu)-Bu-n)-2-(NO2)-5}(2)(mu(2)-OAc)(2)] (1). This complex is hydrolyzed in the presence of bromide and 2,2'-bipyridine (bpy) or PPh3, affording the ortho-formylaryl complexes [Pd{C6H3(CHO)-2-(NO2)-5}Br(bpy)] (2) or trans-[Pd{C6H3(CHO)-2-(NO2)-5}Br(PPh3)(2)] (3), respectively. Complex 2 reacts with pyridine (py) or PPh3 in the presence of Tl(TfO) (TfO = CF3SO3), giving the cationic species [Pd{C6H3(CHO)-2-(NO2)-5}(py)(bpy)](TfO) (4) or [Pd{C6H3(CHO)-2-(NO2)-5}(bpy)(PPh3)](TfO) (5), respectively, Similarly, the compounds [Pd{C6H4C(O)X-2}Br(bpy)] [X = H (6), Me (7)] react with py and Tl(TfO) to give [Pd{C6H4C(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 PhCdropCPh, EtCdropCEt, or MeCdropCPh at room temperature result in the formation of 2,3-R,R'-5-X-1H-inden-1-ol [X = NO2, 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 degreesC for a long period of time give 2,3-R,R'-5-X-inden-1-ones [X = NO2, 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-1H-inden-1-ol [R = R' = Ph (14a), Et (14b), R = Ph, R' = Me (14c)]. Complex 9 reacts with MeCdropCPh to give 14c.