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<INF>6</INF>H<INF>4</INF>(CH&dbd;NⁿBu)(NO<INF>2</INF>)-4 reacts with palladium acetate to give the cyclopalladated [Pd<INF>2</INF>{κ²-C,N-C<INF>6</INF>H<INF>3</INF>(CH&dbd;NⁿBu)-2-(NO<INF>2</INF>)-5}<INF>2</INF>(μ²-OAc)<INF>2</INF>] (<BO>1</BO>). This complex is hydrolyzed in the presence of bromide and 2,2‘-bipyridine (bpy) or PPh<INF>3</INF>, affording the ortho-formylaryl complexes [Pd{C<INF>6</INF>H<INF>3</INF>(CHO)-2-(NO<INF>2</INF>)-5}Br(bpy)] (<BO>2</BO>) or trans-[Pd{C<INF>6</INF>H<INF>3</INF>(CHO)-2-(NO<INF>2</INF>)-5}Br(PPh<INF>3</INF>)<INF>2</INF>] (<BO>3</BO>), respectively. Complex <BO>2</BO> reacts with pyridine (py) or PPh<INF>3</INF> in the presence of Tl(TfO) (TfO = CF<INF>3</INF>SO<INF>3</INF>), giving the cationic species [Pd{C<INF>6</INF>H<INF>3</INF>(CHO)-2-(NO<INF>2</INF>)-5}(py)(bpy)](TfO) (<BO>4</BO>) or [Pd{C<INF>6</INF>H<INF>3</INF>(CHO)-2-(NO<INF>2</INF>)-5}(bpy)(PPh<INF>3</INF>)](TfO) (<BO>5</BO>), respectively. Similarly, the compounds [Pd{C<INF>6</INF>H<INF>4</INF>C(O)X-2}Br(bpy)] [X = H (<BO>6</BO>), Me (<BO>7</BO>)] react with py and Tl(TfO) to give [Pd{C<INF>6</INF>H<INF>4</INF>C(O)X-2}(py)(bpy)](TfO) [X = H (<BO>8</BO>), Me (<BO>9</BO>)]. The reactions of the neutral complex <BO>2</BO> or <BO>6</BO> with Tl(TfO) and the alkynes PhC&tbd1;CPh, EtC&tbd1;CEt, or MeC&tbd1;CPh at room temperature result in the formation of 2,3-R,R‘-5-X-1H-inden-1-ol [X = NO<INF>2</INF>, R = R‘ = Ph (<BO>10a</BO>), Et (<BO>10b</BO>), R = Ph, R‘ = Me (<BO>10c</BO>); X = H, R = R‘ = Ph (<BO>11a</BO>), Et (<BO>11b</BO>), R = Ph, R‘ = Me (<BO>11c</BO>)]. By contrast, the reactions of the cationic complex <BO>4</BO> or <BO>8</BO> 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<INF>2</INF>, R = R‘ = Ph (<BO>12a</BO>), Et (<BO>12b</BO>), R = Ph, R‘ = Me (<BO>12c</BO>); X = H, R = R‘ = Ph (<BO>13a</BO>), Et (<BO>13b</BO>), R = Ph, R‘ = Me (<BO>13c</BO>)]. This contrasting behavior is discussed and compared with the result of the reaction of the 2-acetylarylpalladium(II) complex <BO>7</BO> with the same alkynes which renders 2,3-R,R‘-1-methyl-1H-inden-1-ol [R = R‘ = Ph (<BO>14a</BO>), Et (<BO>14b</BO>), R = Ph, R‘ = Me (<BO>14c</BO>)]. Complex <BO>9</BO> reacts with MeC&tbd1;CPh to give <BO>14c</BO>.