Synthesis and Reactivity of Dipalladated Derivatives of Terephthalaldehyde.

The polynuclear complex [{μ- C 1, C 4, N , N ″-C 6 H 2 {C(H)=N( n Bu)} 2 -2,5}{Pd(μ-OAc)}] 2 ( I ) reacts with tbbpy (4,4'-di- tert -butyl-2,2'-bipyridine) and TlOTf to form the dinuclear complex [{μ- C 1, C 4, N , N ″-C 6 H 2 {C(H)=N( n Bu)} 2 -2,5}{Pd(tbbpy)} 2 ] ( 1 ). The hydrolysis of I with acetic acid in a 5:1 acetone/water mixture, in the presence of two equivalents of tbbpy and excess NaX (X = Br, I), yields the dipalladated terephthalaldehyde complexes [C 6 H 2 {PdX(tbbpy)} 2 -1,4-(CHO) 2 -2,5] [X = Br ( 2a ), X = I ( 2b )], which are the first fully characterized complexes of this type. The reaction of 2a,b with CO results in the insertion of CO into both aryl-Pd bonds, forming [C 6 H 2 {C(O){PdX(tbbpy)}} 2 -1,4-(CHO) 2 -2,5] [X = Br ( 3a ), X = I ( 3b )], which are the first examples of complexes with CO inserted into two separate aryl-metal bonds involving the same ligand. The bromo complex 2a reacts with excess XylNC in acetone, causing the precipitation of the dinuclear complex 2,3,6,7-tetrahydrobenzo[1,2- c :4,5- c ']dipyrrole-1,5-dione-2,6-dixylyl-3,7-bis{=C(NHXyl)-C(=NXyl)-[PdBr(CNXyl) 2 ]} ( 4 ), which is the result of the insertion of three molecules of the isocyanide into each aryl-Pd bond and the nucleophilic attack of one of them at each formyl group. When complex 4 reacts with TlOTf and residual water in 1,2-dichloroethane at 70 °C, depalladation occurs, and the organic compound 2,3,6,7-tetrahydrobenzo[1,2- c :4,5- c ']dipyrrole-1,5-dione-2,6-dixylyl-3,7-bis{=C(NHXyl)-C(O)NHXyl} ( 5 ) can be isolated. The crystal structures of 1 ·4CHCl 3 , 4 ·2CH 2 Cl 2 ·3hexane, and 5 ·2CDCl 3 have been determined by X-ray crystallography.