Synthesis and Reactivity of Dipalladated Derivatives of Terephthalaldehyde

Abstract

The polynuclear complex [{μ-C1,C4,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-C1,C4,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.