Study of the Reactivity of 2-Acetyl-, 2-Cyano-, 2-Formyl-, and 2-Vinylphenyl Palladium(II) Complexes. Mono- and Triinsertion of an Isocyanide into the Pd−C Bond. A 2-Cyanophenyl Palladium Complex as a Ligand

We have studied the reactivity of the complexes [Pd(C 6 H 4 X-2)Br(bpy)] (bpy = 2,2‘-bipyridine; X = C(O)Me ( 1a ), CN ( 1b ), CHO ( 1c )), [Pd{C 6 H 4 CH CH 2 -2}(PPh 3 )(bpy)](TfO) (TfO = CF 3 SO 3; 2d ), trans- [Pd(C 6 H 4 X-2)Br(PPh 3 ) 2 ] (X = C(O)Me ( 3a ), CN ( 3b ), CH CH 2 ( 3d )), and [Pd(μ-Br)(C 6 H 4 X-2)(PPh 3 )] 2 (X = C(O)Me ( 4a ), CN ( 4b )). Their reactions with XyNC (Xy = 2,6-dimethylphenyl) depend on the nature of X and the other ligands and on the reaction conditions. The products of these reactions are mono- and triinserted complexes. Among the former are [Pd{C( NXy)C 6 H 4 X-2}Br(L 2 )] (L 2 = bpy, X = C(O)Me ( 5a ), CN ( 5b ); L = CNXy, X = C(O)Me ( 6a ), CN ( 6b ), CH CH 2 ( 6d )) and trans- [Pd{C( NXy)C 6 H 4 CH CH 2 -2}(CNXy) 2 (PPh 3 )](TfO) ( 7d ). The reaction of 1c with XyNC (1:5 molar ratio) gives 10, a product resulting after substitution of bpy, coordination of two molecules of XyNC, triinsertion of XyNC, and a cyclization resulting after the attack of the nitrogen of the first inserted molecule at the carbon atom of the formyl group. The complexes [Pd{κ 2 C 1, N 3 -C( NXy)C( NXy)C( NXy)C 6 H 4 X-2}Br(CNXy)] (X = C(O)Me ( 8a ), CN ( 8b )) were obtained by reacting (i) 3a or 3b with XyNC (1:4 molar ratio) or (ii) Pd(dba) 2 (dba = dibenzylideneacetone) with BrC 6 H 4 X-2 and XyNC (1:1:4 molar ratio). When this oxidative addition reaction was carried out with BrC 6 H 4 CHO-2, the resulting product decomposed to give the Pd(I) complex [Pd 2 Br 2 (CNXy) 4 ] ( 9 ). Tl(TfO) was reacted with (i) 8a and 8b (1:1 molar ratio) to give the corresponding triflato complexes 11a and 11b, (ii) 4a (1:2 molar ratio) in the presence of moisture to give the cyclopalladated aquo complex [Pd{κ 2 C, O- C 6 H 4 {C(O)Me-2}(OH 2 )(PPh 3 )](TfO) ( 12a ), and (iii) 4b (3:1 molar ratio) to give [Pd(C 6 H 4 CN-2)(κ 2 N, N- 4b )(PPh 3 )](TfO) ( 13b ), in which 4b behaves as a ligand through the two cyano groups. The crystal structures of 5b, 6b, 7d, 8a, b, 9, 10, 11a, b, 12a, and 13b have been determined by X-ray diffraction studies.