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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

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journal contribution
posted on 13.09.2002, 00:00 by José Vicente, José-Antonio Abad, Eloísa Martínez-Viviente, Peter G. Jones
We have studied the reactivity of the complexes [Pd(C6H4X-2)Br(bpy)] (bpy = 2,2‘-bipyridine; X = C(O)Me (1a), CN (1b), CHO (1c)), [Pd{C6H4CHCH2-2}(PPh3)(bpy)](TfO) (TfO = CF3SO3; 2d), trans-[Pd(C6H4X-2)Br(PPh3)2] (X = C(O)Me (3a), CN (3b), CHCH2 (3d)), and [Pd(μ-Br)(C6H4X-2)(PPh3)]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)C6H4X-2}Br(L2)] (L2 = bpy, X = C(O)Me (5a), CN (5b); L = CNXy, X = C(O)Me (6a), CN (6b), CHCH2 (6d)) and trans-[Pd{C(NXy)C6H4CHCH2-2}(CNXy)2(PPh3)](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{κ2C1,N3-C(NXy)C(NXy)C(NXy)C6H4X-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 BrC6H4X-2 and XyNC (1:1:4 molar ratio). When this oxidative addition reaction was carried out with BrC6H4CHO-2, the resulting product decomposed to give the Pd(I) complex [Pd2Br2(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{κ2C,O-C6H4{C(O)Me-2}(OH2)(PPh3)](TfO) (12a), and (iii) 4b (3:1 molar ratio) to give [Pd(C6H4CN-2)(κ2N,N-4b)(PPh3)](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.