Reactivity towards nitriles, cyanamides, and carbodiimides of palladium complexes derived from benzyl alcohol. Synthesis of a mixed Pd2Ag complex

Abstract

The chelate complex [Pd(κ²-C,O-C₆H₄CH₂O-2)(bpy)] (II) reacts with acetonitrile, cyanamides, or carbodiimides, in the presence of AgOTf (1 : 5 : 1 molar ratio) and residual water, to form complexes [Pd{κ²-C,N-C₆H₄{CH₂OC(NX)Y}-2}(bpy)](OTf), where X = H, Y = Me (1), NMe₂ (2a), NEt₂ (2b), X = R, Y = NHR (R = ⁱPr (3a), Tol (3b)), as a result of the insertion of the unsaturated reagent into the O–Pd bond of II and the protonation of one of the N atoms. In the absence of AgOTf the reaction of II with TolNCNTol (Tol = p-Tolyl) results in the formation of the neutral complex [Pd{κ²-C,N-C₆H₄{CH₂OC(NTol)NTol}-2}(bpy)] (4). Complexes 3b and 4 can be interconverted by deprotonation (3b + KO^tBu) or protonation (4 + KOTf + HOTf) reactions. When the reaction of II with TolNCNTol in the presence of AgOTf is carried out in a 1 : 1 : 1 stoichiometric ratio, or for a short period of time, a mixture of 3b and a mixed heterometallic Ag₂Pd complex 5 is obtained (5 = [Ag(N-4)₂](OTf)). Complex 5 is the major product when the AgOTf is added before the carbodiimide, and the reaction is stopped immediately. 5 can also be obtained by reaction of 4 with 0.5 equiv. of AgOTf. When complex [PdI(C₆H₄CH₂OH-2)(bpy)] (I) reacts with ⁱPrNCNⁱPr in the presence of TlOTf, instead of AgOTf, a ca. 1 : 1 mixture of 3a and [Pd{κ²-O,N-OCH₂{C₆H₄{C(NHⁱPr)NⁱPr}-2}}(bpy)](OTf) (6) forms. Complex 6 is the result of the insertion of the carbodiimide into the C–Pd bond. Complexes 1–6 have been extensively characterized by NMR spectroscopy, and the crystal structures of 2a, 3a, and 5·2.5CHCl₃·0.5Et₂O have been determined by X-ray diffraction studies.