Mono- and Dipalladated Derivatives of 2,5-Distyrylbenzene. Reactivity toward XyNC and Alkynes. Synthesis of Complexes with Indacenediide Ligands

The dinuclear complexes [C6H2{PdBr­(N∧N)}2-1,4-((E)-CHCHPh)2-2,5] (N∧N = tbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine (1a), tmeda = N,N,N′,N′-tetramethylethylenediamine (1b)) have been synthesized by oxidative addition of trans,trans-2,5-distyryl-2,4-dibromobenzene to 2 equiv of “[Pd­(dba)2]” (dba = dibenzylideneacetone) in the presence of the N∧N ligands. A similar reaction with N∧N = bpy = 2,2′-bipyridine afforded the mononuclear complex [PdBr­{C6H2(Br-4)­{((E)-CHCHPh)2-2,5}­(bpy)] (2). The reaction of 1a,b with PhCCPh, MeCCMe, and PhCCMe in the presence of TlOTf or AgClO4 gave the dipalladated indacenediide complexes [(μ-η,η-C12H2Bn2-1,5-R4-2,3,6,7)­{Pd­(N∧N)}2]­(OTf)2 (Bn = benzyl, R = Ph, N∧N = tbbpy (3a), tmeda (3b); R = Me, N∧N = tbbpy (4a), tmeda (4b)) and [(μ-η,η-C12H2Bn2-1,5-Ph2-2,6-Me2-3,7)­{Pd­(N∧N)}2]­(A)2 (N∧N = tbbpy, A = OTf (5a), ClO4 (5a′); N∧N = tmeda, A = OTf (5b)). The reactions of 2 with the same alkynes afforded the indenyl complexes [Pd­(η-C9H2Bn-1-R2-2,3-((E)-CHCHPh)-5-Br-6)­(bpy)]­(A) (R = Ph, A = OTf (6), ClO4 (6′); R = Me, A = OTf (7)) and [Pd­(η-C9H2Bn-1-Ph-2-Me-3-((E)-CHCHPh)-5-Br-6)­(bpy)]­OTf (8). By reaction of either 1a or 1b with XyNC (Xy = 2,6-dimethylphenyl) the dinuclear complex [C6H2{C­(NXy)­{PdBr­(CNXy)2}2-1,4-((E)-CHCHPh)2-2,5] (9) was obtained, while the oxidative addition of trans,trans-2,5-distyryl-2,4-dibromobenzene to [Pd­(dba)2] in the presence of 8 equiv of XyNC afforded the dinuclear complexes [C6H2{C­(NXy)­{C­(NXy)}2{PdBr­(CNXy)}}2-1,4-((E)-CHCHPh)2-2,5] (10, 10*) as a mixture of isomers (1:0.3 ratio) which are in slow exchange in solution, as shown by an EXSY spectrum. The crystal structures of a-3a·7CDCl3, s-3b·CH2Cl2, a-5a′·4CH2Cl2, 6, and 8 have been determined by X-ray diffraction studies.