Dinuclear Pd(II) and Pt(II) compounds bearing a bridging π-conjugated moiety: synthesis and reactivity toward alkynes and isocyanides

Dinuclear Pd(II) halides that contain bridging pi-conjugated groups, trans,trans-[(PR3)(2)(X)Pd-Y-Pd(X)(PR3)(2)] (X = Br; YH2 = terpyridine, fluorenone, benzil, benzthiadiazole), were prepared by the oxidative addition of corresponding dihalo pi-conjugated reagents to [Pd(styrene)(PR3)(2)]. Similar reactions involving dihalobenzil, dihalobithiophene, or dihaloterthiophene afforded dinuclear Pt(II) halides containing bridging pi-conjugated groups. Additionally, when the dihalosilole derivatives {2,5-dibromo-1,1-dimethyl (or diphenyl)-3,4-diphenylsilole} reacted with [Pd(styrene)(PR3)(2)], mono or dinuclear Pd(II) complexes bearing a dimethyl (or diphenyl)-3,4-diphenylsilole group were obtained. pi-Conjugation extension reactions of dinuclear bithiophene-bridged Pd(II) halides with HC equivalent to C-R {R = SiPh3, C(O)OMe} in the presence of CuI and HNEt2 led to the unexpected formation of bis(acetylide) Pd(II) complexes of the form, [Pd(C equivalent to C-R)(2)(PR3)(2)] and bithiophene. In contrast, treatment of the dinuclear Pd(II) halides with two equiv of organic isocyanide resulted in isocyanide insertion into the Pd - C bonds to afford pi-conjugation-extended dinuclear Pd(II) compounds bearing a pi-conjugated moiety.