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

Abstract

Dinuclear Pd(II) halides that contain bridging π-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 π-conjugated reagents to [Pd(styrene)(PR3)2]. Similar reactions involving dihalobenzil, dihalobithiophene, or dihaloterthiophene afforded dinuclear Pt(II) halides containing bridging π-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. π-Conjugation extension reactions of dinuclear bithiophene-bridged Pd(II) halides with HC≡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≡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 π-conjugation-extended dinuclear Pd(II) compounds bearing a π-conjugated moiety.