Platinum(ii) and palladium(ii) complexes derived from 1-ferrocenylmethyl-3,5-diphenylpyrazole. Coordination, cyclometallation or transannulation?

Abstract

The synthesis and characterization of the novel pyrazole derivative [1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)] (2) {Fc = (η⁵–C₅H₅)Fe(η⁵–C₅H₄)–} with a ferrocenylmethyl substituent on position 1 of the heterocycle is described. The study of the reactivity of 2 with cis-[MCl₂L₂] (M = Pt and L = dmso or M = Pd and L = dmso or CH₃CN), Pd(AcO)₂ or Na₂[PdCl₄] under different experimental conditions, has allowed us to isolate and characterize a wide variety of platinum(II) or palladium(II) complexes: trans-[Pt{1-(Fc–CH₂)-3,5-Ph₂-(C₃HN₂)}Cl₂(dmso)] (3), the cis- isomers of [M{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}Cl₂(dmso)] {M = Pt (4) or Pd (7)}, trans-[Pd{1-(Fc–CH₂)-3,5-Ph₂–(C₃HN₂)}₂Cl₂] (8), the cyclometallated compounds [M{1-(Fc–CH₂)-(3–C₆H₄)-5-Ph–(C₃HN₂)}Cl(L)] {with M = Pt and L = dmso (5) or PPh₃ (6) or M = Pd and L = PPh₃ (9)} and the palladium(II) complex [Pd{1-[(η⁵–C₅H₄)Fe{(η⁵–C₅H₄)–CH₂]-3,5-Ph₂–(C₃HN₂)}Cl(PPh₃)] (10) that arises from a transannulation process. The crystal structures of the free ligand 2 and compounds 4, 7, 9 and 10 are also reported and confirm the cis- disposition of the Cl⁻ ligands in 4 and 7, the trans- arrangement of the phosphorous and the nitrogen atoms in 9 and 10, the mode of binding of the ligand in 4, 7, 9 and 10 and the nature of the metallated carbon atom {C(sp², phenyl) in 9 or the C(sp², ferrocenyl) of the C₅H₅ ring in 10}. In order to rationalize the different nature of the products isolated in the reactions of 2 with Pd(AcO)₂ or Na₂[PdCl₄] and NaAcO density functional theory (DFT) calculations of the complexes have also been carried out.