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-Ph-2-(C3HN2)] (2) {Fc = (eta(5) -C5H5)Fe(eta(5)-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 Na-2[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)} Cl-2(dmso)] (3), the cis-isomers of [M{1-(Fc-CH2)-3,5-Ph-2-(C3HN2)}Cl-2(dmso)] {M = Pt (4) or Pd (7)}, trans-[Pd{1-(Fc-CH2)-3,5-Ph-2-(C3HN2)}(2)Cl-2] (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-[(eta(5)-C5H4)Fe{(eta(5)-C5H4)-CH2]-3,5-Ph-2-(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(sp(2), phenyl) in 9 or the C(sp(2), 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 Na-2[PdCl4] and NaAcO density functional theory (DFT) calculations of the complexes have also been carried out.