Providing support in favor of the existence of a Pd(II)/Pd(IV) catalytic cycle in a Heck-type reaction.

The complex [Pd(O,N,C-L)(OAc)], in which L is a monoanionic pincer ligand derived from 2,6-diacetylpyridine, reacts with 2-iodobenzoic acid at room temperature to afford the very stable pair of Pd(IV) complexes (OC-6-54)- and (OC-6-26)-[Pd(O,N,C-L)(O,C-C(6)H(4)CO(2)-2)I] (1.5:1 molar ratio, at -55 °C). These complexes and the Pd(II) species [Pd(O,N,C-L)(OX)] and [Pd(O,N,C-L')(NCMe)]ClO(4), (X = MeC(O) or ClO(3), L' = another monoanionic pincer ligand derived from 2,6-diacetylpyridine), are precatalysts for the arylation of CH(2)=CHR (R = CO(2)Me, CO(2)Et, Ph) using IC(6)H(4)CO(2)H-2 and AgClO(4). These catalytic reactions have been studied and a tentative mechanism is proposed. The presence of two Pd(IV) complexes was detected by ESI(+)-MS during the catalytic process. All the data obtained strongly support a Pd(II)/Pd(IV) catalytic cycle.

Synthesis, isolation, and characterization of an organometallic triiodopalladium(IV) complex. Quantitative and regioselective synthesis of two C-I reductive elimination products.

Iodine and the pincer complex [Pd(O,N,C-L)I], where L is the monoanionic ligand resulting from deprotonation of the acetyl group of the dimethylmonoketal of 2,6-diacetylpyridine, are in equilibrium at low temperatures with the palladium(IV) complex [Pd(O,N,C-L)I(3)], which can be isolated at -40 °C and characterized by (1)H NMR spectroscopy and X-ray diffraction studies, in spite of its great instability. When the same reaction is carried out at room temperature, a quantitative reductive elimination process occurs, giving L-I, which in the presence of water affords L'-I, resulting from hydrolysis of L-I.

Quantitative synthesis and full characterization of the first isolated and stable pincer palladium(IV) complexes. Quantitative and regioselective synthesis of the C-X (X = Cl, Br) reductive elimination products.

The pincer complexes [Pd(O(1),N(1),C(1)-L)X], where X = Cl, Br and L is the monoanionic ligand resulting from deprotonation of the acetyl methyl group of the monoketal of 2,6-diacetylpyridine (dap), react with excess of Cl(2) or Br(2) affording, quantitatively, the Pd(IV) complexes [Pd(O(1),N(1),C(1)-L)X(3)], which have been characterized by X-ray diffraction, and their decomposition that quantitatively affords the reductive elimination products L-X has been studied.

An unprecedented process involving normal and redox transmetallation reactions between Hg and Pt affording the unexpected K[Pt2[CH2C(O)Me]6(mu-Cl)3] complex: the key role of X-ray powder diffraction in unravelling its nature and structure.

[Hg{CH2C(O)Me}2] reacts with K[PtCl3(CH2=CH2)](2 : 1 molar ratio) to give K[Pt2{CH2C(O)Me}6(mu-Cl)3] (1); the intermediate [Pt{CH2C(O)Me}Cl2(CH2=CH2)]- has been detected in solution and isolated as a Me4N+ salt; the process occurs through successive normal and redox transmetallation reactions and an ab initio X-ray powder diffraction study of has proven to be essential to establish its nature.