Oxidation of Diorganopalladium(II) Complexes by Water and Halogens:  Reactions Involving Methyl Group Transfer and Structural Studies of Hydrogen-Bonded Adducts Formed by Aryl Alcohols with the Pallada(IV)cyclopentane Complex Pd(CH₂CH₂CH₂CH₂)(OH){(pz)₃BH} ([(pz)₃BH]^-= Tris(pyrazol-1-yl)borate)

Abstract

The first observations of oxidation of palladium(II) by water are reported. The pallada(II)cyclic complex ion [Pd(CH2CH2CH2CH2){(pz)3BH}]- [(pz)3BH = tris (pyrazol-1-yl)borate)] is oxidized by water in acetone or tetrahydrofuran to form Pd(CH2CH2CH2CH2)(OH){(pz)3BH} and hydrogen, and oxidation by hydrogen peroxide gives the same complex. Oxidation by halogens results in the formation of Pd(CH2CH2CH2CH2)(X){(pz)3BH} (X = Cl, Br, I), and these complexes, together with the hydroxopalladium(IV) complex, represent the first examples of stable dihydrocarbylpalladium(IV) complexes. The octahedral complex Pd(CH2CH2CH2CH2)(OH){(pz)3BH} forms adducts with phenol, 3-methylphenol, and pentafluorophenol with an overall composition of Pd(CH2CH2CH2CH2)(OH){(pz)3BH}·2ArOH (5 and 6) and Pd(CH2CH2CH2CH2)(OH){(pz)3BH}·C6F5OH (7). Complex hydrogen-bonding interactions occur in the adducts, consistent with the assignment of the phenol and 3-methylphenol adducts as hydroxopalladium(IV) complexes and the pentafluorophenol adduct as an aquapalladium(IV) complex. Complexes 5 and 6 are considered to contain the hydrogen-bonding motifs H−O(Pd)···HO(Ph)···HOPh and Ar(H)O···H−O(Pd)···HOAr, respectively, and 7 to contain an aquapalladium(IV) cation in which both hydrogen atoms of the aqua ligand act as hydrogen-bond donors to pentafluorophenoxide ions in a centrosymmetric dimer, [Pd(CH2CH2CH2CH2)(OH2){(pz)3BH}·C6F5O]2. The complex ions [PdMeR{(pz)3BH}]- (R = Me, Ph) react with water or halogens to form the PdMe2R{(pz)3BH} and PdIIR species, and in the case of water as the oxidant, hydrogen is also formed. These reactions occur via initial oxidation to form undetected palladium(IV) species, presumably PdMeR(X){(pz)3BH} (X = OH, Cl, Br, I), which undergo rapid methyl group exchange reactions with [PdMeR{(pz)3BH}]- to form PdIIR species and PdMe2R{(pz)3BH}. The oxidation of palladium(II) by water and the structural analysis of hydroxo- and aquapalladium(IV) complexes represent the first examples of organopalladium(IV) chemistry in aqueous media.

Organopalladium and platinum chemistry in oxidising milieu as models for organic synthesis involving the higher oxidation states of palladium

“…3). 36 The unstable Pd IV complex 52 is formed on reaction of the monochloropalladium(II) precursor with IPhCl 2 and its formulation was confirmed by comparison of 1 H NMR spectra with the stable Pt IV analogue 53 prepared in the same manner (Fig. 3).…”

Access to α‐Amino Acid Esters through Palladium‐Catalyzed Oxidative Amination of Vinyl Ethers with Hydrogen Peroxide as the Oxidant and Oxygen Source

“…On the basis of the above results, we propose the following mechanism for the palladium‐catalyzed intermolecular oxidative amination (Scheme ): First, 2 a is activated by coordination with the Pd II catalyst, thus suggesting that an aminopalladation process occurs with the formation of an alkyl palladium intermediate int‐I . Subsequently, H 2 O 2 oxidizes int‐I to form an [(alkyl)Pd IV (OH)] intermediate int‐II , which might undergo direct reductive elimination to generate int‐III , which would then be oxidized to the final product 3 aa . Alternatively, H 2 O 2 may act as a nucleophile and attack int‐II to produce int‐IV , which would then undergo a dehydration process to afford 3 aa .…”

Organopalladium(iv) chemistry

“…Carbopallada(II)cycle 14 can be oxidized by H 2 O 2 to form dihydrocarbylhydroxylpalladium(IV) complexes 15 with support of hydrotris(pyrazolyl)borate (TP). 13 Surprisingly, even with the use of water instead of H 2 O 2 as oxidant, the same adduct 15 was obtained upon release of hydrogen. This can be attributed to the low reductive potential of Pd(II) complexes 14, which were supported by the high electron donating alkyl and TP group (eqn (7)).…”