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

The first observations of oxidation of palladium(II) by water are reported. The pallada-(II) complex ion [Pd(CH2CH2CH2CH2){(pz)(3)BH = tris (pyrazol-1-yl)borate)] is oxidized by water in acetone or tetrahydrofuran to form Pd(CH2CH2CH2CH2)(OH){(pz)(3)BH} and hydrogen, and oxidation by hydrogen peroxide gives the samie complex. Oxidation by halogens results in the formation of Pd(CH2CH2CH2CH2)(X){(pz)(3)BH} (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)(3)BH} forms adducts with phenol, 3-methylphenol, and pentaflurophenol with an overall composition of Pd(CH2CH2CH3CH2)(OH){(pz)(3)BH}. 2ArOH (5 and 6) and Pd(CH2CH2CH2CH2)(OH){(pz)(3)BH}. C6F5OH (7). Complex hydrogen-bonding interactions occur in the adducts, consistent with the assignment of the phenol and 3-methylphenol 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)therefore ... 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 centro-symmetric dimer, [Pd(CH2CH2CH2CH2)(OH2){(pz)(3)BH}. C6F5O](2). The complex ions [PdMeR{(pz)(3)BH}](-) (R = Me, Ph) react with water or halogens to form the PdMe(2)R{(pz)(3)-BH} and PD(II)R 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)(3)BH}](-) to form Pd(II)R species and PdMe(2)R{(pz)(3)BH}. 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.