Water and Protic Acids as Oxidants for Platinum(II):  Diorgano(hydrido)platinum(IV) and Diorgano(hydroxo)platinum(IV) Chemistry, Including Structural Studies of Poly(pyrazol-1-yl)borate Complexes Pt(OH)R2{(pz)3BH} (R = Methyl, p-Tolyl) and Pt(OH)Me2{(pz)4B}·H2O

The tris(pyrazol-1-yl)borate complexes K[PtR2{(pz)3BH}] (R = Me (1), p-tolyl (2)) may be isolated on addition of K[(pz)3BH] to solutions of [PtR2(SEt2)]2. Complexes 1, 2, and [PtMe2{(pz)4B}]- react with acetic acid to form PtHR2{(pz)3BH} (R = Me (3), p-tolyl (5)) and PtHMe2{(pz)4B} (4). The hydridoplatinum(IV) complexes decompose at ∼140 (3) and ∼85 (4) °C in toluene-d8 and ∼90 °C (5) in nitrobenzene-d5 to form methane (3, 4) and toluene (5), where isolation of 5 has provided the first opportunity to study the decomposition of aryl(hydrido)platinum(IV) complexes. The hydridoplatinum(IV) complexes are deprotonated on addition of aqueous sodium hydroxide in acetone-d6 to form 1, 2, and [PtMe2{(pz)4B}]-. The hydroxoplatinum(IV) complexes Pt(OH)R2{(pz)3BH} (R = Me (6), p-tolyl (8)) or Pt(OH)Me2{(pz)4B}·H2O (7) may be readily isolated in 45−82% yield upon oxidation of the platinum(II) anions 1, 2, or [PtMe2{(pz)4B}]- by water. The hydridoplatinum(IV) complexes 35 also react slowly with water in acetone-d6 to form hydrogen and complexes 68. The anions [PtR2{(pz)3BH}]- undergo oxidative-addition reactions with iodomethane to form PtMeR2{(pz)3BH} (R = Me, p-tolyl). The octahedral hydroxoplatinum(IV) complexes 68 are the first examples of platinum(IV) complexes formed on oxidation by water to be characterized by X-ray crystallography. The complexes display Pt−O distances of 1.974(8)−1.996(6) Å, and the Pt−N bond distances reflect the relative trans influences of the hydroxo and methyl groups. The aqua group in Pt(OH)Me2{(pz)4B}·H2O (7) is hydrogen-bonded to the hydroxoplatinum(IV) group to form a centrosymmetric dimer, such that it is not possible to ascertain whether the coordination environment of platinum is [Pt(OH)···H2O]2 or [Pt(OH2)+···OH-]2, although the former is believed to be more likely.