ACTIVATION OF WATER MOLECULE .2. GENERATION OF STRONG HYDROXO BASES BY THE REACTION OF WATER WITH PLATINUM(0) PHOSPHINE COMPLEXES AND THE APPLICATIONS AS CATALYSTS FOR H-D EXCHANGE AND HYDRATION REACTIONS

The dissociation of Pt(PEt3)4in organic solvents (THF, w-heptane) occurs to give Pt(PEt3)3(Kl = 0.5 M in THF at 20 °C), no further dissociation being detected, while Pt[P(i-Pr)3]3, upon dissolution in the above solvents, exists mainly as Pt[P(i-Pr)3]2(Kl = 0.14 M in THF at 20 °C). Addition of water to PtL3(L = PEt3, P(i-Pr)3) generates strong hydroxy bases, [PtHL3]OH (L = PEt3) or trans-[PtH(S)L2]OH (L = P(i-Pr)3, S = solvent), while the addition to Pt[P(/-Pr)3]2gives a σ-drido hydroxo compound, trans-PtH(OH)[P(i-Pr)3]2. Quantitative study OR the reversible water addition to PtL3in organic solvents was carried out by pH and conductance measurements. The conductometric behaviors of the system PtL3(L = PEt3)/ H20 in pyridine and THF are described in terms of two equilibria: (1) PtL3+ H20 ⇌ [PtHL3]OH, K0; (2) [PtHL3]OH ⇌ [PtHL3]++ OH-, Kd (K0= 0.6 (0.3) M-1, Kd= 4.2 (0.2) X 10-2exp(-l1.9(0.1)/[H2O)) M in pyridine at 0.5 °C). The system PtL3(L = P(i-Pr)3)/H20 involved (1) PtL3⇌ PtL2+ L, KL, vide supra; (2) PtL2+ H20 ⇌ PtH(OH)L2, K0; (3) PtH(OH)L2+ S ⇌ [PtH(S)L2]OH, Ks; (4) [PtH(S)L2]OH ⇌ [PtH(S)L2]++ OH-Kd(only composite constants can be calculated, (1 + KS)K0= 0.1 (0.06) M-1, Kskd/ (1 + Ks) = 1.2 (0.1) X 10-1exp(-20.8(0.2)/[H20]) M in pyridine at 0.5 °C). Systems with PtL3/H20 proved to be efficient catalysts for H-D exchange of organic substances and for hydration of organic unsaturated bonds. Thus, activated C-H bonds such as a-hydrogen atoms of ketones, aldehydes, sulfones, sulfoxides, and nitroalkanes undergo the H-D exchange. The mechanism was studied for H-D exchange of C6H5COCH3to show that the reaction follows a rate equation, R =K[Pt][C6H5COCH3], and involves a reversible condensation, M+OD-+ C6H5COCH3⇌ MCH2COC6H5+ DHO, as the rate-determining step. Unlike the alkaline base-catalyzed reaction, α-olefinic, allylic, and aldehydic hydrogen atoms of α,β-unsaturated carbonyl compounds were exchanged. The hydration of the nitrile and double bonds of RCH═CHCN catalyzed by [PtHL3]OH or [PtH(S)I.2]OH and trans-Pt(OH)(R)(PPh3)2occurs with excellent chemical yields. © 1979, American Chemical Society. All rights reserved.