MULTIPLE BONDS BETWEEN MAIN-GROUP ELEMENTS AND TRANSITION-METALS .152. HYDROLYSIS AND POLYMERIZATION-PRECIPITATION OF METHYLTRIOXORHENIUM IN AQUEOUS-SOLUTION

Methyltroxorhenium CH3ReO3 (1; MTO), hydrolyzes rapidly in basic aqueo us solutions and much more slowly in acidic media. At low concentratio ns (c(MTO) < 8.0 x 10(-3) M) the formation of CH4 gas and perrhenate w as detected. The hydrolysis was followed by spectrophotometry, and the rate constants were determined as a function of temperature and press ure according to the rate law -d[MTO]/dt = k(1)[OH-][MTO]. The rate co nstant, activation enthalpy, entropy, and volume at 298.2 K are as fol lows: k(1)/M(-1) s(-1) = (8.6 +/- 0.3) x 10(2), Delta H(1)kJ mol(-1) = 15.9 +/- 1, Delta S-1(double dagger)/J mol(-1) K-1 = -135 +/- 3, and Delta V-1(double dagger)/cm(3) mol(-1) = -2.4 +/- 0.4. Attempts to per form the reverse reaction, the synthesis of MTO from [ReO4](-) and CH4 (200 MPa), failed: the decomposition of MTO seems to be irreversible. At higher MTO concentrations a second reaction, a faster reversible p olymerization-precipitation, takes place to yield a gold solid of net formula (C0.92H3.3ReO3.0)(n). The rate of polymerization-precipitation was studied as a function of temperature in D2O by H-1 NMR spectrosco py; it follows first-order reversible kinetics. The rate constant, act ivation enthalpy, and entropy of polymerization-precipitation at 298.2 K are as follows: k(2)/s(-1) = (2.1 +/- 0.4) x 10(-6), Delta H-2(doub le dagger)/kJ mol(-1) = 111.9 +/- 5, Delta S-2(double dagger)/J mol(-1 ) K-1 = 25 +/- 16 (the parameters for the dissolution of the polymer a re estimated data). The rate of the polymerization-precipitation is in dependent of the concentration of H+, and the reaction does not occur in the presence of [ClO4](-), [NO3](-), and other oxidants.