Multiple Bonds between Main-Group Elements and Transition Metals. 152.¹ Hydrolysis and Polymerization−Precipitation of Methyltrioxorhenium in Aqueous Solution

Abstract

Methyltrioxorhenium, CH 3 ReO 3 (1; MTO), hydrolyzes rapidly in basic aqueous solutions and much more slowly in acidic media. At low concentrations (c MTO < 8.0 × 10 -3 M) the formation of CH 4 gas and perrhenate was detected. The hydrolysis was followed by spectrophotometry, and the rate constants were determined as a function of temperature and pressure according to the rate lawThe rate constant, activation enthalpy, entropy, and volume at 298.2 K are as follows:) 15.9 ( 1, ∆S 1 q /J mol -1 K -1 ) -135 ( 3, and ∆V 1 q /cm 3 mol -1 ) -2.4 ( 0.4. Attempts to perform the reverse reaction, the synthesis of MTO from [ReO 4 ] -and CH 4 (200 MPa), failed: the decomposition of MTO seems to be irreversible. At higher MTO concentrations a second reaction, a faster reversible polymerization-precipitation, takes place to yield a gold solid of net formula (C 0.92 H 3.3 ReO 3.0 ) n . The rate of polymerizationprecipitation was studied as a function of temperature in D 2 O by 1 H NMR spectroscopy; it follows first-order reversible kinetics. The rate constant, activation enthalpy, and entropy of polymerization-precipitation at 298.2 K are as follows: k 2 /s -1 ) (2.1 ( 0.4) × 10 -6 , ∆H 2 q / kJ mol -1 ) 111.9 ( 5, ∆S 2 q /J mol -1 K -1 ) 25 ( 16 (the parameters for the dissolution of the polymer are estimated data). The rate of the polymerization-precipitation is independent of the concentration of H + , and the reaction does not occur in the presence of [ClO 4 ] -, [NO 3 ] -, and other oxidants.

Methyltrioxorhenium Catalysis in Nonconventional Solvents: A Great Catalyst in a Safe Reaction Medium

“…[35] Irrespective to the experimental conditions (CH 4 pressure, pH, temperature, reaction time), MTO decomposition in water is not a reversible reaction.…”

Methyltrioxorhenium and its applications in olefin oxidation, metathesis and aldehyde olefination

“…At higher concentrations a second reaction, a faster reversible polymerization-precipitation, takes place to yield a golden colored solid of the empirical composition {H 0.5 [(CH 3 ) 0.92 ReO 3 ]} (poly-MTO) in about 70% yield (Eq. (1)) [31][32][33][34][35][36] follows first-order reversible kinetics. The rate of polymerization-precipitation is independent of the concentration of H + , and the reaction does not occur in the presence of oxidants [31].…”

In Situ Spectroscopic Investigation of the Rhenium‐Catalyzed Deoxydehydration of Vicinal Diols

“…The identification of the compound responsible for this vibration was hampered by the limited spectroscopic information, [47] but the calculation of the IR spectra of a number of possible Re compounds revealed that only ReO 4 À and ReO 3 (diolate) À displayed a strong band close to the correct wavenumber, and the unknown compound was concluded tentatively to be a hydrolyzed rhenium species. The hydrolysis of CH 3 ReO 3 to ReO 4 À is a well-established reaction-at least in aqueous solutions [48][49][50] -and the related complex Cp*ReO 3 is converted into perrhenate ions in nonaqueous solvents in the presence of oxygen. [51] Although some differences in reactivity have been found upon comparison of CH 3 ReO 3 and various perrhenate salts, they are minor and are presumably the result of different solubilities and beneficial or detrimental effects of the counter ions.…”