Multiple Bonds between Main-Group Elements and Transition Metals. 136.¹“Polymerization” of an Organometal Oxide: The Unusual Behavior of Methyltrioxorhenium(VII) in Water

The title compound CH₃ReO₃ (1), the simplest organometallic oxide known to date, undergoes an aggregation process in aqueous solution which is unprecedented in organometallic chemistry. From the acidic colorless solutions of 1 in water, a golden-colored, highly refractory precipitate separates slowly at room temperature or within hours at 70 °C. The product 2 forms in 70% yield, with the composition of vacuum-dried material being {H_0.5[(CH₃)_0.92ReO₃]}_∞. Thus, only 8% of the original methyl groups eliminate during formation of 2 in water. The nonstoichiometric compound (“poly-MTO”) represents the first known “polymeric” organometallic oxide. The most striking physical properties—golden color, graphite-like consistence, reflectance, electric conductivity, weak paramagnetism—result from a two-dimensional structure containing a sufficient concentration of d¹ Re^VI centers to establish the electric conductivity of the material. The Re^VI centers mostly originate from homolytic loss of methyl groups (Re^VII→ Re^VI) during formation of “poly-MTO” (2). Thermal degradation in moist atmosphere yields highly pure, crystalline rhenium trioxide, which itself is an electrically conducting material.