Surface organometallic chemistry: Easy reductive carbonylation of silica-supported [Re(CO)(3)(OH)](4) to [Re-2(CO)(10)] via silica-anchored [Re(CO)(5)(OSi equivalent to)] and the thermal behavior of silica-supported [Re-2(CO)(10)]

摘要

Silica-supported [Re(CO)(3)(OH)](4) is easily converted to [Re-2(CO)(10)] by reductive carbonylation under very mild conditions (1 atm CO). This reaction does not occur in solution, suggesting that the silica surface plays a unique role via the surface-anchored species [Re(CO)(5)(OSi drop)]. This latter intermediate, of particular interest since organometallic species of the type [Re(CO)(5)(OR)] have so far eluded isolation, reacts with HCl, HReO4, and water to give [Re(CO)(5)Cl], [Re(CO)(5)OReO3], and [Re(CO)(3)(OH)](4), respectively. No evidence was reached for the previously proposed formation of [HRe3(CO)(14)] in the reductive carbonylation of silica-physisorbed [Re(CO)(3)(OH)](4). In addition, silica-supported [Re-2(CO)(10)] can be easily reoxidized to [Re(CO)(3)(OH)](4) on the silica surface by thermal treatment at 150-250 degrees C under nitrogen. Some highly oxidized rhenium species such as ROReO3 (R = H, Si drop) are formed in parallel, as suggested by an XPS study and confirmed by further treatment under 1 atm of CO at 200 degrees C, which affords mixtures containing also [Re(CO)(5)OReO3]. The latter was isolated and fully characterized by X-ray diffraction. Obviously these oxidation reactions, in which the silica surface plays an important positive role, are faster in air than under nitrogen. [References: 50]