Oligomers with silicon and transition metal groups: Thermolysis of poly[1,1′-bis(diorganosilylethynyl) ferrocenes] and poly[{(diorganosilylene) diacetylene}dicobalthexacarbonyls] to give iron silicide- and cobalt silicide-based ceramics

Abstract

The pyrolysis of transition-metal-containing organosilicon-diacetylene oligomers was performed in order to prepare multiphase ceramics. Poly[1,1′-bis(diorganosilylethynyl)ferrocenes] ( 2) were pyrolysed, under argon, up to 1350°C to give Fe x Si y C z phases with good yields, owing to the incorporation of the cyclopentadiene groups in the carbon matrix and the participation of nearly all silicon and iron in the ceramic residue. The pyrolysis of poly[{(diorganosilylene) diacetylene} dicobalt hexacarbonyls] ( 3) at 1350°C gave Co 2Si and graphite-like carbon. Evolution of part of the carbon monoxide of 3 in the early stage of the pyrolysis (100°C) showed that the cross-linking of the diacetylene units was induced by reactive cobalt species. Furthermore, at higher temperatures (200–500°C), cobalt clusters catalysed the ceramic formation. Co 2Si was shown to result from the reaction of SiC with Co above 1000°C, both formed during the pyrolysis process. Finally, at 1100°C, a carboreduction reaction led to the elimination of the oxygen incorporated in the carbon matrix during the cross-linking process.