Grubbs thermal decomposition

Catalyst stability at elevated temperatures typically experienced during injection molding, resin curing cycles, and so on, is a necessity. Thermal decomposition of Grubbs catalysts in solution is known to occur at mildly elevated temperatures (>55 C) [92], but solid-state catalyst particles protected from air, as is the case when embedded in self-healing materials, afford some shielding from thermal decomposition [27]. 

Ru]-II is stable for Ih at 100°C in toluene-dg, while. [Ru]-I decomposes by up to 75% under the same conditions. [Ru]-III is also thermally stable and survives chromatography on silica gel, thus enabling it to be purified, recovered, and reused after the reaction. See, Hong SY, Day MW, Grubbs RH. Decomposition of a key intermediate in rathenium-catalyzed olefin metathesis reactions. J. Am. Chem. Soc. 2004 126 7414-7415. 

The fate of the benzylidene fragment in these ruthenium complexes is another matter of debate [20a, 25]. The thermal stability of benzylidene complexes 4-6 was tested at 85 °C, under conditions mimicking polymerisation of methyl methacrylate. As monitored by H NMR, complete disappearance of the benzylidene fragment of the mixed phosphine/Af-heterocyclic carbene complex 5 (R = Cy, R = (5j-CHMePh) was observed within 20 min, whereas the Grubbs complex, RuCl2(=CHPh)(PCy3)2, showed only 55 % decomposition, and the bis-A/ -heterocyclic carbene ruthenium complex 6 (R = Cy) 88 % decomposition over the same time interval (Figure 6). 

Analysis of literature showed tiiat most of information concerning thermal stability, degradation, and deactivation of Ru-carbene catalysts has been obtained for first- and second-generation Grubbs catalysts. There are only solitary reports about decomposition of Hoveyda-type catalysts without details. 

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