Investigation of β-alkynol inhibition mechanism and Ru/Pt dual catalysis in Karstedt catalyzed hydrosilylation cure systems

• Published in: Journal of organometallic chemistry Vol. 928; pp. 121541 - 121548
• Main Authors: Li, Zhanjie, Chevalier, Pierre M., Niu, Zhenbin
• Format: Journal Article
• Language: English
• Published: LAUSANNE Elsevier B.V 07.12.2020; Elsevier
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Dual catalysis; Hydrosilylation; Karstedt catalyst; Low temperature cure; Physical Sciences; Science & Technology; β-Alkynol inhibitor; β-Alkynol inhibitor; Dual catalysis; Hydrosilylation; Karstedt catalyst; Low temperature cure; TERMINAL ALKYNES; OLEFINS; beta-Alkynol inhibitor; RUTHENIUM COMPLEX
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2020.121541

•Illustration of the selective alkyne hydrosilylation being key for the inhibition mechanism of β-alkynol inhibitor in the Karstedt catalyzed curable silicone composition.•Discovery of complex [Cp*Ru(MeCN)3]+OTf- as highly effective co-catalyst for the selective consumption of β-alkynol inhibitor.•Demonstration of the efficiency of Ru/Pt dual catalysis in a silicone release coating application with command cure temperature as low as 85oC and a short cure time of 4 seconds. β-Alkynol inhibitors play an important role in Karstedt catalyzed hydrosilylation cure silicone chemistry by providing a long working time at low temperatures, while allowing for rapid cure at elevated temperatures. Using 13C-labeled 1-ethynyl-1-cyclohexanol (13C-1) as a representative of the β-alkynol inhibitor, it was possible to monitor the change in this component in an actual silicone composition by 1H and 13C NMR during cure. The data showed that 13C-1 was selectively consumed by Pt-catalyzed hydrosilylation with the Si—H siloxane in the formulation in spite of the presence of large excess of vinyl groups from the vinyl polysiloxane component. The reaction rate was highly dependent on the Si—H siloxane used, the reaction temperature and presence of the tertiary -OH group in 13C-1. These results suggest that the high selectivity of the terminal alkyne over vinyl for hydrosilylation and the temperature dependent reaction kinetics are keys to understanding the inhibition mechanism for β-alkynols. These studies also inspired a Ru/Pt dual catalyst approach to lower the cure temperature of the silicone composition while maintaining a suitable working time. This approach is based on the hypothesis that the Ru co-catalyst can selectively catalyze the hydrosilylation of the β-alkynol in a temperature dependent manner, and its consumption would subsequently release the Pt-catalyst to rapidly cure the composition. Evaluation of a range of Ru-complexes led to the identification the complex [Cp*Ru(MeCN)3]+OTf- and its dodecanenitrile derivatives as a prototype from which the effectiveness of the dual catalysis approach was validated in a silicone release coating application with a cure temperature of 85oC and cure time of 4 seconds. [Display omitted]