Title : Beta Alkynol inhibition in Ru/Pt dual catalysis for hydrosilylation of silicones
Abstract:
The platinum-catalyzed hydrosilylation reaction between a silicon-hydrogen and a carbon-carbon double bond is one of the foundational chemistries for the silicone industry. Since first reported in 1957, this addition reaction has been extensively used for the industrial production of intermediates and to form three-dimensional crosslinked networks into a wide range of cured performance silicones such as into fluids, coatings, sealants, rubbers and composites for building and construction, personal care, and pressure sensitive adhesives markets to name a few. β-Alkynol inhibitors play a determinant role in this Karstedt-catalyzed hydrosilylation providing a long working time or bath life at room temperature, while allowing for rapid command cure at elevated temperature, being paramount for viable industrial processes. Using 13C-labeled 1-ethynyl-1-cyclohexanol (13C-1) β-alkynol inhibitor in a SiH/SiVinyl reactive model system, it was possible to monitor the composition change by Nuclear Magnetic Resonance spectroscopy during cure showing that 13C-1 was selectively consumed by Pt-catalysed hydrosilylation with the Si-H group despite the large excess of reactive vinyl siloxanes. This hydrosilylation selectivity of terminal alkyne over vinyl and the temperature dependent kinetics are keys to the inhibition mechanism. We wish to report here the Ru/Pt dual catalysis to lower the cure temperature while maintaining a suitable working time through the evaluation of a range of Ru-complexes leading to the identification of [Cp*Ru(MeCN)3 ]+OTf- complex promoting the selective ruthenium-catalyzed alkyne hydrosilylation of the inhibitor thus triggering the platinum-catalyzed olefin hydrosilylation and crosslinking at a cure temperature as low as 85OC and within 4 seconds, being critical for industrial silicone release coating applications onto low heat deflection temperature (HDT) commodity plastic substrates.
