Latency and Immobilization in Silicone Resin by (NHC)Pt(dvtms) Complexes through a Partially Self-Consuming Ligand

Silicones have a plethora of uses but have limitations in placement errors and continuous cross-linking. To address these challenges, we sought to develop a catalyst that would not only contain a latency period, thereby limiting placement errors but could be immobilized in an elastomer, thus thwarting continued cross-linking. Five new N-heterocyclic carbene ligands were synthesized to feature alkene pendant arms of various lengths, (1,3-di(pent-4-en-1-yl)-1H-imidazol-3-ium bromide ([C5Im]Br), 1,3-di(but-3-en-1-yl)-1H-imidazol-3-ium bromide ([C4Im]Br), and sterics (1-(2,6-diisopropylphenyl)-3-(pent-4-en-1-yl)-1H-imidazol-3-ium bromide ([C5ImDipp]Br), and 1-methyl-3-pent-4-en-1-yl)-1H-imidazol-3-ium bromide ([C5ImMe]Br) were targeted to understand how alkene length influences latency. An alkane version of the ligand (1,3-dipentyl-1H-imidazol-3-ium bromide ([C5satIm]Br) was also developed for comparison. Upon deprotonation and subsequent reaction of the ligand with Karstedt's catalyst, a new family of Markó's catalysts were developed. Stoichiometric reactions with silanes demonstrated that the pendant ligand arms can be hydrosilylated. Immobilization of the catalyst via intramolecular hydrosilylation effectively prevented post-cure cross-linking.