A palladium thiolate-SNS complex-catalyst for Mizoroki-Heck cross-coupling
Saeed Ataie1, Atousa Khanzadeh1, R Tom Baker1
1Department of Chemistry and Biomolecular Sciences and Centre for Catalysis Research and Innovation, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada. rbaker@uottawa.ca.
Abstract:
Phosphine-free catalysts for the Mizoroki-Heck cross-coupling reaction offer significant advantages in terms of air and moisture stability. We synthesized two palladium(II) complexes featuring a thiolate-imine-thioether SNS pincer ligand: Pd(κ2-SNSMe)2 (Pd-1) and PdI(κ3-SNSMe) (Pd-2). Their catalytic activities were compared, with Pd-2 demonstrating excellent reactivity at a low catalyst loading of 1.5 mol%, efficiently producing olefin products across various substrates within 5 hours. Conversely, Pd-1 showed no catalytic activity due to its isomerization to a Pd(II)-N2S2 complex via imine C-C bond formation at elevated temperatures, which restricted access to coordination sites necessary for oxidative addition and alkene coordination. Heating Pd-2 with excess NEt3 affords a Pd dithiolate tetramer, [Pd(μ-κ3-SNS)]4via selective C-S bond activation.
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