Browsing by Author "Humke, Jenna N."

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Combined Experimental and Computational Mechanistic Investigation of the Palladium-Catalyzed Decarboxylative Cross-Coupling of Sodium Benzoates with Chloroarenes
(American Chemical Society, 2021-08) Humke, Jenna N.; Daley, Ryan A.; Morrenzin, Aaron S.; Neufeldt, Sharon R.; Topczewski, Joseph J.
Reported herein is a mechanistic investigation into the palladium catalyzed decarboxylative cross-coupling of sodium benzoates and chloroarenes. The reaction was found to be first order in Pd. A minimal substituent effect was observed with respect to the chloroarene and the reaction was zero order with respect to chloroarene. Palladium mediated decarboxylation was assigned as the turn-over limiting step based on an Eyring plot and DFT computations. Catalyst performance was found to vary based on the electrophile, which is best explained by catalyst decomposition at Pd(0). The COD ligand contained in the precatalyst CODPd(CH2TMS)2 (Pd1) was shown to be a beneficial additive. The bench stable Buchwald complex XPhos-PdG2 could be used with exogenous COD and XPhos instead of complex Pd1. Adding exogenous XPhos significantly increased the catalyst TON and enhanced reproducibility.
N-Heterocyclic Carbene Ligand-Controlled Chemodivergent Suzuki–Miyaura Cross Coupling
(2019-09) Reeves, Emily K.; Humke, Jenna N.; Neufeldt, Sharon R.
Two N-heterocyclic carbene ligands provide orthogonal chemoselectivity during the Pd-catalyzed Suzuki–Miyaura (SM) cross-coupling of chloroaryl triflates. The use of SIPr [SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene] leads to selective cross-coupling at chloride, while the use of SIMes [SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene] provides selective coupling at triflate. With most chloroaryl triflates and arylboronic acids, ligand-controlled selectivity is high (≥10:1). The scope of this methodology is significantly more general than previously reported methods for selective SM coupling of chloroaryl triflates using phosphine ligands. Density functional theory studies suggest that palladium’s ligation state during oxidative addition is different with SIMes compared to SIPr.