Browsing by Author "Morrenzin, Aaron S."

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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.
Gold Catalyzed Decarboxylative Cross-Coupling of Iodoarenes
(2020-07) Daley, Ryan A.; Morrenzin, Aaron S.; Neufeldt, Sharon R.; Topczewski, Joseph J.
This report details a decarboxylative cross-coupling of (hetero)aryl carboxylates with iodoarenes in the presence of a gold catalyst (>25 examples, up to 96% yield). This reaction is site specific, which overcomes prior limitations associated with gold catalyzed oxidative coupling reactions. The reactivity of the (hetero)aryl carboxylate correlates qualitatively to the field effect parameter (Fortho). Reactions with isolated gold complexes and DFT calculations support a mechanism proceeding through oxidative addition at a gold(I) cation with decarboxylation being viable at either a gold(I) or a silver(I) species.
Mechanistic Investigation into the Gold-Catalyzed Decarboxylative Cross-Coupling of Iodoarenes
(American Chemical Society, 2021-07) Daley, Ryan A.; Morrenzin, Aaron S.; Neufeldt, Sharon R.; Topczewski, Joseph J.
While many gold catalyzed reactions have been thoroughly developed, most are not thought to involve redox events at gold. In contrast, recent advances have demonstrated the feasibility of redox gold catalysis. This report describes a detailed mechanistic investigation of the gold catalyzed decarboxylative cross-coupling, which likely proceeds via a high valent Au(I/III) pathway. This investigation includes a kinetic analysis, stoichiometric experiments with Au(III) complexes, and DFT calculations. These data support a turnover limiting oxidative addition to form an Au(III) aryl complex, with an off cycle resting state. The dominant pathway appears to proceed through a silver mediated decarboxylation with a subsequent Ag(I) to Au(III) transmetalation. These data provide some rationale for the significant counterion effects between SbF6– and NTf2– and may explain why MeDalphos is not a superior ligand for the catalytic reaction.