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Dissecting transmetalation reactions at the molecular level: role of the coordinated anion in gas-phase models for the transmetalation step of the Hiyama cross-coupling reaction

Citation

Stewart, AWE and Ma, HZ and Weragoda, GK and Khairallah, GN and Canty, AJ and O'Hair, RAJ, Dissecting transmetalation reactions at the molecular level: role of the coordinated anion in gas-phase models for the transmetalation step of the Hiyama cross-coupling reaction, Organometallics, 40, (12) pp. 1822-1829. ISSN 0276-7333 (2021) [Refereed Article]

Copyright Statement

Copyright 2021 American Chemical Society

DOI: doi:10.1021/acs.organomet.0c00795

Abstract

Palladium-catalyzed cross-coupling protocols have become a cornerstone in organic synthesis. Here, a gas-phase model of the Hiyama cross-coupling reaction was designed to shed light on the roles of coordinated anions (fluoride versus chloride) in transmetalation from Si to Pd. A combination of mass spectrometry experiments and DFT calculations was used. The ligated palladium fluoride and chloride cationic complexes, [(phen)Pd(X)]+ (X = F and Cl), readily react with vinyltrimethylsilane, Me3Si(CH═CH2), via transmetalation to give [(phen)Pd(CH═CH2)]+ as the major product. DFT calculations reveal that this transmetalation reaction is concerted and proceeds via a four-centered transition state, illustrating the role of coordinated halide in this gas-phase system. Two minor side products are observed corresponding to transmetalation to give [(phen)Pd(CH3)]+ and [(phen)Pd(SiMe2X)]+. DFT calculations suggest that these arise from the same initial Si to Pd methyl transmetalation pathway to give the [(phen)Pd(CH3) + Me2(CH═CH2)SiX]+ intermediate, which either then loses Me2(CH═CH2)SiX or reacts via CC bond coupling to ultimately yield propene and [(phen)Pd(SiMe2X)]+. [(phen)Pd(CH═CH2)]+ undergoes a reaction with a second molecule of vinyltrimethylsilane to form an adduct, which upon collision-induced dissociation liberates 1,3-butadiene to form [(phen)Pd(SiMe3)]+. DFT calculations suggest a mechanism in which CC bond formation is followed by migration of SiMe3 from C to Pd. Links between the observed gas-phase chemistry and solution-phase Pd-mediated homocoupling reactions of vinyltrimethylsilanes are explored.

Item Details

Item Type:Refereed Article
Research Division:Chemical Sciences
Research Group:Inorganic chemistry
Research Field:Transition metal chemistry
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the chemical sciences
UTAS Author:Canty, AJ (Professor Allan Canty)
ID Code:145111
Year Published:2021
Deposited By:Chemistry
Deposited On:2021-07-01
Last Modified:2021-08-31
Downloads:0

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