Isomerization of a cis‐(2‐Borylalkenyl)Gold Complex via a Retro‐1,2‐Metalate Shift: Cleavage of a C−C/C−Si Bond trans to a C−Au Bond

• Published in: Angewandte Chemie International Edition 2021-09, Vol.60 (38), p.21007-21013
• Main Authors: Suzuki, Akane, Wu, Linlin, Lin, Zhenyang, Yamashita, Makoto
• Format: Article
• Language: English
• Subjects: alkyne insertion; Alkynes; Boron; boryl complex; Carbon; Exchanging; Gold; Insertion; Isomerization; retro-1,2-metalate shift; Silicon
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202108530

This manuscript describes the first example of an alkyne insertion to the Au−B bond of a di(o‐tolyl)borylgold complex to afford a cis‐2‐borylalkenylgold complex, and its isomerization to result in interchanging substituents on the alkenyl carbon atom and the boron atom. The former reaction is the first example of an alkyne insertion to a Au−B bond. In the latter reaction, the regiochemistry of the isomerized alkenylgold products varied depending on the substituents. DFT calculations revealed the formation of gold alkynylborates as a common intermediate via a “retro‐1,2‐metalate shift”, which can be considered as an anti‐β‐carbon/silicon elimination, and identified a subsequent 1,2‐metalate shift as the regiochemistry‐determining step. Relative energies of the transition states to each isomer and natural‐bond‐orbital (NBO) analyses were used to clearly rationalize the regiochemistry of the products. Unexpected isomerization of cis‐2‐borylalkenylgold complexes, which formed through the first alkyne insertion to a Au−B bond, was observed with structural characterization of intermediates and products. Kinetic analysis for isomerization of isolated intermediate and detailed DFT calculations revealed a new elementary reaction, i.e., a “retro‐1,2‐metalate shift” that contains anti‐β‐carbon/silicon elimination.