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

Abstract

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.

Mechanistic Study of Alkyne Insertion into Cu–Al and Au–Al Bonds: A Paradigm Shift for Coinage Metal Chemistry

“…From a more general perspective, insertion reactions of organic molecules into heterobimetallic M–M’ or M–E (E = B, Si) bonds represent an attractive approach to synthetic organic chemistry and industrial catalysis, although examples of this heterobimetallic reactivity are still scarce. − ,, One challenge in heterobimetallic catalysis is identifying a metal cooperative effect (if any) and its origin through mechanistic investigation, which can provide the necessary insight to understand how these catalysts work and possibly how modifications can be planned to increase both the activity and selectivity.…”

“…The syn dimetallated alkenes (9-Cu, 11-Cu) can give a selective insertion of CO leading to the formation of copper acyl compounds. 9 Strictly related gold silyl 10,11 and boryl 12 complexes have been also experimentally reported to insert alkynes into Au−Si and Au−B bonds. Amgoune and Bourissou reported that alkynes can be activated via insertion into the Au−Si bond of the gold silyl (R 3 P)AuSiR'Ph .…”

“…Amgoune and Bourissou reported that alkynes can be activated via insertion into the Au−Si bond of the gold silyl (R 3 P)AuSiR'Ph . 12 We have recently demonstrated that the Au−Al and Au−B bonds in [LAuX] (L = phosphine, N-heterocyclic carbene (NHC); X = Al(NON), B(o-tol) 2 ) complexes possess a similar electron-sharing nature, with diarylboryl complexes displaying a slightly more polarized bond as Au(δ + )−B(δ − ), which is responsible for a reduced radical-like reactivity toward CO 2 8 (consistent with the reaction of complex [IPrAuB(o-tol) 2 ] with carbon dioxide having not been experimentally reported). 13 The ancillary ligand of gold (phosphine or carbene) has been shown to have a negligible electronic trans effect on the Au−X bond and only a minor impact on the formation of the insertion product, although modification of the steric hindrance at the carbene site may exert a sizable control over the reaction.…”

C–C σ-Bond Oxidative Addition and Hydrofunctionalization by a Macrocycle-Supported Diiron Complex

“…Alkynyl–aryl connections are particularly resistant to unassisted activation and functionalization. While a few systems are known that generate products of C­(sp)–C­(sp 2 ) bond functionalization, this chemistry uses precious metals and occurs through mechanisms that do not involve direct C­(sp)–C­(sp 2 ) bond activation. − The direct oxidative addition of C­(sp)–C­(sp 2 ) bonds has been reported only at a family of ( cis -L 2 )­Pt 0 (η 2 -alkyne) (L = phosphine, amine) complexes (Figure , middle). ,− These require the use of photochemical conditions to access endergonic Pt II products that in turn thermally revert to the Pt 0 (η 2 -alkyne) starting materials. Computational studies have been used to support the proposal that these systems undergo C–C bond cleavage following initial photoisomerization to a Pt–arene adduct .…”

Experimental Observation of β-Carbon Elimination from Alkenylrhodium Complexes through Exchange Reactions of the Alkenyl Unit

“…The 1,2-insertion of an unsaturated bond into a metal–carbon bond represents a prevalent elementary step in organometallic chemistry and is involved in a variety of catalytic reactions of alkenes, alkynes, and other unsaturated compounds. Its reverse process, namely, β-carbon elimination, has also been well-explored, because these studies provide not only valuable insights into the control of insertion/elimination processes in catalytic reactions but also opportunities to enable novel molecular transformations such as C–C bond activations . Among several types of β-carbon elimination reactions, β-carbon elimination from alkyl complexes has been investigated extensively in the last few decades.…”