Transmetalation of boronic acids and their derivatives: mechanistic elucidation and relevance to catalysis

Abstract

The Suzuki–Miyaura reaction (cross-coupling reaction of boronic acids with organic halides catalysed by Pd complexes) has been recognised as the useful synthetic organic reaction that forms a C(sp2)–C(sp2) bond. The...

Dynamic Au–C σ-Bonds Leading to an Efficient Synthesis of [n]Cycloparaphenylenes (n = 9–15) by Self-Assembly

“…There were several reports on the exchange reaction of M–C σ-bonds (M = Pt­(II), Pd­(II), Au­(I), etc.) (see supporting Scheme S3b), − and the reactions were generally regarded as a slow process compared to those of the noncovalent metal–ligand bonds, that is, Pd–N and Pt–N bonds (see Scheme S3a). However, the exchange reactions involving aryl–Au­(I) complexes have never been reported to date. − …”

“…The negative value of Δ S ⧧ implies that the bond-exchange process proceeds via an associative mechanism. ,,,− Considering the deceleration of the aryl exchange reaction upon the addition of catalytic amounts of dcpm in the former section, it is plausible that a ligand dissociation precedes an associative transition state. To combine the above results, we could propose the putative mechanism that the bond exchange or metathesis between the metal centers and their organic ligands proceeded via a mechanism with three steps: (i) a ligand dissociation to form reactive Au species [i.e., AuAr or ArAu–AuAr­(dcpm)]; (ii) formation of an associative transition state; ,,− ,, (iii) the Au–C aryl bond exchange (Figure c). The complexes with bridging organic ligands, presumed to be the intermediate of organic ligand exchange, have been proposed in kinetic studies in which aryl–Cu­(I) and aryl–Au­(I) complexes caused trans–cis isomerization of Pd­(II) complexes , and exchange of their aryl and alkynyl ligands bound to Pd­(II) and Rh­(I) complexes …”

Pretransmetalation Intermediates in Suzuki–Miyaura C–C and Carbonylative Cross-Couplings: Synthesis and Structural Authentication of Aryl- and Aroylnickel(II) Boronates

“…The Suzuki–Miyaura (SM) cross-coupling, first reported in 1979, is renowned for its versatility and reliability, and has emerged as one of most important carbon–carbon bond-forming reactions . The mechanism of this transformation has been the subject of considerable study, and transmetalation represents, arguably, the most nuanced fundamental step involved in the catalytic cycle . Organopalladium­(II) boronates are recognized as fundamental pretransmetalation intermediates in palladium-catalyzed SM couplings (Figure A); however, their fleeting nature has made studying these on-cycle species particularly challenging …”

Structural authentication of intermediates of mechanistic significance in palladium- and nickel-catalysed cross-couplings: case studies

“…26 Following oxidation, transmetalation occurs either via the reaction of arylpalladium( ii ) halide 1b with the arylboronate (path A) or via the reaction of arylpalladium( ii ) hydroxide 1c with the neutral boronic acid (path B). 27,28 Experimental studies suggest that the latter pathway (path B) is kinetically favoured over the former. 29 The products of these pathways converge to afford arylpalladium( ii ) boronate pre-transmetalation intermediates, which feature a distinctive Pd–O–B linkage (see, for example: 1d ).…”