Pd-catalyzed Suzuki cross-Coupling reaction of bromostilbene: insights on the nature of the boron Species

Abstract

Sais e ésteres derivados de ácidos aril borônicos podem ser usados na reação de acoplamento Suzuki com (E)-bromoestilbeno usando uma mistura Pd(OAc) 2 /PPh 3 como precursor catalítico. Enquanto que a adição de uma base como KOH é necessária para a reação de acoplamento com ácido borônico ou seu éster derivado do pinacol, o uso de um aril borato de sódio permite que a reação seja realizada na ausência de base. A comparação entre os diferentes compostos organoboro via reações competitivas e análise por espectrometria de massas com ionização por "electrospray" mostram que a base inicialmente reage com o ácido ou éster aril borônico para formar um aril borato que é a espécie envolvida na reação de transmetalação com o catalisador de paládio.Arylboronate esters and arylborate salts can be used as partner for the Suzuki reaction of (E)-bromostilbene in the presence of Pd(OAc) 2 /PPh 3 as catalyst precursor. While KOH is necessary for the coupling reaction with arylboronic acids and pinacol esters, aryl borate sodium salt can be used in a base-free protocol. The comparison between the three organoboron compounds using competitive experiments and electrospray ionization mass spectrometry analysis supports the proposition that the base initially reacts with the arylboronic acid or ester to form an arylborate species which undergoes the transmetallation process with the palladium catalyst.

Role of the base and endogenous anions in “ligand-free” catalytic systems for the Suzuki–Miyaura reaction

“…Obviously, the presence of a base in the Suzuki-Miyaura reaction leads, to a certain extent, to the real ization of equilibria involving arylpalladium halide complexes (reaction (II)) and those involving phenyl boronic acid molecules (reaction (III)), as is con firmed by the formation of the corresponding experi mentally observable products under catalytic and model conditions (see, e.g., [7][8][9][10]). However, detec tion of some compounds in the reaction mixture still does not allow one to reliably conclude that these compounds are involved in catalysis.…”

Substrate‐Selective Catalysis

“…In two subsequently published works, Monteiro and co‐workers investigated the effect on the reactivity of various substituents in the para ‐position of arylboronic acids in the Pd‐catalyzed Suzuki cross‐coupling reaction: first with vinyl bromide93 and later on with ( E )‐bromostilbene 94…”

DFT simulations and Vibrational spectra of 4‐chloro and 4‐bromophenylboronic acid molecules

“…[18] The use of boron compounds in the coupling reaction presents several advantages, such as stability to heat, oxygen, and water; flexibility towards functional groups; and commercial availability. [19] In recent studies, inhibition by boronic acids has been studied with some bacterial ureases and plant ureases. Ravi et al [20] reported that among boric acid, boronic acid, and 4-bromophenylboronic acid, the latter was found to be the most potent competitive inhibitor for pigeon pea urease.…”