Cyclopalladated Ferrocenylimine as Efficient Catalyst for the Syntheses of Arylboronate Esters

Abstract

The cyclopalladated ferrocenylimine I and its phosphine adducts IIa-f were prepared and evaluated in the borylation of aryl halides. The tricyclohexylphosphine adduct IIb exhibited highly catalytic activity for the coupling of aryl and heteroaryl bromides containing various functional groups with low catalyst loading (2 mol%). Aryl and heteroaryl chlorides were smoothly converted into the corresponding boronates in the presence of the monophosphinobiaryl ligand (XPhos) adduct IIf. It was proposed that palladacycle was only a reservoir of the catalytically active species from the investigation on the reaction mechanism.

Scope of the Palladium-Catalyzed Aryl Borylation Utilizing Bis-Boronic Acid

“…Through a thorough literature search of heteroaryl boronates synthesized from B 2 Pin 2 or H-BPin, two trends can be found: either the method reported is purely for one functionalized heteroaryl, 50–60 or only a few examples were synthesized under reaction conditions considered under a “general” methods procedure. 14,40,42,44,61–64 Also noteworthy is that the heteroaryls examined in this search are among just a handful of heteroaryl borylated products that can be found in the literature, and there is no publication dedicated solely to the Miyaura borylation of heteroaryls using B 2 Pin 2 . Our findings, coupled with the literature results, provide evidence that a general method for the borylation of hetereoaryls remains elusive, and that each substrate or general class of substrates may need to be treated on a case-by-case basis.…”

Tri-p-tolylphosphine-cyclopalladated ferrocenylpyrimidine complexes: synthesis, crystal structures, catalytic activity, and a palladacycle cocrystallization adduct

“…In this context, the active species was proposed to be a Pd(0) ''Pd-PR 3 '' species, and it was shown that the cyclopalladated ligand was released from the metal center during activation [27,28]. We have also found that these monophosphine-palladacycles are far more active than the corresponding dimeric palladacycles.…”

Recent progress in the synthesis of pyridinylboronic acids and esters

“…The most commonly used tetraalkoxydiboron was bis(pinacolato)diboron (B 2 Pin 2 , 9). [54][55][56][57][58][59][60][61][62] Other tetraalkoxydiboron compounds such as (neopentylglycolato)diboron (10) were also reported. 63 Dialkoxyhydroborane compounds like (pinacolato)-hydroborane (HBPin, 11) are occasionally reported as well.…”

“…13, where L = 12). 57 KOAc is generally used as the base, as stronger bases (e.g. K 3 PO 4 and K 2 CO 3 ) may lead to side reactions such as homo-coupling.…”

“…K 3 PO 4 and K 2 CO 3 ) may lead to side reactions such as homo-coupling. 56,57 Dioxane, DMSO, and DMF are usually employed as solvents, and the duration and temperature of the reactions are variable. 57 A summary of the literature results is presented in Table 3.…”