Esters are valuable electrophiles for cross-coupling due to their ubiquity and ease of synthesis. However, harsh conditions are traditionally required for the effective cross-coupling of ester substrates. Utilizing a recently discovered precatalyst, Pd-catalyzed Suzuki-Miyaura and Buchwald-Hartwig reactions involving cleavage of the C(acyl)-O bond of aryl esters that proceed under mild conditions are reported. The Pd(II) precatalyst is highly active because it is reduced to the Pd(0) active species more rapidly than previous precatalysts.

Aryl carbonates, a common protecting group in synthetic organic chemistry, are potentially valuable electrophiles in cross-coupling reactions. Here, after performing a thorough evaluation of different precatalysts, we demonstrate that (dcypf)­Ni­(2-ethylphenyl)­(Br) (dcypf = 1,1-bis­(dicyclohexylphosphino)­ferrocene) is an efficient precatalyst for Suzuki–Miyaura reactions using a variety of aryl carbonates as substrates. Mechanistic studies indicate that (dcypf)­Ni­(2-ethylphenyl)­(Br), which contains a bidentate phosphine that binds in a trans geometry, is an effective precatalyst for these reactions for two reasons: (i) it rapidly forms the Ni(0) active species and (ii) it minimizes comproportionation reactions between the Ni(0) active species and both the unactivated Ni­(II) precatalyst and on-cycle Ni­(II) complexes to form catalytically inactive Ni­(I) species. In contrast, the state of the art precatalyst (dppf)­Ni­(o-tolyl)­(Cl) (dppf = 1,1-bis­(diphenylphosphino)­ferrocene), which contains a bidentate phosphine that binds in a cis geometry, forms Ni­(I) species during activation and is essentially inactive for aryl carbonate couplings. Although the exact reasons on a molecular level why the dcypf system is more active than the dppf system are unclear, our results indicate that in general Ni catalysts supported by the dcypf ligand will give better performance for catalytic reactions involving substrates which undergo relatively slow oxidative addition, such as aryl carbonates.

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