β-Boration of α,β-unsaturated carbonyl compounds in ethanol and methanol catalyzed by CCC-NHC pincer Rh complexes

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

“…Investigations into the catalytic potential of zerovalent palladium or nickel complexes in asymmetric β-borylation of α,β-unsaturated esters were conducted by Fernández, Westcott, and co-workers, while Oshima et al reported a zerovalent nickel phosphine system that catalyzed the borylation of α,β-unsaturated esters and amides . Similar reactivity has been observed with [RhCl­(PPh 3 ) 3 ] for the borylation of α,β-unsaturated carbonyls and nitriles with B 2 pin 2 and B 2 neop 2 , while recently a CCC–NHC pincer Rh complex was shown to quantitatively borylate α,β-unsaturated carbonyl compounds with B 2 pin 2 , with the latter used to generate products with boron-substituted quaternary carbon centers . Additionally, Nishiyama and co-workers reported the rhodium­(I)-catalyzed enantioselective β-borylation of α,β-unsaturated ketones, esters, and amides with B 2 pin 2 . , In contrast to Fernández’s palladium and nickel systems, the rhodium­(I) catalyst showed decreased enantioselectivity with bulkier ester functionalities. , The use of palladium as a catalyst for the borylation reaction was further exploited by Fernández and co-workers, who performed a tandem borylation/arylation of α,β-unsaturated carbonyls with the use of a single palladium catalyst …”

“…546 Similar reactivity has been observed with [RhCl(PPh 3 ) 3 ] for the borylation of α,βunsaturated carbonyls and nitriles with B 2 pin 2 and B 2 neop 2 , 547 while recently a CCC−NHC pincer Rh complex was shown to quantitatively borylate α,β-unsaturated carbonyl compounds with B 2 pin 2 , with the latter used to generate products with boron-substituted quaternary carbon centers. 548 Additionally, Nishiyama and co-workers reported the rhodium-(I)-catalyzed enantioselective β-borylation of α,β-unsaturated ketones, esters, and amides with B 2 pin 2 . 549,550 In contrast to Fernańdez's palladium and nickel systems, 545 the rhodium(I) catalyst showed decreased enantioselectivity with bulkier ester functionalities.…”

Multidentate NHC complexes of group IX metals featuring carbon-based tethers: Synthesis and applications

“…The group of Hollis [69,105] was successful in applying complexes 34, 99, and 100 as active catalysts in the hydroboration of alkene and carbonyl-containing compounds. In their pilot study utilising the cobalt complex 34 (0.3 mol%), the hydroboration of styrene at room temperature was investigated.…”

Development of Methods to the Synthesis of β‐Boryl Acyls, Imines and Nitriles

“…Inspired by their initial work on rhodium-catalyzed 1,4addition of aryl boronic acids to α,β-unsaturated ketones, and aldehydes, [102] recently the Hollis group reported the first example of CCC-NHC pincer rhodium-complex catalyzed βborylation of cyclic and acyclic enones (Scheme 19c). [103] Substrates with alkyl and aryl group at β-position can easily be borylated and furnish the tertiary and quaternary boronsubstituted product in good yield. The outcome is compatible with the catalytic cycle proposed by the Nishiyama group.…”