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Regiodivergent Conjugate Addition Controlled by Rhodium(I) and Palladium(II) Catalysts: A Combined Computational and Experimental Study
Author(s) -
Jung Hoimin,
Lee Ansoo,
Kim Jin,
Kim Hyunwoo,
Baik MuHyun
Publication year - 2017
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201700628
Subject(s) - regioselectivity , chemistry , rhodium , palladium , catalysis , alkene , selectivity , reductive elimination , combinatorial chemistry , phosphoramidite , ligand (biochemistry) , medicinal chemistry , conjugate , stereochemistry , organic chemistry , biochemistry , receptor , dna , oligonucleotide , mathematical analysis , mathematics
A new divergent catalytic method for the 1,4‐ and 1,6‐selective conjugate additions of arylboronic acids to α,β,γ,δ‐unsaturated imino esters mediated by two different transition metal systems was developed. The rhodium complex carrying briphos, a new bicyclic, bridgehead phosphoramidite ligand, showed excellent regioselectivity towards 1,4‐addition with product ratios of >50:1, whereas the palladium catalyst Pd(OPiv) 2 reversed the regiochemistry to afford the 1,6‐product with mild levels of selectivity of ≈1:7. Both theoretical and experimental studies were utilized to understand the catalytic systems and to elucidate the molecular level mechanism leading to the selective reactions. Since Rh(I) and Pd(II) are both d 8 ‐complexes, their electronic structures and binding behaviours can be compared. Our calculations suggest that the outcome of the catalysis in the Rh(I) system is under kinetic control, where the migratory insertion of the alkene is the step that determines the regiochemistry. When the Pd(II) catalyst is used, the regiochemistry is under thermodynamic control where the relative stability of the η 3 ‐π‐allyl‐ over the η 3 ‐aza‐π‐allyl‐intermediate dictates the selectivity at the 1,6‐migratory insertion step.