Fig. 2: Mechanistic insights into the synergistic catalysis through control experiments, kinetic investigation and DFT computations.
a, Control experiment using achiral dppf as the ligand revealed depletion of yields and stereoselectivity. b, Control experiment adding 4 Å molecular sieves (MS) to sequester H2O was deleterious to product yield. c, Control experiment adding 5.5 equiv. H2O under standard conditions gave trace product yield. d, Temporal kinetic profile by in situ NMR monitoring. e, Influence of rhodium catalyst concentration on the kinetic profile. f, Influence of boronic acid catalyst 26 on the kinetic profile. g, Burés overlaid plot with respect to rhodium catalyst concentration. h, Burés overlaid plot with respect to boronic acid 26 concentration. i, Proposed mechanism of the site-selective functionalization by Rh/organoboron synergistic catalysis. The two interlocking catalytic cycles are comprised of the organoboron catalytic cycle (left) and the rhodium catalytic cycle (right). The reversible covalent complexation of the boronic acid 26 and the polyol 15a forms eventually the resting-state organoboronate 33. Similarly, the Rh(I)/Rh(III) redox couple forms the resting-state bridged Rh(III) intermediate 30a. Compounds 33 and 30a then react in the rate-limiting step (RLS) through multiple stereocontrol to generate stereoselectively 17. j, Computed transition state with Gibbs free energy barrier of 18.3 kcal mol–1 of the rate-limiting step at the ωB97M-V/def2-QZVPP/CPCM(THF)//r2SCAN-3c/CPCM(THF) level of theory.
