No abstract

The Buchwald-Hartwig amination has been investigated theoretically and experimentally to examine the scope of possible bases under different reaction conditions. Nonpolar solvents resist the formation of new charges. Therefore, the base should be anionic to be able to deprotonate the neutral palladium-amine complex and/or expel the anionic leaving group (bromide). The calculated barrier for the organic base DBU was found to be prohibitively high. In polar solvent, dissociation of bromide becomes possible, but here the base will instead form a complex with palladium, creating an overly stable resting state. The conclusions for both solvent classes hold for both a hindered monodentate phosphine and the labile bidentate ligand BINAP. The computational studies were supported by experimental testing of a range of bases using BINAP in two different solvents, toluene and DMF.

The ruthenium-catalyzed asymmetric hydrogenation of simple ketones to generate enantiopure alcohols is an important process widely used in the fine chemical, pharmaceutical, fragrance, and flavor industries. Chiral diphosphine-RuCl2-1,2-diamine complexes are effective catalysts for the reaction giving high chemo- and enantioselectivity. However, no diphosphine-RuCl2-1,2-diamine complex has yet been discovered that is universal for all kinds of ketone substrates, and the ligands must be carefully chosen for each substrate. The procedure of finding the best ligands for a specific substrate can be facilitated by using virtual screening as a complement to the traditional experimental screening of catalyst libraries. We have generated a transition state force field (TSFF) for the ruthenium-catalyzed asymmetric hydrogenation of simple ketones using an improved Q2MM method. The developed TSFF can predict the enantioselectivity for 13 catalytic systems taken from the literature, with a mean unsigned error of 2.7 kJ/mol.

The mechanism for the iridium-catalyzed asymmetric 13 hydrogenation of prochiral imines has been investigated for an 14 experimentally relevant ligand−substrate combination using DFT 15 calculations. The possible stereoisomers of the stereodetermining hydride 16 transfer transition state were considered for four possible hydrogenation 17 mechanisms starting from the recently disclosed active catalyst consisting 18 of iridium phosphine-oxazoline with cyclometalated imine substrate. The 19 hydrogenation was found to proceed via an outer-sphere pathway. The 20 transition state accurately describes the experimental observations of the 21 active catalyst and provides a structural rationale for the high 22