A Ruthenium‐(Ph‐BPE) Catalyst for Asymmetric Alkynylation of Fluoral: Enantioselection From 1 of 12 Fluxional Stereogenic‐at‐Ruthenium Complexes

and (S,S)-Ph-BPE catalyzes highly enantioselective alkynylations of terminal alkynes 1a-1y with fluoral hydrate 2a and related α,α-difluoro-aldehydes 4a-4f. The ruthenium-(Ph-BPE)-catalyst is air- and water-tolerant, operates in the absence of exogenous base, and is chemoselective for alkynylation of fluorinated aldehydes in the presence of aromatic aldehydes. Calculations of the 12 possible stereogenic-at-metal ruthenium-(Ph-BPE) acetylide complexes bound by fluoral reveal that 2 of the 12 octahedral complexes comprise 99.9% of the Boltzmann population, yet, in a Curtin-Hammett-type scenario, the less stable of these two diastereomers dominates the kinetics of carbonyl addition. Fuzzy bond order (FBO) analysis of formyl-hydrogen bonds to iodide versus chloride in the transition states for fluoral addition reveals that the C-H···I hydrogen bonds are stronger due to iodide's greater size and polarizability, which, in part, accounts for the enhanced enantioselectivities of the iodide-bound catalyst.