Asymmetric autocatalysis: crystallization-induced highly enantioselective synthesis of a conglomerating oxo-rhenium(V) complex

Experiments designed to elucidate the mechanistic foundation and origins of enantioselectivity in a symmetry breaking synthesis are described. The autocatalytic enantioselective preparation of the title complex cis-[ReOCl2(P ∼ O)py] [py = pyridine; P ∼ O = (OCMe2CMe2O)POCMe2CMe2O(1−)], either C or A handed, from optically inactive substrates can be controlled by catalytic quantities of the non-racemic conglomerating product. The synthesis can be accomplished due to enantioselective complex formation and concomitant isomerization processes if the system reacts under strongly disturbed conditions (i.e., under vigorous stirring and boiling). For the first time we demonstrate practically that the two intrinsic mirror-image symmetry breaking phenomena, that is, enantioselective synthesis and spontaneous resolution of chemical compounds, can cooperate effectively leading to strong asymmetric amplification and high enantioselectivity in the system. When such cooperation is inadequate, sluggish deracemization occurs solely due to spontaneous resolution, known also as crystallization-induced asymmetric disequilibration mechanism. The experimental data obtained are in good accordance with recently developed theoretical models for chiral symmetry breaking processes. We assume that the system represents at least formally a highly efficient, inorganic, one-pot congener of the renowned organometallic Soai system.

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[OC-6-52-C]-Dichlorooxo{2,3-dimethyl-3-(4,4,5,5-tetramethyl-[1,3,2]dioxaphospholan-2-yloxy)-butan-2-oxo}(pyridine)rhenium(V)C13H27Cl2O5PReEe = 100%[α]D25=+1380 (c 0.05, CH2Cl2)Source of chirality: autocatalytic asymmetric synrhesisAbsolute configuration: C