Collect. Czech. Chem. Commun. 2009, 74, 255-273
Published online 2009-02-14 09:21:11

Gaseous Ni+ complexes with BINOL derivatives and chiral esters in the gas phase: an experimental and theoretical investigation

Francesca R. Novaraa, Xinhao Zhanga, Detlef Schröderb,* and Helmut Schwarza,*

a Institut für Chemie der Technischen Universität Berlin, Strasse des 17. Juni 135, 106 23 Berlin, Germany
b Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo nám. 2, 166 10 Prague 6, Czech Republic


The gas-phase behavior of monocationic Ni(II) complexes that contain as building blocks optically pure BINOL derivatives and two chiral hydroxy esters is investigated by means of electrospray ionization (ESI) mass spectrometry. Upon collision-induced dissociation (CID), the complexes containing ethyl 2-hydroxypropionate (ethyl lactate) only lose the ester ligand. The complexes bearing ethyl 3-hydroxybutyrate instead either lose the ester ligands or undergo bond activation followed by elimination of the corresponding β-ketoester (ethyl acetylacetate) as revealed by deuterium labeling. Comparison of the results obtained for com- plexes with different chiralities reveals the operation of a significant stereochemical effect (SE) in the gas-phase dehydrogenation of ethyl 3-hydroxybutyrate by gaseous [(BINOLato)Ni]+ ions. Instead, no substantial differences in the CID patterns for the complexes bearing the ester-substituted BINOL derivative are found. The results provide insights into the gas-phase coordination of metal cations by BINOL derivatives and into the molecular features, which are responsible for gas-phase enantioselective processes. Additional mechanistic aspects are disclosed by exploratory calculations employing density functional theory using the B3LYP method.

Keywords: BINOL; Enantioselectivity; Ethyl butyrate; Ethyl lactate; Mass spectrometry; Nickel; Binaphthyls; Binaphthols; Collision-induced dissociation; DFT calculations.

References: 37 live references.