title: Mixed Aggregates of the Dilithiated Koga Tetraamine: NMR Spectroscopic and Computational Studies.
abstract: A combination of (1) H, (6) Li, (13) C, and (15) N NMR spectroscopies and density functional theory computations explores the formation of mixed aggregates by a dilithium salt of a C2 -symmetric chiral tetraamine (Koga's base). Lithium halides, acetylides, alkoxides, and monoalkylamides form isostructural trilithiated mixed aggregates with few exceptions. (6) Li-(13) C and (6) Li-(15) N couplings reveal heretofore undetected transannular contacts (laddering) with lithium acetylides and lithium monoalkylamides. Marked temperature-dependent (15) N chemical shifts seem to be associated with this laddering. Computational studies shed light on the general structures of the aggregates, their penchant for laddering, and the stereochemical consequences of aggregation.
authors.affiliation: Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853-1301, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Ma
authors.affiliation: Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853-1301, USA.
authors.forename: Kyle A
authors.initials: KA
authors.lastname: Mack
authors.affiliation: Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853-1301, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Liang
authors.affiliation: Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853-1301, USA.
authors.forename: Ivan
authors.initials: I
authors.lastname: Keresztes
authors.affiliation: Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853-1301, USA. dbc6@cornell.edu.
authors.forename: David B
authors.initials: DB
authors.lastname: Collum
authors.affiliation: Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA, 93106, USA. zakarian@chem.uscb.edu.
authors.forename: Armen
authors.initials: A
authors.lastname: Zakarian
mesh_terms: D000588:Amines / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011789:Quantum Theory
chemical_list: D000588:Amines; D056831:Coordination Complexes; D008094:Lithium
keywords: NMR spectroscopy; aggregation; enantioselectivity; lithium; synthetic methods