Solution structures of chiral lithium amides with internal sulfide coordination: sulfide versus ether coordination in chiral lithium amides

Correlation between the 6Li,15N Coupling Constant and the Coordination Number at Lithium

“…[5][6][7][8] Maddaluno, Williard and our group have reported NMR studies revealing the reactive species in stereoselective additions of n-butyllithium (nBuLi), methyllithium and lithioacetonitrile to aldehydes. [7][8][9][10][11] Because of the importance of chiral lithium amides with chelating groups, it is essential that their structures and the effect of chelating groups are better understood. Recently, there has been an increased focus on studies of structure-reactivity relationships for the development of efficient and selective transformations, often needed within, for example, the pharmaceutical industry.…”

“…[4,8,10,11,14,15] It is known that the specific solvation at lithium may affect not only the reactivity, but also the stereoselectivity obtained in reactions with chiral lithium amides. Unfortunately, the design of new and powerful chiral lithium amides and catalytic systems is limited by lack of a thorough understanding of the factors determining the solvation at lithium.…”

NMR studies of chiral lithium amides with phosphine chelating groups reveal strong Li-P-interactions in ethereal solvents

“…alkyllithium reagents. 7 Detailed NMR studies on the dynamic processes, e.g. lithium-lithium and ligand-ligand exchange 8 and the magnitude of the 15 N, 6 Li coupling constant 9 have revealed important facts towards a better understanding of these synthetically important reagents.…”

“…To the best of our knowledge there are only a handful of reports of lithium chelating phosphine groups, were direct 7 Li, 31 P couplings have been observed. 11 Interestingly some of these chelates are also observed in tetrahydrofuran (THF) solution but these structures also exhibit substantial sterical hinderance that may force them to yield short lithium-phosphine distances, which are reflected in the observation of 7 Li, 31 P couplings.…”

“…11 Interestingly some of these chelates are also observed in tetrahydrofuran (THF) solution but these structures also exhibit substantial sterical hinderance that may force them to yield short lithium-phosphine distances, which are reflected in the observation of 7 Li, 31 P couplings. Herein we now report detailed NMR studies of the structures and dynamics of chiral N,P-lithium amides by low temperature NMR.…”