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Steric and Solvation Effects on the Aggregation of Lithium Thioamidates:  Single-Strand Polymers with (LiS)n and (LiNCS)n Backbones

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posted on 04.11.1999, 00:00 authored by Tristram Chivers, Andrew Downard, Masood Parvez
The addition of methyllithium or n-butyllithium to alkyl isothiocyanates produces lithium thioamidates {Li[RCS(NR‘)]}n. Three such compounds were structurally characterized after recrystallization from THF. When R = n-Bu and R‘ = t-Bu, an unsolvated hexamer {Li[n-BuCS(N-t-Bu)]}6 (1) is obtained. By contrast, the solvated derivatives {Li·THF[MeCS(N-t-Bu)]} (2·THF) and {Li·2THF[MeCS(NMe)]} (3·2THF) form single-strand polymers. The monosolvated complex 2·THF involves four-membered rings with an (LiS)n backbone whereas the disolvate 3·2THF is comprised of LiNCS repeating units. The structures of all three aggregates can be generated via sterically directed solvation of a common dimeric precursor. Crystal data for 2·THF: C10H20NLiOS, monoclinic, P21/a (#14), a = 9.129(2) Å, b = 11.099(2) Å, c = 12.537(2) Å, β = 94.14(2)°, V = 1267.0(4) Å3, Z = 4. Crystal data for 3·2THF: C11H22NLiSO2, monoclinic, P21/a (#14), a = 10.974(3) Å, b = 8.575(5) Å, c = 14.898(5) Å, β = 91.33(3)°, V = 1401.6(10) Å3, Z = 4.