Reactivity of 1,3-Disubstituted Indoles with Lithium Compounds: Substituents and Solvents Effects on Coordination and Reactivity of Resulting 1,3-Disubstituted-2-Indolyl Lithium Complexes

摘要

Reactivity of 1,3-disubstituted indolyl compounds with lithium reagents was studied to reveal the substituents and solvent effects on coordination modes and reactivities resulting in different indolyl lithium complexes. Treatment of 1-alkyl-3-imino functionalized compounds 1-R-3,(R'N=CH)C8H5N [R = Bn, R' = Dipp (HL1); R = Bn, R' = Bu-t (HL2); R = CH3OCH2, R' Dipp (HL3); Dipp = (Pr2C6H3)-Pr-i] with Me3SiCH2Li or (BuLi)-Bu-n in hydrocarbon solvents (toluene or n-hexane) produced 1,3-disubstituted-2-indolyl lithium complexes [eta(1):(;mu(2)-eta(1)':eta(1))-1-Bn-3-(DippN=CH)-C8H4NLi](2) (1), {[eta(1):(mu(3)-eta(1):eta(1):eta(1)")-1-Bn-3-((BuN)-Bu-t=CH)C8H4N] [eta(2):eta(1):(mu(2)-eta(1):eta(1))-1 Bn 3 ((BuN)-Bu-t-7-CH) C8H4N] [eta(1):(mu(2)eta(1):eta(1))-1-Bn-3-((BON)-B-t= CH) C8H4N]Li-3} (2), and [eta(1):eta(1): (mu(2)eta(1):eta(1))-1-CHOCH2-3-(DippN=CH)C8H4NLi](2) (3), respectively. The bonding modes of the indolyl ligand were kept in 1 by coordination with donor solvent, affording [eta(1):(mu(2)-eta(1):eta(1))-1-Bn-3-(DippICH)C8H4NLi(THF)](2) (4). The trinuclear complex 2 was converted to dinuclear form with a change of bonding modes of the indolyl ligand by treatment of 2 with donor solvent THF, producing [eta(1):(mu(2),eta(1):eta(1))-1-Bn-3-(BuN=CH)C8H4NLi(THF)](2) (5). X-ray diffraction established that compounds. 1, 3, 4, and 5 crystallized as dinuclear structures with the carbanionic sp2 carbon atoms of the indolyl ligands coordinated to lithium ions in a mu(2)-eta(1):eta(1) manner, while compound 2 crystallized as a trinnclear structure and the carbanionic atoms of the indolyl Moieties coordinated to lithium ions in mu(2)-eta(1):eta(1) and mu(3)-eta(1):eta(1):eta(1) manners. When the lithiation reaction of HL1 with 1 equiv of "BuLi was carried out in THF, the monomeric lithium complex;(eta(1):eta(1)-1-Bn-3-(DippN=CH)-2-1[1'-Bn-3'-(DippNCH)C8H5N]C8H4NLi(THF)} (6) having coupled indolyl moieties was obtained: The compound 6 can also be prepared by the reaction of 1 with 0.5 equiv of HL1 with a higher isolated yield. Accordingly, the lithium Complexes [eta(1):eta(4)-1-Bn-3-'BuN=CH-2-(1'-Bn-3'-tBuNCHC(8)H(5)N)C8H4NLi(L)] (L = THF, 7a; L = Et2O, 7b) with the coupled indolyl moieties in 174 mode were isolated by treatment of HL2 with 2 in THF or Et2O. All complexes were characterized by spectroscopic methods, and their structures were determined by X-ray diffraction study.