Surprising reactivity of the unsymmetrically substituted amidinate anion [MeC(NEt)(NtBu)

Abstract

Three unexpected products derived from the unsymmetrically substituted amidinate anion [MeC(NEt)(NtBu)]− are reported. Treatment of 1-tert-butyl-3-ethyl-carbodiimide, tBu-NCN–Et, with 1 equiv. of methyllithium in diethyl ether afforded colorless crystals of the unusual octanuclear lithium amidinate derivative {[LiN(Et)C(Me)N(tBu)]2⋅LiN(Et)C(CH2Li)N(tBu) Et2O}2 (1) in 57% yield instead of the expected lithium amidinate Li[MeC(NEt)(NtBu)]. In the molecule of 1, one central methyl group in a trimer of Li[MeC(NEt)(NtBu)] is deprotoned and two of these partially deprotonated trimers are linked through a central eight-membered [C–N–Li–CH2]2 ring to afford the octanuclear product 1. The same reaction carried out in 1,2-dimethoxyethane (DME) solution produced the oxygen-centered, heptanuclear lithium amidinate cluster {Li[MeC(NEt)(NtBu)]}5⋅Li2O (2) (21% yield). Treatment of anhydrous praseodymium trichloride with in situ-prepared Li[MeC(NEt)(NtBu)] in Et2O/THF afforded green (THF)Li[Pr{MeC(NEt)(NtBu)}4] (3) as the first anionic tetrakis(amidinato)lanthanide(III) complex in 55% isolated yield. The molecular and crystal structures of all three new compounds have been elucidated by X-ray diffraction.