METAL DERIVATIVES OF MOLECULAR-COMPOUNDS .6. LITHIUM AND (TETRAHYDROFURAN)LITHIUM CYANOTRIMETHYLSILYLAMIDE - SYNTHESES AND STRUCTURE

At different temperatures NN'-bis(trimethylsilyl)carbodiimide (1) and lithium methanide react either under addition or substitution. When co mpound 1, however, is treated at -40-degrees-C with an equimolar amoun t of (1,2-Dimethoxyethan-O,O')lithium phosphanide (2) in 1,2-dimethoxy ethane, only exchange of one trimethylsilyl group versus lithium is ob served and in addition to phosphane and tris(trimethylsilyl)phosphane a very pure lithium derivative insoluble in n-pentane can be isolated. The vibrational spectra prove the compound to be lithium cyanotrimeth ylsilylamide (3). Recrystallization from tetrahydrofuran (+40/+20-degr ees-C) yields (tetrahydrofuran)lithium cyanotrimethylsilylamide (3'). As shown by an X-ray structure analysis {C2/c; a = 2261.1(5); b = 1106 .4(2); c = 1045.9(2) pm; beta = 113,63(1)-degrees; Z = 8 formula units }, compound 3' is polymeric in the solid state. Coordinative Li-N2' bo nds allow a head-to-tail addition of two monomeric units each to give an eight-membered heterocycle with two linear N1-C2=N2 fragments (N1-C 2 126.1; C2=N2 117.5; N1-Si 171.4; Li-N1 203.2; Li-N2'206.1 pm; C2-N1- Li 109.0; N1-Li-N2' 115.9; N2=C2-N1 177.2-degrees). Forming planar fou r-membered Li-N2-Li-N2 rings (Li-N2'''' 198.3 pm; Li'-N2-Li'' 80.3; N2 '-Li-N2'''' 99.5-degrees) these heterocycles polymerize to slightly fo lded tapes.