The IR spectra of oligo-lithium butadienyl and of its deuterized analogues

In an attempt to interpret the IR spectra of the oligolithium butadienyl (LOB) terminal chain units we produced and studied those containing various numbers of D atoms, namely the 6 (D6), the D4-1, 1, 4,4-LOB and the D2-2,3-LOB, and also their complexes in iso-octane with THF at LOB : THF = 4 : 0·1 in the temperature range from +25 to −100°C. A preliminary correlation of the CLi valence oscillation lines in the terminal chain units was made with those of the CαH2 and =CH2 deformation lines. Three types of LOB-THF complexes were found, of which the first has the composition [LOB]4·4THF. The second and third type of complex will form when an excess of THF is used (1 : 10), but these exist at various temperatures. The high temperature complex 2 seems to belong to less associated forms of LOB when compared with complex 1; the former has strongly ionized CLi bonds. A transformation of the CαH2 group takes place in complex 3 in the range from −60 to −100°C which is accompanied by a CLi frequency increase.