Oligomerization of Cyclohexylisonitrile by ^tBuELi₂ (E = P, As)

The reaction of tBuAsLi2 with cHexNC in THF at 20 °C leads to a trimerization of the isonitrile. Crystallization from cyclohexane/diglyme gave the salt [Li4{tBuAs(CNcHex)3}2(diglyme)2] (1). In contrast to that, six molecules of cHexNC were consumed in a similar reaction with tBuPLi2 in THF at 20 °C. Recrystallization from DME gave the salt [Li2{tBuP(CNcHex)5(CH)}(DME)2] (2). By treatment of the reaction mixture containing 2 with wet THF, the octanuclear Li+ complex [Li8(O)(cHexNC(H)NHexc)6]·THF (3) was obtained. The existence of 3 is a strong hint at the intermediate NcHex, which had reacted with the isonitrile to give the carbodiimide cHexNCNcHex. Reduction of the carbodiimide with excess tBuPLi2 is probably responsible for the formation of the anion [cHexNC(H)NcHex]- in 3. 1−3 have been characterized by NMR and IR spectroscopy as well as by X-ray analyses. According to this, 1 can be described as a vicinal dilithiated amine in which one negative charge is delocalized over a allylic C3 sequence connected to imine functions and the other negative charge is more or less localized at a nitrogen atom. This arrangement forms dimers in the solid state with a 10-membered LiNC ring. The basic structural motif in 2 is the four-membered EC4 ring already observed in 1 with two additional units of cHexNC and one CH unit, which form a five-membered N2C3 ring. In 1 and 2 the isonitrile molecules are connected to each other by head-to-head linking. 3 consists of an O-centered Li8-cube, the faces which are capped by six anions [cHexNC(H)NcHex]-.