Crystal Structure of η3‐lithio‐1,3,3‐triphenylpropyne‐(diethyl ether)2 and [1‐lithio‐1‐(2‐methoxyphenyl)‐3,3‐diphenylallene–diethyl ether]2: Propargyl‐ versus allenyl‐type structures

Crystal structure investigations reveal that η3‐lithio‐1,3,3‐triphenylpropyne‐(diethyl ether)2 [6 · (OEt2)2] is of the propargyl structural type while [1‐lithio‐1‐(2‐methoxyphenyl)‐3,3‐diphenylallene‐(diethyl ether)]2 {[7 · OEt2]2} is of the allenyl type. The assignment of the different structural types is mainly based on a comparison of the bond lengths C1‐C2 and C2‐C3 as well as of the difference ΔCC of these two bond lengths with the corresponding values of theoretical models of the propargyl and allenyl type. This leads also to a correction of an earlier assigned structural type.