Synthesis, Structure, and Electronic Properties of Bis(tetramethylcyclopropylidene)methane and Bis(cyclopropylidene)methane

Abstract

Bis(tetramethylcyclopropylidene)methane ( 5 ) was prepared by treating 1‐(dichloroethenylidene)‐2,2,3,3‐tetramethylcyclopropane ( 3 ) with tert ‐butyllithium in the presence of 2,3‐dimethyl‐2‐butene. The parent allene 6 was obtained along a new route from bis(1‐bromocyclopropyl) ketone ( 11 ) with low‐valent titanium. Both 5 and 6 show unusually intense allene stretching bands in the IR spectra, and the signals of their central carbon atoms appear at remarkably high field in the 13 C‐NMR spectra. The unique structural features of 5 and 6 , as evidenced by an X‐ray crystal structural analysis of 5 and 1 J cc values, agree remarkably well with theoretical predictions made by semiempirical (MNDO) and ab initio (4‐31G) calculations and on the basis of the simple picture offered by the hybridization model using the iterative maximum overlap (IMO) approach.