A “Lithium-Bonded” Cyclopropyl Edge: The X-ray Crystal Structure of [Li−O−C(Me)−(c-CHCH2CH2)2]6 and Computational Studies

The short Li−C distances (Li 1 −C 2 = 2.615(3) Å, Li 1 −C 3 = 2.644(3) Å) in the X-ray crystal structure of [Li−O−C(Me)−(c-CHCH 2 CH 2 ) 2 ] 6 ( 7 ) 6 characterize Li−cyclopropane edge coordinations. The Li−cyclopropane interactions increase the C 2 −C 3 distances (1.519(3) Å) relative to those of the free cyclopropyl edges (C 2 −C 4 = C 6 −C 7 = 1.499(2) Å) by 0.02 Å. The bent bonds of cyclopropane give rise to an electrostatic potential pattern, which strongly favors edge coordination as is observed experimentally in ( 7 ) 6, but also permits a metastable Li + face complex. The cyclopropane edge also is the favored site for hydrogen bonding, but not for protonation. The C−C bond length elongations, the coordination energies E coord, and the charge redistributions upon metal cation edge interactions all are related to the distances between the cyclopropane C−C bond centers and the cations. This is evaluated for the alkali metal cation−cyclopropane complexes (cation = Li + to Cs + ). More generally, the cyclopropane C−C bond length variations can be employed as a structural measure for the magnitudes of electrostatic interactions.