Solid-State and Theoretical Model Structures of Monolithiated (Organosulfonyl)acetonitriles and the Characterization and Reactivity of Their Geminated Dilithio Derivatives

Abstract

Two monolithiated (organosulfonyl)acetonitriles [PhSO2CHCNLi·TMEDA], 1, and [t-BuSO2CHCNLi·THF], 2, have been synthesized and, in turn, characterized in the solid state by X-ray crystallography. The complexes form novel chain and sheet polymeric structures in preference to the more common (SO2Li)2 or Li2N2 ring dimers associated with lithiated sulfones or nitriles. The X-ray crystal structures of the parent ligands RSO2CH2CN, where R = Ph 5 or t-Bu 6, were also elucidated to allow a direct evaluation of the effects of metalation on the bonding within the complexes. Ab initio calculations at the HF/6-31G* level of theory support the view that the simple dimers are not formed due to the inflexibility of the ligand backbone, precluding chelation and consequently destabilizing these structures. In contrast, polymer formation allows the metal to bridge between separate ligands, eliminating the need for internal chelation. Both 1 and 2 contain “naked” anions where there is no direct bond between the anionic C atoms and the metal centers. The anionic C atom in 2 is essentially planar, whereas in 1 this center is distinctly pyramidylized. Crystal structure and solution 1H and 13C NMR data, in combination with ab initio (HF/6-31G*) and density functional (B3LYP/6-31++G**) calculations on model systems, indicate that both the sulfonyl and the nitrile units of the ligands participate in delocalizing the charge of the anions throughout the SCC⋮N linkage. In addition, the dilithiated salts [PhSO2CCNLi2·THF], 3, and [t-BuSO2CCNLi2·0.75THF], 4, have been prepared by the reaction of 2 equiv of MeLi with 5 or 6 in THF solution. Both complexes have been characterized by 1H and 13C NMR spectroscopy and found to be authentic geminal organodimetallic species, with the methylene group being doubly deprotonated. Complexes 3 and 4 react cleanly with excess MeI to form the dialkylated products PhSO2CMe2CN, 7, and t-BuSO2CMe2CN, 8, respectively, in a single step.