3 research outputs found
Mixed Crystalline Lithium Organics and Interconversion in Solution
Scrambling, but not the Humpty Dumpty way! The crystallographically
confirmed mixed lithium organic [<sup><i>t</i></sup>BuLi]<sub>4</sub>·4Â[Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li]<sub>4</sub> (<b>1</b>) consists of independent alkyl- and
aryllithium tetramers in a 1:4 ratio. It has been employed to study
the interconversion in solution. <sup>7</sup>Li-DOSY and <sup>7</sup>Li-EXSY NMR spectroscopy was utilized to establish the nature of
that exchange and to determine related rate constants along the equilibria
to give [Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li]<sub>4</sub> (<b>A</b>), [(Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li)<sub>3</sub>(<sup><i>t</i></sup>BuLi)] (<b>B</b>), [(Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li)<sub>2</sub>(<sup><i>t</i></sup>BuLi)<sub>2</sub>] (<b>C</b>), [(Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li)Â(<sup><i>t</i></sup>BuLi)<sub>3</sub>] (<b>D</b>), and [<sup><i>t</i></sup>BuLi]<sub>4</sub> (<b>E</b>)
Mixed Crystalline Lithium Organics and Interconversion in Solution
Scrambling, but not the Humpty Dumpty way! The crystallographically
confirmed mixed lithium organic [<sup><i>t</i></sup>BuLi]<sub>4</sub>·4Â[Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li]<sub>4</sub> (<b>1</b>) consists of independent alkyl- and
aryllithium tetramers in a 1:4 ratio. It has been employed to study
the interconversion in solution. <sup>7</sup>Li-DOSY and <sup>7</sup>Li-EXSY NMR spectroscopy was utilized to establish the nature of
that exchange and to determine related rate constants along the equilibria
to give [Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li]<sub>4</sub> (<b>A</b>), [(Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li)<sub>3</sub>(<sup><i>t</i></sup>BuLi)] (<b>B</b>), [(Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li)<sub>2</sub>(<sup><i>t</i></sup>BuLi)<sub>2</sub>] (<b>C</b>), [(Me<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>Li)Â(<sup><i>t</i></sup>BuLi)<sub>3</sub>] (<b>D</b>), and [<sup><i>t</i></sup>BuLi]<sub>4</sub> (<b>E</b>)
Aggregation of Donor Base Stabilized 2-Thienyllithium in a Single Crystal and in Solution: Distances from X-ray Diffraction and the Nuclear Overhauser Effect
Various 2-thienyllithium derivatives were investigated
in the solid
state by X-ray diffraction and in solution by 2D NMR experiments.
The determined structures of [(Et<sub>2</sub>O)ÂLiÂ(C<sub>4</sub>H<sub>3</sub>S)]<sub>4</sub> (<b>1</b>), [(THF)<sub>2</sub>LiÂ(C<sub>4</sub>H<sub>3</sub>S)]<sub>2</sub> (<b>2</b>), [(DME)ÂLiÂ(C<sub>4</sub>H<sub>3</sub>S)]<sub>2</sub> (<b>3</b>), [(TMEDA)ÂLiÂ(C<sub>4</sub>H<sub>3</sub>S)]<sub>2</sub> (<b>4</b>), and [(PMDETA)ÂLiÂ(C<sub>4</sub>H<sub>3</sub>S)] (<b>5</b>) (DME = 1,2-dimethoxyethane,
TMEDA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylene-1,2-diamine, and PMDETA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>″,<i>N</i>″-pentamethyldiethylenetriamine)
were solved in nondonating toluene and provide firm ground for diffusion-ordered
NMR spectroscopy as well as heteronuclear Overhauser enhancement NMR
spectroscopy. The distance relation of nuclear Overhauser effects
with a factor of <i>r</i><sup>–6</sup> is employed
to gain further insight into the aggregation degree of <b>1</b>–<b>5</b> in solution. Comparison of the slope provided
by the linear region of the buildup curves and of the ∑<i>r</i><sup>–6</sup> calculated distances from the crystal
structures offers a handle to judge the structure retention versus
conversion in solution. The structures of <b>3</b>–<b>5</b> are maintained in toluene solution. The data of <b>2</b>, however, indicate a partial dissociation or a rapid exchange between
the vertices of a tetrameric core and free THF molecules. Auxiliary
exchange spectroscopy investigations showed that the signals of the
nitrogen donor base containing compounds <b>4</b> and <b>5</b> exchange with the signals of nonlithiated thiophene. This
is explained by exchange of the deuterium by a hydrogen atom via lithiation
of toluene molecules