Structural Studies of (<i>rac</i>)‑BIPHEN
Organomagnesiates and Intermediates in the Halogen–Metal Exchange
of 2‑Bromopyridine
Javier Francos
Philippe C. Gros
Alan R. Kennedy
Charles T. O’Hara
10.1021/om501225g.s001
https://acs.figshare.com/articles/dataset/Structural_Studies_of_i_rac_i_BIPHEN_Organomagnesiates_and_Intermediates_in_the_Halogen_Metal_Exchange_of_2_Bromopyridine/2160574
Four
lithium magnesiate complexes (<b>2</b>–<b>5</b>) containing the dianionic (<i>rac</i>)-BIPHEN
ligand have been prepared and characterized using X-ray crystallography
and NMR spectroscopy. (THF)<sub>3</sub>·Li<sub>2</sub>Mg{(<i>rac</i>)-BIPHEN}<sup><i>n</i></sup>Bu<sub>2</sub>, <b>2</b>, (THF)<sub>3</sub>·Li<sub>2</sub>Mg{(<i>rac</i>)-BIPHEN}(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>, <b>3</b>, and (THF)<sub>2</sub>·Li<sub>2</sub>Mg{(<i>rac</i>)-BIPHEN}<sup><i>neo</i></sup>Pe<sub>2</sub>, <b>4</b>, have been prepared by complexation of the appropriate dialkylmagnesium
compound with <i>in situ</i> prepared Li(<i>rac</i>)<i>-</i>BIPHEN in a mixture of hydrocarbon/THF. For all
structures, the Mg centers are four-coordinate (and retain the alkyl
groups); however, in <b>2</b> and <b>3</b> the two Li
centers have different coordination spheres (one binding to one THF
molecule, the other to two). The solid-state structures of <b>2</b> and <b>3</b> are essentially isostructural with that of <b>4</b> except that both Li atoms in this molecule have equivalent
coordination spheres. The solution behaviors of these three molecules
have been studied by <sup>1</sup>H, <sup>13</sup>C, and DOSY NMR spectroscopy.
During the synthesis of <b>2</b>, it was discovered that a (<i>rac</i>)-BIPHEN-rich (or <i>n</i>-butyl-free) lithium
magnesiate, (THF)<sub>4</sub>Li<sub>2</sub>Mg{(<i>rac</i>)-BIPHEN}fo<sub>2</sub>, <b>2b</b>, could be isolated. The
lithium precursor to <b>2</b>–<b>5</b>, (THF)<sub>4</sub>·Li<sub>4</sub>{(<i>rac</i>)-BIPHEN)}<sub>2</sub>, <b>1</b>, has also been isolated. Within the molecular structure
of this tetranuclear complex, there are three different Li coordination
environments. Finally, <b>2</b> has already shown promise as
a reagent in a halogen–metal exchange reaction with 2-bromopyridine.
The structural chemistry at play in this reaction was probed by X-ray
crystallography and NMR spectroscopy. The organometallic intermediate
pyridyl-magnesiated <b>5</b>, (THF)<sub>2</sub>·Li<sub>2</sub>Mg{(<i>rac</i>)-BIPHEN}(2-pyridyl)<sub>2</sub>,
was isolated in high yield.
2015-06-08 00:00:00
Li coordination environments
THF
NMR spectroscopy
DOSY NMR spectroscopy
equivalent coordination spheres
rac
lithium
molecule