Structural and metal–halogen exchange reactivity studies of sodium magnesiate biphenolate complexes

Bimetallic sodium magnesiates have been employed in metal–halogen exchange for the first time. Utilising the racemic phenoxide ligand 5,5′,6,6′-tetramethyl-3,3′-di-tert-butyl-1,1′-biphenyl-2,2′-diol [(rac)-BIPHEN-H2], the dialkyl sodium magnesiates [(rac)-BIPHEN]Na2MgBu2(TMEDA)2 3 and [(rac)-BIPHEN]Na2MgBu2(PMDETA)2 4 have been synthesised. Both 3 and 4 can be easily prepared through co-complexation of di-n-butylmagnesium with the sodiated (rac)-BIPHEN precursor which can be prepared in situ in hydrocarbon solvent. Prior to the main investigation, synthesis of the sodiated precursor [BIPHEN]2Na4(THF)4 1 was explored in order to better understand the formation of sodium magnesiates utilising the dianionic (rac)-BIPHEN ligand as the parent ligand. In addition, a BIPHEN-rich sodium magnesiate [BIPHEN]2Na2Mg(THF)4 2 was prepared and characterised, and its formation was rationalised. Complex 1 and 4 have also been fully characterised in both solid and solution state. In terms of onward reactivity, 3 and 4 have been tested as potential exchange reagents with aryl and heteroaryl iodides to produce aryl and heteroaryl magnesium phenoxides utilising toluene as a non-polar hydrocarbon solvent. Complex 3 reacted smoothly to give a range of aryl and heteroaryl magnesium phenoxides, whilst 4′s reactivity is more sluggish.