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-H-2], 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](2)Na-4(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](2)Na2Mg(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.