Complexation of dimethylmagnesium with alpha-diimines; structural and EPR characterisation of single electron and alkyl transfer products.

Treatment of dimethylmagnesium with the alpha-diimine ligands Ar'N=C(R)C(R)=NAr' [R = naphth-1,8-diyl (1), H (2), CH3 (3); Ar' = 2,6-diisopropylphenyl] in diethyl ether provides the neutral methyl-bridged dimeric complexes [(alpha-diimine-.)Mg+(mu-CH3)]2 via single electron transfer (SET) to the coordinated diimine and elimination of a methyl radical. These biradical species have been characterised by EPR spectroscopy and, for the ligand , X-ray crystallography. In the presence of THF the reaction of ligand proceeds to the diamagnetic [(ene-1,2-diamide)Mg(THF)3] complex in which the diimine ligand has been doubly reduced to an ene-diamide by two successive SET processes. Comparison of the structural data for the free ligand with that obtained for the alpha-diimine radical anion and ene-diamide complexes shows the expected increases in C-N, and decreases in C-C, bond lengths within the N-C-C-N unit consistent with the progressive reduction of the ligand. In the case of ligand , reaction at low temperature provides the complex [Mg(mu2-Me){Ar'NC(Me)2C(Me)NAr'}]2 in which methyl transfer to a ligand imine carbon atom has occurred. This species has also been structurally characterised. This contrasts with the formation of the radical species at room temperature, and indicates the involvement of an intermediate in which the radical products of the SET process are held in close proximity by the solvent cage. Two competing processes of methyl radical escape and methyl transfer to the ligand account for the formation of the observed products at different temperatures.

Structural and EPR characterisation of single electron and alkyl transfer products from reaction of dimethyl magnesium with bulky alpha-diimine ligands.

Treatment of dimethylmagnesium with bulky alpha-diimine ligands provides either the biradical methyl-bridged complexes [(alpha-diimine-.)Mg+(mu-CH3)]2 via single electron transfer (SET), or the product of methyl transfer to an imine carbon atom depending upon conditions.

The first structural characterisation of a group 2 metal alkylperoxide complex: comments on the cleavage of dioxygen by magnesium alkyl complexes.

A new high-yield synthesis of [(PhCH(2))(2)Mg(thf)(2)] and [[(PhCH(2))CH(3)Mg(thf)](2)] via benzylpotassium has allowed a simple entry into benzylmagnesium coordination chemistry. The syntheses and X-ray crystal structures of both [(eta(2)-Me(2)NCH(2)CH(2)NMe(2))Mg(CH(2)Ph)(2)] and [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] (Ar'=2,6-diisopropylphenyl) are reported. The latter beta-diketiminate complex reacts with dioxygen to provide a 1:2 mixture of dimeric benzylperoxo and benzyloxo complexes. The benzylperoxo complex [[eta(2)-HC[C(CH(3))NAr'](2)Mg(mu-eta(2):eta(1)-OOCH(2)Ph)](2)] is the first example of a structurally characterised Group 2 metal-alkylperoxo complex and contains the benzylperoxo ligands in an unusual mu-eta(2):eta(1)-coordination mode, linking the two five-coordinate magnesium centres. The O[bond]O separation in the benzylperoxo ligands is 1.44(2) A. Reaction of the benzylperoxo/benzyloxo complex mixture with further [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] results in complete conversion of the benzylperoxo species into the benzyloxo complex. This reaction, therefore, establishes the cleavage of dioxygen by this system as a two-step process that involves initial oxygen insertion into the Mg[bond]CH(2)Ph bond followed by O[bond]O/Mg[bond]C sigma-bond metathesis of the resulting benzylperoxo ligand with a second Mg[bond]CH(2)Ph bond. The formation of a 1:2 mixture of the benzylperoxo and benzyloxo species indicates that the rate of the insertion is faster than that of the metathesis, and this is shown to be consistent with a radical mechanism for the insertion process.