Structural elucidation of tmeda-solvated alkali metal diphenylamide complexes

Lithium, sodium and potassium salts of diphenylamine have been prepared by using a deprotonative route and characterised in both, solid state (by X-ray crystallography) and solution(by NMR spectroscopic studies). In each case the metal atom's coordination sphere is completed by coordination to the synthetically important co-ligand N,N,N,N-tetramethylethylenediamine (tmeda). Complexes 1 and 2 [{(tmeda)- M(NPh2)}2] (M = Li for 1, Na for 2) can be prepared by treating 1 mol.-equiv. of the parent amine with an equimolar quantity of nBuM and tmeda in hexane solution. In the solid state, 1 and 2 are essentially isostructural, being dimeric with a four-atom M-N-M-N framework. The coordination sphere of each M atom is completed by a bidentate tmeda molecule. Complex 3 [{(tmeda)3/2K(NPh2)}2] has been prepared in a similar way to 1 and 2 except that benzylpotassium has been Alkali metal amides and their solvates are continuing to attract a great deal of interest due to their use in alkali metal/hydrogen exchange reactions.[1-5] In particular, the metal salts of diisopropylamine [da(H)], 1,1,1,3,3,3-hexamethyldisilazane [hmds(H)] and 2,2,6,6-tetramethylpiperidine [tmp(H)] are widely utilised across synthetic laboratories primarily because of the desirable combination of high Brønsted basicity and low nucleophilicity. Of particular interest in this study, another amido reagent, the thermally highly stable lithium diphenylamide (LiNPh2), has shown promise in a range of synthetic transformations. As well as regioselective deprotonation reactions,[6-10] it has also been used in catalytic aldol reactions involving silyl enol ethers and aldehydes;[11,12] in elimination applications;[13,14] in metathetical reactions;[15-27] during the preparation of amino-containing carbenes,[28] and as an initiator in the polymerisation of methyl methacrylate.[29]