Synthesis and Reactivity of Alkali Metal Hydrido-Magnesiate Complexes which Exhibit Group 1 Metal Counter-Cation Specific Stability.

Reactions of the series of alkali metal amides M(HMDS) (M = Li-Cs; HMDS = [N(SiMe 3 ) 2 ] - ) with the neutral magnesium(II) hydride compound [Mg(BDI Dipp )(μ-H)] 2 (BDI Dipp = [CH{C( Me )NDipp} 2 ], Dipp = 2,6- i Pr 2 -C 6 H 3 ) have been carried out. When M = Li or Na, the reactions yielded Mg(BDI Dipp )(HMDS) and MH as the primary products. In the sodium amide reaction, [Na 2 (HMDS)][{Mg(BDI Dipp )} 2 (H) 3 ] was obtained as a low-yield by-product. When M = K-Cs, the reactions gave the group 1 metal hydrido-magnesiates, M 2 [Mg(BDI Dipp )(HMDS)(H)] 2 ·(benzene) n ( n = 0 or 1), the thermal stability of which increases with the increasing molecular weight of the alkali metal involved. Reactions of Cs 2 [Mg(BDI Dipp )(HMDS)(H)] 2 ·(benzene) with 18-crown-6 and CO gave the first monomeric alkali metal hydrido-magnesiate [Cs(18-crown-6)][Mg(BDI Dipp )(HMDS)(H)] and the ethenediolate complex Cs 2 [{Mg(BDI Dipp )(HMDS)} 2 (μ-C 2 H 2 O 2 )], respectively. The new synthetic route to alkali metal hydrido-magnesiates described herein may facilitate further reactivity studies of this rare compound class.