Coordination behavior of bidentate bis(carbenes) at alkali metal bis(trimethylsilyl)amides.

Abstract

Lithiation of HN(SiMe3)2 in hexane and crystallization in the presence of 2,2,5,5-tetramethyltetrahydrofuran (Me4THF) allows the isolation of crystalline tetrameric [LiN(SiMe3)2]4 (1) with an average Li-N distance of 208.9 pm. Deprotonation of a methylene-bridged bis(imidazolium) diiodide with NaN(SiMe3)2 in tetrahydrofuran (THF) yields 1,1'-diisopropyl-3,3'-methylene-diimidazole-2,2'-diylidene (H2C(NHCiPr)2) and layering of this orange reaction mixture with pentane yield [{H2C(NHCiPr)2}{(thf)NaI}2]∞ (2). The reaction of this bis(imidazolium) diiodide with excess of KN(SiMe3)2 in THF leads to the formation of [{H2C(NHCiPr)2}KN(SiMe3)2]2 (3). Due to the fact that 2 and 3 are polymeric in the crystalline state, the bulkier 1,1'-bis(2,6-diisopropylphenyl)-3,3'-methylene-diimidazole-2,2'-diylidene (H2C(NHCDipp)2) has been used. Thus, addition of H2C(NHCDipp)2 with the bulky 2,6-diisopropylphenyl (Dipp) groups to AN(SiMe3)2 (A = Li, Na, K) in toluene yields mononuclear [{H2C(NHCDipp)2}LiN(SiMe3)2] (4) and dinuclear [{H2C(NHCDipp)2}AN(SiMe3)2]2 for sodium (5) and potassium (6). The rather short alkali metal-carbon bonds lie in the range of alkylmetal derivatives.