Solvent‐Free and TMEDA‐Solvated Mixed Alkali Metal‐Magnesium Tris‐diisopropylamides

Abstract

A trio of heterobimetallic tris-diisopropylamides, the solventfree potassium-magnesium amide [{KMg(NiPr 2 ) 3 } ϱ ], its TMEDA solvate [KMg(NiPr 2 ) 3 ·TMEDA] and the sodium congener [NaMg(NiPr 2 ) 3 ·TMEDA] has been synthesised by mixing the appropriate metal alkyl reagents with three molar equivalents of diisopropylamine in a hydrocarbon medium, to which, in the last two cases, TMEDA is added. All three amides have been successfully crystallographically characterised by X-ray diffraction studies. Representing the first pure s-block mixed-metal diisopropylamide free of solvent molecules or other stabilising anionic co-ligands, the first

Advances in alkaline earth-nitrogen chemistry

“…Use of HN(Cy) 2 under similar reaction conditions resulted in [(thf)LiMg{N(Cy) 2 } 3 ] after addition of THF [41]. Similar structural motifs are observed for the smaller di-isopropylamine ligand, HN( i Pr) 2 , where a trio of heterobimetallic species have been isolated: [{KMg{N( i Pr) 2 } 3 } ∞ ] and [(tmeda)KMg{N( i Pr) 2 } 3 ], both stabilized by K agostic interactions and [(tmeda)NaMg{N( i Pr) 2 } 3 ] where use of the bidentate donor TMEDA suppresses noncovalent interactions[145].…”

cis-2,6-Dimethylpiperidide: a structural mimic for TMP (2,2,6,6-tetramethylpiperidide) or DA (diisopropylamide)?

“…Magnesiate 5, was prepared by a similar mixed-metallation approach which was adopted for the preparation of its tris-DA analogue. 27 An equimolar mixture of BuNa and Bu 2 Mg in hexane was treated with three molar equivalents of cis-DMP(H) and subsequently with one molar equivalent of TMEDA. In contrast to the zincate scenario, this led to the complete conversion of all the alkyl substituents to gaseous alkane, resulting in the formation of the desired TMEDA-solvated heterobimetallic tris(amido) complex 5.…”

Recent developments in the field of organic heterobimetallic compounds of the alkaline-earth metals

“…The alkali metal atom is chelated by this anion and bound to two of the nitrogen atoms thus leading to a fourmembered M I MgN 2 cycle. An example for a coligand-free complex is polymeric [iPr 2 N-Mg(l-NiPr 2 ) 2 K] ∞ ; 19 in the chain all amide groups are in a bridging position between potassium and magnesium (average Mg-N bond length 204.2(2) pm). The addition of bis(dimethylamino)ethane (TMEDA) leads to a break-up of the polymeric chain and discrete molecules [(tmeda)K(l-NiPr 2 ) 2 Mg-NiPr 2 ] with similar central four-membered rings are isolated; the bridging amide ligands show Mg-N bond lengths of 204.2(1) pm whereas the terminally bound amide displays a Mg-N value of 197.2(1) pm.…”

“…In these complexes the coordination sphere is saturated by additional agostic interactions to the N-bound alkyl groups. 19 Lithium magnesiates with benzylamide ligands are also well known for compounds with Li : Mg ratios of 1 : 1 and 2 : Larger amido ligands such as N(SiMe 3 ) 2 prevent the formation of central four-membered cycles and isolated magnesiate anions are observed. In these [Mg{N(SiMe 3 ) 2 } 3 ] − anions the magnesium atoms are in a trigonal planar environment with Mg-N bond lengths between 201.7 and 203.4 pm.…”