Mononuclear Three-Coordinate Magnesium Complexes of a Highly Sterically Encumbered β-Diketiminate Ligand

Abstract

The highly sterically encumbered chelating β-diketiminate ligand, [HC{C(Me)N(2,6-CHPh2-4-MeC6H2)}2](-), (Ar)L(-), has been used to prepare a series of heteroleptic three-coordinate magnesium complexes. Both the bis(imine) and imine-enamine tautomers of the ligand precursor, (Ar)LH, as well as the diethyl ether adduct of the bromide complex [(Ar)LMgBr(OEt2)], the monomeric methyl complex [(Ar)LMgMe], the THF-solvated and unsolvated n-butylmagnesium complexes [(Ar)LMg(n)Bu(THF)] and [(Ar)LMg(n)Bu], and the 1-hexynyl analogue [(Ar)LMgC≡C(n)Bu] have been crystallographically characterized. Both n-butylmagnesium complexes showed remarkable stability in air, both in the solid state and in solution. Single crystals of the highly sensitive magnesium hydride, [(Ar)LMgH], underwent partial hydrolysis by solid-state water diffusion to the isostructural hydroxide compound [(Ar)LMgOH].

An Extremely Bulky Tris(pyrazolyl)methanide: A Tridentate Ligand for the Synthesis of Heteroleptic Magnesium(II) and Ytterbium(II) Alkyl, Hydride, and Iodide Complexes

“…[5a, 16] One of the most common routes to magnesium hydride complexes is to treat corresponding magnesium n-butyl complexes with PhSiH 3 . Surprisingly, this was not successful for 6, and its reaction with the silane only returned 1.…”

Methanediide Formation via Hydrogen Elimination in Magnesium versus Aluminium Hydride Complexes of a Sterically Demanding Bis(iminophosphoranyl)methanediide

“…Three-coordinated Mg complexes with terminal nBu-groups are rare and are best described for the β-diketiminate class of ligand that allows some comparison with the sterics of HL − . Comparable monomeric complexes of [{HC(RCNAr) 2 }MgnBu] with an overall molecular structure similar to 1 were found for R = Me and Ar = 2,6-(Ph 2 CH) 2 -4-MeC 6 H 2 (≡ Ar*) [27], and R = tBu and Ar = Dip [28]. For the respective complex with R = Me and Ar = Dip [29] and smaller β-diketiminates, molecular structures with bridging nBu groups and four-coordinate Mg centres were found.…”

“…For the respective complex with R = Me and Ar = Dip [29] and smaller β-diketiminates, molecular structures with bridging nBu groups and four-coordinate Mg centres were found. Thus, the steric profile of HL − , at least when coordinated to Mg, can be approximately compared with [{HC(tBuCNDip) 2 were found for R = Me and Ar = 2,6-(Ph2CH)2-4-MeC6H2 (≡ Ar*) [27], and R = tBu and Ar = Dip [28]. For the respective complex with R = Me and Ar = Dip [29] In analogy to the synthesis of a sterically less hindered methanediide Mg complex of type B (M = Mg, E = NSiMe3) [16], which was synthesized at 140 °C using MgnBu2, we heated [HLMgnBu] 1 to various high temperatures (up to 200 °C) though only obtained a complex product mixture were found for R = Me and Ar = 2,6-(Ph2CH)2-4-MeC6H2 (≡ Ar*) [27], and R = tBu and Ar = Dip [28].…”

“…For the respective complex with R = Me and Ar = Dip [29] In analogy to the synthesis of a sterically less hindered methanediide Mg complex of type B (M = Mg, E = NSiMe3) [16], which was synthesized at 140 °C using MgnBu2, we heated [HLMgnBu] 1 to various high temperatures (up to 200 °C) though only obtained a complex product mixture were found for R = Me and Ar = 2,6-(Ph2CH)2-4-MeC6H2 (≡ Ar*) [27], and R = tBu and Ar = Dip [28]. For the respective complex with R = Me and Ar = Dip [29] In analogy to the synthesis of a sterically less hindered methanediide Mg complex of type B (M = Mg, E = NSiMe3) [16], which was synthesized at 140 °C using MgnBu2, we heated [HLMgnBu] 1 to various high temperatures (up to 200 °C) though only obtained a complex product mixture In analogy to the synthesis of a sterically less hindered methanediide Mg complex of type B (M = Mg, E = NSiMe 3 ) [16], which was synthesized at 140 • C using MgnBu 2 [27,[30][31][32]. No reaction was observed between 1 and one equivalent of PhSiH 3 at room temperature; however, at elevated temperatures, for example in toluene at 80 • C, this afforded colourless crystals of the new homoleptic methanediide complex [(LMg) 2 ] 2 in moderate isolated yield, see Scheme 1 and Figure 3.…”

“…Hydrogen could be detected when the reaction was followed by 1 H NMR spectroscopy, and the metathesis by-product n-butylphenylsilane was furthermore found in 1 2 ] with an unusually coordinated Mg(µ-H) 2 Mg core due to the approximately orthogonal arrangement of the β-diketiminate metal chelates caused by the steric bulk of the ligand [32]. The molecular structure of [{HC(MeCNAr*) 2 }MgH], however, does show that the monomeric coordination mode with a three-coordinate Mg centre is possible if sufficient steric protection from the ligand is provided [27].…”