Magnesiacycloalkanes with Different Ring Sizes

Abstract

Di-Grignard compounds are prepared via the direct synthesis of magnesium with Br2C­{Si­(CH3)3}2, α,ω-dihalides of XCH2YCH2X (X: Cl, Br; Y: Si­(CH3)2, (CH2) n with n = 4, 5, 6), and with ClC­(CH3)2(CH2) n (CH3)2CCl (n = 3, 4) in tetrahydrofuran (THF) or diethyl ether. After removal of the sparingly soluble magnesium halides after addition of 1,4-dioxane (dx) the corresponding magnesium alkanediides remain in solution. Only the geminal di-Grignard complex (BrMg)2(μ-C­{Si­(CH3)3}2) forms the corresponding dioxane adduct [{(dx)2MgBr}2(μ-C­{Si­(CH3)3}2)] (1). The magnesium alkanediides can be recrystallized from THF and characterized with X-ray crystallography and NMR spectroscopy. Preferably dinuclear rings of the types [(thf)2Mg­(μ-CH2-Y-CH2)}2] (Y: Si­(CH3)2 (2), (CH2)6 (5)) and [({thf}2Mg­{μ-C­(CH3)2­(CH2)4C­(CH3)2})2] (7) crystallize. From a 1 M solution the strand-like coordination polymer [({thf}2Mg­{μ-(CH2)6})∞] (3) precipitates. Only [(thf)2Mg­{C­(CH3)2­(CH2)3(CH3)2C}] (6) crystallizes as a mononuclear compound. The NMR spectra of 2, 3, 5, and 6 show only one set of resonances for the alkanediyl moieties in [D8]­THF solutions. The NMR spectra of 7 showed also at 50 °C two signal sets with the intensity ratios depending on the measurement temperature. Complex 7 shows a temperature-dependent monomer–dimer equilibrium in THF solution.

Chasing Multiple Bonding Interactions between Alkaline‐Earth Metals and Main‐Group Fragments

“…[90] Only three years later Mg II alkylidene [(Me 3 Si) 2 C{MgBr(thf) 2 } 2 ]( 1, Figure 2) was crystallographically authenticated, featuring Mg-C distances of 2.10(4) and 2.14(4) ,r espectively. [91] Treatment of 1 with 1,4-dioxane and hence manipulation of the Schlenke quilibrium did not afford the desired homoleptic [75,82] TheM g-C distances of 2.125(5) and 2.134 (5) in compound 2 are comparablet o those in the thf adduct 1 (vide supra). The SiMe 3 groups in 1 and 2 not only enhanced the solubility of the corresponding compounds, but more importantly,i mparted considerable stabilization of the carbdianion, both via steric shielding (kinetic stabilization) and partial delocalization of the negative charge (thermodynamic stabilization).…”

“…Only three years later Mg II alkylidene [(Me 3 Si) 2 C{MgBr(thf) 2 } 2 ] ( 1 , Figure ) was crystallographically authenticated, featuring Mg–C distances of 2.10(4) and 2.14(4) Å, respectively . Treatment of 1 with 1,4‐dioxane and hence manipulation of the Schlenk equilibrium did not afford the desired homoleptic [Mg=C(SiMe 3 ) 2 ] but donor‐ligand exchanged [(Me 3 Si) 2 C{MgBr(diox) 2 } 2 ] ( 2 , Figure ) . The Mg–C distances of 2.125(5) and 2.134(5) Å in compound 2 are comparable to those in the thf adduct 1 (vide supra).…”

“…Remarkably,b ye xtending the CH 2 2À unit to oligomeric (CH 2 ) n 2À ,W esterhausen and co-workers were able to access the correspondingt hf coordinated alkanediides [(thf) 2 Mg(CH 2 ) n ] x (n = 5, 8; x = 2; n = 4, 6; x = 1). [82][83][84] Only recently these compounds and relatedl ithium andm agnesium alkanediides werec omprehensively covered in ar eview article. [75] Already in 1955 Karl Ziegler reported on the synthesis of homoleptic magnesium methylidene [MgCH 2 ] n ,v ia thermally induced a-elimination of methane from analytically pure and halide-free dimethylmagnesium [MgMe 2 ] n (route b).…”

“…A potential decomposition pathway during the direct synthesis of such heteroleptic compounds involves the formation of ethylene in Wurtz‐type coupling reactions. Remarkably, by extending the CH 2 2− unit to oligomeric (CH 2 ) n 2− , Westerhausen and co‐workers were able to access the corresponding thf coordinated alkanediides [(thf) 2 Mg(CH 2 ) n ] x ( n =5, 8; x =2; n =4, 6; x =∞) . Only recently these compounds and related lithium and magnesium alkanediides were comprehensively covered in a review article …”

Dilithium and Magnesium Alkanediides and 1‐Oxaalkanediides

“…In contrast to the other derivatives, where the addition of 1,4‐dioxane allowed the precipitation of the magnesium halides and the isolation of halide‐free alkylmagnesium derivatives, ether exchange reactions are observed and the dioxane adduct (Me 3 Si) 2 C[Mg(diox) 2 Br] 2 formed. However, shifting of the Schlenk equilibrium toward the homoleptic compounds MgBr 2 and oligomeric [MgC(SiMe 3 ) 2 ] x failed and hence, it was impossible to remove the magnesium halides from the reaction mixtures . According to a similar protocol, oligomeric [Mg(CH 2 ) 2 SiMe 2 ] x ( Mg‐3 Si ) was prepared and reacted immediately with metallocene dihalides of titanium, zirconium, and hafnium in a metathetical approach yielding Cp 2 M (CH 2 ) 2 SiMe 2 ( M = Ti, Zr, Hf) .…”