Synthesis and Molecular Structures of Meta-Substituted Arylcalcium Iodides

Abstract

The reduction of meta-methyl-substituted iodobenzene with activated calcium in tetrahydrofuran (THF) yields [(3-MeC 6 H 4 )CaI(thf) 4 ] (1) and [(3,5-Me 2 C 6 H 3 )CaI(thf) 4 ] (2). The reaction of 3-halo-1-iodobenzene with calcium powder leads to the formation of the corresponding post-Grignard reagents [(3-XC 6 H 4 )CaI(thf) 4 ] [X = F (3), Cl (4), Br (5), and I (6)]. The synthesis of the thf adducts of 3-methoxyphenylcalcium iodide (7) and β-naphthylcalcium iodide (8) follows the same strategy. All post-Grignard reagents show a characteristic low-field shift for the calciumbound carbon atoms in 13 C NMR spectra. The molecular structures of 1, 2, 4, and 8 show distorted octahedral environments for the calcium centers with the aryl and halide anions in a trans arrangement. ■ INTRODUCTIONGrignard reagents represent widely used organomagnesium compounds that were introduced into preparative organic and organometallic chemistry more than a century ago. 1−3 Because of the importance of these reagents, Grignard was honored with the Nobel Prize in 1912. Despite the fact that early attempts to prepare arylcalcium halides also date back more than a 100 years, 4 the first structurally characterized arylcalcium complexes consisted of oxygen-centered oligonuclear arylcalcium clusters. 5,6 Nevertheless, this success of isolation of arylcalcium derivatives intensified the efforts to also isolate and characterize arylcalcium halides that can be considered as post-Grignard reagents with mesitylcalcium iodide being the first structurally characterized representative 7 and entering the textbooks shortly thereafter. 8 Knowing the requirements to isolate crystalline arylcalcium complexes, many of such derivatives were prepared and investigated spectroscopically as well as via derivatization reactions. Several recent review articles summarize this vastly growing arylcalcium (post-Grignard) chemistry. 9−12The synthesis of arylcalcium complexes succeeds with high yields if iodoarenes are reduced with activated calcium in Lewis basic solvents, such as ethers. 9−12 Amines were also used to stabilize arylcalcium complexes. 13 As also observed for classical Grignard reagents, a Schlenk-type equilibrium converts arylcalcium halides into homoleptic diarylcalcium and calcium dihalides depending mainly on solvent and temperature. Substitution of iodide by an alkoxide shifts this equilibrium quantitatively to the side of the homoleptic complexes. 14 Because of the high reactivity of the arylcalcium complexes, degradation of ethers often was observed, 7,15,16 as is also known for organyllithium 17 and, in minor extent, for Grignard reagents, 18 justifying to consider these organometallics as superbases. 19 On the basis of similar electronegativities of lithium and calcium, a comparable reactivity can be envisioned that should be higher than that of Grignard reagents due to a larger ionic character of the metal−carbon bonds.Despite the vastly growing knowledge of post-Grignard reagents, the influence of the substitution pattern on reactivity an...

Halide‐Free Diarylcalcium Complexes—Syntheses, Structures, and Stability

“…The presence of two strongly basic carbanions in the coordination sphere of calcium leads to lengthening of the metal carbon bonds in comparison to naphthylcalcium halide complexes 9. 15–17 For the known compound [Ca(α ‐ Naph){N(SiMe 3 ) 2 }(thf) 3 ]15 an analogous finding might be expected due to the presence of a strongly basic amide, but here the simultaneous reduction of the coordination number from six to five, which leads to an overall contraction, overcompensates this effect. Selected bond lengths and angles of 1 and 2 are listed together with the corresponding values of naphthylcalcium halides and amides in Table 1.…”

“…Calcium was activated by dissolution in liquid NH 3 and subsequent reduction of the deep‐blue solution to dryness, resulting in finely divided calcium powders. The complexes [CaI(Ph)(thf) 4 ],10 [CaI(Tol)(thf) 4 ],10 and [CaI(β‐Naph)(thf) 4 ]17 were prepared according to known procedures and recrystallized from THF prior to use. Compounds 1 and 4 were synthesized as preliminarily reported 12.…”

1‐Alkenylcalcium Iodide: Synthesis and Stability

“…Bond lengths Ca1C4 and Ca1I1 of 253.0(4) and 318.63(8) pm, respectively, were established. The closely related α‐ and β‐naphthylcalcium iodides [Ca(α‐Naph)(I)(thf) 4 ], [Ca(β‐Naph)(I)(thf) 4 ], and [Ca(β‐Naph)(I)(thf) 4 ] showed similar CaC bond lengths of 255.2(6),19 252.8(5),20 and 253.4(6) pm,21 respectively. The Ca1O bond lengths of 2 varied between 236.9(3) and 241.5(3) pm.…”

The emergence of super-canonical stars in R136-type starburst clusters

“…To take into account an appropriate mass-loss for the SC stars, we consider the stellar evolutionary models of rotating MS stars by Köhler & Langer (2012) which encompass the SC mass range and are computed for the LMC metallicity. The above authors use the one-dimensional hydrodynamic binary evolution code of Heger et al (2000) which includes direct treatments of stellar rotation, magnetic field and detailed stellar winds.…”

“…Stellar wind is the most important factor for the evolution of the mass of an isolated massive star during its main sequence. In the computations by Köhler & Langer (2012), the MS stellar wind of Vink et al ( 2001) is applied that includes the bi-stability jump. During the bi-stability jump, a linear interpolation is applied as in Brott et al (2011).…”