Hunting for the Magnesium(I) Species: Formation, Structure, and Reactivity of some Donor‐Free Grignard Compounds

Abstract

Magnesium bromide radicals have to be prepared as high-temperature molecules and trapped as a metastable solution because a seemingly simple reduction of donor-free Grignard compounds failed. However, the essential role of magnesium(I) species during the formation of Grignard compounds could be demonstrated experimentally.

Magnesium(I) Halide versus Magnesium Metal: Differences in Reaction Energy and Reactivity Monitored in Reduction Processes of P−Cl Bonds

“…Previously, we transferred this cocondensation process to magnesium(I) halides and presented the first metalloid magnesium cluster [Mg 16 Cp* 8 Br 4 K] − as a snapshot during the formation of Grignard compounds: The average oxidation number of Mg in this metalloid cluster is 0.69, that is, just between the value of 0 of Mg metal and 2.0 of the Grignard compound MgRX. In addition to the investigation of the formation process of Grignard compounds (reduction of alkyl halides), we want to demonstrate the reduction power and the role of Mg I halides and of metalloid Mg clusters via further reduction processes, to understand a little bit more about the complex reaction mechanism of any reaction of base metals such as bulk magnesium.…”

“…Using the cocondensation technique (Mg I Br + toluene + N n Bu 3 ), black solutions of “Mg I Br⋅N n Bu 3 ” ( 1 ) are obtained. As reported before, the structure of 1 can be regarded as dimeric in a simplified view . Scheme shows a schematic description of the reduction reactions of [Mg I Br⋅N n Bu 3 ] 2 ( 1 ) with [ClP(μ‐NTer)] 2 ( 2 ) and (Me 3 Si) 2 N‐PCl 2 ( 3 ).…”

Two‐Coordinate Magnesium(I) Dimers Stabilized by Super Bulky Amido Ligands

“…Problematically, all prior attempts to prepare magnesium(I) dimers devoid of chelating ligands (for example, Cp*MgMgCp*) have met with failure . Indeed, based on the results of experimental and computational studies, Schnöckel and co‐workers have suggested that the synthesis of stable non‐chelated magnesium(I) dimers will be “difficult, and perhaps impossible” . It should be noted that the same group have developed specialized synthetic routes to metastable (decomposition > ca.…”

“…It should be noted that the same group have developed specialized synthetic routes to metastable (decomposition > ca. −40 °C) solutions of XMgMgX (X=Cl or Br), though the metal centers of these dimers are possibly coordinated by additional donors (for example, NEt 3 ) present in those solutions …”

Many Mg–Mg bonds form the core of the Mg16Cp*8Br4K cluster anion: the key to a reassessment of the Grignard reagent (GR) formation process?

“…between naked Mg n clusters 10 and oligomeric MgX 2 (X = halide) molecules, or in the solid state], we developed a novel synthesis of a metastable MgBr solution. 11 This procedure was in principle similar to the experimentally sophisticated synthesis of metastable solutions of the monohalides of group 3 elements ( e.g. AlCl, GaCl), from which, via their disproportionation and substitution reaction, metal-rich intermediates have been obtained.…”