A simple synthesis of group 2 anthracenides and their use as reducing agents for polypnictogen ligand complexes

By using an improved synthetic pathway, the anthracenides of the group 2 metals Ca, Sr, and Ba are straightforwardly accessible for subsequent organometallic syntheses. These highly reactive compounds are slightly soluble in tetrahydrofuran and can be used as synthons for group 2 metal transfer due to the lability of the anthracene substituent. These features were used to explore their reactivity towards the polyphosphorus ligand complexes [Cp*Fe(η⁵-P₅)] (Cp* = C₅(CH₃)₅) and [Cp*Fe(η^3:1-(1-CH₃-2-PPh₂-P₅))], respectively. The resulting products, [Cp*Fe(μ-η^4:2:1-P₅)Mg(thf)₃] 0.5 thf (thf = tetrahydrofuran) and [{Cp*Fe(μ-η^2:2:1-(1-CH₃-2-PPh₂-P₅))}₂Mg(thf)₂]·3 thf, are first examples of molecular magnesium-containing polypnictogenide transition metal complexes without stabilization by N-donor ligands that are soluble in organic N-donor-free solvents. The P₁₂ ligand in the latter complex is the first example of a 2,2'-diphosphanyl-substituted decaphosphadihydrofulvalen-shaped structural motif (2,2'-bis(diphenylphosphanyl)-1,1'-dimethyl-3,3'-bipentaphosphole). The complexes [Cp*Fe(μ₃-η^4:4:1-P₅)Sr(thf)₄]₂·2 thf and [Cp*Fe(μ₃-η^2:1:1:1:1-(1-CH₃-2-PPh₂-P₅))Sr(thf)₃]₂·2 thf represent the first examples of molecular polypnictogen compounds of strontium that are stable in organic solvents.