Umpolung of an Aliphatic Ketone to a Magnesium Ketone‐1,2‐diide Complex with Vicinal Dianionic Charge

The new β‐diketimine ^iPrDipnacnacH, HC(iPrCNDip)₂H, Dip=2,6‐iPr₂‐C₆H₃, was converted to the magnesium(I) complex [{(^iPrDipnacnac)Mg}₂] and reaction with 2‐adamantanone (OAd) afforded the ketone‐1,2‐diide complex [{(^iPrDipnacnac)Mg}₂(μ‐OAd)]. The complex contains the first stable dianion of an aliphatic ketone with an electropositive metal and shows an OAd²⁻ unit with long C−O bond and pyramidal carbon centre. DFT studies reveal an anionic charge on both neighbouring C and O atoms. Reductions of aliphatic ketones with magnesium(I) complexes show that these likely proceed via highly reactive dianions and afforded a 1 : 1 mixture of an alkoxide and an enolate when an enolisable ketone was used, and rapid CH activations reactions, e.g., of stabilising ligand moieties, when non‐enolisable ketones were employed.

Single- and double-bridged PNP ligands in chromium-catalysed ethylene oligomerisation

Chromium catalysts with diazaphospholane ligands have shown good activities and selectivities for ethylene tri- and tetramerisation. Oligomerisations with a doubly N-bridged cyclodiphosphazane result in a Schulz–Flory distribution of α-olefins.

Structure-Solubility Relationship of 1,4-Dioxane Complexes of Di(hydrocarbyl)magnesium

Systematic variation of the 1,4‐dioxane (dx) concentration during the precipitation of sparingly soluble [MgBr₂(dx)₂] from ethereal Grignard solutions of RMgBr has allowed the structural investigation of crystallized [R₂Mg(dx)_n] (n=1, 1.5, 2, and 3), which form during this dioxane method, depending on the bulkiness of R. The numbering of the complexes explored in this study is based on the number n of dioxane molecules per magnesium atom, followed by the substituent R; an apostrophe denotes coordination polymers. The following derivatives were studied by X‐ray crystal‐structure determination and NMR spectroscopy: n=1: [Me₂Mg(μ‐dx)]_∞ (1′‐Me) and [nPr₂Mg(μ‐dx)]_∞ (1′‐nPr); n=1.5: [{iPr₂Mg(dx)}₂(μ‐dx)] (1.5‐iPr), [{oTol₂Mg(dx)}₂(μ‐dx)] (1.5‐oTol), and [(Me₃Si‐C≡C)₂Mg(dx)_1.5]_∞ (1.5′‐C₂SiMe₃); n=2: [tBu₂Mg(dx)₂] (2‐tBu) and [oTol₂Mg(dx)₂] (2‐oTol); n=3: [Ph₂Mg(dx)₃] (3‐Ph). In the structure types 1′, 1.5, and 2, the magnesium atom exhibits the coordination number 4, whereas pentacoordinate metal atoms are observed in types 3 and 1.5′. The structure type 2′ is realized for [(Ph‐C≡C)₂Mg(dx)₂]_∞ (2′‐C₂Ph), [MgCl₂(dx)₂]_∞ (2′‐Cl), and [MgBr₂(dx)₂]_∞ (2′‐Br) with hexacoordinate metal atoms. The solubility of the dioxane adducts in common organic solvents strongly depends on the degree of aggregation with the solubility decreasing from molecular to strand to layer structures.

Acyclic 1,2-dimagnesioethanes/-ethene derived from magnesium(i) compounds: multipurpose reagents for organometallic synthesis

Reactions of three magnesium(i) dimers, [{(ArNacnac)Mg-}2] (ArNacnac = [(ArNCMe)2CH]-; Ar = xylyl (Xyl), mesityl (Mes) or 2,6-diethylphenyl (Dep)), with either 1,1-diphenylethylene (DPE), α-methylstyrene (MS), trans-stilbene (TS) or diphenylacetylene (DPA) led to the 1,2-addition of the Mg-Mg bond across the substrate, giving rise to the 1,2-dimagnesioethanes, [{(XylNacnac)Mg}2(μ-DPE)], [{(DepNacnac)Mg}2(μ-MS)], [{(ArNacnac)Mg}2(μ-TS)] (Ar = Mes or Dep); and a 1,2-dimagnesioethene, [{(MesNacnac)Mg}2(μ-DPA)]. The reactions involving the 1,1-substituted alkenes are shown to be readily redox reversible, in that the reaction products are in equilibrium with a significant proportion of the starting materials at room temperature. Variable temperature NMR spectroscopy and a van't Hoff analysis point to low kinetic barriers to these weakly exergonic reactions. [{(MesNacnac)Mg}2(μ-DPE)] and [{(MesNacnac)Mg}2(μ-DPA)] behave as 1,2-di-Grignard reagents in their reactions with very bulky amido-zinc bromides, yielding the first examples of a 1,2-dizincioethane, [(L*Zn)2(μ-DPE)] (L* = -N(Ar*)(SiPri 3); Ar* = C6H2Me{C(H)Ph2}2-4,2,6), and a 1,2-dizincioethene, [(TBoLZn)2(μ-DPA)] (TBoL = -N(SiMe3){B(DipNCH)2}, Dip = 2,6-diisopropylphenyl), respectively. Divergent reactivity is shown for [{(MesNacnac)Mg}2(μ-DPE)], which behaves as a two-electron reducing agent when treated with amido-cadmium and amido-magnesium halide precursors, yielding the cadmium(i) and magnesium(i) dimers, [PhBoLCdCdPhBoL] (PhBoL = -N(SiPh3){B(DipNCH)2}) and [L†MgMgL†] (L† = -N(Ar†)(SiMe3); Ar† = C6H2Pri{C(H)Ph2}2-4,2,6), respectively. A further class of reactivity for [{(MesNacnac)Mg}2(μ-DPE)] derives from its reaction with the bulky amido-germanium chloride, L*GeCl, which gives a magnesio-germane, presumably via intramolecular C-H activation of a highly reactive magnesiogermylene intermediate, [:Ge(L*){Mg(MesNacnac)}]. [{(MesNacnac)Mg}2(μ-DPE)] can be considered as acting as a two-electron reducing, magnesium transfer reagent in this reaction.