Magnesium(I) Dimers Bearing Tripodal Diimine–Enolate Ligands: Proficient Reagents for the Controlled Reductive Activation of CO₂ and SO₂

Abstract

The first examples of magnesium(I) dimers bearing tripodal ligands, [(Mg{κ(3) -N,N',O-(ArNCMe)2 (OCCPh2 )CH})2 ] [Ar=2,6-iPr2 C6 H3 (Dip) 7, 2,6-Et2 C6 H3 (Dep) 8, or mesityl (Mes) 9] have been prepared by post-synthetic modification of the β-diketiminato ligands of previously reported magnesium(I) systems, using diphenylketene, OCCPh2 . In contrast, related reactions between β-diketiminato magnesium(I) dimers and the isoelectronic ketenimine, MesNCCPh2 , resulted in reductive insertion of the substrate into the MgMg bond of the magnesium(I) reactant, and formation of [{(Nacnac)Mg}2 {μ-κ(2) -N,C-(Mes)NCCPh2 }] (Nacnac=[(ArNCMe)2 CH](-) ; Ar=Dep 10 or Mes 11). Reactions of the four-coordinate magnesium(I) dimer 8 with excess CO2 are readily controlled, and cleanly give carbonate [(LMg)2 (μ-κ(2) :κ(2) -CO3 )] 12 (L=[κ(3) -N,N',O-(DepNCMe)2 (OCCPh2 )CH](-) ; thermodynamic product), or oxalate [(LMg)2 (μ-κ(2) :κ(2) -C2 O4 )] 13 (kinetic product), depending on the reaction temperature. Compound 12 and CO are formed by reductive disproportionation of CO2 , whereas 13 results from reductive coupling of two molecules of the gas. Treatment of 8 with an excess of N2 O cleanly gives the μ-oxo complex [(LMg)2 (μ-O)] 14, which reacts facilely with CO2 to give 12. This result presents the possibility that 14 is an intermediate in the formation of 12 from the reaction of 8 and CO2 . In contrast to its reactions with CO2 , 8 reacts with SO2 over a wide temperature range to give only one product; the first example of a magnesium dithionite complex, [(LMg)2 (μ-κ(2) :κ(2) -S2 O4 )] 16, which is formed by reductive coupling of two molecules of SO2 , and is closely related to f-block metal dithionite complexes derived from similar SO2 reductive coupling processes. On the whole, this study strengthens previously proposed analogies between the reactivities of magnesium(I) systems and low-valent f-block metal complexes, especially with respect to small molecule activations.

On the non-innocence of “Nacnacs”: ligand-based reactivity in β-diketiminate supported coordination compounds

“…In their recent investigation on the activation of CS 2 by [K(L)][(BDI Dipp,tBu )Ni(S)] (L = 18-C-6 or 2,2,2-cryptand), the Hayton group reported that following addition of a first CS 2 molecule to the nickel sulphide moiety, yielding trithiocarbonate, a further molecule of CS 2 is sequestered through C-C bond formation at the central methine carbon of the BDI ligand and yields an unexpected Ni derivative shown on Scheme 31. 138 Interestingly, the resulting tripodal monoanionic diamine-enolate skeleton has proven to be a good platform to support alkaline-earth and Ti chemistry. 77,137 In an analogous way, treatment of (BDI*)MgI (OEt 2 ) or (BDI*)Mg-Mg(BDI*) with diphenylketene yields the corresponding diamine-enolate cycloaddition products (Scheme 31).…”

“…136 Metal-ligand cooperative activation of ketene OvCvCPh 2 by the four-coordinate Ti(IV) imide (BDI*)Ti(NDipp)(OTf ) affords the tripodal diamine-enolate complex represented on Scheme 31. 77,137,138 The reactivity of (BDI*)Mg-Mg(BDI*) with OvCvCPh 2 is unique since other heteroallenes such as CO 2 , NCO and azides preferentially insert into the Mg-Mg bond. 138 Interestingly, the resulting tripodal monoanionic diamine-enolate skeleton has proven to be a good platform to support alkaline-earth and Ti chemistry.…”

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

“…in 1 and 2. [3][4][5][6][7] In addition to these, a remarkable mixed valence More than being just chemical curiosities, dimeric magnesium(I) complexes, especially those incorporating β-diketiminate ligands, have been widely applied as soluble, selective and safe reducing agents in a diverse range of inorganic and organic synthetic transformations. [3] The growing popularity of these reagents lies with the fact that their use can lead to synthetic outcomes that are not achievable with traditional reducing agents, such as alkali metals, KC 8 and sodium naphthalide.…”

Anorganische Molekülchemie

“…Alkali-und Erdalkalimetalle S Das ionische Supramolekül Li + @C 60 ⊂[10]CCP bildet sich bei der Reaktion von Li + @C 60 mit dem Cycloparaphenylen [10]CCP. Die Kristallstrukturanalyse bestätigt die vermutete 1:1-Komplexierung, wobei zwei kristallographisch unabhängige Li + @C 60 ⊂[10]CCP-Strukturen existieren.…”

“…In der Natriumverbindung (2) umgeben jeweils drei Chelatliganden die Ionen verzerrt oktaedrisch, die langen Na-P-Abstände (2,95 -3,03 Å) weisen (11). 10) Über Berylliumverbindungen ist im Vergleich zu den schweren Homologen relativ wenig bekannt. Jetzt gelang es, die beiden Berylliumcarbonate OCBeCO 3 und COBeCO 3 in einer Neonmatrix zu isolieren und zu untersuchen.…”