Application of the Redox‐Transmetalation Procedure to Access Divalent Lanthanide and Alkaline‐Earth NHC Complexes**

Abstract

Divalent lanthanide and alkaline-earth complexes supported by N-heterocyclic carbene (NHC) ligands have been accessed by redox-transmetalation between air-stable NHC-AgI complexes and the corresponding metals. By using the small ligand 1,3-dimethylimidazol-2-ylidene (IMe), two series of isostructural complexes were obtained: the tetra-NHC complexes [LnI 2 (IMe) 4 ] (Ln=Eu and Sm) and the bis-NHC complexes [MI 2 (IMe) 2 (THF) 2 ] (M=Yb, Ca and Sr). In the former, distortions in the NHC coordination were found to originate from intermolecular repulsions in the solid state. Application of the redox-transmetalation strategy with the bulkier 1,3-dimesitylimidazol-2-ylidene (IMes) ligand yielded [SrI 2 (IMes)(THF) 3 ], while using a similar procedure with Ca metal led to [CaI 2 (THF) 4 ] and uncoordinated IMes. DFT calculations were performed to rationalise the selective formation of the bis-NHC adduct in [SrI 2 (IMe) 2 (THF) 2 ] and the tetra-NHC adduct in [SmI 2 (IMe) 4 ]. Since the results in the gas phase point towards preferential formation of the tetra-NHC complexes for both metal centres, the differences between both arrangements are a result of solid-state effects such as slightly different packing forces.

Rare Earth Starting Materials and Methodologies for Synthetic Chemistry

“… 195 Finally, the reaction between (IMe 2 )Ag(I) and Yb affords the bis-NHC adduct [Yb(IMe 2 ) 2 (I) 2 (THF)] ( 90 ), while the tetra-NHC adducts [Ln(IMe 2 ) 4 (I) 2 ] ( 91-Ln ; Ln = Sm, Eu) are obtained with the larger divalent lanthanoids. 196 …”

“…, Hg and Tl) . Their implementation in synthetic protocols has given access to complexes supported by a wide array of ligands such as cyclopentadienyl, ,,,, carboranes, monodentate amides, ,− bidentate amides, ,− pyrazolates, ,, aryloxides, ,,,, thiolates , and N- heterocyclic carbenes (NHCs). , These methodologies have been covered extensively in other review articles; , therefore, this section will focus on key examples that best demonstrate their applications in RE chemistry.…”

“…Roesky and co-workers have also shown that RT reactions with Ag­(I)-NHC reagents can be employed for the synthesis of heteroleptic Ln-NHC complexes (Scheme ). , In these methodologies, Ag salts “(NHC)­Ag­(I)” [NHC = 1,3-bis­(R)­imidazolin-2-ylidene; R = Me (IMe 2 ), Mes (IMes), and Dipp (IDipp)] are reacted with Sm, Eu or Yb powders in THF at room temperature, and the outcome of these reactions is dictated by the steric demands of the NHC ligand employed and the ionic radii of the metal centers. With the most sterically demanding IDipp, the products of this reaction are free carbene and [Ln­(I) 2 (THF) n ] (RE = Eu, Yb) .…”

“…On the other hand, when the smaller IMes ligand is employed, the heteroleptic NHC complexes [Ln­(IMes)­(I) 2 (THF) 3 ] ( 89-Ln ; Ln = Eu, Yb) are obtained . Finally, the reaction between (IMe 2 )­Ag­(I) and Yb affords the bis-NHC adduct [Yb­(IMe 2 ) 2 (I) 2 (THF)] ( 90 ), while the tetra-NHC adducts [Ln­(IMe 2 ) 4 (I) 2 ] ( 91-Ln ; Ln = Sm, Eu) are obtained with the larger divalent lanthanoids …”

Solid-state and solution-phase characterization of SmII-aza[2.2.2]cryptate and its methylated analogue

“…Complexes of divalent lanthanide (Ln II ) ions have attracted attention in recent years owing to their interesting luminescence, magnetic, and electrochemical properties. 1–25 One such group of Ln II complexes that have been the subject of extensive investigation with regard to their structural, photophysical, and electrochemical properties is the Ln II -cryptates. 2,26–42 In many studies, cryptands such as 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (222) and 5,6-benzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacos-5-ene are used to encapsulate Ln II ions, 26–32,37–42 and reported Ln II -cryptates have luminescence and electrochemical properties that are useful in applications including light-emitting diodes, imaging, and catalysis.…”