Nice cleavage: Two new strategies for the transition‐metal‐free activation of σ bonds are presented, namely, Bertrand's activation of dihydrogen by carbenes (see picture, left) and Stephan's “frustrated” Lewis acid/base pairs (right; R=Me3C6H2).

Aktiv dank Frustration: Mit zwei innovativen Strategien lassen sich σ‐Bindungen übergangsmetallfrei aktivieren: Bei der Methode nach Bertrand et al. wird Diwasserstoff durch Carbene aktiviert (links im Schema), bei der Methode nach Stephan et al. durch „frustrierte Lewis‐Säure‐Base‐Paare“ (rechts im Schema; R=Me3C6H2).

Several organoyttrium complexes stabilized by β-diketiminato ligands (Ar)NC(R)CHC(R)N(Ar) (Ar = 2,6- i Pr2C6H3; R = CH3 (ligand a), R = i Bu (ligand b)) have been prepared. Ligand-supported yttrium diiodides LYI2(THF) n were alkylated with organolithium or potassium reagents, yielding low-coordinate bis-alkyl derivatives. Several of these compounds have been characterized by X-ray crystallography, and a discussion of these structures in comparison to similar scandium complexes is presented. An out-of-plane bonding mode is observed in the solid state, analogous to that seen in scandium bis-alkyls, and spectroscopic studies reveal that fluxional behavior in solution is also comparable to that observed for the scandium species. The bis-alkyls LYR2 are susceptible to metalative alkane elimination at room temperature in solution. Activation of (Liga)YR2 with [HNMe2Ph][B(C6F5)4] generates alkyl cations stabilized with η6-arene-bound NMe2Ph. This unique coordination mode was studied via 1D 1H, 13C, and 15N NMR and 2D ROESY spectroscopy and appears to stabilize the alkyl cations against metalative alkane elimination.

A new ligand design for the widely used β-diketiminato framework implements a “remote steric bulk” strategy for the stabilization of low-coordinate, metalation-resistant organoscandium complexes. In comparison to standard ligands, substantial improvements in thermal stability for neutral dialkyl and cationic alkyl organoscandium complexes are observed.