N‐Heterocyclic‐Carbene‐Induced Monomerization of Sterically Encumbered Dialkylmagnesium and Dialkylmanganese Polymers

The sterically encumbered polymeric dialkyl complexes [M(CH 2 SiMe 3 ) 2 ] ∞ [M = Mg, Mn II ] were deaggregated by the potent two‐electron σ‐donor, 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene (IPr), to yield the first examples of the monomeric three‐coordinate [M(CH 2 SiMe 3 ) 2 ] · donor complexes [M = Mg ( 1 ); Mn ( 2 )]. Similarly, monomeric three‐coordinate species M[CH(SiMe 3 ) 2 ] 2 · IPr [M = Mg, ( 3 ); Mn, ( 4 )] were obtained from the bulkier disilyl‐substituted alkyl [CH(SiMe 3 ) 2 ] congeners M[CH(SiMe 3 ) 2 ] 2 · ether by displacement of the ether by IPr. Complexes 1 – 4 , which represent rare examples of N‐heterocyclic‐carbene‐stabilized dialkylmagnesium and dialkylmanganese species, were crystallographically characterized; the diamagnetic magnesium complexes were also characterized in an arene solution by 1 H and 13 C NMR spectroscopy.