A Close Look at Short CCH3⋅⋅⋅Potassium Contacts: Synthetic and Theoretical Investigations of M2Co2(μ3‐OtBu)2(μ2‐OtBu)4(thf)n (M=Na, K, Rb, thf=tetrahydrofuran)

Agostic interactions of the type Si-CH3M+ (M = alkali metal) are frequently mentioned in discussions of solid-state structures of trimethylsilyl compounds and the purpose of this work was to elucidate if they also exist in the related tert-butyl species by using density functional theory. The compounds M2Co2(mu3-OtBu)2(mu2-OtBu)4(thf)n (M = Na, n = 2; M = K, n = 0; M = Rb, n = 1) have been synthesised and their crystal structures determined. Close contacts of methyl groups with K atoms are observed in the solid-state structure of K2Co2(mu3-OtBu)2(mu2-OtBu)4, and calculations of the rotational barrier of a tert-butoxy group about the axis through the C-O bond were performed. It was shown that apparent short C-CH3K distances are in this case a consequence of the packing in the extended solid-state structure.