Crystal structure of a heavier alkali metal diisopropylamide complex: a discrete (KN)(2) ring dimer with TMEDA chelation and short intramolecular K center dot center dot center dot H(C)contacts

Synthesized by treating diisopropylamine with a potassium reagent (the solid isolated from a 1:1 reaction mixture of potassium t-butoxide and n-butyllithium) in the presence of N,N,N',N'-tetramethylenediamine (TMEDA), the potassium diisopropylamide complex [((Pr2NK)-Pr-i. TMEDA)(2)] has been subjected to a low temperature X-ray diffraction study. This reveals a discrete dimeric arrangement centred on an asymmetrical (KN)(2) cyclic ring, with bond lengths of 2.706(2) and 2.837(2) Angstrom and endocyclic bond angles of 100.54(5) and 79.46(5)degrees (at K and N, respectively). Terminal, chelating TMEDA ligands complete the distorted tetrahedral N, primary coordination sphere about the K+ cations. However, there are several secondary intramolecular K ... H(C) contacts involving methyl fragments of the diisopropylamido ligands. (C) 1998 Elsevier Science S.A. All rights reserved