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 an d 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. T his reveals a discrete dimeric arrangement centred on an asymmetrical (KN)(2) cyclic ring, with bond lengths of 2.706(2) and 2.837(2) Angstr om and endocyclic bond angles of 100.54(5) and 79.46(5)degrees (at K a nd N, respectively). Terminal, chelating TMEDA ligands complete the di storted tetrahedral N, primary coordination sphere about the K+ cation s. However, there are several secondary intramolecular K ... H(C) cont acts involving methyl fragments of the diisopropylamido ligands. (C) 1 998 Elsevier Science S.A. All rights reserved.