1,1,3,3'-Tetrakis(p-dimethylaminobenzyl)-2,2'-biimidazolidinylidene, L-2(R) (R = CH2C6H4NMe2-p) which contains four peripheral NMe2 substituents, was obtained from 4-dimethylaminobenzaldehyde by a three-step reaction sequence, and was used for the preparation of imidazolidin-2-ylidene Ru(II) and Rh(I) complexes 1 and 2. Etherial HCl readily protonates the NMe2 functionality on the carbene ligand of 1 to give the corresponding salt, 1'; whereas the reaction of 2 with HCl gave a hygroscopic and ill-defined rhodium species. In aqueous solution the salt 1' is an efficient and active catalyst for intramolecular cyclisation of (Z)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran. The catalyst 1' could be recovered by simple phase separation and the catalytic reaction was maintained for five different runs. All of the new compounds were characterised by elemental analyses, IR and NMR spectroscopy and the molecular structure of I was determined by X-ray crystallography. (C) 2001 Elsevier Science B.V. All rights reserved.
C1 Inonu Univ, Dept Chem, TR-44069 Malatya, Turkey.
Ege Univ, Dept Chem, TR-35100 Bornova, Turkey.
Hacettepe Univ, Dept Engn Phys, TR-06532 Ankara, Turkey.