Neutral zinc(II) and molybdenum(0) complexes with chiral guanidine ligands:: synthesis, characterisation and applications

The synthesis and properties of three bidentate zinc(II) complexes with several chiral bidentate and one molybdenum(0) with analogous tridendate neutral chiral guanidine ligands are reported. N',N''-Diisopropyl-(S)-2-(N,N-dialkylaminomethyl) pyrrolidine- 1-carboximid-amides 1-3 reacted with anhydrous zinc(II) chloride to form mono-ligand complexes 4 6, which exist as chain structures in solid state with an NH center dot center dot center dot Cl interaction between the monomer units. The X-ray crystal structures of 4 6 show the zinc(II) ion in a tetrahedral environment in which the C2 side chain nitrogen atom and the imine group coordinate with the metal centre. Chiral guanidine 2 was treated with (nbd)MO(CO)(4) to yield the corresponding molybdenum complex 7. The molecular structure of 7 has been determined by X-ray crystallography. In contrast to 5, guanidine 2 acts as a tridentate ligand in 7 and the Mo(0) centre is in an octahedral coordination environment. NMR spectroscopy was performed to determine solution structures which were further supported by X-ray analysis. The chiral zinc guanidine complexes 4-6 were prepared in an effort to design chiral guanidine catalysts for asymmetric synthesis. (c) 2005 Elsevier Ltd. All rights reserved.