Transition metal complexes with sterically demanding ligands. I. Synthesis and X-ray crystal structure of 1,5-cyclooctadiene palladium methyl triflate, (COD)Pd(Me)(OTf) and its cationic penta-coordinate adducts with sterically demanding 2,9-diaryl-substituted 1,10-phenanthroline ligands

The synthesis, use and X-ray crystal structure of the novel cyclooctadiene Pd-triflate methyl complex 1 is described. Evidence for ionization of the triflate ligand in 1 in solution is presented through IR, F-19-NMR and conductivity measurements. The high reactivity of this starting material is exemplified through the preparation of the novel cationic pentacoordinate Pd complexes 4 and 5, from 1 and the sterically demanding 2,9-diarylsubstituted 1,10-phenanthroline ligands 2 and 3. Complexes 4 and 5 have a pseudo-trigonal bipyramidal structure and display significant differences of the binding mode of the two olefin moieties of the cyclooctadiene ligand, This has been substantiated through H-1- and C-13-NMR spectroscopic data and for complex 4 by an X-ray crystallographic study. (C) 1999 Elsevier Science S.A. All rights reserved.