The di-(2-pyridyl)amine (dpa) complexes M(CO)4dpa (M = Cr, Mo or W) and their anionic derivatives [MX(CO)3dpa]- (X = halide) have been prepared and compared chemically and spectroscopically with the corresponding 2,2'-bipyridyl (bipy) complexes. During these investigations a new procedure has been developed for determining the CO force constants for cis-L2M(CO)4 complexes. This procedure was tested by successfully predicting the spectra of C18O labelled cis-I2Fe(CO)4 species and then applied to a wide range of complexes and the results compared with Cotton-Kraihanzel and Jernigan force constant calculations. The tetracarbonyl and anionic tricarbonyl derivatives, M(CO)4L2 and [MX(CO)3L2]- (L2 = bipy or dpa), have been used to extend the range of known molybdenum and tungsten complexes containing the M(n3-allyl)(CO)2 unit, and by employing a new low temperature synthesis the previously unknown chromium(II) complexes [CrX(n3-allyl)(CO)2bipy] (X = Cl, Br, I or NCS) have also been isolated as maroon solids. These complexes are essentially diamagnetic and appear to be analogous to the molybdenum and tungsten compounds but due to their lack of stability in solution a complete spectral characterisation was not possible. It was found that some potentially three-electron donor ligands (LLa) react in the presence of pyridine (py) to displace both the acido-group (X = Cl or Br) and the bidentate ligand dpa or bipy from the complexes [MX(n3-allyl)(CO)2L2] to give the complex [M(LLa)(3-allyl)(CO)2py] o Variable temperature n.m.r. spectroscopy showed these complexes to be fluxional in solution, and the data was consistent with a pseudo-molecular rotation mechanism. While this thesis was in preparation, the crystal structure of [MO(acac)(n3-allyl)(CO)2py] was determined independently and shown to be of lower symmetry than other [M(3-allyl) (CO)2(bidentate) (monodentate)] complexes.
|Date of Award||1978|