Organotransition-metal complexes of multidentate ligands XVI. On the nature of the sigma-donicity of the saturated nitrogen ligands; chelate-assisted weakening of the α-N-H bond: synthesis, and spectral and structural study of (N-N=saturated nitrogen bidentate ligands)

Article abstract of DOI:10.1016/0022-328X(91)80263-J

A series of complexes, (N-N = saturated nitrogen bidentate ligands), were prepared from (pip = piperidine) and N-N in CH2Cl2 at 40 deg C.The structure of (CO)4> was also determined by X-ray crystallography: space group Pbca, a = 14.895(7), b = 11.947(4), c = 19.189(8) Angstroem, V = 3415(2) Angstroem³, Z = 8, d_calc = 1.503 g/cm³, R = 0.026 and R_w = 0.026 based on 1646 reflections with Ι above 3.0 ?(Ι).Both the spectral and structural data of the complexes indicate that the electron-density donating from the ligands comprises not only the lone electron pair of the nitrogen atom but the electron-density deprived from the neighboring groups by the highly electronegative nitrogen atom.These data also show that the more electron density of the α-N-H bond relative to that of the α-N-R bond (R = alkyl or aryl) is removed upon coordination of the nitrogen donor ligands, apparently explaining why a chelate-assisted oxidative addition of the N-H bond occurs more readily than the N-R bond through prior coordination and concurrent weakening of the N-H bond.