Tetracarbonylmolybdenum complexes of 2-(phenylhydrazino)pyridine ligands. Correlations of spectroscopic data with pyridyl substituent effects

The 2-(phenythydrazino)pyridine (2-PHP) complexes cis-Mo(CO)(4)(X-2-(phenylhydrazino)pyridine) (X = 4-CH3O, 4-CH3, H, 4-Cl, 5-Br, 6-CH3, 4,6-(CH3)(2)) and CiS-MO(CO)(4)(2-(2-CH3-phenylhydrazino)pyridine) have been synthesized and characterized. The properties of these complexes are compared with those of the analogous 2-(phenylazo)pyridine (2-PAP) complexes. The lack of the pi-accepting azo group in the 2-PHP ligands leads to less stable complexes, including the inability even to isolate the complex with X = CF3. The 2-PHP complexes show very good correlations among the Mo-95-NMR chemical shift, the sum of the carbonyl stretching frequencies, and the Hammett sigma parameter for the pyridyl substituents. There is also an excellent correlation (r = 0.978, n = 7) of the Mo-95 chemical shift of the 2-PHP complexes with the shift for the 2-PAP complexes. The failure of the complexes with X 6-CH3 or 4,6-(CH3)(2) or the complexcis-Mo(CO)(4)(2-(2-CH3-phenylhydrazino)pyridine) to fit some of the correlations is attributed to steric or electronic effects. The 2-hydrazinopyridine complex cis-Mo(CO)(4)(H2NHNC5H4N) also was characterized. (C) 2002 Elsevier Science B.V. All rights reserved.