Crystal structure of (CO)_2(NO)Cr{η~5-C_5H_4C(CH_3) = NNH[2,4-(NO_2)_2 C_6H_3]} and unequivocal assignments of C(2,5) and C(3,4) on the cyclopentadienyl ring of cynichrodene, tricarbonyl(η~5-cyclopentadienyl)methylmolybdenum and tricarbonyl(η~5-cyclopentadienyl)methyltungsten bearing a 2,4-dinitrophenyl hydrazinyl substituent in ~(13)C NMR spectra

摘要

The Schiff's base complexes (CO)_2(NO)Cr{η~5-C_5H_4C(R) = NNH[2,4-(NO_2)_2C_6H_3]} (4 R =H, 5 R = CH_3, 6 R = C_6H_5)) and (CO)_3(CH_3)M{η~5-C_5H_4C(R) = NNH[2,4-(NO_2)_2C_6H_3]} (13, M = Mo, R = H; 14, M = Mo, R = CH_3; 17 M = W, R = H; 18 M = W, R = CH_3) were obtained from condensation reactions. The structure of 5 was determined by X-ray diffraction studies. The chemical shifts of the C(2)-C(5) carbon atoms of 4-6, 13, 14, 17 and 18 have been assigned using two-dimensional HetCOR NMR spectroscopy. We observed that C(2,5) resonates at a lower field than C(3,4) in 4 and 6, whereas C(3,4) resonates at a lower field than C(2,5) in 5. The correlation between the magnitude of the non-planarity of the Cp-exocyclic carbon to the π-acceptor substituents and the extent of deshielding on C(3,4) of the Cp ring is discussed. The electron density distribution in the cyclopentadienyl ring is discussed on the basis of the ~(13)C NMR data and those of 5 and 14 were compared with calculations using the density functional B3LYP exchange-correlation method.