Unequivocal assignments of C(2,5) and C(3,4) on the cyclopentadienyl ring of Cp2Fe, CpCr(CO)2(NO), and CpW(CO)3(CH3) bearing an electron-donating or electron-withdrawing substituent via resonance in 13C NMR spectra

• Cp(M) (M = Cr, Fe, W) complexes bearing an ED (NH2) or EW (COR) were synthesized.
• C(3,4) resonates at a lower field than C(2,5) in all Cp(M) (M = W, Fe) derivatives.
• C(2,5) resonates at a lower field than C(3,4) for Cr derivatives bearing an EW group.
• H(2,5) resonates at a lower field than H(3,4) for Fc derivatives bearing NH2 group.
• The rationalizations are proposed and compared with calculations using B3LYP method.

Complexes (NO)2(X)Cr(η5-C5H4NHCOOCH2C6H5) (X = Cl 2; I, 3; CH3, 4) were synthesized. A reaction between (CO)3(CH3)W(η5-C5H4COY) 8 (Y = OH) and PCl5 yielded 9 (Y = Cl). 9 was converted to 10 (Y = N3) with NaN3. 10 underwent Curtius rearrangement in the presence of CH3OH to give (CO)3(CH3)W(η5-C5H4NHCOOCH3) 7. Reaction of 9 with aniline led to carboxamide 11 (Y = NHC6H5). We observed that C(3,4) resonates at a lower field than C(2,5) in all Cp(M) (M = W, Fe) metallocene derivatives bearing either an electron-donating substituent or an electron-withdrawing substituent via resonance. The hypothesis to elucidate these data assignments was proposed. The electron density distribution in the cyclopentadienyl ring was discussed on the basis of 13C NMR data and those of 5–7, 10, 11, 13, 16, and 17 were compared with calculations using the density functional B3LYP exchange-correlation method based on their X-ray structural data.

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