Unequivocal assignments of C(2,5) and C(3,4) on the cyclopentadienyl ring of dicarbonyl(η5-cyclopentadienyl)nitrosylchromium, dicarbonyl(η5-cyclopentadienyl)cobalt, and tricarbonyl(η5-cyclopentadienyl)methyltungsten derivatives bearing an electron-withdrawing carbonyl substituent in 13C NMR spectra

Abstract

The chemical shifts of C(2)–C(5) carbon atoms of the series of substituted-cyclopentadienyl Cp(M) derivatives—(CO)2Co[η5-(C5H4-sub)] (1–5), (C4Ph4)Co[η5-(C5H4COOCH3)] (6), (CO)3(CH3)W[η5-(C5H4-sub)](7–9), (CO)3(Cl)W[η5-(C5H4COOCH3)] (10), (CO)2(NO)Cr[η5-(C5H4-sub)] (11–23), and (NO)2(Cl)Cr[η5-(C5H4COOCH3)] (24)—have been assigned using two-dimensional HETCOR NMR spectroscopy. The assigned chemical shifts were compared with the NMR data of their ferrocene analogs. We observed that H(3,4) resonate at a lower field than H(2,5) resonate in (CO)2Co(η5-C5H4CHO) 1. The structure of (CO)3(CH3)W[η5-(C5H4COCH3)] 8 has been determined by X-ray diffraction studies. The electron density distribution in the cyclopentadienyl ring is discussed on the basis of 13C NMR data and that of 10 and (CO)2Co[η5-(C5H4COONS)] (NS=N-succinimidyl) (25) is compared with calculations using the density functional B3LYP exchange-correlation method.