Crystal structure of (CO)2(NO)Cr{η5-C5H4C(CH3) = NNH[2,4-(NO2)2C6H3]} and unequivocal assignments of C(2,5) and C(3,4) on the cyclopentadienyl ring of cynichrodene, tricarbonyl(η5-cyclopentadienyl)methylmolybdenum and tricarbonyl(η5-cyclopentadienyl)

The chemical shifts of the C(2)-C(5) carbon atoms of a series of substituted-cyclopentadienyl Cp(M) derivatives - (CO)2(NO)Cr[η5-(C5H4-sub)], (CO)3(CH3)W[η5-(C5H4-sub)] and (CO)3(CH3)Mo[η5-(C5H4-sub)] (CO)3(CH3) - have been assigned using 2D HetCOR NMR. We obtained inverse assignments of C(2,5) and C(3,4) between (CO)2(NO)Cr(η5-C5H4CR = NNH[2,4-(NO)2C6H3)] 4 (R = H) and 5 (R = CH3). The reasons behind this have been rationalized.