Crystal structure of (CO)3(CH3)Mo[(η5-C5H4)C(CH3)N–NC(CH3)(η5-C5H4)]Mo(CO)3(CH3) and unequivocal assignments of C(2,5) and C(3,4) on the cyclopentadienyl ring of cynichrodene, tricarbonyl(η5-cyclopentadienyl)methylmolybdenum, tricarbonyl(η5-cyclopentadien

Schiff's bases (η5-formylcyclopentadienyl)tricarbonylmethylmolybdenum 2,4-dinitrophenylhydrazone (6), (η5-acetylcyclopentadienyl)tricarbonylmethylmolybdenum 2,4-dinitrophenylhydrazone (7), and (η5-acetylcyclopentadienyl)tricarbonylmethylmolybdenum azine (8) were obtained from condensation reaction of (CO)3(CH3)Mo(C5H4CHO) (3) or (CO)3(CH3)Mo(C5H4COCH3) (4) with each corresponding primary amine. The structures of 7 and 8 were determined by X-ray diffraction studies.The chemical shifts of C(2)–C(5) carbon atoms of the series of substituted-cyclopentadienyl Cp(M) derivatives—(CO)2(NO)M[η5-(C5H4COOCH3)] (1 M = Cr, 2 M = Mo), (CO)3(CH3)Mo[η5-(C5H4-sub)] (3–5, 6, 7, 8)—have been assigned using two-dimensional HetCOR NMR spectroscopy. The assigned chemical shifts were compared with the NMR data of other organometallic Cp(M) analogs, (CO)2(NO)CrCp, (CO)3(CH3)WCp, Cp2Fe, and (CO)2CoCp. We observed that C(3,4) resonate at a lower field than C(2,5) in (CO)3(CH3)Mo[η5-(C5H4CHO)] 3 and 4, whereas C(2,5) resonate at a lower field than C(3,4) in (CO)3(CH3)Mo[η5-(C5H4COOCH3)] 5. The correlation between the magnitudes of nonplanarity of Cp-exocyclic carbon to π-acceptor substituents and the extent of deshielding on the C(3,4) of the Cp ring was discussed. The electron density distribution in the cyclopentadienyl ring was discussed on the basis of 13C NMR data and those of 4, 7, and 8 were compared with calculations using the density functional B3LYP exchange-correlation method.

Graphical abstractThe chemical shifts of C(2–5) of some Cp-sub derivatives of (CO)2(NO)CrCp and (CO)3(CH3)MoCp were assigned using 2D HetCOR. We obtained the inverse assignments of C(2,5) and C(3,4) between (CO)3(Me)Mo(η5-C5H4CHO)] 3 and (CO)3(Me)Mo(η5-C5H4COOCH3) 5. The reasons behind were rationalized and compared with those of the organometallocenyl carbocations.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Some new Cp-sub derivatives of (CO)3(Me)MoCp were synthesized. ► (CO)3(Me)Mo(C5H4-R) 3 (R = CHO) and 5 (R = COOMe) were characterized by 2D HetCOR. ► The inverse assignments of C(2,5) and C(3,4) between 3 and 5 were rationalized. ► Cp(M) complexes bearing E.W. sub. and organometallocenyl carbocations were compared. ► Their resemblance in X-ray structure and 13C chemical shifts were rationalized.