Cyclopentadienyl chromium complexes with halide, methyl, isothiocyanate and isoselenocyanate ligands: Structures of [η5-(C5H4-COOCH3)]Cr(NO)2(Br) and [η5-(C5H4-COOCH3)]Cr(NO)2(Ndouble bond; length as m-dashCdouble bond; length as m-dashS)

Bromination/nitrosylation of [η5-(carbomethoxy)cyclopentadienyl]dicarbonylnitrosylchromium (8) (hereafter called carbomethoxycynichrodene) with hydrogen bromide/isoamyl nitrite gives bromo [η5-(carboxymethoxy)cyclopentadienyl]dinitrosylchromium (10) in 84%. Compounds 15 in 74% and 16 in 90% were obtained from the corresponding cynichrodene derivatives via the same method. Compounds [η5-(carbomethoxy)cyclopentadienyl](isothiocyanato)dinitrosylchromium (13) and [η5-(carbomethoxy)cyclopentadienyl](isoselenocyanato)dinitrosylchromium (14) were prepared from [η5-(carbomethoxy)cyclopentadienyl]chlorodinitrosylchromium (9) with excess potassium thiocyanate and selenocyanate, respectively, after detaching the chloride by the action of silver nitrate. One of the nitrosyl groups in each compound is located at the site away from the exocyclic carbonyl carbon of the Cp(Cr) ring with twist angles of 168.5° and 172.3°, respectively. The chemical shifts of C(2)–C(5) carbon atoms of a series of substituted-cyclopentadienyldinitrosylchromium derivatives, [η5-(C5H4-sub)]Cr(NO)2X, have been assigned using two-dimensional HetCOR NMR spectroscopy. The assigned chemical shifts were compared with the NMR data of their analogues of ferrocene, and the opposite correlation on the assignments was observed. The electron density distribution in the cyclopentadienyl ring is discussed on the basis of 13C NMR data and those of 10 and 13 are compared with the calculations via density functional B3LYP correlation-exchange method.