Syntheses and spectra of (CO) 2(NO) Cr(η 5-C 5H 4-R) (R = −C(O)N 3, −NCO, −NH 2, −NHC(O)O-CH 2C 6H 5 or −NHC(O)NH(η 5-C 5H 4 Cr(CO) 2(NO)) and crystal structure of (CO) 2(NO) Cr[(η 5-C 5H 4)NHC(O)NH(η 5-C 5H 4)]Cr(CO) 2(NO)

Abstract

(η 5-Isocyanatocyclopentadienyl)dicarbonylnitrosylchromium( 5) (hereafter called isocyanatocynichrodene) was prepared from cynichrodenoic acid ( 2) via the Curtius rearrangement. Hydrolysis of 5 with 20% aqueous potassium hydroxide solution gave dicynichrodenylurea ( 8) with a 40% and aminocynichrodene ( 6) with a 30% yield. The structure of 8 was solved by an X-ray diffraction study: space group, I4 1/ a; tetragonal; a = 20.383(4) and c = 18.001(4); Z = 16. Compound 8 adopts a transoid conformation at the organic imido bridge. The dihedral angle between the two planes of imido-substituted cyclopentadienyl rings is 38.9°. The nitrosyl group in each cynichrodenyl moiety is located at the site towards the corresponding imido nitrogen atom with twist angles of 8.3° and 9.7° respectively. The chemical shifts of H(2)−H(5) protons and C(2)−C(5) carbon atoms of a series of cynichrodene derivatives have been assigned using two-dimensional HetCOR NMR spectroscopy. The assigned chemical shifts of selected monosubstituted cynichrodene derivatives were compared with the NMR data of their analogues of ferrocene and benzene derivatives. For derivatives with electron-donating substituents, an analogy was observed between the shielding of C(2,5) and C(3,4) carbon atoms of cynichrodene derivatives and ferrocene derivatives and ortho- and para-carbon atoms of benzene derivatives. For derivatives bearing electron-withdrawing substituents, the opposite correlation on the assignments was observed between cynichrodene derivatives and the derivatives of ferrocene and benzene. The electron density distribution in the cyclopentadienyl ring is discussed on the basis of 13C NMR data and that of 8 is compared with the ab-initio calculations.