Synthesis, spectra and crystal structure of ( E)-(CO) 2(NO)Cr[( η5-C 5H 4)–CHCH( η5-C 5H 4)]Cr(CO) 2(NO)

Abstract

Compounds 1,2-bis[( η 5-cyclopentadienyl)dicarbonylnitrosylchromium]ethene ( 7) (hereafter called 1,2-dicynichrodenylethene) and 1,2-diferrocenylethene ( 10) were prepared from formylcynichrodene ( 3) and formylferrocene ( 9), respectively, via the McMurry’s low-valent titanium coupling method. Compounds ( η 5-vinylcyclopentadienyl)dicarbonylnitrosylchromium ( 6) and vinylferrocene ( 11) were obtained by the dehydration of the corresponding alcohols. The structure of 7 was solved by an X-ray diffraction study: space group, P2 1/ c; monoclinic; a=6.379(5), b=11.295(3) and c=11.9352(24); Z=2. It turns out that compound 7 adopts a transoid conformation at the ethenylene bridge and the two cyclopentadienyl rings are coplanar. The nitrosyl group in each cynichrodenyl moiety of 7 is located at the side towards the corresponding ethenylene carbon atom with a twist angle of 46.5°. The chemical shifts of H(2)–H(5) protons and C(2)–C(5) carbon atoms of a series of vinyl derivatives of compounds bearing cyclopentadienyl rings have been assigned using two-dimensional HetCOR-NMR spectroscopy. For the derivatives of cynichrodene ( 1) and ferrocene, it was found that the shielding of C(2,5) and C(3,4) carbon atoms is parallel to the shielding of the ortho- and para-carbon atoms of benzene derivatives. The electron density distribution in the cyclopentadienyl ring is discussed on the basis of 13C-NMR data. Surprisingly, the vinyl group donates electron density to the adjacent cynichrodene moieties rather than withdraws from them.