Synthesis, spectra and crystal structure of (E)-(CO)(2)(NO)Cr[(eta(5)-C5H4)-CH=CH(eta(5)-C5H4)]Cr(CO)(2)(NO)

Compounds 1,2-bis[(eta(5)-cyclopentadienyl)dicarbonylnitrosylchromium]ethen e (7) thereafter called 1,2-dicynichrodenylethene and 1,2-diferrocenylethen e (10) were prepared from formylcynichrodene (3) and formylferrocene (9), r espectively, via the McMurry's low-valent titanium coupling method. Compoun ds (eta(5)-vinylcyclopentadienyl)dicarbonylnitrosylchromium (6) and vinylfe rrocene (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 ethen ylene 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 degrees. Th e chemical shifts of H(2)-H(5) protons and C(2)-C(5) carbon atoms of a seri es of vinyl derivatives of compounds bearing cyclopentadienyl rings have be en assigned using two-dimensional HetCOR-NMR spectroscopy. For the derivati ves 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- an d papa-carbon atoms of benzene derivatives. The electron density distributi on in the cyclopentadienyl ring is discussed on the basis of C-13-NMR data. Surprisingly, the vinyl group donates electron density to the adjacent cyn ichrodene moieties rather than withdraws from them. (C) 1999 Elsevier Scien ce S.A. All rights reserved.