Synthesis of electron donor–acceptor polyunsaturated methylenepyran Fischer type carbene complexes: dynamic 1H-NMR study and solvatochromic properties

Condensation of α and γ methylenepyran aldehydes with the Fischer carbene complexes (CO)5MC(OCH3)Me (M=Cr, W) or (CO)5WC(OCH3)CHCH–CH3 in the presence of ClSiMe3/NEt3 yield donor acceptor complexes, in which the electron donating group is connected to the organometallic accepting group by a conjugated ethylenic spacer. 1H- and 13C-NMR studies, suggest that the carbene fragment and the unsaturated chain lie in the same plan, allowing a mesomeric interaction between the oxygen atom of the heterocycle and the metal via the spacer. The positive solvatochromism of the molecules obtained is reported.