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

Condensation of alpha and gamma methylenepyran aldehydes with the Fischer c arbene complexes (CO)(5)M=C(OCH3)Me (M = Cr, W) or (CO)(5)W=C(OCH3)CH=CH-CH 3 in the presence of ClSiMe3/NEt3 yield donor acceptor complexes, in which the electron donating group is connected to the organometallic accepting gr oup by a conjugated ethylenic spacer. H-1- and C-13-NMR studies, suggest th at the carbene fragment and the unsaturated chain lie in the same plan, all owing a mesomeric interaction between the oxygen atom of the heterocycle an d the metal via the spacer. The positive solvatochromism of the molecules o btained is reported. (C) 2001 Elsevier Science B.V. All rights reserved.