The first example of an organo-tungsten pyrylium. complex (4-cyclopentadien
yl-2,6-diphenylpyrylium)W(CO)(3)CH3 has been prepared, fully characterized
and transformed in an aqueous basic medium to the corresponding pseudobase
(3-cyclopentadienyl-1,5-diphenylpent-2-ene-1,5-dione)W- (CO)(3)CH3 which is
the first X-ray structure analysed organometallic, pseudobase.