ORGANOMETALLICS AS POTENTIAL PROTEIN LABELS - PYRYLIUM AND PYRIDINIUM SALTS BEARING (C6H5)CR(CO)(3), (C5H4)MN(CO)(3), AND FERROCENYL SUBSTITUENTS

A series of 2,6-dimethyl- or 2,6-diphenylpyrylium cations, [R'-C(5)H(2)R ''O-2](+), which bear organometallic substituents at the 4-position, have been synthesized. The molecules in which R' = (C6H5)Cr(CO)(3), R '' = Me, 1, R' = (C5H4)Mn(CO)(3), R '' = Ph, 8, R' = (C5H4)Fe(C5H5), R '' = Me, 9, and R' = (C5H4)Re(CO)(3), R '' = Ph, 10, have been identified spectroscopically, and the complexes 1 and 8 have also been characterized by X-ray crystallography as CrC16H13O4+ PF6- and MnC25H16O4+ BF4-, respectively. The pi-complexed ring bearing either a Cr(CO)(3) or a Mn(CO)(3) moiety is almost coplanar with the pyrylium ring, as are the phenyl rings in 8. The structural and spectroscopic data indicate that the delocalization of the positive charge on the pyrylium ring onto the metal is rather minimal. These pyrylium salts react readily with benzylamine, or with beta-alanine ethyl ester, to form the corresponding pyridinium salts. In particular, the ferrocenyl derivative, 9, yields a crystalline pyridinium salt, 15, with the ethyl ester of beta-alanine.