Preparation of stable α-(nonamethylmetallocenyl)-α-hydroxycarbocations and their transformations

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Abstract It has been shown that the structure of α-(nonamethylmetallocenyl)-α-hydroxycarbocations (M = Fe, Ru, Os), prepared by protonation of formylnonamethylmetallocenes with HBF4 and CF3COOH, depends on the nature of the metal and anion and is determined by the relative basicities. The Fe-containing salts have an open fulvenoid structure with an interionic hydrogen bond O-H … X irrespective of the nature of anion (X = BF4−, CF3COO−). The Ru- and Os-containing salts, in which the metal atoms are more basic than Fe, have, in the case of the weakly basic BF4− anion, a cyclic structure with an intramolecular M … HO hydrogen bond, while in the case of the more basic X = F− or CF3COO− anions they are transformed to the open fulvenoid structure with an interionic hydrogen bond OH … X, the structure of which has been established by an X-ray diffraction study of C 5 Me 5 RuMe 4 C + H − OH … F − . When the Fe-containing salts are kept in polar solvents or stored in the solid state for a long time they are entirely converted into paramagnetic salts of formylnonamethylferrocenium, the structure of which was confirmed by the oxidation of formylnonamethylferrocene using AgBF4.