Synthesis of protonated ferrocene isomers in the gas phase and their study by mass spectrometry

Abstract

Gas phase protonation of ferrocene has been studied experimentally in four different reaction systems, using high energy Collision Induced Decomposition mass spectrometry to follow the progress of reaction at different temperatures and pressures. Experimental evidence is obtained for the existence of three stable isomers as predicted theoretically. The most stable form is shown to be most probably metal-protonated, but the energies of the metal-protonated and agostic forms are within 10 kJ mol -1 of each other. The ring-protonated isomer is higher in energy by ≤ 62 kJ mol -1 . Intramolecular isomerization could not be detected, indicating relatively high energy or entropy barriers separating the isomers. The intermediate complex formed by exo attack of t-C 4 H 9 + on ferrocene was also studied and observed to change structure, from a σ-to a π-complex, leading to the population of different protonated isomers of ferrocene, depending on the temperature.

Helium-Plasma-Ionization Mass Spectrometry of Metallocenes and Their Derivatives

“…However, results similar to our H/D exchange data have also been reported by Karlsson et al, who observed by low-temperature 1 H NMR recordings that [ 2 H 10 ]-ferrocene in superacid undergoes only one primary protonation . Moreover, Mason and Kelly did not detect any intramolecular isomerization in their gas-phase protonation study conducted using high-energy collision-induced dissociation mass spectrometry …”

“…75 Moreover, Mason and Kelly did not detect any intramolecular isomerization in their gas-phase protonation study conducted using high-energy collision-induced dissociation mass spectrometry. 76 Contrary to the small energy difference predicted by computational results, which slightly favors the agostic structure, our own experimental observations on H/D exchange agree with the suggestion that the incipient proton ensconces itself in a sterically unique position and undergoes only one H/D exchange when exposed to D 2 O vapor (Figure 6D). Since experimental evidence, not computational predictions, should take precedence when postulating mechanistic models, we propose that upon collisional activation, the charge-imparting proton migrates to a cp ring and randomizes with its hydrogen atoms (Scheme 1).…”

Low temperaturein situsynthesis and the formation mechanism of various carbon-encapsulated nanocrystals by the electrophilic oxidation of metallocene complexes

“…+ and H + [24]. The NH 4 + ions in (NH 4 ) 2 S 2 O 8 would likely attach directly onto the metal atoms and the Cp ligands were tilted and loosely bound with metal atoms as a result of the formation of a metastable intermediate phase, decreasing the stability of the metallocene complex [25]. Then the decomposition of persulfate anion (S 2 O 8 2-) took place by this means, cleaving the O-O bond between the two S atoms as the temperature increases, thus converting to a powerful oxidant known as sulfate-free radicals.…”