Regioselective protonation of ferrocene in superacid and formation of a C—H—Fe bond. An experimental and theoretical study of the structure and dynamics of the ferrocenonium ion

Abstract

Protonation of ferrocene has been suggested to take place on carbon (exo-protonation) or iron (endo-protonation). However, experiments have not been conclusive because of interfering exchange reactions. Now low-temperature protonation of ferrocene and [2H10]-ferrocene in superacid and direct observation of the carbocation by 1H NMR at low temperature shows only primary protonation and that it exclusively takes place in an endo-fashion. Studies by DFT calculations using B3LYP hybrid functional indicate the presence of an intramolecular nonlinear C—H—Fe bond and that the proton might be delocalized between carbon and iron. Potential energy barriers for degenerate rearrangements of the hydride bridged carbocation are low, suggesting that the proton might be delocalized between all 10 carbons and iron. The NMR results are consistent with such an interpretation.Key words: regioselective, protonation, superacid, ferrocenonium ion.

The Rational Design of Time‐Dependent (“Mechanical”) Homogeneous Catalysts. A Literature Survey of Multicentered Homogeneous Catalysis

“…It also indicated that the H þ ions present on the ferrocene iron atoms in protonated 8a were effectively activated atomic hydrogen (H † ), with most of their positive charge residing on the metal [56]. This was verified in subsequent density functional theory (DFT) calculations [57,58]. Cyclic voltammetry studies indicated that 8a exhibits two, one-electron oxidations centered on the respective metal ions [59].…”

Kinematic molecular manufacturing machines

“…The binding at each Fe center involved a dynamic equilibrium, which included direct Fe-H binding, as well as protonation at the ring carbons, as depicted in Scheme 10 [41,42]. The exchange processes were too rapid to be resolved on the NMR timescale, even at -122 o C [41,43].…”

“…Theoretical studies showed however that, when bound to the ferrocene Fe atoms, most of the positive charge of the H + ions relocated to the metal, causing them to be, effectively, activated atomic hydrogen (H · ) [41,43]. An X-ray crystal structure, along with molecular modelling, showed the Fe … Fe distance in 15a to oscillate between 3.4 -4.8 Å during flexing [46].…”

Determination of acidic dissociation constants of glutamine and isoleucine in water using ab initio methods

“…With the high speed development of computer technology and the wide applications of G98 program package [16,17], more and more quantum chemical computations on transition metal complexes, in particular, the computations applying density functional theory (DFT), which account better for electron correlation energies and reduces greatly the computation expenses, have been reported [18]. Recently, more and more quantum chemical density functional theory (DFT) [19][20][21] investigations, which are based upon a strategy of modeling electron correlation via general functional of electron density, have been reported [22][23][24][25][26][27][28]. DFT method can better consider the electron correlations and needs less computational expense.…”

“…Recently, more and more quantum chemical density functional theory (DFT) [19][20][21] investigations, which are based upon a strategy of modeling electron correlation via general functional of electron density, have been reported [22][23][24][25][26][27][28]. DFT method can better consider the electron correlations and needs less computational expense.…”