Ulrich T. Mueller-Westerhoff

The lithiation of ferrocene and ruthenocene: a retraction and an improvement

Abstract We reported in 1993 an efficient synthesis of ferrocene and ruthenocene mono- and dialdehydes which suggested the first truly specific monolithiation of these two metallocenes (U.T. Mueller-Westerhoff, Z. Yang and G. Ingram, J. Organomet. Chem., 463 (1993) 163). Unfortunately, these results were based on inappropriate experimental methods. We have now meticulously analyzed a wide spread of reaction conditions and have concluded that an effective monolithiation of ferrocene and of ruthenocene is possible, but not under the previously described reaction conditions.

Improved electrochemistry of multi-ferrocenyl compounds: investigation of biferrocene, terferrocene, bis(fulvalene)diiron and diferrocenylethane in dichloromethane using [NBu4][B(C6F5)4] as supporting electrolyte

Abstract Cyclic voltammetry in CH 2 Cl 2 containing 0.1 M [NBu 4 ][B(C 6 F 5 ) 4 ] gives enhanced behavior for the oxidation of complexes containing two or more ferrocenyl groups, owing to better stabilities and solubilities of the multiply-charged oxidation products. The lower ion-pairing interaction of the anion [B(C 6 F 5 ) 4 ] − with oligoferrocenyl multiply-charged cations leads to larger separations of the oxidation waves which may be exploited in studies of mixed-valent systems.

A simple synthesis of metallocene aldehydes from lithiometallocenes and N,N-dimethylformamide: Ferrocene and ruthenocene aldehydes and 1,1′-dialdehydes☆

Abstract Lithioferrocene, 1,1′-dilithioferrocene, lithioruthenocene and 1,1′-dilithioruthenocene all react with N , N -dimethylformamide in diethyl eth

The protonation mechanism of metallocenes and [1.1]metallocenophanes

Abstract A study of the protonation and deuteration of [1.1]metallocenophanes has revealed several details of the mechanism of metallocene protonation. In [1.1]ferrocenophane, protonation at both metallocenes is immediately followed by elimination of dihydrogen. The resulting bis-ferrocenium ion is substitutionally inert and no longer takes part in protonation or deuteration. This convenient circumstance permits us to analyze the protonation mechanism in greater detail than monomeric ferrocenes would allow. The reaction of [1.1]ferrocenophanes with deuterated acids leads to partially or completely deuterated rings, depending on their structure and the reaction conditions. The experimental results on ferrocene-containing systems are not compatible with a reaction path in which the incoming electrophile binds first to the iron and then transfers to the ring. Substitution must rather occur by exo -attack on the ring, followed by transfer of the proton to the metal and back to either one of the rings. For protonated ferrocene, a rapid equilibrium between ring- and metal-protonated species exists; deuterated acids lead to rapid and complete H/D exchange. In contrast to the protonation of ferrocene, the protonation of ruthenocene occurs at the metal only, without any participation of the Cp rings. Consequently, ruthenocene reacts with deuterated acids without H/D exchange. Studies on [1.1]ferroceno-ruthenocenophane demonstrate the differences in the protonation of these two metallocenes.

A simple synthesis of symmetrical α-diones from organometallic reagents and 1,4-dimethyl-piperazine-2,3-dione

Abstract Short reflux of an equimolar mixture of N-N′-dimethyl ethylenediamine and diethyl oxalate in i-propanol or diethyl ether leads to 1,4-dimethyl-piperazine-2,3-dione, which is able to react with two equivalent of organolithium or Grignard compounds to form symmetrically substituted α-diones in excellent yields.

Homogeneous catalysts with a mechanical ("machine-like") action.

Chemical reactions may be controlled by either: 1) the minimum threshold energy that must be overcome during collisions between reactant molecules/atoms (the activation energy, E(a)), or: 2) the rate at which reactant collisions occur (the collision frequency, A)--for reactions with low E(a). Reactions of type 2 are governed by the physical, mechanical interaction of the reactants. Such mechanical processes are unusual, but not unknown in molecular catalysts. In this work we examine the machine-like nature of the action in various abiological mechanical catalysts and consider the implications for mimicry of biological catalysts.

Azines and Imines of 4- and 5-t-Bu-Pyrrole-2-aldehyde. A Useful Synthesis of the Aldehydes

Abstract The preparation of 4- and 5-t-Bu-pyrrole-2-aldehyde can be brought about in a high yield and purity using Vilsmeier-Haack type reactions as conclusions to reaction sequences involving a 1-benzenesulfonyl directing group on pyrrole (4-substitution) or the formamidinium salt of pyrrole (5-substitution). Azines/imines were prepared and characterised.

Investigations of Ruthenium (II) Sources for the Synthesis of Ruthenocene and [1.1]Ferro-Ruthenocenophane

Abstract In order to find alternate sources of rathenium(II) in which the metal is coordinated to easily removed ligands and which would be useful in the synthesis of [1.1]metallocenophanes, a number of candidate Ru(II) compounds were examined for the preparation of ruthenocene. In general, the “Ru[II]” compounds were prepared by methanol reduction (without hydrogen) and are known to be more complicated complexes. These compounds were as follows: RuCl2 in THF, RuCl2 in ethylene glycol diethyl ether (DEE), dibenzeneruthenium(II) hexafluorophophosphate, ruthenium(II) chloride tris-(tri-phenylstibine), and di-μ.-chloro-bis-(benzene-chlororutheni-um(II)]. RuCl2·3(Ph3Sb) produced ruthenocene yields of 75% for. It was selected for the synthesis of [l.l] ferro-ruthenocenophane from l,l′-bis-(6-fulvenyl)ferrocene with the best yields (15%) ever reported. The use of [(Et2S)3RuCl3) with in-situ reducing agents lead to the same [l.l]metallocenophane, but in slightly lower yields (11%). However, a number of attempts ...

A Proposed Reversible Mechanism Confirming Conformational Retention in 1, 12-Dimethyl[l. l]Ferrocenophane

Abstract Upon examination of the reaction of l, 12-dimethyi[l.l]ferrocenophane with the strong non-oxidizing acid boron trifluoride, a dication was formed. Upon dilution widi H2O, a bridge carbocation results. A mixture of exo-exo l, 12-dimethyl[l.l]ferro-cenophane and exo-endo l, 12-dimethyl[l.l]ferrocenophane should be observed, if the hydride is added direcdy back to the methylene bridge carbocation. However, when the hydride is added, retention of configuration is realized, indicating a significandy more complex mechanism of reaction. We propose that the iron centers and the methylene bridge participate through an intramolecular hydride migration which leads to retention of configuration.

Synthesis of Ruthenocene, [l.l]Ferroceno-Ruthenocenophane and [l.l]Ruthenocenophane Using Di-Ruthenium(II)-Tetracarboxylates

Abstract A new synthetic route to ruthenocene, [1.1]ferroceno-ruthenocenophane, and [1.1]ruthenocenophane involves the use of ruthenium(II) carboxylates, (Ru2OCR)4,R = C3H7 and C7H15), the metal source and does not, as most alternate sytheses do, require an excess of the ligand. The long chain chloro-Ru(II,III) carboxylates were obtained from chloro-ruthenium(II,III) tetraacetate by reaction with the respective carboxylic acids and were subsequently reduced to the Ru(II,II) species. Ruthenocene was produced in >90% yield by reacting either of these carboxylates with stoichiometric amounts of sodium cyclopentadienide. The synthesis of the metallocenophanes involved addition of the Ru(II) carboxylate to the dianions of 1,1′-bis(cyclopenta-dienylmethyl) ferrocene or 1,l′-bis(cyclopentadienyl-methyl)ruthenocene and produced 11–12% yields of the two cyclic systems. Considerable amounts of the dimers (Cp-CH2-Cp)4M4 were formed in these reactions.