D. W. Slocum

Electronic Effects in Metallocenes and Certain Related Systems

Publisher Summary Electronic substituents can affect organic molecules in diverse ways. Because all aromatic organometallic π-complex systems possess several possible sites for which substituent effects could be analyzed, it seems best that the various sites be studied independently of one another. The study of relative site reactivities for aromatic electrophilic substitution reactions has provided useful information for assessing homoannular electronic effects within the ferrocene system. The product distribution from various electrophilic substitution reactions of monosubstituted ferrocenes has been studied by a number of workers. Although numerous π-bonded organometallic complexes are known today, ligand-exchange studies have been performed on systems other than the metallocenes, and of these only ferrocenes have been studied extensively. The mass spectra of many substituted ferrocenes have been published and various pathways have been postulated to account for the fragments observed. The mass spectrum of ferrocenes exhibits a high abundance for the m/e 121 peak M, which has been attributed to the fragment (C5H5Fe)+ presumed to arise from the cleavage of the ring–metal bond. Electron-donating groups attached to benzene greatly enhance the rings reactivity toward electrophilic substitution reactions, whereas electron-attracting groups decrease such reactivity markedly.

Preparation and synthetic utility of 2-chloromercuric[(dimethtlamino)methyl]ferrocene

Abstract 2-(Chloromercuri)[(dimethylamino)methyl]ferrocene I has been successfully synthesized from 2-lithio[(dimethylamino)methyl]ferrocene II and 2-[(dimethylamino)methyl]ferroceneboronic acid III. Chloromercuri-amine I was transmetalated to give improved yields of 2-lithio-amine II. Chloromercuri-amine I was readily converted to 2-iodo[(dimethylamino)methyl]ferrocene V. The PMR spectrum of chloromercuri-amine I served to extend the concept of a contact interaction between the 2-substituent and the adjacent diastereotopic methylene protons.

Directed metalation reactions 2-position of methoxy- and chloroferrocene : II. Demonstraion of directed Lithiation at the 2-position of methoxy- and chloroferrocene

Abstract Unequivocal demonstration that the position of lithiation of chloro- and methoxyferrocene is the 2-position is provided. 2-Methylchloroferrocene and 2-(methoxymethyl)methoxyferrocene were prepared from the respective 2-lithio intermediates. These derivatives were shown to be identical to samples of these compounds prepared by the lithiation of [(dimethylamino)methyl]ferrocene, a procedure well documented to produce 1,2-disubstituted ferrocenes.

A predicative model for certain directed metalations. II: Application to the behavior of p-fluoroanisole

Abstract A model whereby the relative ability of the methoxy group to direct metalations in aromatic systems is described. Evidence is presented for a dramatic acceleration of the rate of metalation of anisole provided by the presence of TMEDA resulting in the largest yield of ortho-metalation (95%) heretofore reported. Lastly, significant acceleration of the rate of metalation of anisole has been found using a catalytic amount of TMEDA.

Ortho-metalation of p-chloroanisole: A media study

Abstract As the chlorophenyl group is a pharmacophore, its stability toward metalation conditions in conjunction with the methoxy substituent was assessed. For p-chloroanisole metalation ortho to the methoxy group was achieved in high yield using increments of THF in cyclohexane; numerous other regimes afforded lower yields and a competing benzyne pathway.

Media effects in directed ortho metalation

Abstract Rates and extents of directed ortho metalation (DoM) of anisole and p-methylanisole (p-MA) with n-BuLi have been measured in THF/n-hexane. About a 14% (v/v) solution of THF in the hydrocarbon provides an extent of metalation which exceeds that in neat. THF at the same concentration. Impressive regioselectivity results from the DoM of p-MA in this solvent system; virtually no metalation of the lateral methyl group occurs.

The Preparation of Several N-Substituted and N,N-Disubstituted Ferrocenesulfonamides

Abstract Several N-mono and N,N-disubstituted ferrocene-sulfonamides were prepared from ferrocene via ferrocenesulfonyl chloride. It was found that modification of the usual two-step procedure allowed synthesis of ferrocenesulfonyl chloride directly from ferrocene. All attempts to hydrolyze N,N-dimethylferrocenesulfonamide met with failure.

A predicative model for certain directed metalations, III; The ability of a methyl substituent to influence the directed metalation of anisole

Abstract Significant increases in both rate and yield of metalation of p-methylanisole (p-MA) are afforded by use of incremental and stoichiometric amounts of TMEDA. Little metalation of the methyl protons in p-MA is observed under all conditions.

Substrate-promoted ortho-metallation in hydrocarbon solvents

Certain o- and m-disubstituted aromatics where both substituents are directing metallation groups (DMGs) should, in contrast to singly substituted DMG-containing arenes, undergo metallation in hydrocarbon solvents. It is proposed that the activation of such systems towards ortho-metallation is a synergistic generation of the appropriate bis-chelated alkyllithium dimer structure as well as complexed stabilization of the transition state.

Models for Highly Phenylated Transition Metal-Containing Polymers: Derivatives of the Pentaphenylcyclopentadienyl Ligand

Numerous η5-cyclopentadienyl derivatives of most of the transition metals are known.1 Over the past decade attention has been directed to transition metal complexes containing peralkylated η5-cyclopentadienyl groups, particularly those involving the pentamethylcyclopentadienyl ligand.2–6 Such complexes usually possess, when compared to the relevant cyclopentadienyl analogs, properties reflecting their increased bulk and steric character, e.g., enhanced oxidative, reductive and thermal stability, coupled with reduced volatility. These peralkylated complexes have proved to be more easily isolable and their chemical reactivity and catalytic activity more amenable to study.