Iminium substituent directs cyanide and hydride additions to triiron vinyliminium complexes?

New Journal of Chemistry Pub Date: 2023-04-04 DOI: 10.1039/D2NJ05810C

Abstract

The reactivity of diiron bis-cyclopentadienyl cationic complexes containing a vinyliminium ligand coordinated to a diiron scaffold and decorated with a ferrocenyl group, [1a–g]CF3SO3, was investigated towards NBu4CN (in CH2Cl2) and NaBH4 (in THF). Thus, (amino)cyano-allylidene derivatives, 2a–2d, were synthesized in good yields by cyanide attack to the iminium carbon C1 in the respective precursors. However, this outcome is influenced by the nature of one iminium substituent (R), when the other one is methyl: when R[double bond, length as m-dash]CH2CHCH2, a μ-alkylidene-alkenyl by-product (3), is obtained, while R[double bond, length as m-dash]4-C6H4OMe determined the concurrent cyanide addition to the vinyl carbon C2 leading to a bis-alkylidene complex (4d). The analogous bis-alkylidene 4e was selectively prepared in the case of R[double bond, length as m-dash]2,6-C6H3(Me)(Cl) (XylCl), and this substituent exerted steric protection on C1. Similarly, hydride addition took place at either C1 (complex 5a, R[double bond, length as m-dash]4-C6H4OMe) or C2 (6, R[double bond, length as m-dash]XylCl). The reactions of [1g]CF3SO3, containing two benzyl groups as iminium substituents, with NBu4CN and NaBH4 led to the selective formation of the C1 addition derivatives, 2e and 5b. All products were purified by alumina chromatography and fully characterized using analytical and spectroscopic methods, while DFT calculations were extensively carried out to shed light on structural and thermodynamic aspects. The representative complexes 2e, 4e, 5b and 6 were further characterized by cyclic voltammetry and IR-spectroelectrochemistry studies.

Graphical abstract: Iminium substituent directs cyanide and hydride additions to triiron vinyliminium complexes
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