E/ZSwitchable Ring-Closing Metathesis in 1,1′-Bis(but-3-enyl)ferrocenes: Synthesis and Characterization of Axially Chiralansa[6]-Ferrocenes

Abstract

A series of ansa[6]-ferrocenes were obtained through the ruthenium-catalyzed ring-closing olefin metathesis in 1,1′-bis(but-3enyl)ferrocenes. The stereoselectivity of this reaction depended on the structure of substrates, that is, mixtures of (E) and (Z) isomers were obtained for alkyl-substituted 3a−3d while (Z)-isomers only for arylsubstituted 3e and 3f. The ansa[6]-ferrocenes are axially chiral in the solid state according to single-crystal X-ray analysis. In the case of methyl-substituted derivative 4a, spontaneous resolution of the racemate was observed during crystallization. The solution properties of (E) and (Z) isomers are remarkably different; the latter displays inequivalence of the two formally identical parts of the molecule at low temperature.

Ferrocenophanes with two nitrogen atoms in bridging positions via olefin metathesis: synthesis, structure, and solution dynamics

“…Two cyclopentadienyl protons (d and d') that resonate at δ = 3.76 ppm at 25 °C decoalescence at −80 °C into two broad signals (δ = 3.99 and 3.45 ppm) (Figure2a, see also FigureS8for the corresponding 1 H-13 C HSQC spectrum). We wish to note that these 1 H NMR spectra resemble those recorded for (E)-[6]ferrocenophanes in toluene-d8 with four cyclopentadienyl and two allylic signals at low temperature[5].…”

“…The reactions of 1,1'-diallylferrocenes (Scheme 1a) with Grubbs' catalysts [Ru(=CHPh)Cl2(PCy3)2] (GI) resulted in all-carbon bridged [4]ferrocenophanes with (Z)-configuration of the newly formed carbon-carbon double bond [3,4]. More recently, 1,1'-bis(but-3-enyl)ferrocenes (Scheme 1b), in the presence of catalyst GI or [Ru(=CHPh)Cl2(PCy3)(SIMes)] (GII), yielded [6]ferrocenophanes with geometry of the bridge depending on the type of substituents in the alkenyl chains [5].…”

Ferrocenophanium Stability and Catalysis

“…Ferrocenophanes or ansa -ferrocenes are a well-known compound class [ 74 ]. The bridges can be all-carbon [ 74 , 75 ] or contain heteroatoms [ 76 , 77 ], and several synthetic methods for their access have been described [ 78 ]. Either the two ring systems are connected by a series of organic transformations, or a preformed, bidentate dicyclopentadienyl ligand is coordinated to an iron center (“flytrap method”) [ 79 ].…”