Tetrakis(ferrocenylethynyl)ethene: Synthesis, (Spectro)electrochemical and quantum chemical characterisation

Abstract

Tetra(ferrocenylethynyl)ethene (1) has been prepared in four steps from ethynyl ferrocene (2). In a dichloromethane solution containing 10 -1 M NBu 4 PF 6 , only a single oxidation process is observed by cyclic voltammetry, corresponding to the independent oxidation of the four ferrocenyl moieties. However, in dichloromethane containing 10 -1 M NBu 4 BAr F 4 electrolyte, where [BAr F 4 ]is the weakly associating anion [B{C 6 H 3 (CF 3 ) 2 -3,5}] -, four distinct oxidation processes are resolved, although further spectroelectrochemical investigation revealed essentially no through bond interaction between the individual ferrocene moieties. Quantum chemical treatment of 1 identified several energetic minima corresponding to different relative orientations of the ferrocene moieties and the plane of the all-carbon bridging fragment. Further computational investigation of the corresponding monocation [1] + supported the notion of charge localisation with no evidence for significant through bond electronic interactions.

Optical and Infrared Spectroelectrochemical Studies of CN-Substituted Bipyridyl Complexes of Ruthenium(II)

“…30,31 Excitation of [W(CO) 5 (pyCN)] to a 3 MLCT state results in a shift of −124 cm −1 , as was determined by time-resolved resonance Raman spectroscopy. 32 The IR intensity enhancement upon reduction or oxidation has been described for molecular species such as terphenyl, 33 conjugated oligomers and polymers of fluorene and thiophene, 34 and various conducting polymers as well as for vibrations of bridging groups in mixed-valence complexes, 35,36 partially oxidized tetrakis(ferrocenylethynyl)ethene, 37 and porphyrin oligomers, 38 whose one-electron oxidation enhanced the IR band due to the stretching vibration of the −CC− linker about 40 times. In the present case, the ν(CN) IR band intensified about 35 times upon the first reduction and 5−7 times upon excitation to the 3 MLCT lowest excited state, mostly because of intensity enhancement of the B 1 antisymmetric stretching vibration of the two terminal −C N groups.…”

Rational Control of Conformational Distributions and Mixed‐Valence Characteristics in Diruthenium Complexes

“…[6] More recently,t he distribution of molecular conformations and in turn distributions in metal(d)bridge(p)o verlaps and metal-metal coupling has begunt ob e exploreda safurtherf actor in the appearance of NIR band shapes in organic and organometallic' mixed-valence' systems; [7][8][9][10][11][12][13][14][15][16] the concept is gaining increased attention. [9,[17][18][19][20][21][22] In seekingt op robe these conformational effectsi nm ixed-valence compounds in more detail,weh ave turned our attention to af amily of complexes featuring the simple pseudo-1D bridge buta-1,3-diyndiyl. [23,24] Metal complexes of buta-1,3-diyndiyl ligandsw eref irst explored in detail duringt he 1970s as part of the seminal work from the Hagihara group on metal-containing polyynep olymers.…”

Redox Properties of Ferrocenyl Ene-diynyl-Bridged Cp*(dppe)M–C≡C–1,4-(C6H4) Complexes

“…[25][26][27][28] Indeed, in recent times there has been a resurgence of interest in mixed-valence models of intramolecular charge-transfer processes, with the development of theoretical descriptions and spectroscopic analysis of the charge-transfer event 29 to the development of novel optoelectronic materials and the design of molecular electronic components. 30 Some of the present authors have explored aspects, including mixed-valence characteristics, of cross-conjugated 1,1-bis(alkynyl)-2-ferrocenylethene derivatives (A), 31 including 1,1-bis(ferocenylalkynyl)-2-ferrocenylethene (B) 32 and tetrakis(ferrocenylethynyl)ethene (C) 33 (Chart 1). However, efforts to incorporate the half-sandwich building blocks M(PP)Cp', which have been so successful in exploring other aspects of organometallic mixed-valency when linked through linearly conjugated all-carbon and carbon-rich bridging ligands, [34][35][36][37][38][39][40]…”

“…Some of the present authors have explored aspects, including mixed-valence characteristics, of cross-conjugated 1,1-bis­(alkynyl)-2-ferrocenylethene derivatives ( A ), including 1,1-bis­(ferocenylalkynyl)-2-ferrocenylethene ( B ) and tetrakis­(ferrocenylethynyl)­ethene ( C ) (Chart ). However, efforts to incorporate the half-sandwich building blocks M­(PP)­Cp′, which have been so successful in exploring other aspects of organometallic mixed valency when these building blocks are linked through linearly conjugated all-carbon and carbon-rich bridging ligands, − within the cross-conjugated 1,1-bis­(alkynyl)-2-ferrocenylethene framework through desilylation–metalation reactions of 1,1-bis­(trimethylsilylethynyl)-2-ferrocenylethene (Chart ; A , R = SiMe 3 ) or via vinylidenes formed from 1,1-bis­(ethynyl)-2-ferrocenylethene (Chart ; A , R = H) have so far proved fruitless …”