1-Cyano-1 '-ethynyl-ferrocene: Synthesis and reaction chemistry

Several consecutive synthetic methodologies for the preparation of Fe(eta(5)-C5H4C N)(eta(5)-C5H4C CH) (3) are described. Ferrocene Fe(eta(5)-C5H4C N)(eta(5)-C5H4C(O)Me) (1) reacts under typical Vilsmeier conditions to give as the main product Fe(eta(5)-C5H4C N)(eta(5)-C5H4CCl=CH2) (2) and in minor yield Fe(eta(C5H4C)-C-5 N)(eta(5)-C5H4CCl=CHC(O)H) (4). Compound 2 could be directly converted to 3 by addition of (KOBu)-Bu-t. The title compound is also accessible by the gradual reaction of 4 with NaOH to give Fe(eta(C5H4C)-C-5(O)NH2)(eta(5)-C5H4C CH) (5), which upon treatment with 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU) and P(O)Cl(OEt)(2) produced 3. Organometallic 3 could be homo-coupled to [Fe(eta(5)-C5H4C N)(eta(C5H4C)-C-5 C)](2) (7) in an Eglinton coupling upon addition of [Cu(OAc)(2)]. With [CuI] and NEt2H in dichloromethane, compound Fe(eta(5)-C5H4C N)(eta(5)-C5H4C CCH2NEt2) (6) was produced by copper-catalyzed three-component coupling. The structures of 3-5 in the solid state were determined by single crystal X-ray structure analysis. While the X-ray structures of 3 and 4 show no peculiarities, the structure of 5 possesses a network structure due to hydrogen bridge bond formation. The electrochemical behavior of 3, 6 and 7 was studied by cyclic voltammetry. It could be shown that 3 possesses a reversible redox event at 550 mV (Delta E = 65 mV), while in homo-coupled 7 two consecutive redox processes at 524 and 680 mV were found indicating that the ferrocenyl units in 7 can be oxidized in a stepwise manner to 7(+) and 7(2+), respectively. The redox separation Delta E with 156 mV implies a possible electron transfer in the mixed-valent species 7(+), which was confirmed by spectroelectrochemical studies. From these studies, 7 could be classified as a weakly coupled class II system according to Robin and Day. (C) 2015 Elsevier B.V. All rights reserved.