Photochemistry of a Puckered Ferracyclobutadiene in Liquid Solution Studied by Time‐Resolved Fourier‐Transform Infrared Spectroscopy

Abstract

Flash photolysis combined with step-scan and rapid-scan Fourier-transform infrared spectroscopy was carried out to explore the photochemistry of a puckered, quasi-square pyramidal ferracyclobutadiene, [Fe{κ(2) -C3 (NEt2 )3 }(CO)3 ]BF4 ([1]BF4 ), that features three additional carbonyl ligands in the metal coordination sphere. In liquid solution at room temperature, an excitation with λ=355 nm light resulted in the loss of one CO ligand, which is cleaved from a basal metal-coordination site. Within the time resolution of the experiment, a solvent molecule promptly refills the resultant vacancy at the coordinatively unsaturated metal center. In the weakly interacting liquid, dichloromethane, the counterion of the complex is subsequently able to substitute the solvent in the coordination sphere of the iron center, thereby forming as a stable product a neutral dicarbonyl tetrafluoroborato iron(0) species containing a four-membered ferracycle.

The Femtochemistry of a Ferracyclobutadiene

“…Figure a) and time‐resolved Fourier‐transform infrared (FTIR) spectroscopy for monitoring the ensuing photochemical reactions . The FTIR‐data gave evidence for a light induced substitution of a basal CO by a solvent molecule, S. In a strongly interacting solvent, such as acetonitrile, the resultant photoproduct, [Fe{κ 2 ‐C 3 (NEt 2 ) 3 }(CO) 2 (NCCH 3 )] + ([ 2 ]), is a stable isolable species ,. However, owing to an insufficient time‐resolution the primary dynamics and the underlying molecular level substitution mechanism remained undisclosed.…”

“…Details of the synthesis, the molecular structure, and the reactivity of this class of compounds can be found in Refs. ,. We have recently explored the optical properties of FeCBDs with the goal to access yet unknown ferracyclic species with light.…”

“…In particular, we carried out laser flash photolysis of the tricarbonyl complex, [Fe{κ 2 ‐C 3 (NEt 2 ) 3 }(CO) 3 ]BF 4 ([ 1 ]BF 4 , L=CO, Et=C 2 H 5 , cf. Figure a) and time‐resolved Fourier‐transform infrared (FTIR) spectroscopy for monitoring the ensuing photochemical reactions . The FTIR‐data gave evidence for a light induced substitution of a basal CO by a solvent molecule, S. In a strongly interacting solvent, such as acetonitrile, the resultant photoproduct, [Fe{κ 2 ‐C 3 (NEt 2 ) 3 }(CO) 2 (NCCH 3 )] + ([ 2 ]), is a stable isolable species ,.…”

“…Figure c). These bands arise from the totally symmetric combination (A 1 species in the local C 3 v symmetry of the Fe(CO) 3 moiety) and the nearly degenerate pair of asymmetric combinations (E species) of the three CO stretching modes ,. The linear FTIR spectrum of the photoproduct [ 2 ] is also shown in Figure c. Again, two resonances are detected that peak at 1938 cm −1 and 2003 cm −1 .…”

Wacker Silicone Award: A. C. Filippou / Herman Skolnik Award: D. A. Winkler / Erwin‐Schrödinger‐Preis: C. Barner‐Kowollik

“…Sein Forschungsinteresse gilt Verbindungen mit Dreifachbindungen zwischen Übergangsmetallen und den schwereren Elementen der Gruppe 14, Si–Pb, sowie der Molekülchemie von Silicium in niedrigen Oxidationsstufen. In der Angewandten Chemie hat er ein NHC‐stabilisiertes Disilavinyliden vorgestellt und in Chemistry—A European Journal die Photochemie eines gefalteten Ferracyclobutadiens beschrieben …”