Ultraviolet photodissociation of gas-phase transition metal complexes: dicarbonylcyclopentadienyliodoiron(II)

Abstract

The ultraviolet photodissociation of the prototypical organometallic half-sandwich compound dicarbonylcyclopentadienyliodoiron(II) [η 5-CpFe(CO)2I] has been studied in the gas phase across the wavelength range 260 ≤ λ ≤ 310 nm using multi-mass velocity-map ion imaging with photoproducts detected using both resonance enhanced multiphoton and vacuum ultraviolet (λ = 118.2 nm) single photon ionization methods. Ion images recorded for the atomic iodine and the cyclopentadienyl photoproducts reveal fast, anisotropic components to their recoil velocity distributions. The experimental work is supported by multi-reference (spin-orbit averaged) electronic structure calculations that suffice to illustrate the high electronic state density in such transition metal complexes and provide insights into the rival fragmentation dynamics. The ground state parent molecule has singlet spin multiplicity, but the product energy disposal measured following Fe-Cp bond fission shows the involvement of nominally spin-forbidden transitions. The Fe-I and Fe-Cp bond fissions should both be viewed as homolytic and occurring on excited state potentials that are dissociative in the relevant ligand elimination coordinate.

Primary and Secondary Processes in the Ultraviolet Photodissociation of CpCo(CO)2 (Cyclopentadienylcobalt Dicarbonyl)

“…While the signal indicating Cp loss such as Co­(CO) 1,2 + was unobserved, the coordinatively unsaturated complexes with a partially decomposed Cp ligand (CoC 3 H n + , CoC 2 H n + , and CoCH n + ) were detected with comparable intensity to CpCo + . The absence of Cp loss signal was consistent with the photodissociation result of CpCo­(CO) 2 in the previous study; however, Cp loss can occur depending on relative reactivity to other ligands in the excited states . Notably, the observed wavelength dependence of the fragment ion yields (Figure ) can be attributed to both the neutral fragmentations in the potential pathways (Figure ) and the ionization efficiency of the individual fragments.…”

“…The absence of Cp loss signal was consistent with the photodissociation result of CpCo(CO) 2 in the previous study; 35 however, Cp loss can occur depending on relative reactivity to other ligands in the excited states. 36 Notably, the observed wavelength dependence of the fragment ion yields (Figure 3) can be attributed to both the neutral fragmentations in the potential pathways (Figure 1) and the ionization efficiency of the individual fragments. These processes occur via one-photon absorption in a single laser pulse.…”