Initial metal–metal bond breakage detected by fs X-ray scattering in the photolysis of Ru3(CO)12 in cyclohexane at 400 nm

Abstract

Using femtosecond resolution X-ray solution scattering at a free electron laser we were able to directly observe metal-metal bond cleavage upon photolysis at 400 nm of Ru3(CO)12, a prototype for the photochemistry of transition metal carbonyls. This leads to the known single intermediate Ru3(CO)11(μ-CO)*, with a bridging ligand (μCO) and where the asterisk indicates an open Ru3-ring. This loses a CO ligand on a picosecond time scale yielding the newly observed triple bridge intermediate, Ru3(CO)8(μ-CO)3 * . This loses another CO ligand to form the previously observed Ru3(CO)10, which returns to Ru3(CO)12 via the known single-bridge Ru3(CO)10(μ-CO). These results indicate that contrary to long standing hypotheses, metal-metal bond breakage is the only chemical reaction immediately following photolysis of Ru3(CO)12 at 400 nm. Combined with previous picosecond resolution X-ray scattering data and time resolved infrared spectroscopy these results yield a new mechanism for the photolysis of Ru3(CO)12.

Ultrafast X-ray Photochemistry at European XFEL: Capabilities of the Femtosecond X-ray Experiments (FXE) Instrument

“…In addition to identifying electronic relaxation pathways towards the lowest laying high spin excited state in prototypical spin-crossover systems [22][23][24] and charge transfer complexes [25], vibrational wavepackets were recently observed in Fe-carbene compounds using combined XES and WAXS tools [27]. Hereby transient molecular bond formation [30,45] and vibrational dynamics [29,31] were observed together with ultrafast molecular environment rearrangements in the immediate solvation shell [28], indicating the ability to also include intermolecular dynamic processes. At the same time, femtosecond XAS tools have been utilized for various 3d metal complexes as a combined local and selective probe to deliver detailed information on the coupled electronic and structural changes throughout ultrafast photochemical processes [46,47], including nuclear wavepacket dynamics [48,49].…”

“…As the proof-of-principle for femtosecond XES measurements at FXE, we studied photoexcited aqueous [Fe(bpy) 3 ] 2+ (concentration 15 mM). This molecular model system represents a prototypical example of an iron spin transition complex and has been extensively studied in the past both at synchrotrons [4,16,18,19,51] and XFELs [22,24,26,45,47]. The photochemical dynamics of [Fe(bpy) 3 ] 2+ are well known and comprise major electronic and structural changes spanning timescales from tens of femtoseconds to several nanoseconds.…”

“…The femtosecond time resolution can be preserved by adapting the laser time delay to the varying X-ray pulse arrival times during such monochromator scans, which changes the X-ray beam path length through the monochromator in a predictable way, i.e., continuously increasing the photon energy geometrically leads to shortening of the beam path through the 4 bounces due to the decreasing Bragg angle, thus shifting the X-ray pulse arrival to earlier times. Both X-ray absorption techniques are indispensable for probing the electronic and local structural dynamics during the course of ultrafast photochemical processes [45][46][47][48]54].…”

Estimating signal and noise of time-resolved X-ray solution scattering data at synchrotrons and XFELs

“…Fast processes in solutions involving short-lived intermediates are often investigated by time-resolved spectroscopy, but the associated molecular structural changes in general are not direct observables of time-resolved spectroscopy, which relies on the transitions between energy states. In this regard, time-resolved X-ray solution scattering (TRXSS), also known as time-resolved X-ray liquidography (TRXL), has been established as a powerful tool for studying molecular structural dynamics in the liquid solution phase Haldrup et al, 2012Haldrup et al, , 2019Salassa et al, 2010;Kim et al, 2012;Ahn et al, 2018;Biasin et al, 2018;Canton et al, 2015;Kong et al, 2019;Leshchev et al, 2018;Berntsson et al, 2017;Josts et al, 2018;Kim, Ganesan, et al, al., 2009;Christensen et al, 2009;Cammarata et al, 2006Cammarata et al, , 2008Kong et al, 2007;Ihee et al, 2005;Plech et al, 2004). In a typical experiment, an optical laser pulse is used to initiate a reaction and after a time delay an X-ray pulse is sent to probe the reaction progress via X-ray scattering.…”

“…In a typical experiment, an optical laser pulse is used to initiate a reaction and after a time delay an X-ray pulse is sent to probe the reaction progress via X-ray scattering. TRXL has been applied to a wide range of molecules ranging from small molecules such as organometallic compounds (Biasin et al, 2018;Kong et al, 2019;Leshchev et al, 2018;Canton et al, 2015;Haldrup et al, 2012;Salassa et al, 2010;Haldrup et al, 2019;Kong et al, 2007) and hydrocarbons (Ahn et al, 2018;Kim et al, 2012;Ihee et al, 2005;Davidsson et al, 2005) to macromolecules such as proteins (Berntsson et al, 2017;Josts et al, 2018;Kim, Ganesan, et al, 2018;Rimmerman et al, 2017;Arnlund et al, 2014;Kim, Muniyappan, et al, 2016;Malmerberg et al, 2011Malmerberg et al, , 2015Konuma et al, 2011;Westenhoff et al, 2010;Cho et al, 2010;Andersson et al, 2009;Cammarata et al, 2008). Due to the successful applications of TRXL to a wide range of molecules and reactions, applications of TRXL are expected to increase in the future.…”