Nature and Role of Bridged Carbonyl Intermediates in the Ultrafast Photoinduced Rearrangement of Ru₃(CO)₁₂

Abstract

The photochemistry of the trimetal cluster, Ru 3 (CO) 12 , was investigated on the ultrafast timescale using UV-vis pump, infrared probe spectroscopy in order to study the transient intermediates formed upon photoexcitation. The dynamics of these intermediates can only be unambiguously identified by monitoring the small but distinct infrared absorptions of bridging carbonyls. The nature and role of bridged carbonyl intermediates in the photochemistry of Ru 3 (CO) 12 in both coordinating and noncoordinating solvents is discussed. In an inert solvent such as cyclohexane, photoexcitation of Ru 3 (CO) 12 with 400 nm light produces two different species that have never been observed simultaneously. The first species is a carbonyl loss complex with a bridged carbonyl that forms in 134 ± 22 ps and survives beyond 800 ps; the second species is a bridged carbonyl complex with one metalmetal bond cleaved that forms in 23 ± 3 ps and has a lifetime of 60 ± 5 ps. When 266 nm light was used to photoexcite the cluster, both species exhibit similar dynamics. This is the first time multiple bridged carbonyl intermediates have been observed simultaneously for this cluster and this observation resolves an inconsistency in the literature. Interestingly, in neat solutions of THF only one feature was observed in the bridging carbonyl region, yet the dynamics of the feature and density functional theory (DFT) results indicate that there are, in fact, two bridging carbonyl complexes with overlapping bands. These results were surprising as it was previously unknown whether THF would block formation of bridging carbonyl complexes by solvating and stabilizing the coordinatively unsaturated metal.

Ionization and photofragmentation of Ru3(CO)12 and Os3(CO)12

“…A small translational energy can be inferred from the fact that dissociation is a statistical ground state process where not much excess energy is stored in the vibrational mode leading to dissociation. Even for the excited state dissociation of Ru 3 (CO) 12 with 400 and 267 nm photons, time constants on the order of 100 ps were measured by Glascoe et al 45 in the liquid phase, which does not point toward a direct dissociation channel and hence is in agreement with our study.…”

“…Moreover, a C= =O vibrational mode has an energy of about 0.25 eV. [43][44][45][46] which would cause an extra loss in potential energy in the remaining metal complex if the dissociated CO molecule were to be vibrationally excited. Such a loss is not observed in our data.…”

Synchrotron ultrafast techniques for photoactive transition metal complexes

“…A recent transient IR study was performed on Ru 3 (CO) 12 in cyclohexane solution upon both visible (400 nm) and UV (266 nm) excitation [197]. The results revealed the presence of two reaction intermediates.…”

“…Furthermore, this derivative acts as a photocatalyst in photo-activated synthesis, inducing the breaking of selective bonds depending on the excitation wavelength [188,189]. Owing to the high practical and fundamental interest in the metal-metal bond cleavage mechanism, the Ru 3 (CO) 12 metal cluster has been widely investigated, both in solution and in solid matrices, using various spectroscopic methods [189][190][191][192][193][194][195][196][197].…”

Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

“…Pump-probe spectroscopy has been extensively used to understand these types of dynamics [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], and this work applies the same pump-probe methodologies as well as a relatively new technique, two dimensional infrared spectroscopy, to the photophysics and reactions of several prototypical organometallic complexes [20][21][22][23][24][25][26].…”