OsB9−: An Aromatic Osmium-Centered Monocyclic Boron Ring

Transition-metal-centered monocyclic boron wheels are important candidates in the family of planar hypercoordinate species that show intriguing structure, stability and bonding situation. Through the detailed potential energy surface explorations of MB9− (M = Fe, Ru, Os) clusters, we introduce herein OsB9− to be a new member in the transition-metal-centered borometallic molecular wheel gallery. Previously, FeB9− and RuB9− clusters were detected by photoelectron spectroscopy and the structures were reported to have singlet D9h symmetry. Our present results show that the global minimum for FeB9− has a molecular wheel-like structure in triplet spin state with Cs symmetry, whereas its heavier homologues are singlet molecular wheels with D9h symmetry. Chemical bonding analyses show that RuB9− and OsB9− display a similar type of electronic structure, where the dual σ + π aromaticity, originated from three delocalized σ bonds and three delocalized π bonds, accounts for highly stable borometallic molecular wheels.

Primary Photochemical Dynamics of a Triply-Bonded Metal Carbonyl Dimer Probed Via Ultrafast Infrared Spectroscopy

<div>The primary photochemical dynamics of [Cp*Cr(CO)2]2 have been studied using picosecond time-resolved infrared (TRIR) spectroscopy. Upon visible or UV photoexcitation, the primary photochemical pathway is formation of a transient rear- rangement isomer with a weakened Cr≡Cr bond and two terminal carbonyl ligands rearranged to a bridging conformation. This species reverts to the parent dimer on the time scale of 378 ± 15 ps, and Density Functional Theory calculations suggest that this transient species is characterized by a triplet spin state and a trans conformation of the two terminal CO ligands. Photolysis in neat THF solution is unable to trap the transient intermediate via solvent-coordination. The excited state transient rearrangement isomer appears to adopt a distorted structure in THF, relative to cyclohexane, evidenced by the observation of an additional bridging-CO stretching band in THF solution. The lifetime of the transient in THF is just slightly shorter at 344 ± 17 ps. The CO-loss product of 1 has been characterized previously and adopts an asymmetric arrangement of the three bridging CO ligands. In neat THF solution, the CO-loss complex is not observed to react with THF on the picosecond timescale, although a previous study on longer timescales observed formation of a THF adduct of the CO-loss complex in dilute alkane/THF solutions. Though the molybdenum congener, [Cp*Mo(CO)2]2, is unstable in solution, decaying on the timescale of a few hours in cyclohexane, TRIR experiments demonstrate that no bridged photoproducts (transient or long-lived) are formed from the Mo complex in cyclohexane solution. </div><div><br></div>

Primary Photochemical Dynamics of a Triply-Bonded Metal Carbonyl Dimer Probed Via Ultrafast Infrared Spectroscopy

<div>The primary photochemical dynamics of [Cp*Cr(CO)2]2 have been studied using picosecond time-resolved infrared (TRIR) spectroscopy. Upon visible or UV photoexcitation, the primary photochemical pathway is formation of a transient rear- rangement isomer with a weakened Cr≡Cr bond and two terminal carbonyl ligands rearranged to a bridging conformation. This species reverts to the parent dimer on the time scale of 378 ± 15 ps, and Density Functional Theory calculations suggest that this transient species is characterized by a triplet spin state and a trans conformation of the two terminal CO ligands. Photolysis in neat THF solution is unable to trap the transient intermediate via solvent-coordination. The excited state transient rearrangement isomer appears to adopt a distorted structure in THF, relative to cyclohexane, evidenced by the observation of an additional bridging-CO stretching band in THF solution. The lifetime of the transient in THF is just slightly shorter at 344 ± 17 ps. The CO-loss product of 1 has been characterized previously and adopts an asymmetric arrangement of the three bridging CO ligands. In neat THF solution, the CO-loss complex is not observed to react with THF on the picosecond timescale, although a previous study on longer timescales observed formation of a THF adduct of the CO-loss complex in dilute alkane/THF solutions. Though the molybdenum congener, [Cp*Mo(CO)2]2, is unstable in solution, decaying on the timescale of a few hours in cyclohexane, TRIR experiments demonstrate that no bridged photoproducts (transient or long-lived) are formed from the Mo complex in cyclohexane solution. </div><div><br></div>