Hydrogen Generation from Water upon CpMn(CO)3 Irradiation in a Hexane/Water Biphasic System

Photochemistry of transition metal carbonyls

The purpose of this Tutorial Review is to outline the fundamental photochemistry of metal carbonyls, and to show how the advances in technology have increased our understanding of the detailed mechanisms, particularly how relatively simple experiments can provide deep understanding of complex problems. We recall some important early experiments that demonstrate the key principles underlying current research, concentrating on the binary carbonyls and selected substituted metal carbonyls. At each stage, we illustrate with examples from recent applications. This review first considers the detection of photochemical intermediates in three environments: glasses and matrices; gas phase; solution. It is followed by an examination of the theory underpinning these observations. In the final two sections, we briefly address applications to the characterization and behaviour of complexes with very labile ligands such as N₂, H₂ and alkanes, concentrating on key mechanistic points, and also describe some principles and examples of photocatalysis.

The mechanistic investigations of photochemical carbonyl elimination and oxidative addition reactions of (η5-C5H5)M(CO)3, (M = Mn and Re) complexes

We used computational methods to explore the mechanisms of the photochemical decarbonylation and the Si–H bond activation reaction of the group 7 organometallic compounds, η⁵-CpM(CO)₃ (M = Mn and Re). The energies of both conical intersections and the intersystem crossings, which play a decisive role in these photo-activation reactions, are determined. Both intermediates and transition states in either the singlet or triplet states are also computed to furnish a mechanistic interpretation of the whole reaction paths. In the case of Mn, four types of reaction pathways (path I–path IV) that lead to the final insertion product are examined. The theoretical findings suggest that at the higher-energy band (295 nm) the singlet-state channel is predominant. As a result, the conical intersection mechanism (i.e., path I) prevails. However, at the lower-energy band (325 nm) the triplet-state channel occurs. In such a situation, the intersystem crossing mechanism (i.e., path IV) can successfully explain its CO-photodissociation mechanism. In the case of Re, on the other hand, the theoretical evidence reveals that only the singlet state-channel is superior. In consequence, the conical intersection mechanism (i.e., path V) can more effectively explain its photochemical decarbonylation mechanism. These theoretical analyses agree well with the available experimental observations.

The theoretical works suggest that under UV photoirradiation, η⁵-CpMn(CO)₃ follows either the conical intersection mechanism or the intersystem crossing mechanism to obtain the final oxidative addition product. However, η⁵-CpRe(CO)₃ proceeds only the singlet state channel.

Photochemical Water-Splitting with Organomanganese Complexes

Certain organometallic chromophores with water-derived ligands, such as the known [Mn(CO)₃(μ₃-OH)]₄ (1) tetramer, drew our attention as possible platforms to study water-splitting reactions. Herein, we investigate the UV irradiation of various tricarbonyl organomanganese complexes, including 1, and demonstrate that dihydrogen, CO, and hydrogen peroxide form as products in a photochemical water-splitting decomposition reaction. The organic and manganese-containing side products are also characterized. Labeling studies with ¹⁸O-1 suggest that the source of oxygen atoms in H₂O₂ originates from free water that interacts with 1 after photochemical dissociation of CO (1-CO) constituting the oxidative half-reaction of water splitting mediated by 1. Hydrogen production from 1 is the result of several different processes, one of which involves the protons derived from the hydroxido ligands in 1 constituting the reductive half-reaction of water splitting mediated by 1. Other processes that generate H₂ are also operative and are described. Collectively the results from the photochemical decomposition of 1 provide an opportunity to propose a mechanism, and it is discussed within the context of developing new strategies for water-splitting reactions with organomanganese complexes.

1,2-Bis{[3,5-bis-(2,6-diisopropyl-phen-yl)phen-yl]imino}-acenaphthene toluene monosolvate

In the title compound, C₇₂H₈₀N₂·C₇H₈, the acenaphthene ring system is essentially planar, with a maximum deviation of 0.041 (3) Å. The benzene rings bonded to the the N atoms are essentially parallel, forming a dihedral angle of 0.80 (11)°, and these rings form dihedral angles of 87.49 (9) and 88.25 (10)° with the mean plane of the acenaphthene ring system. The methyl C atoms of three of the isopropyl groups are disordered of two sets of sites of equal occupancy.