A Molecular Dynamics of Photo-Excited Ligand Exchange Dynamics in Tungsten-Complexes

Transition-metal complexes (TMCs) play a pivotal role in areas such as optoelectronics, solar energy conversion, and biomedical applications. In this study, we delve deep into the dynamics of ligand exchange reactions in six distinct W(CO)₄(bpy) complexes using time-dependent excited-state molecular dynamics (TDESMD) based on Rabi oscillations between ground and excited states under optical irradiation. Our objective is to explore the mechanism of how the photo-induced charge transfer dynamics facilitates the mechanistic pathway in which a mix of W(CO)₆ and bipyridine (bpy) transforms into a W(CO)₄(bpy) complex. Preliminary findings suggest that the photoreactions are facilitated by excited states corresponding more closely to ligand-to-metal charge transfer (LMCT) character. It is this photoactivation, particularly of the LMCT type, that weakens the W-C bonds, thereby facilitating the subsequent dissociation of CO ligands. Consequently, this gives rise to the reactive W(CO)₅ radical, which then establishes a coordination bond with the nitrogen of the bpy ligand. At the next stage, second CO ligand desorbs allowing for formation of two stable coordination bonds between tungsten and bpy. Several approaches have been committed to explore the possibility of the subsequent formation of W(CO)₂(bpy)₂ and W(bpy)₃ complexes. Our study enables the exploration of the pathways of photoactivated reaction dynamics and assessment of the intermediates formed during the reaction and the transition states along this path. Such insights are instrumental in interpreting synthetic endeavors, aiming for an efficient exploration of near-infrared (NIR) emitters composed of earth-abundant metals and a variety of organic ligands.<br/>BR, SK, WS acknowledge support of DOE DE-SC0022239 for study of near-infrared emissive metal-organic complexes. KNK, YH, DK thanks NSF-1944921 for the support of excited state methods development.<br/>[1] J. Phys. Chem. Lett. <b>2022</b>, <i>13</i> (39), 9210-9220. DOI: 10.1021/acs.jpclett.2c02115.