Systematic exploration of the mechanism of chemical reactions: the global reaction route mapping (GRRM) strategy using the ADDF and AFIR methods

Abstract

Global reaction route mapping (GRRM), a fully-automated search for all important reaction pathways relevant to a given purpose, on the basis of quantum chemical calculations enables systematic elucidation of complex chemical reaction mechanisms. However, GRRM had previously been limited to very simple systems. This is mainly because such calculations are highly demanding even in small systems when a brute-force sampling is considered. Hence, we have developed two independent but complementary methods: anharmonic downward distortion following (ADDF) and artificial force induced reaction (AFIR) methods. ADDF can follow reaction pathways starting from local minima on the potential energy surface (PES) toward transition structures (TSs) and dissociation channels. AFIR can find pathways starting from two or more reactants toward TSs for their associative reactions. In other words, ADDF searches for A → X type isomerization and A → X + Y type dissociation pathways, whereas AFIR finds A + B → X (+ Y) type associative pathways. Both follow special paths called the ADDF path and the AFIR path, and these tend to pass through near TSs of corresponding reaction pathways, giving approximate TSs. Such approximate TSs can easily be re-optimized to corresponding true TSs by standard geometry optimizations. On the basis of these two methods, we have proposed practical strategies of GRRM. The GRRM strategies have been applied to a variety of chemical systems ranging from thermal- and photochemical-reactions in small systems to organometallic- and enzyme-catalysis, on the basis of quantum chemical calculations. In this perspective, we present an overview of the GRRM strategies and some results of applications. Their practical usage for systematic prediction is also discussed.

Analyses of bifurcation of reaction pathways on a global reaction route map: A case study of gold cluster Au5

“…This is a case of non-totally symmetric bifurcation, although the terminal of the IRC becomes a minimum, i.e., MIN5. The zero-frequency mode at VRT3 is related to the mode leading to MIN5 ′ through a rotation of the triangle of Au 3 fragment in Au 5 . Since the energy difference between the VRT3 and TS5-5 is very small, 0.4 kJ/mol, it can be expected that a potential energy profile along the rotational motion of the Au 3 fragment is very flat, and the rotation can occur easily in the actual dynamics.…”

“…The ADDF method 2-6 is applied to a global search for minima (MINs) and TSs of Au 5 . The IRC pathways are simultaneously determined for the respective TSs without symmetry restriction.…”

“…Further details of the ADDF method are described in recent reviews. 5,6 Moreover, Maeda and Morokuma developed a new methodology to locate a TS geometry for A + B type reactions, named as artificial force induced reaction (AFIR), 7 which has made possible applications of GRRM more extensively. In 2014, the target of AFIR is extended to finding TSs of intramolecular reactions.…”

“…28,[30][31][32] To our knowledge, all previous studies have focused on the specific IRC that accompanies VRT. In the present study, the bifurcation analyses of the IRC are combined with GRRM computations, and the appearance of VRT in the global reaction route map and the connection of VRT with additional product minimum are examined for a small gold cluster, Au 5 . Since the pioneer work of Haruta et al, 35 gold clusters have been paid attention extensively [36][37][38] due to a large interest in its unique catalytic activity.…”

Exploring Pathways of Photoaddition Reactions by Artificial Force Induced Reaction Method: A Case Study on the Paternò–Büchi Reaction

“…Thus, practical methods that can find all reaction pathways without any guess need to be developed. To achieve this goal, we have developed automated reaction path search methods under the title of global reaction route mapping (GRRM) strategy [36]. One of them, the artificial force induced reaction (AFIR) method [37,38], can efficiently explore pathways for A + B → X (+ Y) type addition reactions, and thus is effective for study of complex organic and organometallic reactions [39][40][41].…”