Reaction Mechanism and Kinetics study on Addition of CCl₄ to 1‐hexene Catalyzed by Mo‐Mo Quintuply‐bond

Abstract

Transition metal-catalyzed atom transfer radical addition (ATRA) reactions are an effective and versatile strategy for constructing carbon-carbon bonds in organic synthesis. Typically, the metal center in this metal-assisted radical transformation undergoes a reversible redox process. In this work, a quintuply-bonded dinuclear complex, Mo 2 (N^N) 2 {N^N = μ-κ 2-CH[N(2,6-iPr 2 C 6 H 3)] 2 }, has been investigated as potential catalyst for radical addition of CCl 4 to 1-hexene by performing density functional theory (DFT) calculations. The study shows that the Mo 2 (N^N) 2-mediated radical addition reaction is computationally predicted to occur with acceptable activation energies, indicating that the Mo-Mo quintuple bond can be applied as an effective catalyst for this transformation under mild conditions. The whole reaction involves 3 steps, two of which are metal-mediated. Firstly, the C-Cl bond activiation catalyzed by Mo 2 (N^N) 2 to obtain Mo 2 (N^N) 2 Cl and •CCl 3 radical; Then the •CCl 3 radical interacts with 1-hexene to get an addition, the addition product reacts with the Mo 2 (N^N) 2 Cl to get the last product and regenerate the catalyst Mo 2 (N^N) 2. Both the thermodynamic and kinetic study show that the second step is the rate-determine step. When coordinating solvent pyridine is added to the catalytic reaction, the reaction is suppressed due to their high energies barriers, which is consistent with experimental results.

Tuning Catalytic Activity of Dimolybdenum Paddlewheel Complexes by Ligands:Mechanism Study on the Radical Addition Reaction of CCl4 to 1-Hexene

“…Our calculated ΔG # is slightly smaller than that determined by kinetic experimental results, 26.0kcal/mol at 303K [24]. The experimental value is larger because it is determined in the presence of excess CCl 4 and pyridine; the coordination of pyridine suppresses the reaction, which has been found in former studies [2,8]. CCl 3 addition to 1-hexene: The dissociated •CCl 3 radical attacks the C1 atom of 1-hexene with a energy barrier of 9.0 kcal/mol (Fig.…”

“…In this reaction process, the spin electron density migrates from the C atom of CCl 3 radical to the C1 atom of 1-hexene, COM7 forms. This step has been discussed in our former work [8]. Then the calculated Gibbs free energies were converted to absolute electron redox potential according to Nernst equation:…”

“…Since the rst dimolybdenum complex (molybdenum(II) acetate) containing Mo-Mo multiple bond was isolated and characterized [1], a large number of polymetal-metal bonding complexes have been synthesized [2][3][4][5][6][7][8]. In particular, the metal-metal bonded compounds with unique paddlewheel structures have played a major role in development of coordination chemistry [9] and continue to be of interest for their catalytic [10], photophysical [11], electronic [12], and structural properties [13] as well as reactivity [14,15].…”

Cooperative Effects in Multimetallic Complexes Applied in Catalysis

“…Mashima and co‐workers demonstrated that this reactivity allows for catalytic hydrodehalogenation, addition and polymerization reactions [59] . Experimental as well as quantum chemical studies [60] show that the quadruple bond undergoes one‐electron reductive abstraction of the halide allowing for subsequent radical pathways.…”