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The photo carboxylation of the benzylic C(sp3)-H bond catalyzed by xanthone/nickel were examined by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. This study corroborates the previous proposal that light promotes the H-transfer from benzylic C(sp3)-H bond of the p-methoxytoluene to excited state of photocatalyst xanthone. Meanwhile, Ni(0) catalyst could mediate the H-transfer to occur via an electroncoupled-proton transfer manner, and then remarkably facilitates the carboxylation step (compared to the Niabsent systems). After that, the generated Ni(I) intermediate and ketyl radical anion complete the carboxylation and electron transfer processes independently., QC 20211015

Photocarboxylation of alkyne with carbon dioxide represents a highly attractive strategy to prepare functionalized alkenes with high efficiency and atomic economy. However, the reaction mechanism, especially the sequence of elementary steps (leading to different reaction pathways), reaction modes of the H-transfer step and carboxylation step, spin and charge states of the cobalt catalyst, etc., is still an open question. Herein, density functional theory calculations are carried out to probe the mechanism of the Ir/Co-catalyzed photocarboxylation of alkynes. The overall catalytic cycle mainly consists of four steps: reductive-quenching of the Ir catalyst, hydrogen transfer (rate-determining step), outer sphere carboxylation, and the final catalyst regeneration step. Importantly, the cobalt catalyst can facilitate the H-transfer by an uncommon hydride coupled electron transfer (HCET) process. The pivotal electron delivery effect of the Co center enables a facile H-transfer to the alpha-C(alkyne) of the aryl group, resulting in the high regioselectivity for beta-carboxylation., QC 20210531

Ni-Catalyzed dicarboxylation of 1,3-dienes with CO2 provides a regioselective method for the construction of adipic acids. Here, density functional theory (DFT) calculations have been carried out to elucidate the detailed mechanisms of this reaction and the origin of regioselectivity. The computed results reveal that the catalytic cycle mainly proceeds via Ni(0)-catalyzed 1(st) carboxylation, followed by a reduction of the Ni(ii) to Ni(i) intermediate and finally a Ni(i)-catalyzed 2(nd) carboxylation. The first and second carboxylations are rate- and regioselectivity-determining steps, respectively. In the first carboxylation, a new activation mode of CO2 by insertion into the uncoordinated alkene group has been found to be optimal. This is in contrast to other mechanisms described in the literature. Furthermore, we found that the interaction between the allyl group and nickel center in the alkyl Ni(i) intermediate significantly stabilizes the d(9) electron configuration. This stabilizing interaction results in the preferential 1,4-dicarboxylation., QC 20210113

DFT calculations have been carried out to study the detailed mechanisms of the O-abstraction reaction of N2O with Cp2Ti(II). The reaction is initiated by coordination of N2O to Cp2Ti via the N-end to form a linear N2O-coordinated species Cp2Ti(N2O), from which the metal center transfers one of its metal d electrons to one pi{*} orbital of the N2O ligand and gives a bent N2O-coordinated intermediate CP2Ti\_N-<-=N-O. The intermediate then reacts barrierlessly with another molecule Of Cp2Ti to form an N2O-bridged intermediate Cp2Ti\_N-<-=N-O-TiCp2, from which the singly oxo-bridged product (Cp2Ti)(2)O is formed with a release of N-2. Reactions of N2O with other middle transition metal complexes have also been calculated and discussed. General mechanisms for O-abstraction reactions of N2O with early and middle transition metal complexes have been provided.

DFT calculations have been carried out to study the mechanisms for reactions of O-2 with a series of metal complexes, including d(6) CpRuL2, d(6) ML5, and d(8) ML4 complexes. The calculation results indicate that the reaction is initiated by a end-on coordination of O-2 to the metal center, which gives an (n(1)-O-2)[M) intermediate. The uncoordinated oxygen atom of the n(1)-O-2 ligand then approaches the metal center to give a new n(1)-O-2 intermediate in which the n(1)-O-2 ligand is oriented approximately the same as the one defined in the product. An intersystem conversion from the triplet to singlet energy surface (MECP) then occurs to enable the metal peroxide product to be formed.

DFT Calculations have been carried out to study the mechanisms of Pd(OAc)(2)-catalyzed intramolecular diamination reactions in the presence of bases and oxidants. Oil the basis of the Calculation results, a mechanism involving an anti-aminopaladation/syn-C-sp3-N bond formation was proposed.

DFT calculations have been carried out to study the mechanism of the N2O O-insertion into the Ru-H bonds of ruthenium hydride complexes (dmpe)2Ru(H)(X) (X = OH, H). The reaction pathways for the formation of the monoinsertion product (dmpe)2Ru(H)(OH) and the bis(hydroxo) complex (dmpe)2Ru(OH)(OH), which were obtained directly from the reactions of N20 with the ruthenium hydride complexes, have been investigated in detail. Focus has been made to understand how the kinetically inert NO is activated by the hydride complexes. It is found that N20 is activated through the hydride ligand nucleophilically attacking the terminal nitrogen of N20 followed by coordination of the activated N20 via the O-end.

DFT calculations have been carried out to study the activation of N2O by the transition-metal alkyne complexes CP2M(eta(2)-alkyne) (M = Ti, Zr). The mechanism for the formation of the five-membered metallacyclic complexes CP2M(RC=CR'NN(O)), which were obtained directly from the reactions of N2O with the metal alkyne complexes, and the conversion of the five-membered metallacyclic complexes CP2M(RC=CR'NN(O)) via N-2 loss to the oxametallacyclobutene complexes CP2M(RC=CR'O) have been investigated in detail. An effort has been made to understand how the kinetically inert N2O can be activated. We concluded that N2O is best activated by metal fragments that possess high capability of :pi-back-bonding interactions with the pi{*} orbitals of N2O.