Cunyuan Zhao

Bio: Cunyuan Zhao is an academic researcher from Sun Yat-sen University. The author has contributed to research in topics: Catalysis & Carbenoid. The author has an hindex of 23, co-authored 110 publications receiving 2264 citations. Previous affiliations of Cunyuan Zhao include Northwest Normal University & University of Science and Technology of China.

Intermolecular electronic coupling of organic units for efficient persistent room-temperature phosphorescence

Abstract: Although persistent room-temperature phosphorescence (RTP) emission has been observed for a few pure crystalline organic molecules, there is no consistent mechanism and no universal design strategy for organic persistent RTP (pRTP) materials. A new mechanism for pRTP is presented, based on combining the advantages of different excited-state configurations in coupled intermolecular units, which may be applicable to a wide range of organic molecules. By following this mechanism, we have developed a successful design strategy to obtain bright pRTP by utilizing a heavy halogen atom to further increase the intersystem crossing rate of the coupled units. RTP with a remarkably long lifetime of 0.28 s and a very high quantum efficiency of 5 % was thus obtained under ambient conditions. This strategy represents an important step in the understanding of organic pRTP emission.

Key mechanistic features of Ni-catalyzed C-H/C-O biaryl coupling of azoles and naphthalen-2-yl pivalates.

Abstract: The mechanism of the Ni-dcype-catalyzed C–H/C–O coupling of benzoxazole and naphthalen-2-yl pivalate was studied. Special attention was devoted to the base effect in the C–O oxidative addition and C–H activation steps as well as the C–H substrate effect in the C–H activation step. No base effect in the C(aryl)–O oxidative addition to Ni-dcype was found, but the nature of the base and C–H substrate plays a crucial role in the following C–H activation. In the absence of base, the azole C–H activation initiated by the C–O oxidative addition product Ni(dcype)(Naph)(PivO), 1B, proceeds via ΔG = 34.7 kcal/mol barrier. Addition of Cs2CO3 base to the reaction mixture forms the Ni(dcype)(Naph)[PivOCs·CsCO3], 3_Cs_clus, cluster complex rather than undergoing PivO– → CsCO3– ligand exchange. Coordination of azole to the resulting 3_Cs_clus complex forms intermediate with a weak Cs–heteroatom(azole) bond, the existence of which increases acidity of the activated C–H bond and reduces C–H activation barrier. This conclu...

A DFT study on the mechanism of Rh2(II,II)-catalyzed intramolecular amidation of carbamates.

Abstract: The potential-energy surfaces of the reactions of dirhodium tetracarboxylate (Rh2(II,II)) catalyzed nitrene (NR) insertion into C-H bonds were examined by a DFT computational study. A pure Becke exchange functional (B88) rather than a hybrid exchange functional (B3, BHandH) was found to be appropriate for the calculation of the energy difference between the singlet and triplet Rh2(II,II)-NH nitrene species. Rh2(II,II)-NR1 (R1 = (S)-2-methyl-1-butylformyl) is thermodynamically more favorable with a free energy lower than that of Rh2(II,II)-N(PhI)R1. The singlet and triplet states of Rh2(II,II)-NR1 have similar stability. Singlet Rh2(II,II)-NR1 undergoes a concerted NR insertion into the C-H bond with simultaneous formation of the N-H and N-C bonds during C-H bond cleavage; triplet Rh2(II,II)-NR1 undergoes H atom abstraction to produce a diradical, followed by subsequent bond formation by diradical recombination. The singlet pathway is favored over the triplet in the context of the free energy of activation and leads to the retention of the chirality of the C atom in the NR insertion product. The reactivities of the C-H bonds toward the nitrene-insertion reaction follow the order tertiary > secondary > primary. Relative reaction rates were calculated for the six reaction pathways examined in this work.

cis-β-Bis(carbonyl) Ruthenium−Salen Complexes: X-ray Crystal Structures and Remarkable Catalytic Properties toward Asymmetric Intramolecular Alkene Cyclopropanation

Abstract: cis-β-[RuII(salenA)(CO)2] (salenA = N,N′-bis(3-R1-5-R2-salicylidene)-1,2-cyclohexenediamine dianion; R1 = R2 = But, 1a; R1 = Pri, R2 = H, 1b; R1 = But, R2 = H, 1c) complexes were prepared by treating Ru3(CO)12 with the respective H2salenA in 1,2,4-trichlorobenzene and structurally characterized by X-ray crystallography. Complexes 1a−c catalyze intramolecular cyclopropanation of trans-allylic diazoacetates N2CHCO2CH2CH═CHR (3, R = Ph, 4-ClC6H4, 4-BrC6H4, 4-MeC6H4, 4-MeOC6H4, 2-MeC6H4, 2-furanyl) under light irradiation to give cyclopropyl lactones 4 in up to 96% yield and up to 98% ee. DFT calculations on intramolecular cyclopropanation of 3a (R = Ph) with model catalyst cis-β-[RuII(salenA0)(CO)2] (salenA0 = N,N′-bis(salicylidene)-1,2-cyclohexenediamine dianion) reveal the intermediacy of both cis-β- and trans-[Ru(salenA0)(CHCO2CH2CH═CHPh)(CO)] bearing salenA0 in a nonplanar and planar coordination mode, respectively, with the cis-β-carbene species being a major intermediate in the catalytic carbenoid tran...

Applications of metal–organic frameworks in heterogeneous supramolecular catalysis

Abstract: This review summarizes the use of metal–organic frameworks (MOFs) as a versatile supramolecular platform to develop heterogeneous catalysts for a variety of organic reactions, especially for liquid-phase reactions. Following a background introduction about catalytic relevance to various metal–organic materials, crystal engineering of MOFs, characterization and evaluation methods of MOF catalysis, we categorize catalytic MOFs based on the types of active sites, including coordinatively unsaturated metal sites (CUMs), metalloligands, functional organic sites (FOS), as well as metal nanoparticles (MNPs) embedded in the cavities. Throughout the review, we emphasize the incidental or deliberate formation of active sites, the stability, heterogeneity and shape/size selectivity for MOF catalysis. Finally, we briefly introduce their relevance into photo- and biomimetic catalysis, and compare MOFs with other typical porous solids such as zeolites and mesoporous silica with regard to their different attributes, and provide our view on future trends and developments in MOF-based catalysis.

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Transition Metal-Catalyzed C–H Amination: Scope, Mechanism, and Applications

Abstract: Catalytic transformation of ubiquitous C–H bonds into valuable C–N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C–H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.

3d Transition Metals for C-H Activation.

Abstract: C–H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C–H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C–H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C–H activation until summer 2018.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

Abstract: The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C–C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of...