Probing the origin of the stereoselectivity and enantioselectivity of cobalt-catalyzed [2 + 2] cyclization of ethylene and enynesSubmitted by Jun Zhu on Sun, 02/21/2021 - 10:19
The cyclobutane unit is important to prepare complex natural products with biological activity due to the high ring strain. Among various approaches, [2 + 2] cycloaddition is one of the major strategies to prepare cyclobutane under light conditions. Recently, Rajanbabu's group reported tandem catalysis for asymmetric coupling of inactivated ethylene and enynes to functionalized cyclobutenes or cyclobutanes. However, the reaction mechanisms remain unproven.
Probing hyperconjugative aromaticity in 2H-pyrrolium and cyclopentadiene containing Group 9 transition metal substituent: Bridged carbonyl ligands can enhance aromaticitySubmitted by Jun Zhu on Sun, 01/10/2021 - 10:34
Aromaticity and hyperconjugation are two fundamental concepts in organic chemistry. By combination of the two concepts together, the resulting hyperconjugative aromaticity has attracted considerable attention from both theoretical and computational chemists. However, previous studies are mainly focused on the main group chemistry. For the hyperconjugative aromaticity in the transition metal chemistry, the studies are limited to groups 10 and 11.
Rational design of the nickel‐borane complex for efficient hydrogenation of styreneSubmitted by Jun Zhu on Sun, 01/10/2021 - 10:24
The Ni‐B complex 1BCF with a facilely accessible monophosphine (PtBu3) unit was theoretically designed, which was found to be more active than that with an ambiphilic ligand for hydrogenation of styrene. Substituting PtBu3 with a stronger electron donating ligand N‐heterocyclic carbene largely improves the activity of the Ni‐B complex.
Probing the Tautomerization of Disilenes, Disilabenzenes with Their Isomeric Silylenes: Significant Substituent, Aromaticity and Base EffectsSubmitted by Jun Zhu on Thu, 11/12/2020 - 19:24
Disilene has attracted considerable interests due to the trans-bending geometry which is significantly different from the planar alkene. However, the equilibrium between disilene and isomeric silylsilylene has not been fully understood. Here, we report a density functional theory (DFT) study on this equilibrium. Calculations reveal significant effects of substituent, aromaticity and base. Specifically, the parent disilene is thermodynamically more stable than the isomeric silylene.
Open questions on aromaticity in organometallicsSubmitted by Jun Zhu on Wed, 11/11/2020 - 16:44
While sp2-hybridized carbon atoms in hydrocarbons typically contribute only one electron to their aromaticity, metals have more electrons from d or f orbitals available for participating in conjugation in organometallics, complicating the electron counting as well as analysis of their aromaticity. Here, the author comments on the challenges towards understanding aromaticity in organometallics and outlines several remaining questions that have yet to be answered.
Chemoselectivity for B–O and B–H Bond Cleavage by Pincer-Type Phosphorus Compounds: Theoretical and Experimental StudiesSubmitted by Jun Zhu on Mon, 11/09/2020 - 14:28
Selective cleavage of the B–O bond or B–H bond in HBpin can be achieved by adjusting the pincer ligand of a phosphorus(III) compound guided by a combination of theoretical prediction and experimental verification. Theoretical calculations reveal that a pincer-type phosphorus compound with an [ONO]3– ligand reacts with HBpin, leading to cleavage of the stronger B–O bonds (ΔG°⧧ = 23.2 kcal mol–1) rather than the weaker B–H bond (ΔG°⧧ = 26.4 kcal mol–1).
Carbon-halogen bond activation by a structurally constrained phosphorus(III) platformSubmitted by Jun Zhu on Mon, 11/09/2020 - 11:27
The σ-bond activation by main group element has received enormous attention from theoretical and experimental chemists. Here, the reaction of C-X (X = Cl, Br, I) bonds in benzyl and allyl halides with a pincer-type phosphorus(III) species was reported. A series of structurally robust phosphorus(V) compounds were formed via the formal oxidative addition reactions of C-X bonds to the phosphorus(III) center. Density functional theory calculations show that the nucleophilic addition process is more favorable than the direct oxidative addition mechanism.
Aromaticity Survival in Hydrofullerenes: The Case of C66H4 with its π‐Aromatic CircuitsSubmitted by Jun Zhu on Mon, 11/09/2020 - 11:17
The isolated‐pentagon rule (IPR) is a determining structural feature accounting for hollow fullerene stabilization and properties related to Cn (n ≥ 60) cages. The recent characterization of an unprecedented non‐IPR hydrofullerene, C2v‐C66H4, bearing two heptagons with adjacent fused‐pentagons motif, largely dismiss this feature. Herein, employing DFT calculations, we explore the 13C‐NMR pattern and aromatic behavior of C2v‐C66H4.
Facile Dinitrogen and Dioxygen Cleavage by a Uranium(III) Complex: Cooperativity Between the Non‐innocent Ligand and the Uranium CenterSubmitted by Jun Zhu on Wed, 09/16/2020 - 15:48
Activation of dinitrogen (N2, 78%) and dioxygen (O2, 21%) has fascinated chemists and biochemists for decades. The industrial conversion of N2 to ammonia requires extremely high temperatures and pressure. Here we report the first example of N2 and O2 cleavage by a uranium complex, [N(CH2CH2NPiPr2)3U]2(TMEDA), under ambient conditions without an external reducing agent. The N2 triple bond breaking implies a U(III)-P(III) six-electron reduction. The hydrolysis of the N2 reduction product allows the formation of ammonia or nitrogen-containing organic compound.
Tuning the Properties of Corannulene-Based Polycyclic Aromatic Hydrocarbons by Varying the Fusing Positions of CorannuleneSubmitted by Jun Zhu on Fri, 09/11/2020 - 14:35
The selective fusions with pyrene derivative to the rim and flank bonds of corannulene generated 4 and 7, respectively, which underwent a Scholl reaction to provide novel distorted PAHs CORA-1 and CORA-2, consisting of corannulene and dibenzocoronene units with different connections between them. The studies revealed that the properties of these PAHs are highly dependent on the fusing positions of corannulene.