Phosphine Supported Mono-and Polynuclear Ni Complexes for Inert Bond Activation: Mechanisms and Isolation of Reactive Intermediates

Inert C−O bond activation has been an important research area because ethers have the potential to replace organohalides as relatively economic and less toxic building blocks. Phosphine supported Ni complexes have been found to be reactive towards C−O bonds. A number of cross-coupling reactions using Ni catalysts for C−O activation have been developed. However, mechanistic understanding lags behind current application. Multiple mechanisms have been proposed based on DFT studies, while few intermediates have been isolated or observed experimentally. This dissertation focuses on the mechanistic details of Ni mediated C(sp2)−O activation. The number of ligand coordinated to Ni in the critical bond cleavage step remains unclear, and previous DFT studies have suggested that both L2Ni and LNi species might be the active species, where L is a neutral phosphine donor. The lack of easily accessible LNi(0) sources has been an obstacle to examining the ability of the LNi moiety to facilitate C−O bond cleavage. This work provides a synthesis to a series of (Cy3P)Ni(η6-arene) complexes that provide a source of the (Cy3P)Ni(0) moiety. We compared the stability of (Cy3P)Ni(η6-arene) complexes with different substituents. Arenes with electron-withdrawing substituents form the most thermodynamically stable adducts. More fluorinated arenes form less stable adducts. This trend is opposite to the adducts of L2Ni(0) species where more fluorinated substituents form more stable adducts. In the preparation of (Cy3P)Ni(η6-arene) complexes we also correct a longstanding error in the nature of the starting material [(Cy3P)2Ni]2(μ-N2) in solution. In our mechanistic studies of C(sp2)−O acitvation, (Cy3P)Ni(η6-arene) and [(Cy3P)2Ni]2(μ-N2) were used as the LNi(0) and L2Ni(0) sources. The reactions of naphthyl substrates with LNi(0) or L2Ni(0) produce different products. However, the isolation of these adducts proved impossible, so other substrates were examined. The reactions of alkenyl ethers with LNi(0) or L2Ni(0) at room temperature provided (Cy3P)2Ni(η2-alkenylether). The reactions of vinyl ethers (RH2COCH=CH2, R is aliphatic groups) with [(Cy3P)2Ni]2(μ-N2) produces esters through nickel mediated homocoupling of ethers. [(Cy3P)2Ni]2(μ-N2) can also mediate the coupling of acetaldehyde and vinyl ethers. A mechanism of the ether-acetaldehyde coupling was proposed based on the experimental and computational studies. Apart from the traditional mononuclear complexes, electron-deficient transition metal clusters are emerging as powerful catalysts to inert bond activations. They are able to cooperatively activate bonds under mild conditions. Our previous work reported the synthesis of a pentanuclear nickel clusters, [(iPr3P)Ni]5H6, which shows high reactivities with inert C−O bonds. This thesis examines the role of the supporting phosphine donor in cluster formation and reactivity. A series of phosphines were investigated; PtBuMe2 provided [(tBu2MeP)Ni]5H6, which is even more reactive than the PiPr3 analogue. PCy2Me is able to form a dinuclear complex [(Cy2MeP)2Ni]2(μ-H)2. In the case of PCy3 and PCyp3, P−C bond cleavage occurred and led to the production of a dinuclear Ni complex [(R3P)HNi]2(μ-H)(μ-PR2). We also proposed mechanisms of the production of these nickel hydride complexes based on the experimental studies

A Contrastive Analysis of Chinese Humor and English Humor in Intercultural Communication

Humor plays an important role in daily life and also quite useful in interpersonal communication. Nowadays, the cross-cultural communication between the English-speaking countries and China becomes more and more frequent while some humor is difficult to appreciate with diverse cultural backgrounds. Therefore, this paper aims at analyzing the Chinese and English humor from their similarities, like the use of ambiguity and figure of speech, as well as differences, especially in functions, topics and ways of expression. Related causes are further discussed the differences. Hopefully, the findings will help to reduce the obstacles in understanding humor in different culture and promote transcultural communication in a delightful manner

High-quality Image Restoration from Partial Mixed Adaptive-Random Measurements

A novel framework to construct an efficient sensing (measurement) matrix, called mixed adaptive-random (MAR) matrix, is introduced for directly acquiring a compressed image representation. The mixed sampling (sensing) procedure hybridizes adaptive edge measurements extracted from a low-resolution image with uniform random measurements predefined for the high-resolution image to be recovered. The mixed sensing matrix seamlessly captures important information of an image, and meanwhile approximately satisfies the restricted isometry property. To recover the high-resolution image from MAR measurements, the total variation algorithm based on the compressive sensing theory is employed for solving the Lagrangian regularization problem. Both peak signal-to-noise ratio and structural similarity results demonstrate the MAR sensing framework shows much better recovery performance than the completely random sensing one. The work is particularly helpful for high-performance and lost-cost data acquisition.Comment: 16 pages, 8 figure

Parameter Optimization for Interaction between C-Terminal Domains of HIV-1 Capsid Protein

HIV-1 capsid proteins (CAs) assemble into a capsid that encloses the viral RNA. The binding between a pair of C-terminal domains (CTDs) constitutes a major interface in both the CA dimers and the large CA assemblies. Here, we attempt to use a general residue-level coarse-grained model to describe the interaction between two isolated CTDs in Monte Carlo simulations. With the standard parameters that depend only on the residue types, the model predicts a much weaker binding in comparison to the experiments. Detailed analysis reveals that some Lennard-Jones parameters are not compatible with the experimental CTD dimer structure, thus resulting in an unfavorable interaction energy. To improve the model for the CTD binding, we introduce ad hoc modifications to a small number of Lennard-Jones parameters for some specific pairs of residues at the binding interface. Through a series of extensive Monte Carlo simulations, we identify the optimal parameters for the CTD–CTD interactions. With the refined model parameters, both the binding affinity (with a dissociation constant of 13 ± 2 μM) and the binding mode are in good agreement with the experimental data. This study demonstrates that the general interaction model based on the Lennard-Jones potential, with some modest adjustment of the parameters for key residues, could correctly reproduce the reversible protein binding, thus potentially applicable for simulating the thermodynamics of the CA assemblies