Bridged [2.2.1] bicyclic phosphine oxide facilitates catalytic γ-umpolung addition-Wittig olefination.

A novel bridged [2.2.1] bicyclic phosphine oxide, devised to circumvent the waste generation and burdens of purification that are typical of reactions driven by the generation of phosphine oxides, has been prepared in three steps from commercially available cyclopent-3-ene-1-carboxylic acid. The performance of this novel phosphine oxide was superior to those of current best-in-class counterparts, as verified experimentally through kinetic analysis of its silane-mediated reduction. It has been applied successfully in halide-/base-free catalytic γ-umpolung addition-Wittig olefinations of allenoates and 2-amidobenzaldehydes to produce 1,2-dihydroquinolines with good efficiency. One of the 1,2-dihydroquinoline products was converted to known antitubercular furanoquinolines

New Conducting and Electrically Switching Molecular Materials based on Main Group and Transition Metal Ions Bridged by TCNQ Derivatives

The field of molecular electronics has been under investigation by materials scientists for the last two decades, activity that has increased in recent years as their potential to be components in modern quantum computing devices began to be discussed in a more sophisticated manner. In this field, the challenge is to obtain stable highly conducting materials and to manipulate their properties with external stimuli. As one of the most stable organic radicals, the singly reduced form of TCNQ (7,7,8,8-tetracyanoquinodimethane) has played a central role in the design of many unprecedented conducting materials including the first purely organic conductor (TTF)(TCNQ) (TTF = tetrathiafulvalene) which is nearly metallic and the electrically bistable switching material Cu(TCNQ). The research in this dissertation focused on the application of TCNQ and its derivatives in order to tune the structure and conductivity of these materials, with the overarching goal being to understand the mechanism of conductivity. This dissertation reports the details of the first main-group TCNQ binary compound, Tl(TCNQ). Two distinct polymorphs have been discovered and a remarkable water-induced phase transition from one to the other was observed. With different modes of TCNQ stacking (alternating or homogenous distances), the two polymorphs exhibit very different conductivities, namely 2.4×10^-4 S/cm and 5.4×10^-1 S/cm. With this inspiration, a series of semiconductors, Tl(TCNQX2) (X =Cl, Br, I) was prepared and structurally characterized. The steric effect of the halogen substituents leads to a variety of structures and a band structure simulation has suggested a clear structure-property relationship that involves perturbation of the Tl 6s orbital into the conduction band. Inspired by the switching material Ag(TCNQ), semiconducting frameworks Ag(TCNQCl2) and Ag(TCNQBr2) were prepared by electrocrystallization methods. Importantly, the former material exhibits a high room temperature conductivity of 0.25 S/cm and an unusual room temperature negative differential resistance (NDR) which is the source of intrinsic switching behaviors. The effect of solvent on the structure of these binary phases was also investigated. The series M(TCNQX2)(MeCN)n (M = Cu, Ag; X = Br, I; n =1, 2) was discovered and the interconversion of these solvated phases was studied. The effect of coordinated solvent molecules decreases the density of conducting stacks, consequently leading to a decrease of conductivity

Poly[di-μ2-chlorido-tri-μ2-terephthalato-tetra­lead(II)]

The title compound, [Pb4(C8H4O4)3Cl2]n, consists of a three-dimensional inorganic–organic hybrid framework. The asymmetric unit contains two Pb2+ cations, one Cl− anion and one and a half terephthalate anions, the latter being completed by inversion symmetry. The two Pb2+ cations are each surrounded by five O atoms and one Cl atom in the form of irregular polyhedra. The cations are linked by μ2-O and μ2-Cl atoms into binuclear units, which are further extended through Pb—O inter­actions into an undulated inorganic layer parallel to (001). These layers are connected along [001] by the terephthalate groups into a three-dimensional framework

Direct single-molecule dynamic detection of chemical reactions.

Single-molecule detection can reveal time trajectories and reaction pathways of individual intermediates/transition states in chemical reactions and biological processes, which is of fundamental importance to elucidate their intrinsic mechanisms. We present a reliable, label-free single-molecule approach that allows us to directly explore the dynamic process of basic chemical reactions at the single-event level by using stable graphene-molecule single-molecule junctions. These junctions are constructed by covalently connecting a single molecule with a 9-fluorenone center to nanogapped graphene electrodes. For the first time, real-time single-molecule electrical measurements unambiguously show reproducible large-amplitude two-level fluctuations that are highly dependent on solvent environments in a nucleophilic addition reaction of hydroxylamine to a carbonyl group. Both theoretical simulations and ensemble experiments prove that this observation originates from the reversible transition between the reactant and a new intermediate state within a time scale of a few microseconds. These investigations open up a new route that is able to be immediately applied to probe fast single-molecule physics or biophysics with high time resolution, making an important contribution to broad fields beyond reaction chemistry