Asymmetric reduction of ortho-multisubstituted benzophenones catalyzed by diamine-Zn-diol complexes

The asymmetric reduction of benzophenones multisubstituted at the ortho-positions was achieved via hydrosilylation catalyzed by in situ generated chiral diamine-Zn-diol complexes under mild conditions, wherein polymethylhydrosiloxane (PMHS) served as a safe and inexpensive source of hydride.     

Numerical Study of a Free-Burning Argon Arc with Anode Melting

Numerical modeling of free burning arcs and their electrodes is useful for clarifying the heat transfer phenomena in the welding process and to elucidate those effects which determine the weld penetration. This paper presents predictions for a stationary welding process by the free-burning argon arc. The whole region of the welding process, namely, tungsten cathode, arc plasma and stainless steel anode is treated in a unified numerical model to take into account the close interaction between the arc plasma and the molten anode. The time dependent development of two-dimensional distributions of temperature and velocity, in the whole region of the welding process, are predicted at a current of 150 A. The weld penetration geometry as a function of time is thus predicted. It is shown also that different surface tension properties can change the direction of re-circulatory flow in the molten anode and dramatically vary the weld penetration geometry.     

A decomposition of the beta distribution,related order and asymptotic behavior

Let β _{v, w} be any beta variate with p.d.f.(Γ(v+w)/Γ(v)Γ(w))x ^v−1(1−x) ^w−1 and letU _{v, w} =-log β _{v, w} . ThenU _v,w =U ^CM +U ^PF , whereU ^CM andU ^PF are independent with completely monotone andPF _∞ densities, respectively. It is shown thatU _{v, w} is infinitely divisible and β _{v, w} correspondingly infinitely factorable. The asymptotic behavior ofU _{v, w} and β _{v, w} for largev, w is described. For different modes of increase ofv andw,U _{v, w} is asymptotically normal, gamma or extreme value distributed. The decomposition is employed to provide an algorithm for generating random β _{v, w} distributed numbers. Many of the results are based on insights provided by the classical theory of the Gamma function in the complex plane. This work was supported in part by the United States Air Force, Office of Scientific Research, under grant No. AFOSR-79-0043.     

Synthesis, structure, and transannular pi-pi interaction of multilayered [3.3]metacyclophanes

The synthesis of a series of three- to six-layered [3.3]metacyclophanes ([3.3]MCPs) 3-6 has been successfully accomplished by the (p-tolylsulfonyl)methyl isocyanide (TosMIC) method as a critical coupling reaction. Their important synthetic intermediates are the two- and three-layered bis(bromomethyl) compounds 11, 17, 21, and tetrakis(bromomethyl) compounds 25 and 28. The structures of the three- to six-layered [3.3]MCPs (3-6) as well as three- to six-layered [3.3]MCP-di- (22-24) and tetraones (26, 27, and 29) as the synthetic intermediates have been elucidated based on the 1H NMR data and X-ray structural analysis. These multilayered cyclophanes are constructed with two different geometries, syn-[3.3]MCP and anti-[3.3]MCP-2,11-dione. In principle, their geometries are maintained in the multilayered [3.3]MCPs, but deformation of the dihedral angle of the two benzene rings of the syn-[3.3]MCP moiety is generally observed. In the four-layered MCP 4, the central [3.3]MCP moiety takes an anti geometry. These data indicate the structural flexibility of the [3.3]MCP moiety. In the electronic spectra, rather simple and structureless absorption curves are observed, and the most significant spectral change is observed for the two to three layers and becomes less effective even if it is more layered. In the charge-transfer (CT) bands of the multilayered [3.3]MCPs with tetracyanoethylene (TCNE), the lambdamax gradually shifts to the longer wavelength region, but the extent of the shift is much smaller as the number of layers increases. In the multilayered [3.3]MCP-di- and tetraones, the anti-[3.3]MCP-dione moiety works as an insulator. Therefore, the CT interaction of the four- and five-layered [3.3]MCPs with one anti-[3.3]MCP-dione moiety (23 and 24) shows the almost comparable magnitude of the interaction with the two- and three-layered [3.3]MCPs (2 and 3), respectively. The tetraones of the three and four-layered MCPs (29 and 26) do not show CT interactions except for the six-layered MCP 27.     

Hierarchical amplification of macromolecular helicity of dynamic helical poly(phenylacetylene)s composed of chiral and achiral phenylacetylenes in dilute solution, liquid crystal, and two-dimensional crystal

Optically active poly(phenylacetylene) copolymers consisting of optically active and achiral phenylacetylenes bearing L-alanine decyl esters (1L) and 2-aminoisobutylic acid decyl esters (Aib) as the pendant groups (poly(1L(m)-co-Aib(n))) with various compositions were synthesized by the copolymerization of the optically active 1L with achiral Aib using a rhodium catalyst, and their chiral amplification of the macromolecular helicity in a dilute solution, a lyotropic liquid crystalline (LC) state, and a two-dimensional (2D) crystal on the substrate was investigated by measuring the circular dichroism of the copolymers, mesoscopic cholesteric twist in the LC state (cholesteric helical pitch), and high-resolution atomic force microscopy (AFM) images of the self-assembled 2D helix-bundles of the copolymer chains. We found that the macromolecular helicity of poly(1L(m)-co-Aib(n))s could be hierarchically amplified in the order of the dilute solution, LC state, and 2D crystal. In sharp contrast, almost no chiral amplification of the macromolecular helicity was observed for the homopolymer mixtures of 1L and Aib in the LC state and 2D crystal on graphite.     

Structural properties of charge-transfer complexes of four- and five-layered [3.3]metacyclophanes

In the solid state, the cyclophane (CP) moieties of the charge-transfer (CT) complexes of four- and five-layered [3.3]metacyclophanes (MCPs) 1 and 2 with tetracyanoethylene (TCNE) take different conformations from those in the solid state of the free MCPs. In the four-layered [3.3]MCP 1-TCNE complex, the CP moiety takes an s-shaped syn-anti-syn geometry, whereas the inner three benzene rings take the all-syn geometry and the two outer [3.3]MCP moieties have deformed anti-conformations in the five-layered [3.3]MCP 2-TCNE complex. In the crystal-packing diagrams of each complex, intermolecular CH/π-type interactions are observed between adjacent molecules.     

Synthesis and redox properties of π-conjugated 4,5-diazafluorene derivatives incorporating 9-cyanomethylene moiety as an electron acceptor

We have synthesized π-conjugated acceptor-type molecules 3a-d containing a cyanomethylene unit as the electron acceptor site and a 4,5-diazafluorene ligand for metal complexation. In the crystal, the planar 3a molecules stack along the b axis in the head-to-tail fashion. Compound 3a shows distinctive electrochromism and its three differently colored redox states (dianion (3²⁻), anion radical (3⁻), neutral (3)) exhibit remarkable stability.