A crystal's structure has significant impact on its resulting biological, physical, optical and electronic properties. In organic electronics, 6,13(bis-triisopropylsilylethynyl)pentacene (TIPS-pentacene), a small-molecule organic semiconductor, adopts metastable polymorphs possessing significantly faster charge transport than the equilibrium crystal when deposited using the solution-shearing method. Here, we use a combination of high-speed polarized optical microscopy, in situ microbeam grazing incidence wide-angle X-ray-scattering and molecular simulations to understand the mechanism behind formation of metastable TIPS-pentacene polymorphs. We observe that thin-film crystallization occurs first at the air-solution interface, and nanoscale vertical spatial confinement of the solution results in formation of metastable polymorphs, a one-dimensional and large-area analogy to crystallization of polymorphs in nanoporous matrices. We demonstrate that metastable polymorphism can be tuned with unprecedented control and produced over large areas by either varying physical confinement conditions or by tuning energetic conditions during crystallization through use of solvent molecules of various sizes.

In situ combination of diphosphinic amides and Zr(NMe 2 ) 4 results in the formation of chiral zirconium bis(amido) complexes. The complexes are competent catalysts for intramolecular asymmetric alkene hydroamintion, providing piperidines and pyrrolidines in up to 80% ee and high yield. This system utilizes an inexpensive zirconium precatalyst and readily prepared ligands and is the first asymmetric alkene hydroamination catalyst based upon a neutral zirconium bis(amido) complex.The development of catalysts for intramolecular asymmetric alkene hydroamination has been the subject of intense investigation over the past 15 years. 1,2,3,4,5 While considerable advances have been made using catalysts containing a variety of metals, no general solution has emerged. To date, catalysts based on Group 3 and lanthanide metals have shown the most promise for unactivated alkenes. 1,2,3 However, even within this class only a small number (4) of highly enantioselective reactions (>90% ee) have been reported. 3c Thus alkene hydroamination remains an open area of research.Recently, Schafer 6 (and subsequently Livinghouse 7 ) reported that neutral Group IV bis (amido) complexes bearing achiral ligands are competent catalysts for intramolecular alkene hydroamination. Our group has previously reported that closely related catalysts containing chiral dialkoxide and diamide ligands are effective in intramolecular allene and alkyne hydroamination. 8 We decided to explore the possibility that these types of chiral complexes could be applied to asymmetric alkene hydroamination. Herein, we report the first examples of asymmetric, intramolecular alkene hydroamination catalyzed by Group 4 bis(amido) complexes. 9 The reported catalysts employ readily available chiral ligands and provide enantioselectivities of up to 80% ee.Having previously demonstrated that in situ combination of various diamines or diols and Group IV tetrakis(dimethyl)amides provides competent hydroamination catalysts, 8 we screened various combinations of these compounds as catalysts in the cyclization of 1 (eq 1). 10,11 In an effort to develop a practical catalyst, we focused exclusively on commercially available or readily prepared diols, diamines and aminoalcohols (Table 1). 12 Although enantioselective catalysts based on titanium and hafnium 13 were also identified, the zirconium catalyst prepared by combination of diphosphinic amide 3c 12c and Zr(NMe 2 ) 4 (entry 11) proved significantly more enantioselective than others that we studied. Under unoptimized conditions (see footnote, Table 1), pyrrolidine 2 was obtained in 67% ee and excellent yield. Given this initial promise, we elected to explore additional ligands of the same general structure.Correspondence to: Robert G. Bergman. NIH Public Access Author ManuscriptOrganometallics. Author manuscript; available in PMC 2008 December 11. A series of diphosphinic amides was prepared using one of two short synthetic sequences. 14 These ligands were investigated in the cyclization of 1 (Table 2). Ligands containi...

This work details the development of ruthenium(II) catalysts for the enantioselective alkylation of chiral racemic secondary phosphines. The reactions proceed through the intermediacy of nucleophilic phosphido species, which have low barriers to pyramidal inversion; this allows for a dynamic kinetic asymmetric alkylation. The initially discovered [((R)-iPr-PHOX)(2)Ru(H)][BPh(4)] (6) catalyst was found to be effective in the reaction with benzylic chlorides; moreover, the alkylation displayed an unusual temperature dependence. However, the limited scope of alkylation of 6 motivated further studies which led to the development of two complementary chiral mixed ligand Ru(II) catalysts of type [L(1)L(2)Ru(H)](+). These catalysts were derived from a combination of one chiral and one achiral ligand, where a synergistic interaction of the two ligands creates an effective asymmetric environment around the ruthenium center. The (R)-MeO-BiPHEP/dmpe (dmpe = 1,2-bis(dimethylphosphino)ethane) catalyst (10) was found to be effective for the asymmetric alkylation of benzylic chlorides, while the (R)-DIFLUORPHOS/dmpe catalyst (11) was optimal for the nucleophilic substitution of less activated alkyl bromides; the scope of the respective catalysts was also explored.

Deterministic methods for tuning polymer dispersity are rare, especially for nonradical polymerizations. Reported here is the first example of photomodulating dispersity in controlled cationic polymerizations of vinyl ethers using carboxy‐functionalized dithienylethene initiators. Reversible photoisomerization of these initiators induces changes in their acidities by up to an order of magnitude. Using the more acidic, ring‐closed isomers as initiators results in polymers with lower dispersities. The degree of light‐induced pKa change in the initiators correlates with the degree of dispersity change in polymers derived from the isomeric initiators. The polymerizations are controlled, and dynamic photoswitching of dispersity during the polymerization reaction was demonstrated. This work provides a framework for photomodulating dispersity in other controlled polymerizations and developing one‐pot block copolymerization reactions in which the dispersities of component blocks can be controlled using light.

The crystal structure of methylene blue, 3,7-bisdimethylaminophenazothionium chloride pentahydrate, was determined by direct methods from single-crystal X-ray diffraction data. C16HIsN3SC1.5H20 crystallizes in the monoclinic system, space group e2x/c, with a= 9"646 (9), b= 31.106 (17), c= 6.992 (2) /~,, fl= 96.70 (6). The structure was refined by full-matrix least-squares calculations to R= 0"057. The dye molecules are essentially planar, with twenty molecules of water of hydration per unit cell, forming an interesting hydrogen-bonding network through the lattice. Positions for C, N, S, O, and C1 atoms were determined from Fourier electron-density maps. Hydrogen atom positions were refined from a clathrate ice-like model.