Selectivity in propene polymerization with metallocene catalysts.

Learning how to control the formation and twoand three-dimensional assembly of molecular scale building blocks into well-defined mesoand macroscopic structures is the essence of nanotechnology and materials chemistry. DNA is arguably one of the most programmable “assemblers” available to the synthetic chemist and materials scientist, yet until recently, it has been an underutilized synthon in materials chemistry. The purpose of this review is to summarize advances made involving new strategies that rely on the use of both naturally occurring DNA and synthetic oligonucleotides to assemble nanoscale nonbiological building blocks into extended mesoand macroscopic structures. Although early in their development, some of these strategies already have been shown to be useful in generating novel nanostructured materials,1-4 arranging inorganic nanoparticles into “anatural” configurations,5,6 understanding interparticle electronic interactions,1 templating the growth of nanocircuitry,7 and developing a promising new detection technology for DNA.8,9 There are two basic types of building blocks that are applicable to a variety of assembly schemes: molecules with synthetically programmed recognition sites or bits of matter with nanoscale dimensions and well-defined surface chemistries. The latter type of building block is often referred to as a “nanoparticle” or “nanocrystal”. Assembly of such building blocks into extended, well-defined structures can provide a variety of functional materials with applications including ultrasmall electronic devices,10-13 spectroscopic enhancers,14,15 high-density information storage media,16,17 and highly sensitive and selective chemical detectors.8,9,18 The assembly of nanoparticle and molecular building blocks into functional structures has been accomplished through both physical and chemical methods.19 Physical methods include the use of scanning probe microscopy,20-22 electrophoretic strategies,23,24 LB films,25,26 or templatedriven sedimentation27 to position particles in a preconceived fashion within a matrix or on a substrate. Although effective for preparing certain types of nanoscale architectures, many of these physical methods are limited because they are often slow and do not lend themselves to preparing designed nanostructured architectures that canvas macroscopic dimensions. Chemical methods include ordering particles based upon interparticle electrostatic interactions,28-30 covalent assembly,31,32 template recognition,33,34 template recognition with subsequent covalent cross-linking reactions,35,36 crystallization based upon weak intermolecular interactions,37-41 or linking reactions involving designed organic or biological recognition sites.1,2,4,42 The advantages of chemical methods are that building block linking processes can occur in a massively parallel fashion and in some cases possess self-annealing or correcting properties. This makes them particularly attractive for constructing twoand three-dimensional structures on a faster time scale. The disadvantage is that at present chemical methods, when compared with some of the aforementioned physical deposition methods, are difficult to control. Recently, there has been substantial interest in utilizing biomolecules to direct the formation of extended mesoand macroscopic architectures.43,44 The advantage of using biomolecules is that molecular recognition is already built into the building block of interest (e.g., peptides, oligonucleotides, and proteins). In some cases, synthetic versions of the biomolecules are readily available and easily adaptable to both inorganic and organic building blocks and substrates.45 This review examines the use of one class of these biomolecules, DNA, to organize nanometer-sized structures into preconceived extended, functional structures and materials. It is divided into three categories; the use of (1) oligonucleotides (singlestranded DNA) to prepare mesoand macroscopic organic structures, (2) duplex DNA as a physical template for growing inorganic wires and organizing nonbiological building blocks into extended hybrid materials, and (3) oligonucleotide functionalized nanoparticles and sequence-specific hybridization reactions for organizing such particles into periodic, functional structures. 1849 Chem. Rev. 1999, 99, 1849−1862

Programmed Materials Synthesis with DNA.

numerous polyethylene or polypropylene compounds have been synthesized by metal-catalyzed coordination-insertion polymerization. On the other hand, organometallic catalysts * To whom correspondence should be addressed. E-mail: nozaki@chembio.t.utokyo.ac.jp. Akifumi Nakamura (left) was born in 1984 in Kanagawa, Japan. He received his B.S. degree in 2007 and M.S. degree in 2009 from the University of Tokyo under the guidance of Professor Kyoko Nozaki. During that time he joined Professor Keiji Morokuma’s group at Kyoto University as a visiting student. In 2009, he started his Ph.D. study at the University of Tokyo under the guidance of Professor Kyoko Nozaki. He is also a research fellow of the Japan Society for the Promotion of Science. His research interests include synthetic organic chemistry, organometallic chemistry, computational chemistry, and polymer chemistry.

Coordination−Insertion Copolymerization of Fundamental Polar Monomers

Multinuclear olefin polymerization catalysts

We report the preparation, structural characterization, and detailed lactide polymerization behavior of a new Zn(II) alkoxide complex, (L(1)ZnOEt)(2) (L(1) = 2,4-di-tert-butyl-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenolate). While an X-ray crystal structure revealed the complex to be dimeric in the solid state, nuclear magnetic resonance and mass spectrometric analyses showed that the monomeric form L(1)ZnOEt predominates in solution. The polymerization of lactide using this complex proceeded with good molecular weight control and gave relatively narrow molecular weight distribution polylactide, even at catalyst loadings of <0.1% that yielded M(n) as high as 130 kg mol(-)(1). The effect of impurities on the molecular weight of the product polymers was accounted for using a simple model. Detailed kinetic studies of the polymerization reaction enabled integral and nonintegral orders in L(1)ZnOEt to be distinguished and the empirical rate law to be elucidated, -d[LA]/dt = k(p)[L(1)ZnOEt][LA]. These studies also showed that L(1)ZnOEt polymerizes lactide at a rate faster than any other Zn-containing system reported previously. This work provides important mechanistic information pertaining to the polymerization of lactide and other cyclic esters by discrete metal alkoxide complexes.

Highly active zinc catalyst for the controlled polymerization of lactide.

Lactide Polymerization with Chiral β-Diketiminate Zinc Complexes

Ion pairs of the type Cpx2ZrMe+···A- containing various ansa-zirconocene methyl cations in contact with Me-B(C6F5)3- or B(C6F5)4- anions have been studied with regard to their anion exchange kineti...

Anion Exchange in Alkyl−Zirconocene Borate Ion Pairs. Are Solvated Alkyl−Zirconocene Cations Relevant Intermediates?

Ligands in which multiple metal-binding domains are linked by a metal-containing moiety rather than a conventional organic group are described as “expanded ligands”. The use of 4,4′-difunctionalised {Ru(tpy)2} units provides a linear spacer between metal-binding domains and we have extended this motif to expanded ligands containing two carboxylic acid metal-binding domains. In this paper, we describe the synthesis and structural characterisation of ruthenium(II) complexes of 2,2′:6′,2″-terpyridine-4′-carboxylic acid and 4′-carboxyphenyl-2,2′:6′,2″-terpyridine. The ability of the ruthenium(II) centre to charge compensate deprotonation of the carboxylic acid leads to Zwitterionic complexes and three representative compounds have been structurally characterised.

Expanded ligands: bis(2,2′:6′,2″-terpyridine carboxylic acid)ruthenium(II) complexes as metallosupramolecular analogues of dicarboxylic acids

Displacement of H3CB(C6F5)3- Anions from Zirconocene Methyl Cations by Neutral Ligand Molecules: Equilibria, Kinetics, and Mechanisms

Copper(II) pyridyliminoarylsulfonate complexes with chloride or triflate counteranions were employed in Chan–Evans–Lam (CEL) couplings of N-nucleophiles and arylboronic acids. The complexes avoided typical side reactions in CEL couplings, and an excess of boronic acid was not required. Water was tolerated, and addition of neither base nor other additives was necessary. Primary amines, acyclic and cyclic secondary amines, anilines, aminophenol, imidazole, pyrazole, and phenyltetrazole can be quantitatively arylated at either 25 or 50 °C with 2.5 mol % of the catalyst. Reaction kinetics were investigated in detail. Kinetic and spectroscopic studies provide evidence for the formation of unproductive copper–substrate complexes. Formation of an aniline–phenylboronic acid adduct was responsible for the zero-order dependence of reaction rates on phenylboronic acid concentration. Kinetic evidence indicates that the order of reaction steps is transmetalation, nucleophile coordination, and oxidation. Couplings perf...

Frank Schaper

Papers

Lactide Polymerization with Chiral β-Diketiminate Zinc Complexes

Anion Exchange in Alkyl−Zirconocene Borate Ion Pairs. Are Solvated Alkyl−Zirconocene Cations Relevant Intermediates?

Expanded ligands: bis(2,2′:6′,2″-terpyridine carboxylic acid)ruthenium(II) complexes as metallosupramolecular analogues of dicarboxylic acids

Displacement of H3CB(C6F5)3- Anions from Zirconocene Methyl Cations by Neutral Ligand Molecules: Equilibria, Kinetics, and Mechanisms

Chan–Evans–Lam Couplings with Copper Iminoarylsulfonate Complexes: Scope and Mechanism