Several classes of nucleic acid analogs have been reported, but no synthetic informational polymer has yet proven responsive to selection pressures under enzyme-free conditions. Here, we introduce an oligomer family that efficiently self-assembles by means of reversible covalent anchoring of nucleobase recognition units onto simple oligo-dipeptide backbones [thioester peptide nucleic acids (tPNAs)] and undergoes dynamic sequence modification in response to changing templates in solution. The oligomers specifically self-pair with complementary tPNA strands and cross-pair with RNA and DNA in Watson-Crick fashion. Thus, tPNA combines base-pairing interactions with the side-chain functionalities of typical peptides and proteins. These characteristics might prove advantageous for the design or selection of catalytic constructs or biomaterials that are capable of dynamic sequence repair and adaptation.

Reactions of meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm) with Cu(I) species in the presence of NaBH4 afforded di- and tetranuclear copper hydride complexes, [Cu2(μ-H)(μ-dpmppm)2]X (1) and [Cu4(μ-H)2(μ4-H)(μ-dpmppm)2]X (2) (X=BF4, PF6). Complex 1 undergoes facile insertion of CO2 (1 atm) at room temperature, leading to a formate-bridged dicopper complex [Cu2(μ-HCOO)(dpmppm)2]X (3). The experimental and DFT theoretical studies clearly demonstrate that CO2 insertion into the Cu2(μ-H) unit occurred with the flexible dicopper platform. Complex 2 also undergoes CO2 insertion to give a formate-bridged complex, [Cu4(μ-HCOO)3(dpmppm)2]X, during which the square Cu4 framework opened up to a linear tetranuclear chain.

A tiara-like octanuclear palladium thiolate complex, [Pd(-SCH 2 CO 2 Me) 2 ] 8 that has a toroidal structure, was synthesized via reactions of either PdCl 2 with methyl thioglycolate/N,N-diisopropylethylamine (DIEA) (conventional method) or [PdCl 2 (MeCN) 2 ] with m-C 6 H 4 (CMe 2 SCH 2 CO 2 Me) 2 (alternative method). In the latter method, the tiara-like complex formed via the corresponding SCS-pincer complex and/or 1:1 PdCl 2 and ligand complexes. With respect to the platinum analogs, the alternative method efficiently produced the tiara-like octanuclear complex, [Pt(-SCH 2 CO 2 Me) 2 ] 8 , in high purity. Small molecules, such as CH 2 Cl 2 , ClCH 2 CH 2 Cl, CH 2 Br 2 , and CH 3 I, were accommodated in the inner voids of the tiara rings to form 1:1 inclusion complexes. These complexes are stabilized by weak CH···X hydrogen bonds (X = Cl or Br) between the methylene protons of four or eight axially positioned methoxycarbonylmethyl groups on the tiara rings and the halogen atoms of the guest molecules, as well as weak coordination of the halogen atoms to the transition-metal atoms.2

No abstract

Enamides are contained in many natural products such as salicylihalamide [1] and lobatamide, [2] and have recently been synthesized using transition-metal catalysts, as represented by a) the vinylation of amides, [3] b) the chelation-assisted coupling reaction of N-vinylamides with 1,3-butadiene, [4] c) the addition of amides to alkynes, [5] d) the oxidative amidation of alkenes, [6] and e) the isomerization of N-allylamides. [7] Dienamides are also important building blocks for preparing several alkaloids by the Diels-Alder reaction.[8] However, there are still few examples of transition-metal-mediated or -catalyzed synthesis of dienamides. [9] In considering potential new methods for the synthesis of enamides and dienamides, we have focused our efforts on ruthenium-catalyzed regio-and stereoselective codimerization reactions. Many examples of transition-metal-catalyzed codimerization reactions of alkenes with alkynes have been reported.[10] We also have already developed and reported the reactions of [2+2] cycloaddition [11] and linear codimerization reactions [12] of alkenes with alkynes. In sharp contrast, a codimerization reaction of "different alkenes" is still quite difficult except for hydrovinylation [13] and a challenging subject in modern organic and organometallic chemistry.[14]Herein we report zero-valent ruthenium-catalyzed codimerization reaction of different alkenes, that is, a codimerization reaction of N-vinylamides with alkenes as well as a cooligomerization reaction of N-vinylamides, acrylates, and ethylene, which offer novel and atom-economical methods for the synthesis of enamides with high regio-and stereoselectivity in one step. [15,16] As expected, the present catalyst system can be applied to the codimerization of N-vinylamides with alkynes, which enables the selective synthesis of dienamides.Treatment of N-methyl-N-vinylacetamide (1 a, 1.1 mmol) with ethyl acrylate (2 a, 1.0 mmol) in the presence of a catalytic amount of [Ru(h 6 -cot)(h 2 -dmfm) 2 ] (0.020 mmol; cot = 1,3,5-cyclooctatriene, dmfm = dimethyl fumarate) in N,N-dimethylacetamide (DMA, 3.0 mL) [14b, 17] at 160 8C for 3 h gave the linear codimer, ethyl 5-(N-methylacetylamino)-pent-4-enoate (3 a), in 90 % yield with 95 % E selectivity [Eq. (1) The reaction in Equation (1) required a temperature of over 150 8C for complete conversion of both substrates, and the best result was obtained at 160 8C (3 a, 90 %). However, at 170 8C, the reaction became sluggish, and the yield of 3 a decreased to 65 %.Several enamides were prepared by this method in good to high yields with high E selectivity [Eq. (2)]. Electrondeficient alkenes are suitable for this reaction; for example, codimerization of N-methyl-N-vinylacetamide (1 a) with ethyl vinyl ketone (2 c) or dimethyl maleate (2 d) gave 3 c and 3 d in respective yields of 70 % and 76 %. Although 2-norbornene (2 e) and ethylene (2 f) could also be used, the yields of the codimers, 3 e (exo only) and 3 f, were rather low. For the

A copper hydride cluster [Cu (μ-H) (μ-dppm) ](PF ) (dppm=bis(diphenylphosphino)methane) was prepared from reaction of [CuH(PPh )] with dppm in the presence of [Cu(CH CN) ]PF and exhibited fluxional behaviors in solution where the hydrides and the phosphines are scrambling around the trans-bicapped octahedral Cu framework. The Cu H complex showed facile reactivity with CO (1 atm, RT) to afford a tricopper complex, [Cu (μ-H)(μ-O CH)(μ-dppm) ]PF , which could be developed to unprecedented hydrosilylation of CO catalyzed by multinuclear CuH species under mild conditions.

No abstract

Hexanuclear copper hydride complexes, [Cu 6 (μ 3 -H) 2 (meso-L 4 ) 3 (RNC) 4 ](PF 6 ) 4 (R = t Bu (6a), Cy (6b)), were prepared by using a new linear tetraphosphine, meso-Ph 2 PCH 2 P(Ph)(CH 2 ) 4 P(Ph)-CH 2 PPh 2 (meso-L 4 ), and were converted into active catalysts of [Cu 2 (μ-O 2 CH)(meso-L 4 )(RNC) 2 ] + under the reaction conditions of formic acid dehydrogenation, where unsymmetric dinuclear copper sites supported by the tetradentate phosphine and isocyanide ligands were essential to demonstrate effective catalytic activity.