LongLarf

Abstract

Bis(phosphinite) pincer platinum hydride complexes, [2,6‐(R₂PO)₂C₆H₃]PtH (R=^tBu, ⁱPr), were synthesized, characterized and applied to the hydrosilylation of aldehydes and ketones. NMR study and single crystal X‐ray diffraction analysis indicated that the hydrides in these two platinum complexes are comparatively less hydridic: down‐field ¹H NMR resonances (0.71 and 0.98 ppm) and weak Pt−H interactions were observed. Both the platinum complexes were found to be good catalysts for the hydrosilylation of aldehydes and ketones with phenylsilane. The corresponding alcohols were isolated in good to excellent yields following basic hydrolysis of the resultant hydrosilylation products and turnover frequencies (TOFs) up to 3200 h⁻¹ were achieved at 60 °C in toluene, which are much higher than those of the hydrosilylation catalysed by the corresponding nickel pincer hydride complexes. A possible mechanism for the present hydrosilylation process was discussed.

Abstract

Unnatural amino acids (UAAs) are key building blocks with widespread application across several scientific fields. Therefore, it is highly attractive to develop straightforward and simple methodologies capable of granting quick access to these species. Herein we report a light‐mediated protocol for the synthesis of UAA via radical decarboxylative processes. This methodology, which employs readily available and abundant starting materials – such as carboxylic and α‐keto acids – proceeds under very mild reaction conditions and shows a high functional group tolerance. In addition, the products of the radical reaction can be readily derivatized to grant rapid access to complex UAAs.

Alkylation with ruthenium: Eight new Ru pincer complexes were prepared by introduction of C,N‐bound phenyl heterocycle ligands. These complexes were applied as catalysts in the α‐alkylation of ketones with alcohols through hydrogen autotransfer. Here, superior yields in comparison to [RuHCl(CO)(HN(CH₂CH₂PPh₂)₂)] (Ru‐MACHO) were achieved and 21 different alkylated ketones were synthesized in up to 97 % yield. Moreover, investigations regarding the catalyst species present during the reaction were conducted.

Abstract

Ruthenium PNP pincer complexes bearing supplementary cyclometalated C,N‐bound ligands have been prepared and fully characterized for the first time. By replacing CO and H⁻ as ancillary ligands in such complexes, additional electronic and steric modifications of this topical class of catalysts are possible. The advantages of the new catalysts are demonstrated in the general α‐alkylation of ketones with alcohols following a hydrogen autotransfer protocol. Herein, various aliphatic and benzylic alcohols were applied as green alkylating agents for ketones bearing aromatic, heteroaromatic or aliphatic substituents as well as cyclic ones. Mechanistic investigations revealed that during catalysis, Ru carboxylate complexes are predominantly formed whereas neither the PNP nor the CN ligand are released from the catalyst in significant amounts.

Hu and Ruckenstein state that our findings were overclaimed and not new, despite our presentation of evidence for the Nanocatalysts on Single Crystal Edges (NOSCE) mechanism. Their arguments do not take into account fundamental differences between our Ni-Mo/MgO catalyst and their NiO/MgO preparations.

Song et al. (Reports, 14 February 2020, p. 777) ignore the reported efficient Ni/MgO solid-solution catalysts and overstate the novelty and importance of the Mo-doped Ni/MgO catalysts for the dry reforming of methane. We show that the Ni/MgO solid-solution catalyst that we reported in 1995, which is efficient and stable for the dry reforming, is superior to the Mo-doped Ni/MgO catalyst.

A highly efficient method for protein functionalization with commonly used bioorthogonal motifs for Diels–Alder cycloaddition with inverse electron demand (DA_inv) is presented. This technology enables fast and routine access to tailored and hitherto inaccessible protein chimeras.

Abstract

Bioorthogonal chemistry holds great potential to generate difficult‐to‐access protein–protein conjugate architectures. Current applications are hampered by challenging protein expression systems, slow conjugation chemistry, use of undesirable catalysts, or often do not result in quantitative product formation. Here we present a highly efficient technology for protein functionalization with commonly used bioorthogonal motifs for Diels–Alder cycloaddition with inverse electron demand (DA_inv). With the aim of precisely generating branched protein chimeras, we systematically assessed the reactivity, stability and side product formation of various bioorthogonal chemistries directly at the protein level. We demonstrate the efficiency and versatility of our conjugation platform using different functional proteins and the therapeutic antibody trastuzumab. This technology enables fast and routine access to tailored and hitherto inaccessible protein chimeras useful for a variety of scientific disciplines. We expect our work to substantially enhance antibody applications such as immunodetection and protein toxin‐based targeted cancer therapies.

The isolation and characterization of the zwitterionic intermediate in 1,1‐carboboration reactions is reported. The highly reactive zwitterionic intermediates are generated from tris(pentafluorophenyl)borane and alkynes under reaction conditions of 1,1‐carboboration.

Abstract

The reaction of a Lewis acidic borane with an alkyne is a key step in a diverse range of main group transformations. Alkyne 1,1‐carboboration, the Wrackmeyer reaction, is an archetypal transformation of this kind. 1,1‐Carboboration has been proposed to proceed through a zwitterionic intermediate. We report the isolation and spectroscopic, structural and computational characterization of the zwitterionic intermediates generated by reaction of B(C₆F₅)₃ with alkynes. The stepwise reactivity of the zwitterion provides new mechanistic insight for 1,1‐carboboration and wider B(C₆F₅)₃ catalysis. Making use of intramolecular stabilization by a ferrocene substituent, we have characterized the zwitterionic intermediate in the solid state and diverted reactivity towards alkyne cyclotrimerization.

The long and the short of it : An efficient approach has been established to separate homogeneous, triazole‐linked ubiquitin (Ub) chains. Affinity‐based proteomic profiling allowed the identification of length‐selective interaction partners of K27‐, K29‐, and K33‐linked chains, thereby showing the implications of chain length on Ub chain recognition.

Abstract

The attachment of ubiquitin (Ub) chains of various length to proteins is a prevalent posttranslational modification in eukaryotes. The fate of a modified protein is determined by Ub‐binding proteins (UBPs), which interact with Ub chains in a linkage‐selective manner. However, the impact and functional consequences of chain length on the binding selectivity of UBPs remain mostly elusive. We have generated Ub chains of defined length and linkage by using click chemistry and GELFrEE fractionation. These defined polymers were used in affinity‐based enrichment assays to identify length‐ and linkage‐selective interaction partners on a proteome‐wide scale. For the first time, it is revealed that the length of a Ub chain generally has a major impact on its ability to be selectively recognized by UBPs.

Green light! For the first time, a titanium complex, Cp₂TiCl₂, is used in photoredox catalysis. Irradiation with green light enables an efficient catalytic radical chemistry with epoxides under very mild conditions and with reagent control.

Abstract

Irradiation of Cp₂TiCl₂ with green light leads to electronically excited [Cp₂TiCl₂]*. This complex constitutes an efficient photoredox catalyst for the reduction of epoxides and for 5‐exo cyclizations of suitably unsaturated epoxides. To the best of our knowledge, our system is the first example of a molecular titanium photoredox catalyst.

I mean defunct . Combinations of the boron Lewis acid B(C₆F₅)₃ and hydrosilanes enable the reductive cleavage ofC−N bonds in various, mainly benzylic amines and heterocumulenes. By this, these functionalized substrates can be converted into the corresponding hydrocarbons in moderate to good yields.

Abstract

The strong boron Lewis acid tris(pentafluorophenyl)borane B(C₆F₅)₃ is known to catalyze the dehydrogenative coupling of certain amines and hydrosilanes at elevated temperatures. At higher temperature, the dehydrogenation pathway competes with cleavage of the C−N bond and defunctionalization is obtained. This can be turned into a useful methodology for the transition‐metal‐free reductive deamination of a broad range of amines as well as heterocumulenes such as an isocyanate and an isothiocyanate.