Unusual Kinetics Induced by Ligands in Rhodium(III)-Catalyzed Dehydrogenative Olefination Reactions.

In this study, we investigate the effects of ligands on C-H activation during rhodium(III)-catalyzed C-H bond olefination reactions using well-defined [CpXRhIII] catalytic systems with three representative CpX (Cp (η5-C5H5), CpCF3 (η5-C5Me4CF3), and Cp* (η5-C5Me5)) ligands. Our results demonstrate that C-H activation as the rate-limiting step is significantly influenced by the steric properties of the CpX ligands. Moreover, we observe a dramatic acceleration of the simple [CpRhIII]-catalyzed C-H olefination reaction with acid coproducts such as HOAc, implying an autocatalytic C-H activation process.

Cyclometalated Platinum(II) Metallomesogens Based on Half-Disc-Shaped ß-Diketonate Ligands with Hexacatenar: Crystal Structures, Mesophase Properties, and Semiconductor Devices.

A series of new half-disc-shaped platinum(II) complexes [Pt(ppy)(ALn-6OCnH2n+1)] (Pt-An), [Pt(ppyF)(ALn-6OCnH2n+1)] (Pt-Bn), and [Pt(ppyCF3)(ALn-6OCnH2n+1)] (Pt-Cn) (ALn-6OCnH2n+1 = 1,3-bis(3,4,5-trialkoxyphenyl)propane-1,3-dionato; n = 1, 6, 12) with concise structures have been designed and synthesized, in which 2-phenylpyridine (ppy) derivatives were used as cyclometalated ligands and hexacatenar ß-diketonate derivatives ALn-6OCnH2n+1 as auxiliary ligands. The single-crystal data of the methoxy diketonate analogues Pt-A1, Pt-B1, and Pt-C1 indicate that they all display excellent square planarity. These platinum(II) complexes show a certain emission tunability (ranging from λ = 506-535 nm) by the introduction of fluorine or trifluoromethyl into ppy. Thermal studies reveal that the fluorine-substituted complexes are liquid crystals but the trifluoromethyl-substituted complexes are not. The platinum(II) complexes Pt-A12, Pt-B6, and Pt-B12 can form a hexagonal columnar mesophase via intermolecular π-π interactions. In addition, compared to the reported platinum(II) metallomesogens, Pt-A12 and Pt-B12 exhibit improved ambipolar carrier mobility behaviors in semiconductor devices at the liquid crystal states.

Extension of the Simmons-Smith reaction to metal-carbynes: efficient synthesis of metallacyclopropenes with σ-aromaticity.

The Simmons-Smith reaction offers a direct route for conversion of an alkene into a cyclopropane with a zinc carbenoid as the active intermediate. Zinc carbenoids, however, have never delivered a methylene unit to substrates with metal-carbon multiple bonds. Herein, we describe this type of reaction and the construction of three-membered rings has now been applied in organometallic systems by combining classical zinc carbenoid reagents with a range of structurally and electronically diverse metal carbynes. A variety of metallacyclopropene derivatives prepared in this way represent rare examples with σ-aromaticity in an unsaturated three-membered ring. The structures of such products are supported by experimental observations and theoretical calculations.

Scalable Rhodium(III)-Catalyzed Aryl C-H Phosphorylation Enabled by Anodic Oxidation Induced Reductive Elimination.

Transition metal catalyzed C-H phosphorylation remains an unsolved challenge. Reported methods are generally limited in scope and require stoichiometric silver salts as oxidants. Reported here is an electrochemically driven RhIII -catalyzed aryl C-H phosphorylation reaction that proceeds through H2 evolution, obviating the need for stoichiometric metal oxidants. The method is compatible with a variety of aryl C-H and P-H coupling partners and particularly useful for synthesizing triarylphosphine oxides from diarylphosphine oxides, which are often difficult coupling partners for transition metal catalyzed C-H phosphorylation reactions. Experimental results suggest that the mechanism responsible for the C-P bond formation involves an oxidation-induced reductive elimination process.

Trisulfur radical anion-triggered stitching thienannulation: rapid access to largely π-extended thienoacenes.

Largely π-extended rylene diimide-fused thienoacenes, a new family of fully fused electron donor-acceptor (D-A) molecules, have been readily synthesized by a novel trisulfur radical anion (S3˙-)-triggered stitching thienannulation strategy. The ladder-type fused thiophene cores are constructed in a stitching manner through multiple carbon-sulfur bond formation between acetylenic rylene dyes and S3˙-. A detailed mechanistic study of these stitching thienannulations unveiled the multiple reactivities of S3˙-. Physical properties of the newly formed D-A, A-D-A, and D-A-D type thienoacenes have also been investigated, which revealed their precisely controllable electronic properties.

Isolation of an Eleven-Atom Polydentate Carbon-Chain Chelate Obtained by Cycloaddition of a Cyclic Osmium Carbyne with an Alkyne.

Carbon ligands have long played an important role in organometallic chemistry. However, previous examples of all-carbon chelating ligands are limited. Herein, we present a novel complex with an eleven-atom carbon chain as a polydentate chelating ligand. This species was formed by the [2+2+2] cycloaddition reaction of two equivalents of an alkyne with an osmapentalyne that contains the smallest carbyne bond angle (127.9°) ever observed. Density functional calculations revealed that electron-donating groups play a key role in the stabilization of this polydentate carbon-chain chelate. This process is also the first [2+2+2] cycloaddition reaction of an alkyne with a late-transition-metal carbyne complex. This study not only enriches the chemistry of polydentate carbon-chain chelates, but also deepens our understanding of the chelating ability of carbon ligands.

Efficient endo Cycloisomerization of Terminal Alkynols Catalyzed by a New Ruthenium Complex with 8-(Diphenylphosphino)quinoline Ligand and Mechanistic Investigation.

Several new ruthenium complexes supported by the P,N-donor ligand 8-(diphenylphosphino)quinoline (DPPQ) were synthesized, including [RuCl2 (DPPQ)2 ] (1), [Ru(µ-Cl)(DPPQ)2 ]2 (BPh4 )2 (2), and [RuCl(DPPQ)2 Py](BF4 ) (3). Complex 2, with only 1 mol % loading, was found to be catalytically active for the endo cycloisomerization of various terminal alkynols to endo-cyclic enol ethers in moderate to excellent yields. In particular, the 7- and 8-endo heterocyclization can be achieved efficiently to give the seven-membered 3-benzoxepine and eight-membered 3-benzo[d]oxocine derivatives. The stoichiometric reactions of 2 with various alkynol substrates have been carried out to investigate the mechanism, which led to a series of seven-, six-, and five-membered oxacyclocarbene ruthenium complexes including [RuCl(DPPQ)2 {=CCH2 C6 H4 CH2 CH2 O}](BPh4 ) (12) and [RuCl(DPPQ)2 {=CCH2 (CH2 )n CH2 O}](BPh4 ) (n=3, 12'; n=2, 13; n=1, 14). The quantitative transformation of oxacyclocarbene 12 into catalyst 2 and 3-benzoxepine 5 a as well as the efficient catalytic activity of 12 for the endo-cyclization of 2-(2-ethynylphenyl)ethanol (4 a) demonstrated that 12 is a key intermediate involved in the catalytic cycle. Moreover, comparative studies on the modeling reactions and catalytic activity of the series of oxacyclocarbene complexes indicated that the different catalytic activity of 2 for the endo-cycloisomerization of different types of alkynols can be related to the reactivity of the respective ruthenium oxacyclocarbene intermediates.

Rhodium-Catalyzed ß-Selective Oxidative Heck-Type Coupling of Vinyl Acetate via C-H Activation.

An efficient Rh(III)-catalyzed direct ortho-C-H olefination of acetanilides with vinyl acetate was developed. This protocol provides a straightforward pathway to a series of (E)-2-acetamidostyryl acetates, giving access to indole derivatives following a simple hydrolysis/cyclization process.

Synthesis of α-Aminonaphthalenes via Copper-Catalyzed Aminobenzannulation of (o-Alkynyl)arylketones with Amines.

A copper-catalyzed aminobenzannulation of (o-alkynyl)arylketones with amines has been developed. This method features the use of a cheap copper catalyst, the facile annulation involving various amines, and the good functional group tolerance.

Correction: Silver-mediated direct phosphorylation of benzothiazoles and thiazoles with diarylphosphine oxides.

Correction for 'Silver-mediated direct phosphorylation of benzothiazoles and thiazoles with diarylphosphine oxides' by Hui-Jun Zhang et al., Chem. Commun., 2015, 51, 3450-3453.

Copper-Catalyzed Direct C2-Benzylation of Indoles with Alkylarenes.

The copper-catalyzed regioselective cross-dehydrogenative coupling of N-pyrimidylindoles with benzylic C(sp(3))-H bonds has been developed. Di-tert-butyl peroxide was employed as a mild oxidant, and benzaldehyde proved to be an effective additive. This reaction provides a direct and pratical route to a variety of 2-benzylindoles.

Highly Active Gold(I)-Silver(I) Oxo Cluster Activating sp³ C-H Bonds of Methyl Ketones under Mild Conditions.

The activation of C(sp(3))-H bonds is challenging, due to their high bond dissociation energy, low proton acidity, and highly nonpolar character. Herein we report a unique gold(I)-silver(I) oxo cluster protected by hemilabile phosphine ligands [OAu3Ag3(PPhpy2)3](BF4)4 (1), which can activate C(sp(3))-H bonds under mild conditions for a broad scope of methyl ketones (RCOCH3, R = methyl, phenyl, 2-methylphenyl, 2-aminophenyl, 2-hydroxylphenyl, 2-pyridyl, 2-thiazolyl, tert-butyl, ethyl, isopropyl). Activation happens via triple deprotonation of the methyl group, leading to formation of heterometallic Au(I)-Ag(I) clusters with formula RCOCAu4Ag4(PPhpy2)4(BF4)5 (PPhpy2 = bis(2-pyridyl)phenylphosphine). Cluster 1 can be generated in situ via the reaction of [OAu3Ag(PPhpy2)3](BF4)2 with 2 equiv of AgBF4. The oxo ion and the metal centers are found to be essential in the cleavage of sp(3) C-H bonds of methyl ketones. Interestingly, cluster 1 selectively activates the C-H bonds in -CH3 rather than the N-H bonds in -NH2 or the O-H bond in -OH which is traditionally thought to be more reactive than C-H bonds. Control experiments with butanone, 3-methylbutanone, and cyclopentanone as substrates show that the auration of the C-H bond of the terminal methyl group is preferred over secondary or tertiary sp(3) C-H bonds; in other words, the C-H bond activation is influenced by steric effect. This work highlights the powerful reactivity of metal clusters toward C-H activation and sheds new light on gold(I)-mediated catalysis.

Rh/Cu-catalyzed multiple C-H, C-C, and C-N bond cleavage: facile synthesis of pyrido[2,1-a]indoles from 1-(pyridin-2-yl)-1H-indoles and γ-substituted propargyl alcohols.

An unusual Rh/Cu-catalyzed synthesis of pyrido[2,1-a]indoles starting from 1-(pyridin-2-yl)-1H-indoles and γ-substituted propargyl alcohols was presented. The multi-step cascade transformations formally involve the cleavage of two C-H, three C-C, and one C-N bonds with concomitant construction of two C-H, four C-C, and one C-N bonds with excellent chemoselectivity in one-pot reaction.

Silver-mediated direct phosphorylation of benzothiazoles and thiazoles with diarylphosphine oxides.

A silver nitrate-mediated, efficient phosphorylation of benzothiazoles and thiazoles with diarylphosphine oxides was developed. This process provides a convenient route for the synthesis of a variety of 2-diarylphosphoryl benzothiazoles and thiazoles which are promising precursors of a series of hemilabile P,N-ligands with small bite angles.

Rh(III)-Catalyzed Oxidative Coupling of Benzoic Acids with Geminal-Substituted Vinyl Acetates: Synthesis of 3-Substituted Isocoumarins.

The Rh(III)-catalyzed C-H activation initiated cyclization of benzoic acids with electron-rich geminal-substituted vinyl acetates was described. The reaction was employed to prepare a range of 3-aryl and 3-alkyl substituted isocoumarins selectively.

A half-sandwich 1,2-azaborolyl ruthenium complex: synthesis, characterization, and evaluation of its catalytic activities.

A half-sandwich 1,2-azaborolyl (Ab) ruthenium complex, (Ab-C≡CPh)RuCl(PPh3)2 (1), has been synthesized by treating RuCl2(PPh3)3 with lithium 1,2-azaborolide L-1, or by treating either RuCl2(PPh3)3 or RuHCl(PPh3)3 directly with 1,2-azaborole LH-1. It is evaluated as a suitable precatalyst in [2 + 2] cycloadditions of norbornene derivatives with DMAD and in atom transfer radical additions of halogenated compounds with olefins.

From osmium hydrido vinylidene to osmacycles: the key role of osmabutadiene intermediates.

Osmium hydrido vinylidene 1 shows diverse cyclization reactivity with activated terminal alkynes. Treatment of 1 with HC≡CCOR' (R'=OEt and Me) gave osmafurans 3a and 3b via osmium alkenyl/vinylidenes 2a and 2b. In addition, 1 reacted with HC≡CCH(OH)C≡CH to yield osmabenzene 4, in which the alkynol acted as a C(5) fragment to cyclize with 1. Mechanistic analysis indicates that these reactions and the previous formal [3+3] cycloadditions between 1 and HC≡CCH(OH)R (R=Ph, Et, and vinyl) or HC≡CCH(OEt)(2) all go through similar osmabutadiene intermediates. Subsequently, the intermediates either took a "coordination and cyclization" process or a "carbon-carbon coupling" path to cyclization, depending on the coordination ability of substituents on the terminal alkenyl carbon atom.

A rhodamine-deoxylactam based sensor for chromo-fluorogenic detection of nerve agent simulant.

N-(rhodamine B)-deoxylactam-5-amino-1-pentanol (dRB-APOH) was designed and prepared as the chromo-fluorogenic sensor for detection of a nerve agent simulant via analyte triggered tandem phosphorylation and opening of the intramolecular deoxylactam. The successful detection of diethyl chlorophosphate suggests the utility of rhodamine-deoxylactams as the chromo-fluorogenic signal reporting platform for design of sensors targeting reactive chemical species via various chemistries.

Electrophilic substitution reactions of metallabenzynes.

The electrophilic substitution reactions of metallabenzynes Os(≡CC(R)═C(CH(3))C(R)═CH)Cl(2)(PPh(3))(2) (R = SiMe(3), H) were studied. These metallabenzynes react with electrophilic reagents, including Br(2), NO(2)BF(4), NOBF(4), HCl/H(2)O(2), and AlCl(3)/H(2)O(2) to afford the corresponding bromination, nitration, nitrosation, and chlorination products. The reactions usually occur at the C2 and C4 positions of the metallacycle. These observations support the notion that metallabenzynes exhibit aromatic properties.