A RhIII–N-heterocyclic carbene complex from metal–metal singly bonded [RhII −RhII] precursor

Metal–metal singly bonded [Rh₂(CO)₄(acac)₂][OTf]₂ (1) has been synthesized and characterized by spectroscopic and analytical techniques. A density functional theory (DFT) optimized structure has been computed for the unbridged centro-symmetric structure. Reaction of 1 with PIN.HBr results in the [Rh(PIN)₂(H₂O)Br][OTf]₂ (2) in high yield. The reaction involves metal-oxidation from RhII to RhIII accompanied by the metal–metal bond cleavage. The X-ray structure of 2 has been determined which reveals the incorporation of two N-heterocyclic carbene (NHC) ligands to each rhodium. This work demonstrates the general utility of the metal–metal bonded compounds for the easy synthesis of metal-NHC compounds.This work was financially supported by the Department of Science and Technology (DST), India. J K B thanks DST for the Swarnajayanti Fellowship. SD thanks DST, India and AS thanks University Grants Commission (UGC), India for fellowships

Facile and reversible double dearomatization of pyridines in non-phosphine MnI complexes with N,S-donor pyridinophane ligand

Single and double dearomatization of pyridine rings was observed in Mn(I) complexes with an N2S2 pyridinophane ligand via deprotonation of one or two CH2 arms, respectively. In contrast to other N,S-donor pincer-like systems, the dearomatized (N2S2)Mn species were found to be stable, with the dearomatization being reversible

Single and double deprotonation/dearomatization of the N,S-donor pyridinophane ligand in ruthenium complexes

We report a series of ruthenium complexes with a tetradentate N,S-donor ligand, 2,11-dithia[3.3](2,6)pyridinophane (N2S2), that undergo single and double deprotonation in the presence of a base leading to the deprotonation of one or both pyridine rings. Both singly and doubly deprotonated complexes were structurally characterized by single-crystal X-ray diffraction. The NMR spectra are indicative of the dearomatization of one or both pyridine rings upon the deprotonation of the CH2–S arm, similar to the dearomatization of phosphine-containing pincer ligands. The deprotonated (N2S2)Ru complexes did not show appreciable catalytic or stoichiometric reactivity in transfer hydrogenation, hydrogenation and dehydrogenation of alcohols, and attempted activation of H2, CO2, and other substrates. Such a lack of reactivity is likely due to the low stability of the deprotonated species as evident from the structural characterization of one of the decomposition products in which shrinkage of the macrocyclic ring occurs via picolyl arm migration.journal articl

Aryl–X Bond-Forming Reductive Elimination from High-Valent Mn–Aryl Complexes

C–X bond reductive elimination and oxidative addition are key steps in many catalytic cycles for C–H functionalization catalyzed by precious metals; however, engaging first row transition metals in these overall 2e– processes remains a challenge. Although high-valent Mn aryl species have been implicated in Mn-catalyzed C–H functionalization, the nature and reactivity of such species remain unelucidated. In this work, we report rare examples of stable, cyclometalated monoaryl MnIII complexes obtained through clean oxidative addition of Ar–Br to MnI(CO)5Br. These isolated MnIII–Ar complexes undergo unprecedented 2e– reductive elimination of the Ar–X (X = Br, I, and CN) bond and MnII induced by 1e– oxidation, presumably via transient reactive MnIV species. Mechanistic studies suggest a nonradical pathway

Bulky, spherical, and fluorinated anion BAr<SUP>F</SUP> induces 'on-water' activity of silver salt for the hydration of terminal alkynes

AgBAr<SUP>F</SUP> displays remarkable 'on-water' activity for catalytic hydration of terminal alkynes although it is ineffective in common organic solvents. Liquid alkynes do not require additive or co-solvent whereas a small amount of ethyl acetate triggers quantitative conversions for solid alkynes

Ferrocene-appended anionic N-heterocyclic carbene and its complex with silver(I): Synthesis, structure and catalytic evaluation

1072-1077A binuclear Ag(I) complex (1) bridged by two anionic N-heterocyclic carbene (NHC) ligands <span style="mso-ansi-language: DE;mso-bidi-font-weight:bold" lang="DE">ferrocenoyl(1-mesityl-imidazol-2-ylidine-3-yl)amide is synthesized. X-ray structure reveals a [Ag<span style="mso-fareast-font-family: " ms="" mincho";mso-ansi-language:de;mso-fareast-language:ja"="" lang="DE">···Ag] core spanned by two ligands, each bridging two metals through carbene carbon and amido nitrogen. The neutral complex (<b style="mso-bidi-font-weight: normal">1) is highly soluble in a variety of organic solvents and is thermally stable. Complex (1) efficiently catalyses aniline-mediated synthesis of substituted quinolines from 2-aminobenzaldehyde and terminal alkynes. </span

Amide synthesis from alcohols and amines catalyzed by a Ru<SUP>II</SUP>–N-heterocyclic carbene (NHC)–carbonyl complex

Treatment of [Ru2(CO)4(CH3CN)6](BF4)2 with 3-methyl-1-(pyridin-2-yl)-imidazolium bromide in the presence of tetrabutylammonium bromide at room temperature in dichloromethane affords a RuII–N-heterocyclic carbene–carbonyl complex [Ru(py-NHC)(CO)2Br2] (1). Catalyst 1 displays diverse substrate scope for phosphine-free acceptorless coupling between alcohols and amines to amides at low catalyst loading. A RuII-dihydride/Ru0 sequence is proposed in the catalytic cycle

A highly efficient catalyst for selective oxidative scission of olefins to aldehydes: abnormal-NHC–Ru(II) complex in oxidation chemistry

The utility and selectivity of the catalyst [Ru(COD)(L<SUP>1</SUP>)Br<SUB>2</SUB>] (1) bearing a fused &#960;-conjugated imidazo[1,2-a][1,8]naphthyridine-based abnormal N-heterocyclic carbene ligand L<SUP>1</SUP> is demonstrated toward selective oxidation of C&#9552;C bonds to aldehydes and C&#8801;C bonds to &#945;-diketones in an EtOAc/CH<SUB>3</SUB>CN/H<SUB>2</SUB>O solvent mixture at room temperature using a wide range of substrates, including highly functionalized sugar- and amino acid-derived compounds

C–C Bond Elimination from High-Valent Mn Aryl Complexes

Manganese complexes have been considered as a cheap and readily available alternative to commonly used precious metal catalysts in C–C bond coupling reactions. Although high-valent Mn aryl intermediates have been proposed in such reactions, a mechanistic understanding of possible organometallic intermediates in Mn-mediated C–C coupling is still lacking due to their high reactivity. We report the synthesis of stable, isolable Mn(III) aryl complexes obtained by oxidative addition of aryl bromide or aryl chloride. These complexes react with a range of organometallic alkylating or arylating reagents (alkyl and aryl Grignard reagents, MeLi, ZnMe2) to undergo C(sp2)–C(sp3) or C(sp2)–C(sp2) bond coupling, and a preliminary catalytic system could be demonstrated. The reagent scope and yield of the C(sp2)–C(sp3) coupled product can further be increased by addition of TEMPO as an oxidant, generating alkyl radicals