Synthesis of Backbone P-Functionalized Imidazol-2-ylidene Complexes: En Route to Novel Functional Ionic Liquids

Gold complexes with remote-substituted amino N-heterocyclic carbenes

The 4-RN-1,3-Ar₂-imidazolium salt, R = iPr, tBu, Ar = Mes, Dipp, Mes = mesityl, Dipp = 2,6-bis-diisopropyl-phenyl was metalated by Au^I at the C2-, C5- and 4-RN positions depending on the reactants and conditions employed; a rare direct rearrangement of a Au^I aminide to an abnormal imidazol-5-ylidene Au^I complex was also observed and based on a DFT study it may involve TfO^- facilitated H⁺ transfer.

One-Step Access to Heteroatom-Functionalized Imidazol(in)ium Salts

Imidazolium salts have ubiquitous applications in energy research, catalysis, materials and medicinal sciences. Here, we report a new strategy for the synthesis of diverse heteroatom-functionalized imidazolium and imidazolinium salts from easily available 1,4-diaza-1,3-butadienes in one step. The strategy relies on a discovered family of unprecedented nucleophilic addition/cyclization reactions with trialkyl orthoformates and heteroatomic nucleophiles. To probe general areas of application, synthesized N-heterocyclic carbene (NHC) precursors were feasible for direct metallation to give functionalized M/carbene complexes (M = Pd, Ni, Cu, Ag, Au), which were isolated in individual form. The utility of chloromethyl function for the postmodification of the synthesized salts and Pd/carbene complexes was demonstrated. The obtained complexes and imidazolium salts demonstrated good activities in Pd- or Ni-catalyzed model cross-coupling and C-H activation reactions.

Generation and reactivity of an elusive base-stabilised phosphinidene

Reduction of phosphorus dichloride 6, supported by the diaryloxyphenyl group (OCO) featuring two bulky phenoxy wingtips, by PMe₃, generates a reactive intermediate that behaves as a base-stabilized phosphinidene (OCO)P (5). Warming up a solution of this species in toluene to room temperature results in trimerization to give the isolable cyclic triphosphine [(OCO)P]₃, whereas in situ trapping with 2,3-dimethylbutadiene-1,3 afforded a 3,4-dimethylphospholene-3. Investigation of the reduction of 6 by the phosphine PMe₃ by NMR led to the observation of a persistent species between -10 °C and 10 °C. A DFT study of this process suggests that this compound cannot be the proposed phosphinidene 5, and is more likely the diphosphine (OCO)ClP-PCl(OCO) (12). Attempted reduction of 5 by the bulky carbene IPr resulted in unusual electrophilic substitution in the carbene olefin backbone by the chlorophosphinyl group.

New frontiers: 1,4-diphosphinines and P-bridged bis(NHCs)

This review describes synthetic concepts and breakthroughs in 1,4-diphosphinine and related P-bridged bis(NHCs) chemistry, covering the last four decades, starting from monocyclic 1,4-dihydro-1,4-diphosphinines in the early 80s to the most recent and promising achievements of tricyclic 1,4-dihydro-1,4-diphosphinines and tricyclic 1,4-diphosphinines. Theoretical aspects are presented for 1,4-dihydro- and 1,4-diphosphinines considering HOMO LUMO situations as well as the degree of aromaticity. Moreover, fundamental characteristics of analytical data of these compounds are highlighted with special focus on substituent effects, structural aspects and trends of electrophilicity. The two P-centers and the heterocyclic rings of 1,4-dihydro- and 1,4-diphosphinines constitute a broad platform for substitution, reduction/oxidation, alkylation, complexation and cycloaddition reactions, i.e., a comprehensive compilation of reactivity aspects is presented. Furthermore, very recent developments in the synthesis and reactivity of tricyclic PV/V- and PIII/III-bridged bis(imidazole-2-ylidenes) will be discussed together with new perspectives derived from an antiaromatic middle ring. In total, our intention is to show new frontiers, i.e., new synthetic paths, thus creating novel opportunities for potential applications in molecular and materials chemistry.

Diverse reactivity of carbenes and silylenes towards fluoropyridines

The reaction of IDipp with C5F5N led to functionalization of all three carbon atoms of the imidazole ring with HF2- as the counter-anion (1). Reactivity with 2,3,5,6-tetrafluoropyridine gives only C-F bond activation leaving C-H bonds intact (5b). The reaction of SIDipp with C5F5N in the presence of BF3 afforded the ring cleavage product (3). Analogous reactions with silylene led to oxidative addition at the Si(ii) center.

Recent Advances in Imidazoliumyl-Substituted Phosphorus Compounds

This review aims to highlight the recent developments in the chemistry of selected imidazoliumyl-substituted phosphorus compounds. The synthetic approaches for their preparation with phosphorus in various oxidation states and coordination environments are discussed. Their intriguing properties and versatile chemistry strongly depends on the bonding motif at the P atoms, which is given special focus.

N-Phosphine Oxide-Substituted Imidazolylidenes (PoxIms): Multifunctional Multipurpose Carbenes

This article discusses the concept of N-heterocyclic carbenes (NHCs) equipped with more than one functional moiety, which allows using these NHCs for multiple purposes. A pioneering example for such NHCs is N-phosphine oxide-substituted imidazolylidenes (PoxIms), and their synthesis and strategic use are highlighted. The utility of PoxIms by far exceeds the conventional use as multidentate ligands for metal complexes on account of the synergetic functions of the carbene and the N-phosphine oxide group(s).

Exploring the chemistry of backbone amino(chloro)phosphanyl-substituted imidazole-2-thiones

Backbone amino(chloro)phosphanyl-substituted imidazole-2-thiones were synthesized and their potential as starting material for backbone phosphaalkenyl substituted imidazole-2-thiones studied.

Post-coordination backbone functionalization of an imidazol-2-ylidene and its application to synthesize heteropolymetallic complexes incorporating the ambidentate IMesCO2−ligand

The C4-carboxylation of the archetypal IMes ligand was achieved directly on its complexed form for the first time, and the resulting ambidentate IMes^CO2−ligand was exploited for the formation of heteropolymetallic complexes.

Synthesis and reactions of C-phosphanylated thiazol-2-thiones

Regioselective synthesis of the P(iii) substituted thiazole-2-thione I is presented. Oxidation of I resulted in P(V) chalcogenide thiazole-2-thiones (E = O, S, Se). Desulfurization of I (E = O) using hydrogenperoxide led to the first C-phosphanoyl thiazolium salt II. Deprotonation of II and reaction with cyclooctadiene rhodium(i) chloride dimer yielded thiazole-2-ylidene rhodium(i) complex III.

Cationic 5-phosphonio-substituted N-heterocyclic carbenes

Cationic NHCs featuring a phosphonium moiety in the 5-position are prepared from the reaction of imidazolium salts with a tert. phosphane. They are used as ligands for the preparation of transition metal complexes, dehydrogenation reactions of prim. and sec. phosphanes and the preparation of a N-heterocyclic olefin (NHO).

From bis(imidazole-2-thion-4-yl)phosphane to a flexible P-bridged bis(NHC) ligand and its silver complex

Synthesis of the first P(v)-bridged bis(NHC) ligand 7 was achieved via deprotonation of P(v)-functionalized bis(imidazolium) salt 6, which was obtained via oxidative desulfurization of bis(imidazole-2-thion-4-yl)phosphane 2.