N-heterocyclic Carbene IPr Research Articles

A Ni0(cod)(dq) (COD: 1,5-cycloctadiene; DQ: duroquinone) complex as a catalyst precursor for oligothiophene and polythiophene synthesis.

Nickel-catalyzed syntheses of oligothiophene and polythiophene were carried out with Ni(cod)(dq) (COD: 1,5-cycloctadiene; DQ: duroquinone) as a catalyst precursor. Studies on the ligand exchange of Ni(cod)(dq) revealed that a high temperature was necessary to replace COD and DQ with PPh3 and N-heterocyclic carbene IPr. A coupling reaction of a metalated 3-hexylthiophene with 2-chloro-3-hexylthiophene employing Ni(cod)(dq) with IPr proceeded with a remarkably reduced amount of homocoupling byproduct. Polymerization of 2-chloro-3-hexylthiophene with Ni(cod)(dq)/DPPP also resulted in the reduction of the regioregularity defect.

Iron-Catalyzed Benzene Ring Expansion of α-Azido-N-phenylamides

AbstractNitrenoid-mediated C–H insertion and cycloaddition reactions are gaining increasing importance in modern organic synthesis. However, the nitrene-mediated benzene ring expansion, which constitutes a potent tool for breaking the benzene ring, has sparely been explored for synthetic purposes. Herein we report that nitrene cycloaddition to the benzene ring can be enabled intramolecularly by iron catalysis. By using FeCl2 and N-heterocyclic carbene SIPr·HCl as the catalyst, α-azido-N-phenylamides can be converted into 1,3-dihydro-2H-azepin-2-ones in good yields through a novel skeleton rearrangement. The rearrangement features a cascade of nitrene cycloaddition, C–N cleavage, water addition, and electrocyclic ring-opening. In the case that the N-phenyl ring is substituted with a methoxy group at the meta or para position, azepin-2-one-fused imidazolinones can also be obtained. The present reactions provide an effective method for benzene ring expansion as well as for the preparation of azepin-2-one compounds.

Iron-Catalyzed 1,4-Phenyl Migration/Ring Expansion of α-Azido N-Phenyl Amides.

Herein, we report a novel iron-catalyzed skeleton rearrangement of alkyl azides. Upon treatment with FeCl2 and N-heterocyclic carbene SIPr·HCl in the presence of H2O and Et3N, 2-azido-N,N-diphenylamides underwent 1,4-phenyl migration and ring expansion to give azepin-2-ones in good yield. The reaction proceeds via intramolecular nitrene cycloaddition followed by C-N cleavage, water addition, and electrocyclic ring opening.

Photoinduced Site-Selective C(sp3)-H Chlorination of Aliphatic Amides.

Herein, we report a new photochemical method for C(sp3)-H chlorination of amides which employs tert-butyl hypochlorite as the chlorinating agent and a household compact fluorescent lamp as the light source. The reaction proceeds via N-heterocyclic carbene SIPr·HCl-promoted N-H chlorination and subsequent photoinduced Hofmann-Löffler-Freytag chlorine atom transfer. The latter process is facilitated by (diacetoxyiodo)benzene. This protocol exhibits a broad scope and is suitable for site-selective chlorination of methyl hydrogen as well as methylene and methine hydrogen.

Iron-catalysed 1,2-aryl migration of tertiary azides.

1,2-Aryl migration of α,α-diaryl tertiary azides was achieved by using the catalytic system of FeCl2/N-heterocyclic carbene (NHC) SIPr·HCl. The reaction generated aniline products in good yields after one-pot reduction of the migration-resultant imines.

Facile Access to NaOC≡As and Its Use as an Arsenic Source To Form Germylidenylarsinidene Complexes.

A facile, one-pot synthesis of [Na(OC≡As)(dioxane)x ] (x=2.3-3.3) in 78 % yield is reported through the reaction of arsine gas with dimethylcarbonate in the presence of NaOt Bu and 1,4-dioxane. It has been employed for the synthesis of the first arsaketenyl-functionalized germylene [LGeAsCO] (2, L=CH[CMeN(Dipp)]2 ; Dipp=2,6-i Pr2 C6 H3 ) from the reaction with LGeCl (1). Upon exposure to ambient light, 2 undergoes CO elimination to form the 1,3-digerma-2,4-diarsacyclobutadiene [L2 Ge2 As2 ] (3), which contains a symmetric Ge2 As2 ring with ylide-like Ge=As bonds. Remarkably, the CO ligand located at the arsenic center of 2 can be exchanged with PPh3 or an N-heterocyclic carbene iPr NHC donor (iPr NHC=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) to afford the novel germylidenylarsinidene complexes [LGe-AsPPh3 ] (4) and [LGe-As(iPr NHC)] (5), respectively, demonstrating transition-metal-like ligand substitution at the arsinidene-like As atom. The formation of 2-5 and their electronic structures have been studied by DFT calculations.

Silylphosphido complexes of gold(I) coordinated with NHC ligands

The N-heterocyclic carbenes IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and iPr2-bimy (iPr2-bimy = 1,3-di-isopropylbenzimidazole-2-ylidene) were utilized as a basis for the preparation of four gold–silylphosphido complexes: [(IPr)AuP(Ph)SiMe3] (1), [(IPr)AuP(SiMe3)2] (2), [(iPr2-bimy)AuP(Ph)SiMe3] (3), and [(iPr2-bimy)AuP(SiMe3)2] (4). These complexes represent rare examples of terminally bonded Au–PR2 and the first examples where phosphorus retains reactive P-SiMe3 moieties. The reactivity of the P–Si bonds in 1 and 3 was explored via the addition of PhC(O)Cl. The products of these reactions were the formation of the phosphido-bridged [(IPrAu)2(μ-PPhC(O)Ph)][AuCl2] (5) and, in the case of the smaller N-heterocyclic carbenes, the tertiary phosphine PPh(C(O)Ph)2 (6) was isolated together with the known gold complex [(iPr2-bimy)AuCl]. Both reactions proceed via the elimination of ClSiMe3.

Aromatic C–H Borylation by Nickel Catalysis

Abstract The first nickel-catalyzed aromatic C–H borylation is described. In the presence of catalytic amounts of [Ni(cod)2], tricyclopentylphosphine, and CsF, benzene and indole derivatives can be borylated with B2pin2. The N-heterocyclic carbene IPr was also found to be an effective ligand. Kinetic isotope effect experiments showed that C–H cleavage is likely involved in the rate-determining step.

Metal-free dehydrogenation of amine–boranes by an N-heterocyclic carbene

The dehydrogenation of primary and secondary amine-boranes (RNH(2)·BH(3) and R(2)NH·BH(3); R = alkyl groups) was studied using the bulky N-heterocyclic carbene IPr (IPr = [(HCNDipp)C:]; Dipp = 2,6-(i)Pr(2)C(6)H(3)) as a stoichiometric dehydrogenation agent. In the case of primary amine-boranes, carbene-bound adducts IPr·BH(2)-NH(R)-BH(3) were obtained in place of the desired polymers [RNH-BH(2)](n). The secondary amine-borane (i)Pr(2)NH·BH(3) participated in dehydrogenation chemistry with IPr to afford the aminoborane [(i)Pr(2)N=BH(2)] and the dihydroaminal IPrH(2) as products. Attempts to induce H(2) elimination from the arylamine-borane DippNH(2)·BH(3) yielded a reaction mixture containing the known species IPr·BH(2)NHDipp, IPr·BH(2)NH(Dipp)-BH(3), free DippNH(2) and IPrH(2). The new hindered aryl-amine borane adduct Ar*NH(2)·BH(3) [Ar* = 2,6-(Ph(2)CH)(2)-4-MeC(6)H(2)] underwent a reaction with IPr to give IPr·BH(3) and free Ar*NH(2), consistent with the presence of a weaker N-B dative bond in Ar*NH(2)·BH(3) relative to its less hindered amine-borane analogues.

Coordination complexes of TiX4 (X = F, Cl) with a bulky N-heterocyclic carbene: Syntheses, characterization and molecular structures

Reactions of the sterically encumbered N-heterocyclic carbene IPr (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, [:C{[N(2,6-iPr2C6H3)]CH}2]) (1) with TiX4 (X=Cl, F) in diethyl ether or THF afford the metal halide mono- and bis-carbene complexes, [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] (2), [Cl4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (3) and [F4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (4). Compounds 2–4 have been completely characterized by elemental analysis, NMR spectroscopic methods (1H, 13C and 19F NMR) and single crystal X-ray structure determination. Furthermore, the reaction of [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] (2) with ZnMe2 yields monomeric [ZnCl2·IPr] (5), involving the transfer of carbene and chlorido ligands from Ti (IV) to Zn(II).

Three-Coordinate N-Heterocyclic Carbene Nickel Nitrosyl Complexes

The N-heterocyclic carbene IPr serves as a supporting ligand in a series of low-coordinate nickel nitrosyl complexes which display a range of nitrosyl bonding modes. Attempts to form a cationic two-coordinate nickel nitrosyl led to the three-coordinate {[IPr][IPr′]Ni(NO)}+[BArF4]−, in which one of the IPr ligands exhibits unusual C(5) coordination.

Synthesis and coordination compounds of a bis(imino)acenaphthene (BIAN)-supported N-heterocyclic carbene

The bis(imino)acenaphthene-supported N-heterocyclic carbene IPr(BIAN) has been prepared by deprotonation of the precursor imidazolium chloride. Treatment of IPr(BIAN) imidazolium chloride with Ag(2)O afforded the silver complex [IPr(BIAN)]AgCl which can be converted into the corresponding gold complex [IPr(BIAN)]AuCl by reaction with (tht)AuCl (tht = tetrahydrothiophene). The iridium complex [IPr(BIAN)]Ir(COD)Cl was prepared by reaction of the imidazolium chloride with KO(t)Bu and [Ir(COD)Cl](2) and subsequently converted to the carbonyl complex [IPr(BIAN)]Ir(CO)(2)Cl by exposure to an atmosphere of CO. All new compounds were characterized by single-crystal X-ray diffraction, multinuclear NMR, MS and HRMS data.

Synthesis and Characterization of Gold(I) N-Heterocyclic Carbene Complexes Bearing Biologically Compatible Moieties

Two new gold(I) complexes bearing the bulky N-heterocyclic carbene IPr (IPr = bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and respectively 2,3,4,6-tetra-O-acetyl-1-thio-β-d-pyranosatothiolato [(IPr)AuTgt (1)] and a saccharin ligand [(IPr)AuSac (2)] have been synthesized in good yield and are fully characterized by NMR spectroscopy and by inert-atmosphere MALDI-TOF. These complexes are well-behaved compounds analogous to gold drugs such as Auranofin and Solganol.