The bis(ethylene) IrI complex [TpIr(C2H4)2] ( 1 ; Tp=hydrotris(3,5‐dimethylpyrazolyl)borate) reacts with two equivalents of aromatic or aliphatic aldehydes in the presence of one equivalent of dimethyl acetylenedicarboxylate (DMAD) with ultimate formation of hydride iridafurans of the formula [TpIr(H){C(R1)?C(R2)C(R3)O }] (R1=R2=CO2Me; R3=alkyl, aryl; 3 ). Several intermediates have been observed in the course of the reaction. It is proposed that the key step of metallacycle formation is a C? C coupling process in the undetected IrI species [TpIr{η1‐O‐R3C(?O)H}(DMAD)] ( A ) to give the trigonal‐bipyramidal 16 e? IrIII intermediates [TpIr{C(CO2Me)?C(CO2Me)C(R3)(H)O }] ( C ), which have been trapped by NCMe to afford the adducts 11 (R3=Ar). If a second aldehyde acts as the trapping reagent for these species, this ligand acts as a shuttle in transfering a hydrogen atom from the γ‐ to the α‐carbon atom of the iridacycle through the formation of an alkoxide group. Methyl propiolate (MP) can be used instead of DMAD to regioselectively afford the related iridafurans. These reactions have also been studied by DFT calculations. 相似文献
Picky ferryl : The complex [Fe(Tp)(BF)] (Tp=hydrotris(3,5‐diphenylpyrazolyl)borate; BF=benzoylformate) reacts with O2 to generate an oxidant (see picture; O red, pink; Fe yellow; N blue; C gray; H white) that oxidizes added hydrocarbons shape‐selectively. Discrimination derives from a cleft formed by two phenyl groups of the Tp ligand, favoring oblate spheroidal substrates.
The mechanism of copper‐mediated Sonogashira couplings (so‐called Stephens–Castro and Miura couplings) is not well understood and lacks clear comprehension. In this work, the reactivity of a well‐defined aryl‐CuIII species ( 1 ) with p‐R‐phenylacetylenes (R=NO2, CF3, H) is reported and it is found that facile reductive elimination from a putative aryl‐CuIII‐acetylide species occurs at room temperature to afford the Caryl?Csp coupling species ( IR ), which in turn undergo an intramolecular reorganisation to afford final heterocyclic products containing 2H‐isoindole ( P , P , PHa ) or 1,2‐dihydroisoquinoline ( PHb ) substructures. Density Functional Theory (DFT) studies support the postulated reductive elimination pathway that leads to the formation of C?Csp bonds and provide the clue to understand the divergent intramolecular reorganisation when p‐H‐phenylacetylene is used. Mechanistic insights and the very mild experimental conditions to effect Caryl?Csp coupling in these model systems provide important insights for developing milder copper‐catalysed Caryl?Csp coupling reactions with standard substrates in the future. 相似文献
[(ArPMI)Mo(CO)4] complexes (PMI=pyridine monoimine; Ar=Ph, 2,6‐di‐iso‐propylphenyl) were synthesized and their electrochemical properties were probed with cyclic voltammetry and infrared spectroelectrochemistry (IR‐SEC). The complexes undergo a reduction at more positive potentials than the related [(bipyridine)Mo(CO)4] complex, which is ligand based according to IR‐SEC and DFT data. To probe the reaction product in more detail, stoichiometric chemical reduction and subsequent treatment with CO2 resulted in the formation of a new product that is assigned as a ligand‐bound carboxylate, [(PMI)Mo(CO)3(CO2)]2?, by NMR spectroscopic methods. The CO2 adduct [(PMI)Mo(CO)3(CO2)]2? could not be isolated and fully characterized. However, the C?C coupling between the CO2 molecule and the PDI ligand was confirmed by X‐ray crystallographic characterization of one of the decomposition products of [(PMI)Mo(CO)3(CO2)]2?. 相似文献
The complexes Fn‐TpAg(L) (Fn‐Tp=a perfluorinated hydrotris(indazolyl) borate ligand; L=acetone or tetrahydrofuran) efficiently catalyze the functionalization of non‐activated alkanes such as hexane, 2,3‐dimethylbutane, or 2‐methylpentane by insertion of CHCO2Et units (from N2CHCO2Et, ethyl diazoacetate, EDA) into their C? H bonds. The reactions are quantitative (EDA‐based), with no byproducts derived from diazo coupling being formed. In the case of hexane, the functionalization of the methyl C? H bonds has been achieved with the highest regioselectivity known to date with this diazo compound. This catalytic system also operates under biphasic conditions by using fluorous solvents such as Fomblin or perfluorophenanthrene. Several cycles of catalyst recovery and reuse have been performed, with identical chemo‐ and regioselectivities. 相似文献
A cyclohexyl‐based POCOP pincer ligand (POCOP=cis‐1,3‐bis(di‐tert‐butylphosphinito)cyclohexyl) cyclometalates with nickel to generate a series of new POCOP‐supported NiII complexes, including the halide, hydride, methyl, and phenyl species. trans‐[NiCl{cis‐1,3‐bis(di‐tert‐butylphosphinito)cyclohexane}], [(POCOP)NiCl] ( 1 a ) and the analogous bromide complex ( 1 b ) were synthesized and fully characterized by NMR spectroscopy and X‐ray crystallography. Cyclic voltammetry measurements of 1 a and 1 b alongside their bis(phosphine) analogues [(PCP)NiCl] ( 2 a ) and [(PCP)NiCl] ( 2 a ) (PCP=cis‐1,3‐bis(di‐tert‐butylphosphino)cyclohexyl) indicate a reduced electron density at the metal center upon introducing electron‐withdrawing oxygen atoms in the pincer arms. The methyl [(POCOP)NiMe] ( 3 ) and phenyl [(POCOP)NiPh] ( 4 ) complexes were formed from 1 a by reaction with the corresponding organolithium reagents. 1 a also reacts with LiAlH4 to give the hydride complex [(POCOP)NiH] ( 5 ). The methyl complex 3 reacts with phenyl acetylene to give the acetylide complex [(POCOP)NiCCPh] ( 6 ). The reactivity of compounds 3 – 5 towards CO2 was studied. The hydride complex 5 and the methyl complex 3 both underwent CO2 insertion to form the formate species [(POCOP)NiOCOH] ( 7 ) and acetate species [(POCOP)NiOCOCH3] ( 8 ), respectively, although with a higher barrier of insertion in the latter case. Compound 4 was unreactive towards CO2 even at elevated temperatures. Complexes 3 – 8 were all characterized by NMR spectroscopy and X‐ray crystallography. 相似文献
This contribution describes the reactivities of CO2, CO, O2, and ArNC with the pincer‐type complexes [(κP,κC,κP′‐POCOP)NiX] (POCOP=(R2POCH2)2CH; R=iPr; X=OSiMe3, NArH; Ar=2,6‐iPr2C6H3). Reaction of the amido derivative with CO2 and CO leads to a simple insertion into the Ni?N bond to give stable carbamate and carbamoyl derivatives, respectively, the pincer ligand backbone remaining intact in both cases. In contrast, the analogous reactions with the siloxide derivative produced kinetically labile insertion products that either revert to the starting material (in the case of CO2) or react further to give the mixed‐valent, dinickel species [(POCOP)NiII{μ,κO,κP,κP′‐OCOCH(CH2CH2OPR2)2}Ni0(CO)2]. The zero‐valent center in the latter compound is ligated by a new ligand arising from transformation of the POCOP ligand backbone. The carbonylation and carboxylation of the siloxido derivative also produced minor quantities of a side‐product identified as the trinickel species, [{(η3‐allyl)Ni(μO,κP‐R2PO)2}2Ni], arising from total dismantling of the POCOP ligand. Similar reactivities were observed with isonitrile, ArNC: reaction with the siloxido derivative resulted in a complex sequence of steps involving initial insertion, a 1,3‐hydrogen shift, and an Arbuzov rearrangement to give [Ni(CNAr)4] and a methacrylamide based on fragments of the POCOP ligand. Oxygenation of the amido and siloxido derivatives led to the phosphinate derivative, [(POCOP)Ni(OP(O)R2)], arising from oxidative transformation of the original ligand frame; the reaction with the Ni‐NHAr derivative also gave ArHNP(O)R2 through a complex N?P bond‐forming reaction. 相似文献
Dramatic rate enhancement of reductive elimination of [Ar‐Pd‐C] was observed in the presence of a phosphine/electron‐deficient olefin ligand. Through systematic kinetic investigations of the Negishi coupling of ethyl 2‐iodobenzoate with alkylzinc chlorides (see scheme), the rate constants for reductive elimination of [Ar‐Pd‐C] were determined to be greater than 0.3 s?1, which is about four or five orders of magnitude greater than values reported previously.
Reaction of the tin cluster Sn8(Ar)4 (Ar=C6H2‐2,6‐(C6H3‐2,4,6‐Me3)2) with excess ethylene or dihydrogen at 25 °C/1 atmosphere yielded two new clusters that incorporated ethylene or hydrogen. The reaction with ethylene yielded Sn4(Ar)4(C2H2)5 that contained five ethylene moieties bridging four aryl substituted tin atoms and one tin–tin bond. Reaction with H2 produced a cyclic tin species of formula (Sn(H)Ar)4, which could also be synthesized by the reaction of {(Ar)Sn(μ‐Cl)}2 with DIBAL‐H. These reactions represent the first instances of direct reactions of isolable main‐group clusters with ethylene or hydrogen under mild conditions. The products were characterized in the solid state by X‐ray diffraction and IR spectroscopy and in solution by multinuclear NMR and UV/Vis spectroscopies. Density functional theory calculations were performed to explain the reactivity of the cluster. 相似文献
Thermally doped nitrogen atoms on the sp2‐carbon network of reduced graphene oxide (rGO) enhance its electrical conductivity. Atomic structural information of thermally annealed graphene oxide (GO) provides an understanding on how the heteroatomic doping could affect electronic property of rGO. Herein, the spectroscopic and microscopic variations during thermal graphitization from 573 to 1 373 K are reported in two different rGO sheets, prepared by thermal annealing of GO (rGOtherm) and post‐thermal annealing of chemically nitrogen‐doped rGO (post‐therm‐rGO). The spectroscopic transitions of rGO in thermal annealing ultimately showed new oxygen‐functional groups, such as cyclic edge ethers and new graphitized nitrogen atoms at 1 373 K. During the graphitization process, the microscopic evolution resolved by scanning tunneling microscopy (STM) produced more wrinkled surface morphology with graphitized nanocrystalline domains due to atomic doping of nitrogen on a post‐therm‐rGO sheet. As a result, the post‐therm‐rGO‐containing nitrogen showed a less defected sp2‐carbon network, resulting in enhanced conductivity, whereas the rGOtherm sheet containing no nitrogen had large topological defects on the basal plane of the sp2‐carbon network. Thus, our investigation of the structural evolution of original wrinkles on a GO sheet incorporated into the graphitized N‐doped rGO helps to explain how the atomic doping can enhance the electrical conductivity. 相似文献
Three diplatinum(II) complexes [{PtL}2(μ‐thea)] (H4thea=2,3,6,7‐tetrahydroxy‐9,10‐dimethyl‐9,10‐dihydro‐9,10‐ethanoanthracene) have been prepared, with diphosphine or bipyridyl “L” co‐ligands. One‐electron oxidation of these complexes gave radical cations containing a mixed‐valent [thea]3? ligand with discrete catecholate and semiquinonate centers separated by quaternary methylene spacers. The electronic character of these radicals is near the Robin–Day class II/III border determined by UV/Vis/NIR and EPR spectroscopies. Crystal‐structure determinations and a DFT calculation imply that oxidation of the thea4? ligand may lead to an increased through‐space interaction between the dioxolene π systems. 相似文献
Diversification of the β‐carboline skeleton has been demonstrated to assemble a β‐carboline library starting from the tetrahydro‐β‐carboline framework. This strategy affords feasible access to heteroaryl‐, aryl‐, alkenyl‐, or alkynyl‐substituted β‐carbolines at the C1, C3, or C8 position through three categorically different types of transition‐metal‐catalyzed C?C bond‐forming reactions, in the presence of multiple potentially reactive positions. These site‐selective functionalizations include; 1) the Cu‐catalyzed C1/C3‐selective decarboxylative C?C and C?Csp coupling of hexahydro‐β‐carboline‐3‐carboxylic acid with a C?H bond of a heteroarene or terminal alkyne; 2) the chelation‐assisted Pd‐catalyzed C1/C8‐selective C?H arylation of hexahydro‐β‐carboline with aryl boron reagents; and 3) the chelation‐assisted Pd‐catalyzed C1/C3‐selective oxidative C?H/C?H cross‐coupling of β‐carboline‐N‐oxide with arenes, heteroarenes, or alkenes. The saturated structural feature of the hexahydro‐β‐carboline framework can increase reactivity and control site selectivity. The robustness of these approaches has been demonstrated through the synthesis of hyrtioerectine analogues and perlolyrine. We believe that these strategies could provide inspiration for late‐stage diversifications of bioactive core scaffolds. 相似文献