Supported Lanthanum Borohydride Catalyzes CH Borylation Inside Zeolite Micropores.

The zeolite-supported lanthanide La(BH4 )x -HY30 catalyzes C-H borylation of benzene with pinacolborane (HBpin), providing a complementary approach to precious, late transition metal-catalyzed borylations. The reactive catalytic species are generated from La grafted at the Brønsted acid sites (BAS) in micropores of the zeolite, whereas silanoate- and aluminoate-grafted sites are inactive under the reaction conditions. During typical catalytic borylations, conversion to phenyl pinacolborane (PhBpin) is zero-order in HBpin concentration. A turnover number (TON) of 167 is accessed by capping external silanols, selectively grafting at BAS sites, and adding HBpin slowly to the reaction.

Iron pentacarbonyl ligands on silver scorpionates.

Fluorinated tris(pyrazolyl)borate supporting ligands enable the stabilization of silver(I) bonded to a neutral, organometallic Fe(CO)5 ligand. The Ag-Fe interaction in these molecules is mainly electrostatic in nature, but σ-donor and backbonding contributions between the two metal fragments also play notable roles, which can be modulated by the scorpionate substituents.

Indirect Access to Carbene Adducts of Bismuth- and Antimony-Substituted Phosphaketene and Their Unusual Thermal Transformation to Dipnictines and [(NHC)2OCP][OCP].

The synthesis and thermal redox chemistry of the first antimony (Sb)- and bismuth (Bi)-phosphaketene adducts are described. When diphenylpnictogen chloride [Ph2PnCl (Pn = Sb or Bi)] is reacted with sodium 2-phosphaethynolate [Na[OCP]·(dioxane)x], tetraphenyldipnictogen (Ph2Pn-PnPh2) compounds are produced, and an insoluble precipitate forms from solution. In contrast, when the N-heterocyclic carbene adduct (NHC)-PnPh2Cl is combined with [Na[OCP]·(dioxane)x], Sb- and Bi-phosphaketene complexes are isolated. Thus, NHC serves as an essential mediator for the reaction. Immediately after the formation of an intermediary pnictogen-phosphaketene NHC adduct [NHC-PnPh2(PCO)], the NHC ligand transfers from the Pn center to the phosphaketene carbon atom, forming NHC-C(O)P-PnPh2 [Pn = Sb (3) or Bi (4)]. In the solid state, 3 and 4 are dimeric with short intermolecular Pn-Pn interactions. When compounds 3 and 4 are heated in THF at 90 and 70 °C, respectively, the pnictogen center PnIII is thermally reduced to PnII to form tetraphenyldipnictines (Ph2Pn-PnPh2) and an unusual bis-carbene-supported OCP salt, [(NHC)2OCP][OCP] (5). The formation of compound 5 and Ph2Pn-PnPh2 from 3 or 4 is unique in comparison to the known thermal reactivity for group 14 carbene-phosphaketene complexes, further highlighting the diverse reactivity of [OCP]- with main-group elements. All new compounds have been fully characterized by single-crystal X-ray diffraction, multinuclear NMR spectroscopy (1H, 13C, and 31P), infrared spectroscopy, and elemental analysis (1, 2, and 5). The electronic structure of 5 and the mechanism of formation were investigated using density functional theory (DFT).

s-Block Multiple Bonds: Isolation of a Beryllium Imido Complex.

A common feature of d- and p-block elements is that they participate in multiple bonding. In contrast, the synthesis of compounds containing homo- or hetero-nuclear multiple bonds involving s-block elements is extremely rare. Herein, we report the synthesis, molecular structure, and computational analysis of a beryllium imido (Be=N) complex (2), which was prepared via oxidation of a molecular Be0 precursor (1) with trimethylsilyl azide Me3 SiN3 (TMS-N3 ). Notably, compound 2 features the shortest known Be=N bond (1.464 Å) to date. This represents the first compound with an s-block metal-nitrogen multiple bond. All compounds were characterized experimentally with multi-nuclear NMR spectroscopy (1 H, 13 C, 9 Be) and single-crystal X-ray diffraction studies. The bonding situation was analyzed with density functional theory (DFT) calculations, which supports the existence of π-bonding between beryllium and nitrogen.

Synthesis and characterization of N-heterocyclic carbene-MOEt2 complexes (M = Cu, Ag, Au). Analysis of solvated auxiliary-ligand free [(NHC)M]+ species.

We report the synthesis, characterization and computational analysis of coinage metal-ether complexes supported by N-heterocyclic carbenes (NHC), SIPr and Et2CAAC. The related water adducts are also included. The [(NHC)M]+(M = Cu, Ag, Au) species show the noteworthy ability to bind Et2O and H2O. This interaction towards Et2O and H2O is partly ascribed to a σ-hole bonding with an almost linear disposition, taking advantage of the enhanced σ-hole potential evaluated for such [(NHC)M]+ species. This enhanced ability is larger than those found for non-covalent interactions involving main group species.

Carbodicarbene Bismaalkene Cations: Unravelling the Complexities of Carbene versus Carbone in Heavy Pnictogen Chemistry.

We report a combined experimental and theoretical study on the first examples of carbodicarbene (CDC)-stabilized bismuth complexes, which feature low-coordinate cationic bismuth centers with C=Bi multiple-bond character. Monocations [(CDC)Bi(Ph)Cl][SbF6 ] (8) and [(CDC)BiBr2 (THF)2 ][SbF6 ] (11), dications [(CDC)Bi(Ph)][SbF6 ]2 (9) and [(CDC)BiBr(THF)3 ][NTf2 ]2 (12), and trication [(CDC)2 Bi][NTf2 ]3 (13) have been synthesized via sequential halide abstractions from (CDC)Bi(Ph)Cl2 (7) and (CDC)BiBr3 (10). Notably, the dications and trication exhibit C ⇉ Bi double dative bonds and thus represent unprecedented bismaalkene cations. The synthesis of these species highlights a unique non-reductive route to C-Bi π-bonding character. The CDC-[Bi] complexes (7-13) were compared with related NHC-[Bi] complexes (1, 3-6) and show substantially different structural properties. Indeed, the CDC ligand has a remarkable influence on the overall stability of the resulting low-coordinate Bi complexes, suggesting that CDC is a superior ligand to NHC in heavy pnictogen chemistry.

Synthesis and characterization of heterometallic complexes involving coinage metals and isoelectronic Fe(CO)5, [Mn(CO)5]- and [Fe(CO)4CN]- ligands.

The chemistry of coinage metal ions with Fe(CO)5, [Mn(CO)5]- and [Fe(CO)4CN]- has been explored using Mes3P and N-heterocyclic carbene supporting ligands. A comparison of [(SIPr)Au-Fe(CO)5][SbF6], [(Et2CAAC)Au-Fe(CO)5][SbF6] and [(Mes3P)Au-Fe(CO)5][SbF6] shows that the ligand donor strength towards Au(i) follows the order Mes3P > Et2CAAC > SIPr. These Fe(CO)5 complexes show significant blue shifts in [small nu, Greek, macron]CO bands relative to those observed for free Fe(CO)5 as a result of it serving as a net electron donor to Au(i). Au(i) is a much stronger acceptor in (SIPr)Au-Mn(CO)5 compared to Ag(i) in (SIPr)Ag-Mn(CO)5. The structural details of Mes3PAu-Mn(CO)5 are also presented. [Fe(CO)4CN]- afforded CN bridged coinage metal complexes with (IPr*)Au+, (SIPr)Ag+ and (SIPr)Cu+ moieties, rather than molecules with direct Fe/coinage metal bonds. The computed total interaction energies indicate that both [Mn(CO)5]- and [Fe(CO)4CN]- are stronger donors toward Au(i) than Fe(CO)5. A detailed analysis of the bonding interactions between the coinage metal ions and Fe(CO)5, [Mn(CO)5]- and [Fe(CO)4CN]- suggests that the largest contribution comes from electrostatic attraction, while the covalent component follows the Dewar-Chatt-Duncanson model. The σ-donor interactions of these organometallic ligands with coinage metal ions are considerably stronger than the π-backbonding from the coinage metal ions.

A Stable, Crystalline Beryllium Radical Cation.

The alkaline-earth elements (Be, Mg, Ca, Sr, and Ba) strongly favor the formation of diamagnetic compounds in the +2 oxidation state. Herein we report a paramagnetic beryllium radical cation, [(CAAC)2Be]+• (2) [CAAC = cyclic (alkyl)(amino)carbene], prepared by oxidation of a zero-valent beryllium complex with 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO). Compound 2 was characterized by EPR spectroscopy, elemental analysis, X-ray crystallography, and DFT calculations. Notably, the isolation of 2 represents the first s-block charged radical and the first crystalline beryllium radical.

Organic Azide and Auxiliary-Ligand-Free Complexes of Coinage Metals Supported by N-Heterocyclic Carbenes.

Organic azide complexes of copper(I) and silver(I), [(SIPr)CuN(1-Ad)NN][SbF6], [(SIPr)CuN(2-Ad)NN][SbF6], [(SIPr)CuN(Cy)NN][SbF6], and [(SIPr)AgN(1-Ad)NN][SbF6] have been synthesized by using Ag[SbF6] and the corresponding organic azides with (SIPr)CuBr and (SIPr)AgCl (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene). The copper and silver organic azide complexes were characterized by various spectroscopic techniques and X-ray crystallography. Group trends of isoleptic Cu(I), Ag(I), and Au(I) organic azide complexes are presented on the basis of experimental data and a detailed computational study. The νasym(N3) values of the metal-bound 1-AdNNN in [(SIPr)MN(1-Ad)NN]+ follow the order Ag < Cu < Au. DFT calculations show that gold(I) forms the strongest bond with 1-AdNNN in this series, while silver has the weakest interaction. Furthermore, auxiliary ligand free coinage metal N-heterocyclic carbene complexes, [(SIPr)M][SbF6], have been synthesized via metathesis reactions of (SIPr)MCl (M = Cu, Ag, Au) with Ag[SbF6]. X-ray crystal structures of dinuclear [(SIPr)Ag]2[SbF6]2 and [(SIPr)Au]2[SbF6]2 are also reported. They show close metallophilic contacts. [(SIPr)Au]2[SbF6]2 reacts with OEt2, SMe2, and CNtBu to afford [(SIPr)Au(OEt2)][SbF6], [(SIPr)Au(SMe2)][SbF6], and [(SIPr)Au(CNtBu)][SbF6] adducts, respectively.

Cyclic(alkyl)(amino) Carbene-Promoted Ring Expansion of a Carbodicarbene Beryllacycle.

Recent synthetic efforts have uncovered several bond activation pathways mediated by beryllium. Having the highest charge density and electronegativity, the chemistry of beryllium often diverges from that of its heavier alkaline earth metal congeners. Herein, we report the synthesis of a new carbodicarbene beryllacycle (2). Compound 2 converts to 3 via an unprecedented cyclic(alkyl)(amino) carbene (CAAC)-promoted ring expansion reaction (RER). While CAAC activates a carbon-beryllium bond, N-heterocyclic carbene (NHC) coordinates to beryllium to give the tetracoordinate complex 4, which contains the longest carbeneC-Be bond to date at 1.856(4) Å. All of the compounds were fully characterized by X-ray crystallography, Fourier transform infrared spectroscopy, and 1H, 13C, and 9Be NMR spectroscopy. The ring expansion mechanism was modeled with both NHC and CAAC using density functional theory calculations. While the activation energy for the observed beryllium ring expansion with CAAC was found to be 14 kJ mol-1, the energy barrier for the hypothetical NHC RER is significantly higher (199.1 kJ mol-1).

Stepwise Reduction at Magnesium and Beryllium: Cooperative Effects of Carbenes with Redox Non-Innocent α-Diimines.

In the past two decades, the organometallic chemistry of the alkaline earth elements has experienced a renaissance due in part to developments in ligand stabilization strategies. In order to expand the scope of redox chemistry known for magnesium and beryllium, we have synthesized a set of reduced magnesium and beryllium complexes and compared their resulting structural and electronic properties. The carbene-coordinated alkaline earth-halides, (Et2CAAC)MgBr2 (1), (SIPr)MgBr2 (2), (Et2CAAC)BeCl2 (3), and (SIPr)BeCl2 (4) [Et2CAAC = diethyl cyclic(alkyl)(amino) carbene; SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazole-2-ylidene] were combined with an α-diimine [2,2-bipyridine (bpy) or bis(2,6-diisopropylphenyl)-1,4-diazabutadiene (DippDAB)] and the appropriate stoichiometric amount of potassium graphite to form singly- and doubly-reduced compounds (Et2CAAC)MgBr(DippDAB) (5), (Et2CAAC)MgBr(bpy) (6), (Et2CAAC)Mg(DippDAB) (7), (Et2CAAC)Be(bpy) (8), and (SIPr)Be(bpy) (9). The doubly-reduced compounds 7-9 exhibit substantial π-bonding interactions across the diimine core, metal center, and π-acidic carbene. Each complex was fully characterized by UV-vis, FT-IR, X-ray crystallography, 1H, 13C, and 9Be NMR, or EPR where applicable. We use these compounds to highlight the differences in the organometallic chemistry of the lightest alkaline earth metals, magnesium and beryllium, in an otherwise identical chemical environment.

Metal-Free Electrochemical Reduction of Carbon Dioxide Mediated by Cyclic(Alkyl)(Amino) Carbenes.

Carbenes are known to activate carbon dioxide to form zwitterionic adducts. Their inherent metal-free redox activity remains understudied. Herein, we demonstrate that zwitterionic adducts of carbon dioxide formed with cyclic(alkyl)(amino) carbenes are not only redox active, but they can mediate the stoichiometric reductive disproportionation of carbon dioxide to carbon monoxide and carbonate. Infrared spectroelectrochemical experiments show that the reaction proceeds through an intermediate radical anion formed by one-electron reduction, ultimately generating a ketene product and carbonate in the absence of additional organic or inorganic reagents.

Isolation of Cyclic(Alkyl)(Amino) Carbene-Bismuthinidene Mediated by a Beryllium(0) Complex.

The long-sought carbene-bismuthinidene, (CAAC)Bi(Ph), has been synthesized. Notably, this represents both the first example of a carbene-stabilized subvalent bismuth complex and the extension of the carbene-pnictinidene concept to a non-toxic metallic element (Bi). The bonding has been investigated by single-crystal X-ray diffraction studies and DFT calculations. This report also highlights the hitherto unknown reducing and ligand transfer capability of a beryllium(0) complex.

s-Block carbodicarbene chemistry: C(sp3)-H activation and cyclization mediated by a beryllium center.

The first examples of carbodicarbene (CDC)-s-block complexes have been synthesized. The addition of base or reducing agent to a CDC-beryllium (chloride)(hexamethyldisilazide) adduct results in the unprecedented activation of a pendant C(sp3)-H bond and cyclization of the CDC to form a five-membered beryllium metallacycle. This also represents the first example of chemical activation of a CDC which transforms the ligand from monodentate neutral to chelating anionic.

Highly Reactive Cyclic(alkyl)(amino) Carbene- and N-Heterocyclic Carbene-Bismuth(III) Complexes: Synthesis, Structure, and Computations.

Cyclic(alkyl)(amino) carbene (CAAC)-stabilized complexes of phosphorus, one of the lightest group 15 elements, are well-established and can often be obtained in high yields. In contrast, analogous CAAC compounds of bismuth, the heaviest nonradioactive member of group 15, are unknown. Indeed, reactivity increases as you descend the group, and as a result there are only a few examples of N-heterocyclic carbene (NHC)-bismuth complexes. Moreover, activated bismuth compounds often readily extrude bismuth metal, making isolation of stable complexes highly challenging. We report that CAACs react with phenylbismuth dichloride (PhBiCl2) to afford Et2CAAC-Bi(Ph)Cl2 and CyCAAC-Bi(Ph)Cl2. Significantly, these complexes represent the first structurally characterized examples of CAAC-coordination to bismuth. The CAAC-stabilized bismuth compounds can also be obtained from air-stable salts, [Et2CAAC-H]22+ [Cl2(Ph)Bi(µ-Cl2)Bi(Ph)Cl2]2- and [CyCAAC-H]22+ [Cl2(Ph)Bi(µ-Cl2)Bi(Ph)Cl2]2-, by deprotonation with potassium bis(trimethylsilyl)amide, K[N(SiMe3)2]. The electronic effects of the ligand on the bismuth center were investigated by comparing the CAAC-Bi(Ph)Cl2 complexes to the NHC analogues, SIPr-Bi(Ph)Cl2(THF) and IPr-Bi(Ph)Cl2 (SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazole-2-ylidene; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). Interestingly, the "normal" IPr-Bi(Ph)Cl2 slowly isomerizes to the "abnormal" carbene complex, Cl2(Ph)Bi-IPr-H, at -37 °C. In the solid-state, the CAAC-, NHC-, and abnormal NHC-bismuth compounds exhibit Bi atomic centers in unique coordination environments. The complexes were fully characterized by NMR, elemental analysis, and single crystal X-ray diffraction studies. In addition, the bonding was probed by natural bond orbital (NBO) calculations.

The origin, type and hydrocarbon generation potential of organic matter in a marine-continental transitional facies shale succession (Qaidam Basin, China).

This organic-rich shale was analyzed to determine the type, origin, maturity and depositional environment of the organic matter and to evaluate the hydrocarbon generation potential of the shale. This study is based on geochemical (total carbon content, Rock-Eval pyrolysis and the molecular composition of hydrocarbons) and whole-rock petrographic (maceral composition) analyses. The petrographic analyses show that the shale penetrated by the Chaiye 2 well contains large amounts of vitrinite and sapropelinite and that the organic matter within these rocks is type III and highly mature. The geochemical analyses show that these rocks are characterized by high total organic carbon contents and that the organic matter is derived from a mix of terrestrial and marine sources and highly mature. These geochemical characteristics are consistent with the results of the petrographic analyses. The large amounts of organic matter in the Carboniferous shale succession penetrated by the Chaiye 2 well may be due to good preservation under hypersaline lacustrine and anoxic marine conditions. Consequently, the studied shale possesses very good hydrocarbon generation potential because of the presence of large amounts of highly mature type III organic matter.

Heterobimetallic Complexes Featuring Fe(CO)5 as a Ligand on Gold.

Iron(0) pentacarbonyl complexes of gold(I), [Mes3 PAu-Fe(CO)5 ][SbF6 ] (1) and [(IPr*)Au-Fe(CO)5 ][SbF6 ] (2) (Mes=2,4,6-trimethylphenyl; IPr*=1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) have been synthesized using Mes3 PAuCl and (IPr*)AuCl as the gold(I) precursor, AgSbF6 halide ion abstractor, and the Lewis base Fe(CO)5 . The Au-Fe bond lengths of these metal-only Lewis pair complexes are significantly shorter than the sum of the experimentally derived covalent radii of Au and Fe. The v̄(CO) bands of the molecules show a notable blueshift relative to those observed for free Fe(CO)5 , indicating a substantial reduction in Fe→CO backbonding upon its coordination to gold(I) with either Mes3 P or IPr* supporting ligands (L). The analysis of the electronic structure with quantum chemical method suggests that the Au-Fe bond consists mainly of [LAu]+ ←Fe(CO)5 σ-donation and weaker [LAu]+ →Fe(CO)5 π-backdonation. The donor strength of Fe(CO)5 is similar to that of CO.

Heterobimetallic Silver-Iron Complexes Involving Fe(CO)5 Ligands.

Iron(0) pentacarbonyl is an organometallic compound with a long history. It undergoes carbonyl displacement chemistry with various donors (L), leading to molecules of the type Fe(CO)x(L)5-x. The work reported here illustrates that Fe(CO)5 can also act as a ligand. The reaction between Fe(CO)5 with the silver salts AgSbF6 and Ag[B{3,5-(CF3)2C6H3}4] under appropriate conditions resulted in the formation of [(µ-H2O)AgFe(CO)5]2[SbF6]2 and [B{3,5-(CF3)2C6H3}4]AgFe(CO)5, respectively, featuring heterobimetallic {Ag-Fe(CO)5}+ fragments. The treatment of [B{3,5-(CF3)2C6H3}4]AgFe(CO)5 with 4,4'-dimethyl-2,2'-bipyridine (Me2Bipy) and Fe(CO)5 afforded a heterobimetallic [(Me2Bipy)AgFe(CO)5][B{3,5-(CF3)2C6H3}4] species with a Ag-Fe(CO)5 bond and a heterotrimetallic [{Fe(CO)5}2(µ-Ag)][B{3,5-(CF3)2C6H3}4] with a (CO)5Fe-Ag-Fe(CO)5 core, respectively, illustrating that it is possible to manipulate the coordination sphere at silver while keeping the Ag-Fe bond intact. The chemistry of [B{3,5-(CF3)2C6H3}4]AgFe(CO)5 with Et2O and PMes3 (Mes = 2,4,6-trimethylphenyl) has also been investigated, which led to [(Et2O)3Ag][B{3,5-(CF3)2C6H3}4] and [(Mes3P)2Ag][B{3,5-(CF3)2C6H3}4] with the displacement of the Fe(CO)5 ligand. X-ray structural and spectroscopic data of new molecules as well as results of computational analyses are presented. The Fe-Ag bond distances of these metal-only Lewis pairs range from 2.5833(4) to 2.6219(5) Å. These Ag-Fe bonds are of primarily an ionic/electrostatic nature with a modest amount of charge transfer between Ag+ and Fe(CO)5. The ν̅(CO) bands of the molecules with Ag-Fe(CO)5 bonds show a notable blue shift relative to those observed for free Fe(CO)5, indicating a significant reduction in Fe→CO back-bonding upon its coordination to silver(I).

Heterobimetallic cerium(iv) oxo clusters supported by a tripodal oxygen ligand.

Heterometallic Ce(IV)/M (M = Mo(VI), Re(VII), V(V)) oxo clusters supported by the Kläui tripodal oxygen ligand [(η(5)-C5H5)Co{P(O)(OEt)2}3](-) (LOEt(-)) have been synthesized and structurally characterized, and the catalytic activity of the Ce(IV)/V(V) oxo cluster in the oxidation of thioanisoles has been studied. Treatment of [Ce(LOEt)Cl3] (1) with [Ag2MoO4] afforded the reported Ce(IV)/Mo(VI) cluster [H4(CeLOEt)6Mo9O38] (2), whereas that with [AgReO4] yielded the Ce(IV)/Re(VII) cluster [{LOEtCe(ReO4)2(H2O)(µ-ReO4)}2] (3) that contains an 8-membered Ce2Re2O4 ring. Treatment of 1 with [Ag3VO4] afforded the Ce(IV)/V(V) cluster [H2(CeLOEt)4(V[double bond, length as m-dash]O)4(µ4-O)(µ3-O)12] (4) containing a {Ce4V4O13} oxo-metallic core. The solid-state structure of 4 consists of four {VO4}(3-) units bridged by four {LOEtCe(3+)} moieties and a µ4-oxo ligand. Each Ce atom in 4 is 9-coordinated, whereas the geometry around each V atom is pseudo square pyramidal with a terminal oxo at the apical position. Cluster 4 is an active catalyst for the oxidation of substituted thioanisoles with tert-butyl hydroperoxide. For example, the oxidation of thioanisole with tert-butyl hydroperoxide in the presence of 0.01 mol% of 4 gave a ca. 30 : 1 mixture of the sulfoxide and sulfone products in 96% yield.