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A multigram method for the preparation of thallium trispyrazolylborate complexes is described., The authors wish to thank MINECO for financial support (CTQ2014-52769-C03-01 and CTQ2015-73693-JIN). A.P. thanks MEC for the FPU fellowship.

Nickel catalysis is gaining in popularity in recent years, mostly within the area of cross-coupling. However, unlike Pd, the mechanisms of Ni-catalyzed C–C and C–heteroatom bond forming reactions have been much less studied, in particular when N-heterocyclic carbenes are used as ligands. Here, we present a thorough study of the mechanism of C–N cross-coupling reactions catalyzed by an NHC-Ni complex. Focusing on the coupling of 2-chloropyridines with indole catalyzed by [(IPrNi(styrene)2] (IPr = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), we have examined each of the elementary steps: i.e., oxidative addition, ligand substitution, and reductive elimination. All relevant catalytic intermediates have been isolated and structurally characterized by both spectroscopic and crystallographic methods. Kinetic studies have revealed that the reductive elimination is the rate-limiting step. Catalyst deactivation is related to the formation of unproductive dinuclear pyridyl-bridged NHC-NiII species, which can...

Two iridium(III) complexes containing a C,N-bidentate pyridyl-triazolylidene ligand were prepared that are structurally very similar but differ in their pendant substituent. Whereas complex 1 contains a non-coordinating pyridyl unit, complex 2 has a phenyl group on the triazolylidene substituent. The presence of the basic pyridyl unit has distinct effects on the catalytic activity of the complex in the oxidative dehydrogenation of benzylic amines, inducing generally higher rates, higher selectivity towards formation of imines versus secondary amines, and notable quantities of tertiary amines when compared to the phenyl-functionalized analogue. The role of the pyridyl functionality has been elucidated from a set of stoichiometric experiments, which demonstrate hydrogen bonding between the pendant pyridyl unit and the amine protons of the substrate. Such Npyr···H-N interactions are demonstrated by X-ray diffraction analysis, 1H NMR, and IR spectroscopy, and suggest a pathway of substrate bond-activation that involves concerted substrate binding through the Lewis acidic iridium center and the Lewis basic pyridyl site appended to the triazolylidene ligand, in agreement with ligand–metal cooperative substrate activation.

The mild generation of nitrogen-centred radicals from N–F reagents has become a convenient synthetic tool. This methodology provides access to the aminative difunctionalisation of alkenes and alkynes and the radical ring-opening of cyclopropanes, among other similar transformations. This review article aims to provide an overview of recent developments of such processes involving radical reactions and N–F reagents using copper-based catalysts., We thank Ministerio de Economía y Competitividad (MINECO) (CTQ2017-82893-C2-1-R) and Universidad de Huelva (PO FEDER 2014-2020 UHU-1254043) for grants.

The dual function of the N-F bond as an effective oxidant and subsequent nitrogen source in intramolecular aliphatic C-H functionalization reactions is explored. Copper catalysis is demonstrated to exercise full regio- and chemoselectivity control, which opens new synthetic avenues to nitrogenated heterocycles with predictable ring sizes. For the first time, a uniform catalysis manifold has been identified for the construction of both pyrrolidine and piperidine cores. The individual steps of this new copper oxidation catalysis were elucidated by control experiments and computational studies, clarifying the singularity of the N-F function and characterizing the catalytic cycle to be based on a copper(I/II) manifold., We thank MINECO for Grants CTQ2017-82893-C2-1-R, CTQ2017-87792-R, CTQ2017-88496-R, COST Action CA15106 “C–H Activation in Organic Synthesis (CHAOS)”and Red Intecat (CTQ2016-81923-REDC).

The functionalization of the primary sites of alkanes is one of the more challenging areas in catalysis. In this context, a novel effect has been discovered that is responsible for an enhancement in the reactivity of the primary C-H bonds of alkanes in a catalytic system. The copper complex Cu(NCMe) (=hydrotris{[3,5-bis(trifluoromethyl)-4-bromo]-pyrazol-1-yl}borate) catalyzes the functionalization of CnH2n+2 with ethyl diazoacetate upon inserting the CHCO2Et unit into C-H bonds. In addition, the selectivity of the reaction toward the primary sites significantly increased relative to that obtained in neat alkane upon using supercritical carbon dioxide as the reaction medium. This was attributed to the effect of the carbon dioxide molecules that withdraw electron density from the fluorine atoms of the ligand, which enhances the electrophilic nature of the metal center. DFT studies validated this proposal.

The copper complex Tp(CF3)2,BrCu(NCMe) (1, Tp(CF3)2,Br = hydrotris((3,5-bis(trifluoromethyl)-4-bromo)-pyrazol-1-yl)borate) catalyzes the insertion of the CHCO2Et group (from ethyl diazoacetate N2CHCO2Et, EDA) into the C–H bonds of methane, in a homogeneous process that uses supercritical carbon dioxide (scCO2) as the reaction medium. Other light alkanes such as ethane, propane, and butane have been also functionalized with this copper-based catalyst, in the first example of the derivatization of the series of C1–C4 alkanes with this metal and a soluble catalyst.

The first example of a diazo palladium adduct is reported. The complexes [(ArNHC−PPh)M(η-NC(Ph)COEt)] (M=Ni, 3; M=Pd, 4; ArNHC−PPh=3-(2,6-diisopropylphenyl)-1-[(diphenylphosphino)ethyl]imidazol-2-ylidene) were prepared by ligand exchange with styrene-coordinated precursors [(ArNHC−PPh)M(styrene)] (M=Ni, 1; M=Pd, 2). Complex 4 was fully characterized, including X-ray analyses; this constitutes the first example of a diazo adduct compound with palladium, thereby closing the gap between Groups 8 and 10 regarding this type of compounds., The authors wish to thank MINECO for financial support (CTQ2014‐52769‐C03‐01 and CTQ2011‐24502). S. G. R. thanks MINECO for a FPI fellowship.

Two families of nickel complexes bearing chelating diphenylphosphine-functionalized NHC ligands [NiII(ArNHCPPh2)(allyl)]Cl 1a (Ar = Mes); 1b, (Ar = 2,6-iPr2-C6H3) and [Ni0(ArNHCPPh2)(alkene)] 2a (Ar = 2,6-iPr2-C6H3, alkene = styrene); 2b (Ar = 2,6-iPr2-C6H3, alkene = diethyl fumarate) have been prepared and fully characterized. VT-NMR experiments in solution reveal that the allyl derivatives 1a–b are stereochemically nonrigid. The solid-state structure of the Ni0 derivative 2b is also reported. These complexes display interesting catalytic properties in various cross-coupling reactions. The precatalyst [Ni0(ArNHCPPh2)(styrene)] 2a was found to be the most active system. The bulkiness of the N-substituent on the imidazole ring and the low oxidation state of the metal center in 2a accounted for its enhanced catalytic performance. This system catalyzed effectively the coupling of (hetero)aryl chlorides with a range of nucleophiles including Grignard reagents, boronic acids, secondary amines and indoles.

The Pd0 complexes [(NHC)PdLn] (NHC=N-heterocyclic carbene ligand; L=styrene for n=2 or PR3 for n=1) efficiently catalyse olefin cyclopropanation by using ethyl diazoacetate (EDA) as the carbene source with activities that improve on previously described catalytic systems based on this metal. Mechanistic studies have shown that all of these catalyst precursors deliver the same catalytic species in solution, that is, [(IPr)Pd(sty)], a 14e- unsaturated intermediate that further reacts with EDA to afford [(IPr)Pd(=CHCO2Et)(sty)], from which the cyclopropane is formed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., We thank Prof. P. J. Pérez (Univ. Huelva) for helpful and constructive comments on these studies. We thank the Ministerio de Ciencia e Innovación (grants CTQ2008–00042BQU and CTQ2011–24502) and the Junta de Andalucía (Proyecto P07-FQM-02794) for financial support. CM thanks the MEC for a research fellowship

Copper homoscorpionate complexes TpxCu(I)(NCMe) efficiently catalyze the Atom Transfer Radical Polymerization (ATRP) of methacrylate (MMA) and other methacrylates at 50 °C in the absence of any red...

A series of complexes of general formulae Tp x Cu have been employed as the catalyst for the styrene cyclopropanation reaction with ethyl diazoacetate, both under homogeneous and heterogeneous conditions. Several solid supports have been tested, with silica gel being the most convenient for this transformation. A comparison of the results obtained under both conditions has shown that the catalytic pocket is affected by the support.

Thermal reactions between [RuCl2(diene)]n (diene = 2,5-norbornadiene, nbd; 1,5-cyclooctadiene, cod) with an excess of N,N,N',N'-tetramethylethylene diamine (tmeda) afforded derivatives [RuCl2(diene)(tmeda)] (diene = nbd, 1; cod, 2) as a mixture of cis and trans isomers. When thermolysis was performed under H2 mixtures of hydride species [RuCl(H)(diene)(tmeda)] (diene = nbd, 3; cod, 4) and the bis-tmeda adduct trans-[RuCl2(tmeda)2] (5) were obtained in different ratios depending upon the reaction conditions and reaction times. Heating polymeric Ru(II) precursors in toluene in the presence of a 5-fold excess of the bulkier N,N,N',N'-tetraethylethylene diamine (teeda) resulted in a rare diamine dealkylation process with formation of trans-[RuCl2(nbd)(Et2NCH2CH2NHEt)] (6) and trans-[RuCl2(cod)(EtHNCH2CH2NHEt)] (7) in high yields. The presence of N-H functionalities in the coordinated diamine ligands of 6 and 7 was unambiguously established by single-crystal X-ray diffraction studies. The dealkylation process of the teeda ligand seems to proceed intramolecularly as shown by solution NMR studies performed with the soluble Ru(II) precursors trans-[RuCl2(amine)2(diene)] (diene = nbd, amine = morpholine, 9; diene = cod, amine = Et2NH, 10). The above complexes [RuCl2(diene)(diamine)] have been tested as precatalysts in the hydrogenation of ketones both for transfer as well as direct hydrogenation, the latter route being the most effective.

A study of the variables that affect the insertion of the :CHCO2Et group (formed from ethyl diazocetate, EDA) into the C–H bonds of cyclohexane in the presence of a TpxCu complex as the catalyst (Tpx = trispyrazolylborate ligand) has demonstrated an anomalous effect of the catalyst loading. The use of low concentrations of catalyst produces an increase in the yield of the C–H activation product ethyl cyclohexaneacetate. This effect has also been found in the case of other less elaborated catalysts such as [BpBr3Cu] or [(bipy)2Cu][I]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Cu(I) complexes containing trispyrazolylborate ligands efficiently catalyze the atom transfer radical addition (ATRA) of polyhalogenated alkanes to various olefins under mild conditions. The catalytic activity is enhanced when bulky and electron donating Tpx ligands are employed. Kinetic data have allowed the proposal of a mechanistic interpretation that includes a Cu(II) pentacoordinated species that regulates the catalytic cycle.

The complexes [TpBr3Ag]2·CH3COCH3 (1) and TpBr3Ag(thf) (2) catalyze the insertion of the :CHCO2Et group from ethyl diazoacetate (EDA) into the saturated C−H bonds of several C5, C6, and C8 linear and branched alkanes. In addition to secondary and/or tertiary sites, the unprecedented insertion into the primary C−H bonds of the substrates studied has been observed with variable regioselectivity, toward the methyl groups, within the range of 40−60% for branched and nearly 25% for linear alkanes.

Complexes of general formula TpxCu (Tpx = homoscorpionate ligand) have been employed as catalysts for the insertion of ethyl diazoacetate into C−H bonds of a variety of hydrocarbons and ethers, in moderate to high yields: tertiary, secondary, and primary C−H bonds have been functionalized by this methodology. Particularly interesting is the homologation of O-methyl groups in ethers, which has been achieved for a group of substrates. The existence of electron-withdrawing groups in the Tpx ligand seems to be crucial for the activity and the selectivity of the catalyst.

A novel carbene transfer reaction from diazoesters to carboxylic acids is developed using a highly fluorinated tris(indazolyl)borate silver complex as catalyst.

International audience; Copper–carbene [TpxCu=C(Ph)(CO2Et)] and copper–diazo adducts [TpxCuη1-N2C(Ph)(CO2Et)] have been detected and characterized in the context of the catalytic functionalization of O–H bonds through carbene insertion by using N2=C(Ph)(CO2Et) as the carbene source. These are the first examples of these type of complexes in which the copper center bears a tridentate ligand and displays a tetrahedral geometry. The relevance of these complexes in the catalytic cycle has been assessed by NMR spectroscopy, and kinetic studies have demonstrated that the N-bound diazo adduct is a dormant species and is not en route to the formation of the copper–carbene intermediate.

Homoscorpionate ligands, with organic sulfides as cocatalyst, promote the reaction of phenyldiazomethane (II) with aldehydes (I) to form epoxides (III), with activities exceeding or, at least similar to those of reported rhodium-based systems.

Fe, Co, and Ni complexes of bulky Bp‘ ligands that contain two M···H−B three-center, two-electron interactions have been prepared and structurally characterized.

A series of ester-carbene complexes was synthesized. These complexes were found to be highly active for the metathesis of olefinic substrates, including acrylates and trisubstituted olefins. In addition, the ester-carbene moiety is thermodynamically high in energy. As a result, these complexes react to ring-open cyclohexene by metathesis to alleviate the thermodynamic strain of the ester-carbene ligand.

The fixation of the preformed polypyrazolylborate copper(I) complexes BpCu (1), Tp*Cu (2), and [B(pz)4]Cu (3) (Bp = dihydrobispyrazolylborate, H2B(pz)2; Tp* = hydrotris(3,5-dimethyl)pyrazolylborate, HB(pz*)3; B(pz)4 = tetrakispyrazolylborate) on silica gel and their use, under heterogeneous conditions, as catalysts for the olefin cyclopropanation reaction are reported. The catalytic activity is very similar to that observed under homogeneous conditions, as a consequence, according to the studies presented herein, of a ligand-to-support interaction that would involve the hydroxyl groups of the silica surface and the borohydride B−H group and/or the pyrazolyl nitrogen atoms. The strength of such interactions allows the recovery and recycling of the supported catalysts for a number of cycles.

The stepwise, low-temperature reaction of {Pd[CH(SiMe3)2](μ-Cl)(PMe3)}2 (1) with CNBu-t and NaCp‘ (Cp‘ = C5H5, C5H4Me) or LiInd (Ind = C9H7) affords metal-substituted fulvenes of composition Pd[C(NHBu-t)C(C4H3R)][CH(SiMe3)2](CNBu-t)(PMe3) (R = H, Me) and Pd[C(NHBu-t)C(C8H6)][CH(SiMe3)2](CNBu-t)(PMe3), of which the C5H4Me-derived complex 5a has been characterized by X-ray crystallography. The mononuclear species Pd[CH(SiMe3)2]Cl(CNBu-t)(PMe3) (2) has been isolated as an intermediate of this reaction. An alternative synthesis of the palladabenzofulvene complex 6 involves the reaction of the 16 electron indenyl derivative (η3-Ind)Pd[CH(SiMe3)2](PMe3) (7) with 2 equiv of CNBu-t. In this case an η1-indenyl intermediate of composition (η1-Ind)Pd[CH(SiMe3)2](CNBu-t)(PMe3) (8) can be observed by low-temperature NMR spectroscopy. The complex Pt[CH(SiMe3)2]Cl(CNBu-t)(PMe3) (12) has been synthesized by the comproportionation reaction of Pt[CH(SiMe3)2]Cl(PMe3)2 (10) and Pt[CH(SiMe3)2]Cl(CNBu-t)2 (11), in the presence...

Regioselective methods for allene hydrosilylation have been developed, with regioselectivity being governed primarily by the choice of metal. Alkenylsilanes are produced via nickel catalysis with larger N-heterocyclic carbene (NHC) ligands, and allylsilanes are produced via palladium catalysis with smaller NHC ligands. These complementary methods allow either regioisomeric product to be obtained with exceptional regiocontrol.

Epoxides have been obtained from alde-hydes and phenyldiazomethane using catalytic amounts of both the copper homoscorpionate com-plexes Tp xCuL (Tpx = homoscorpionate ligand; L = acetonitrile or tetrahydrofuran, THF) and dimethyl sulfide (SMe2) in high yields and diasteroselectivities, and with activities higher (TOF = 46 h-1) than those already known with rhodium-or copper-based cata-lysts. Among the copper(I) homoscorpionate com-plexes tested, TpBr3Cu(NCCH 3) showed the highest catalytic activity under mild conditions. The catalytic activity is controlled by electronic effects induced by the Tp x ligand as well as by the stability of the TpxCu(SR 2) adducts. Indeed, in the case of TpMs as ligand, the TpMsCu(THT) (THT = tetrahydrothio-phene) and Tp MsCu(SMe2) species could be isolated as very stable crystalline solids, the molecular struc-ture of the former being confirmed by single-crystal X-ray diffraction analysis. The in situ generation of PhCHN 2 from benzaldehyde tosylhydrazone sodium salt at 60 °C in methyl tert-butyl ether as solvent and TpMsCu(THF) as the catalyst also showed high cata-lytic activities, improving those already reported with copper-based catalysts. © 2013 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.

A set of barium aryl oxides of composition [Ba(OC6H2But2-2,6-X-4)2(thf)n](X = H 1, Me 2, OMe 3 or But4; thf = tetrahydrofuran) has been prepared together with the related adducts [Ba(OC6H2But2-2,6-X-4)2{P(NMe2)3O}2](X = H 5 or Me 6), which can be obtained by treating compounds 1 and 2 with neat P(NMe2)3O respectively. X-Ray studies showed that 6 has a distorted-tetrahedral structure, with the two Ba–O bonds to the aryl oxide ligands somewhat shorter than those to the P(NMe2)3O groups [2.414(8)vs. 2.579(8)A]. Samples of complex 4 and [Ti(OC6H3Pri2-2,6)4], respectively, and a third homogeneous sample obtained by mixing equimolar amounts of these have been subjected to bombardment by Ar+ and O2+ ions of relatively low energy (3.5 keV) and the ensuing transformation investigated by X-ray photoelectron spectroscopy. No significant variation of the C/M ratio was observed when employing Ar+ ions, but O2+ produced a remarkable decrease in the carbon content which leads eventually to the formation of inorganic compounds, BaCO3, TiO2 and BaTiO3, respectively, for the three samples. Action of oxygen plasma on the titanium aryl oxide did not result in a marked decrease in the C/M ratio, but it produced instead high concentrations of carbon- and oxygen-containing species.

The alkylation of [NiCl 2 (PMe 3 ) 2 ] with Mg[CH(SiMe 3 ) 2 ]Cl yielded the alkyl dimer [Ni{CH(SiMe 3 ) 2 }(μ-Cl)(PMe 3 )] 2 ( 1 ), which readily inserted CNBu t to afford [Ni{ η 2 -C(NBu t )CH(SiMe 3 ) 2 }Cl(PMe 3 )] ( 4 ); spectroscopic and X-ray studies reveal this complex contains an η 2 -alkaneimidoyl ligand.

Experimental as well as theoretical studies have been carried out with the aim of elucidating the mechanism of the atom transfer radical addition (ATRA) of styrene and carbon tetrachloride with a TpxCu(NCMe) complex as the catalyst precursor (Tpx = hydrotrispyrazolyl−borate ligand). The studies shown herein demonstrate the effect of different variables in the kinetic behavior. A mechanistic proposal consistent with theoretical and experimental data is presented., We thank the MICINN (Grants CTQ2008-00042BQU, CTQ2008-06866-CO2-02/BQU, and Consolider Ingenio 2010 CSD2006-0003) and the Junta de Andalucía (Proyecto P07-FQM-02794) for financial support.

Equimolar mixtures of ethyl diazoacetate and alkynes can be converted into cyclopropenes in very high yields, at room temperature, through the intermediacy of readily available Cu(I) catalysts containing trispyrazolylborate ligands.

The oxidative addition of ClCH2CO2Et, ClCH2CN and BrCH2OMe to [Ni(cod)2](cod = cycloocta-1,5-diene), in the presence of 2 equivalents of PMe3, affords the β-functionalized nickel(II) methyl derivatives trans-[Ni(CH2R)X(PMe3)2](R = CO2Et, X = Cl 1; R = CN, X = Cl 2; R = OMe, X = Br 3). The interaction of these complexes with carbon monoxide has been studied. The methoxymethyl derivative 3 forms a stable acyl of composition trans-[Ni{C(O)CH2OMe}Br(PMe3)2]7, but for the ethoxycarbonylmethyl complex 1 the corresponding acyl 8 forms reversibly and, although stable as a solid, only exists in solution under an atmosphere of carbon monoxide. No stable acyl has been observed from the reaction of 2 with CO; only decomposition occurs. Stable 18-electron alkyl and acyl cyclopentadienyl derivatives of composition [Ni(CH2R)(η-C5H5)(PMe3)](R = CO2Et 4; CN 5, or OMe 6) and [Ni{C(O)CH2R}(η-C5H5)(PMe3)](R = OMe 9 or CO2Et 10) are easily obtained upon reaction of the above 16-electron complexes with Na(C5H5). The new compounds have been fully characterized by analytical and spectroscopic (IR and 1H, 13C and 31P NMR) methods.

Efficient and selective ATRA reactions of CCl(4), CBr(4), TsCl (Ts = tosyl), or Cl(3)CCO(2)Et with activated olefins (styrene, methyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate) using the Tp(tBu)Cu(NCMe) complex as a catalyst have been achieved in the absence of any reductant and with low catalyst loadings.

A novel and convenient one-pot synthesis of ruthenium(II) dihydride phosphine complexes from the air-stable [RuCl_2(COD)]_x, the appropriate phosphine, and NaOH in sec-butyl alcohol under argon at 80 °C is reported. A series of chelating (dcpm, dcpe, dppe, dppb, dppp, dppf, and depe) and monodentate phosphine (PEt3 and PPh3) complexes have been synthesized using this methodology. The crystalline products are isolated in high yield. These dihydride complexes have been shown to be useful precursors to cationic dihydrogen hydride complexes, some of which exhibit significant activity as hydrogenation catalysts.

The synthesis of ruthenium carbenes by the reaction of a Ru(0) compound or Ru(0) precursors with dihalo compounds is reported. A new procedure for the preparation of [Ru(H)2(H2)2(PCy3)2] and the use of this complex as a starting material for the synthesis of ruthenium carbenes are presented.

A procedure for generating the ruthenium hydride complex Ru(H)(H2)Cl(PCy3)2 in 95% yield is presented. Following a novel insertion−elimination pathway, this hydride can react with propargyl or vinyl halides to make metathesis-active vinyl and alkyl carbene species with the general formulas (PCy3)2Cl2RuCH−CHCR2 and (PCy3)2Cl2RuCHR, respectively. Tertiary propargyl chlorides work best, giving Ru−vinyl carbenes in extremely high yield.

The complexes Tp(x)Cu (Tp(x) = homoscorpionate ligand) catalyze the high yield addition of the carbene fragment :CHCO(2)Et, from ethyl diazoacetate, to furans under mild conditions to give different cyclopropanes and dienes with ratios that depend on the Tp(x) ligand employed, therefore inducing the control of the selectivity in this transformation.

A series of complexes TpxCu (Tpx = homoscorpionate ligand) have been tested as the catalysts for the olefin aziridination reaction using PhINTs as the nitrene source. Very high yields of aziridines have been obtained with a group of representative substrates, including nonactivated terminal olefins. The high activity of these catalysts has allowed the use of equimolar amounts of PhINTs and olefins, avoiding the requirement of excess olefin. In an effort to eliminate nondesired byproducts, chloramine-T has been employed as the nitrene source, in a reaction that produces sodium chloride as the sole residue, with high degrees of conversions also being obtained.

The complexes TpXCu (TpX = homoscorpionate) catalyse the insertion of diazo compounds into nitrogen–hydrogen bonds of amines and amides, under very mild conditions, with quantitative yields being obtained with equimolar ratios of reactants.

The complexes BpCu (1) and Tp*Cu (2) catalyse the transformation of styrene into styrene oxide using Oxone as the oxidising agent; the use of silica gel-supported 1 or 2 as heterogeneous catalysts affords similar results, using water as the sole solvent.

The catalytic dechlorination of aryl chlorides performed by RuHCl(H_2)_2(PCy_3)_2 and RuH_2(H_2)_2(PCy_3)_2 in alcohols is rapid and complete within 1 h. The mechanism involves a transfer hydrogenation step with participation of the alcohol. The system exhibits significant functional group tolerance. The catalyst can be generated in situ from [RuCl_2(COD)]_x (COD = cyclooctadiene) and 2 equiv of phosphine (PCy_3 or P^iPr_3). Catalytic conversions are similar to those observed when an isolated precatalyst is used. Mechanistic considerations and the scope of the process are discussed.

A novel synthetic entry to 2-azabicyclo[3.3.1]nonanes based on a copper(I)-catalyzed intramolecular coupling of amino-tethered trichloroacetamides and unsaturated nitriles, esters and alkenes, as well as enol acetates, is described. A study of the reaction conditions and the scope of the process is reported.

The use of the bulky hydrotris(3-mesitylpyrazolyl)borate anionic ligand has allowed the synthesis of stable Tp(Ms)Cu(alkyne) complexes (alkyne = 1-hexyne, 1, phenylacetylene, 2, and ethyl propiolate, 3). The spectroscopic and structural features of these compounds and their relative reactivity have been examined, indicating the existence of a low π back-bonding from the copper(I) centre to the alkyne. Ligand exchange experiments have shown that terminal alkyne adducts are more stable than internal alkyne analogues. In good accordance with this, the previously reported alkyne cyclopropenation reaction catalysed by the Tp(x)Cu complexes can be rationalized and correlated with their relative stability.

The 16e- pseudoallylic complex Ni(η3-CH2C6H4-O-Me)Cl(PMe3) effects α-C-H abstraction from the benzoannelated nickelacycle Ni(CH2CMe2-o-C6H4)(PMe 3)2 (1) under very mild conditions, with formation of the tetrametallic species [Ni2(μ2-CHCMe2-o-C6H 4)(PMe3)2]2(μ-Cl)2 (2), in which two identical metal-metal-bonded bimetallic subunits are held together by chloride bridges. Each of these moieties incorporates a bifunctional organic fragment that possesses alkylidene and aryl termini that bridge the two metal atoms. Rupture of the (Ni2)2-(μ-Cl)2 bridges by PMe3 produces a binuclear nonsymmetric alkylidene, Ni2(μ2-CHCMe2-o-C6H 4)Cl(PMe3)3 (3), also exhibiting alkylidene and aryl bridges. A similar reaction of 2 with Me2PCH2CH2PMe2 (dmpe) furnishes the related, albeit cationic, alkylidene species [ÍÚ2(ì2-CHCMe2-o-C6H4) (dmpe)2]Cl (4). Interaction of the tetranuclear alkylidene 2 with NaCp produces the bimetallic product CpNi(μ2-CHCMe2-o-C6H4)Ni(PMe 3)2 (5). This complex can also be obtained by α-H abstraction from the methylene group of the metallacycle 1 by the 18-electron allyl derivative CpNi(η3-C3H5). The former reaction route also allows the synthesis of the analogous derivatives (C5H4R)Ni(η2-CHCMe2-o-C 6H4)Ni(PMe3)2 (R = Me (6), i-Pr (7)). Different kinds of μ-alkylidene compounds are furnished by the reaction of 2 and the poly(pyrazolyl)-borate salts K[HB(pz)3] (pz = pyrazolyl) and Tl[H2B(3-t-Bu-pz)2]. These new complexes have η2-bonded poly(pyrazolyl)borate ligands that bridge the two Ni atoms, i.e. Ni2(μ2-CHCMe2-o-C6H 4)[μ2-η1:η1-HB(pz) 3](PMe3)2 (8) and Ni2(μ2-CHCMe2-o-C6H 4)[μ2-η1:η1-H 2B(3-t-Bu-pz)2]-(PMe3)2 (9), respectively. Complexes 2 and 3 have been characterized by X-ray crystallography. Compound 2 crystallizes in the monoclinic space group P21/n with a = 9.815(4) Å, b = 10.550(4) Å, c = 19.669(7) Å, β= 104.39(3)°, and Z = 4. Crystals of 3 are orthorhombic, Pbca, with a = 17.152(4) Å, b = 18.431(3) Å, c = 32.577(5) Å, and Z = 16. Both display short metal-metal contacts (2.384(3) and 2.393(3) Å, respectively) suggestive of strong Ni-Ni bonding interactions. The alkylidene fragment symmetrically bridges the two Ni atoms in 2 and 3, but while in 2 the aryl bridges are also symmetric, in 3 one of the Ni-Caryl distances at 2.17(1) Å is perceivably longer than the other (1.99(2) Å). Compound 5 has also been characterized by X-ray crystallography. It crystallizes in the monoclinic space group P21/n, with unit cell constants a = 9.013(2) Å, b = 16.675(2) Å, c = 15.291(7) Å, β= 91.04(3)°, and Z = 4. © 1993 American Chemical Society.

Equimolar mixtures of ethyl diazoacetate and alkynes can be converted into cyclopropenes in very high yields, at room temperature, through the intermediacy of readily available Cu(I) catalysts containing trispyrazolylborate ligands.

The complexes BpCu (1) and Tp*Cu (2) catalyse the transformation of styrene into styrene oxide using Oxone as the oxidising agent; the use of silica gel-supported 1 or 2 as heterogeneous catalysts affords similar results, using water as the sole solvent.