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The aryl-substituted α-diimine (DI) nickel vinyl complex (iPrDI)Ni(CH═CH2) (iPrDI = [2,6-(iPr)2C6H3N═C(CH3)]2) was synthesized and structurally characterized. The complex is dimeric in the solid state and has a distorted-square-planar geometry at nickel. A combination of single-crystal X-ray diffraction, EPR, magnetic susceptibility, and NMR analyses was used to elucidate the electronic structure of the compound, and it is best described as a low-spin Ni(II) derivative with a singly reduced α-diimine chelate. Addition of CO2 to the nickel vinyl complex resulted in insertion into the nickel–carbon bond to yield the corresponding nickel acrylate (iPrDI)Ni(κ2-O2CCH═CH2). EPR spectroscopy coupled with DFT calculations established that the S = 1/2 product maintains the nickel(II) oxidation state with an α-diimine-centered radical. Addition of acrylic acid to (iPrDI)Ni(CH═CH2) induced rapid, net bimetallic reductive elimination to release butadiene and produced the metastable olefin-bound acrylic acid complex (...

Reduced pyridine(diimine) molybdenum olefin complexes have been synthesized and structurally characterized. Examples with 1,5-cyclooctadiene, (PDI)Mo(η2:η2-1,5-COD) (COD = 1,5-cyclooctadiene) adopt a distorted-trigonal-bipyramidal geometry and are best described as low-spin Mo(II) compounds arising from significant π back-donation to the ligand from a reduced molybdenum center. With the 2,6-diisopropyl N-aryl-substituted variant of the pyridine(diimine) ligand, a molybdenum bis(ethylene) complex was obtained. Reducing the size of the N-aryl substituents to 2,4,6-trimethyl resulted in isolation of (MesPDI)Mo(η4-butadiene)(η2-ethylene) following sodium amalgam reduction of the corresponding molybdenum(III) trichloride complex in the presence of excess ethylene. Analysis of the byproducts of the reaction and olefin addition experiments demonstrate that butadiene formation is consistent with a pathway involving ethylene coupling to form 1-butene followed by allylic dehydrogenation to produce butadiene. Excess...

Two mononuclear TmIII complexes, [Tm(COT)I(THF)2] (1-Tm) and [K(18-crown-6)(THF)2][Tm(COT)2] (2-Tm), display slow relaxation of the magnetization, making these compounds rare examples of non-Kramers TmIII single-molecule magnets (SMMs). Utilizing a stepwise synthetic approach for the installation of cyclooctatetraenide (COT) ligands, we can observe the effect of symmetry optimization at the metal center. This method results in an 85% increase in the energy barrier to magnetization reversal (Ueff) for 2-Tm (Ueff = 53.3 K) over 1-Tm (Ueff = 7.93 K). The increased local symmetry of 2-Tm reduces the need for large static fields, eliciting SMM behavior under a small field of 200 Oe. This illustrates the power of fine-tuning the ligand environment to enhance the magnetic relaxation properties of non-Kramers ions.

Cobalt fluorocarbene complex CpCo(═CF(CF3))(PPh2Me) (Cp = η5-cyclopentadienyl) reacts with para-substituted phenylacetylenes to furnish partially fluorinated cobaltacyclobutene complexes [Cp(PPh2Me)Co{κ2-C(Ar)═CHCF(CF3)}], which were isolated and characterized by elemental analysis, multinuclear NMR and UV–vis spectroscopy, and X-ray crystallography. The scope of reactivity between CpCo(═CFRF)(L) and various alkynes was explored. The detailed pathway for the [2 + 2] cycloaddition reaction was investigated using a combination of kinetic studies and DFT computational chemistry (M06/def2-TZVP), with a 1,4 diradical species identified as the key intermediate.

The thermal properties of a series of monomeric copper(I) hexamethyldisilazide complexes supported by N-heterocyclic and acyclic diamino carbenes were evaluated to study the impact of N-alkyl substituents and backbone character on volatility and thermal stability of copper amides. The series of complexes were either liquids or solids with melting points in the broad range of 45–184 °C. Vaporization rates were measured by stepped-isothermal TGA experiments and found to be between 110–170 °C. Enthalpies of vaporization were determined to be 63–90 kJ/mol. Temperatures for 1 Torr vapor pressure were estimated to be 143–172 °C, showing a general dependence on molecular weight. The imidazolylidene complexes were thermally unstable with convincing evidence indicating the unsaturated backbone as a point of weakness. The imidazolinylidene complexes showed excellent thermal stability with comparable results for the formamidinylidenes complexes. The steric parameter of the carbene, %VBur, was calculated for all comp...

First-row transition metal catalysis offers a cheaper, more environmentally sustainable alternative to second- and third-row transition metal catalysts. Nickel has shown great promise as a tool for the borylation of unsaturated compounds to yield boronic esters, but Markovnikov-selective hydroborations of simple styrenes have not been well-explored. Herein, we report the synthesis of benzyl boronic esters via nickel-catalyzed hydroboration of styrenes using a heteroleptic N-heterocyclic carbene (NHC)–phosphine nickel complex, IMes(Cy3P)NiCl2. The IMes(Cy3P)NiCl2 complex displays a broad substrate scope and maintains the integrity of yield and regioselectivity when challenged with substrates bearing increased steric hindrance. The heteroleptic complexes also tolerate both electron-withdrawing and -donating groups, in contrast to traditional bis-phosphine and Ni(0) complexes.

Reactions of carbene complex [Cp(IPr)Ru(pyr)2][BF4] (6, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with excess acetonitrile and LiCl in THF afford complexes [Cp(IPr)Ru(NCCH3)2][PF6] (7) and Cp(IPr)RuCl (8), respectively. Complex 8 was characterized by NMR and X-ray diffraction analysis. Addition of hydrosilanes to 8 results in silane σ-complexes Cp(IPr)Ru(η2-HSiR3)Cl (4), which were characterized by NMR and X-ray studies of Cp(IPr)Ru(η2-HSiMeCl2)Cl (4b) and Cp(IPr)Ru(η2-H3SiPh)Cl (4d). The hydrogen–silicon coupling constants of complexes 4 show an unusual trend in that the J(H–Si) values increase from the less-chlorinated complex Cp(IPr)Ru(η2-HSiMe2Cl)Cl (4c) to the trichloro derivative Cp(IPr)Ru(η2-HSiCl3)Cl (4a). Reaction of Cp(IPr)RuCl (8) with two equivalents of HSiCl3 gave the ruthenate complex [IPrH]+[CpRuCl(H) (SiCl3)2]−, characterized by NMR and X-ray study. Addition of hydrosilanes to the cationic complex [Cp(IPr)Ru(NCCH3)2][BArF4] (9) furnished very unstable cationic silane σ-comple...

We report the first isolable nickel difluorocarbene complexes (NiP2[P(OMe)3](═CF2); P2 = Ph2P(CH2)2PPh2, 2 P(OMe)3), which are also the only examples of formally d10 metal fluorocarbenes. These [Ni0]═CF2 complexes react with tetrafluoroethylene (TFE) to yield the rare perfluorometallacyclobutanes [NiP2(κ2-CF2CF2CF2−)], with potential relevance to fluoroalkene metathesis and polymerization. Preliminary kinetic experiments establish that the reactions of the new [Ni]═CF2 compounds with TFE are considerably faster than the analogous reactions of their previously reported [Co]═CF2 counterparts. Further, we show that TFE addition to 2 is a dissociative process, in contrast to [Co]═CF2, which reacts with TFE in an associative fashion. Finally, the preliminary reactivity of NiP2(κ2-CF2CF2CF2−) (P2 = Ph2P(CH2)2PPh2) is described.

An improved synthesis of the known trifluoromethyl cobalt compound Co(CO)4(CF3) (1), which gives significantly higher yields than previously reported methods, allows for an investigation of its carbonyl substitution chemistry. Treatment of 1 with P-donor ligands of varying denticity under thermal conditions afforded Co[P(O-o-tolyl)3](CO)3(CF3) (2), Co(DPPE)(CO)2(CF3) (3), and Co(P3)(CO)(CF3) (4) in high isolated yields [DPPE = Ph2PCH2CH2PPh2; P3 = PhP(CH2CH2PPh2)2]. The new cobalt N-heterocyclic carbene complex Co(SIPr)(CO)3(CF3) (5) [SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene)] was obtained by phosphine substitution from Co(PPh3)(CO)3(CF3), a known compound efficiently prepared from 1. Additionally, we report the synthesis of two rare cobalt difluorocarbene complexes ([Co] = CF2) produced by fluoride abstraction from 3 or 4. These results are relevant to our efforts to assess the reactivity of first-row metal perfluoroalkyl and fluorocarbene complexes.

The synthesis, structure, and magnetic properties of a uranium(III) sandwich complex, [Li(DME)3][UIII(COT″)2] (COT″ = bis(trimethylsilyl)cyclooctatetraenyl dianion), and its coordinatively analogous tetravalent equivalent, [UIV(COT″)2], were investigated. Additionally, a full structural and magnetic comparison to the isostructural and isoelectronic lanthanide complex, [Li(DME)3][NdIII(COT″)2], is provided. DFT calculations reveal that the UIII complex leads to weaker ligand-to-metal donation as compared with the tetravalent equivalent complex. Alternating current magnetic susceptibility results reveal slow magnetic relaxation in both UIII and NdIII complexes. The enhanced magnetic performance of the UIII congener further encourages the use of actinides in the design of single-molecule magnets.

Ethylene oligomerization activities of chromium catalysts stabilized by different dipyrrole-based ancillary ligands, [(Ph2C(C4H4N)2)] (2), [Ph2C(C4H4N)(C5H6N)] (3), [(Et)2C(C4H4N)2] (4), and [(C6H5)(C5H4N)C(C4H4N)(C5H6N)] (5), have been investigated using different activation methods, and the results have been compared with the commercial Chevron-Phillips ethylene trimerization system. Upon activation with triethylaluminum (TEA), chromium catalysts stabilized by dipyrrole-based ligands 2-5 showed a lower activity and selectivity compared to the Chevron-Phillips trimerization system based on 2,5-dimethylpyrrole (1) as the ancillary ligand. However, unprecedented increases in both activity and selectivity have been observed by carrying out the oligomerization in methylcyclohexane using depleted-methylaluminoxane (DMAO) along with triisobutylaluminum (TIBA) (1:2 ratio) as cocatalyst system under mild conditions, even for the Chevron-Phillips system itself. Well-defined chromium complexes, [(Ph2C(C4H3N)2)Cr(Cl)(THF)3] (6) and {[Ph2C(C4H3N)(C5H6N]Cr(THF)(μ-Cl)}2 (7), have been synthesized and fully characterized. Upon activating with MAO, catalyst 7 produced a statistical distribution of oligomers, whereas under identical oligomerization conditions catalyst 6/MAO was found to be inactive. The use of MeAlCl2 as cocatalyst to activate 7 resulted in the switching of the catalyst's behavior from producing a statistical distribution of LAOs to the selective trimerization of ethylene to 1-hexene. The addition of dialkylzinc along with MAO resulted in an unprecedented activity increase. (Figure Presented).

Herein we disclose experimental and in silico gas-phase studies of β-methyl and β-hydride elimination from cationic diphosphine palladium(II) neopentyl and isobutyl complexes. In particular, we have determined activation barriers for these transformations through mass-spectrometric threshold collision-induced dissociation (T-CID) studies. These systems can undergo at least one of the several competitive processes: (1) β-methyl elimination, (2) Pd–C bond homolysis, or (3) β-hydride elimination. We also confirm that qualitative trends in the branching ratios between these processes depend on the diphosphine bite angle, whereas electronic modifications of phosphine electron-donating ability have no significant effect on the barriers for β-methyl elimination within the experimental error. The full reaction manifold has been investigated with density functional theory (DFT) and affords a valuable experimental benchmark for types of organometallic transformations described herein.

Iminopyrrole, aminopyrrole, and aminophosphine ligands were complexed with various chromium sources, producing eight complexes that were tested for their catalytic behavior toward epoxide-CO2 copolymerization. As elucidated by MALDI-TOF-MS, copolymerizations afforded polycarbonates and poly(ether-carbonates) exhibiting linear or cyclic topologies.

Chromium complexes bearing a series of pyridinephosphine ligands have been synthesized and examined for their catalytic behavior in ethylene oligomerization. The choice of solvent, toluene versus methylcyclohexane, shows a pronounced influence on the catalytic activity for all these complexes. Variations of the ligand system have been introduced by modifying the phosphine substituents affecting ligand bite angles and flexibility. It has been demonstrated that minor differences in the ligand structure can result in remarkable changes not only in catalytic activity but also in selectivity toward a-olefins versus polyethylene and distribution of oligomeric products. Ligand PyCH2N(Me)(PPr2)-Pr-i, in combination with CrCl3(THF)(3) afforded selective ethylene tri- and tetramerization, giving 1-hexene and 1-octene with good overall selectivity and high purity, albeit with the presence of small amounts of PE.

The ligand 2,6-[(Ph2)2PN]2C5H3N based on the popular PNP motif has been used to generate the corresponding chromium adduct {2,6-[(Ph2)2PN]2C5H3N}CrCl3·2.5THF (1). Its reaction with Et2AlCl and Cl2AlEt afforded the two nearly isostructural complexes {2,6-(Ph2PNH)[(Et2ClAl)NPPh2]C5H3N}CrCl(PEtPh2)·0.5(toluene) (2) and {2,6-(Ph2PNH)[(EtCl2Al)NPPh2]C5H3N}CrCl(PEtPh2)·0.5(toluene) (3). The formation of these two species is the result of a multiple attack of the activator at both the ligand system and the metal center. During the reaction, the two nitrogen atoms lost one phosphine residue each, the metal was reduced, one of the two nitrogens was protonated, and one EtPPh2 molecule was formed and retained by the metal center. The three complexes characterized in this work display activity for catalytic and nonselective ethylene oligomerization.

Oxidative addition of very robust C–F and C–O bonds has been accomplished in reactions of the aluminum(I) compound NacNacAl (1, NacNac = [ArNC(Me)CHC(Me)NAr]− and Ar = 2,6-Pri2C6H3) with fluoroarenes, fluoroalkanes, and ethers. Similar to the transition metals, the ease of aryl C–F oxidative addition decreases as the degree of fluorination diminishes on the aromatic substrate. As well, kinetic studies on the addition of 1,2,3,4-tetrafluorobenzene to compound 1 revealed a second-order reaction characterized by a very negative entropy of activation (ΔS⧧ = −113.6(3) J/K·mol), consistent with a transition metal-like oxidative addition process.

The gas-phase reactivity of the [(NN)(PtMe3)-Me-IV](+) (NN = alpha-diimine) complex 1 and its acetonitrile adduct has been investigated by tandem mass spectrometry. The only observed reaction from the octahedral d(6) complex 1 center dot MeCN is the simple dissociation of the coordinated solvent molecule with a binding energy of 24.5(6) kcal mol(-1) measured by energy-resolved collision-induced dissociation experiments. Further reactions of 1 are observed. In addition to the expected reductive elimination of ethane from 1, competitive loss of methane occurs. Methane is generated from the initially formed ethane agostic complex via either C-H activation/bond formation or sigma-bond metathesis with the third methyl group. Energy-resolved collision-induced dissociation experiments indicate that the initial reductive C-C coupling step is rate limiting for both ethane and methane elimination, and afford a gas-phase barrier of 22.6(7) kcal mol(-1) for this process. Density functional theory calculations confirm the reaction mechanisms, and a variety of functionals are benchmarked. The results at the M06-L/SDB-cc-pVTZ//mPW1K/SDD(d,p) level of theory agree well with the experiments and suggest that the generation of [(NN)PtH](+) at higher collision energy proceeds through sequential loss of methane and ethylene.

The first example of a [P,S]-ligated metal perfluorocyclopentane is reported. The new metallacycle undergoes Cα–F activation in the presence of a Lewis acid, followed by chemoselective ligand migration, affording a fused metallabicyclic product. Reactivity of this product includes an unprecedented nucleophile-induced ring-opening reaction, involving loss of a β-fluoride. Additionally, hydrolysis of the metallabicyclic product affords a single isomer of hexafluoro-1-butene.

Two novel highly fluorescent blue light emitting compounds were synthesized: 9,9-bis(diquinaldinatoalumino)-1,3-diphenyl-9-silafluorene (4) and 9,9-bis(diquinaldinatoalumino)-9-silafluorene (7). Co...

Di- and trivalent chromium complexes of the pyridine-based ligand [2,6-(Ph2PCH2)2 C5H3N]CrCl3 (1) and {[2,6-(Ph2CH2)2C5H3N]CrCl2}.(THF) (2) and their aluminate aggregates [2,6-(Ph2CH2)2C5H3NCrCl(μ-Cl)AlClMe2] (3), {[(2,6-(Ph2CH2)2C5H3NCrCl(μ-Cl)AlClEt2]}. (toluene)0.5 (4), {2,6-(Ph2CH2)2C5H3NCrEt(μ-Cl)2AlEt2}{AlCl3Et} (5), {2,6-(PPh2CH2) C5H3N (PPh2CH)Al(i-Bu)2(μ-Cl)Cr(μ-Cl)2Al(i-Bu)2}.(toluene)1.5 (6), and {[2,6-(PPh2CH2)2C5H3 N]2Cr} {(μ-Cl)[Al(i-Bu)3]2} (7) were prepared, isolated, and their activities toward ethylene oligomerization tested. While complexes 3, 5, and 6 were directly accessible by reacting catalyst precursor 1 with Me3Al, DEAC, and TIBA, respectively, complexes 4 and 7 were prepared using catalyst precursor 2 with DEAC and TIBA, respectively. All these complexes, with the exception of 7, showed good activities for a polymer-free ethylene oligomerization. Complex 7 contains cationic chromium in its monovalent state and its encapsulation in an octahedral ligand field as defined by two liga...

A trivalent chromium complex of a PN(pyridine) ligand system, {[(2,6-Ph2P-NH)2C5H3N]CrCl3}(THF)2 (1), was prepared and tested as a catalyst for ethylene oligomerization and polymerization, with the purpose of probing the ability of a pyridine ring substituent as a stabilizing factor on catalytically active intermediates. Its nonselective catalytic behavior indicated that ready reduction of the metal center to the divalent state occurred during the activation process. To substantiate this point, we have reacted 1 with a few common aluminate activators and isolated both the divalent complexes {[2,6-Ph2PNHC5H3NAlClEt2NPPh2]Cr(μ-Cl)2AlEt2}(toluene) (3) and {[2,6-Ph2PNHC5H3NAlCl-i-Bu2NPPh2]Cr(μ-Cl)2Al-i-Bu2}2 (toluene) (4) and the trivalent complexes {[2,6-Ph2PNHC5H3NAlClMe2NPPh2]CrMe(μ-Cl)2AlMe2}(toluene)1.5 (2) and {[2,6-Ph2PNHC5H3 NHNPPh2]CrEt(μ-Cl)2AlEt2}AlEtCl3(hexane)0.5 (5). The reaction of the ligand with the divalent chromium precursor CrCl2(THF)2 in the presence of alkylaluminum afforded {[2,6-Ph2PNH...

Mono- and dianions of a polycyclic compound with a central sp3-hybridized silicon atom, spirosilabifluorene (C24H16Si, 1), were prepared by reduction with alkali metals. The salts containing 1•– and 12– anions were isolated and studied by single-crystal X-ray diffraction. The lithium salt of the C24H16Si•– radical monoanion ([Li(THF)4+][1•–], 2) exists as a solvent-separated ion pair in the solid state. Substantially different geometrical parameters were found for each of the fluorene groups within the C24H16Si•– anion of 2 due to asymmetric charge distribution. The C24H16Si2– dianion was isolated in the form of its sodium ([{Na(THF)3+}{Na(THF)+(12–)], 3) or potassium ([{K(THF)+}2(12–)], 4) salt. The environment at the central silicon atom in the dianion is flattened in comparison to the monoanion and neutral compound, with the angle between the two fluorene planes measured at 55° in 12– vs 89° in 1•– and 83° in 10. The aggregation of dianions and alkali-metal counterions leads to the formation of dimeric...

Several 1,3-diphenyl-substituted silafluorene compounds were synthesized and characterized as potential fluorescent materials for OLED fabrication and bioimaging. Introducing phenyl groups into the silafluorene ring at the 1- and 3-positions led to a red shift in the emission, resulting in blue light emitting compounds (λmax 368–375 nm in solution; λmax 362–371 and 482 nm in the solid state), and improved the quantum yield efficiency both in solution and as solids. Aggregation enhanced emission of the silafluorenes (AEE) was also investigated. Theoretical MO calculations were carried out to aid in understanding the optical properties of these molecules. Since these compounds might be useful in bioimaging, their toxicity was also investigated in skin fibroblast cells. All compounds were found to be nontoxic to the investigated cell cultures.

The pyrazolyl pyridylimine ligands [2-(3,5-dimethylpyrazol-1-yl)ethyl]pyridin-2-ylmethyleneimine (L1) and [2-(3,5-di-tert-butylpyrazol-1-yl)ethyl]pyridin-2-ylmethyleneimine (L2) and pyrazolyl thienylimine ligands [2-(3,5-dimethylpyrazol-1-yl)ethyl]thiophen-2-ylmethyleneimine (L3), [2-(3,5-di-tert-butyl-pyrazol-1-yl)ethyl]thiophen-2-ylmethyleneimine (L4), [2-(3,5-dimethylpyrazol-1-yl)ethyl]-2-bromothiophen-2-ylmethyleneimine (L5), and [2-(3,5-di-tert-butyl-pyrazol-1-yl)ethyl]-2-bromothiophen-2-ylmethyleneimine (L6) were synthesized by condensation of the appropriate pyrazolylamine and the corresponding aldehyde. Reactions of L1–L6 with [PdCl(Me)(cod)] gave the corresponding palladium(II) complexes [PdCl(Me)(L)] (where L = L1 (1a), L2 (2a), L3 (3a), L4 (4a), L5 (5a), L6 (6a)) in very good yields. The pyridylimine ligands L1 and L2 were found to coordinate via the imine and pyridine nitrogen atoms, while the thienylimine ligands L3–L6 coordinate via imine and pyrazolyl nitrogen atoms to the palladium. The ca...

Unusual nucleophilic cobalt fluorocarbene complexes ([CoI]═CFR; R = F, CF3) are described. Only a handful of fluorocarbenes of first-row transition metals have been reported, and these have exhibited electrophilic reactivity at the metal–carbene bonds. The title compounds are the first persistent/isolable cobalt fluorocarbenes and also rare examples of metal fluorocarbenes with relatively nucleophilic M═C bonds (vs other metal fluorocarbene complexes), demonstrated by their reactions with H+ and Me+ and their unusual stability toward water. X-ray crystal structures reveal the shortest terminal cobalt–carbene bonds reported to date, and DFT studies provide details into the nature of these bonds.

Chromium complexes of three new ligands, Ph2PN(Me)(CH2)2-X [X = NMe2(PNN); PPh2 (PNP); Py (PNPy)], have been examined vis-a-vis their ability to promote ethylene tetramerization, (PNN)CrCl3(L) [L = THF (1); CH3CN (2)], (PNPy)CrCl3(L) [L = THF (3); CH3CN (4)], and (PNP)CrCl3(THF) (5). In the case of 2 and 4, it was possible to grow crystals suitable for X-ray diffraction. The reaction of 3 with Et3Al afforded the dinuclear [(HN(Me)(CH2)2Py)CrCl2Et]2 (6) containing a trivalent chromium connected to an Et group. During the alkylation though, the ligand has been fragmented with removal of the side arm and protonation of the N atom of the remaining NP residue. All the complexes have been tested for ethylene oligomerization activity. Complex 1 displayed the highest selectivity for 1-octene, upon activation with DMAO in MeCy. Contrary to expectations, complex 6 is not a self-activating catalyst.

The reaction of phenazine with standard aluminum alkyls AlR3 (R = Me (a), Et (b), Et/Cl (c), i-Bu (d)) afforded, after initial coordination and formation of [AlMe3]2(μ-η1:η1-C12H8N2) (1), a further slow and complex transformation. As a result, the dinuclear and diamagnetic [AlR2]2(μ-η1:η1-C12H8N2)2 (R = Me (2a), Et (2b), Et/Cl (2c), i-Bu (2d)) were formed in parallel to the paramagnetic and monomeric (AlR3)[η1-C14H13NN(R)] (3). The diamagnetism of 2 is obtained via dimerization and implementation of an efficient intramolecular antiferromagnetic coupling. In the case of the reaction with Et2AlCl, the corresponding (AlEtCl2)[η1-C14H13NN(Et)] (3c) was isolated and fully characterized. In all the other cases, only compelling ESR evidence was obtained for the formation of isostructural species. On the basis of the isolation of both 2c and 3c from the same reaction, a mechanism is proposed involving ligand-assisted homolysis of Al−C bonds.

The formally Co(0) complex LCo(N2) (L =2,6-bis(2,6-dimethylphenyliminoethyl)pyridine) can be prepared via either Na/Hg reduction of LCoCl2 or hydrogenolysis of LCoCH2SiMe3. In the latter reaction, LCoH could be trapped by reaction with NCC6H4-4-Cl to give LCoN=CHC6H4-4-Cl. LCo(N2) reacts with many alkyl and aryl halides RX, including aryl chlorides, to give a mixture of LCoR and LCoX in a halogen atom abstraction mechanism. Intermediacy of free alkyl and aryl radicals is confirmed by the ring-opening of cyclopropylmethyl to crotyl, and the rearrangement of 2,4,6-tBu3C6H2 to 3,5-tBu2C6H3CMe2CH2, before binding to Co. The organocobalt species generated in this way react further with activated halides R′X (alkyl iodides; allyl and benzyl halides) to give cross-coupling products RR′ in what is most likely again a halogen abstraction mechanism. DFT studies support the proposed radical pathways for both steps. MeI couples smoothly with LCoCH2SiMe3 to give LCoI and CH3CH2SiMe3, but the analogous reaction of tBuI leads in part to radical attack at the 3 and 4 positions of the pyridine ring to form (tBu2-L)CoI and (tBu2-L)CoI2.

Reduction of the tetranuclear {((t-Bu)NPPh2)- Cr(μ-(t-Bu)NPPh2)2Cr}2(μ-Cl)2 (1) with either KC8 or vinyl Grignard afforded the dinuclear, mixed-valence (Me3P)Cr(μ- (t-Bu)NPPh2)3Cr (2) with the two metals possessing distinctively different coordination environments. According to the formulation of 2 as Cr(I)/Cr(II) mixed-valence species, 2 acts as a self-activating catalyst, producing under pressure of ethylene a mixture of 1-butene and 1-hexene. Activation with three different activators selectively produced three different products, namely, 1-butene with TEAL, 1-hexene with DMAO/TEAL, and LAO-free highly linear HMWPE with DMAO. Mixtures of 1-hexene and 1-butene were also obtained upon activation with vinyl Grignard. In this case it was possible to isolate, albeit in very low yield, an intriguing butadiene/butadiene-diyl cluster, {((η 4 -butadiene)Cr (μ,η 4 -butadienediyl)(μ- NP)Mg)2(μ-Cl)4Mg(THF)2}{((THF)3Mg)2(μ-Cl)3}2 (3), which is also a highly selective self-activating trimerization catalyst.

Two pyridine-SNS ligands (2,6-CH2SR)(2)C5H5N (R = t-Bu (a), n-decyl (b)) were prepared and tested for the possibility of forming active and selective chromium trimerization catalyst precursors. The two trivalent derivatives [(2,6-CH2SR)(2)C5H5N]CrCl3 (1a,b), and the divalent [(2,6-CH2S(t-Bu)(2)C5H5N]CrCl2 center dot THF (2a) were isolated and characterized. Upon treatment of la with Me3Al, the self-activating, single-component, highly selective chromium trimerization catalyst [2,6-CH2S(t-Bu)(2)C5H5N]CrMe[mu-Cl)AlMe3)](2) (3a) was obtained and fully characterized.

The reactions of the deprotonated form of cis-{[(mu-N)(t-Bu)](2)PN(H) (o-OMeC6H4)](2)} (a) with either CrCl2(THF)(2) or CrCl3(THF)(3) afforded the corresponding dimeric Cr(II) and monomeric Cr(III) complexes {cis-[(mu-N)(t-Bu)](2)[PN (o-MeOC6H4)](2)Cr}(2) (1a) and cis-[(mu-N)(t-Bu)](2)[PN-2-MeOC6H4](2)CrCl (2a). By replacing the ligand's o-OMeC6H4 groups with less-crowded CH2CH2N(i-Pr)(2) functionalities and reacting the deprotonated form of cis-{[(mu-N)(t-Bu)](2)[PN(H)CH2CH2N(i-Pr)(2))](2)} (b) with CrCl2(THF)(2), the dimetallic, divalent {cis-[(mu-N)(t-Bu)](2)[PNCH2CH2N(i-Pr)(2))](2)Cr}(2) (1b) was obtained in crystalline form. Upon activation with MAO, both la and 1b afforded highly active, polyethylene-free ethylene oligomerization catalysts. Complex 2a is instead catalytically inactive.

Metal boryl complexes have received significant attention in the literature in recent years due to their role as key intermediates in a number of metal-catalyzed borylation reactions. The ligand scaffold is known to have a significant impact on the observed reactivity of these metal boryl complexes. A synthetic strategy to access ruthenium boryl analogues of the Shvo metal-ligand catalysts is described. Heating a precursor to Shvo's catalyst (1) with bis(catecholato)diboron at 50 °C provided ruthenium boryl complex 3 [2,5-Ph(2)-3,4-Tol(2)(η(5)-C(4)COBcat)Ru(CO)(2)Bcat] (Bcat = catecholatoboryl). Addition of bis(catecholato)diboron to complex 1 in the presence of a phenol results in ruthenium boryl complex5 [2,5-Ph(2)-3,4-Tol(2)(η(5)-C(4)COH)Ru(CO)(2)Bcat] at 22 °C in 30% isolated yield. A single crystal X-ray analysis of complex 5 confirmed the assigned structure. An improved synthesis of ruthenium boryl complex 5 was developed by the in situ formation of complex 3 [2,5-Ph(2)-3,4-Tol(2)(η(5)-C(4)COBcat)Ru(CO)(2)Bcat] followed by addition of the phenol, resulting in a 51% yield.

Reactions of the tetranuclear (Cp*RuCl)4 (1) with the corresponding butadienesulfinate salts Li[SO2CH═CR′CH═CHR] [R = R′ = H, (2a); R = H, R′ = Me, (2b); R = R′ = Me, (2c)] in THF result in the formation of tetrameric [Cp*Ru(1,2,5-η-SO2CH═CR′CH═CHR)LiCl]4 [R = R′ = H, (3); R = H, R′ = Me, (4); R = R′ = Me, (5)] complexes. Compound 5 has been isolated in two pseudo-polymorphic crystal forms as 5 in space group P421c and as 5·3THF, where there are three molecules of solvated THF per tetramer, in space group I4. Both tetramers occupied a crystallographic 4-fold-roto inversion axis. In both structures the tetramer symmetry is S4, and these distorted cubane-like kernel structures are similar to the one found in compound 1. If potassium butadienesulfinates are used in the reaction with 1 instead of lithium salts 2a−c, mononuclear allylsulfene ruthenium compounds [Cp*Ru(1−5-η-SO2CH═CR′CH═CHR)] [R = R′ = H, (6); R = H, R′ = Me, (7)] are isolated. The analogous compound 8 [R = R′ = Me] was prepared directly from...

The reaction of the dienone ruthenium dicarbonyl dimer {[2,5-Ph-3,4-Tol(η5-C4CO)]Ru(CO)2}2 (7) with propargyl alcohol at room temperature gave a high yield of β-ruthenium-enal (E)-[2,5-Ph-3,4-Tol(η5-C4COH)]Ru(CO)2(CH═CHCHO) (8E), which was characterized spectroscopically and by X-ray crystallography. Reaction of 7 with pent-2-yn-1-ol led to the kinetic formation of the E-isomer (E)-[2,5-Ph-3,4-Tol(η5-C4COH)]Ru(CO)2[C(CH2CH3)═CHCHO] (10E-Et), which isomerized to an equilibrium mixture of Z- and E-isomers upon heating. The intramolecular nature of the 1,2-hydrogen shifts involved in these reactions was established by the absence of crossover products in the reaction of 7 with a mixture of PhC≡CCH2OH and PhC≡CCD2OH. A primary deuterium isotope effect (kH/kD ≈ 11) was seen on the product-forming step in the reaction of 7 with PhC≡CCHDOH. The reaction of PhC≡CCH3 with 7 produced the alkyne complex [2,5-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)2(η2-PhC≡CCH3) (14). The key step in the mechanism of the reaction of 7 with pro...

A bis-pyrrolide ligand containing a nonconjugated aromatic ring in the backbone was reacted with ThCl4(DME)2, affording the corresponding η6-{1,3-[(2-C4H3N)(CH3)2C]2C6H4}ThCl3][Li(DME)3] (1) complex. In this species, the π-bonding interaction of the actinide with the ring is probably induced by steric constraint. The bonding mode of the pyrrolide rings was switched from σ to π upon treatment of complex 1 with Et3Al. This reaction was also accompanied by deprotonation of the aromatic ring and formation of two similar compounds with the ring σ-bonded to the Th metal center. The two compounds {[{1,3-[(η5-2-C4H3N)(CH3)2C]2C6H4}Th(μ-Cl-AlEt2)2](μ-Cl)2[{1,3-[(η5-2-C4H3N)(CH3)2C]C6H4}Th] (μ-AlEt2)Cl]}·(C7H8)0.5 (2a) and {[{1,3-[(η5-2-C4H3N)(CH3)2C]2C6H4}ThCl(μ-Cl)2[Li(DME)]2 (2b) were isolated and fully characterized. The common feature among these two species is that the switching of bonding mode of the pyrrolide rings, resulting from the coordination of the aluminum residues, is accompanied by deprotonation of...

Treatment of the lithium salt of t-BuN(H)PPh2 in THF with CrCl2 (THF)(2) afforded a dinuclear, [(t-BuNPPh2)Cr-2(mu-t-BuNPPh2)(3)]center dot(toluene)(1.5) (1), and a tetrameric cluster, [(t-BuNPPh2)Cr(mu-t-BuNPPh2)(2)Cr(mu-Cl)](2)center dot(toluene)(2) (5), depending on the reagents' stoichiometric ratio. Complex 1 is dimeric with a long intermetallic distance and the ligands adopting an asymmetric and distorted bridging-chelating bonding mode. Complex 5 is instead a symmetry-generated tetramer with two identical dimetallic units, each closely related in geometry to 1, linked by two bridging chlorine atoms. The reactions of 1 with alkyl aluminum activators afforded a series of divalent complexes, [{(mu-AlMe3)(t-BuNPPh2)}(2)Cr]center dot(toluene) (2), [{(mu-AlMe2Cl)(t-BuNPPh2)}(2)Cr]center dot(toluene) (3), and [{(mu-AlEt2Cl)(t-BuNPPh2)}(2)Cr]center dot(toluene) (4), containing organo-aluminum residues. Similarly, reaction of 5 with AlMe3 gave [{(mu-AlMe2)(t-BuNPPh2)(2)}Cr(mu-Cl)(2)center dot(toluene)(1.9) (6), also characterized by an X-ray crystal structure. Finally, the trivalent complex [(t-BuNPPh2)(3)Cr] (7) was readily prepared via reaction of the lithiated ligand with CrCl3(THF)(3). Upon treatment with AlMe3 or Et2AlCl, complexes 2 and [{(mu-AlEtCl2)(t-BuNPPh2)}(2)Cr]center dot(toluene) (8) were isolated and fully characterized. In turn, this indicated that reduction to the divalent state is the primary stage of the activation process of the trivalent species. The catalytic behavior of all of these complexes has been assessed in the presence and absence of cocatalyst and with different solvents. The result showed a pronounced solvent effect, allowing switching from nonselective oligomerization to selective trimerization.

Proton exchange reaction of isolated or in situ prepared heterobimetallic peralkylated Sm complexes with sterically demanding mono- and bisphenols led to the formation of aluminum alkyl samarium-ar...

The reactions of 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2,6-bis(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L2) with NiCl2 or NiBr2 gave the nickel(II) complexes [NiCl2(L1)] (1), [NiBr2(L1)] (2), [NiCl2(L2)] (3), and [NiBr2(L2)] (4) in high yields. Compounds 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L3) and 2-(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L4) on the other hand gave either mononuclear or dinuclear nickel(II) complexes, depending on the steric bulk of the substituents on the pyrazolyl unit. While L3 gave the dinuclear complexes [Ni2(μ2-Cl)2Cl2(L3)2] (5) and [Ni2(μ2-Br)2Br2(L3)2] (6), L4 gave the mononuclear complexes [NiCl2(L4)] (7) and [NiBr2(L4)] (8). Activation of 1−8 with EtAlCl2 resulted in the oligomerization of ethylene to C4, C6, and C8 alkenes, followed by subsequent Friedel−Crafts alkylation of the toluene solvent. Activities as high as 15 660 kg of alkylated products/mol Ni/h were observed for 5 at 40 bar. However, when hexane was used as solvent, only trace...

Bis(imido)W(VI) complexes of dianionic N,N′-disubstituted 1,8-diamidonaphthalene (R2DAN2−) (R = iPr, 3,5-Me2C6H3) are reported, and an X-ray structure and computational analysis of W(═NtBu)2[1,8-(iPrN)2C10H6] 1 revealed that the nonplanar coordination of the iPr2DAN2− ligand to the W center is favored to allow for increased electron donation from the amido N centers to the W. Experimental studies revealed that the R2DAN2− amido linkage is the preferred reaction site with isocyanates to yield tridentate amido/N,N′-ureato ligands and that reactions with Al2Me6 lead to methylation of W and formation of heterobimetallic species via a μ2-bridging interaction of the R2DAN2− ligand.

The tri- and divalent complexes of the 2,6-bis(RSCH2)pyridine [R = Ph, Cy] ligands have been prepared. Upon activation with MAO, both species are catalysts for ethylene oligomerization of moderate activity. However, while the trivalent catalysts produced only 1-hexene, the divalent species gave a statistical distribution of oligomers. This clear difference in catalytic behavior indicates that the two oxidation states are not interconnected during the catalytic cycle as it happens instead with other oligomerization catalytic systems. The trivalent precursor is not reduced and the divalent is not oxidized. Treatment of the trivalent catalyst precursors with either MAO or other R3Al species afforded intractable materials. Instead, similar reactions with the divalent complexes gave new cationic species, which have been characterized by X-ray analysis. These complexes have preserved the divalent state of chromium during the reaction and still produce, upon further activation, a statistical distribution of oligomers. This reiterates the non-interconvertibility of the di- and trivalent oxidation states and the different degree of selectivity for which they are responsible.

The synthesis and comprehensive characterization of a new series of N-heterocyclic phosphine, arsine, and stibine compounds is presented. The diamidochloropnictines ClPn(NR)2C10H6 (Pn = P, As, Sb) were prepared via the dehydrohalide coupling reactions of N,N‘-diisopropyl-1,8-diaminonaphthalene, (iPrNH)2C10H6, or N,N‘-diphenyl-1,8-diaminonaphthalene, (PhNH)2C10H6, with the appropriate pnictogen trichloride. Reaction of these pnictines with appropriate halide abstraction agents yielded the corresponding phosphenium and arsenium salts. These planar pnictogenium cations {Pn(NR)2C10H6}+ (Pn = P, As; R = iPr, Ph) display dicoordinate pnictogen centers that are stabilized by an electron-rich diamidonaphthalene framework and represent rare examples of six-membered N-heterocyclic pnictogenium cations possessing a π-conjugated carbon backbone. The related stibenium salts could not be prepared via this route; however, the reaction of the new heteroleptic triamidostibene, (Me2N)Sb(iPrN)2C10H6, with triflic acid does ...

A family of N,N‘-disubstituted perimidinium cation salts were employed as precursors to persistent monomeric carbenes with novel molecular architectures and electronic structures. Depending on the substituents, reaction of these 1,3-disubstituted perimidinium cations with LiN(SiMe3)2 led either to deprotonation and generation of new carbenes or to enetetramines. In addition to spectroscopic characterization, crystallographic analysis of C10H6(iPrN)2C (10), C10H6(iPrN)(Me3CCH2N)C (11), {C10H6[N(3,5-Me2C6H3)]2C}2 (13), and C10H6(iPrN)(3,5-Me2C6H3N)C (14) definitively confirmed the nature of these species. The mixed benzyl/cycloheptyl-substituted carbene C10H6(cyclo-C7H13N)(p-MeC6H4CH2N)C (17) was observed to undergo dimerization upon heating to yield both cis and trans isomers of the enetetramine {C10H6(cyclo-C7H13N)(p-MeC6H4CH2N)C}2, (17)2. Rhodium complexes of these perimidine-based carbenes were accessed via reactions with either monomeric carbene or enetetramine. Spectroscopic and crystallographic analy...

The structures of three ortho-lithiated phenyloxazolines, the parent (1), the para-tert-butyl analogue (2), and the para-chloro analogue (3), were studied in solution. All three compounds are mixtures of monomers and dimers in THF/ether mixed solvents, with 2 the most aggregated and 3 the least. They are converted to monomers with HMPA and PMDTA. In the PMDTA complexes, the lithium appears to still be chelated to the oxazoline ring. Single-crystal X-ray structures were obtained for 1 and 2. Both are centrosymmetric dimers of B-type (each lithium coordinated to one oxazoline ring).