Synthesis and structure of a boron cation supported by a β-diketiminate ligand

The salt [HC(CMe)₂(NAr)₂BPh][Al₂Cl₇] (3); Ar = 2,6-i-Pr₂C₆H₃) has been synthesized via the in situ preparation of [HC(CMe)₂(NAr)₂BClPh], followed by treatment with AlCl₃. X-ray analysis of 3 reveals that the BN₂C₃ ring of the boron cation is planar and DFT calculations indicate π-type interactions in the HOMO-6 and HOMO-7 orbitals.     

Magnesium complexes containing β-ketiminate and β-diketiminate ligands with dimethylamino substituents on the ligand core nitrogen atoms

Treatment of dibutylmagnesium with two equivalents of 4-(2,2-dimethylhydrazino)dimethylhydrazone-3-penten-2-one (L¹H) in diethyl ether afforded Mg(L¹)₂ (76%), which contains η²-L¹ ligands with tetrahedral coordination at the magnesium ion. Similar treatment of dibutylmagnesium with 4-(2,2-dimethylhydrazino)-3-penten-2-one (L²H) or 5-(2,2-dimethylhydrazino)-2,6-dimethyl-4-hepten-3-one (L³H) and 4-tert-butylpyridine (4-tBupy) in diethyl ether afforded the octahedral complexes Mg(L²)₂(4-tBupy)₂ (85%) and Mg(L³)₂(4-tBupy)₂ (79%). Treatment of dibutylmagnesium with two equivalents of L²H or L³H in the absence of 4-tBupy afforded [Mg(L²)₂]₂ and Mg(L³)₂, however, these complexes were difficult to isolate due to the sticky nature of the crude products. A better synthetic approach entailed sublimation of Mg(L²)₂(4-tBupy)₂ or Mg(L³)₂(4-tBupy)₂ at 95-100 °C/0.05 Torr, which afforded [Mg(L²)₂]₂ (94%) and Mg(L³)₂ (80%) as colorless crystalline solids that were easily isolated. Treatment of [MgCp(CH₃)(OEt₂)]₂ with two equivalents each of 4-tBupy and L¹H afforded MgCp(L¹)(4-tBupy) (65%). Similar treatment of [MgCp(CH₃)(OEt₂)]₂ with two equivalents of L²H or L³H afforded the dimeric complexes [MgCp(L²)]₂ (81%) and [MgCp(L³)]₂ (84%), respectively. [MgCp(L²)]₂ and [MgCp(L³)]₂ decompose upon attempted sublimation at 125-130 °C/0.05 Torr to afford Cp₂Mg (47-53%) and [Mg(L²)₂]₂ (67%) or Mg(L³)₂ (74%). The X-ray crystal structures of Mg(L¹)₂, Mg(L³)₂(4-tBupy)₂, [Mg(L²)₂]₂, Mg(L³)₂, MgCp(L¹)(4-tBupy), [MgCp(L²)]₂, and [MgCp(L³)]₂ are described. The thermal stability and volatility of the complexes were determined through preparative sublimation experiments. Many of the complexes sublime without decomposition at moderate temperatures and low pressures, and thus represent new potential precursors for thin film growth using chemical vapor deposition and related techniques.     

Synthesis and properties of group 9 metal complexes bearing a β-ketophosphenato ligand

A novel β-ketophosphenato ligand bearing a bulky substituent, Tbt(2,4,6-tris[bis(trimethylsilyl)methyl]phenyl), on the phosphorus atom was newly designed and synthesized as a heavier congener of a β-ketoiminato ligand. Rhodium and iridium complexes bearing this new β-ketophosphenato ligand have been synthesized and fully characterized by spectroscopic and elemental analyses together with X-ray crystallographic analyses. The results of NMR spectroscopic studies and the X-ray structural analyses suggested that the β-ketophosphenato ligand has unique electronic features due to the low-coordinated phosphorus atom. Comparison of properties between rhodium β-ketophosphenates 2a,b and rhodium β-ketoiminate 7 revealed the character of the β-ketophosphenato ligand, where the trans influence of the phosphorus atom should be stronger than the nitrogen atom of the β-ketoiminato ligand.     

Synthesis and fluorescence properties of novel pyrazine-boron complexes bearing a β-iminoketone ligand

A novel fluorescence dye based on pyrazine-boron complexes bearing a β-iminoketone ligand has been synthesized by using a simple two-step reaction. Synthesized complexes exhibited fluorescence in solution (F(max): 472-604 nm) and in the solid state (F(max): 496-624 nm). These complexes showed a larger Stokes shift (3690-4900 cm(-1)) than well-known boron dipyrromethene dyes (400-600 cm(-1), in most cases).     

Synthesis and X-ray structure of cationic methallyl palladium complexes supported by unsymmetrical β-diimine ligands

Treatment of the unsymmetrical β-iminoamine ligands [PhCN(Ar)CHCNH(Ar)Me] with the zerovalent complex Pd(dba)₂ in the presence of the methallyloxyphosphonium salt, gives high yields of the cationic β-diimine complexes [PhCN(Ar)CH₂CN(Ar)(Me)Pd(η³-C₄H₇)]⁺[PF₆]⁻ (Ar = 2-Me-C₆H₄ (7); 2-MeO-C₆H₄ (8); 2,6-Me₂-C₆H₃ (9); 2,6-iPr₂-C₆H₃ (10)). All the new complexes have been characterised by NMR and IR spectroscopy. The structure of the cationic methallyl palladium complex (10) has been solved by X-ray crystallography.     

Synthesis and X-ray structure of neutral Pd(IV) hydride complexes supported by β-ketoimine ligands

A series of neutral palladium(IV) hydride complexes supported by β-ketoimine ligands was synthesized. Reaction of dichlorobis(acetonitrile)palladium(II) with β-ketoamines (1–4) in dichloromethane at room temperature generated dark red solids of [PdCl₂(β-ketoimine)(H)] (6–9) in which the central carbon of the ketoimine ligand is σ-bound to the palladium. All the new complexes have been characterized by NMR and IR spectroscopy. The structure of complex(9) has been solved by X-ray crystallography.     

Synthesis and reactivity of cationic niobium and tantalum methyl complexes supported by imido and β-diketiminato ligands

The synthesis and reactivity of the cationic niobium and tantalum monomethyl complexes [(BDI)MeM(N(t)Bu)][X] (BDI = [Ar]NC(CH(3))CHC(CH(3))N[Ar], Ar = 2,6-(i)Pr(2)C(6)H(3); M = Nb, Ta; X = MeB(C(6)F(5))(3), B(C(6)F(5))(4)] was investigated. The cationic alkyl complexes failed to irreversibly bind CO but formed phosphine-trapped acyl complexes [(BDI)(R(3)PC(O)Me)M(N(t)Bu)][B(C(6)F(5))(4)] (R = Et, Cy) in the presence of a combination of trialkylphosphines and CO. Treatment of the monoalkyl cationic Nb complex with XylNC (Xyl = 2,6-Me(2)-C(6)H(3)) resulted in irreversible formation of the iminoacyl complex [(BDI)(XylN[double bond, length as m-dash]C(Me))Nb(N(t)Bu)][B(C(6)F(5))(4)], which did not bind phosphines but would add a methide group to the iminoacyl carbon to provide the known ketimine complex (BDI)(XylNCMe(2))Nb(N(t)Bu). Further stoichiometric chemistry explored i) migratory insertion reactions to form new alkoxide, amidinate, and ketimide complexes; ii) protonolysis reactions with Ph(3)SiOH to form thermally robust cationic siloxide complexes; and iii) catalytic high-density polyethylene formation mediated by the cationic Nb methyl complex.     

Paramagnetic aluminium β-diketiminate

The β-diketiminate ligand framework is shown to undergo reduction to form a neutral main group radical stabilized by spiroconjugation of the unpaired electron over the group 13 element centre. The synthesized paramagnetic complex was characterized by EPR spectroscopy and computational chemistry.     

Electronic perturbations of iron dipyrrinato complexes via ligand β-halogenation and meso-fluoroarylation

Systematic electronic variations were introduced into the monoanionic dipyrrinato ligand scaffold via halogenation of the pyrrolic β-positions and/or via the use of fluorinated aryl substituents in the ligand bridgehead position in order to synthesize proligands of the type 1,9-dimesityl-β-R(4)-5-Ar-dipyrrin [R = H, Cl, Br, I; Ar = mesityl, 3,5-(F(3)C)(2)C(6)H(3), C(6)F(5) in ligand 5-position; β = 2,3,7,8 ligand substitution; abbreviated ((β,Ar)L)H]. The electronic perturbations were probed using standard electronic absorption and electrochemical techniques on the different ligand variations and their divalent iron complexes. The free-ligand variations cause modest shifts in the electronic absorption maxima (λ(max): 464-499 nm) and more pronounced shifts in the electrochemical redox potentials for one-electron proligand reductions (E(1/2): -1.25 to -1.99 V) and oxidations (E(1/2): +0.52 to +1.14 V vs [Cp(2)Fe](+/0)). Installation of iron into the dipyrrinato scaffolds was effected via deprotonation of the proligands followed by treatment with FeCl(2) and excess pyridine in tetrahydrofuran to afford complexes of the type ((β,Ar)L)FeCl(py) (py = pyridine). The electrochemical and spectroscopic behavior of these complexes varies significantly across the series: the redox potential of the fully reversible Fe(III/II) couple spans more than 400 mV (E(1/2): -0.34 to +0.50 V vs [Cp(2)Fe](+/0)); λ(max) spans more than 40 nm (506-548 nm); and the (57)Fe M?ssbauer quadrupole splitting (|ΔE(Q)|) spans nearly 2.0 mm/s while the isomer shift (δ) remains essentially constant (0.86-0.89 mm/s) across the series. These effects demonstrate how peripheral variation of the dipyrrinato ligand scaffold can allow systematic variation of the chemical and physical properties of iron dipyrrinato complexes.     

Enantioselective chlorination of β-keto esters and amides catalyzed by chiral copper（Ⅱ） complexes of squaramide-linked bisoxazoline ligand

Enantioselective chlorination of b-keto esters and amides catalyzed by squaramide-linked bisoxazoline ligand–Cu（OAc）2complexes was investigated. The corresponding chlorinated products were obtained in excellent yields with moderate enantioselectivities. The effect of solvent, temperature, Lewis acid, and ligand structure on the reaction is discussed. This was the first investigation of catalytic asymmetric achlorination of b-keto amides. This study has highlighted that a simple chiral squaramide–oxazoline with cheap Cu（OAc）2 H2 O complexes can catalyze this chlorination.     

Unexpected results of the reactions of manganese and vanadium β-diketiminate halide complexes with Na[HBEt3]

The reaction of [(^Menacnac^Dipp)Mn(μ-Cl)]₂(2) (^Menacnac^Dipp = HC(C(Me)NDipp)₂; Dipp = 2,6-Prⁱ₂C₆H₃) with sodium triethylborohydride in a toluene—THF mixture afforded the complex [(^Menacnac^Dipp)Mn(μ-H)₂BEt₂(THF)] (3). The reaction of 2 with Na[HBEt₃] in toluene under THF-free conditions gave a mixture of products. The set and the ratio of these products in the resulting crystalline mixture were established by quantitative powder X-ray diffraction analysis: [(^Menacnac^Dipp)Mn(μ-H)]₂(1), [(^Menacnac^Dipp)?Mn(μ-H)₂BEt₂] (4), and unreacted compound 2 in the ratio of 15:4:1 and traces of an unknown crystalline phase. The reaction of [(^Menacnac^Dipp)VCl₂] (5) with Na[HBEt₃] yielded the compound [(^Menacnac^Dipp)V(μ-H)(μ,κ^1:1?C:C′?C₂H₄)BEt₂] (6) containing the unusual ligand [HBEt₂(CH₂CH₂)]^2?. The vanadium analog of compound 3, [(^Menacnac^Dipp)V(μ-H)₂BEt₂(THF)] (7), was isolated in one experiment. Besides. a small amount of the complex [(^Menacnac^Dipp)V(μ-H)BEt₃(THF)] (8) was detected in the mixture of crystalline products. The structures of compounds 3, 4, 6, 7, and 8 were determined by single-crystal X-ray diffraction.

     

Can an ancillary ligand lead to a thermodynamically stable end-on 1 : 1 Cu-O2 adduct supported by a beta-diketiminate ligand?

The finding that dioxygen binds end-on to the Cu(B) site in the crystal structure of a precatalytic complex of peptidylglycine alpha-hydroxylating monooxygenase has spurred the search for biomimetic model complexes exhibiting the same dioxygen coordination. Recent work has not only indicated that sterically hindered beta-diketiminate ligands (L(1)) could support side-on 1 : 1 Cu-O(2) adducts, but also that an end-on L(1)Cu(THF)O(2) structure occurs as an unstable intermediate in the oxygenation mechanism of the Cu(I) complex. In this work, density functional theory and multireference methods are used to determine the potential of ancillary ligands, X, other than THF to yield thermodynamically stable end-on L(1)CuXO(2) species. A diverse set of ligands X, comprising phosphines, thiophene, cyclic ethers, acetonitrile, para-substituted pyridines, N-heterocyclic carbenes, and ligands bearing hydrogen bond donors, has been considered in order to identify ligand characteristics which energetically favor end-on L(1)CuXO(2) over: a) reversion to the Cu(I) complex and dioxygen, b) isomerization to side-on L(1)CuXO(2), and c) decay to L(1)CuO(2) and X. Ancillary ligands with judiciously chosen degrees and orientation of steric bulk and which bear potential hydrogen bond donors to an end-on bound dioxygen moiety most favor oxygenation of L(1)CuX to yield end-on L(1)CuXO(2). Conversion to the side-on isomer can be deterred through the use of a sufficiently bulky ligand X, such as one that is at least the size of a 5-membered ring. Loss of X to give L(1)CuO(2) can be made prohibitively endergonic by employing ligands X which are highly electron donating and which backbond strongly with and sigma-donate significantly to copper.     

The β-nucleation of polypropylene random copolymer filled by nano-CaCO3 supported β-nucleating agent

In this article, ??-nucleation of nano-CaCO₃ (CC) supported ??-nucleating agent (Sup-??-NA) for random polypropylene copolymer (PPC) crystallization was studied by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. The results showed that Sup-??-NA not only increased the peak temperature of the crystallization of PPC but also induced PPC to form almost pure ??-modification. It indicated that Sup-??-NA possessed effective ??-nucleation. The content of Sup-??-NA had little influence on the crystallization behavior and melting characteristics together with the ??-modification content of PPC, but those were affected by the mass ratio of CC/??-NA (calcium pimelate) in the Sup-??-NA. The final temperature of the melt between 300 and 180?°C did not affect the ??-nucleation of Sup-??-NA, although the ??-nucleation of Sup-??-NA would be decreased with the final temperature of the melt lower than 170?°C. In addition, DSC multiple heating and cooling scanning had little influence on the thermal stability of ??-nucleation of Sup-??-NA.     

Rare-earth metal amido complexes supported by bridged bis(β-diketiminato) ligand as efficient catalysts for hydrophosphonylation of aldehydes and ketones

A series of rare-earth metal amides supported by a cyclohexyl-linked bis(β-diketiminato) ligand were synthesized,and their catalytic activities for hydrophosphonylation of aldehydes and ketones were developed.Reaction of [(Me3Si)2N]3 RE(Cl)Li(THF)3 with the cyclohexyl-linked bis(-diketimine) H2L(1)(L=Cy[NC(Me)CHC(Me)NAr]2,Cy = cyclohexyl,Ar=2,6-i-Pr2C6H3) gave the rare-earth metal amides LREN(SiMe3)2(RE = Nd(2),Sm(3),Dy(4),Er(5),Y(6)).All complexes were fully characterized by elemental,spectroscopic and single-crystal X-ray analyses.Investigation of the catalytic properties of the complexes reveals that these complexes exhibited a high catalytic activity towards the hydrophosphonylation of aldehydes and ketones in the presence of a very low loading of rare-earth metal amides(0.1-1 mol%) at room temperature in a short time.     

Synthesis and X-ray structure of cationic β-diimine palladium complexes containing π-methallyl ligand

High yield of cationic palladium β-diimine complexes [(CH₂(MeCNAr)₂)Pd(η³-C₄H₇)][Y] (Ar = C₆H₅, Y = PF₆ (8); 2-Me-C₆H₄, Y = PF₆ (9); 2,6-Me₂-C₆H₃, Y = PF₆ (10); 2,6-iPr₂-C₆H₃, Y = PF₆ (11), Y = B(3,5-(CF₃)₂-C₆H₃)₄ (12)) have been obtained by an oxidative addition of the methallyloxyphosphonium salts (5, 6) to a preformed complex Pd(dba)₂ (7) in the presence of the β-iminoamine ligands (1-4).These complexes are thermally stable and have been characterized by ¹H and ¹³C{¹H} NMR as well as IR spectroscopy. The structure of the cationic allyl palladium complex (12) has been solved by X-ray crystallography.     

Theoretical binding affinities and spectra of complexes formed by a cyclic β-peptoid with amino acids

Binding affinities of a cyclic β-peptoid to amino acids were studied using the density functional theory (DFT) at the B3LYP/6-311G(d,p) level after the basis set superior error (BSSE). The host molecule possesses binding ability to amino acids since the binding energies of the complexes formed are negative. The complexes were stabilized via hydrogen bonds between the host and the guest molecules. Based on the B3LYP/6-31G(d) optimized geometries, electronic spectra of the complexes were calculated using the INDO/CIS method. ¹³C NMR spectra and nucleus-independent chemical shift (NICS) values of the complexes were computed at the B3LYP/6-31G(d) level. Carbon atoms in the carboxyl groups of the complexes are shifted downfield relative to those of the host. Some complexes exhibit aromaticity although the host shows anti-aromaticity. Formation of hydrogen bonds leads to cyclic current formation in these complexes.     

Oxidation and coupling of β-diketiminate ligand in lanthanide complexes: novel eight-nuclear lanthanide clusters with μ-, μ3-Cl, and μ4-O bridge

Two novel eight-nuclear lanthanide oxide and chloride clusters Ln(8)(μ-η(2)-L(4))(2)(μ(3)-Cl)(4)(μ-Cl)(10)(μ(4)-O)(3)(THF)(8) (Ln = Er(3), Dy(4); L(4) = [OC{(Me)CN-2,6-(i)PrC(6)H(3)}(2)](2-)) have been synthesized by the reaction of β-diketiminate rare-earth metal chlorides with oxygen, providing a new oxidation and coupling reaction of the β-diketiminate ligand.     

Zirconium complexes with versatile β-diketiminate ligands: Synthesis, structure, and ethylene polymerization

A series of zirconium complexes (2c, 2d, 2f, 2g, 2h, 2i) containing symmetrical or unsymmetrical β-diketiminate ligands were synthesized by the reaction of ZrCl₄ · 2THF with lithium salt of the corresponding ligand in 1:2 molar ratio. X-ray crystal structures reveal that complexes 2d and 2g adopt distorted octahedral geometry around the zirconium center. These complexes showed moderate activities for ethylene polymerization, when methylaluminoxane (MAO) was used as cocatalyst. The steric and electronic effects of the substituents at the phenyl rings had considerable influence on the catalytic activities of the metal complex, as well as the molecular weights and molecular weight distributions (MWD) of produced polymers. Introduction of electron-withdrawing CF₃ group to phenyls in the ligand led to a significant increase of catalytic activities, and complex 2f (p-CF₃) exhibited the highest catalytic activity of 7.45 × 10⁵ g PE/mol-Zr · h among the investigated complexes. Complexes 2a-d could produce ultra-high molecular weight polyethylenes (UHMWPE) that were hardly dissolvable in decahydronaphthalene or 1,2-dichlorobenzene under the molecular weight measurement conditions. Nevertheless, polyethylenes with broad MWD could be afforded by complexes 2g-i, which was probably due to the introduction of bulky unsymmetrical ligands leading to the formation of multi active species under polymerization conditions. High-temperature ¹³C NMR data indicate the linear structure of obtained polyethylenes.     

Reduction of sterically hindered β-diketiminato europium(III) complexes by the β-diketiminato anion: a convenient route for the synthesis of β-diketiminato europium(II) complexes

The metathesis reaction of anhydrous EuCl(3) with sodium salt of bulky β-diketiminato NaL (L = [N(2, 4, 6- Me(3)C(6)H(2))C(Me)](2)CH(-), L(2, 4, 6-Me3); [N(2,6-(i)Pr(2)C(6)H(3))C(Me)](2)CH(-), L(2, 6-ipr2) and [(2, 6-(i)Pr(2)C(6)H(3))NC(Me)CHC(Me)N(C(6)H(5))](-), L(2, 6-ipr2)(Ph)) in THF at 60 °C afforded the corresponding Eu(II) complexes: Eu(II)(L(2, 4, 6-Me3))(2)(THF) (1), Eu(II)(L(2, 6-ipr2))(2) (2) and Eu(II)(L(2, 6-ipr2)(Ph))(2) (5) with the formations of dimers (L(2, 4, 6-Me3))(2) (3) and (L(2, 6-ipr2))(2) (4) for the former two reactions and proligand L(2, 6-ipr2)(Ph)H (6) for the latter one. Compounds 1-6 were confirmed by an X-ray crystal structure analysis. The central metal Eu(II) in 1 is coordinated by two monoanionic L(2, 4, 6-Me3) ligands and one THF molecule in a trigonal bipyramid. The Eu(II) in each of 2 and 5 is ligated by two monoanionic ligands to form a tetrahedral geometry. The BVS (Bond Valence Sum) calculation indicates the oxidation state of Eu in all the three complexes is 2+ (2.12 for 1, 1.86 for 2 and 1.99 for 5). The isolation of dimers of (L(2, 4, 6-Me3))(2) and L(2, 6-ipr2))(2) and proligand L(2, 6-ipr2)(Ph)H demonstrates that the reducing agent in the present reduction of a Eu(III) ion to a Eu(II) ion might be the (L(2, 4, 6-Me3))(-), (L(2, 6-ipr2))(-) and (L(2, 6-ipr2)(Ph))(-), respectively. The possible mechanism for the reduction pathway is presented.