The synthesis and polymerization behavior of bimetallic pyridine diamide complexes containing transition metal (Ti,Zr)

Titanium and zirconium complexes with a pyridine diamide ligand, [2,6-(RNCH₂)₂NC₅H₃]²⁻ (PDMP; R = 2,6-dimethylphenyl) have been synthesized and their catalytic behaviors investigated for ethylene polymerization. It was found that the zirconium complexes, [PDMP]ZrCl₂ (7) and [PDMP][ZrCl₃ × THF]₂ (8), gave higher activities than the titanium complexes, [PDMP]TiCl₂ (5) and [PDMP][TiCl₃]₂ (6). The bimetallic complexes (6, 8) gave higher activities than the corresponding monometallic complexes (5, 7). The titanium complexes gave polymers with higher molecular weight (M_w) than the zirconium complexes. The molecular weight distribution (M_w/M_n) of the polymers obtained from the pyridine diamide complexes were much broader than that of the normal metallocene catalysts. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3756–3762, 1999     

Synthesis and characterisation of group nine transition metal complexes containing new mesityl and naphthyl based azaindole scorpionate ligands

Two novel boron-based flexible scorpionate ligands based on 7-azaindole, Li[HB(azaindolyl)(2)(1-naphthyl)] and Li[HB(azaindolyl)(2)(mesityl)] {Li[(Naphth)Bai] and Li[(Mes)Bai] respectively}, have been prepared (mesityl = 2,4,6-trimethylphenyl). These salts have been isolated in two forms, either as dimeric structures which contain bridging hydride interactions with the lithium centres or as crystalline material containing mono nuclear bis-acetonitrile solvates. The newly formed ligands have been utilised to prepare a range of group nine transition metal complexes with the general formula [M(COD){κ(3)-NNH-HB (azaindolyl)(2)(Ar)}] (where M = rhodium, iridium; Ar = 1-naphthyl, mesityl; COD = 1,5-cyclooctadiene) and [Rh(NBD){κ(3)-NNH-HB (azaindolyl)(2)(Ar)}] (where NBD = 2,5-norbornadiene; Ar = 1-naphthyl, mesityl). These new complexes have been compared to the previously reported compounds which contain the related scorpionate ligands Li[HB(azaindolyl)(2)(phenyl)] and K[HB(azaindolyl)(3)] {Li[(Ph)Bai] and K[Tai] respectively}. Structural characterisation of the complexes [Rh(COD){κ(3)-NNH-HB (azaindolyl)(2)(mesityl)}], [Ir(COD){κ(3)-NNH-HB (azaindolyl)(2)(mesityl)}] and [Rh(NBD){κ(3)-NNH-HB (azaindolyl)(2)(naphthyl)}] confirm the expected κ(3)-NNH coordination mode for these new ligands. Spectroscopic analysis suggests strong interactions of the B-H functional group with the metal centres in all cases.     

Synthesis, structural characterization, and theoretical investigation of compounds containing an Al-O-M-O-Al (M=Ti, Zr) core

We report a facile route to the first molecular compounds with the Al-O-M-O-Al (M=Ti, Zr) structural motif. Synthesis of L(Me)Al(mu-O)M(NMe2)2(mu-O)Al(Me)L [L=CH{N(Ar)(CMe)}2, Ar=2,6-iPr2C6H3; M=Ti (7), Zr (8)] was accomplished by reacting the monometallic hydroxide precursor L(Me)Al(OH) (1) with Ti(NMe2)4 or Zr(NMe2)4 under elimination of Me2NH in good yield. The crystal structural data confirm the trimetallic Al-O-M-O-Al core in both 7 and 8. Preliminary investigation on catalytic activity of these complexes reveals low activity of these complexes in ethylene polymerization as compared to the related oxygen-bridged metallocene-based heterobimetallic complexes L(Me)Al(mu-O)M(Me)Cp2 (M=Ti, Zr) which could be attributed to the relatively lower stability of the supposed cationic intermediate as revealed by DFT calculations.     

Theoretical study of M(+)-RG complexes (M = Ga, In; RG = He-Rn)

We present potential energy curves calculated at the CCSD(T) level of theory for Ga(+)-RG and In(+)-RG complexes (RG = He-Rn). Spectroscopic parameters have been derived from these potentials and compared to previously calculated parameters for the Al(+)-RG and Tl(+)-RG complexes. Additionally, for some cases, we compare these parameters with those obtained from electronic spectroscopic studies on excited states of the neutral species, arising from atomic-based d ← p excitations. The Ga(+)-RG and In(+)-RG potentials have also been used to calculate the transport coefficients for M(+) traveling through a bath of RG atoms.     

High-pressure synthesis of the polymorph of layer structured compounds MNX (M = Zr, Hf; X = Cl, Br, I)

Transition metal nitride halides MNX (M = Zr, Hf; X = Cl, Br, I) have two types of layer structured polymorphs, the alpha-form with the FeOCl type and the beta-form with the SmSI type. Both polymorphs consist of corrugated double M-N layers sandwiched between halogen layers, but with different atomic arrangements within the layers. The beta-form had been considered to be a high-temperature polymorph, because some beta-forms were obtained by thermal treatment of the corresponding alpha-forms. Here, the alpha-form was successfully transformed into the beta-form under high-pressure and high-temperature conditions; the new members of the beta-form were prepared for the first time from alpha-HfNBr, alpha-ZrNI, and alpha-HfNI using a high pressure of 3-5 GPa at 900 degrees C. The beta-form should be characterized as the high-pressure form rather than the corresponding high-temperature polymorph. This is the first high-pressure study on the polymorphs of metal nitride systems.     

Preparation and physical properties of early-late heterobimetallic compounds featuring Ir-M bonds (M = Ti, Zr, Hf)

Treatment of Cp*Ir N(t)Bu (1) with the appropriate metallocene equivalent is an effective route for the preparation of the heterobimetallic complexes Cp*Ir(μ-N(t)Bu)MCp(2) (2-M, M = Ti, Zr, Hf). The electronic structures of the isostructural series of compounds, 2-M, are described with reference to single-crystal X-ray, Raman, UV-vis, and cyclic voltammetry data. Density functional theory (DFT) calculations were used to aid in the interpretation of this experimental work. Treatment of the zirconium or hafnium congeners with 2,6-lutidinium triflate leads to protonation of the Ir-M bond, to afford Cp*Ir(μ-N(t)Bu)(μ-H)MCp(2)OTf (3-M, M = Zr, Hf). Compound 3-Zr was characterized by single-crystal X-ray diffraction and independently prepared by the reaction of 1 and Cp(2)Zr(H)Cl in the presence of Me(3)SiOTf. In reactions analogous to those for 2-Zr, 2-Hf reacts with S(8) and aryl azides to insert an S-atom or aryl azide fragment into the metal-metal bond, yielding Cp*Ir(μ-N(t)Bu)(μ-S)HfCp(2) (6-Hf) and Cp*Ir(μ-N(t)Bu)(N(3)Ph)HfCp(2) (4-Hf), respectively. Heating 4-Hf results in N(2) extrusion to form Cp*Ir(μ-N(t)Bu)(NPh)HfCp(2) (5-Hf). The kinetics of the latter reaction were studied to obtain activation parameters and a Hammett trend; these data are compared to those for the analogous reaction involving Ir-Zr heterobimetallics.     

Spectroscopic, and thermal studies of some new binuclear transition metal(II) complexes with hydrazone ligands containing acetoacetanilide and isoxazole

A new chelating ligand, 2-(2-(5-tert-butylisoxazol-3-yl)hydrazono)-N-(2,4-dimethylphenyl)-3-oxobutanamide (HL), and its four binuclear transition metal complexes, M(2)(L)(2) (micro-OCH(3))(2) [M=Ni(II), Co(II), Cu(II), Zn(II)], were synthesized using the procedure of diazotization, coupling and metallization. Their structures were postulated based on elemental analysis, (1)H NMR, MALDI-MS, FT-IR spectra and UV-vis electronic absorption spectra. Smooth films of these complexes on K9 glass substrates were prepared using the spin-coating method and their absorption properties were evaluated. The thermal properties of the metal(II) complexes were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). Different thermodynamic and kinetic parameters namely activation energy (E*), enthalpy of activation (DeltaH*), entropy of activation (DeltaS*) and free energy change of activation (DeltaG*) are calculated using Coats-Redfern (CR) equation.     

New trinuclear metal string complexes containing rigid Hdzp ligands: synthesis, structure, magnetism and DFT calculation (Hdzp = 1,9-diazaphenoxazine)

The synthesis, crystal structure, magnetic properties, and single-molecule conductance of two new trinuclear metal string complexes, [Ni(3)(dzp)(4)(NCS)(2)] (2) and [Co(3)(dzp)(4)(NCS)(2)] (3), containing the rigid Hdzp ligand (1, 1,9-diazaphenoxazine) are reported. X-ray structural analyses show that compounds 2 and 3 exhibit smaller torsion angles and longer metal-metal distances than those exhibited by the corresponding dpa(-) analogues (dpa(-) = dipyridylamido anion) due to the rigidity of Hdzp ligands. The longer metal-metal distance observed for 2 and 3 results in variations in their magnetic properties. The exchange interaction (J = -160 cm(-1)) between two high spin (HS) Ni(II) ions in 2 decreases slightly in comparison with those of trinickel dpa(-) analogues. The doublet-quartet gap of 3 is smaller than that of [Co(3)(dpa)(4)(NCS)(2)] (4), which causes compound 3 to show spin-crossover behavior even at low temperature.     

1, 1-Dithiolato-bridged heterobimetallic complexes containing a transition metal ion and oxouranium(VI)

Summary Anionic complexes [UO₂(1, 1-dithiolate)₂]^2– interact strongly with transition metal ions to yield a new class of dithiolato-bridged heterobimetallic complexes MUO₂(1, 1-dithiolate)₂ (M=Co^II, Ni^II, Cu^II, Zn^II or Pb^II, 1, 1-dithiolate = isomaleonitrile dithiolate (i-MNT^2–) and trithiocarbonate (CS ₃ ^2– )). (Et₄N)₂[UO₂(i-MNT)₂] and (Et₄N)₂[UO₂(CS₃)₂] have also been prepared. The complexes have been characterized by elemental analysis, i.r., u.v.-vis. and e.s.r. spectral studies. The heterobimetallic complexes are non-electrolytic, whereas (Et₄N)₂-[UO₂ (i-MNT)₂] and (Et₄N)₂[UO₂(CS₃)₂] are 21 electrolytes. The i.r. data indicate symmetrical bidentate bridging behaviour for the dithiolate ligands. Magnetic moments, electronic spectra and e.s.r. studies are commensurate with a square planar environment around Co^II, Ni^II and Cu^II.     

Theoretical studies of group 1 metal complexes with hydrogen fluoride, M(HF)n, M = Li, Na, and K: a new type of electrides

Small clusters of group 1 metal complexes with hydrogen fluoride molecules M(HF)n, M = Li, Na, and K, are studied with the ab initio molecular orbital method. The trimer M(HF)3 forms a C3v cluster, in which the metal atom is ionized and the ejected electron is trapped on the top of three equivalent HF molecules. The optimized geometric structure of Li(HF)3 is almost identical with that of the ion pair Li+(HF)3Cl- by replacing a Cl- anion with an ejected electron {e-}; thus Li(HF)3 can be described as Li+(HF)3{e-}. The entity {e-} is trapped under the electrostatic field created by three HF bond dipoles; and at the same time, the HF bonds are polarized and weakened. A triplet anion {e-}(HF)3Li+(HF)3{e-} is stable and is a possible anion unit of electrides.     

Rare-earth metal dichloride and bis(alkyl) complexes containing amidinate-amidopyridinate ligands: synthesis,structure, and reactivity

A reaction of anhydrous yttrium chloride with an equimolar amount of lithium amidinateamidopyridinate obtained in situ by metallation of N,N’-bis(2,6-dimethylphenyl)-N-{6-[(2,6-dimethylphenyl)amino]pyridin-2-yl}acetimidamide ((2,6-Me₂C₆H₃)NH(2,6-C₆H₃N)N(2,6-Me₂C₆H₃)C(Me)=N(2,6-Me₂C₆H₃), L¹H) (1) with n-butyllithium in THF at–70 °C was used to synthesize the yttrium dichloride complex (L¹)YCl₂(THF)₂ (2). The lutetium bis(alkyl) complex, namely, N’-(2,6-diisopropylphenyl)-N-(2,6-dimethylphenyl-N-{6-[(2,6-dimethylphenyl)amido]pyridin-2-yl}acetimidoamidinatebis(trimethylsilylmethyl)lutetium (4), was obtained by the reaction of N’-(2,6-diisopropylphenyl)-N-(2,6-dimethylphenyl)-N-(6-((2,6dimethylphenyl)amino)pyridin-2-yl)acetimidamide ((2,6-Me₂C₆H₃)NH(2,6-C₆H₃N)N-(2,6-Me₂C₆H₃)C(Me)=N(2,6-Pr ₂ ⁱ C₆H₃), L²H (3)) with an equimolar amount of Lu(CH₂SiMe₃)₃(THF)₂. Complex 4 was found to be very stable and did not show indications of C—H-activation and other kinds of disintegration in benzene or toluene solution even upon prolonged heating at 60 °C. The reaction of complex 4 with an equimolar amount of 2,6-diisopropylaniline in toluene solution at room temperature led to the formation of the lutetium alkyl-anilide complex (L²)Lu(CH₂SiMe₃)(NH-2,6-Pr ₂ ⁱ C₆H₃) (5). A three-component system 4—AlBu ₃ ⁱ —[X][B(C₆F₅)₄] ([X] = [Ph₃C], [PhNHMe₂], the molar ratio of 1: 10: 1) was found to catalyze polymerization of isoprene.     

Synthesis, characterization, and lactide polymerization activity of group 4 metal complexes containing two bis(phenolate) ligands

A series of group 4 metal complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2), Zr-(5)(2), Hf-(1)(2), and Hf-(4)(2) containing two bridged bis(phenolate) ligands of the (OSSO)-type were prepared by the reaction of the corresponding bis(phenol) and group 4 metal precursor MX(4) (X = O(i)Pr, CH(2)Ph) and isolated as robust, colorless crystals. NMR spectra indicate D(2) symmetry, in agreement with the solid state structure determined by single crystal X-ray diffraction study of the complexes Zr-(1)(2), Hf-(1)(2), Zr-(3)(2), Zr-(4)(2), and Zr-(5)(2). The complexes with the 1,4-dithiabutanediyl bridged ligands exhibit a highly symmetric coordination around the metal center. The introduction of the rigid trans-1,2-cyclohexanediyl bridged ligands led to a distorted coordination around the metal center in Zr-(4)(2) and Zr-(5)(2) when the ortho substituent is tert-butyl and the para substituent is larger than methyl. The complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2) as well as Hf-(1)(2) and Hf-(4)(2) initiated the ring-opening polymerization of meso-lactide at 100 °C to give heterotactic polylactide with pronounced heterotacticity (>70%) and varying polydispersity (1.05 < M(w)/M(n) < 1.61). As shown by kinetic studies, zirconium complex Zr-(1)(2) polymerized meso-lactide faster than the homologous hafnium complex Hf-(1)(2).     

Mixed phosphine and group-13 metal ligator complexes [(PR3)(a)M(ECp*)b] (M = Mo, Ni; E = Ga, Al; R = C6H5, cyclo-C6H11, CH3)

Treatment of [Mo(N(2))(PMe(3))(5)] with two equivalents GaCp* (Cp* = η(5)-C(5)(CH(3))(5)) leads to the formation of cis-[Mo(GaCp*)(2)(PMe(3))(4)] (1), while AlCp* did not react with this precursor. In addition, [Ni(GaCp*)(2)(PPh(3))(2)] (2a), [Ni(AlCp*)(2)(PPh(3))(2)] (2b), [Ni(GaCp*)(2)(PCy(3))(2)] (3a), [Ni(GaCp*)(2)(PMe(3))(2)] (3b), [Ni(GaCp*)(3)(PCy(3))] (4) and [Ni(GaCp*)(PMe(3))(3)] (5) have been prepared in high yields by a direct synthesis from [Ni(COD)(2)] and stoichiometric amounts of the ligands PR(3) and ECp* (E = Al, Ga), respectively. All compounds have been fully characterized by (1)H, (13)C, and (31)P NMR spectroscopy, elemental analysis and single crystal X-ray diffraction studies.     

Heterocyclic compounds M1M2E1E2H8 (M1, M2 = Al,Ga, In; E1, E2 = N,P, As): A quantum chemical study

Structural and thermodynamic characteristics of heteroelement inorganic heterocycles M¹M²E¹E²H₈ (M¹, M² = Al, Ga, In; E¹, E² = N, P, As) were calculated by the density functional theory B3LYP/LANL2DZ(d,p) method. It was shown that energetic characteristics of heterocycle dissociation processes can be calculated by simple a additive scheme with the use of the average M-E bond energy. Dissociation of heteroelement heterocycles into monomeric H₂MEH₂ molecules proceeds according to the hardsoft acid-base (HSAB) concept.     

Synthesis, structure and characterization of M---Sn (M=Mo, W) bonded heterobimetallic complexes containing bis(pyrazol-1-yl)methane ligands

The reaction of bis(pyrazol-1-yl)methane tetracarbonylmolybdenum(0) or tungsten(0) complexes with RSnCl₃ (R=Ph, Cl) at room temperature yielded heterobimetallic complexes CH₂(Pz)₂M(CO)₃(Cl)(SnCl₂R) (Pz represents substituted pyrazole; M=Mo or W; R=Ph or Cl) in good yields, which have been characterized by elemental analysis, ¹H NMR and IR spectroscopy. The reaction of bis(3,5-dimethyl-4-halopyrazol-1-yl)methane tetracarbonyl tungsten with PhSnCl₃ did not take place even in refluxing CH₂Cl₂. The electronic and steric characteristics of substituents on the pyrazole ring remarkably influence the structures of the products. The structures of CH₂(3,5-Me₂-4-BrPz)₂W(CO)₃(Cl)(SnCl₃) (8) and CH₂(4-BrPz)₂Mo(CO)₃(μ-Cl)(SnCl₂Ph) (17) (Pz: pyrazole) determined by X-ray crystallography show that no chlorine-bridged W---Sn bond is observed in complex 8, while one chlorine-bridged Mo---Sn bond exists in complex 17. The Sn---M bond length is 2.7438(5) Å in complex 8 (W---Sn) and 2.7559(4) Å in complex 17 (Mo---Sn).     

Half-sandwich metal diselenolate complexes Cp#M(NO)(SePh)2 (M = Mo or W; Cp# = Cp or MeCp) as ligands. Synthesis of selenolate-bridged heterobimetallic compounds

The reactions of half-sandwich diselenolate Mo and W complexes Cp^#M(NO)(SePh)₂ (M = Mo; Cp^# = Cp (1a), MeCp (1b); M = W; Cp^# = Cp (1c)) with (Norb)Mo(CO)₄, Ni(COD)₂ and Fe(CO)₅ have been investigated. Treatment of (1a), (1b) and (1c) with (Norb)Mo(CO)₄ in PhMe gave the bimetallic complexes: CpMo(NO)(-SePh)₂Mo(CO)₄ (2a), MeCpMo(NO)(-SePh)₂Mo(CO)₄ (2b) and CpW(NO)(-SePh)₂Mo(CO)₄ (2c) in moderate yields. Irradiation of (1a) and (1c) in the presence of Fe(CO)₅ gave heterobimetallic complexes CpMo(CO)(-SePh)₂Fe(CO)₃ (3a) and CpW(NO)(-SePh)₂Fe(CO)₃ (3c). Ni(COD)₂ reacts with two equivalents of (1a), (1b) and (1c) to give [CpMo(NO)(-SePh)₂]₂Ni (4a), [MeCpMo(NO)(-SePh)₂]₂Ni (4b) and [CpW(NO)(-SePh)₂]₂Ni (4c) in good yields. The new heterobimetallic complexes were characterized by i.r., ¹H-n.m.r., ¹³C-n.m.r. and EI-MS spectroscopy.     

Intercalation compounds of TIS2 with lithium and transition metals LixMyTiS2 (M=Ti,Fe, Ni)

Conclusions The titanium disulfide intercalation compounds obtained that contained both lithium and transition metals with the composition Li_xMyTiS₂ (M=Ti, Fe, Ni) had an interlayer distance that was greater than in the original MyTiS₂, but less than in Li_xTiS₂ with the same lithium content.Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 478–483, March, 1987.     

Bonding of seven carbonyl groups to a single metal atom: theoretical study of M(CO)n (M = Ti, Zr, Hf; n = 7, 6, 5, 4)

The equilibrium geometries, thermochemistry, and vibrational frequencies of the homoleptic metal-carbonyls of the group 4 elements, M(CO)n (M = Ti, Zr, Hf; n = 7, 6, 5, 4) were predicted using density functional theory. Analogous M(CO)n structures were found for all three metals. The global minima for the 18-electron M(CO)7 molecules are all singlet C(3v) capped octahedra. The global minima for the 16-electron M(CO)6 species are triplet M(CO)6 structures distorted from O(h) symmetry to D(3d) symmetry. However, the corresponding singlet M(CO)6 structures lie within 5 kcal/mol of the triplet global minima. The global minima for M(CO)n (n = 5, 4) are triplet structures derived from the D(3d) distorted octahedral structures of M(CO)6 by removal of one or two CO groups, respectively. Quintet D(3h) trigonal bipyramidal structures for M(CO)5 and singlet T(d) tetrahedral structures for M(CO)4 are also found, as well as higher energy structures for M(CO)6 and M(CO)7 containing a unique CO group bonded to the metal atom through both M-C and M-O bonds. The dissociation energies M(CO)7 --> M(CO)6 + CO are substantial, indicating no fundamental problem in bonding seven CO groups to a single metal atom.     

Theoretical determination of lowest structures of all‐metal aromatic clusters M4L2 (M = Al,Ga, In,Tl; L = Li,Na, K,Rb, Cs)

The researches of all‐metal aromatic clusters have been a thermic theme in inorganic aromaticity domain both experimentally and theoretically since the Al₄L^? (L = Li, Na, Cu) clusters were created by laser vaporization. In systemic determination of the lowest structures of 20 gaseous all‐metal aromatic clusters M₄L₂ (M = Al, Ga, In, Tl; L = Li, Na, K, Rb, Cs), the isomer energy differences of four low‐lying structures of each cluster were evaluated at high‐quality quantum chemistry levels. Single point calculations at the coupled cluster level were performed at geometries optimized at the MP2, B3LYP, and B3PW91 levels, and harmonic frequency calculations and zero point energy corrections were implemented following optimizations at the B3LYP and B3PW91 levels. In addition to Li‐ and Na‐containing species, theoretical investigations came down to those new clusters including K, Rb, and Cs. For many clusters, the most convincing theoretical evidences indicate that the lowest structures are a square bipyramidal isomer rather than an edge‐caped square pyramidal species. A few discrepancies were addressed at the MP2, B3LYP, and B3PW91 levels in comparison with the coupled cluster results. These findings are significant because some clusters were generated by laser vaporization and served as theoretical prototypes to test the new means for assessing aromaticity. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010