Binuclear Metallocene Research Articles

Chemical Information revealed by Mössbauer spectroscopy and DFT calculations

Mixed-valence state of binuclear metallocene derivatives and spin-crossover (SCO) phenomena of the assembled Fe(II) complexes have been studied by using Mossbauer spectroscopy. The understanding of the results obtained by Mossbauer spectra is well supported by means of X-ray structural analysis and density functional theory (DFT) calculation. Benchmark study of relativisitic DFT calculation by using Mossbauer isomer shifts of Eu, Np complexes reveals the validity of the calculation. Such study sheds light on the bonding character of 4f and 5f electron. These results are reviewed.

Synthesis and oxidation study of the simplest binuclear metallocene compound of osmium, biosmocene

Selective mono-lithiation method of bis(cyclopentadienyl)osmium(II) (osmocene) was established. Iodoosmocene(C5H4I)Os(C5H5) (OcI), which is the first monohalogenated product of osmocene, was prepared by the reaction of lithioosmocene with I2. Ullmann coupling reaction of iodoosmoene allowed to prepare biosmocene(C5H5)Os(μ2-η5:η5-C10H8)Os(C5H5) (OcOc). OcOc reacted with I2, giving mixed-valence biosmocenium salt [(C5H5)OsII(μ2-η5:η5-C10H8) (C5H5)OsIVI]I3(A). The structure of A was determined by single crystal X-ray structural analysis. The intramolecular electron transfer reaction between OsII and Os IV was observed by using 1H NMR spectroscopy, accompanied by the exchange of I− anion between the two units. The activation energy of the electron transfer reaction was estimated and the value was larger than that of binuclear ruthenocenium salt [(C5H5)RuII(μ2-η5:η5-C10H8) (C5H5)RuIVI]I3(B).

Asymmetric binuclear metallocene complexes and their application for olefin polymerization

ABSTRACTAsymmetric double silylene‐bridged binuclear complexes [(η5‐RC5H4)MCl2]2[μ, μ‐(SiMe2)2(η5‐t‐BuC5H2)(η5‐C5H3)][R = H, M = Ti (1); R = Me, M = Ti (2); R = allyl, M = Ti(3); R = H, M = Zr (4); R = allyl, M= Zr (6)]; and [(η5‐C5H5)TiCl2]2[μ, μ‐(SiMe2)2(η5‐Me3SiC5H2)(η5‐C5H3)] (5) were synthesized by the reaction of (η5‐RC5H4) TiCl3 or (η5‐RC5H4)ZrCl3·DME (R = H, allyl) with [μ, μ‐ (SiMe2)2(η5‐t‐BuC5H2)(η5‐C5H3)] Li2 or [μ, μ‐(SiMe2)2(η5‐Me3Si C5H2)(η5‐C5H3)]Li2 in THF, and they were all well characterized by 1H NMR, MS, IR, and EA. When activated with methylaluminoxane (MAO), they are efficient catalysts for the polymerization of ethylene (Complex 4, 5.99 × 105 g‐PE/mol·Zr·h) and the polymer with multipeak broaden molecular weight distribution (PD = Mw/Mn) was obtained (polymer sample gained by complex 3, PD = 25.03). The copolymerization results indicate that 1‐hexene could incorporate into the growing PE chain with these complexes in the presence of MAO (Complex 4, 1.07 × 106 g‐PE/mol·Zr·h; 1‐hexene content, 1.57% mol). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2891–2900, 2013

Metal–Metal and Metal–Ligand Bonds in (η5-C5H5)2M2 (M = Be, Mg, Ca, Ni, Cu, Zn)

The metal–metal and metal–ligand bonds in a series of binuclear metallocenes (η5-C5H5)2M2 (M = Be, Mg, Ca, Ni, Cu, Zn) have been characterized within the framework of the atoms in molecules (AIM) theory, electron localization function (ELF), and molecular formation density difference (MFDD). The calculated results show that the metal–metal bonds in the binuclear main-group-metal metallocenes are different from those in binuclear transition-metal metallocenes. In binuclear main-group-metal metallocenes, the metal–metal bonds are linked by two metal–“non-nuclear attractor (NNA)” bonds, while such NNAs do not exist in the binuclear transition-metal metallocenes. In addition, the transition-metal–transition-metal bonds are more delocalized than those of the main-group-metal–main-group-metal bonds. The main-group-metal–main-group-metal bonds show covalent characteristics while the transition-metal–transition-metal bonds display “closed shell” ionic characteristics. The metal–ligand bonds are mainly ionic. There are both σ and π characteristics in the metal–ligand interactions, and the π interaction is predominant.

D 3h Al3N: a novel promising ligand for coordination chemistry

Several prior experimental and theoretical studies have been reported on Al3N and have shown that the D3h isomer is the global minimum. In this work, we attempt to theoretically design new molecular materials containing the D3h Al3N as unit. A novel series of metal complexes with the Al3N ligand, including [(Al3N)K(Al3N)]+ (traditional homo-decked sandwich), [(Al3N)ZnZn(Al3N)]2+ (binuclear metallocene), and [(Al3N)Zn(C5H5)]+ (hetero-decked sandwich), are predicted to be local minima on their corresponding potential hyper surfaces at the B3LYP, B3PW91, and BP86 levels of theory with the 6–311+G(d) basis set. Natural bond orbital and AOMix analyses indicate that the interaction between the metal ions and the Al3N ligands is mostly electrostatic. This fact suggests that the Al3N is a promising ligand for coordination chemistry.

Synthesis of double silylene-bridged binuclear metallocenes and their cooperation effect during ethylene polymerization and ethylene/1-hexene copolymerization

Novel double silylene-bridged binuclear Group 4 metallocene complexes [(η5-C5H5)MCl2]2[μ, μ-(SiMe2)2 (η5-RC5H2)2] [R = Me, M = Zr (1); R = allyl, M = Ti (2); R = allyl, M = Zr (3); R = nBu, M = Ti (5); R = Me3Si, M = Zr (6)] and [(η5-CH3C5H4)ZrCl2]2[μ, μ-(SiMe2)2 (η5-allyl-C5H2)2, (4)] were synthesized by the reaction of CpMCl3 (M = Ti, Zr) with [μ, μ-(SiMe2)2 (η5-RC5H2)2]2- (L2-) in THF, and they were all well characterized by 1H-NMR, MS, and EA. When activated with methylaluminoxane (MAO), this series complexes are active catalysts for Ethylene polymerization (Complex 3, 3.86 × 106 g-PE/mol-M h, Al/Zr = 500) and copolymerization of ethylene with 1-hexene (Complex 3,30.87 × 105 g-polymer/mol-M h, 1-hexene content in polymer 2.34 mol %, Al/Zr = 1000). The result of polymerization implies that there is a cooperative effect between the two metals in the double-bridged binuclear molecules. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Novel diphenyl thioether-bridged binuclear metallocenes of Ti and Zr for synthesis of polyethylene with broad molecular weight distribution

Two diphenyl thioether-bridged binuclear metallocenes of Ti and Zr, [(C5H5)Cl2MC5H4CH2(p-C6H4)]2S [M = Ti (1) and Zr (2)], have been synthesized by treating the dilithium salts of the corresponding ligand [(C5H5CH2(p-C6H4)]2S with two equivalents of C5H5TiCl3 and C5H5ZrCl3(DME), respectively, in toluene at 0°C. Both new complexes have been characterized by 1H-NMR spectroscopy and elemental analysis. Homogeneous ethylene polymerization using both complexes was performed in the presence of methylaluminoxane (MAO). The influences of molar ratio of [MAO]/[Cat], concentration of the catalysts, time, and temperature have been studied systematically. The catalytic activity of 1 is higher than that of the corresponding oxygen-bridged catalyst [(C5H5)Cl2TiC5H4CH2(p-C6H4)]2O. The catalytic activity of 2 is at least two times higher than that of 1 under any tested polymerization conditions. The melting points of polyethylene (PE) produced by 1 and 2 are higher than 130°C, indicating a highly linear and highly crystalline PE. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Novel compounds with cobalt, copper, and nickel dimers sandwiched between benzene molecules: A DFT study

After the profoundly experimental and theoretical investigations of the binuclear metallocenes, we prospected a new series of sandwich compounds, C 6H 6–M–M–C 6H 6 (M = Co, Ni, and Cu) using density functional theory. The cobalt complex has the stable coaxial structures, while the nickel and copper complexes have the new stable ones with the metal atom η 2 bonding to the benzene ring. NBO analyses show that there exits a clear triple bond between the two cobalt atoms, and a single bond between the other two metal atoms in their complexes. For the cobalt complex, the multilayer sandwich clusters have also been studied.

Synthesis, characterization, and reactivities of the polysiloxane-bridged binuclear metallocenes tetramethyldisiloxanediylbis(cyclopentadienyltitanium trichloride) and hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride)

The reaction of dithallium salts of tetramethyldisiloxanediylbis(cyclopentadienyl), 3, and hexamethyltrisiloxanediylbis(cyclopentadienyl), 4, with two equivalents of TiCl 4 gives the title compounds tetramethyldisiloxanediylbis(cyclopentadienyltitanium trichloride), 5 and hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride), 6 respectively. The stoichiometric reaction of 5 and 6 with water results in the formation of new oxygen-bridged metallocenes [(TiCl 2) 2( μ 2-O)-( η 5-C 5H 4) 2- μ 2-(SiMe 2) 2O], 7, and [(TiCl 2) 2( μ 2-O)-( η 5-C 5H 4) 2- μ 2-(SiMe 2) 3O 2}], 8. In addition, further reaction of 7 and 8 with another one equivalent of water or the treatment of 5 and 6 with an excess amount of water gives rise to the formation of the metallocene compounds having Ti 4O 4 rings [(TiCl) 2( μ 2-O)-( η 5-C 5H 4) 2- μ 2-(SiMe 2) 2O] 2( μ 2-O) 2, 9, and [(TiCl) 2( μ 2-O)-( η 5-C 5H 4) 2- μ 2-(SiMe 2) 3O 2] 2 ( μ 2-O) 2, 10. All the new kinds of metalocenes prepared have been characterized by IR, NMR, mass spectrometry, or elemental analysis. Especially an investigation of the Δδ values in 1H NMR and a comparison between the theoretical and observed isotopic ratio in a mass spectra among the synthesized bridged compounds have been very conveniently utilized to study their structures. Polymerization experiments with the dinuclear complexes in the presence of methylaluminoxane as a cocatalyst indicate that the compounds 5 and 6 do exhibit catalytic activity for syndiotactic polymerization of styrene.

1H NMR Spectra and electronic structure of binuclear niobocene and titanocene containing fulvalene ligands

1H NMR spectra of binuclear metallocene hydride complexes, (η 5 : η 5-C 10H 8)(C 5H 5) 2M 2(μ-H) 2 (M = Nb, 20°C and Ti, (−60 to +25°C), were studied. The Nb complex is diamagnetic and gives a high resolution spectrum. The coordination of bridging hydride H atoms provides Nb atoms with complete 18 electron configuration. In its ground state, the Ti complex is also diamagnetic (the spectrum at −60°C agrees to that) in spite of only 17 electron configuration of each Ti atom. However, the population of the excited triplet state in the case of the Ti complex is appreciable at temperatures higher than −30°C, the proton resonance lines being shifted downfield and significantly broadened as compared with the spectrum at −60°C.