Jan H. Teuben

Switching a catalyst system from ethene polymerization to ethene trimerization with a hemilabile ancillary ligand

A drastic ligand effect was observed in the catalytic ethene conversion by the substituted mono(cyclopentadienyl)titaniumtrichloride/methylalumoxane (MAO) catalysts shown. The catalyst with R=Me produces polyethene, whereas the catalyst with R=Ph selectively trimerizes ethene to 1-hexene. This switch in catalyst performance appears to be the result of a hemilabile behavior of the cyclopentadienyl ligand with the pendant arene group, involving reversible coordination of the arene moiety.

Early transition metal catalyzed-hydroboration of alkenes

A variety of well-defined early transition metal complexes were tested as catalyst for the hydroboration of 1-hexene using catecholborane as boration agent. The variations applied concerned both metal (Y, La, Ti, Zr) and spectator ligand system (bis(cyclopentadienyl), bis(pentamethylcyclopentadienyl), bis(benzamidinate), cyclopentadienyl-benzamidinate, cyclopentadienyl-aryloxy, and cylopentadienyl-amido). Most systems proved to be catalytically active (anti-Markovnikov regioselectivity, side reactions negligible), but the observed activity was in all cases lower than reported for Cp∗2LaCH(SiMe3)2 [1]. Inactivation of the catalyst by catecholborane or Lewis base-metal complex induced disproportionation of catecholborane appeared to compete effectively with the catalytic conversion, thus leading to inefficient catalytic performance and complicated product mixtures. Systems with bidentate, cyclopentadienyl ligands with a pending anionic (aryloxy, amido) function showed a moderate catalytic activity but excellent catalyst stability and open up interesting perspectives for further exploration.

MONO-ETA-CYCLOPENTADIENYL-BENZAMIDINATO CHLORO COMPOUNDS OF TITANIUM, ZIRCONIUM AND HAFNIUM

The new compounds {M(eta-C(5)R(5))[eta-CPh(NSiMe(3))(2)]]Cl-2} (where R = H, M = Ti, Zr, Hf or R = Me, M = Ti or Zr), are described. The crystal structures of {M(eta-C(5)R(5))([eta-CPh(NSiMe(3))(2)]Cl-2} (R = H, M = Zr or Hf) have been determined. The compound {Zr(eta-C5H5)[eta-CPh(NSiMe(3))(2)]Cl-2} acts as a co-catalyst for the polymerisation of ethylene and propene.

(Cyclopentadienylamine)scandium(2,3-dimethyl-1,3-butadiene): A 1,3-Diene Complex of Scandium with Sc(I)- and Sc(III)-like Reactivity

The scandium 2,3-dimethyl-1,3-butadiene complex [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (2) reacts with PhCN via initial nitrile insertion into the Sc−diene bond to give a dimeric μ2-imido species, but with a 2,2‘-bipyridine via the elimination of the free diene. The latter shows that 2 can be used to generate the reactive fragment [η5,η1-C5H4(CH2)2NMe2]ScI.

On the synthesis of monopentamethylcyclopentadienyl derivatives of yttrium, lanthanum, and cerium

Abstract Two routes leading to monopentamethylcyclopentadienyl-yttrium, -lanthanum and -cerium complexes have been explored. Transmetallation of LnCl3(THF)x with Cp⋆Li (Cp⋆ C5Me5) proved useful only in some particular cases. Acid-base reactions of homoleptic complexes LnR3 with Cp⋆H generally gave Cp⋆2LnR compounds, although Cp⋆LnR2 complexes were observed as intermediates. The mono-Cp⋆ complex Cp⋆Y(o-C6H4CH2NMe2)2 was obtained from Y(o-C6H4CH2NMe2)3 and Cp⋆H, and is the first salt-free mono-Cp⋆ yttrium complex with two carbyl ligands.

Novel, highly symmetrical halogen-centered polynuclear lanthanide complexes: [Cp6Yb6Cl13](-) and [Cp12Sm12Cl24]

If THF is removed from the complexes [CpLnCl2(thf)3] (Cp=C5H5, Ln=Sm, Yb), halogen-centered polynuclear complexes are formed. [{CpSmCl2}12] displays an icosahedral arrangement of the 12 Sm atoms with 20 Cl atoms in the “outer envelope” and four further Cl atoms within the icosahedron (see structure on the right). The partially desolvated [CpYbCl2]⋅1/3 THF consists of trinuclear cations [Cp3Yb3Cl5(thf)3]+ and octahedral anions [Cp6Yb6Cl13]−.

Formation and molecular structure of permethylyttrocene methyl tetrahydrofuranate

Abstract The reaction of Cp * 2 YCl·THF with MeLi in THF at −80°C gives the monomeric Cp * 2 YMe·THF ( 1 ), which has been characterized by spectroscopy, elemental analyses and a single crystal X-ray diffraction study. Complex 1 crystallizes in the orthorhombic space group Pnam with lattice parameters a 17.881(4), b 8.621(2), c 15.095(3) A, Z = 4, and D calc 1.274 g cm −3 . Least-squares refinement using 1056 independent observed reflections and 117 parameters gave a final R value of 0.071. The YC(σ) bond distance is 2.44(2) A. IR and NMR spectra indicate an agostic interaction between the metal center and one of the CH bonds of the methyl ligand, but this could not be confirmed by the X-ray structure determination owing to disorder.

ALKYLATION AND REDUCTIVE DIMERIZATION OF HALF-SANDWICH IMIDO VANADIUM DICHLORIDES

Abstract The vanadium imido complex ArNVCl 3 ( 2 ) (Ar = 2,6-C 6 H 3 ( 1 Pr) 2 ) can be converted to the half-sandwich imido vanadium complex CpV(NAr)Cl 2 ( 3 ) by reaction with CpSiMe 3 . Reaction of 3 and of CpV(N- p -tolyl)Cl 2 ( 1 ) with alkylating reagents did not allow the isolation of the pure dialkyl complexes but showed extensive reduction of vanadium. Reaction of 1 with AlMe 3 leads to the formation of a mixture of diamagnetic dimeric, imido-bridged complexes (CpV) 2 ( μ -N- p -tolyl) 2 MeR (R = Me or Cl), which can be converted to the pure chloro compound [CpV( μ -N- p -tolyl)Cl] 2 ( 4 ) by reaction with HCl. Dimerization is prevented when the more bulky ArN ligand is used. Alkylation of 4 with MeLi proceeds cleanly to give the methyl compound [CpV( μ -N- p -tolyl)Me] 2 ( 5 ). The molecular structures of the formally vanadium(IV) complexes 4 and 5 have been obtained, showing a planar cyclovanadazene core with a vanadium-vanadium single bond and VCl and VC Me bond lengths that are characteristic of V(V) compounds. Compound 5 reacts with CO by insertion in the VC bond, but no reaction is observed with other small unsaturated molecules or Bronsted acids. The 51 V NMR chemical shifts of the new complexes are reported and compared with the chemical shifts of known imido vanadium complexes.

Lead dichloride: a mild reagent for the oxidation of tervalent titanium compounds (η2-C5Me5)2TiR to monochloride derivatives (η5-C5Me5)2TiR(Cl)

Lead dichloride reacts smoothly and stoichiometrically with (η5-C5Me5)2TiR (R = Cl, alkoxide, alkyl, hydride, etc.) complexes to form diamagnetic (η5-C5Me5)2TiR(Cl) derivatives and elemental lead.

Monocyclopentadienyl Yttrium Chemistry: Incorporation of Alkoxides as Supporting Ligands and Synthesis of [Y(C5Me5)(OC6H3But2)(μ-H)]2

Reaction of the crystallographically characterised [Y(C5Me5)(OC6H3But2)2]2 with LiCH(SiMe3)2 affords the mixed alkyl–alkoxide species [Y(C5Me5){CH(SiMe3)2}(OC6H3But2)]3 which, on subsequent hydrogenation, gives the hydride bridged dimer [{Y(C5Me5)(OC6H3But2)(µ-H)}2]4; 89Y NMR spectra of these, and related complexes, allows C5Me5, OC6H3But2 and CH(SiMe3)2 group contributions to be determined.