J.H. Teuben

CATALYTIC OLEFIN OLIGOMERIZATION AND POLYMERIZATION WITH CATIONIC GROUP-IV METAL-COMPLEXES [CP-STAR-2TIME(THT)]+, [CP-STAR-2ZRME(THT)]+, [CP-STAR-2 HF ME(THT)]+ [BPH4]-

Abstract Complexes [Cp∗2MMe(THT)]+[BPh4]− (THT = tetrahydrothiophene; M = Ti, Zr, Hf) have been synthesized and their properties with respect to olefin oligomerization and polymerization studied∗∗. For M = Ti no catalytic activity towards ethene and propene was observed. For M = Zr, Hf the complexes [Cp∗2MMe(THT)]+[BPh4]+ are active catalysts for the polymerization of ethene. The polyethene obtained has a relatively high molar mass and low dispersity with few unsaturations and branches. With propene the zirconium and hafnium compounds give catalytic oligomerization. For M = Zr a broad product distribution with oligomers up to C24 is obtained at room temperature whereas for M = Hf only the dimer 4-methyl-1-pentene and the trimer 4,6-dimethyl-1-heptene are formed. The dominant termination mechanism appears to be β-methyl transfer from the growing chain back to the metal centre, as has been demonstrated by deuterium labelling studies. No activity was observed towards other olefins and conjugated dienes such as 1-butene, 1-hexene, styrene or 1,3-butadiene (M = Ti, Zr, Hf). In this paper the following abbreviations are used: Cp = η5-C5H5; Cp∗ = η5-C5Me5.

Phenylethynyl complexes of titanocene and vanadocene

The syntheses and properties of (C5H5)2VIV(Cue5fcCC6H5)2, (C5H5)2VIII(Cue5fcCC6H5), (C5H5)2TiIV(Cue5fcCC6H5)2 and of a diamagnetic complex of composition [(C5)2TiIII(Cue5fcCC6H5)]2 are reported. In the first three compounds the Cue5fcCC6H5 groups are σ-bonded to the metal atoms, while in [(C5H5)2TiIII(Cue5fcCC6H5)]2 the Cue5fcCC6H5 groups are probably bridging ligands. The isolation of (C5H5)2VIV(Cue5fcCC6H5)2 strongly supports our hypothesis1.2 that the failure to obtain other complexes (C5H5)2VIVR2(R = alkyl, aryl) is due to steric reasons. The stability of the compound [(C5H5)2TiIII(Cue5fcCC6H5)]2, which is in marked contrast with the instability of other complexes (C5H5)2TiIIIR, supports our hypothesis that in stable complexes containing the (C5H5)2Ti group the metal atom is coordinated by two ligands (or one bidentate ligand) in addition to the two C5H5 groups1,2.

Thermal Decomposition of Dicyclopentadienyltitanium(IV) Diaryl and Dibenzyl Compounds

Abstract The thermal decomposition of compounds of the type Cp 2 TiR 2 (Cp = cyclopentadienyl, R = aryl or benzyl) in the solid state and in various solvents has been studied. In the solid state and in aromatic and aliphatic hydrocarbon solvents the compounds decompose with quantitative formation of Rue5f8H and a Ti-containing residue which has lost the Cp 2 Ti structure. Experiments with deuterated compounds and solvents showed that decomposition proceeds via intramolecular abstraction of a hydrogen atom either from a cyclopentadienyl ring or from the other coordinated group R. Results of insertion reactions with tolane confirm these two reaction pathways. In tetrahydrofuran and tetrachloromethane, decomposition proceeds in a more complex way, with participation of the solvent.

Reversible Carbon-Carbon Bond Formation in Organolanthanide Systems. Preparation and Properties of Lanthanide Acetylides [Cp*2LnC≡CR], and Their Rearrangement Products [Cp*2Ln]2(μ-η2 : η2-RC4R) (Ln = La, Ce, R = Alkyl)

Lanthanide carbyls Cp*{sub 2}LnCH(SiMe{sub 3}){sub 2}{sup 1} (1, Ln=Ce;2, Ln=La) react with terminal alkynes HC{triple_bond}CR (R = Me, t-Bu) to yield oligomeric acetylides [Cp*{sub 2}LnC{triple_bond}CR]{sub n} (3, Ln = Ce, R = Me; 4, Ln = La, R = Me; 5, Ln = Ce, R = t-Bu). The acetylides are not stable in solution and rearrange to give the carbon-carbon coupled products, [Cp*{sub 2}Ln]{sub 2}({mu}-{eta}{sup 2}:{eta}{sup 2}-RC{sub 4}R) (6, Ln = Ce, R = Me; 7, Ln = La, R = Me; 8, Ln = Ce, R = t-Bu). Thermodynamic and kinetic studies of the C-C coupling process were studied as were the structures of 6 and 8 via XRD.

Tri-1-methallyl- and 1-methallyl-butadiene group IV transition metal complexes

Reaction of Cp´MCl3 (Cp´ = η5-C5(CH3)5; M = Ti, Zr, Hf) with 2-butenylmagnesium bromide at low temperatures gives Cp´M(1-methallyl)3, which is readily converted into Cp´M(η3-1-methallyl)(η4-butadiene) on heating. Only Cp´Hf(1 methallyl)3 could be isolated; it is fluxional and its NMR and IR spectra indicate that it consists of a complex mixture of isomers containing interconverting η1- and η3-1-methallyl groups. The compounds Cp´M(η3-C4H7)(η4-C4H6) are much more thermally stable; they show fluxional behaviour, but this is limited to the η3-1-methallyl group. These complexes are very reactive towards a large variety of organic substrates.

Synthesis and Properties of Aryldicyclopentadienyltitanium(III) Compounds

The synthesis and properties of the compounds Cp2TiR, with R=C6H5, o-, m-, p-CH3C6H4, 2,6-(CH3)2C6H3, 2,4,6-(CH3)3C6H2, C6F5, CH2C6H5, are described. Chemical and physical properties indicate that the R groups are σ-bonded to the titanium atom. The complexes are monomeric, with one unpaired electron per titanium atom. They are very air sensitive, and vary markedly in thermal stability; some of the compounds react with molecular nitrogen, to give complexes of the general formula (Cp2TiR)2N2. Compounds Cp2TiR with R=alkyl could not be isolated.

Dimerization of Organic Cyanides Ligated to Di-η5-cyclopentadienylaryltitanium(III)

Reactions of Cp2TiR (R = C6H5, o-, m-, p-CH3C6H4, CH2C6H5, C6F5, C1) with R′CN (R′ = C6H5, o-CH3C6H4, CH3) have been studied. The products, (Cp2TiR · R′CN)2, identified by chemical and physical methods, form a new class of compounds, in which two Cp2TiR groups are connected by a bridging diimine ligand formed by oxidative coupling of two cyanide ligands via the cyanide carbon atoms. The metal is formally oxidized to titanium(IV).

Preparation and Characterization of Mono-cyclopentadienylvanadium Dihalide Bis-phosphine Complexes; Crystal Structure of (η5-C5H5)VCl2(PMe3)2

Abstract Mono-cyclopentadienyl complexes CpVX 2 (PR 3 ) 2 and Cp′VX 2 (PR 3 ) 2 (Cp = η 5 - C 5 H 5 ; Cp′ = η 5 -C 5 H 4 Me; R = Me, Et; X = Cl, Br) have been prepared by reaction of VX 3 (PR 3 ) 2 with CpM (M = Na, T1, SnBu n 3 , 1/2 Mg) or Cp′Na. Attempts to prepare analogous complexes with other phosphine ligands, PPh 3 , PPh 2 Me, PPhMe 2 , Pcy 3 , DMPE and DPPE failed. Reduction of CpVCl 2 (PEt 3 ) 2 with zinc or aluminium under CO (1 bar) offers a simple method for the preparation of CpV(CO) 3 (PEt 3 ). The crystal structure of the trimethylphosphine complex CpVCl 2 (PMe 3 ) 2 is reported.

REACTIONS OF TITANOCENE ALLYLS

Abstract Cp 2 Tiη 3 -allyl and Cp 2 Tiη 3 -1-methylallyl react with carbon dioxide, phenylisocyanate, benzalaniline, acetone and acetonitrile to give insertion products which are formed via allyl migration. Normal insertion is observed with 2,6 xylylisocyanide. Carbonylation of Cp 2 Tiη 3 -allyl affords Cp 2 Tiη(CO) 2 and triallylmethanol. With carbon disulfide and diphenylacetylene, allyl elimination reactions are observed.

Reaction of Titanocene Alkyls with Pyridines; A Novel Type of Cyclometallation Reaction

Abstract Reaction of Cp2TiR (R ue5fb alkyl) with 2-substituted-pyridines and with quinolines leads to α-metallation of these ligands with formation of triangular titanocylcles containing TiIII. Proof of the metallation at the α-position comes from reactions of the complexes formed with I2 and D2O/DCI which yield the corresponding iodo- and deutero-pyridine and -quinoline derivatives. Reaction of Cp2TiR with the structurally related ligand benzalaniline leads to a side-on coordinated benzalaniline complex of titanocene. Reactions of this diamagnetic complex with I2, CO2 and H2 are described.