H. J. De Liefde Meijer

Phenylethynyl complexes of titanocene and vanadocene

The syntheses and properties of (C5H5)2VIV(CCC6H5)2, (C5H5)2VIII(CCC6H5), (C5H5)2TiIV(CCC6H5)2 and of a diamagnetic complex of composition [(C5)2TiIII(CCC6H5)]2 are reported. In the first three compounds the CCC6H5 groups are σ-bonded to the metal atoms, while in [(C5H5)2TiIII(CCC6H5)]2 the CCC6H5 groups are probably bridging ligands. The isolation of (C5H5)2VIV(CCC6H5)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(CCC6H5)]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 RH 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.

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.

CYCLOPENTADIENYLCYCLOHEPTATRIENYLTITANIUM - SUBSTITUTION-REACTIONS AND CHARGE-DISTRIBUTION

Abstract Metallation of (C 5 H 5 )Ti(C 7 H 7 ) occurs much more readily than that of (C 5 H 5 )V(C 7 H 7 ) and (C 5 H 5 )Cr)C 7 H 7 ). Analysis of the products obtained after addition of CH 3 I shows that metallation of (C 5 H 5 )Ti(C 7 H 7 ) has taken place predominantly in the seven-membered ring; this is in contrast to the behaviour of the corresponding vanadium (and chromium) compounds, which are preferentially metallated in the five-membered ring. These observations are discussed in terms of qualitative molecular orbital considerations on the charge distribution in (C 5 H 5 )M(C 7 H 7 )(M = Cr, V, Ti).

Some complexes containing the dicyclopentadienylniobium group

Abstract The synthesis and properties of the complexes (π-C 5 H 5 ) 2 NbCl 2 , (π-C 5 H 5 ) 2 Nb(C 6 H 5 ) 2 and (π-C 5 H 5 ) 2 Nb(π-C 3 H 5 ) are described. The IR spectra of these complexes are analogous to those of the corresponding titanium complexes. The complex (π-C 5 H 5 ) 2 NbCl 2 has one unpaired electron per niobium atom; its mass spectrum is discussed. The complex (π-C 5 H 5 ) 2 Nb(π-C 3 H 5 ) is diamagnetic; its PMR spectrum indicates that the allyl group is π-bonded to niobium. These niobium complexes show a striking analogy with the corresponding complexes of titanium.

Tetracyclopentadienyltitanium(IV) and tricyclopentadienyltitanium(III)

Abstract The syntheses and properties of the complexes (C 5 H 5 ) 4 Ti and (C 5 H 5 ) 3 Ti are described. IR and NMR spectra show that these complexes have the structures (π-C 5 H 5 ) 2 Ti(σ-C 5 H 5 ) 2 and (π-C 5 H 5 ) 2 Ti(σ-C 5 H 5 ) respectively. The spectra and properties of the two compounds are compared with those of (π-C 5 H 5 ) 2 Nb(σ-C 5 H 5 ) 2 and (π-C 5 H 5 ) 2 V(σ-C 5 H 5 ). The compound (π-C 5 H 5 ) 2 V(σ-C 5 H 5 ) 2 could not be prepared.

Mechanistic aspects of the thermal decomposition of dicyclopentadienyltitanium(IV)diaryl compounds

Abstract The thermal decomposition of a number of compounds Cp 2 TiR 2 (R = aryl was studied in the solid state and in various solvents. A first-order reaction was observed and activation energies of 20–30 kcal mol −1 were found depending on the nature of R. The activation energy for Cp 2 Ti(C 6 H 5 ) 2 (20–22 kcal mol −1 ) appeared to be independent of the reaction medium (solid state or dissolved in cyclohexane, benzene, THF, CCl 4 or in the presence of tolane). Deuteration of the phenyl groups results in a higher value of the activation energy (∼29 kcal mol −1 ), whereas deuteration of the Cp ligands does not. A reaction mechanism is proposed in which the first and rate-determining step of the decomposition is the conversion of one of the σ-bonded ligands R to a π-bonded activated state.

ALLYL COMPLEXES OF DICYCLOPENTADIENYL-NIOBIUM(III) AND DICYCLOPENTADIENYL-TANTALUM(III)

Abstract The synthesis and the properties of the complexes Cp2TaCl2, Cp2M(allyl), Cp2M(1-methylallyl) and Cp2M(2-methylallyl) with M  Nb, Ta are described. The complex Cp2TaCl2 has one unpaired electron per tantalum atom, while the allyl complexes are diamagnetic. The IR and PMR spectra indicate that the allyl group is π-bonded to the metal. The mass spectra of the complexes are discussed; the thermal stability of the Cp2Nb- and Cp2Ta-(allyl) complexes was investigated by differential thermal analysis. The properties of the niobium and tantalum complexes are compared with those of the corresponding titanium complexes.

ELECTRON-SPECTROSCOPY OF SOME CYCLOPENTADIENYLCYCLOHEPTATRIENYLMETAL COMPOUNDS

Abstract X-ray photoelectron spectra of (C5H5)M(C7H7) with M = Ti, V, Cr and some related compounds are reported. Data show that the oxidation state of the metal increases in the sequence Cr