Studies On Relationship Between Catalytic Activity And Electronic Structure For Metallocene Compounds

The molecular structures and electronic structures of [2-(3,4-diphenyl cyclopentadienyl)-4-R-6-R'-phenoxyl] titanium dichorides ( R= t-Bu, H;R'=t-Bu, Meand Ph, respectively), [2-(2,3,4,5-tetramethylcyclopentadienyl)-4-R-6-R'-phenoxyl]titanium dichlorides (R= t-Bu, H;R'=t-Bu, Me and Ph, respectively) and bis[4-R-1,2-diphenylcyclopentadienyl] zirconium dichlorides(R=H, Me, Ph, respectively) were firstly calculated using density functional theory (DFT-B3LYP with6-31G*) in Gaussian 03 of quantum chemistry calculation program package. Theeffects of the molecular structures and electronic structures of the three seriesof eleven complexes on the catalytic activity were also discussed. The resultsof research demonstrated that the catalytic activities of the metallocene dependon their molecular structures and electronic structures, is the result of collectiveaction of the steric effect and electronic effect of substitutents and mainly dependon the preponderant effect of the two effects. It was firstly presented that thereexists close relationship between the catalytic activities of the metallocenes andthe metallic d orbital in LUMO. The metallic d orbital plays an important role in thecatalysis. The essence of the change of substituents to increase the catalyticactivityof catalyst is to increase the coefficients of the molecular orbital dx~2-y~2playing a key role in the catalysis. The UV spectra of the threeseries of elevencompounds were also calculated and the calculated results are consistent with theexperimental results.The molecular structures and electronic structures of the four complexes[2-(3,4-diphenylcyclopentadienyl)-4,6-ditertbutyl-phenoxyl] titanium dichloride,[2-(3,4-diphenylcyclopentadienyl)-6-tertbutyl-phenoxyl] titanium dichloride, [2-(3,4-diphenylcyclopentadienyl)-6-methyl-phenoxyl] titanium dichloride and [2-(3,4-diphenylcyclopentadienyl)-6-phenyl-phenoxyl] titanium dichloride are researched.The result of the research demonstrated that the electronic structures of thefour complexes play a crucial role in catalysis. The calculated coefficients ofthe molecular orbital dx2-y2 in the lowest hollow orbital of the four complexesdecreased in order of B-2Bu > B-Bu > B-Me > B-Ph. The catalytic activityof the four complexes in experiment decreased in order of [2-(3,4-diphenylcyclopentadienyl)-4,6-ditertbutyl-phenoxyl] titanium dichloride > [2-(3,4-diphenylcyclopentadienyl)-6-tertbutyl-phenoxyl] titanium dichloride> [2-(3,4-diphenylclopentadienyl)-6-methyl-phenoxyl] titanium dichloride ~ [2-(3,4-diphenylcyclopentadienyl)-6-phenyl-phenoxyl] titanium dichloride, which is nearly consistent with thecalculated results.The molecular structures and electronic structures of the complexes [2-(2,3,4,5-tetramethylcyclopentadienyl)-4,6-ditertbutyl-phenoxyl] titanium dichloride, [2-(2,3,4,5-tetramethylcyclopentaditenyl)-6-tertbutyl-phenoxyl] titanium dichloride,[2-(2,3,4,5-tetramethylcyclopentadienyl)-6-metinyl-phenoxyl] titanium dichloride and[2-(2,3,4,5-tetramethylcyclopentadienyl)-6-phenyl-phenoxyl] titanium dichloridewerealso researched using the same method as that of the former four complexes.Theresult of the research also demonstrated that the electronic structures ofthefour complexes play a crucial role in catalysis. The calculated coefficients ofthemolecular orbital dx2-y2 of these complexes decreased in order of C-2Bu> C-Bu >C-Me> C-Ph, which is also nearly consistent with the experimental results of thecatalytic activity.Meanwhile, the molecular structures and electronic structures of the complexes bis(1,2-diphenylcyclopentadienyl) zirconium dichloride, bis(4-methyl-1,2-diphenylcyclopentadienyl) zirconium dichloride and bis(4-phenyl-1,2-diphenylcyclopentadienyl) zirconium dichloride were also investigated. The calculated coefficientsof the molecular orbital dx2-y2 of three complexes decreased in order of D-H >D-Me > D-Ph. The experimental results showed that the catalytic activity ofD-H was the greatest. As these three complexes have special molecular structuresand various substitutent effects in steric conformation, their catalyticactivitiesdepend on the collective action of steric effects and electron effects.This theoretic modeling has great importance to instruct the designandsynthesis of catalysts and further investigate the effect of the molecular structuresand electronic structures of metallocenes on the catalytic activity.Three series of fourteen compounds bis(4-R-1,2-diphenylcyclopentadienyl)zirconium dichloride (R=H, methyl, ethyl, n-propyl, n-butyl), [2-(3,4-diphenylcyclopentadienyl)-4-R-6-R′-phenoxyl] titanium dichlorides(R=t-butyl,H;R′=t-butyl,methyl,phenyl)and [2-(2,3,4,5-tetramethylcyclopentadienyl)-4-R-6-R′-phenoxyl]titanium dichlorides (R=t-butyl, H;R′=t–butyl, methyl, phenyl) were synthesizedaccording to the literature methods and characterized by elemental analysisand NMR.The UV spectra of the fourteen metallocenes were determined. The UV absorption wavelength of [2-(3,4-diphenylcydopentadienyl)-4-R-6-R'-phenoxyl] titanium dichlorides (R=t-butyl, H;R′=t–butyl, methyl, phenyl) has regular variationwith the change of the substituent on the fourth and sixth position.The similar result was obtained with the research on the UV absorption spectra of [2-(2,3,4,5-tetramethylcyclopentadienyl)-4-R-6-R′-phenoxyl] titanium dichlorides (R=t-butyl, H;R′=t-butyl, methyl, phenyl). The absorption wavelength ofUV spectra of bis(4-R-1,2-diphenylcyclopentadienyl) zirconium dichloride (R=H, methyl, ethyl, n-propyl, n-butyl) also varied regularly with the change ofthe substituent on the fourth position increasing in order of H < Me~ Et ~ n-Pr ~ n-Bu < Ph. The luminescent properties of bis(4-R-1,2-diphenylcyclopentadienyl) zirconium dichlorides (R=H, methyl, ethyl, n-propyl, n-butyl) were alsoresearched and the effects of substituent of ligands on the wavelength ofabsorption and emission were discussed. The research results demonstrated thatthecomplexes have fluorescence at room temperature in n-hexane solution andthesolid state and the emission wavelength can be tuned through changing thesubstituent on the fourth position of cyclopentadienyl group. The emission wavelength decreased in order of n-Bu > n-Pr > Et > Ph > Me > H. The electrochemistry properties of this series of complexes were researched by cyclicvoltammetry using THF as solvent, TBAPF6 as supporting electrolyte and glassycarbon as working electrode. It was found that the variation of the substituenton the 4-position has different effect on the electrochemistry properties when theadjacent two hydrogen atoms on cyclopentadienyl ring were replaced using twophenyl groups and the five hydrogen atoms were replaced using methyl groupsin order. When the five hydrogen atoms on the cyclopentadiene were graduallyreplaced using methyl groups, its electron effect plays a key role. While in thisseries of compounds, the stereo effect of substituent plays a crucial role and itscathode peak potential shifted to positive potential when R= H, Me, Et, n-Pr, Phand n-Bu. As this series of six compounds were firstly synthesized in our group,it provides theoretic base for the interpretation of possible results.