Reactions of oxygen containing ligands in the coordination sphere of permethylhafnocene and permethyltantalocene
| Data(s) |
1987
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|---|---|
| Resumo |
<p>A series of terl-butylperoxide complexes of hafnium, Cp*<sub>2</sub>Hf(R)(OOCMe<sub>3</sub>) (Cp* = ((η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>); R = Cl, H, CH<sub>3</sub>, CH<sub>2</sub>CH<sub>3</sub>, CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>, CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>, CH<sub>2</sub>CHMe<sub>2</sub>, CH=CHCMe<sub>3</sub>, C<sub>6</sub>H<sub>5</sub>, meta-C<sub>6</sub>H<sub>3</sub>(CH<sub>2</sub>)2) and Cp*(η<sup>5</sup>-C<sub>5</sub>(CH<sub>3</sub>)<sub>4</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>)Hf(OOCMe<sub>3</sub>), has been synthesized. One example has been structurally characterized, Cp*<sub>2</sub>Hf(OOCMe<sub>3</sub>)CH<sub>2</sub>CH<sub>3</sub> crystallizes in space group P2<sub>1</sub>/c, with a = 19.890(7)Å, b = 8.746(4)Å, c = 17.532(6)Å, β = 124.987(24)°, V = 2498(2)Å<sup>3</sup>, Z = 4 and R<sub>F</sub> = 0.054 (2222 reflections, I > 0). Despite the coordinative unsaturation of the hafnium center, the terl-butylperoxide ligand is coordinated in a mono-dentate ligand. The mode of decomposition of these species is highly dependent on the substituent R. For R = H, CH<sub>2</sub>CH<sub>3</sub>, CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>, CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>, CH<sub>2</sub>CHMe<sub>2</sub> a clean first order conversion to Cp*<sub>2</sub>Hf(OCMe<sub>3</sub>)(OR) is observed (for R CH<sub>2</sub>CH<sub>3</sub>, ΔHǂ = 19.6 kcal•mol<sup>-1</sup>, ΔSǂ = -13 e.u.). These results are discussed in terms of a two step mechanism involving η<sup>2</sup>-coordination of the terl-butylperoxide ligand. Homolytic O-O bond cleavage is observed upon heating of Cp*<sub>2</sub>Hf(OOCMe<sub>3</sub>) R (R = C<sub>6</sub>H<sub>6</sub>, meta-C<sub>6</sub>H<sub>3</sub>(CH<sub>3</sub>)<sub>2</sub>). In the presence of excess 9,10-dihydroanthracene thermolysis of Cp*<sub>2</sub>Hf(OOCMe<sub>3</sub>)C<sub>6</sub>H<sub>6</sub> cleanly affords Cp*<sub>2</sub>Hf(C<sub>6</sub>H<sub>6</sub>)OH and HOCMe<sub>3</sub> (ΔHǂ = 22.6 kcal•mol<sup>-1</sup>, ΔSǂ = -9 e.u.). The O-O bond strength in these complexes is thus estimated to be 22 kcal•mol<sup>-1</sup>.</p> <p>Cp*<sub>2</sub>Ta(CH<sub>2</sub>)H, Cp*<sub>2</sub>Ta(CHC<sub>6</sub>H<sub>5</sub>)H, Cp*<sub>2</sub>Ta(C<sub>6</sub>H<sub>4</sub>)H, Cp*<sub>2</sub>Ta(CH<sub>2</sub>=CH<sub>2</sub>)H and Cp*<sub>2</sub>Ta(CH<sub>2</sub>=CHMe)H react, presumably through Cp*<sub>2</sub>Ta-R intermediates, with H<sub>2</sub>O to give Cp*<sub>2</sub>Ta(O)H and alkane. Cp*<sub>2</sub>Ta(O)H was structurally characterized: space group P2<sub>1</sub>/n, a= 13.073(3)Å, b = 19.337(4)Å, c = 16.002(3)Å, β = 108.66(2)°, V = 3832(1)Å<sup>3</sup>, Z = 8 and R<sub>F</sub> = 0.0672 (6730 reflections). Reaction of terlbutylhydroperoxide with these same starting materials ultimately yields Cp*<sub>2</sub>Ta(O)R and HOCMe<sub>3</sub>. Cp*<sub>2</sub>Ta(CH<sub>2</sub>=CHR)OH species are proposed as intermediates in the olefin hydride reactions. Cp*<sub>2</sub>Ta(O<sub>2</sub>)R species can be generated from the reaction of the same starting materials and O<sub>2</sub>. Lewis acids have been shown to promote oxygen insertion in these complexes.</p> |
| Formato |
application/pdf |
| Identificador |
http://thesis.library.caltech.edu/8087/1/Asselt_a_1987.pdf Asselt, Allan van (1987) Reactions of oxygen containing ligands in the coordination sphere of permethylhafnocene and permethyltantalocene. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:02192014-152435840 <http://resolver.caltech.edu/CaltechTHESIS:02192014-152435840> |
| Relação |
http://resolver.caltech.edu/CaltechTHESIS:02192014-152435840 http://thesis.library.caltech.edu/8087/ |
| Tipo |
Thesis NonPeerReviewed |
