Carbon−Carbon Coupling and Carbon−Hydrogen Activation Reactions in Bis(triisopropylphosphine)osmium Complexes<sup>†</sup>
Reaction of the alkenyl complex OsCl(<i>E</i>-CHCHPh)(CO)(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>1</b>) with phenyllithium gives OsH{C<sub>6</sub>H<sub>4</sub>-2-(<i>E</i>-CHCHPh)}(CO)(P<sup>...
محفوظ في:
| المؤلف الرئيسي: | |
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| مؤلفون آخرون: | , , , |
| منشور في: |
1996
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| الموضوعات: | |
| الوسوم: |
إضافة وسم
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| الملخص: | Reaction of the alkenyl complex OsCl(<i>E</i>-CHCHPh)(CO)(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>1</b>) with phenyllithium gives OsH{C<sub>6</sub>H<sub>4</sub>-2-(<i>E</i>-CHCHPh)}(CO)(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>2</b>). The structure of <b>2 </b>(isomer <b>2a</b>) has been determined by X-ray diffraction: triclinic, <i>P</i>1̄, <i>a</i> = 9.230(1) Å, <i>b</i> = 10.092(1) Å, <i>c</i> = 18.525(2) Å, α = 88.667(7)°, β = 87.172(7)°, γ = 71.110(6)°, <i>V</i> = 1630.6(3), <i>Z</i> = 2, <i>R</i> (<i>F</i>, <i>F</i><sub>o</sub> ≥ 4σ(<i>F</i><sub>o</sub>)) = 4.01, <i>wR</i> (<i>F</i><sup>2</sup>, all reflections) = 9.94%. The geometry around the osmium can be described as a distorted octahedron with the two triisopropylphosphine ligands occupying two relative <i>trans</i> positions. The remaining perpendicular plane is formed by the carbonyl and the 2-(<i>E</i>-1‘-styryl)phenyl ligands mutually <i>trans</i> disposed, the hydride ligand and one olefinic hydrogen of the 2-(<i>E</i>-1‘-styryl)phenyl ligand, which shows an agostic interaction with the osmium atom (distance 2.05(7) Å). The solutions of <b>2 </b>show equilibria between the agostic isomer (<b>2a</b>) and a nonagostic isomer (<b>2b</b>). The thermodynamic magnitudes involved in the equilibrium as well as the activation parameters for the conversion between the two isomers were determined in toluene-<i>d</i><sub>8</sub> by <sup>1</sup>H NMR spectroscopy. The values obtained were Δ<i>H</i>° = −1.6 (±0.1) Kcal mol<sup>-1</sup> and Δ<i>S</i>° = −9.6 (±0.6) cal K<sup>-1</sup> mol<sup>-1</sup> for the formation of the agostic isomer, whereas the activation parameters for the breaking of the agostic interaction were Δ<i>H</i><sup>⧧</sup> = 7.6 (±0.2) Kcal mol<sup>-1</sup> and Δ<i>S</i><sup>⧧</sup> = −1.0 (±0.7) cal K<sup>-1</sup> mol<sup>-1</sup>. <b>2</b> reacts with CO to give the octahedral complex OsH{C<sub>6</sub>H<sub>4</sub>-2-(<i>E</i>-CHCHPh)}(CO)<sub>2</sub>(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>3</b>). Reactions of <b>1</b> with methyllithium and CD<sub>3</sub>Li give OsH{C<sub>6</sub>H<sub>4</sub>-2-(<i>E</i>-CHCHCH<sub>3</sub>)}(CO)(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>4</b>) and OsH{C<sub>6</sub>H<sub>4</sub>-2-(<i>E</i>-CHCHCD<sub>3</sub>)}(CO)(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>4-</b><b><i>d</i></b><b><sub>3</sub></b>), respectively. The spectra of these complexes indicate that in solution they also show equilibria between agostic and nonagostic isomers. Reactions of <b>4</b> with P(OMe)<sub>3</sub> and CO afford OsH{C<sub>6</sub>H<sub>4</sub>-2-(<i>E</i>-CHCHCH<sub>3</sub>)}(CO){P(OMe)<sub>3</sub>}(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>5</b>) and OsH{C<sub>6</sub>H<sub>4</sub>-2-(<i>E</i>-CHCHCH<sub>3</sub>)}(CO)<sub>2</sub>(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>6</b>), respectively, in which the incoming ligands coordinate <i>trans</i> to the hydride. <b>4</b> and <b>4-</b><b><i>d</i></b><b><sub>3</sub></b> isomerize in solution to give OsH(η<sup>3</sup>-CH<sub>2</sub>CHCHPh)(CO)(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>11</b>) and OsD(η<sup>3</sup>-CD<sub>2</sub>CHCHPh)(CO)(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>11-</b><b><i>d</i></b><b><sub>3</sub></b>), respectively. Reaction of <b>11</b> with CO leads to OsH(η<sup>1</sup>-CH<sub>2</sub>CHCHPh)(CO)<sub>2</sub>(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>12</b>). The first order constants <i>k</i><sub>obs</sub> and <i>k</i><sub>obs-</sub><i><sub>d</sub></i><sub><sub>3</sub></sub> for the isomerization of <b>4 </b>and <b>4-</b><b><i>d</i></b><b><sub>3</sub></b> to <b>11</b> and <b>11-</b><b><i>d</i></b><b><sub>3</sub></b> were obtained in CDCl<sub>3</sub>, giving activation parameters of Δ<i>H</i><sup>⧧</sup> = 20.8 (±1.7) Kcal mol<sup>-1</sup> and Δ<i>S</i><sup>⧧</sup> = −2.8 (±2.0) cal K<sup>-1</sup> mol<sup>-1</sup> for the isomerization of <b>4</b> to <b>11</b> and a relation <i>k</i><sub>obs</sub>/<i>k</i><sub>obs-</sub><i><sub>d</sub></i><sub><sub>3</sub></sub> = 3.6 at 303 K. |
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