3 research outputs found
Pendant Alkyl and Aryl Groups on Tin Control Complex Geometry and Reactivity with H<sub>2</sub>/D<sub>2</sub> in Pt(SnR<sub>3</sub>)<sub>2</sub>(CNBu<sup>t</sup>)<sub>2</sub> (R = Bu<sup>t</sup>, Pr<sup>i</sup>, Ph, Mesityl)
No full textThe
complex PtĀ(SnBu<sup>t</sup><sub>3</sub>)<sub>2</sub>Ā(CNBu<sup>t</sup>)<sub>2</sub>Ā(H)<sub>2</sub>, <b>1</b>, was obtained
from the reaction of PtĀ(COD)<sub>2</sub> and Bu<sup>t</sup><sub>3</sub>SnH, followed by addition of CNBu<sup>t</sup>. The two hydride ligands
in <b>1</b> can be eliminated, both in solution and in the solid
state, to yield PtĀ(SnBu<sup>t</sup><sub>3</sub>)<sub>2</sub>Ā(CNBu<sup>t</sup>)<sub>2</sub>, <b>2</b>. Addition of hydrogen to <b>2</b> at room temperature in solution and in the solid state regenerates <b>1</b>. Complex <b>2</b> catalyzes H<sub>2</sub>āD<sub>2</sub> exchange in solution to give HD. The proposed mechanism of
exchange involves reductive elimination of Bu<sup>t</sup><sub>3</sub>SnH from <b>1</b> to afford vacant sites on the Pt center,
thus facilitating the exchange process. This is supported by isolation
and characterization of PtĀ(SnMes<sub>3</sub>)Ā(SnBu<sup>t</sup><sub>3</sub>)Ā(CNBu<sup>t</sup>)<sub>2</sub>, <b>3</b>, when the addition of H<sub>2</sub> to <b>2</b> was carried
out in the presence of free ligand Mes<sub>3</sub>SnH (Mes = 2,4,6-Me<sub>3</sub>C<sub>6</sub>H<sub>2</sub>). Complex PtĀ(SnMes<sub>3</sub>)<sub>2</sub>Ā(CNBu<sup>t</sup>)<sub>2</sub>, <b>5</b>, can
be prepared from the reaction of PtĀ(COD)<sub>2</sub> with Mes<sub>3</sub>SnH and CNBu<sup>t</sup>. The exchange reaction of <b>2</b> with Ph<sub>3</sub>SnH gave PtĀ(SnPh<sub>3</sub>)<sub>3</sub>(CNBu<sup>t</sup>)<sub>2</sub>Ā(H), <b>6</b>, wherein both SnBu<sup>t</sup><sub>3</sub> ligands are replaced by SnPh<sub>3</sub>. Complex <b>6</b> decomposes in air to form square planar PtĀ(SnPh<sub>3</sub>)<sub>2</sub>Ā(CNBu<sup>t</sup>)<sub>2</sub>, <b>7</b>. The complex PtĀ(SnPr<sup>i</sup><sub>3</sub>)<sub>2</sub>Ā(CNBu<sup>t</sup>)<sub>2</sub>, <b>8</b>, was also prepared. Out of the
four analogous complexes PtĀ(SnR<sub>3</sub>)<sub>2</sub>Ā(CNBu<sup>t</sup>)<sub>2</sub> (R = Bu<sup>t</sup>, Mes, Ph, or Pr<sup>i</sup>), only the Bu<sup>t</sup> analogue does both H<sub>2</sub> activation
and H<sub>2</sub>āD<sub>2</sub> exchange. This is due to steric
effects imparted by the bulky Bu<sup>t</sup> groups that distort the
geometry of the complex considerably from planarity. The reaction
of PtĀ(COD)<sub>2</sub> with Bu<sup>t</sup><sub>3</sub>SnH and CO gas
afforded <i>trans</i>-PtĀ(SnBu<sup>t</sup><sub>3</sub>)<sub>2</sub>Ā(CO)<sub>2</sub>, <b>9</b>. Compound <b>9</b> can be converted to <b>2</b> by replacement of the CO ligands
with CNBu<sup>t</sup> via the intermediate PtĀ(SnBu<sup>t</sup><sub>3</sub>)<sub>2</sub>Ā(CNBu<sup>t</sup>)<sub>2</sub>Ā(CO), <b>10</b>
MetalāLigand Synergistic Effects in the Complex Ni(Ī·<sup>2</sup>āTEMPO)<sub>2</sub>: Synthesis, Structures, and Reactivity
No full textIn
the current investigation, reactions of the ābow-tieā
NiĀ(Ī·<sup>2</sup>-TEMPO)<sub>2</sub> complex with an assortment
of donor ligands have been characterized experimentally and computationally.
While the NiĀ(Ī·<sup>2</sup>-TEMPO)<sub>2</sub> complex has <i>trans</i>-disposed TEMPO ligands, proton transfer from the CāH
bond of alkyne substrates (phenylacetylene, acetylene, trimethylsilyl
acetylene, and 1,4-diethynylbenzene) produce <i>cis</i>-disposed
ligands of the form NiĀ(Ī·<sup>2</sup>-TEMPO)Ā(Īŗ<sup>1</sup>-TEMPOH)Ā(Īŗ<sup>1</sup>-R). In the case of 1,4-diethynylbenzene,
a two-stage reaction occurs. The initial product NiĀ(Ī·<sup>2</sup>-TEMPO)Ā(Īŗ<sup>1</sup>-TEMPOH)Ā[Īŗ<sup>1</sup>-<i>C</i>CĀ(C<sub>6</sub>H<sub>4</sub>)ĀCCH] is formed first but can react further
with another equivalent of NiĀ(Ī·<sup>2</sup>-TEMPO)<sub>2</sub> to form the bridged complex NiĀ(Ī·<sup>2</sup>-TEMPO)Ā(Īŗ<sup>1</sup>-TEMPOH)Ā[Īŗ<sup>1</sup>-Īŗ<sup>1</sup>-<i>C</i>CĀ(C<sub>6</sub>H<sub>4</sub>)ĀC<i>C</i>]ĀNiĀ(Ī·<sup>2</sup>-TEMPO)Ā(Īŗ<sup>1</sup>-TEMPOH). The corresponding reaction with
acetylene, which could conceivably also yield a bridging complex,
does not occur. Via density functional theory (DFT), addition mechanisms
are proposed in order to rationalize thermodynamic and kinetic selectivity.
Computations have also been used to probe the relative thermodynamic
stabilities of the <i>cis</i> and <i>trans</i> addition products and are in accord with experimental results. Based
upon the computational results and the geometry of the experimentally
observed product, a <i>trans</i>ā<i>cis</i> isomerization must occur
MetalāLigand Synergistic Effects in the Complex Ni(Ī·<sup>2</sup>āTEMPO)<sub>2</sub>: Synthesis, Structures, and Reactivity
No full textIn
the current investigation, reactions of the ābow-tieā
NiĀ(Ī·<sup>2</sup>-TEMPO)<sub>2</sub> complex with an assortment
of donor ligands have been characterized experimentally and computationally.
While the NiĀ(Ī·<sup>2</sup>-TEMPO)<sub>2</sub> complex has <i>trans</i>-disposed TEMPO ligands, proton transfer from the CāH
bond of alkyne substrates (phenylacetylene, acetylene, trimethylsilyl
acetylene, and 1,4-diethynylbenzene) produce <i>cis</i>-disposed
ligands of the form NiĀ(Ī·<sup>2</sup>-TEMPO)Ā(Īŗ<sup>1</sup>-TEMPOH)Ā(Īŗ<sup>1</sup>-R). In the case of 1,4-diethynylbenzene,
a two-stage reaction occurs. The initial product NiĀ(Ī·<sup>2</sup>-TEMPO)Ā(Īŗ<sup>1</sup>-TEMPOH)Ā[Īŗ<sup>1</sup>-<i>C</i>CĀ(C<sub>6</sub>H<sub>4</sub>)ĀCCH] is formed first but can react further
with another equivalent of NiĀ(Ī·<sup>2</sup>-TEMPO)<sub>2</sub> to form the bridged complex NiĀ(Ī·<sup>2</sup>-TEMPO)Ā(Īŗ<sup>1</sup>-TEMPOH)Ā[Īŗ<sup>1</sup>-Īŗ<sup>1</sup>-<i>C</i>CĀ(C<sub>6</sub>H<sub>4</sub>)ĀC<i>C</i>]ĀNiĀ(Ī·<sup>2</sup>-TEMPO)Ā(Īŗ<sup>1</sup>-TEMPOH). The corresponding reaction with
acetylene, which could conceivably also yield a bridging complex,
does not occur. Via density functional theory (DFT), addition mechanisms
are proposed in order to rationalize thermodynamic and kinetic selectivity.
Computations have also been used to probe the relative thermodynamic
stabilities of the <i>cis</i> and <i>trans</i> addition products and are in accord with experimental results. Based
upon the computational results and the geometry of the experimentally
observed product, a <i>trans</i>ā<i>cis</i> isomerization must occur
