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)
- Publication date
- 2015
- Publisher
Abstract
The
complex Pt(SnBu<sup>t</sup><sub>3</sub>)<sub>2</sub>(CNBu<sup>t</sup>)<sub>2</sub>(H)<sub>2</sub>, <b>1</b>, was obtained
from the reaction of Pt(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 Pt(SnBu<sup>t</sup><sub>3</sub>)<sub>2</sub>(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>−D<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 Pt(SnMes<sub>3</sub>)(SnBu<sup>t</sup><sub>3</sub>)(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 Pt(SnMes<sub>3</sub>)<sub>2</sub>(CNBu<sup>t</sup>)<sub>2</sub>, <b>5</b>, can
be prepared from the reaction of Pt(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 Pt(SnPh<sub>3</sub>)<sub>3</sub>(CNBu<sup>t</sup>)<sub>2</sub>(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 Pt(SnPh<sub>3</sub>)<sub>2</sub>(CNBu<sup>t</sup>)<sub>2</sub>, <b>7</b>. The complex Pt(SnPr<sup>i</sup><sub>3</sub>)<sub>2</sub>(CNBu<sup>t</sup>)<sub>2</sub>, <b>8</b>, was also prepared. Out of the
four analogous complexes Pt(SnR<sub>3</sub>)<sub>2</sub>(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>−D<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 Pt(COD)<sub>2</sub> with Bu<sup>t</sup><sub>3</sub>SnH and CO gas
afforded <i>trans</i>-Pt(SnBu<sup>t</sup><sub>3</sub>)<sub>2</sub>(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 Pt(SnBu<sup>t</sup><sub>3</sub>)<sub>2</sub>(CNBu<sup>t</sup>)<sub>2</sub>(CO), <b>10</b>