Preparation of Capped Octahedral OsHC<sub>6</sub> Complexes
by Sequential Carbon-Directed C–H Bond Activation Reactions
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Abstract
A synthetic procedure
based on sequential C-directed C–H
bond activation reactions is reported for the preparation of capped
octahedral OsHC<sub>6</sub> complexes. Reactions of the dimer [OsCl<sub>2</sub>(η<sup>6</sup>-<i>p</i>-cymene)]<sub>2</sub> (<b>1</b>) with PhMeLAgI (PhMeL = 1-phenyl-3-methyl-1<i>H</i>-benzimidazolylidene (PhMeBIm), 1-phenyl-3,5,6-trimethyl-1<i>H</i>-benzimidazolylidene (PhMeBIm*)) afford OsCl<sub>2</sub>(η<sup>6</sup>-<i>p</i>-cymene)(PhMeL)
(L = BIm (<b>2</b>), BIm* (<b>3</b>)), which undergo cyclization
to give OsCl{κ<sup>2</sup>-C,C-(MeL-C<sub>6</sub>H<sub>4</sub>)}(η<sup>6</sup>-<i>p</i>-cymene) (L = BIm (<b>4</b>), BIm* (<b>5</b>)) by stirring in dichloromethane
suspensions of Al<sub>2</sub>O<sub>3</sub>. Complexes <b>4</b> and <b>5</b> exchange the anion with AgOTf (OTf = CF<sub>3</sub>SO<sub>3</sub>). In acetonitrile, at 75 °C, the resulting OTf
derivatives Os(OTf){κ<sup>2</sup>-C,C-(MeL-C<sub>6</sub>H<sub>4</sub>)}(η<sup>6</sup>-<i>p</i>-cymene) (L
= BIm (<b>6</b>), BIm* (<b>7</b>)) release the arene to
yield the tetra(solvento) compounds [Os{κ<sup>2</sup>-C,C-(MeL-C<sub>6</sub>H<sub>4</sub>)(CH<sub>3</sub>CN)<sub>4</sub>]OTf (L
= BIm (<b>8</b>), BIm* (<b>9</b>)). Complexes <b>8</b> and <b>9</b> react with PhMeLAgI to coordinate a second NHC
ligand. The generated species Os{κ<sup>2</sup>-C,C-(MeL-C<sub>6</sub>H<sub>4</sub>)(PhMeL)(CH<sub>3</sub>CN)<sub>3</sub>]OTf (L = BIm (<b>10</b>), BIm* (<b>11</b>)), containing
a C,C-chelate NHC-C<sub>6</sub>H<sub>4</sub> ligand and a monodentate
NHC group, exist as a mixture of <i>mer</i> (<b>a</b> and <b>b</b>) and <i>fac</i> (<b>c</b>) acetonitrile
isomers. The X-ray diffraction structure of <b>10c</b> reveals
aromatic–aromatic interactions between the <i>N</i>-phenyl substituent of the monodentate NHC group and aromatic rings
of the chelate ligand. The π–π stacking has been
analyzed by means of DFT calculations by using the AIM approach. Treatment
of <b>10</b> and <b>11</b> with [PhMeLH]I, in the presence
of an excess of Et<sub>3</sub>N, leads to the capped octahedral target
compounds OsH{κ<sup>2</sup>-C,C-(MeL-C<sub>6</sub>H<sub>4</sub>)}<sub>3</sub> (L = BIm (<b>12</b>), BIm* (<b>13</b>)),
as a result of the coordination of a third NHC group and the orthometalation
of the <i>N</i>-phenyl substituents of the second and third
NHC ligands
