Highly Reactive Cyclopentadienylcobalt(I) Olefin Complexes

The reduction of cobaltocene with metallic potassium in the presence of trimethylvinylsilane yielded the new CpCo(I) complex [CpCo(H<sub>2</sub>CCHSiMe<sub>3</sub>)<sub>2</sub>] (<b>6</b>). Complex <b>6</b> turned out to be an ideal starting material for substitution reactions with functionalized mono- and diolefins, giving access to either new [CpCo(olefin)<sub>2</sub>] complexes such as <b>7</b> (trichlorovinylsilane) and <b>12</b> (dimethyl fumarate) or CpCo(diolefin) complexes such as <b>8</b> (diallyl ether), <b>9</b> (1,5-hexadiene), <b>10</b> (1,4-pentadiene), and <b>11</b> (1,1,3,3-tetramethyldivinyldisiloxane) with essentially quantitative yields. These complexes are rarely accessible by other methods or the direct reduction method using alkali metals. The complexes <b>6</b>−<b>9</b> were unambiguously characterized by X-ray structure analysis, which is reported for the first time for these types of complexes, giving way for the structural comparison. Computational calculations on the olefin ligand exchange processes with <b>6</b> display the different stabilities and reactivity trends of the different CpCo(I)-olefin complexes. The extraordinarily high reactivity and the application of complexes <b>6</b> and <b>9</b> were demonstrated in [2+2+2] cycloaddition reactions of different diynes with nitriles, yielding the substituted isoquinoline derivatives with good yields within short reaction times and under very mild conditions. The presented complexes show higher activities compared to [CpCo(COD)] (<b>3</b>) while possessing advantages in preparation and handling compared to [CpCo(H<sub>2</sub>CCH<sub>2</sub>)<sub>2</sub>] (<b>4</b>).