Synthesis and Applications of RuCl<sub>2</sub>(CHR‘)(PR<sub>3</sub>)<sub>2</sub>:  The Influence of the Alkylidene Moiety on Metathesis Activity

The reactions of RuCl<sub>2</sub>(PPh<sub>3</sub>)<sub>3</sub> with a number of diazoalkanes were surveyed, and alkylidene transfer to give RuCl<sub>2</sub>(CHR)(PPh<sub>3</sub>)<sub>2</sub> (R = Me (<b>1</b>), Et (<b>2</b>)) and RuCl<sub>2</sub>(CH-<i>p</i>-C<sub>6</sub>H<sub>4</sub>X)(PPh<sub>3</sub>)<sub>2</sub> (X = H (<b>3</b>), NMe<sub>2</sub> (<b>4</b>), OMe (<b>5</b>), Me (<b>6</b>), F (<b>7</b>), Cl (<b>8</b>), NO<sub>2</sub> (<b>9</b>)) was observed for alkyl diazoalkanes RCHN<sub>2</sub> and various <i>para</i>-substituted aryl diazoalkanes <i>p</i>-C<sub>6</sub>H<sub>4</sub>XCHN<sub>2</sub>. Kinetic studies on the living ring-opening metathesis polymerization (ROMP) of norbornene using complexes <b>3</b>−<b>9</b> as catalysts have shown that initiation is in all cases faster than propagation (<i>k</i><sub>i</sub>/<i>k</i><sub>p</sub> = 9 for <b>3</b>) and that the electronic effect of X on the metathesis activity of <b>3</b>−<b>9</b> is relatively small. Phosphine exchange in <b>3</b>−<b>9</b> with tricyclohexylphosphine leads to RuCl<sub>2</sub>(CH-<i>p</i>-C<sub>6</sub>H<sub>4</sub>X)(PCy<sub>3</sub>)<sub>2</sub> <b>10</b>−<b>16</b>, which are efficient catalysts for ROMP of cyclooctene (PDI = 1.51−1.63) and 1,5-cyclooctadiene (PDI = 1.56−1.67). The crystal structure of RuCl<sub>2</sub>(CH-<i>p</i>-C<sub>6</sub>H<sub>4</sub>Cl)(PCy<sub>3</sub>)<sub>2</sub> (<b>15</b>) indicated a distorted square-pyramidal geometry, in which the two phosphines are <i>trans</i> to each other, and the alkylidene unit lies in the Cl−Ru−Cl plane. The benzylidenes RuCl<sub>2</sub>(CHPh)(PR<sub>3</sub>)<sub>2</sub> (R = Cy (cyclohexyl) (<b>10</b>), Cp (cyclopentyl) (<b>17</b>), <i>i</i>-Pr (<b>18</b>)) are quantitatively available <i>via</i> one-pot synthesis with RuCl<sub>2</sub>(PPh<sub>3</sub>)<sub>3</sub>, PhCHN<sub>2</sub>, and PR<sub>3</sub> as reaction components. <b>10</b> is an efficient catalyst for metathesis of acyclic olefins:  On reaction with excess ethylene, the methylidene complex RuCl<sub>2</sub>(CH<sub>2</sub>)(PCy<sub>3</sub>)<sub>2</sub> (<b>19</b>) is formed quantitatively, and various alkylidene compounds RuCl<sub>2</sub>(CHR)(PCy<sub>3</sub>)<sub>3</sub> (R = Me (<b>20</b>), Et (<b>21</b>), <i>n</i>-Bu (<b>22</b>)) are isolated as the kinetic products from the reaction of <b>10</b> with an excess of the corresponding terminal or disubstituted olefins. Metathesis of conjugated and cumulated olefins with <b>10</b> results in the formation of vinylalkylidene and vinylidene complexes, as shown by the synthesis of RuCl<sub>2</sub>(CHCHCH<sub>2</sub>)(PCy<sub>3</sub>)<sub>2</sub> (<b>23</b>) and RuCl<sub>2</sub>(CCH<sub>2</sub>)(PCy<sub>3</sub>)<sub>2</sub> (<b>24</b>) from 1,3-butadiene or 1,2-propadiene, respectively. Also, functional groups such as −OAc, −Cl, and −OH can be introduced into the alkylidene moiety <i>via</i> cross metathesis with the appropriate alkene.