Ruthenium Carbene Complexes Analogous to Grubbs‑I Catalysts Featuring Germylenes as Ancillary Ligands

Reactions of the first-generation Grubbs’ catalyst <i>trans</i>-[RuCl₂(CHPh)­(PCy₃)₂] (<b>1</b>) with the amidinatogermylenes Ge­(^<i>t</i>Bu₂bzam)­R (R = ^<i>t</i>Bu (<b>L</b>^<b>1</b>), CH₂SiMe₃ (<b>L</b>^<b>2</b>); ^<i>t</i>Bu₂bzam = <i>N</i>,<i>N</i>′-bis­(tertbutyl)­benzamidinate) have allowed the isolation and full characterization of the first specimens of Grubbs-type carbene complexes featuring heavier tetrylenes as ancillary ligands, namely, the disubstituted derivatives <i>trans-</i>[RuCl₂(CHPh)­(<b>L</b>^<b>1</b>)₂] (<b>3</b>) and <i>cis-</i>[RuCl₂(CHPh)­(<b>L</b>^<b>2</b>)₂] (<b>7</b>), which curiously differ in the arrangement of their germylene ligands. DFT calculations have revealed that the different volumes of <b>L</b>^<b>1</b> and <b>L</b>^<b>2</b> (the former is larger than the latter) are responsible for the different stereochemistry of <b>3</b> and <b>7</b>. NMR-monitoring of the reaction solutions has allowed the observation of the monosubstituted intermediates <i>trans</i>-[RuCl₂(CHPh)­(L)­(PCy₃)] (L = <b>L</b>^<b>1</b> (<b>2</b>), <b>L</b>^<b>2</b> (<b>5</b>)) and their evolution to either the disubstituted final product (for <b>L</b>^<b>1</b>) <i>trans</i>-[RuCl₂(CHPh)­(<b>L</b>^<b>1</b>)₂] (<b>3</b>) or the short-lived disubstituted intermediate (for <b>L</b>^<b>2</b>) <i>trans</i>-[RuCl₂(CHPh)­(<b>L</b>^<b>2</b>)₂] (<b>6</b>). Complex <b>7</b> arises from a <i>trans</i>-to-<i>cis</i> isomerization of intermediate <b>6</b>. As olefin metathesis catalysts, both <b>3</b> and <b>7</b> promoted the ring-closing metathesis of diethyl 2,2-diallylmalonate and the ring-opening metathesis polymerization of norbornene, but their catalytic activity decreased with the reaction time, indicating catalyst decomposition