An Air and Moisture Stable Boat Shaped Hydroxo‐Bridged Ruthenium(II) Binuclear Complex for the Catalytic Hydrogenation of CO₂

A new hydroxo‐bridged ruthenium (II) complex [{Ru(η 6 ‐ p ‐cymene)( i Pr 2 P−O)} 2 (μ‐OH)]Cl ( 2 ) has fortuitously been isolated from the reaction between the known ruthenium(II) complex [RuCl 2 (η 6 ‐ p ‐cymene)( i Pr 2 P‐OH)] ( 1 ) in either CDCl 3 or CHCl 3 solutions in the presence of excess DBU (1,8‐diazabicyclo(5.4.0)undec‐7‐ene) at room temperature. Complex 2 is only formed under specific conditions as an orange‐colored air and moisture stable binuclear complex. It is formed via the deprotonation of the P−OH unit in [RuCl 2 (η 6 ‐ p ‐cymene)( i Pr 2 P‐OH)]. Complex 2 has been fully characterized by spectroscopic and analytical methods. Its structure was determined by single crystal X‐ray diffraction which reveals a boat‐shaped motif containing a bridging hydroxide unit which undergoes hydrogen bonding with a chloride counterion. Complex 2 was utilized as a catalyst for the hydrogenation of CO 2 to formic acid salt using molecular hydrogen. The catalytic reactions were performed at 100 °C in THF in the presence of DBU as a base to isolate [DBU+H][OC(O)H] salt as the final product. Using catalyst loadings down to 0.01 mol%, it was possible to hydrogenate gaseous CO 2 with TONs up to 9900.