Dicarbonyltris(triphenylphosphine)ruthenium (0)

Dicarbonyltris(triphenylphosphine)ruthenium (0) or Roper's complex is a ruthenium metal carbonyl. In Ru(CO)2(PPh3)3 carbon monoxide ligands and three triphenylphosphine ligands are coordinated to a central ruthenium atom. This compound loses a phosphine ligand very easily can replace it alkynes or olefins. The related organometallic complex Ru(CO)2H2(PPh3)2 can be obtained by exposing the complex to hydrogen gas and is a catalyst in the Murai olefin coupling reaction between terminal alkenes and the ortho C-H position of a phenone.

Preparation
The compound can be prepared by magnesium reduction in the presence of a large excess of phosphine. The 16-electron intermediate can actually be isolated.


 * $$ Ru(CO)_2Cl_2(PPh_3)_2 + Mg + PPh_3 \longrightarrow Ru(CO)_2(PPh_3)_2 \longrightarrow Ru(CO)_2(PPh_3)_3 $$

A recent base promoted method involves the reduction of bivalent ruthenium in tricarbonyldichloro ruthenium (II) with triphenylphosphine and the ammonium salt tetraethylammonium hydroxide. The overall reaction for this one-pot synthesis is:


 * $$ Ru(CO)_3Cl_2(THF) + 3 PPh_3 + 4NEt_4OH  \longrightarrow Ru(CO)_2(PPh_3)_2 + (NEt_4)_2CO_3 + 2 NEt_4Cl + 2 H_2O$$

but the reactants are added sequentially. The first step is the formation of a hydroxyl - carbonyl adduct to an anion:


 * $$ Ru(CO)_3Cl_2(THF) + NEt_4OH  \longrightarrow (NEt_4)^+Ru(CO)(COOH)(Cl)_2(THF)^-   $$

next solvatated tetrahydrofuran is replaced by phosphine:


 * $$ (NEt_4)^+Ru(CO)(COOH)(Cl)_2^- +  PPh_3  \longrightarrow (NEt_4)^+Ru(CO)(COOH)(Cl)_2PPh_3^-  + THF  $$

next the carboxylic acid ligand is deprotonated by hydroxide forming the dianion and water


 * $$ (NEt_4)^+Ru(CO)(COOH)(Cl)_2PPh_3^-  +   NEt_4OH    \longrightarrow (NEt_4)_2^+Ru(CO)(COO)(Cl_2)PPh_3^{2-}  + H_2O   $$

in this compound carbon monoxide is effectively oxidized to carbon dioxide with the reduction of Ru (II) to Ru(0) and in a dissociative chemical reaction carbon dioxide is removed. The two remaining chlorine ligands are replaced by two more phosphine groups in the final step.


 * $$ (NEt_4)_2^+Ru(CO)(COO)(Cl)_2PPh_3^{2-} +  2PPh_3 \longrightarrow Ru(CO)_2(PPh_3)_3  + CO_2 +  2 NEt_4Cl $$

The generated carbon dioxide is trapped:


 * $$ CO_2 +  2 NEt_4OH  \longrightarrow (NEt_4)_2CO_3 + H_2O$$

In this sequence low reaction temperatures and the order in which the reagents are added are important. Ru(CO)2(PPh3)3 is air stable when dry but in THF conversion occurs to Ru(CO)2(PPh3)3O2. The compound has a trigonal bipyramidal molecular geometry and exists as a mixture of two isomers that rapidly interconvert in solution.