Dicarbonyltris(triphenylphosphine)ruthenium (0)

Dicarbonyltris(triphenylphosphine)ruthenium (0) or Roper's complex is a ruthenium metal carbonyl ^[1]. 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.

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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 ^[2]. 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.

References

Cavit, B. E.; Grundy, K. R.; Roper, W. R. J. Chem. Soc., Chemical Communications. 1972, 60.
Instant "Base-Promoted" Generation of Roper's-type Ru(0) Complexes Ru(CO)2(PR3)3 from a Simple Carbonylchlororuthenium(II) Precursor Stephane Sentets, Maria del Carmen Rodriguez Martinez, Laure Vendier, Bruno Donnadieu, Vincent Huc, Noël Lugan, and Guy Lavigne J. Am. Chem. Soc.; 2005; 127(42) pp 14554 - 14555; (Communication) DOI: 10.1021/ja055066e Abstract

Categories: Ruthenium compounds | Carbonyl complexes

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Dicarbonyltris(triphenylphosphine)ruthenium_(0)". A list of authors is available in Wikipedia.