[15529-49-4] · C54H45Cl2P3Ru · Dichlorotris(triphenylphosphine)ruthenium(II) · (MW 958.86)
Physical Data: mp 132-134 °C.
Solubility: sol toluene, benzene, CH2Cl2.
Form Supplied in: red-brown or shiny black crystals.
Preparative Method: by refluxing hydrated Ruthenium(III) Chloride and Triphenylphosphine in ethanol according to the procedure of Wilkinson.1b
The title reagent (1) is a versatile homogeneous catalyst. It is used in the reduction, oxidation, cyclization, and isomerization of a variety of organic compounds. It is an effective catalyst for the Kharasch addition of a range of halogenated substances to alkenes.3,4 a-Chloro-g-lactones (eq 1)5a or carbocyclic a,g-dichloroesters5b are formed by reaction of alkenic a,a-dichloro acids and esters in the presence of (1). The process occurs through a metal-complex radical and provides highly functionalized products. The reagent is also used in radical cyclizations of N-allylacetamides6-8 and the stereoselective addition cyclization of 1,6-dienes (eq 2).9 The synthesis of a,b-unsaturated ketones from primary alcohols and allyl acetates is catalyzed by (1).10
The reagent (1) can promote hydrogen transfer from alcohols,14,15 acids,17 and amides, as well as other hydrogen donors, to activated double bonds,14,15 carbonyl compounds, and nitro groups. It is an efficient homogeneous catalyst for the hydrogenation of nitroalkanes to amines,11 nitroarenes to amino arenes,12,13 and imines to amines (eq 3).16
The ruthenium-catalyzed reduction of diallyl-a-oxalyl carboxylates with Formic Acid provides a-hydroxycarboxylic acids in good yields.17
The reagent (1) can catalyze the oxidation of alkanes to tertiary alcohols,18 amides to t-butyldioxyamides,19 and tertiary amines to a-(t-butyldioxy)alkylamines20 using t-Butyl Hydroperoxide. N-Demethylation of tertiary methylamines is accomplished by hydrolysis of the a-(t-butyldioxy)alkylamine (eq 4). Alcohols have been oxidized to aldehydes and ketones in the presence of (1) and oxidants such as Bis(trimethylsilyl) Peroxide,21 molecular Oxygen,22 Acetone,23a or N-Methylmorpholine N-Oxide.23b
The reagent (1) catalyzes the isomerization of a,b-ynones to (E,E)-a,b,g,d-dienones,24 allylic alcohols to ketones,25a and 2-ynols to a,b-unsaturated aldehydes.25b The Claisen rearrangement of unsymmetrical diallyl ethers is catalyzed by (1) to yield a,d-unsaturated aldehyes or ketones.25c
The reagent can be immobilized on a polystyrene support. The immobilized complex can be reused, thereby making this heterogeneous system more efficient than the homogeneous one. This heterogeneous catalyst has been used in the isomerization of allylarenes.2,26
The reagent (1) is used in the N-alkylation of NH groups of azoles with alcohols under neutral conditions,27 and in the synthesis of indoles28 via an intramolecular N-alkylation. It is also used in the syntheses of important biologically active compounds such as imidazo[1,2-a]pyridines (eq 5).29 Other important heterocycles such as 1,3-disubstituted 2,3-dihydroimidazol-2-ones are effectively prepared from N,N-disubstituted ureas and vicinal diols in presence of (1).30 The reagent catalyzes the oxidation of the vicinal diol to the corresponding acyloin, and condensation of the urea with the acyloin followed by dehydration yields the desired product (eq 6).31
Janet S. Plummer
Parke-Davis Pharmaceutical Research, Ann Arbor, MI, USA