Dichlorotris(triphenylphosphine)ruthenium(II)
Dichlorotris(triphenylphosphine)ruthenium(II) is a coordination complex of ruthenium. It is a chocolate brown solid that is soluble in organic solvents such as benzene. The compound is used as a precursor to other complexes including those used in homogeneous catalysis. Synthesis and basic properties. RuCl(PPh) is the product of the reaction of ruthenium trichloride trihydrate with a methanolic solution of triphenylphosphine. The coordination sphere of RuCl(PPh) can be viewed as either five-coordinate or octahedral. One coordination site is occupied by one of the hydrogen atoms of a phenyl group. This Ru---H agostic interaction is long (2.59 Å) and weak . The low symmetry of the compound is reflected by the differing lengths of the Ru-P bonds: 2.374, 2.412, and 2.230 Å. The Ru-Cl bond lengths are both 2.387 Å. Reactions. In the presence of excess of triphenylphosphine, RuCl(PPh) binds a fourth phosphine to give black RuCl(PPh). The triphenylphosphine ligands in both the tris(phosphine) and tetrakis(phosphine) complexes are readily substituted by other ligands. The tetrakis(phosphine) complex is a precursor to the Grubbs catalysts. Dichlorotris(triphenylphosphine)ruthenium(II) reacts with hydrogen in the presence of base to give the purple-colored monohydride HRuCl(PPh). Dichlorotris(triphenylphosphine)ruthenium(II) reacts with carbon monoxide to produce the all trans  isomer of dichloro(dicarbonyl)bis(triphenylphosphine)ruthenium(II). This kinetic product isomerizes to the cis adduct during recrystallization. "trans"-RuCl(dppe) forms upon treating RuCl(PPh) with dppe. RuCl(PPh) catalyzes the decomposition of formic acid into carbon dioxide and hydrogen gas in the presence of an amine. Since carbon dioxide can be trapped and hydrogenated on an industrial scale, formic acid represents a potential storage and transportation medium. Use in organic synthesis. RuCl(PPh) facilitates oxidations, reductions, cross-couplings, cyclizations, and isomerization. It is used in the Kharasch addition of chlorocarbons to alkenes. Dichlorotris(triphenylphosphine)ruthenium(II) serves as a precatalyst for the hydrogenation of alkenes, nitro compounds, ketones, carboxylic acids, and  imines. On the other hand, it catalyzes the oxidation of alkanes to tertiary alcohols, amides to t-butyldioxyamides, and tertiary amines to α-(t-butyldioxyamides) using tert-butyl hydroperoxide. Using other peroxides, oxygen, and acetone, the catalyst can oxidize alcohols to aldehydes or ketones. Using dichlorotris(triphenylphosphine)ruthenium(II) the N-alkylation of amines with alcohols is also possible (see "borrowing hydrogen"). RuCl(PPh) efficiently catalyzes carbon-carbon bond formation from cross couplings of alcohols through C-H activation of sp carbon atoms in the presence of a Lewis acid.