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Dichlorotris(triphenylphosphine)ruthenium(II)

Chemical compound From Wikipedia, the free encyclopedia

Dichlorotris(triphenylphosphine)ruthenium(II)
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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.

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Synthesis and basic properties

RuCl2(PPh3)3 is the product of the reaction of ruthenium trichloride trihydrate with a methanolic solution of triphenylphosphine.[1][2]

2 RuCl3(H2O)3 + 7 PPh3 → 2 RuCl2(PPh3)3 + 2 HCl + 5 H2O + OPPh3

The coordination sphere of RuCl2(PPh3)3 can be viewed as either five-coordinate or octahedral. One coordination site is occupied by one of the hydrogen atoms of a phenyl group.[3] 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.[4] The Ru-Cl bond lengths are both 2.387 Å.

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Reactions

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In the presence of excess of triphenylphosphine, RuCl2(PPh3)3 binds a fourth phosphine to give black RuCl2(PPh3)4. 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.[5]

Dichlorotris(triphenylphosphine)ruthenium(II) reacts with hydrogen in the presence of base to give the purple-colored monohydride HRuCl(PPh3)3.[6]

RuCl2(PPh3)3 + H2 + NEt3 → HRuCl(PPh3)3 + [HNEt3]Cl

Dichlorotris(triphenylphosphine)ruthenium(II) reacts with carbon monoxide to produce the all trans isomer of dichloro(dicarbonyl)bis(triphenylphosphine)ruthenium(II).

RuCl2(PPh3)3 + 2 CO → trans,trans,trans-RuCl2(CO)2(PPh3)2 + PPh3

This kinetic product isomerizes to the cis adduct during recrystallization. trans-RuCl2(dppe)2 forms upon treating RuCl2(PPh3)3 with dppe.

RuCl2(PPh3)3 + 2 dppe → RuCl2(dppe)2 + 3 PPh3

RuCl2(PPh3)3 catalyzes the decomposition of formic acid into carbon dioxide and hydrogen gas in the presence of an amine.[7] Since carbon dioxide can be trapped and hydrogenated on an industrial scale, formic acid represents a potential storage and transportation medium.

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Use in organic synthesis

RuCl2(PPh3)3 facilitates oxidations, reductions, cross-couplings, cyclizations, and isomerization. It is used in the Kharasch addition of chlorocarbons to alkenes.[8]

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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").[8]

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RuCl2(PPh3)3 efficiently catalyzes carbon-carbon bond formation from cross couplings of alcohols through C-H activation of sp3 carbon atoms in the presence of a Lewis acid.[9]

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References

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