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Title: Synthesis of heterobimetallic Ru-Mn complexes and the coupling reactions of epoxides with carbon dioxide catalyzed by these complexes
Authors: Man, ML
Lam, KC
Sit, WN
Ng, SM
Zhou, Z
Lin, Z
Lau, CP
Keywords: Coupling reactions
Cyclic carbonates
Density functional calculations
Heterobimetallic complexes
Reaction mechanisms
Issue Date: 2006
Publisher: Wiley-VCH
Source: Chemistry - a European journal, 2006, v. 12, no. 4, p. 1004-1015 How to cite?
Journal: Chemistry - a European journal 
Abstract: The heterobimetallic complexes [(η 5-C 5H 5)Ru(CO)(μ-dppm)Mn(CO) 4] and [(η 5-C 5Me 5)Ru(μ-dppm)(μ-CO) 2Mn(CO) 3] (dppm= bisdiphenylphosphinomethane) have been prepared by reacting the hydridic complexes [(η 5-C 5H 5)Ru(dppm) H] and [(η-C 5Me 5)Ru(dppm)H], respectively, with the protonic [HMn(CO) 5] complex. The bimetallic complexes can also be synthesized through metathetical reactions between [(η 5-C 5R 5)Ru-(dppm)Cl] (R = H or Me) and Li + [Mn(CO) 5] -. Although the complexes fail to catalyze the hydrogenation of CO 2 to formic acid, they catalyze the coupling reactions of epoxides with carbon dioxide to yield cyclic carbonates. Two possible reaction pathways for the coupling reactions have been proposed. Both routes begin with heterolytic cleavage of the Ru-Mn bond and coordination of an epoxide molecule to the Lewis acidic ruthenium center. In Route I, the Lewis basic manganese center activates the CO 2 by forming the metallocarboxylate anion which then ring-opens the epoxide: subsequent ring-closure gives the cyclic carbonate. In Route II, the nucleophilic manganese center ring-opens the ruthenium-attached epoxide to afford an alkoxide intermediate; CO 2 insertion into the Ru-O bond followed by ring-closure yields the product. Density functional calculations at the B3LYP level of theory were carried out to understand the structural and energetic aspects of the two possible reaction pathways. The results of the calculations indicate that Route II is favored over Route I.
ISSN: 0947-6539
EISSN: 1521-3765
DOI: 10.1002/chem.200500780
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