Substitution of the naphthalene ligand of [(COD)(η 6 -naphthalene)Ru] (2) (COD = 1,5-cyclooctadiene) by suitable haloarenes (halogen = F, Cl, Br, I) affords several new monoand dihaloarene(cyclooctadiene)ruthenium complexes. Depending on the number and position of the halogen and organyl substituents, the haloarenes form achiral or planarchiral π-ligands; [(η 6 -bromoarene)(COD)Ru] complexes are prone to rapid bromine/lithium exchange with nBuLi at low temperatures, while the chloro and fluoro derivatives undergo ortho-metalation under the same conditions. The lithiated species react readily with chiral or achiral electrophiles such as chlorodiorganophosphanes, carbonyl chlorides, aldehydes, lactones, ketones, and epoxides to yield subIntroduction (Arene)ruthenium(0) complexes are useful catalysts for hydrogenation, [2,3] isomerization, [4] and dimerization [5,6] reactions of alkenes. Their (arene)ruthenium() counterparts catalyze enantioselective hydrogen transfer to ketones [7,8] and imines [9] in the presence of enantiomerically pure chiral β-amino alcohols [7] or 1,2-diamines, [8,9] affording high yields and high ees at the same time. Thanks to the particular stability of the areneϪmetal bond, [10] (arene)ruthenium complexes may be converted from Ru 0 into Ru II without the loss of the arene ligand, simply by addition of hydrochloric acid.[2] Only the co-ligands that complete the coordination sphere are exchanged in parallel with the redox process. Of course, it would be very promising to perform the catalytic reactions of (arene)ruthenium complexes in both redox states with enantiopure species whose chirality was connected with the arene ligand. The preparation of [(η 6 -arene)-(COD)Ru] complexes is well known since the work of Bennett, Vitulli, and Pertici, [3,11,12] [13] The lithiated species can be treated with alkyl chloroformates to form ester-substituted [(η 6 -arene)(COD)Ru] compounds. Through the introduction of chiral alkyl chloroformates [alkyl ϭ (Ϫ)-menthyl], this directly affords enantiopure asymmetric complexes. To develop the high potential of this approach, we investigated the preparation and reactivity of (mono-and dihaloarene)ruthenium() complexes systematically. These allow the introduction of many electrophiles of choice. Examples are provided for chlorodiorganophosphanes, carbonyl chlorides, aldehydes, lactones, ketones, and epoxides. Novel (arene)ruthenium() complexes with donor functions such as PR 2 and OH in the side chain are of interest, as these functions should offer the potential to control the reactivity of the different types of (arene)ruthenium catalysts.
Results and Discussion
Preparation of [(COD)(η 6 -haloarene)Ru] ComplexesMono-or dihaloarenes (fluorobenzene, 1,3-difluorobenzene, 3-fluorotoluene, 3-chlorotoluene, 1,4-dichlorobenzene, 2-bromo-1,4-xylene, 1,3-dibromobenzene, 1-bromo-4-fluorobenzene, 1-bromo-4-iodobenzene, and 4,4Ј-difluoro-1,1Ј-biphenyl) replace the naphthalene ligand of [(COD)(η 6 -naphthalene)Ru] (2) in the presence of acetonitrile at room temperatur...
