Pyridyl-Substituted Indenyl Ruthenium Complexes: Synthesis, Structures, and Reactivities

We have investigated the synthesis of a novel pyridyl-substituted indenyl trinuclear ruthenium complex, {μ2-η5:η1-(C5H4N)(C9H5)}Ru3(CO)9 (1), and its reactivities with pyridine derivatives, PPh3, and different types of alkenes. Complex 1 was synthesized in 89% yield from Ru3(CO)12 and 3-(2-pyridyl)indene (1:1 mol ratio) in refluxing heptane. The reaction of 1 with a 5-fold excess of 3-(2-pyridyl)indene gave two complexes, {η1-(C5H4N)(C9H6)}2Ru(CO)2 (2) and {η5-(C5H4N)(C9H6)}{η1-(C5H4N)(C9H6)}Ru2(CO)4 (3). Both were also converted back to 1 in the presence of an equimolar amount of Ru3(CO)12, although the yields were low. Reaction of 1 in refluxing toluene afforded an unexpected complex, {μ3-η6:η3:η1-(C5H4N)(C9H5)}Ru3(CO)7 (4), via the loss of two CO groups. Complex 4 represents a completely new type of coordination mode (μ3-η6:η3:η1) of indenyl ligands in transition metal complexes. The reactions of 1 with 2-(2-pyridyl)indene, 1,2,3,5-tetramethyl-4-(2-pyridyl)cyclopentadiene, 1,2-diphenyl-4-(2-pyridyl)cyclopentadiene, and 2-phenylpyridine in refluxing heptane afforded the mono- and/or dinuclear complexes 5−9 via the cleavage of either a Ru−C(η1) or Ru−C(η5) bond or both. In the case of PPh3, only one of three carbonyls at the pyridyl-coordinated ruthenium center of 1 was replaced by PPh3 to produce {μ2-η5:η1-(C5H4N)(C9H5)}Ru3(CO)8(PPh3) (10). The reactions of 1 with various terminal alkenes (CH2CHR) gave only the dinuclear ruthenium complexes {η5-(C5H4N)(C9H5CHCH2R)}Ru2(CO)5 (11−13, 15, and 17) via the insertion of alkenes into the Ru−C(η1) bond of 1 with the exception of 2-vinylpyridine and CH2CHOCH2CH3, which reacted with 1 to yield the pyridyl-substituted complex {η5-(C5H4N)(C9H5CHCH2(C5H4N))}Ru2(CO)4 (14) and two unexpected complexes, 13 and {η5-(C5H4N)(C9H4CHCH2CH2CH(OCH2CH3))}Ru2(CO)5 (18a and 18b), respectively. Complex 15 was also transformed to {η5-(C5H4N)(C9H5CHCH2CO2CH3)}Ru2(CO)3(η5-CH2CHCO2CH3) (16) in the presence of methyl acrylate. The reactions of 1 with internal alkenes such as norbornene and cyclohexene gave complexes 19−22 in very low yields also via the insertion of alkenes into the Ru−C(η1) bond of 1, with the concomitant formation of a small amount of 4. The molecular structures of 1−5, 8−11, 13−16, 18a, 18b, and 21 were determined by X-ray diffraction analysis. An alternative mechanism for the formation of dinuclear ruthenium complexes via the insertion of alkenes into the Ru−C(η1) bond is proposed.