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

We have investigated the synthesis of a novel pyridyl-substituted indenyl trinuclear ruthenium complex, {μ 2 -η 5:η 1 -(C 5 H 4 N)(C 9 H 5 )}Ru 3 (CO) 9 ( 1 ), and its reactivities with pyridine derivatives, PPh 3, and different types of alkenes. Complex 1 was synthesized in 89% yield from Ru 3 (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, {η 1 -(C 5 H 4 N)(C 9 H 6 )} 2 Ru(CO) 2 ( 2 ) and {η 5 -(C 5 H 4 N)(C 9 H 6 )}{η 1 -(C 5 H 4 N)(C 9 H 6 )}Ru 2 (CO) 4 ( 3 ). Both were also converted back to 1 in the presence of an equimolar amount of Ru 3 (CO) 12, although the yields were low. Reaction of 1 in refluxing toluene afforded an unexpected complex, {μ 3 -η 6:η 3:η 1 -(C 5 H 4 N)(C 9 H 5 )}Ru 3 (CO) 7 ( 4 ), via the loss of two CO groups. Complex 4 represents a completely new type of coordination mode (μ 3 -η 6:η 3:η 1 ) 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(η 1 ) or Ru−C(η 5 ) bond or both. In the case of PPh 3, only one of three carbonyls at the pyridyl-coordinated ruthenium center of 1 was replaced by PPh 3 to produce {μ 2 -η 5:η 1 -(C 5 H 4 N)(C 9 H 5 )}Ru 3 (CO) 8 (PPh 3 ) ( 10 ). The reactions of 1 with various terminal alkenes (CH 2 ═CHR) gave only the dinuclear ruthenium complexes {η 5 -(C 5 H 4 N)(C 9 H 5 CHCH 2 R)}Ru 2 (CO) 5 ( 11 − 13, 15, and 17 ) via the insertion of alkenes into the Ru−C(η 1 ) bond of 1 with the exception of 2-vinylpyridine and CH 2 ═CHOCH 2 CH 3, which reacted with 1 to yield the pyridyl-substituted complex {η 5 -(C 5 H 4 N)(C 9 H 5 CHCH 2 (C 5 H 4 N))}Ru 2 (CO) 4 ( 14 ) and two unexpected complexes, 13 and {η 5 -(C 5 H 4 N)(C 9 H 4 CHCH 2 CH 2 CH(OCH 2 CH 3 ))}Ru 2 (CO) 5 ( 18a and 18b ), respectively. Complex 15 was also transformed to {η 5 -(C 5 H 4 N)(C 9 H 5 CHCH 2 CO 2 CH 3 )}Ru 2 (CO) 3 (η 5 -CH 2 ═CHCO 2 CH 3 ) ( 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(η 1 ) 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(η 1 ) bond is proposed.