Reactivity of a trinuclear ruthenium complex involving C–H activation and insertion of alkene

Abstract

A novel pyridyl-substituted indenyl trinuclear ruthenium complex, {μ₂-η⁵:η¹-(C₅H₃N-6-Br)(C₉H₅)}Ru₃(CO)₉ (1), was synthesized by thermal treatment of 1-(6-bromo-2-pyridyl)indene with Ru₃(CO)₁₂ (1 : 1 mol ratio) in refluxing heptane and its reactivity with pyridine derivatives, toluene, indene, fluorene, phenylethylene and divinylbenzene was studied. The reaction of 1 with 5-fold excess of 1-(6-bromo-2-pyridyl)indene gave two products, complex {η⁵-(C₅H₃N-6-Br)(C₉H₅)}{η¹-(C₅H₃N)(C₉H₆)}Ru₂(CO)₄ (2) and substituted dibenzfulvalene (3). Reaction of 1 in refluxing toluene afforded an unexpected complex {μ₃-η⁶:η³:η¹-(C₅H₃N-6-Br)(C₉H₅)}Ru₃(CO)₇ (4), via the loss of two CO groups. Reaction of 1 with indene in refluxing heptane afforded a known complex [{(η⁵-C₉H₇)Ru(CO)₂}₂] (5). The reaction of 1 with fluorene in refluxing heptane afforded complex {μ₃-η⁶:η³:η¹-(C₅H₃N-6-Br)(C₉H₅)}Ru₃(CO)₇ (4), fluorene was not involved in the reaction, indicating that the reactivity of fluorene is low. The reactions of 1 with phenylethylene or divinylbenzene in refluxing toluene gave the dinuclear ruthenium complexes {η⁵-(C₅H₃N-6-Br)(C₉H₅CHCH₂Ph)}Ru₂(CO)₅ (6) and {η⁵-(C₅H₃N-6-Br)(C₉H₅CHCH₂PhCHCH₂)}Ru₂(CO)₅ (7), respectively. These complexes have been characterized by elemental analysis, IR, and ¹H NMR spectroscopy. The molecular structures of 1–6 were determined by X-ray diffraction. The density functional theoretical calculations on the electronic structure of complex 1 give an illustration to its high reactivity.