Reactivity of 2,3-bis(2-pyridyl)pyrazine with [Re2(CO)8(CH3CN)2]: Molecular structures of [Re2(CO)8(C14H10N4)] and [Re2(CO)8(C14H10N4)Re2(CO)8]

The reaction of the labile compound [Re2(CO)8(CH3CN)2] with 2,3-bis(2-pyridyl)pyrazine in dichloromethane solution at reflux temperature afforded the structural dirhenium isomers [Re2(CO)8(C14H10N4)] (1 and 2), and the complex [Re2(CO)8(C14H10N4)Re2(CO)8] (3). In 1, the ligand is σ,σ′-N,N′-coordinated to a Re(CO)3 fragment through pyridine and pyrazine to form a five-membered chelate ring. A seven-membered ring is obtained for isomer 2 by N-coordination of the 2-pyridyl groups while the pyrazine ring remains uncoordinated. For 2, isomers 2a and 2b are found in a dynamic equilibrium ratio [2a]/[2b]  =  7 in solution, detected by 1H NMR (−50 °C, CD3COCD3), coalescence being observed above room temperature. The ligand in 3 behaves as an 8e-donor bridge bonding two Re(CO)3 fragments through two (σ,σ′-N,N′) interactions. When the reaction was carried out in refluxing tetrahydrofuran, complex [Re2(CO)6(C14H10N4)2] (4) was obtained in addition to compounds 1–3. The dinuclear rhenium derivative 4 contains two units of the organic ligand σ,σ′-N,N′-coordinated in a chelate form to each rhenium core. The X-ray crystal structures for 1 and 3 are reported.

Graphical abstractA new tetranuclear rhenium derivative [Re2(CO)8(C14H10N4)Re2(CO)8] was obtained from the reaction of [Re2(CO)8(CH3CN)2] and 2,3-bis(2-pyridyl)pyrazine. The ligand behaves as an 8e-donor bridge between two Re(CO)3 moieties through two σ,σ′-N,N′ interactions.Figure optionsDownload full-size imageDownload as PowerPoint slide