Reactivity of 2,3-bis(2-pyridyl)pyrazine with [Re 2(CO) 8(CH 3CN) 2]: Molecular structures of [Re 2(CO) 8(C 14H 10N 4)] and [Re 2(CO) 8(C 14H 10N 4)Re 2(CO) 8

Abstract

The reaction of the labile compound [Re 2(CO) 8(CH 3CN) 2] with 2,3-bis(2-pyridyl)pyrazine in dichloromethane solution at reflux temperature afforded the structural dirhenium isomers [Re 2(CO) 8(C 14H 10N 4)] ( 1 and 2), and the complex [Re 2(CO) 8(C 14H 10N 4)Re 2(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, CD 3COCD 3), 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 [Re 2(CO) 6(C 14H 10N 4) 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.