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]

Abstract The reaction of the labile compound [Re 2 (CO) 8 (CH 3 CN) 2 ] with 2,3-bis(2-pyridyl)pyrazine in dichloromethane solution at reflux temperature afforded the structural dirhenium isomers [Re 2 (CO) 8 (C 14 H 10 N 4 )] ( 1 and 2 ), and the complex [Re 2 (CO) 8 (C 14 H 10 N 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 1 H NMR (−50 °C, CD 3 COCD 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 14 H 10 N 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.