Synthesis and catalytic properties of a series of ruthenium carbonyl complexes with 2-substituted pyrazine ligands (pz-R R = Cl, OMe, SMe, CN, NH2) have been studied. Reactions between the [Ru(CO)(3)Cl-2](2) and the pyrazines led mainly to mononuclear compounds of the type [Ru(CO)(3)(R-pz)]. All of these ruthenium pyrazine compounds showed activity in 1-hexene hydroformylation. With an exception of NH2, addition of the substituent to the pyrazine ring was found to improve the catalytic activity compared to the unsubstituted pyrazine. The catalytic cycle was studied by computational DFT methods. The results suggest that the key step in the formation of the active species involves release of one of the carbonyl in the cis position with respect to the pyrazine ring. (c) 2005 Elsevier B.V. All rights reserved.