Novel mono- and dinuclear ruthenium nitrosyls with coordinated pyrazine

The synthesis and characterization of some novel mono- and dinuclear ruthenium nitrosyls bearing either terminal ([NBu4][trans-RuCl4(pyz)(NO)] (1a) and [NBu4][cis-RuCl4(pyz)(NO)] (1b)) or bridging pyrazine ([NBu4]2[{trans/cis-RuCl4(NO)}2(μ-pyz)] (trans,trans2a, cis,cis2b, trans,cis2c)) are reported. Compounds 1 and 2 were prepared from the same precursor, [NBu4][trans-RuCl4(dmso-O)(NO)], upon treatment with pyrazine in different ratios. Pure compounds were obtained by crystallization or column chromatography. All species possess the linear {RuII(NO+)}6 moiety, and the NO stretching frequency is quite sensitive to the nature of the trans ligand (either N or Cl). The unbound termini of the pyrazine ligands in compounds 1a and 1b are capable of further reaction with metal centers; treatment of the two isomers with a stoichiometric amount of [Ru(TPP)(CO)(EtOH)] (TPP=tetraphenylporphyrinate) led to the quantitative formation of the unsymmetrical dinuclear species [NBu4][{trans-RuCl4(NO)}(μ-pyz){Ru(TPP)(CO)}] (3a) and [NBu4] [{cis-RuCl4(NO)}(μ-pyz){Ru(TPP)(CO)}] (3b), respectively, in which pyrazine bridges two ruthenium centers in different environments. Thus monomers 1a and 1b can be considered as new examples of complexed bridging ligands that might be used as building blocks in the construction of supramolecular assemblies. The crystal structures of the mononuclear species 1a and 1b, and of the dinuclear species 3a were also determined.