Charge-transfer and electron-transfer properties of d6 metal complexes with .mu.-pyrazine. Mononuclear and binuclear manganese(I) compounds

A stable carbonyl–pyrazine–metal(0) complex: Synthesis and characterization of cis-tetracarbonylpyrazinetrimethylphosphitetungsten(0)

“…However, two factors can contribute to the rutheniumnitrogen bond strength and, thus, to the stability of this complex: (i) +2 charge of ruthenium leading to a decrease in the demand for p back donation, (ii) the presence of five ammine ligands having no p accepting ability. In fact, the pyrazine complexes of the zero valent d 6 ions are not stable [4]. Although the pyrazine complexes of low-spin d 6 metal centers have been found to be nonfluxional, in contrast to the stereochemically nonrigid ruthenium complexes exhibiting 1,4-metallotropic shift of the pyrazine ligand, the Group 6 metal pyrazine complexes of the type M(CO) 5 (pyz) readily undergo dissociation of the pyrazine ligand even at ambient temperature [5].…”

“…In fact, the pyrazine complexes of the zero valent d 6 ions are not stable [4]. Although the pyrazine complexes of low-spin d 6 metal centers have been found to be nonfluxional, in contrast to the stereochemically nonrigid ruthenium complexes exhibiting 1,4-metallotropic shift of the pyrazine ligand, the Group 6 metal pyrazine complexes of the type M(CO) 5 (pyz) readily undergo dissociation of the pyrazine ligand even at ambient temperature [5]. One consequence of this dissociation is the formation of binuclear complexes for M = Mo, W (Eq.…”

“…One consequence of this dissociation is the formation of binuclear complexes for M = Mo, W (Eq. (1)) [1h, 2,6], similar to the CreutzTaube binuclear ruthenium complexes [7] 2(CO) 5 M(pyz) (OC) 5 M(pyz)M(CO) 5 …”

“…The (OC) 5 M(pyz)M(CO) 5 complexes of the Group 6 metals have been found to be moderately stable in the solid form when kept in the dark at 273 K; storing under argon greatly increased their long-term stability [6]. In solution at 298 K, the complexes exhibit varying degrees of stability, with chromium and molybdenum complexes showing the fastest decomposition, and with tungsten complex being sufficiently stable for photochemical study in solution [6].…”

“…In solution at 298 K, the complexes exhibit varying degrees of stability, with chromium and molybdenum complexes showing the fastest decomposition, and with tungsten complex being sufficiently stable for photochemical study in solution [6]. Instability of the metal(0) pyrazine complexes is obviously due to the weak metal !…”