A molecular structure of mixed valence biruthenocenium (RuIIRuIV) salts [RuIICp(C5H4C5H4)CpRuIVL]2+(BF4-)2 (L = NCCH3, N(CH)4N)

The conformation of the oxidation product (A) of biruthenocene (RcRc) with p-benzoquinone containing boron trifluoride diethylether complex is [RcRcC(6)H(4)O(2)](2+)(BF4-)(2) in which p-benzoquinoen is ligated to the Ru-IV center. The recrystallization of A from the mixture of nitromethane containing small amount of acetonitrile or pyrazine gives mixed-valence cations formulated as [(RuCp)-Cp-II((CH4CH4)-H-5-H-5)(CpRuL)-L-IV](2+) (L = acetonitrile 1 and pyrazine 2), in which L is coordinated to the Ru-IV center. The crystal of 1 formulated as [(RuCp)-Cp-II(C5H4C5H4)(CpRuNCCH3)-N-IV](2+)(BF4-)(2).CH3NO2 (1), is found to be orthorhombic, space group Pbca, a = 14.255(7), b = 37.105(10), c = 10.051(4) Angstrom, V = 5316(4), Z = 8, and the final R = 0.054 and R-w = 0.059. The similar pyrazine salt 2 formulated as [(RuCp)-Cp-II(C5H4C5H4)(CpRuN)-N-IV(CH)(4)N](2+)(BF4-)(2)(CH3NO2)(2) is found to be triclinic, space group P (1) over bar, a = 9.006(2), b = 19.233(4), c = 28.907(10) Angstrom, alpha = 89.45(1)degrees, beta = 86.10(3)degrees, gamma = 87.85(2)degrees, V = 4991(2), Z = 2, and the final R = 0.077 and R-w = 0.090. The unit cell has three independent molecules (2A, 2B, 2C). The Ru(IV)-N distances (2.15(1)Angstrom for 2A, 2.11(1) for 2B and 2.15(1) for 2C) are longer by ca. 0.1 Angstrom than that of 1 because of bulky molecule of pyrazine. Both cations (1,2) have wedge-sharp structure due to the Ru-N bond, the dihedral angles between the Cp and C5H4 rings of the [(LRuCp)-Cp-IV(C5H4)](2+) moiety are 38.70 degrees for 1, 38.77 degrees (2A), 40.84 degrees (2B) and 41.67 degrees (2C) for 2. The nucleophilicity to the Ru-IV increases in the order Cl-> pyrazine > acetonitrile > p-benzoquinone and unlike the case of mixed-valence halobiruthenocenium cations ([RcRcX](+): X = Cl, Br, I), no temperature dependent H-1 - and C-13-NMR spectra were observed for 1 and 2 in solution, implying the absence of two-electron exchange reaction between the Ru-II and Ru-IV. (C) 1997 Elsevier Science S.A.