A molecular structure of mixed valence biruthenocenium (Ru IIRu IV) salts [Ru IICp(C 5H 4C 5H 4)CpRu IVL] 2+(BF 4−) 2 (L  NCCH 3, N(CH) 4N)

Abstract

The conformation of the oxidation product ( A) of biruthenocene (RcRc) with p-benzoquinone containing boron trifluoride diethylether complex is [RcRcC 6H 4O 2] 2+(BF 4 −) 2 in which p-benzoquinoen is ligated to the Ru IV center. The recrystallization of A from the mixture of nitromethhane containing small amount of acetonitrile or pyrazine gives mixed-valence cations formulated as [Ru IICp(C 5H 4C 5H 4)CpRu IVL] 2+ (L = acetonitrile 1 and pyrazine 2), in which L is coordinated to the Ru IV center. The crystal of 1 formulated as [Ru IICp(C 5H 4C 5H 4)CpRu IVNCCH 3] 2+ (BF 4 −) 2. CH 3NO 2 ( 1), is found to be orthorhombic, space group Pbca, a = 14.255(7), b = 37.105(10), c = 10.051(4) A ̊ , V = 5316(4), Z = 8 and the final R = 0.054 and R w = 0.059. The similar pyrazine salt 2 formulated as [Ru IICp(C 5H 4C 5H 4)CpRu IVN(CH) 4N] 2+ (BF 4 −) 2(CH 3NO 2) 2is found to be triclinic, space group P 1 , a = 9.006(2), b = 19.233(4), c = 28.907(10) A ̊ , α = 89.45(1)°, β = 86.10(3)°, γ = 87.85(2)°, 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) Å for 2A, 2.11(1) for 2B and 2.15(1) for 2C) are longer by ca. 0.1 Å 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 C 5H 4 rings of the [LRu IVCp(C 5H 4)] 2+ moiety are 38.70° for 1, 38.77° ( 2A), 40.84° ( 2B) and 41.67° ( 2C) for 2. The nucleophilicity to the Ru IV increases in the order Cl − > pyrazine > acetoritrile > p-benzoquinone and unlike the case of mixed-valence halobiruthenocenium cations ([RcRcX] +: X  Cl, Br, I), no temperature dependent 1H - and 13C-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.