Synthesis and Spectral and Redox Properties of Three Triply Bridged Complexes of Ruthenium

Syntheses are described for the ligand-bridged complexes [(tpm)Ru III (μ-O)(μ-L) 2 Ru III (tpm) n+ (L = O 2 P(O)(OH), n = 0 (1); L =O 2 CO, n = 0 (2); L = O 2 CCH 3 , n = 2 (3); tpm is the tridentate, facial ligand tris(l-pyrazolyl)methane. The X-ray crystal structure of [(tpm)Ru(μ-O)(μ-O 2 P(O)(OH)) 2 Ru(tpm)]⋅8H 2 O was determined from three-dimensional X-ray counter data. The complex crystallizes in the trigonal space group P3 2 21 with three molecules in a cell of dimensions a = 18.759 (4) Å and c = 9.970 (6) Å. The structure was refined to a weighted R factor of 0.042 based on 1480 independent reflections with I ≥ 3σ(I). The structure reveals that the complex consists of two six-coordinate ruthenium atoms that are joined by a μ-oxo bridge(rru-o=1.87 Å; ∠RuORu = 124.6°) and two μ-hydrogen phosphato bridges (average r Ru _ 0 = 2.07 Å) which are capped by two tpm ligands. The results of cyclic voltammetric and coulometric experiments show that the complexes undergo both oxidative and reductive processes in solution. Upon reduction, the ligand-bridged structure is lost and the monomer [(tpm)Ru(H 2 O) 3 ] 2+ appears quantitatively. All three complexes are diamagnetic in solution. The diamagnetism is a consequence of strong electronic coupling between the low-spin d 5 Ru(III) metal ions through the oxo bridge and the relatively small Ru-O-Ru angle. © 1989, American Chemical Society. All rights reserved.