Synthesis and structural characterization of some selenoruthenates and telluroruthenates

The reaction of solid [RuClCp(PPh ₃) ₂] with TeSe ₃ ^2- or Se _n ^2- in DMF leads to the formation of [RuCp(PPh ₃)(μ ₂-Se ₂)] ₂ (1). In the structure of this compound the two bridging Se ₂ groups lead to a six-membered Ru ₂Se ₄ ring in a chair conformation. Attached to each Ru center is a PPh ₃ ligand in an equatorial position and a Cp ring in an axial position. The compound is diamagnetic. The compound [Ru ₂Cp ₂(μ ₃-Se ₂)(μ ₃-Se)] ₂ (2) is obtained under similar conditions in the presence of air. This structure comprises a centrosymmetric Ru ₄Se ₆ dimer formed from the two bridging Se groups and the two bridging Se ₂ groups. Each Ru center is π-bonded to a Cp ring. The reaction of solid [RuClCp(PPh ₃) ₂] with a Te _n ^2- polytelluride solution in DMF leads to the diamagnetic compound [(RuCp-(PPh ₃)) ₂(μ ₂-(1,4-η:3,6- η)Te ₆)] (3). Here the Ru centers are bound to a bridging Te ₆ chain at the 1, 4, 3, and 6 positions, leading to a bicyclic Ru ₂Te ₆ ring. Each Ru atom is bound to a Cp ring and a PPh ₃ group. This dimer possesses a center of symmetry. The structure of 3 is the first example of a bicyclic complex where fusion occurs along a Te-Te bond. If the same reaction is carried out in DMF/CH ₂Cl ₂, rather than DMF, then [(RuCp(PPh ₃)) ₂-(μ2- (1,4-η:3,6-η)Te ₆)]·CH ₂Cl ₂ (4) is obtained. In the solid state it possesses the same Ru ₂Te ₆ structural unit as does 3, but the unit lacks a crystallographically imposed center of symmetry. The electronic structures of 3 and 4 have been analyzed with the use of first principles density functional theory. Bond order analysis indicates that the Te-Te bond where fusion occurs has a shared bonding charge of about 2/3 of that found for Te-Te single bonds.