Synthesis and Structural Characterization of Some Selenoruthenates and Telluroruthenates

The reaction of solid [RuClCp(PPh3)2] with TeSe32- or Sen2- in DMF leads to the formation of [RuCp(PPh3)(μ2-Se2)]2 (1). In the structure of this compound the two bridging Se2 groups lead to a six-membered Ru2Se4 ring in
a chair conformation. Attached to each Ru center is a PPh3 ligand in an equatorial position and a Cp ring in an
axial position. The compound is diamagnetic. The compound [Ru2Cp2(μ3-Se2)(μ3-Se)]2 (2) is obtained under similar
conditions in the presence of air. This structure comprises a centrosymmetric Ru4Se6 dimer formed from the two
bridging Se groups and the two bridging Se2 groups. Each Ru center is π-bonded to a Cp ring. The reaction of
solid [RuClCp(PPh3)2] with a Ten2- polytelluride solution in DMF leads to the diamagnetic compound [(RuCp(PPh3))2(μ2-(1,4-η:3,6-η)Te6)] (3). Here the Ru centers are bound to a bridging Te6 chain at the 1, 4, 3, and 6
positions, leading to a bicyclic Ru2Te6 ring. Each Ru atom is bound to a Cp ring and a PPh3 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/CH2Cl2, rather than DMF, then [(RuCp(PPh3))2(μ2-(1,4-η:3,6-η)Te6)]·CH2Cl2 (4) is obtained. In the solid state it possesses the same Ru2Te6 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.