Late to the Party: Synthesis and Characterization of Tellurium and Selenium Half-Sandwich Complexes

We report the synthesis and characterization of the first series of tellurium and selenium complexes featuring an η5-cyclopentadienyl ligand. Reaction of Ph3TeX (X = Cl, S2CNEt2) with MCpR (M = Li, K; R = H, Me4, Me5) results in high yields of [Cp]­[TePh3] (1), [CpMe4]­[TePh3] (2), and [Cp*]­[TePh3] (3), respectively. Similarly, reaction of Ph3SeCl with LiCp and KCp* furnishes [Cp]­[SePh3] (4) and [Cp*]­[SePh3] (5). Each was characterized by X-ray crystallography, revealing similar η5-coordination with little distortion from an idealized half-sandwich geometry, presumably from the remaining lone pair on tellurium and selenium. The Te–centroid distances are relatively long (1: 2.770(3), 2: 2.746(1), and 3: 2.733(1) Å), suggesting a mostly ionic interaction. Se–centroid distances (4: 2.748(3), 5: 2.707(2), 2.730(2) Å) were found to be surprisingly similar despite its smaller atomic radius. Compounds 2, 3, and 5 display rapid decomposition at room temperature, extruding a phenylated cyclopentadiene and the respective diphenylchalcogenide. The nature of bonding within these complexes was investigated through DFT methods and found to be primarily ionic in nature.