Formation of μ4-Se2 complex by the oxidative coupling of μ-SeH complex: double-site atomic inversion of the μ4-Se2 complex [{(Cp*Rh)2(μ-CH2)2}2(μ4-Se2)]2+ (Cp*=η5-C5Me5)

A reaction of trans-[(Cp*Rh)2(μ-CH2)2Cl2] with H2Se in MeOH formed a μ-SeH complex isolated as a BPh4 salt [(Cp*Rh)2(μ-CH2)2(μ-SeH)](BPh4) (1; Cp*=η5-C5Me5). In solution, complex 1 was oxidized by molecular oxygen giving a tetranuclear diselenide μ4-Se2 complex [{(Cp*Rh)2(μ-CH2)2}2(μ4-Se2)](BPh4)2 (2). The structure involves Se2 bridging two RhRh bonds (RhRh=2.6353(5) Å) in a side-on fashion (Rh(1)Se(1)=2.4715(6), Rh(2)Se(1)*=2.5526(6) Å). The Se(1)Se(1)* distance is 2.3875(9) Å, which corresponds to a SeSe single bond. Complex 2 showed an intriguing dynamic behavior of double-site atomic inversion at the selenium atoms in CD3CN. The line shape analyses of the temperature dependent 1H-NMR spectra of the μ-CH2 groups elucidated the dynamic process and provided the activation parameters: ΔH‡=70±1 kJ mol−1, ΔS‡=15±5 J mol−1 K−1, and ΔG‡=66±1 kJ mol−1 (at 298 K).