Formation of mu(4)-Se-2 complex by the oxidative coupling of mu-SeH complex: double-site atomic inversion of the mu(4)-Se-2 complex [{(Cp*Rh)(2)(mu-CH2)(2)}(2)(mu(4)-Se-2)](2+) (Cp* = eta(5)-C5Me5)

A reaction of trans-[(Cp*Rh)(2)(mu-CH2)(2)Cl-2] with H2Se in MeOH formed a mu-SeH complex isolated as a BPh4 salt [(Cp*Rh)(2)(mu-CH2)(2)(mu-SeH)](BPh4 ) (1; Cp* = eta(5)-C5Me5). In solution, complex 1 was oxidized by molecular oxygen giving a tetranuclear diselenide mu(4)-Se-2 complex [{(Cp*Rh)(2)(mu -CH2)(2)}(2)(mu(4)-Se-2)](BPh4), (2). The structure involves Se-2 bridging two Rh-Rh bonds (Rh-Rh = 2.6353(5) Angstrom) in a side-on fashion (Rh(1)-Se (1) = 2.4715(6), Rh(2)-Se(1)* = 2.5526(6) Angstrom). The Se(1)Se(1)* distan ce is 2.3875(9) Angstrom, 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 de pendent H-1-NMR spectra of the mu-CH2 groups elucidated the dynamic process and provided the activation parameters: Delta H-double dagger = 70 +/- 1 k J mol(-1), Delta S-double dagger = 15 +/- 5 J mol(-1) K-1, and Delta G(doub le dagger) = 66 +/- 1 kJ mol(-1) (at 298 K). (C) 2000 Elsevier Science S.A. All rights reserved.