Reversible oxidative addition of a diaryl diselenide to a diorganopalladium(II) complex, carbon-selenium bond formation at palladium(IV), and structural studies of palladium(II) and platinum(IV) selenolates

Methyl(4-methoxyphenyl)(2,2′-bipyridine)palladium(II) (1) reacts with bis(4-chlorophenyl) diselenide in dichloromethane to form an equilibrium with the Pd(IV) complex Pd(SeC6 H4Cl)2Me(C6H4OMe)(bpy) (2) for which the forward reaction exhibits ΔH=-130±12 kJ mol-1 and ΔS=-472±49 J K-1 mol-1, and with K=754±145 at -25 °C. The Pd(IV) complex is isolable at -40 °C, and when the equilibrium mixture is kept at -25 °C, a temperature at which the Pd(II) complex is stable, selective reductive elimination of Me-SeC6H4Cl occurs very slowly from the Pd(IV) complex to form Pd(SeC6H4Cl)(C6 H4OMe)(bpy) (3). In contrast, (ClC6 H4Se)2 reacts with PdMe2(dmpe) (4) [dmpe=1,2-bis(dimethylphosphino)ethane] to form Pd(SeC6H4Cl)Me(dmpe) (5) and Me-SeC6H4Cl. A second equivalent of (ClC6H4Se)2 reacts with 5 to cleave the second Pd-Me bond to give Pd(SeC6 H4Cl)2(dmpe) (6) and Me-SeC6H4Cl. Similarly, PdMeTol(dmpe) (7) (Tol=4-tolyl) forms predominantly Pd(SeC6 H4Cl)Tol(dmpe) (8) together with some Pd(SeC6H4Cl)Me(dmpe) (5), and 8 reacts with (ClC6H4Se)2 to form Pd(SeC6H4Cl)2(dmpe) (6) and Tol-SeC6H4Cl. Bis(4-chlorophenyl) diselenide reacts with PtTol2(bpy) (9) (Tol=4-tolyl) to form Pt(SeC6H4Cl)2Tol2(bpy) (10) which, together with 2, has a trans-configuration for the selenolate ligands. X-ray structural studies of octahedral 10 as the solvate 10 · 3CHCl3 and square planar 5 are reported. © 2003 Elsevier B.V. All rights reserved.