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

摘要

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(SeC6H4Cl)(2)Me(C6H4OMe)(bpy) (2) for which the forward reaction exhibits DeltaH = -130 +/- 12 kJmol(-1) and DeltaS= -472 +/- 49 JK(-1) mol(-1), and with K = 754 +/- 145 at -25 degreesC. The Pd(IV) complex is isolable at -40 degreesC, and when the equilibrium mixture is kept at -25 degreesC, 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)(C6H4OMe)(bpy) (3). In contrast, (ClC6H4Se)(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 (CIC6H4Se)(2) reacts with 5 to cleave the second Pd-Me bond to give Pd(SeC6H4Cl)(2)(dmpe) (6) and Me-SeC6H4Cl. Similarly, PdMeTol(dmpe) (7) (Tol = 4-tolyl) forms predominantly Pd(SeC6H4Cl)Tol(dmpe) (8) together with some Pd(SeC6H4Cl)Me(dmpe) (5), and 8 reacts With (CIC6H4Se)(2) to form Pd(SeC6H4Cl)(2)(dmpe) (6) and Tol-SeC6H4Cl. Bis(4-chlorophenyl) diselenide reacts with PtTol(2)(bpy) (9) (Tol = 4-tolyl) to form Pt(SeC6H4Cl)(2)Tol(2)(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 . 3CHCl(3) and square planar 5 are reported. (C) 2003 Elsevier B.V. All rights reserved. [References: 12]