Synthesis and Characterization of Pd(IMe)2, and its Reactivity by C-S Oxidative Addition of DMSO

Abstract

Two-electron reduction of PdX2(NHC)(2) with Groups 1, 2 metals (K, Mg) is a convenient route to Pd(NHC)(2) complexes including Pd(IMe)(2) (2a), isolated and crystallographically characterized as the least sterically encumbered d(10) M(0)L-2 species to date. 2a exhibits a regular linear geometry and modest Lewis acidity to coordinating solvents and additional IMe. In contrast to its analogs with bulkier NHC = (IBu)-Bu-t and IPr, 2a undergoes cleanly net oxidative addition of the Me-S(O) Me bond of DMSO, forming trans-PdMe(S(O) Me)IMe2 (3) at RT. DFT calculations suggest this reaction to proceed by substitution of IMe by kappa S-DMSO followed by concerted C-S oxidative addition to Pd with a single IMe, with a preference of ca. 10 kcal/mol in the effective Delta G(s)(double dagger) over the direct pathway. Calculations also identify two facile intramolecular pathways for racemization of Pd(II) methylsulfinyl complexes at sulfur. (C) 2011 Elsevier B.V. All rights reserved.