Palladium-catalyzed reaction of diselenide with isocyanide

A Pd-catalyzed reaction providing the first example of insertion of isocyanide into a Pd-Se bond is described. Tetrakis(triphenylphosphine)palladium [Pd(PPh3)(4)] catalyzes the reaction of a diselenide (ArSe)(2) (1a) with an isocyanide ArNC (2) (Ar = 4-MeC6H4) to afford the adducts (ArSe)(C=NAr)(m)(SeAr) (m = 2, 3). An X-ray crystallographic structure of the palladium intermediate trans-Pd(SeAr)(2)(CNAr)(PPh3) (7a) is determined. In marked contrast to the Pd-catalyzed reaction using a disulfide, the 1:1-adduct 3a (m = 1) is not produced. The stoichiometric reaction of 7a with 1a also did not provide 3a. These facts suggest that the reductive elimination of l:m-adducts takes place only when more than two isocyanides are inserted into Pd-Se bond(s) of 7a to give Pd[(C=NAr)(p)(SeAr)][(C=NAr)(q)(SeAr)]L-n (p, q greater than or equal to 0) (10a). In contrast, the reaction of ditelluride (PhTe)(2) (1c) with 2 is not catalyzed by the Pd complex due in part to the insolubility and instability of the palladium(II) tellurolate intermediates.