Reactivity of [NBU4][(C6F5)2M(μ-PPh2)2M′(acac-O,O′)] (M, M′ = Pt, Pd) toward silver centers.: Synthesis of polynuclear complexes containing M-Ag bonds (M = PdPt)

The binuclear complexes [NBu4][(C6F5)(2)M(mu-PPh2)(2)M'(acac-O,O')] (M = M' = Pt, 1a; M = Pt, M' = Pd, 1b; M = M' = Pd, 1c) have been prepared by reacting [NBu4](2)[(C6F5)(2)M(mu-PPh2)(2)M'(mu-Cl)(2)M'(mu-PPh2)(2)M(C6F5)(2)] with Tl(acac). Complexes la,b react with [Ag(OClO3)-(PPh3)], yielding [MPtAg(mu-PPh2)(2)(C6F5)(2)(acac)(PPh3)] (M = Pt, 2a; M = Pd, 2b). The X-ray structures of both complexes are rather similar, the main difference being related with the Pt-Ag bonds. While in 2b it is clear that there are Pt-Ag and Pd-Ag bonds, in 2a it seems that only one Pt-Ag bond is connecting both Pt and AgPPh3 moieties. The formation of a Pd-Ag bond is rather surprising, because of the known reluctance of the Pd center to engage in this sort of bonding. la,b react with equimolar amounts of AgClO4 in CH2Cl2 to give [PtMAg(mu-PPh2)(2)(C6F5)(2)(acac)](x) (M = Pt, 4a; M = Pd, 4b). The X-ray structure of 4a indicates that the "Pt-2(acac)(C6F5)(2)(mu-PPh2)" fragments are connected to the silver center through two Pt-Ag bonds (2.875(l), 2.864(1) Angstrom) and one C-gamma-Ag bond (of the acac ligand). On the other hand, when the homodinuclear palladium derivative reacts with [Ag(OClO3)(PPh3)] or AgClO4, decomposition takes place and [(C6F5)(PPh3)Pd(mu-PPh2)(2)Pd(acac)] can be detected in the former reaction. These processes are in agreement with the well-known tendency of the pentafluorophenyl-palladate substrates to participate in arylating processes.