Pyrazolato-bridged polynuclear palladium and platinum complexes. Synthesis, structure, and reactivity

Cyclic trinuclear complexes [Pd-3(mu-pz)(6)] (1) and [Pd-3(mu-4-Mepz)(6)] (2) and dinuclear complex [Pd-2(mu-3-t-Bupz)(2)(3-t-Bupz)(2)(3-t-BupzH)(2)] (3) have been prepared by the reactions of [PdCl2(CH3CN)(2)] with pyrazole (pzH), 4-methylpyrazole (4-MepzH), and 3-tert-butylpyrazole (3-t-BupzH), respectively, in CH3CN in the presence of Et3N. In the absence of the base, treatment of [PdCl2(CH3CN)(2)] with pzH gave the mononuclear complex, [Pd(pzH)(4)]Cl-2 (6). The reaction of [PtCl2(C2H5CN)(2)] with pzH in the presence of Et3N under refluxing in C2H5CN afforded the known dimeric Pt(II) complex, [Pt(pz)(2)(pzH)(2)](2) (7). The protons participating in the hydrogen bonding in 3 and 7 are easily replaced by silver ions to give the heterotetranuclear complex [Pd2Ag2(mu-3-t-Bupz)(6)] (4) and the heterohexanuclear complex [Pt2Ag4(mu-pz)(8)] (5). The complexes 1-6 are structurally characterized.