Cage-Type Hexanuclear Platinum(0) Clusters with Diphosphine and Isocyanide Ligands Encapsulating Two Mercury(0) Atoms

Reduction of a mixture containing [PtCl2(cod)], aromatic isocyanide (RNC; R = 2,6-xylyl (Xyl), 2,4,6-mesityl (Mes)), diphosphine (Ph2P(CH2)nPPh2; n = 5 (dpppn), n = 6 (dpphx)), and NH4PF6 by sodium amalgam (<1%) afforded trigonal-antiprismatic hexanuclear platinum(0) clusters encapsulating two mercury(0) atoms, [Hg2Pt6(μ-RNC)6(μ-diphos)3] (diphos = dpphx, R = Xyl (6a); diphos = dpppn, R = Xyl (8a), Mes (8b)). Complexes 6a and 8a were characterized by X-ray crystallographic analyses to demonstrate that two triangular platinum(0) units, {Pt3(μ-RNC)3}, are connected by three diphosphine ligands with long methylene chains to form a closed cage of the cluster-based metallocryptand, in which two mercury(0) atoms are incarcerated with a notably short Hg−Hg distance. In complex 8a (n = 5), the centroids of the two Pt(0) triangles are linearly arranged with respect to the Hg−Hg axis to form a pseudo-D3-symmetrical Hg2Pt6 antiprismatic cluster core (average Pt−Pt = 2.6719 Å, average Pt−Hg = 2.9417 Å, and Hg−Hg = 2.8424(2) Å). In contrast, in complex 6a (n = 6) the two triplatinum planes glide away from the dimercury axis to lose the D3 symmetry (average Pt−Pt = 2.639 Å, average Pt−Hg = 2.923 Å, and Hg−Hg = 2.826(2) Å). The electronic structures of the Pt3Hg2Pt3 cluster frameworks are discussed on the basis of molecular orbital calculations with EHMO and DFT methods. Hg2Pt6 clusters with an incomplete open-cage structure, [Hg2Pt6(μ-RNC)6(RNC)2(μ-diphos)2] (diphos = dpphx, R = Xyl (7a); diphos = dpppn, R = Mes (9b)), were also isolated as minor products and were transformed into the closed-cage clusters 6a and 8b by treatment with an equivalent diphosphine ligand. By using dppb (n = 4), an open-cage mixed-metal cluster with a single mercury atom, [HgPt6(μ-RNC)6(RNC)2(μ-dppb)2] (R = Xyl (10a), Mes (10b)), was obtained as the sole product. When the aliphatic isocyanide t-BuNC was used in the reduction with dpphx, the Hg2Pt6 mixed-metal cluster was not produced, and instead, the PtHgPt trinuclear complex [HgPt2(μ-dpphx)3] (11) was obtained in a low yield and was characterized by X-ray crystallography to demonstrate the linear trinuclear structure with a considerable attractive Pt−Hg interaction (average Pt−Hg = 2.7930 Å and Pt−Hg−Pt = 179.591(3)°). The electronic structures of 11 are also discussed.