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

Abstract

Reduction of a mixture containing [PtCl 2 (cod)], aromatic isocyanide (RNC; R ) 2,6-xylyl (Xyl), 2,4,6-mesityl (Mes)), diphosphine (Ph 2 P(CH 2 ) n PPh 2 ; n ) 5 (dpppn), n ) 6 (dpphx)), and NH 4 PF 6 by sodium amalgam (<1%) afforded trigonal-antiprismatic hexanuclear platinum(0) clusters encapsulating two mercury(0) atoms, [Hg 2 Pt 6 (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, {Pt 3 (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-D 3 -symmetrical Hg 2 Pt 6 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 D 3 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 Pt 3 Hg 2 Pt 3 cluster frameworks are discussed on the basis of molecular orbital calculations with EHMO and DFT methods. Hg 2 Pt 6 clusters with an incomplete open-cage structure, [Hg 2 Pt 6 (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, [HgPt 6 (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 Hg 2 Pt 6 mixed-metal cluster was not produced, and instead, the PtHgPt trinuclear complex [HgPt 2 (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.

Pd and Pt Catalyst Poisoning in the Study of Reaction Mechanisms: What Does the Mercury Test Mean for Catalysis?

“…Apparently, the Hg II ions are stabilized by complexation with solvated ligands L. Complexes M 0 /L are then decomposed by mercury via pathways A–C, as depicted in Scheme . The formation of M 0 x Hg 0 y /L n and [M x Hg y ] m + /L n clusters as intermediates could not be excluded if the literature data is taken into account. − The higher reactivity of M II Py 2 X 2 and M II (PPh 3 ) 2 X 2 complexes containing weakly bound pyridine and phosphine ligands toward mercury in comparison with the lower reactivity of complexes 1a – d , 2 , and 3 containing strongly bonded NHC ligands may be indirect support of this simplified scheme. In addition, the initial formation of HgPy 2 X 2 rather than Hg/NHC complexes from compounds 1a – d and 3 is additional presumptive evidence for this system because pyridine ligands should dissociate preferably from complexes 1a – d and 3 in the first stage.…”

“…In our opinion, all three routes, A , B , and C , can operate in the reaction systems, and the contribution of each route should depend on the specific conditions. Each of the routes can include the formation of M 0 x –Hg 0 y /L n clusters as intermediates as described in the literature for reactions of various metal complexes with mercury or its amalgams. − …”

X-ray-Induced Photoreduction of Hg(II) in Aqueous Frozen Solution Yields Nearly Monatomic Hg(0)

“…The few Hg(0) complexes that have been characterized do show some common structural features. In some, Hg(0) is part of an electron-rich transition-metal-ion chalcogenide cluster , while in others Hg(0) is bound between two phosphine-coordinated Pt(0) or iodide and Mo(0), or it is trapped in a gold­(I)-metallocryptand cage complex with two metal–metal bonds . In all cases thus far reported, the Hg(0) is diffusely bound by very long and weak bonds to the coordinating atoms.…”

Bi- and polymetallic organometallics

“…The reaction takes a somewhat different pathway when t BuNC is used instead of NCXylyl, with analogous reaction conditions leading to the formation of Pt 2 Hg(m-dppn) 3 , in which two three-coordinate Pt centres are linked by three dppn ligands to give an approximately D 3 symmetric cage, in which the single Hg atom is trapped, giving rise to the first example of a linear Pt(0)-Hg(0)-Pt(0) metallic core. 71 The Z 2 -phenyl acetylene complex [Pt(Z 2 -HC 2 Ph)(PPh 3 ) 2 ] reacts with cis-[Pt(C 6 F 5 ) 2 (CO) 2Àn (thf) n ] (n = 1, 2) to give binuclear vinylidene [Pt 2 (m-Z 1 -CQCHPh)(PPh 3 ) 2 (CO)(C 6 F 5 ) 2 ] or acetylide [Pt 2 (m-H)(m-C 2 R)(PPh 3 ) 2 (C 6 F 5 ) 2 ] complexes, respectively. Similar reactions involving related complexes derived from 1,4-diethynyl benzene are also reported, giving rise to bis(binuclear) complexes, such as 36.…”