Intramolecular Metal–Metal Bond Rearrangement in a Pt₂PdHg Heterometallic Cluster Forming a Hg^I–Pd^I Covalent Bond

Abstract

Reaction of the linear trinuclear complex [Pt 2 M(μ-dpmp) 2 (XylNC) 2 ](PF 6 ) 2 (M = Pd (1b)) with HgX 2 afforded the Pt 2 PdHg mixed-metal complexes [Pt 2 PdHgX 2 (μ-dpmp) 2 (XylNC) 2 ](PF 6 ) 2 (X = Cl (2), Br (3), I (4)), which included an unprecedented Hg I −Pd I covalent bond formed via intramolecular metal−metal bond rearrangement. In contrast, reaction of 1a (M = Pt) with HgCl 2 afforded the novel pentagonal-shaped Pt 3 Hg 3 planar cluster [Pt 3 Hg 3 Cl 4 (μ-dpmp) 2 (XylNC) 2 ]Cl 2 (PF 6 ) 2 (5).M etal−metal-bonded small-size clusters are fine-tunable building blocks for nanostructured molecular devices and metal surface mimetic catalytic systems. 1,2 In particular, expanding heterometallic conjugates is a challenging synthetic subject, with the aim of exploring new heterometallic bonding systems and synergistic effects exerted within the heterometallic centers. 1,3 Taking this background into consideration, we have utilized linear tri-and tetraphosphines (bis[(diphenylphosphino)methyl]phenylphosphine (dpmp) and mesobis[((diphenylphosphino)methyl)phenylphosphino]methane (dpmppm)), in which each neighboring P atoms are connected by a methylene unit to support significant interactions between the metals and have synthesized a variety of linearly constrained multimetallic complexes. 4,5 Among them, the linear Pt 3 and Pt 2 Pd complexes [Pt 2 M(μ-dpmp) 2 (XylNC) 2 ](PF 6 ) 2 (M = Pt (1a), Pd (1b); XylNC = 2,6-xylyl isocyanide), 4e recognized as good building blocks for molecular wires, have been investigated to expand by a direct metal−metal bonding interaction, leading to the hexanuclear metal wires of [ P t 2 M 2 P t 2 ( μ -H ) ( μ -d p m p ) 4 ( X y l N C ) 2 ] ( P F 6 ) 3 a n d [Pt 2 M 2 Pt 2 (μ-dpmp) 4 (XylNC) 2 ](PF 6 ) 4 (M = Pt, Pd), 4i and by bis-isocyanide linkers, forming the rigid-rod cluster polymers {[Pt 3 (μ-dpmp) 2 (bisNC)](PF 6 ) 2 } n , where bisNC is 2,3,5,6-tetramethylphenylene-1,4-bis-isocyanide. 4j Further, expanding and assembling the trimetallic units by additional heterometals would be a promising strategy, since d 10 metal ions with Lewis acidic properties, such as Au I , Ag I , and Hg II , are likely to form donor−acceptor interactions with low-valent metal centers. 3 In the present study, reactions of the Pt 2 Pd complex 1b with Hg II ions were examined to find a Hg I −Pd I covalent bond formed through intramolecular metal−metal bond rearrangement in a Pt 2 PdHg mixed-metal system. The reported structures including Hg−Pd fragments have really been limited only to donor−acceptor and metallophilic interactions (2.74− 3.28 Å), 6 and notably, the shortest Hg−Pd contact (2.6915(8) Å) reported thus far was a Hg II −Pd 0 (d 10 −d 10 ) interaction by Braunstein et al. in the Fe 2 PdHg heterometallic complex [Hg{Fe[Si(OMe) 3 ](CO) 3 (μ-dppm)} 2 Pd] (dppm = bis-(diphenylphosphino)methane). 7 The Hg−Pd bond length in the present report is unprecedentedly short (2.5830(5) Å) and is revealed to be the first example of a Hg I −Pd I covalent bond. The relevant reactions of the triplatinum complex...

Forging Unsupported Metal–Boryl Bonds with Icosahedral Carboranes

“…A survey of the CSD discloses only twelve structurally characterized compounds containing a Pd−Hg interaction, with only two of the twelve containing unsupported Pd−Hg interactions, making 3 a structural rarity. The Pd−Hg bond length of 2.5435(5) Å for 3 comes under the sum of the respective covalent radii (2.71(11) Å), and compares favorably with the lengths found for the unsupported interactions reported by Tanase and co‐workers, with 3 having the shortest observed Pd−Hg bond length to date. Compound 3 adopts a square planar geometry, with the coordination sphere around Pd II completed by an ipso interaction of the biaryl ligand .…”

Electron-Deficient Pt2M2Pt2 Hexanuclear Metal Strings (M = Pt, Pd) Supported by Triphosphine Ligands

“…We have developed transition-metal complexes by utilizing the linearly connected tri- and tetraphosphine ligands bis((diphenylphosphino)methyl)phenylphosphine (dpmp), meso -bis(((diphenylphosphino)methyl)phenylphosphino)methane (dpmppm), − and meso -1,3-bis(((diphenylphosphino)methyl)phenylphosphino)propane (dpmppp). , During our studies, the linear trinuclear complexes [Pt 2 M(μ-dpmp) 2 (XylNC) 2 ](PF 6 ) 2 (M = Pt ( 1a ), Pd ( 1b ); XylNC = 2,6-xylyl isocyanide), possessing an electronically unsaturated linear trinuclear core of 44 cluster valence electrons (CVEs) with apparent oxidation state Pt I Pt 0 M I for the metal centers, were synthesized by kinetically controlled site-selective incorporation of d 10 M 0 species into a diplatinum complex, syn -[Pt 2 (μ-dpmp) 2 (XylNC) 2 ](PF 6 ) 2 , and have proven to be good building blocks for further expanded metal strings because they are very reactive toward small organic molecules and metal species. The axial isocyanide ligands of 1a were exchanged by bisisocyanide ligands to afford the rigid-rod cluster polymers {[Pt 3 (μ-dpmp) 2 (bisNC)] 2+ } n (bisNC = 2,3,5,6-tetramethylphenyl-1,4-bisisocyanide, 2,2′,6,6′-tetramethyl-4,4′-biphenylene-1,1′-bisisocyanide) .…”

Transition Metal Chain Complexes Supported by Soft Donor Assembling Ligands

“…305 Its bent Pt 3 unit remains supported by two P3 ligands. 307 These results are consistent with the higher reactivity of Pt−Pd vs Pt−Pt bonds, a feature typical of the enhanced reactivity of heterometallic systems. 146 Furthermore, the chain complexes 121 and 122 could be converted to hexanuclear arrays, with (124,125) or without (126) a hydride between the trinuclear building blocks.…”

“…In contrast, addition of HgCl 2 to the analogous Pt 3 chain complex 122 occurred without breaking of a Pt–Pt bond, but addition of mercury centers to the metal–metal bonds led to a pentagonal-shaped Pt 3 Hg 3 planar cluster . Its bent Pt 3 unit remains supported by two P3 ligands . These results are consistent with the higher reactivity of Pt–Pd vs Pt–Pt bonds, a feature typical of the enhanced reactivity of heterometallic systems …”