Communication Cite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
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Three-Dimensional Sandwich Nanocubes Composed of 13-Atom Palladium Core and Hexakis-Carbocycle Shell Masahiro Teramoto,†,‡ Kosuke Iwata,§ Hiroshige Yamaura,§ Kenta Kurashima,§ Koshi Miyazawa,§ Yuki Kurashige,¶ Koji Yamamoto,§ and Tetsuro Murahashi*,§
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Department of Structural Molecular Science, The Graduate University for Advanced Studies, Myodaiji, Okazaki, Aichi 444-8787, Japan ‡ Research Center of Integrative Molecular Systems (CIMoS), Institute for Molecular Science, Myodaiji, Okazaki, Aichi 444-8787, Japan § Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan ¶ Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan S Supporting Information *
The potential existence of multiple-ligated CUH-(transition metal) compounds containing more than six metal atoms has been discussed previously. Kaya et al. reported that benzenemetal species [Mx(benzene)y]+, where x > y ≥ 3, x ∼ 10, M = Fe, Co, Ni, were detected through a mass spectroscopic study of the gas-phase reaction of the laser-vaporized late transition metals and benzene.5 Although the structures of the Kaya’s benzene clusters have not been identified, their observation has implications that a highly ligand-deficient condition (x > y) may give a large, nanosized three-dimensional sandwich structure. This is reasonable considering that a primary coordination sphere of a metal agglomerate cluster has a limited capacity to accommodate multiple CUH ligands. With the use of cyclopentadienyl or benzene, however, such a highly ligand-deficient structure (x > y) is unlikely obtained in a stable form because each of these CUHs has the propensity to ligate a single apical metal atom of a metal cluster through η5or η6-mode, where several metal atoms at edges or faces of a large metal cluster core are forced to be unsupported, causing an increase in the coordinative unsaturation of the cluster core. It has been shown that the low-valent main-group elements or its combination with group 11 metals are capable of forming the highly ligand-deficient organometallic clusters with substituted cyclopentadienyl ligands, e.g., Schnö c kel’s SiAl 1 4 (C 5 Me 5 ) 6 and Al 5 0 (C 5 Me 5 ) 1 2 and Fischer’s Cu43Al12(C5Me5)12, which indeed possess unsupported metal atoms at the cluster surface.6 Here, we report the synthesis and identification of highly ligand-deficient, three-dimensional sandwich compounds containing a 13-atom transition metal cluster by employing a multiple-metal-binding CUH ligand. We found that a closepacked cuboctahedral Pd13 core is stabilized by a simple octahedral ligand-shell of μ4-cycloheptatrienyl (Tr) ligands to give a unique three-dimensional sandwich nanocube molecule (Figure 1). The one-electron redox coupled products of the Pd13 sandwich nanocuble appear to be isolable.
ABSTRACT: Coordination of cyclic unsaturated hydrocarbons to transition metal generally gives bis-ligated sandwich complexes, which are a fundamental class of organometallic compounds. This sandwich structure may be extended to a higher-order three-dimensional one when more than two carbocyclic ligands surround an agglomerate of many transition metal atoms. Here, we report synthesis of three-dimensional sandwich nanocube compounds containing a close-packed transition metal cluster core. Reduction of a [Pd3(μ3-C7H7)2]2+ with tetraarylborate under neat conditions afforded [Pd13(μ4C7H7)6]2+ containing a cuboctahedral Pd13 core with an octahedral ligand-shell.
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ince a remarkably stable organotransition metal compound, ferrocene, was prepared and its “sandwich”-type molecular structure was elucidated in 1951−52,1,2 sandwich compounds have been the subject of extensive research not only because of their unique molecular structures but also because of their wide utility as molecular catalysts and materials owing to physical and chemical properties characteristic of organometallic compounds.3 Because cyclopentadienyl and benzene, which are used as the single-metal-binding cyclic unsaturated hydrocarbon (CUH) ligand, generally give bisligated sandwich compounds [M1(CUH)2]z, several early studies suggested that lowering the ligand−metal ratio y/x in [Mx(CUH)y]z can potentially provide an intriguing class of higher-order sandwich compounds. For example, it has been shown that three-dimensional sandwich compounds holding ∼6 transition metal atoms are formed in the regime of x = y,4 as exemplified by the hitherto-largest Ni6 octahedron clusters [Ni6(C5H5)6]z (z = 0, +1) reported by Dahl et al.4a However, isolation of larger, nanosized three-dimensional sandwich compounds has not been reported for transition metal elements in groups 3−10 despite the promising potential of this type of structure to provide a novel class of organometallic nanoclusters for catalysis and materials science. © XXXX American Chemical Society
Received: July 14, 2018
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DOI: 10.1021/jacs.8b07430 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
Communication
Journal of the American Chemical Society
Figure 1. Schematic representation of three-dimensional sandwich nanocube compounds.
Our group and others have shown that metal-sheet sandwich compounds [Mx(CUH)2]z (x ≥ 3) are obtained as a class of bis-ligated, ligand-deficient sandwich compounds (x > y = 2), where large carbocyclic rings such as Tr are used as the facecapping ligands. 7,8 During the reactivity study of [Pd3Tr2(CH3CN)3][B(ArF)4]2 (1, ArF = 3,5-(CF3)2C6H3),7a,b we found that an organo-Pd13 cluster can be produced; for example, attempted recrystallization of the methylated complex [Pd3Tr2(CH3CN)2(CH3)][B(ArF)4] (2), which was generated by treatment of 1 with CH3Li, gave a few black crystals of the homoleptic 13-atom Pd cluster [Pd13Tr6][B(ArF)4]2 (3). Unfortunately, however, this method gave only traces of 3 (
