Tetsuro Murahashi

Organopalladium complexes containing palladiumpalladium bonds

Abstract This review covers recent achievements in the field of organopalladium chemistry involving PdPd bonds. Several new aspects are reported with regard to the role of PdPd bonds in catalysis, especially new binding modes and transformations of unsaturated hydrocarbons on a PdPd bond.

Discrete Sandwich Compounds of Monolayer Palladium Sheets

Despite the abundance of “sandwich” complexes, in which two cyclic aromatic hydrocarbon ligands flank a metal center, this motif has not been extended to sheets of multiple metal atoms. We prepared and isolated two such compounds. In the first, three palladium centers form a planar triangular array, capped by chlorides, between two cycloheptatrienyl ligands. In the second, a pentapalladium sheet adopts an edge-sharing triangle-trapezoid skeleton between two naphthacene rings. The compounds were characterized by x-ray crystallography and nuclear magnetic resonance spectroscopy. The nature of bonding in the clusters was analyzed by quantum calculations.

Reductive Coupling of Metal Triangles in Sandwich Complexes

The one-electron reduction of [Pd3(C7H7)2(CH3CN)3][BF4]2 in acetonitrile resulted in the formation of the dimer dication [Pd6(C7H7)4(CH3CN)4][BF4]2, whose structure containing a novel bitriangle hexapalladium skeleton was determined by X-ray crystallographic analysis. The dimer is stable in CD3CN at ambient temperature for several days but is highly air-sensitive. Similarly, the cycloheptatriene tripalladium complex [Pd3(C7H7R)2(CH3CN)3][BF4]2 (R = H, t-Bu) dimerized upon one-electron reduction. Both monomer and dimer of cycloheptatriene complexes were structurally determined by X-ray crystallographic analyses.

Redox-induced reversible metal assembly through translocation and reversible ligand coupling in tetranuclear metal sandwich frameworks

Sandwich structures formed by metal atoms intercalated between sp(2)-carbon planes can be found either in metal-graphite-based materials or discrete multinuclear sandwich complexes. Their reactivity, and in particular their dynamic behaviour, has recently attracted interest both from a structural and a practical aspect, for example in catalysis. However, progress in this area has been rather slow, and it remains difficult to elucidate their structure and behaviour at the molecular level. Here, we report two sandwich complexes--in which four palladium centres are incorporated between two π-conjugated ligands--which exhibit two modes of redox-switchable structural changes. In the first complex, the tetrapalladium chain is split by oxidation into two well-separated dipalladium units. This motion is reversed on reduction. In the second complex, reversible carbon-carbon coupling occurs between the ligands during the redox process.

Oxidative Dinuclear Addition of a PdI–PdI Moiety to Arenes: Generation of μ-η3:η3-Arene-PdII2 Species

We report the oxidative dinuclear addition of a Pd(I)-Pd(I) bond to arenes. The oxidative dinuclear addition products, which have a bi-π-allyl-type arene dipalladium(II) structure, were obtained from [2.2]paracyclophane, anthracene, tetracene, and pentacene. A systematic study of the reaction of [Pd(2)(CH(3)CN)(6)][BF(4)](2) with benzene and polyacenes showed that the larger polyacenes, tetracene and pentacene, afforded the oxidative dinuclear addition products, while benzene, naphthalene, and anthracene gave the π-sandwich Pd(I)-Pd(I) complexes.

Metallocenoids of platinum: Syntheses and structures of triangular triplatinum sandwich complexes of cycloheptatrienyl

A series of bis-cycloheptatrienyl triangular triplatinum complexes are synthesized as a novel class of organoplatinum sandwich compounds. The tris-ethylene triplatinum sandwich complex and the monophenyl bis-ethylene sandwich complex of triangular triplatinum are structurally characterized by X-ray crystallographic analyses. The net assembling of three Pt0 atoms between two tropylium cations is initiated by complexation of a Pt0 moiety by a tropylium ligand, where the mononuclear cycloheptatrienyl PtII intermediate is detectable in situ by NMR. It is revealed that the choice of added ligands is crucial to the efficient formation as well as conversion of the key mononuclear cycloheptatrienyl PtII intermediate.

Stepwise growth of polypalladium chains in 1,4-diphenyl-1,3-butadiene sandwich complexesElectronic supplementary information (ESI) available: structural details. See http://www.rsc.org/suppdata/cc/b4/b403098b/

A series of 1,4-diphenyl-1,3-butadiene multinuclear palladium sandwich complexes are synthesized by stepwise growth of palladium chains within a sandwich framework.

Selective Construction of Pd2Pt and PdPt2 Triangles in a Sandwich Framework: Carbocyclic Ligands as Scaffolds for a Mixed‐Metal System

Sandwich time! The mixed-metal triangular-trinuclear sandwich complexes of Pd(2)Pt and PdPt(2) were selectively synthesized. The Pd(2)Pt and PdPt(2) triangles in a cycloheptatrienyl sandwich framework were identified by (31)P NMR analyses of the tris-triphenylphosphine complexes (see scheme).

Multinuclear metal-binding ability of a carotene

Carotenes are naturally abundant unsaturated hydrocarbon pigments, and their fascinating physical and chemical properties have been studied intensively not only for better understanding of the roles in biological processes but also for the use in artificial chemical systems. However, their metal-binding ability has been virtually unexplored. Here we report that β-carotene has the ability to assemble and align ten metal atoms to afford decanuclear homo- and heterometal chain complexes. The metallo–carotenoid framework shows reversible metalation–demetalation reactivity with multiple metals, which allows us to control the size of metal chains as well as the heterobimetallic composition and arrangement of the carotene-supported metal chains.

Synthesis and Reversible Reductive Coupling of Cationic, Dinitrogen-Derived Diazoalkane Complexes

A series of cationic diazoalkane complexes [4-RC(6)H(4)C(H)NNMo(N[t-Bu]Ar)(3)][AlCl(4)], [1-R][AlCl(4)] (R = NMe(2), Me, H, Br, CN; Ar = 3,5-C(6)H(3)Me(2)) has been prepared by treatment of the N(2)-derived diazenido complex Me(3)SiNNMo(N[t-Bu]Ar)(3) with 4-RC(6)H(4)CHO and 2 equiv of AlCl(3). The structures of [1-H][AlCl(4)] and [1-NMe(2)][AlCl(4)] were determined by X-ray crystallography. The C-N and N-N stretching modes were identified by a combined IR and Raman spectroscopy study, and other physical properties are discussed in detail. The electrochemical reduction potential for [1-R][AlCl(4)] was shown to be linear with the Hammett sigma parameter. This reduction process forms the C-C bonded dimer, mu-(4-RC(6)H(4)C(H)NN)(2)[Mo(N[t-Bu]Ar)(3)](2), that was characterized by X-ray crystallography for R = H. Possible mechanisms for the formation of this dimer are presented. Both electrochemical investigations and quantum chemical calculations are used to describe the odd-electron complex 4-RC(6)H(4)C(H)NNMo(N[t-Bu]Ar)(3), 1-R, that is an intermediate in the formation of [1-R](2). The C-C bond in [1-R](2) is redox-noninnocent and is broken upon oxidation. This reaction was used to prepare [1-H][A] (A = PF(6)(-), OTf(-)), and possible uses of this property in charge-storage devices are discussed.