A Hexanuclear Gold Cluster Supported by Three-Center-Two-Electron Bonds and Aurophilic Interactions

Recent Advances in Ligand Engineering for Gold Nanocluster Catalysis: Ligand Library, Ligand Effects and Strategies

Advances in new ligands in the last decade facilitated in-depth studies on the property-relationship of gold nanoclusters and promoted the rational synthesis and related applications of such materials. Currently, more and more new ligands are being explored; thus, the ligand library of AuNCs is being expanded fast, which also enables investigation of ligand effects of AuNCs via direct comparison of different ligating shell with the identical gold core. It is now widely accepted that ligands influence the properties of AuNCs enormously including stability, catalysis, photoluminescence among others. These studies inspired ligand engineering of AuNCs. One of the goals for ligand engineering is to develop ligated AuNC catalysts in which the ligands are able to exert big-enough influence on electronic and steric control over catalysis as in a transition-metal or an enzyme system. Although increasing attention is paid to the further expansion of ligand library, the investigation of design principles and strategies regarding ligands are still in their infant stage. This review summarizes the ligands for AuNC synthesis, the ligand effects on stability and catalysis, and recently developed strategies in promoting AuNC catalytic performance via ligand manipulation.

Small Gold(I) and Gold(I)-Silver(I) Clusters by C-Si Auration

Auration of o-trimethylsilyl arylphosphines leads to the formation of gold and gold-silver clusters with ortho-metalated phosphines displaying 3c-2e Au-C-M bonds (M=Au/Ag). Hexagold clusters [Au6 L4 ](X)2 are obtained by reaction of (L-TMS)AuCl with AgX, whereas reaction with AgX and Ag2 O leads to gold-silver clusters [Au4 Ag2 L4 ](X)2 . Oxo-trigold(I) species [Au3 O]+ were identified as the intermediates in the formation of the silver-doped clusters. Other [Au5 ], [Au4 Ag], and [Au12 Ag4 ] clusters were also obtained. Clusters containing PAu-Au-AuP structural motif display good catalytic activity in the activation of alkynes under homogeneous conditions.

Metallophilic interactions: observations of the shortest metallophilicinteractions between closed shell (d10⋯d10, d10⋯d8, d8⋯d8) metal ions [M⋯M′ M = Hg(ii) and Pd(ii) and M′ = Cu(i), Ag(i), Au(i), and Pd(ii)]

The salt metathesis reaction of two equivalents of 8-lithioquinoline (C₆H₆NLi) with HgBr₂ afforded bis(quinoline-8-yl)mercury, [(C₆H₆N)₂Hg].

Activation of an Au-Cl Bond by a Pendent SbIII Lewis Acid: Impact on Structure and Catalytic Activity

With the objective of identifying new coordination modes of ambiphilic ligands, we have investigated the bidentate Sb/P ligands (o-(Ph₂ P)C₆ H₄ )SbCl₂ (L^Cl ) and (o-(Ph₂ P)C₆ H₄ )SbPh₂ (L^Ph ). Reaction of these ligands with (tht)AuCl affords the monoligated species L^Cl AuCl (1) and L^Ph AuCl (2), respectively, in which the antimony centers are only weakly engaged with the coordinated gold atom. Treatment of 1 with PPh₃ induces an intramolecular transfer of a chloride ligand from gold to antimony to form the zwitterionic species o-(Cl₃ Sb)C₆ H₄ (Ph₂ P)Au(PPh₃ ) (3). Natural bond orbital (NBO) calculations show that the antimony and gold centers are involved in weak Sb→Au and Au→Sb interactions, the latter reflecting the Lewis acidity of the pendent antimony group. Finally, we demonstrate that the ability of the antimony center in 1 to abstract a gold-bound chloride in the presence of a Lewis basic substrate may be utilized to activate the gold center for the electrophilic cycloisomerization of propargylic amides.

Polynuclear Gold [Au(I) ]4 , [Au(I) ]8 , and Bimetallic [Au(I) 4 Ag(I) ] Complexes: C-H Functionalization of Carbonyl Compounds and Homogeneous Carbonylation of Amines

The synthesis of tetranuclear gold complexes, a structurally unprecedented octanuclear complex with a planar [Au(I) 8 ] core, and pentanuclear [Au(I) 4 M(I) ] (M=Cu, Ag) complexes is presented. The linear [Au(I) 4 ] complex undergoes C-H functionalization of carbonyl compounds under mild reaction conditions. In addition, [Au(I) 4 Ag(I) ] catalyzes the carbonylation of primary amines to form ureas under homogeneous conditions with efficiencies higher than those achieved by gold nanoparticles.

Splitting a Substrate into Three Parts: Gold-Catalyzed Nitrogenation of Alkynes by C-C and C≡C Bond Cleavage

A gold-catalyzed nitrogenation of alkynes for the synthesis of carbamides and amino tetrazoles through C-C and C≡C bond cleavages is described. A diverse set of functionalized carbamide and amino tetrazole derivatives were selectively constructed under mild conditions. The chemoselectivity can be easily switched by the selection of the acid additives. The reaction is characterized by its broad substrate scope, direct construction of high value products, easy operation under air, and mild conditions at room temperature. This chemistry provides a way to transform alkynes by splitting the substrate into three parts.

Platinum complexes of a borane-appended analogue of 1,1'-bis(diphenylphosphino)ferrocene: flexible borane coordination modes and in situ vinylborane formation

A bis(phosphine)borane ambiphilic ligand, [Fe(η(5) -C5 H4 PPh2 )(η(5) -C5 H4 PtBu{C6 H4 (BPh2 )-ortho})] (FcPPB), in which the borane occupies a terminal position, was prepared. Reaction of FcPPB with tris(norbornene)platinum(0) provided [Pt(FcPPB)] (1) in which the arylborane is η(3) BCC-coordinated. Subsequent reaction with CO and CNXyl (Xyl=2,6-dimethylphenyl) afforded [PtL(FcPPB)] {L=CO (2) and CNXyl (3)} featuring η(2) BC- and η(1) B-arylborane coordination modes, respectively. Reaction of 1 or 2 with H2 yielded [PtH(μ-H)(FcPPB)] in which the borane is bound to a hydride ligand on platinum. Addition of PhC2 H to [Pt(FcPPB)] afforded [Pt(C2 Ph)(μ-H)(FcPPB)] (5), which rapidly converted to [Pt(FcPPB')] (6; FcPPB'=[Fe(η(5) -C5 H4 PPh2 )(η(5) -C5 H4 PtBu{C6 H4 (BPh-CPh=CHPh-Z)-ortho}]) in which the newly formed vinylborane is η(3) BCC-coordinated. Unlike arylborane complex 1, vinylborane complex 6 does not react with CO, CNXyl, H2 or HC2 Ph at room temperature.