Monomeric Bis(η2-alkyne) Complexes of Copper(I) and Silver(I) with η1-Bonded Alkyl, Vinyl, and Aryl Ligands

Steric and electronic influence on Cu-Cu short contacts in β-thioketiminato tricopper(I) clusters

A series of β-thioketiminate copper(I) complex trimers [LCuI]3 were synthesized by modifying the ligand framework with electron-withdrawing groups (F and Cl) or electron-donating groups (iPr and Me) at the N-aryl ring as well as with CF3 groups on the chelating backbone. This ligand modification significantly impacts the enhancement of Cu⋯Cu short contacts, which can be rationalized by using steric and electronic factors of the chelated ligand. We observed that this intramolecular cuprophilicity among [LCuI]3 complexes is primarily governed by the size of N-aryl ortho-substituents. These findings were well supported by X-ray crystallography, Raman spectroscopy, and Mayer bond order analysis. The electronic effects induced by the ligand modification on the LCuI fragment were investigated using CO and 2,4,6-CNC6H2Me3 as probe molecules. Corroborated by the FTIR and CV measurements, our results reveal that the β-thioketiminate SN chelators induce more pronounced changes in the electronic character of the LCuI fragment due to the presence of CF3 groups on the chelating backbone in comparison with the F or Cl substituents on the N-aryl ring.

Synthesis and Luminescence Studies of a Tethered, Trigonal, Silver(I) Tris(alkyne) Complex

The synthesis and characterization of a tris(alkyne) ligand, tris[2-(trimethylsilyl)ethynyl-4-tert-butylbenzyl]amine (1), and its silver(I) hexafluorophosphate complex, 1-Ag, are reported. The solid-state structure and luminescence properties of 1-Ag indicate relatively strong silver(I)-alkyne interactions between the metal cation and 1. No significant changes in the bond angles or lengths were observed upon metalation of 1 with Ag+, indicating a relatively unstrained ligand-metal motif. The luminescence properties of 1 and 1-Ag are also disclosed, showing attenuation in the luminescence intensity upon Ag+ metalation, with Stokes shifts of ∼3700 and ∼3200 cm-1 for 1 and 1-Ag, respectively. The lifetimes of 1-Ag (τ1 = 8.383 ± 0.053 ns and τ2 = 4.665 ± 0.061 ns) were longer than those of 1 (τ1 = 6.708 ± 0.085 ns and τ2 = 3.689 ± 0.025 ns), possibly indicating multiple conformers of 1-Ag in solution. This new silver alkyne platform has potential applications in studies of catalysis, luminescent compounds, and sensing.

Copper Complexes with Diazoolefin Ligands and their Photochemical Conversion into Alkenylidene Complexes

Homometallic copper complexes with alkenylidene ligands are discussed as intermediates in catalysis but the isolation of such complexes has remained elusive. Herein, we report the structural characterization of copper complexes with bridging and terminal alkenylidene ligands. The compounds were obtained by irradiation of Cu^I complexes with N-heterocyclic diazoolefin ligands. The complex with a terminal alkenylidene ligand required isolation in a crystalline matrix, and its structural characterization was enabled by in crystallo photolysis at low temperature.

Recent Advances in Transition-Metal-Catalyzed C-H Functionalization of Ferrocene Amides

During the past decades, in synthetic organic chemistry, directing-group-assisted C-H functionalization is found to be a key tool for the expedient and site-selective construction of C-C and hybrid bonds. Among C-H functionalization of ferrocene derivatives, the directed group strategy is undoubtedly the most commonly used method. Compared to the other directing groups, ferrocene amides can be synthesized easily and are now recognized as one of the most efficient devices for the selective functionalization of certain positions because its metal centre permits fine, tuneable and reversible coordination. The family of amide directing groups mainly comprises monodentate and bidentate directing groups, which are categorized on the basis of coordination sites. In this review, various C-H bond functionalization reactions of ferrocene using amide directing groups are broadly discussed.

The copper-catalysed Suzuki–Miyaura coupling of alkylboron reagents: disproportionation of anionic (alkyl)(alkoxy)borates to anionic dialkylborates prior to transmetalation

A novel Cu-catalyzed Suzuki–Miyaura cross-coupling of alkylboron reagents with aryl and heteroaryl iodides is reported.

From bis(silylene) and bis(germylene) pincer-type nickel(II) complexes to isolable intermediates of the nickel-catalyzed Sonogashira cross-coupling reaction

The first [ECE]Ni(II) pincer complexes with E = Si(II) and E = Ge(II) metallylene donor arms were synthesized via C-X (X = H, Br) oxidative addition, starting from the corresponding [EC(X)E] ligands. These novel complexes were fully characterized (NMR, MS, and XRD) and used as catalyst for Ni-catalyzed Sonogashira reactions. These catalysts allowed detailed information on the elementary steps of this catalytic reaction (transmetalation → oxidative addition → reductive elimination), resulting in the isolation and characterization of an unexpected intermediate in the transmetalation step. This complex, {[ECE]Ni acetylide → CuBr} contains both nickel and copper, with the copper bound to the alkyne π-system. Consistent with these unusual structural features, DFT calculations of the {[ECE]Ni acetylide → CuBr} intermediates revealed an unusual E-Cu-Ni three-center-two-electron bonding scheme. The results reveal a general reaction mechanism for the Ni-based Sonogashira coupling and broaden the application of metallylenes as strong σ-donor ligands for catalytic transformations.

The Chemistry of Transition Metal Ethyne-1,2-diyl Complexes

The chemistry and reactivity of ethyne-1,2-diyl compounds, LnM–CC–MLn, is reviewed. These complexes are simple analogues of organic alkynes, or dimetalloalkynes, and there appears to be no general route to the preparation of these complexes, except perhaps using acid/base methodology. Reactivity patterns, in general, mimic those of simple organic alkynes but have the added dimension of reactive M–C(sp) bonds that sometimes participate in the formation of multimetallic compounds with metal electrophiles.

Pentafluorophenyl copper: aggregation and complexation phenomena, photoluminescence properties, and applications as reagent in organometallic synthesis

Recent advances in the chemistry of pentafluorophenyl copper are discussed, including the observation of strongly luminescent adducts with pyridine, the first successful structural characterization of an organocopper-arene complex, and the complexation with electron-rich transition metal complexes such as ferrocene derivatives. In addition, new applications in synthetic organometallic chemistry are discussed, which include the discovery of tin/copper exchange reactions for the preparation of organocopper compounds that are otherwise not readily accessible, and the selective transfer of the C(6)F(5) groups to boron to form catalytically active and electronically interesting organoboron polymers.

Alkyne-containing chelating ligands: synthesis, properties and metal coordination of 1,2-di(quinolin-8-yl)ethyne

A new alkyne-containing chelating ligand, 1,2-di(quinolin-8-yl)ethyne, is shown to form a mononuclear 1:1 complex with silver(I) and chelate the metal ion through both nitrogens and the ethyne moiety as seen by UV and NMR spectroscopy as well as X-ray crystallography.

Structure Determination of Homoleptic AuI, AgI, and CuI Aryl/Alkylethynyl Coordination Polymers by X-ray Powder Diffraction

This article describes the structure determination of five homoleptic d(10) metal-aryl/alkylacetylides [RC triple bond CM] (M=Cu, R=tBu 1, nPr 2, Ph 3; R=Ph, M=Ag 4; Au 5) by using X-ray single-crystal and powder diffraction. Complex 1.C6H6 reveals an unusual Cu20 catenane cluster structure that has various types of tBuC triple bond C-->Cu coordination modes. By using this single-crystal structure as a starting model for subsequent Rietveld refinement of X-ray powder diffraction data, the structure of the powder synthesized from CuI and tBuC triple bond CH was found to have the same structure as 1. Complex 2 has an extended sheet structure consisting of discrete zig-zag Cu4 subunits connected through bridging nPrC triple bond C groups. Complex 3 forms an infinite chain structure with extended Cu-Cu ladders (Cu-Cu=2.49(4)-2.83(2) A). The silver(I) congener 4 is iso-structural to 3 (average Ag-Ag distance 3.11 A), whereas the gold(I) analogue 5 forms a Au...Au honeycomb network with PhC triple bond C pillars (Au-Au=2.98(1)-3.26(1) A). Solid-state properties including photoluminescence, nu(C triple bond C) stretching frequencies and thermal stability of these polymeric systems are discussed in the context of the determined structures.

Acrylonitrile Polymerization by Cy3PCuMe and (Bipy)2FeEt2

Cy(3)PCuMe (1) undergoes reversible ligand redistribution at low temperature in solution to form the tight ion pair [Cu(PCy(3))(2)][CuMe(2)] (3). The structure of 3 was assigned on the basis of (i) the stoichiometry of the 1 = 3 equilibrium, (ii) the observation of a triplet for the PCy(3) C1 (13)C NMR resonance due to virtual coupling to two (31)P nuclei, and (iii) reverse synthesis of 1 by combining separately generated Cu(PCy(3))(2)(+) and CuMe(2)(-) ions. Complex 1 and [Cu(PCy(3))(2)][PF(6)] (5) coordinate additional PCy(3) to form (Cy(3)P)(2)CuMe and [Cu(PCy(3))(3)][PF(6)], respectively, while 3 does not. Complex 1, free PCy(3), and (bipy)(2)FeEt(2) (2) each initiate the polymerization of acrylonitrile. In each case, the polyacrylonitrile contains branches that are characteristic of an anionic polymerization mechanism. The major initiator in acrylonitrile polymerization by 1 is PCy(3), which is liberated from 1. A transient iron hydride complex is proposed to initiate acrylonitrile polymerization by 2.

Argentophilicity and solvent-induced structural diversity in double salts of silver acetylide with silver perfluoroalkyl carboxylates

A series of novel double salts of silver(I) were isolated by dissolving Ag(2)C(2) in a concentrated aqueous solution of R(F)CO(2)Ag (R(F) = CF(3), C(2)F(5)) and AgBF(4). Different ancillary solvento ligands such as H(2)O, CH(3)CN, and C(2)H(5)CN were found to affect the crystallization process that led to the assembly of various silver(I) cages with embedded C(2)(2-) ions. 2Ag(2)C(2) x 12CF(3)CO(2)Ag x 5H(2)O (1) consists of two independent C(2)@Ag(7) cages, each having the shape of a basket with a square base. Ag(2)C(2) x 6CF(3)CO(2)Ag x 3CH(3)CN (2) contains a zigzag chain of edge-sharing triangulated dodecahedra, and 4Ag(2)C(2) x 23CF(3)CO(2)Ag x 7C(2)H(5)CN x 2.5H(2)O (3) features an unusual double-walled silver column constructed from the fusion of four different kinds of irregular polyhedra. Ag(2)C(2) x 10C(2)F(5)CO(2)Ag x 9.5H(2)O (4), Ag(2)C(2) x 9C(2)F(5)CO(2)Ag x 3CH(3)CN x H(2)O (5), and Ag(2)C(2) x 6C(2)F(5)CO(2)Ag x 2C(2)H(5)CN (6) all contain an edge-sharing double cage with each single cage in the shape of a square antiprism, a capped square antiprism, and a triangulated dodecahedron, respectively.