Gold(I) Chloride Complexes of Polyphosphine Ligands with Electron-Rich Arene Spacer: Gold–Arene Interactions

Boosting Gold(I) Catalysis via Weak Interactions: New Fine-Tunable Impy Ligands

A series of modular ImPy-carbene-Au(I) complexes are synthesized and fully characterized both in the solid state and in solution. The presence of oligoaryl units (phenyl and thienyl rings) at the C5-position of the ImPy core (in close proximity to the gold center) imprints on the organometallic species fine-tunable and predictable catalytic properties. A marked accelerating effect was recorded in several [Au(I)]-catalyzed electrophilic activations of unsaturated hydrocarbons when a CF₃-containing aromatic ring was accommodated at the ImPy core.

Ylide-stabilized phosphenium cations: Impact of the substitution pattern on the coordination chemistry

Although N‐heterocyclic phosphenium (NHP) cations have received considerable research interest due to their application in organocatalysis, including asymmetric synthesis, phosphenium cations with other substitution patterns have hardly been explored. Herein, the preparation of a series of ylide‐substituted cations of type [YPR]⁺ (with Y=Ph₃PC(Ph), R=Ph, Cy or Y) and their structural and coordination properties are reported. Although the diylide‐substituted cation forms spontaneous from the chlorophosphine precursor, the monoylidylphosphenium ions required the addition of a halide‐abstraction reagent. The molecular structures of the cations reflected the different degrees of electron donation from the ylide to the phosphorus center depending on the second substituent. Molecular orbital analysis confirmed the stronger donor properties of the ylide systems compared to NHPs with the mono‐ylide substituted cations featuring a more pronounced electrophilicity. This was mirrored by the reaction of the cations towards gold chloride, in which only the diylide‐substituted cation [Y₂P]⁺ formed the expected LAuCl]⁺ complex, while the monoylide‐substituted compounds reacted to the chlorophosphine ligands by transfer of the chloride from gold to the phosphorus center. These results demonstrate the tunability of ylide‐functionalized phosphorus cations, which should allow for further applications in coordination chemistry in the future.

Reductive C-C Coupling from Molecular Au(I) Hydrocarbyl Complexes: A Mechanistic Study

Organometallic gold complexes are used in a range of catalytic reactions, and they often serve as catalyst precursors that mediate C-C bond formation. In this study, we investigate C-C coupling to form ethane from various phosphine-ligated gem-digold(I) methyl complexes including [Au2(μ-CH3)(PMe2Ar')2][NTf2], [Au2(μ-CH3)(XPhos)2][NTf2], and [Au2(μ-CH3)(tBuXPhos)2][NTf2] {Ar' = C6H3-2,6-(C6H3-2,6-Me)2, C6H3-2,6-(C6H2-2,4,6-Me)2, C6H3-2,6-(C6H3-2,6-iPr)2, or C6H3-2,6-(C6H2-2,4,6-iPr)2; XPhos = 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl; tBuXPhos = 2-di-tert-butylphosphino-2',4',6'-triisopropylbiphenyl; NTf2 = bis(trifluoromethyl sulfonylimide)}. The gem-digold methyl complexes are synthesized through reaction between Au(CH3)L and Au(L)(NTf2) {L = phosphines listed above}. For [Au2(μ-CH3)(XPhos)2][NTf2] and [Au2(μ-CH3)(tBuXPhos)2][NTf2], solid-state X-ray structures have been elucidated. The rate of ethane formation from [Au2(μ-CH3)(PMe2Ar')2][NTf2] increases as the steric bulk of the phosphine substituent Ar' decreases. Monitoring the rate of ethane elimination reactions by multinuclear NMR spectroscopy provides evidence for a second-order dependence on the gem-digold methyl complexes. Using experimental and computational evidence, it is proposed that the mechanism of C-C coupling likely involves (1) cleavage of [Au2(μ-CH3)(PMe2Ar')2][NTf2] to form Au(PR2Ar')(NTf2) and Au(CH3)(PMe2Ar'), (2) phosphine migration from a second equivalent of [Au2(μ-CH3)(PMe2Ar')2][NTf2] aided by binding of the Lewis acidic [Au(PMe2Ar')]+, formed in step 1, to produce [Au2(CH3)(PMe2Ar')][NTf2] and [Au2(PMe2Ar')]+, and (3) recombination of [Au2(CH3)(PMe2Ar')][NTf2] and Au(CH3)(PMe2Ar') to eliminate ethane.

The core of the matter - arene substitution determines the coordination and catalytic behaviour of tris(1-phosphanyl-1'-ferrocenylene)arene gold(I) complexes

Changing the aromatic core of C3-symmetric tris(ferrocenyl)arene-based tris-phosphanes has profound effects on their coordination behaviour towards gold(i). Depending on the arene (s-triazine, benzene, or trifluorobenzene), four different coordination modes can be distinguished and their preference has been rationalised using computational methods. The corresponding 1 : 1 ligand-to-metal complexes, studied by variable-temperature NMR spectroscopy, revealed fluctional behaviour in solution. Given the presence of up to three or six ferrocenylene spacers per complex, their electrochemistry was investigated. The redox-responsive nature of the complexes can be advantageously exploited in the catalytic ring-closing isomerisation of N-(2-propyn-1-yl)benzamide, where the benzene-based 2 : 3 ligand-to-metal complex has been shown to display multiple activity states depending on the degree of (reversible) oxidation in a preliminary trial.

Seeing luminescence appear as crystals crumble. Isolation and subsequent self-association of individual [(C6H11NC)2Au]+ ions in crystals

Non-luminescent, isostructural crystals of [(C6H11NC)2Au](EF6)·C6H6 (E = As, Sb) lose benzene upon standing in air to produce green luminescent (E = As) or blue luminescent (E = Sb) powders. Previous studies have shown that the two-coordinate cation, [(C6H11NC)2Au]+, self-associates to form luminescent crystals that contain linear or nearly linear chains of cations and display unusual polymorphic, vapochromic, and/or thermochromic properties. Here, we report the formation of non-luminescent crystalline salts in which individual [(C6H11NC)2Au]+ ions are isolated from one another. In [(C6H11NC)2Au](BArF24) ((BArF24)- is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) each cation is surrounded by two anions that prohibit any close approach of the gold ions. Crystallization of [(C6H11NC)2Au](EF6) (E = As or Sb, but not P) from benzene solution produces colorless, non-emissive crystals of the solvates [(C6H11NC)2Au](EF6)·C6H6. These two solvates are isostructural and contain columns in which cations and benzene molecules alternate. With the benzene molecules separating the cations, the shortest distances between gold ions are 6.936(2) Å for E = As and 6.9717(19) Å for E = Sb. Upon removal from the mother liquor, these crystals crack due to the loss of benzene from the crystal and form luminescent powders. Crystals of [(C6H11NC)2Au](SbF6)·C6H6 that powder out form a pale yellow powder with a blue luminescence with emission spectra and powder X-ray diffraction data that show that the previously characterized [(C6H11NC)2Au](SbF6) is formed. In the process, the distances between the gold(i) ions decrease to ∼3 Å and half of the cyclohexyl groups move from an axial orientation to an equatorial one. Remarkably, when crystals of [(C6H11NC)2Au](AsF6)·C6H6 stand in air, they lose benzene and are converted into the yellow, green-luminescent polymorph of [(C6H11NC)2Au](AsF6) rather than the colorless, blue-luminescent polymorph. Paradoxically, the yellow, green-luminescent powder that forms as well as authentic crystals of the yellow, green-luminescent polymorph of [(C6H11NC)2Au](AsF6) are sensitive to benzene vapor and are converted by exposure to benzene vapor into the colorless, blue-luminescent polymorph.

1,2,3-Triazole based bisphosphine, 5-(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)-phenyl)-4-phenyl-1H-1,2,3-triazole: an ambidentate ligand with switchable coordination modes

The reaction of 1-(2-bromophenyl)-4-phenyl-1H-1,2,3-triazole (1) with Ph₂PCl yielded bisphosphine, 5-(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)phenyl)-4-phenyl-1H-1,2,3-triazole (2). Bisphosphine 2 exhibits ambidentate character in either the κ²-P,N or κ²-P,P coordination mode. Treatment of 2 with [M(CO)₄(piperidine)₂] (M = Mo and W) yielded κ²-P,N and κ²-P,P coordinated Mo⁰ and W⁰ complexes [M(CO)₄(2)] [M = W-κ²-P,N (4); Mo-κ²-P,P (5); W-κ²-P,P (6)] depending on the reaction conditions. Formation and stability of κ²-P,P coordinated Mo⁰ and W⁰ complexes were assessed by time dependent ³¹P{¹H} NMR experiments and DFT studies. The complex 4 on treatment with [AuCl(SMe₂)] afforded the hetero-bimetallic complex [μ-PN,P-{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂AuCl)}-κ²-P,N}W(CO)₄] (7). The 1 : 1 reaction between 2 and [CpRu(PPh₃)₂Cl] yielded [(η⁵-C₅H₅)RuCl{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}}-κ²-P,P] (8), whereas the similar reaction with [Ru(η⁶-p-cymene)Cl₂]₂ in a 2 : 1 molar ratio produced a cationic complex [(η⁶-p-cymene)RuCl{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}}-κ²-P,N]Cl (9). Similarly, treatment of 2 with [M(COD)(Cl)₂] (M = Pd and Pt) in a 1 : 1 molar ratio yielded Pd^II and Pt^II complexes [{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}-κ²-P,P}PdCl₂] (10) and [{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}-κ²-P,P}PtCl₂] (11). The reaction of 2 with 2 equiv. of [AuCl(SMe₂)] afforded [Au₂Cl₂{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}}-μ-P,P] (12). Most of the complexes have been structurally characterized. Palladium complex 10 shows excellent catalytic activity towards Cu-free Sonogashira alkynylation/cyclization reactions.

This paper describes the synthesis of a triazole based bisphosphine and its transition metal chemistry and catalytic utility in Cu-free Sonogashira alkynylation/cyclization reaction.

Gold(iii)-arene complexes by insertion of olefins into gold-aryl bonds

The synthesis and characterization of the first gold(iii)–arene complexes are described.

The synthesis and characterization of the first gold(iii)–arene complexes are described. Well-defined (P,C)-cyclometalated gold(iii)–aryl complexes were prepared and characterized by NMR spectroscopy. These complexes swiftly and cleanly reacted with norbornene and ethylene to provide cationic gold(iii)–alkyl complexes, in which the remote phenyl ring was η²-coordinated to gold. The interaction between the aromatic ring and the gold(iii) center was thoroughly analyzed by NMR spectroscopy, X-ray diffraction, and DFT calculations. The π–arene coordination was found to significantly influence the stability and reactivity of low coordinated gold(iii) alkyl species.

Synthesis and solid-state structures of gold(i) complexes of diphosphines

A series of diphosphine bis(gold) complexes were synthesised and the importance of aurophilic interactions for their structure formation was studied.