The ion [H 3 ] + represents a classic case in molecular orbital theory, the simplest three-center, two-electron bond. [1] The proton affinity of dihydrogen in the gas phase, at 4.4 eV, [2] is nearly equal to the bond enthalpy of H 2 itself. [3] The [H 3 ] + ion has been studied spectroscopically in the laboratory; [4] it has been detected in planetary atmospheres, [5a] and is notably abundant in interstellar space. [5b] The concept of isolobality has been used extensively to draw analogies between [LAu] + and [H] + , [6] and after the discovery of isolable [(LAu) 2 H] + complexes, [7,8] we became interested in the synthesis of an allgold analogue of [H 3 ] + .Complexes of gold(I) with atoms such as oxygen and the heavier chalcogens, nitrogen, and carbon, often exhibit weak but important aurophilic interactions between the d 10 metal centers. [9] Multicenter covalent bonding is observed in formally mixed-valent gold(I)/gold(0) clusters. [10] These include edge-sharing bitetrahedral clusters of the general formula [(LAu) 6 ] 2+ , [11] and tetrahedral clusters of the formula [(LAu) 4 ] 2+ . [12] Clusters such as [(LAu) 6 ] 2+ , (L 6 Au 8 ) 2+ , and [(LAu) 4 ] 2+ , have been synthesized by the reduction of phosphine-supported m 3 -oxo or m 3 -imido cations with carbon monoxide. [13] Whereas gold(II) dimers form covalent goldgold bonds through the interaction of half-filled d-orbitals, [14] the gold-gold bonding in mixed-valent gold(I)/gold(0) clusters [(LAu) n ] x+ arises to an important extent from symmetryadapted combinations of partially filled gold 6 s orbitals. [10b] The interaction of small gold clusters and nanoparticles with O 2 has been studied as a key step in aerobic oxidation catalysis. [15] The [Au 3 ] + -catalyzed oxidation of CO has been studied theoretically, [16] and [Au 3 ] + in the gas phase has been shown to mediate the oxidation of CO by N 2 O. [17] Mass spectrometry studies suggest that a transient [L 2 Au 3 ] + ion, where L 2 is a bridging bisphosphine, undergoes oxidative addition with aryl iodides. [18] Cluster complexes featuring the cyclo-Au 3 moiety bonded to tungsten [19] or to main-group elements [20] are known, as are triangular [Au 2 M] clusters. [21] We now report the characterization of a stable [(LAu) 3 ] + complex, where L is the N-heterocyclic carbene (NHC) 1,3bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IDipp). Density functional theory (DFT) lends insight into the bonding among gold centers. Preliminary studies demonstrate sluggish reactivity with oxygen-atom-transfer agents, but facile reactivity with soft electrophiles.Initially, we planned to obtain [(LAu) 3 ] + through the reduction of a corresponding m 3 -oxo complex [(LAu) 3 O] + . A wide range of phosphorus-based donor ligands support complexes of this type. [22] Our efforts to obtain an analogous NHC-supported species by the established routes gave rise to mixtures of products, including the hydroxide-bridged digold cation [(LAu) 2 OH] + . [23] Reasoning that the formation of strong silicon-heteroatom bonds co...
Dialkylbiarylphosphines are an emerging ligand set that promote catalytic reactions of electrophilic late transition-element centers through dative interactions of the biaryl arm with the metal site. Presented here are syntheses and crystal structures of five new (dicyclohexylbiarylphosphine)gold(I) chlorides and bromides. X-ray diffraction crystallography reveals close approaches between gold(I) and the flanking ipso carbon (mean Au-C ipso distance, compounds 2-6: 3.156 Å). New compounds have been characterized by multinuclear NMR spectroscopy, X-ray diffraction crystallography, and combustion analysis.
Two general protocols for the synthesis of N-heterocyclic carbene- or phosphine-ligated gold(I) and silver(I) azide complexes have been developed. The first utilizes thallium(I) acetylacetonate, followed by treatment with trimethylsilyl azide, while the second protocol exploits the relative weakness of d10 metal−oxygen bonds in the reaction of metal(I) acetate with trimethylsilyl azide. Both methods give products in high yield, but only the metal(I) acetate/trimethylsilyl azide method proceeds to completion for an N-heterocyclic carbene-ligated silver(I) acetate. The successful application of this method to silver(I) suggests that this nonaqueous protocol may have general applicability to late transition element or main group acetate precursors. Eight new complexes are reported, of which six are metal azides; four have been crystallographically characterized. Products have been characterized by vibrational and multinuclear NMR spectroscopies and combustion analysis. The synthesis methods described here provide useful alternatives for the syntheses of azide complexes in cases where protic solvents cannot be used.
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