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The development of gold catalysis has allowed significant levels of activity and complexity in organic synthesis. Recently, the use of very active small gold subnanoclusters (Aun, n<10) has been reported. The stabilization of such nanocatalysts to prevent self-aggregation represents a true challenge that has been partially remediated, for instance, by their immobilization in polymer matrices. Here, we describe the transient stabilization of very small gold subnanoclusters (Aun, n < 5) by alkyl chains or aromatic groups appended to the reactive π bond of simple alkynes. The superior performance toward Brønsted acid-free hydration of medium to long aliphatic alkynes (1-hexyne and 1-docecyne) and benzylacetylene with respect to phenylacetylene is demonstrated experimentally and investigated computationally. A cooperative network of dispersive Au…C-H and/or Au…π interactions, supported by quantum mechanical calculations and time-resolved luminescence experiments, is proposed to be at the origin of this stabilization. [ABSTRACT FROM AUTHOR]

Two different theoretical approaches have been used for the description of the experimentally observed dual luminescence of 4-(dimethylamino)pyridine (DMAP), introducing solvent effects with the polarizable continuum model (PCM), which seems needed to represent the dual fluorescence in polar media. These approaches are the linear response time-dependent density functional theory (TDDFT) and the state-specific complete active space self-consistent field. Both levels of theory represent the expected planar high-energy and the twisted intramolecular charge transfer (ICT) low-energy excited-state structures in the presence of solvent (toluene and acetonitrile). The comparison between both approaches shows that the main distortion of the ICT state is similar for both cases, i.e. twisting to almost 90º of the pyridine ring and the dimethylamino planes, but that other secondary distortions are slightly different. In the case of the TDDFT approach, the geometry optimizations of DMAP in the ground and excited states have been carried out using the conventional linear response approach (LR-PCM) for the solvent inclusion. The LR-PCM and the specific state (SS-PCM) approaches have been used for the prediction of the excitation and emission energies of DMAP in toluene and acetonitrile. The prediction of the emission energies at TDDFT/LR-PCM and CASPT2/PCM (complete active space perturbation theory) levels agrees with the experimental ones. [ABSTRACT FROM AUTHOR]

The structures of the tetragold(I) formamidinate cluster complexes, [Au4(ArNC(H)NAr)4], Ar=C6H4-4-OMe (1), C6H3-3,5-C1 (2), C6H4-4-Me (3), have been characterized by x-ray crystallography. The range of Au···Au distances is 2.8-3.0 Å. The angles at Au···Au···Au are acute and obtuse 70 and 109% 88 and 91°, and 63 and 116° in 1, 2, and 3, respectively. The four gold atoms are located at the comer of a rhomboid with the formamidinate ligands bridged above and below the near plane of the four Au(I) atoms. The tetranuclear gold(I) complexes show a bright blue-green luminescence under UV light, with an emission at ∼490 nm and a weak emission at ∼530 nm in the solid state, at room temp and 77 K. The oxidation of the formamidinate cluster, 1, has been studied electrochemically in 0.1 M Bu4NPF6/CH2Cl2 at a Pt working electrode with different scan rates. Three waves were obtained, 0.75, 0.95, and 1.09 V vs. Ag/AgCl at a scan rate of 500 mV/s, the three waves are reversible. The potentials are independent of the scan rate in the range 50 mV/s to 3 V/s. The current at the third wave is larger than those at the first two. KEY WORDS: Gold; formamidinates; tetrameric; luminescence; electrochemistry. [ABSTRACT FROM AUTHOR]

The tetranuclear Au(I) pyrazolate complex, [(dppm)[sub 2]Au[sub 4](3,5-Ph[sub 2]Pz)[sub 2]](NO[sub 3])[sub 2] · H[sub 2]O, 1, has been synthesized and structurally characterized. It is the first tetranuclear pyrazolate of Au(I) to have been found, although the trinuclear pyrazolates of Au(I) are well known. Complex I exhibits luminescence at 77 K when excited at 333 nm with an emission maximum at 454 nm. The emission has been assigned to ligand to metal charge transfer, LMCT, based upon the vibronic structure that is observed. The complex crystallizes in the monoclinic space group P2[sub 1]/c, with a=19.33(3)Å, b=20.26(3)Å, c=19.80(3)Å, r= 106.74(2)°, V = 7425(17)ų, Z = 8, and R = 0.058. The Au...Au distances are Au(1)...Au(4) = 3.185(3) Å, Au(1)...Au(2) = 3.230(3) Å, Au(2)...Au(3) = 3.079(3) Å, and Au(3)... Au(4) = 3.280(3) Å. [ABSTRACT FROM AUTHOR]

There are four types of gold-heteroatom complexes which display luminescence: dinuclear complexes, triand tetranuclear complexes, polymeric chains, and clusters. The present state of knowledge on the preparation and properties of each of these types is summarized here. [ABSTRACT FROM AUTHOR]