Molecular Aggregation of Annular Dinuclear Gold(I) Compounds Containing Bridging Diphosphine and Dithiolate Ligands

Abstract

A series of annular dinuclear Au(I) complexes containing diphosphine (R(2)P(CH(2))(n)()PR(2); R = Me, n = 1, dmpm; R = Me, n = 2, dmpe; R = Ph, n = 1, dppm; R = Ph, n = 2, dppe) and dithiolate (dtc = S(2)CNEt(2)(-), i-mnt = S(2)C(2)(CN)(2)(2)(-)) ligands were synthesized: [Au(2)(P-P)(S-S)]X (S-S = dtc: P-P = dmpm, X = Cl, 1; P-P = dppm, X = PF(6), 2; P-P = dppe, X = PF(6), 3; P-P = PPh(3), X = PF(6), 4) and [Au(2)(P-P)(S-S)] (S-S = i-mnt: P-P = dmpm,5; P-P = dppm, 6; P-P = dmpe, 7; P-P = dppe, 8). Crystal structures of two complexes are reported. Pertinent crystallographic data: [Au(2)(dmpm)(i-mnt)] (5), space group Fdd2, with a = 19.574(3) Å, b = 48.220(11) Å, and c = 15.273(2) Å, R = 0.0542; [Au(2)(dppe)(i-mnt)] (8), space group P2(1)/n, with a = 11.793(2) Å, b = 19.607(2) Å, and c = 15.349(2) Å, R = 0.0448. Each molecule has two gold atoms bridged by a dithiolate ligand on one side and a diphosphine ligand on the other side, thus forming an eight- or nine-membered ring digold complex. The tendency of the digold(I) compounds to aggregate through an intermolecular Au-Au interaction depends on the ligands. Among the structures determined, complex 5 forms a polymeric chain and compound 8 is monomeric. Molecular aggregation also occurs in solution. Concentration-dependent absorption spectra of Au-dtc compounds suggest that an equilibrium between the monomer and dimer exists. Equilibrium constants corresponding to the intermolecular Au-Au interaction range from 38 to 137 M(-)(1) with DeltaH values of approximately 15 kcal/mol and DeltaS values of approximately -35 to approximately -46 cal/(K mol). Concentration dependence of emission spectra of annular compounds in acetonitrile also supports association in solution. Emissions at approximately 400-440 nm assignable to spin-allowed metal-centered transitions from monomeric Au(2) at lower concentrations and dimeric Au(4) at higher concentrations are observed. Compounds 1-3 and 5-8 in the glass state having spin-forbidden dithiolate ligand to gold charge transfer ((3)LMCT) transitions give emission bands at approximately 550 nm. Compound 4 has a S --> Au (3)LMCT transition at 500 nm. (31)P variable-temperature NMR experiments were performed for 1-3. The dynamic process is attributed to molecular aggregation through an intermolecular Au-Au interaction in solution. The activation energies are approximately 9 kcal/mol for 1 and 2.

Multiple Evidence for Gold(I)⋅⋅⋅Silver(I) Interactions in Solution

“…[18,28] Finally, deviation from the Beer-Lambert law attributed to oligomerization has been reported for other interacting d 10 -d 10 centers. [29] Of these, the only report describing optical changes with concentration due to Au I -Ag I bonding was that of Omary, Fackler et al, [29b] but the spectral changes referred only to the absorption spectrum because the product was not luminescent in solution. Hence, this represents the first example of luminescence in solution due to unsupported argento-aurophilic bonding.…”

Gold(I) Complexes of N‐Heterocyclic Carbenes and Pyridines

“…This attraction provides additional stability for molecular aggregation, both in the solid and in solution, and at times leads to luminescence. [5][6][7][8] Recently, research on the Au I -and Au III -catalyzed reactions has been booming, [9][10][11] earning the phrase "gold rush." It has been proposed that the catalytic property of gold may be affected by a relativistic contraction of 6s and expansion of 5d orbitals.…”

Effects of the Au(I)–Au(I) closed‐shell attraction on the electronic and phosphorescent properties in a series of coordination compounds: A theoretical study

“…Complex 1 has been synthesized by Tang et al [21]. It is an eight-member ring with a thiolate ligand [see Fig.…”

“…An interesting issue to be explored relating the closed-shell attractions is the search of new transition metal complexes containing nucleobases derivatives [21]. This is examined to understand the acid metal-nucleic interactions to get information about several biological phenomena and to stimulate the quest of new biologically active metallodrugs.…”

“…As a matter of fact, the Au(I)-phosphine metallodrugs have been successfully used as antiarthritic and antitumoral agents. However, despite the existence of several metallic complexes structurally characterized, only four systems in which the guanine (H 2 G) molecule is coordinated to metallic ions have been reported [21].…”