Metallophilic Bonding and Agostic Interactions in Gold(I) and Silver(I) Complexes Bearing a Thiotetrazole Unit

Abstract

Gold(I) and silver(I) complexes of 1-methyl-5-thio-tetrazole (1) have been prepared and the coordination chemistry of this ligand toward metal-phosphine frameworks has been explored. As indicated by IR and Raman data, ligand 1 is deprotonated and the resulted anion acts as a bidentate (S,N)-tetrazole-5-thiolato unit in the new gold(I) complexes, [Au(SCN(4)Me)(PPh(3))] (2), [{Au(SCN(4)Me)}(2)(μ-dppm)] (3), and [{Au(SCN(4)Me)}(2)(μ-dppe)] (4), while it is coordinated only through the sulfur atom as its neutral tetrazole-5-thione form in the silver(I) derivative, [Ag(HSCN(4)Me)(PPh(3))](2)(OTf)(2) (5). Further characterization of the new compounds was performed using multinuclear ((1)H, (13)C, (31)P, (19)F) NMR spectroscopy, mass spectrometry, and DSC measurements. Single-crystal X-ray diffraction studies revealed basically linear P-M-S arrangements in complexes 3-5. The bidentate (S,N) coordination pattern results in a T-shaped (S,N)PAu core in 3 and 4, whereas, in 5, a similar coordination geometry is achieved in the dimer association based on S-bridging ligand 1. Herein, weak (C)H···Au and (C)H···Ag agostic interactions were observed. An intramolecular Au···Au contact occurs in 3, while in 4 intermolecular aurophilic bonds lead to formation of a chain polymer. An intermolecular Ag···Ag contact is also present in the dimer unit of 5. Low-temperature (31)P NMR data for 5 evidenced the presence of monomer and dimer units in solution. Theoretical calculations on model of the complexes 2 and 4 are consistent with the geometries found by X-ray diffraction studies.

Argentophilic Interactions

“…[77] It is generally true that Ag-S interactions overrule Ag-Ag interactions owing to the pronounced affinity of silver for sulfur. [78] Similar observations were made with gold(I) thiolate or thiophosphate complexes. [15][16][17][18] Carbene carbon atoms bridging two silver atoms have been discovered in the trinuclear cation [Ag 3 (NHC) 3 ] 3+ with NHC = 1,3-dipicolylbenzylimidazol-2-ylidene.…”

Gold(i) thiotetrazolates as thioredoxin reductase inhibitors and antiproliferative agents

“…The synthesis of compounds 2a and 2b under similar conditions was reported elsewhere earlier. 22,23 Complexes 2c-e were obtained for the first time.…”

“…22,23 New partially split bands at 690-710 cm −1 assigned to the stretching vibrations of the C-S bond 23 were observed. Altogether, these changes support the formation of a covalent Au-S bond between the triarylphosphane gold(I) moiety and the thiolate function of the tetrazole-containing ligands.…”

“…In general the spectral and structural characteristics of complexes 2a and 2b were found to be consistent with previously published results. 23,24 ESI(+) mass spectra of 2a-e showed pseudomolecular ions [M + H] + along with the respective [Au(PR 3 ) 2 ] + species. Assignments of signals observed in 1 H and 13 C NMR spectra of all complexes were made based on previously published data 23,25 and are in agreement with the suggested structures (see Scheme 1).…”

Experimental and Theoretical Evidence for an Agostic Interaction in a Gold(III) Complex

“…[8] Thep resence of short Au···H(C) contacts has been identified in af ew gold(I) and gold(III) complexes,a nd the possible existence of agostic interactions in gold complexes has been speculated upon. [9,10] However, no evidence has been presented to support the presence of acovalent bonding interaction between the CÀHbonds and the gold center,and computational studies suggest that the short Au···H distances result instead from conformational constraints. [11,12] Thetopic has been recently reviewed by Schmidbaur et al, [13] who actually came to the conclusion that "gold(I) and gold(III) centers are generally very poor acceptors for Au···H À C interactions"a nd that "there is currently no evidence for agostic interactions in organogold compounds".…”