Stability of Ag^III towards Halides in Organosilver(III) Complexes

Abstract

The involvement of silver in two-electron Ag I /Ag III processes is currently emerging. However, the range of stability of the required and uncommon Ag III species is virtually unknown. Here, the stability of Ag III towards the whole set of halide ligands in the organosilver(III) complex frame [(CF 3 ) 3 AgX] À (X=F, Cl, Br, I, At) is theoretically analyzed. The results obtained depend on a single factor: the nature of X. Even the softest and least electronegative halides (I and At) are found to form reasonably stable Ag III À X bonds. Our estimates were confirmed by experiment. The whole series of nonradiative halide complexes [PPh 4 ][(CF 3 ) 3 AgX] (X=F, Cl, Br, I) has been experimentally prepared and all its constituents have been isolated in pure form. The pseudohalides [PPh 4 ][(CF 3 ) 3 AgCN] and [PPh 4 ][(CF 3 ) 3 Ag(N 3 )] have also been isolated, the latter being the first silver(III) azido complex. Except for the iodo compound, all the crystal and molecular structures have been established by single-crystal X-ray diffraction methods. The decomposition paths of the [(CF 3 ) 3 AgX] À entities at the unimolecular level have been examined in the gas phase by multistage mass spectrometry (MS n ). The experimental detection of the two series of mixed complexes [CF 3 AgX] À and [FAgX] À arising from the corresponding parent species [(CF 3 ) 3 AgX] À demonstrate that the AgÀ X bond is particularly robust. Our experimental observations are rationalized with the aid of theoretical methods. Smooth variation with the electronegativity of X is also observed in the thermolyses of bulk samples. The thermal stability in the solid state gradually decreases from X=F (145°C, dec.) to X = I (78°C, dec.) The experimentally established compatibility of Ag III with the heaviest halides is of particular relevance to silver-mediated or silver-catalyzed processes.

A Five‐Coordinate Compound with Inverted Ligand Field: An Unprecedented Geometry for Silver(III)

“…In contrast, the Ag‐Cl distance, 228.68(8) pm, is significantly shorter than in the only precedent described to date, namely [PPh 4 ][(CF 3 ) 3 AgCl]: 232.03(4) pm. [17] This difference evidences the marked trans influence of the CF 3 ligand [23] operating in the latter compound. Accordingly, the ν(Ag‐Cl) band observed in the IR spectrum of 1 a (B 1u : 386 cm −1 ) appears at higher frequency than found for [PPh 4 ][(CF 3 ) 3 AgCl] (A 1 : 348 cm −1 ).…”

“…Accordingly, the ν(Ag‐Cl) band observed in the IR spectrum of 1 a (B 1u : 386 cm −1 ) appears at higher frequency than found for [PPh 4 ][(CF 3 ) 3 AgCl] (A 1 : 348 cm −1 ). [17] …”

“…The Ag‐Br distances (255.86(4), 256.69(5) and 265.16(4) pm) are all longer than that found in the square‐planar complex [PPh 4 ][(CF 3 ) 3 AgBr]: 246.25(2) pm. [17] We would like to stress that five‐coordination in 3 is not sterically forced, since every ligand around the metal is monodentate. The overall geometry is surprisingly similar to that reported for the neutral gold(III) compound (Me 3 P) 2 AuI 3 , which exhibits a nearly regular TBPY ‐5 geometry ( τ =0.94).…”

Terminal Au−N and Au−O Units in Organometallic Frames

“…[20] The structure of the [(CF 3 ) 3 Au(N 3 )] À anion in 1' (Scheme 2; Table S2) is similar to that previously established for the homologous silver complex [(CF 3 ) 3 Ag(N 3 )] À . [21] The Au-N α bond length in 1' (204.4(5) pm) is also indistinguishable from the Pt-N α distance found in the related Pt compound (PNP)Pt(N 3 ): 203.1(5). [17] However, the higher ν a (NNN) frequency observed in the IR spectrum of the gold compound 1 (2061 cm À 1 ) when compared to that of the silver counterpart (2042 cm À 1 ) might suggest higher covalent character in the AuÀ N 3 bond.…”

Cover Feature: Cross‐Coupling through Ag(I)/Ag(III) Redox Manifold (Chem. Eur. J. 62/2021)

“…[36] In 2020, four thiolate−Ag III intermediates [Ag III (SR)(CF3)3] − , built from the fluorido−Ag III complex II and thiols, were characterized in situ by Menjón using NMR spectroscopy and mass spectrometry before RS−CF3 coupling and fluoroform (HCF3) release. [12] O'Hair, Ogle and Koszinowski examined the reductive elimination step from tetraorganylargentate(III) complexes [Ag III (R)(CH3)3] − through gas phase fragmentations (ESI-MS) coupled to DFT calculations and highlighted the ability of Ag III to undergo cross-coupling [37,38] overpassing the activity of parent [Cu III (R)(CH3)3] − species. [39] Nevertheless, a precise study taking place from an isolable, fully characterized aryl−Ag III −X fragment (with X being any coupling partner) was lacking until very recently.…”