Do 2-Coordinate Iodine(I) and Silver(I) Complexes Form Nucleophilic Iodonium Interactions (NIIs) in Solution?

The interaction of a [bis(pyridine)iodine(I)]+ cation with a [bis(pyridine)silver(I)]+ cation, in which an iodonium ion acts as a nucleophile by transferring electron density to the silver(I) cation, is reinvestigated herein. No measurable interaction is observed between the cationic species in solution by NMR; DFT reveals that if there is an attractive interaction between these complexes in solution, it is dominantly the π-π interaction of pyridines.


General Information
The solvents CH2Cl2 and CD2Cl2 were distilled over CaH2, whilst n-hexane was distilled over Na, benzophenone and tetraglyme. These dry solvents were stored in a glovebox over 3 Å molecular sieves, with CD2Cl2 being stored at -35 °C. All chemicals were purchased from commercial suppliers and were used without prior purification. For all syntheses and analyses, glassware was either dried at 150 °C or under high vacuum overnight prior to use. A glovebox was used for preparation of Ag + and I + complex samples, where Ag + salts and I2 were stored prior to use. An Eppendorf Centrifuge 5702 was used to centrifuge samples. NMR spectra were recorded on an Agilent MR400-DD2 spectrometer fitted with a OneNMR probe. Chemical shifts were reported on the δ scale (ppm), with the residual solvent signal or with TMS as an internal reference; CD2Cl2 (δH 5.32, δC 53.84), TMS (δH 0.00, δC 0.00). Nitromethane (δN 0.0) was used as an external standard for 15 N. For 1 H, 15 N HMBC spectra, a capillary containing 1-methyl pyridinium iodide (0.45 M) in CD3CN was inserted into the sample to act as an external reference (δH 5.18, δN -177.79). For most 1 H, 15 N HMBC spectra, a spectral window of 10 ppm ( 1 H) and 80 ppm ( 15 N) were used, with 721 points in the direct dimension and 256 increments used in the indirect dimension, affording a resolution of 0.31 ppm/point in f1. 1 H NMR resonances were assigned considering chemical shift (δ), multiplicity, coupling constants (J Hz) and the number of hydrogens, and multiplicities of these were denoted as s (singlet), d (doublet), t (triplet), q (quartet), hep (heptet) and m (multiplet). MestReNova 14.2.1 was used to process NMR spectra.
Diffusion coefficients for 1 H nuclei were calculated according to an adjusted Stokes-Einstein equation, 1 which takes into account a correction factor for small, flat, linear molecules.
where D is the diffusion coefficient (m 2 s -1 ), kB is Boltzmann's constant, T the temperature, c the cfactor for small molecules, fs the form factor for non-spherical molecules, η the dynamic viscosity and rH the hydrodynamic radius. The expected VvdW from Eq. 1 for Ag + and I + complexes, (1) and (2), is ~200 Å 3 (from an rvdW ~3.6 Å) -comparable to that of tolane, a monomeric species.
Diffusion NMR was also performed on 19 F nuclei upon the counter-anion of the Ag + and I + 4methylpyridine complexes, PF6 -. Diffusion coefficients were calculated using a standard Stokes-Einstein equation (left, Eq. 1), as the anion itself is spherical in shape. Values were corrected for the gyromagnetic ratio of 19 F, relative to those of 1 H, using γ 19 F/γ 1 H = 0.8858. 2 Results are shown in Table  S1.

Synthesis
[Bis(4-methylpyridine)silver(I)]hexafluorophosphate (1). 3 In a glovebox, AgPF6 (0.100 g, 0.40 mmol) was dissolved in dry CH2Cl2 (2 mL) with stirring in a dry vial. 4-Methylpyridine (0.077 mL, 0.79 mmol) was added and the mixture was stirred for 5 min before removal of stirrer bar. Dry n-Hexane (4 mL) was added to the mixture to precipitate the Ag + complex 1. The vial was then centrifuged for 10 min at 4400 rpm, the supernatant was removed, and the precipitate was dried in vacuo overnight to yield 1 as a white powder (0.171 g, 0.39 mmol, 98 %). 1  [Bis(4-methylpyridine)iodine(I)]hexafluorophosphate (2). 3 In a glovebox, 1 (0.075 g, 0.17 mmol) was dissolved in dry CH2Cl2 (1 mL) in a dry vial with stirring. Next, I2 (0.043 g, 0.17 mmol) was dissolved in dry CH2Cl2 (1 mL) and was added dropwise over 10 min to the solution of 1, until a faint purple colour was observed (indicating a minute excess of I2). A yellow precipitate, AgI, was observed immediately upon addition of I2 solution. The mixture was stirred for a further 20 min before centrifugation for 10 min at 4400 rpm. The resulting supernatant was transferred to another vial, where dry n-Hexane (2 mL) was added. The vial was cooled to -35 °C for 30 min to complete precipitation of 2. Centrifugation of this solution for 10 min at 4400 rpm, followed by removal of supernatant, addition of 2 mL n-hexane to wash, further centrifugation for 10 min at 4400 rpm and removal of supernatant, gave a white precipitate. The solid was dried in vacuo overnight to yield 2 as a crystalline, white solid (0.066 g, 0.14 mmol, 85 %). 1  [(1,2-bis(pyridin-2-ylethynyl)benzene)silver(I)]tetrafluoroborate (4). [4][5][6] In a glovebox, 3 (0.008 g, 0.029 mmol) and AgBF4 (0.006 mg, 0.029 mmol) were dissolved in dry CH2Cl2 with stirring for 5 min. Thereafter, dry n-Hexane (2 mL) was added to precipitate the Ag + complex. The mixture was then centrifuged for 10 min at 4400 rpm, the supernatant removed and the white solid dried in vacuo overnight. The product, 4, a white powder (0.012 g, 0.025 mmol, 87 %) was obtained. 1  In a glovebox, 4 (0.012 g, 0.025 mmol) was dissolved in dry CH2Cl2 in a dry vial with stirring for 5 min. I2 (0.007 g, 0.027 mmol) was dissolved in dry CH2Cl2 (0.5 mL) and this solution was added dropwise over 10 min to the solution of 4, until a faint purple colour was observed (indicating a minute excess of I2). A yellow precipitate, AgI, was observed immediately upon addition of I2 solution. The mixture was stirred for a further 20 min before centrifugation for 10 min at 4400 rpm. The resulting supernatant was transferred to another vial, where dry n-Hexane (1 mL) was added. The vial was cooled to -35 °C for 30 min to complete precipitation of 5. Centrifugation of this solution for 10 min at 4400 rpm, followed by removal of supernatant, addition of 1 mL n-Hexane to wash, further centrifugation for 10 min at 4400 rpm and removal of supernatant, gave a white precipitate. The solid was dried in vacuo overnight to yield 5 as a crystalline, white solid (0.012 g, 0.024 mmol, 98 %). 1   S7 Figure S2. 13  S8 Figure S3. 1 Figure S6. 19  S12 Figure S7. 19  S13 Figure S8. 1  S14 Figure S9. 13  S15 Figure S10. 1  S20 Figure S15. 1

Computational Methods
Starting from the previously reported X-ray structure, 7 the equilibrium geometries of 2-coordinate iodine(I) and silver(I) complexes in solution were obtained using the M06-2X 8 , B97X-D 9 and B3LYP 10,11 functionals augmented with Grimme's D3 dispersion correction 12 and Ahlrichs' Def2-TZVP basis set. 13 These three functionals are known to accurately describe systems exhibiting weak interactions. 14 The polarizable continuum model (PCM) was used to account for dichloromethane solvation effects. 15 Vibrational frequency calculations were conducted at the same level of theory to ensure the equilibrium geometry corresponding to a minimum on the potential energy surface by the absence of imaginary frequency.
All geometry optimization calculations were performed using the Gaussian 16 Rev. C.01, 16 while the interaction energy calculations were conducted using the ORCA 5.0.1. 17 The counterpoise correction of Boys and Bernadi procedure 18 was used to deal with the basis set superposition error (BSSE) as implemented in ORCA. The free energy calculations were corrected using the Grimme's quasi rigid rotor approximation, 19 as implemented in ORCA and in the Goodvibes program. 20 The electron density and energy density at the Ag + I + and  bond critical points were calculated using the AIMALL version 19.10.12 software. 21 Reduced density gradient (RDG), 22 independent gradient model (IGM), 23 density overlap regions indicator (DORI), 24 interaction region indicator (IRI), 25 and van der Waals surface analyses were carried out using the Multiwfn 3.7 program. 26 The RDG plot were constructed using the 0.4 a.u. isosurface cutoff and color scale of -0.035 -0.035 a.u. Local mode force constants were calculated using the LModeA 2.02 program. 26 All analyses were computed using the M06-2X/def2-TZVP level of theory.   The energies shown in Table S4, in contrast to those in Table 2 in the main text, do not include correction for basis set superposition error (BSSE). The Gibbs free energies shown were calculated at the optimized structure and at the given level of theory, whereas for the energies given in Table 2, the geometries were computed on the M06-2X/Def2-TZVP level of theory. The electronic, enthalpic and entropic contributions were estimated at 1 atm, 298 K at various levels of theory, with the overall conclusion from the different computations showing identical trend apart from that performed with B97X-D/def2-TZVP. In our hands, computations performed at the B97X-D/def2-TZVP level of theory are not suitable for the estimation of the interaction energy of the studied iodine(I) and silver(I) complexes. All other functionals provide comparable electronic energies, enthalpies, entropies and Gibbs free energies, thereby mutually confirming each other.

Figure S70. Interaction region indicator (IRI) plot. The green surfaces show the weak attractive interactions
between Ag + I + . The red, green, and blue surfaces correspond to repulsive, weak and strong attractive interactions, respectively. IRI plot show the weak interactions between Ag + I + . Figure S71. Van