Ligand-enabled oxidation of gold(i) complexes with o-quinones

Chelating P^P and hemilabile P^N ligands were found to trigger the oxidation of Au(i) complexes by o-benzoquinones. The ensuing Au(iii) catecholate complexes have been characterized by NMR spectroscopy, single crystal X-ray diffraction and X-ray absorption spectroscopy. They adopt tetracoordinate square-planar structures. Reactivity studies substantiate the reversibility of the transformation. In particular, the addition of competing ligands such as chloride and alkenes gives back Au(i) complexes with concomitant release of the o-quinone. DFT calculations provide insight about the structure and relative stability of the Au(i) o-quinone and Au(iii) catecholate forms, and shed light on the 2-electron transfer from gold to the o-quinone.


Reactions of 5a
3.1 Reaction of 5a with (nBu)4NCl To a solution of 5a (5 mg, 0.005 mmol) CD2Cl2 (0.4 mL) a solution of (nBu)4NCl in CD2Cl2 (100 μL, 1 equiv. 5 x 10 -2 M) was added at rt. Upon addition the grey green solution became orange instantaniously. A 1 H and 31 P NMR spectrum was recorded before and after the addition. 13 C NMR was also recorded after the addition to confirm the release of o-chloranil.  Figure S34. 13 C{ 1 H} NMR spectrum of an equimolar mixture of 5a and (nBu)4NCl in CD2Cl2. S25 3.2 Reaction of 5a with ethylene 1. A solution of 5a (5 mg, 0.005 mmol) CD2Cl2 (0.5 mL) was placed into a J Young NMR tube. ( 1 H/ 31 P NMR was recorded). 2. Then the headspace was replaced with ethylene (1 bar). The tube was shaken during 2 minutes at rt, while the grey-green solution became gradually orange. ( 1 H/ 31 P was recorded). 3. The solvent was removed under reduced pressure and the tube was left under vacuum for another 30 minutes at rt. The solid material was resolubilized (CD2Cl2). ( 1 H/ 31 P NMR was recorded).  Figure S36. 31 P{ 1 H} NMR spectrum of the reaction of 5a with an excess of ethylene in CD2Cl2. S27 3.3 Reaction of 5a with styrene 1. A solution of 5a (5 mg, 0.005 mmol) CD2Cl2 (0.4 mL) was placed into a J Young NMR tube. ( 1 H/ 31 P NMR was recorded). 2. Then a solution of styrene in CD2Cl2 (5 x 10 -2 M) was added at rt in increasing amounts.

Figure S37
. 1 H NMR spectra of the reaction of 5a after the addition of increasing amounts of styrene in CD2Cl2. Figure S38. 31 P{ 1 H} NMR spectra of the reaction of 5a after the addition of increasing amounts of styrene in CD2Cl2.

Crystallographic data
Crystallographic data were collected at 193(2) K on a Bruker-AXS D8-Venture equipped with a PHOTON III detector and using MoKα radiation (λ=0.71073 Å). Phi-and omega-scans were used. An empirical absorption correction was applied [4] . The structures were solved using an intrinsic phasing method (SHELXT) [5] and refined using the least-squares method on F 2 [6] . All non-H atoms were refined with anisotropic displacement parameters. Hydrogen atoms were refined isotropically at calculated positions using a riding model. For 3b, as in the related structure of the Au(III) complex deriving from nido-o-carboranyl diphosphines, the four carborane open-face H atoms were located in difference Fourier maps and the H atom bridging two boron atoms was refined using the same B-H distance restraints as in the previous report by Laguna et al. [7] For 6c, the SQUEEZE function of PLATON [8] was used to eliminate the contribution of the electron density in the final refinement of highly disordered solvent.

X-ray absorption analyses
Samples were prepared as solid pellets in a cellulose matrix. Au L3-edge data was acquired at cryogenic temperatures in transmission mode using liquid He cryostats available at the ALBA CLAESS beamline and ESRF BM23. Several XAS repeats were collected to ensure reproducibility and statistics Data processing was carried out with the Athena software package. [9] The energy scale was calibrated by setting the first inflection point of the Au foil spectra at 11919 eV. EXAFS were extracted using the autobk algorithm employing a spline in the 0 to 20 Å -1 region of k-space having an Rbkg of 1. The FEFF6 code was used for scattering path generation, and multi (k 1 , k 2 , k 3 )-weighted fits of the data were carried out in r-space over an r-range of 1.0 to 2.5 Å and a k-range of 3-17 Å -1 . [10] The S0 2 value was set to 0.9, and a global E0 was employed with the initial E0 value set to the first inflection point of the rising edge. Single scattering paths were fit in terms of a reff and  2 ,. To assess the goodness of the fits both the Rfactor (%R) and the reduced  2 ( 2 ) were minimized, ensuring that the data was not over-fit. [11,12] An increase in the number of variables is generally expected to improve the Rfactor,however  2 may go through a minimum then increase, which is an indication that the model is over-fitting the data. Best fit models were determined using a grid search with fixed values for path coordination numbers (N) by employing larch, the Python implementation of Artemis. [13] S34 Figure S42. EXAFS fits of 5a. Multi (k 1 , k 2 , k 3 )-weighted fits carried out in r-space (1-2.5 Å) over a k-range of 3-17 Å -1 using a Hanning window (dk 1), and S0 = 0.9. Bond distances and disorder parameters (reff and  2 ) were allowed to float having initial values of 0.0 Å and 0.003 Å 2 respectively, with a universal E0 and E0 = 0 eV. Best model fits are highlighted in bold and  2 values reported as (x10 3 Figure S43. EXAFS fits of MeDalPhosAuCl (4). Multi (k 1 , k 2 , k 3 )-weighted fits carried out in r-space (1-2.5 Å) over a k-range of 3-17 Å -1 using a Hanning window (dk 1), and S0 = 0.9. Bond distances and disorder parameters (reff and  2 ) were allowed to float having initial values of 0.0 Å and 0.003 Å 2 respectively, with a universal E0 and E0 = 0 eV. Best model fits are highlighted in bold and  2 values reported as (x10 3

Computational details
All calculations were performed with the Gaussian 16 package [14] with the B3PW91 [15] hybrid functional and D3 dispersion correction of Grimme with Becke-Johnson damping (DFT-D3(BJ)), [16] by taking into account solvent effect (Dichloromethane : DCM) by means of the polarizable continuum model PCM [17] on real systems. The gold atom was described with the relativistic electron core potential SDD and associated basis set, [18] augmented by a set of f-orbital polarization functions. [19] The 6-31G** basis set were employed for all other atoms. All stationary points involved were fully optimized by taking into account solvent effect and dispersion. Frequency calculations were undertaken to confirm the nature of the stationary points, yielding one imaginary frequency for transition states (TS) and all of them positive for minima. The connectivity of the transition state TS1 and their adjacent minima was confirmed by intrinsic reaction coordinate (IRC) [20] calculations.
To have better insights on the process and know when Au to o-quinone electron transfer occurs, the Potential Energy Surface (PES) was scrutinized, from TS1 to 5a, by scanning the reaction coordinate OcistoPAuPCPh degree by degree. Due to the large number of points to be calculated, we performed this scan at B3PW91-D3(BJ)/SDD+f(Au),6-31G**(C,H,N,O,P,Cl) level of theory by removing solvent effect. Then, Intrinsic Bond Orbitals (IBO) analysis was carried out on the main points of the PES. To do this, the calculations of wave functions have been made with version 7.4.2 of Turbomole [21] at B3LYP-D3(BJ)/def2-TZVP level of theory on the main points of the scan optimized at B3LYP-D3(BJ)/SDD+f(Au), 6-31G(d,p) level of theory by using Gaussian 16. Orbital visualizations were produced with IboView (v20150427), [22] program developed to analyze molecular electronic structure, based on Intrinsic Atomic Orbitals (IAOs).
Electronic configuration of all structures along the path, from TS1 to 5a, was determined using Natural Bond Orbital [23] analyses (NBO). These calculations were performed with NBO, 5.9 version. [24] For this purpose, the NBO orbitals associated with the d-orbitals of gold have been analyzed in detail as well as their occupancy.
The 13 C, 1 H, 31 P NMR chemical shifts ( in ppm) were computed at PCM(DCM)-B3PW91-D3(BJ) level by taking into account solvent effects (DCM), employing the direct implementation of the Gauge Including Atomic Orbitals (GIAO), [25] with the IGLOII [26] basis set on C, H, O, N, Cl and P atoms, SDD+f on Au and using as reference SiMe4 or H3PO4 optimized at the same level of theory, for respectively H, C or P atoms. Relative stability (G in kcal/mol).