Dicoordinate Au(I)–Ethylene Complexes as Hydroamination Catalysts

A series of gold(I)–ethylene π-complexes containing a family of bulky phosphine ligands has been prepared. The use of these sterically congested ligands is crucial to stabilize the gold(I)–ethylene bond and prevent decomposition, boosting up their catalytic performance in the highly underexplored hydroamination of ethylene. The precatalysts bearing the most sterically demanding phosphines showed the best results reaching full conversion to the hydroaminated products under notably mild conditions (1 bar of ethylene pressure at 60 °C). Kinetic analysis together with density functional theory calculations revealed that the assistance of a second molecule of the nucleophile as a proton shuttle is preferred even when using an extremely congested cavity-shaped Au(I) complex. In addition, we have measured a strong primary kinetic isotopic effect that is consistent with the involvement of X–H bond-breaking events in the protodeauration turnover-limiting step.


Formation of Au(I)-Ag(I) multimetallic species
Reaction of the gold(I) chloride complexes 3-8 with AgSbF6 in the absence of ethylene atmosphere did not lead to instant precipitation of AgCl, arguing in favor of the presence of silver within the resulting structure.
Complexes 3-8 bearing bulky biphenyl and terphenylyl phosphine ligands formed species characterized by broad NMR resonances that we tentatively attribute to gold(I)-silver(I) multimetallic complexes by analogy with our prior studies on compound 1. 1 The 1 H and 31 P{ 1 H} NMR spectra recorded at 25 °C of the resulting gold(I)-silver(I) multimetallic species derived from the reaction of complex 6 and AgSbF6 is presented as an example:

Formation of Au(I)-amine adducts
Different bulky amines were tested as substrates in the hydroamination of ethylene using gold(I) complexes 1 and 2, but no conversion was observed. In these cases, new signals were detected in the 31 P{ 1

Kinetic experiments.
Complex 1·MeCN (6 mg, 0.003 mmol) and 1-methyl-imdazolidin-2-one (6 mg, 0.06 mmol) were dissolved in CDCl3 (0.5 mL) in a high-pressure NMR tube. The tube was freeze-pumped to remove the nitrogen gas, filled with 4 bar of ethylene pressure and heated at 100 °C. The reaction was monitored by 1 H NMR spectroscopy at different times. As stated in the main text, the reaction follows a second order dependence on the amide as evinced by the representation of the corresponding integrated rate law ( Figure 4 in the main text). For comparison, zero and first order representations are depiteced in Figures S58 and S59, respectively.  The activation energy (G) of the process was calculated at 373.15 K (T) from the Arrenhius equation: where k is the kinetic constant obtained from the second-order kinetic representation (k = 6.07 x 10 -5 s -1 ), kB is the Boltzmann constant (1.38 x 10 -23 J·K -1 ), h is the Planck constant (6.63 x 10 -34 J·s) and R is the gas constant (8.314 J·K -1 ·mol -1 ) giving G373 K = 29.2 kcal/mol as the free energy of activation.

Crystal structure determinations
Crystallographic details. Low-temperature diffraction data were collected on a D8 Quest APEX-III single crystal diffractometer with a Photon III detector and a IμS 3.0 microfocus X-ray source ( (7), and 2 diclhoromethane molecules (12), in the unit cell.
A summary of the fundamental crystal and refinement data are given in Table S1 and Table S2

Buried volume analysis
The steric description of percent buried volume (%Vbur) has been shown to be a valid measure of the steric properties of monodentate ligands such as phosphines. Comparison of all phosphines used in this study is shown in Figure S63. 5 Figure S63. Schematic (a) and 3D representation (b) of the ligands, together with the corresponding steric maps (c) and calculated %Vbur for all the gold(I) chloride complexes in the study. The %Vbur of each quadrant are also indicated in red.

Computational details
Calculations were performed at the DFT level with the Gaussian 09 (Revision D.01) program. 6 The hybrid functional PBE0 7 was used throughout the computational study, and dispersion effects were accounted for by using Grimme's D3 parameter set with Becke−Johnson (BJ) damping at the optimization stage. 8 Geometry optimizations were carried out without geometry constraints, using the 6-31G(d,p) 9 basis set to represent the C, H, N, O and P atoms and the Stuttgart/Dresden Effective Core Potential and its associated basis set (SDD) 10