Fluorinated vs Nonfluorinated PR2(biaryl) Ligands and Their [AuCl(L)] Complexes: Synthesis, X-ray Structures, and Computational Study of Weak Interactions. Bond, No Bond, and Beyond.

Six fluorinated PR2(biaryl) phosphines, Ln, with R = Ph, Cy and biaryl = C6H4-C6F5, C6F4-C6H5, C6F4-C6F5, have been prepared. Their [AuCl(Ln)] complexes and H congeners with PhJohnPhos or CyJohnPhos have been studied in order to examine the interactions that bring the distal aryl close to the Au-Cl bond region. X-ray, DFT structure optimization, QTAIM, and NCI methods allow for some understanding of the forces involved. The "no bond" noncovalent distal-aryl/Au-Cl weak interactions are produced at forced short distances achieved under intramolecular structural ligand pressure. Enhanced vdW distal-aryl/Au interactions at "no bond" distances shorter than the sum of Au and C vdW radii and weaker distal-aryl/Cl interactions at "no bond" distances beyond the sum of Cl and C vdW radii counterbalance the unfavorable structural distortion of the free ligand, providing some extra stability of the molecule on the order of 2-10 kcal mol-1. The F substituents in the distal aryl induce shorter aryl distances to the Au-Cl zone, pointing overall to stronger π-aryl polarization as being mainly responsible for the NCIs with gold. The interactions in the C···Cl zone, where the distances are larger than the sum of vdW radii, contribute only about 5%, according to energy estimations using NBOs.