Diphosphine-bridged digold(I) compounds: Structural and computational studies on the aurophilic interaction in Au2Cl2(μ-bpcd) and Au2Cl2(μ-bmi)

The reaction of AuCl(tht) with the diphosphine donors 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and 2,3-bis(diphenylphosphino)-N-phenylmaleimide (bmi) in a 2:1 stoichiometry affords the diphosphine-bridged digold(I) complexes Au2Cl2(bpcd) (1) and Au2Cl2(bmi) (2), respectively. 1 and 2 have been isolated and characterized in solution by IR and NMR spectroscopy (H-1 and P-31), and the solid-state structures established by X-ray crystallography. The X-Au-Au-X (X = Cl, P) atoms in both Au-2 dimers exhibit a gauche-type (staggered) interaction based on a torsion angle of 54 for I (X = Cl) and 70 for 2 (X = Cl, mean angle for the two independent molecules). Each Au-2 product displays a weak aurophilic interaction based on a Au-Au internuclear distance on the order of 2.9 angstrom. The bonding in 1 and 2 has been investigated by electronic structure calculations and the composition of the HOMO and LUMO levels determined in the case of 2. The potential energy surface for the interconversion of 2 to an alternative staggered conformation has been computed, and this transformation takes place through an eclipsed transition structure. The preference for a structure that contains a staggered orientation of Cl-Au-Au-Cl and P-Au-Au-Cl atoms is discussed. (C) 2016 Elsevier B.V. All rights reserved.