Structural Features of Antitumor Gold(i)- Phosphine Derivatives Analyzed with Theoretical Methods

A Density Functional Theory (DFT) analysis of the mixed phosphine complexes Au(PPh 3 )(Ph 2 P(CH 2 ) 3 PPh 2 )X shows a clear trend in the metal geometry as the anion X is varied: the softer the anion, the more it is tetrahedral, or alternatively, the more ionic the complex, the more the complex geometry approaches trigonal planar. A strong (soft) donor as cyanide (X = CN) penetrates markedly the coordination sphere and establishes the most tetrahedral geometry. In the antitumor compound Au(PPh 3 )(Ph 2 P(CH 2 ) 3 PPh 2 )Cl (X = Cl), the weaker donor chloride is slightly displaced from the coordination sphere with consequent strengthening of Au-P bonds, thus stabilizing a more pyramidal geometry. If the anion is completely out of the coordination sphere, the cation [Au(PPh 3 )(Ph 2 P(CH 2 ) 3 PPh 2 )] shows further strengthening of Au-P bonds and a geometry very close to the trigonal planar “AuP 3 ” system. X-ray and DFT data for Au(PPh 3 )(Ph 2 P(CH 2 ) 3 PPh 2 )Cl show generally good agreement; however, in the crystal the Au-Cl bond appears lengthened with consequent strong Au-P bonds. This is probably due to packing effects; nevertheless, the X-ray structure agrees with the trend mentioned above as well.