CH/π-stabilization controls the architecture of the PPh3 propeller in transition-metal complexes. CH/π- and Cl/π-interactions determine its orientation within the molecule

Abstract

The architecture of the triphenylphosphine propeller in Cr-PPh3 complexes and in the compounds trans-[MCl2(PPh3)2], M=Ni, Pd, and Pt, is analyzed on the basis of a CSD search. The three phenyl rings interact with each other by formation of weak CH/π bonds comparable to the archetypal T-shaped benzene dimer. ortho-CH bonds from inside the propeller bind to ipso- and ortho-carbon atoms of adjacent phenyl rings. In the broad energy minimum A/B there is a discontinuity in the transition from A to B. Binding switches from inside to outside ortho-carbon atoms. ortho-CH bonds from outside the propeller establish similar weak bonds with unsaturated ligands (and the metal atom) which control the arrangement of the PPh3 propeller within the molecule. In the trans-[MCl2(PPh3)2] complexes it is the Cl/π interaction which determines the orientation of the PPh3 propeller in the molecule.