Chelating organophosphines: The use of comparative structural investigations to determine ligand properties

Chelating organophosphines are commonly used in stoichiometric or transition metal catalyzed reactions. Minor geometric or electronic changes in these ligands can cause substantial changes in the selectivity and reactivity of ligand modified catalysts. In continuation of our systematic investigations of the steric requirements of typical ligands to transition metals, we wish to report the molecular structures of five chelating organophosphines. Four of these compounds are liquids at ambient temperature, and their crystal structures have been determined using single crystals obtained by use of in situ zone melting techniques on a diffractometer. The fifth phosphine presented in this work solidifies at elevated temperatures, and high resolution data in conjunction with the X-X method was used to locate the orientation and size of the lone pairs at the phosphorus atoms. A novel technique to describe the accessibility of the phosphorus atom and its lone pair by molecular modeling techniques is also presented. (C) 1997 Elsevier Science S.A.