GEOMETRIC FEATURES OF D4 METAL DICARBONYL MONOMERS WITH CIS-PI-DONOR LIGANDS

Molecular orbital descriptions for five closely related cis-dicarbonyl tungsten(II) d4 model complexes are presented. The idealized compounds considered are [H3W(CO)2(SH)]2-, [H3W(CO)2(OH)]2-, [H3W(CO)2(NH2)]2-, [H3W(CO)2(NMe2)]2-, and [H3W(CO)2(HC=CH)]-. These five compounds were chosen to reveal the interplay between the OC-W-CO bond angle and the orientation of a cis single-faced pi-donor ligand, and the conclusions are based on Extended Huckel calculations. These compounds display similar orientations for the pi-donor ligand with respect to the OC-W-CO angle, and each pi-donor ligand encounters a barrier to rotation around the tungsten-ligand axis. Coordinates for the computer model [H-3(CO)2W(HC=CH)]- were based on the results of a single-crystal x-ray diffraction study of [Tp'W(CO)2(PhC=CMe)][BPh4] (Tp'= tris (3,5-dimethylpyrazolyl) borate) that is reported here.