Quantification of steric interactions in phosphine ligands from single crystal X-ray diffraction data. Crystal structures of (η5-C5H4Me)Mo(CO)2(PR3)I (R3 = PhMe2, PhEt2, Et3)

Distorted square pyramidal complexes of molybdenum (η5-C5H4Me)Mo(CO)2(PR3)I (R3 = PhMe2 (2a); PhEt2 (3a) and Et3 (4a)) have been synthesized and the structures of the lateral (cis) isomers have been determined by X-ray diffraction. The cone (Θ) and solid (Ω) angles as well as the angular profiles of the phosphine ligands in the complexes have been computed using the program steric. Values for the crystallographic cone and solid angles calculated for 2a, 3a and 4a are Θ (129°, 135° and 139°) and Ω (2.73, 2.99 and 2.93 sr), respectively. A search of the Cambridge Structural Database (CSD) was made for piano stool, 5- and 6-coordinate complexes containing the title phosphine ligands. Results from this study show a wide range of sizes for each of the ligands and even the seemingly simple PPhMe2 ligand exhibited a wide range of values for the cone (113–137°) and solid (2.49–3.07 sr) angles. These observations have been rationalized and related to the possible group conformations from the crystallographic data.