Quantification of steric interactions in phosphine ligands from single crystal X-ray diffraction data. Crystal structures of (g5 -C5H4Me)Mo(CO)2(PR3)I (R3 = PhMe2, PhEt2, Et3)
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Date
2005-12-05
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Abstract
Distorted square pyramidal complexes of molybdenum (g5
-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 (H) and solid
(X) 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 H (129 , 135 and 139 ) and X (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
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Keywords
Piano-stool molybdenum complexes, Phosphine ligands, CSD search, Steric interactions