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Kinetics and mechanisms of ligand substitution reactions of molybdenum SO2 complexes. Synthesis and X-ray structure of trans-Mo(CO)2 (dmpe) (PPh3) (SO2) |
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| Authors: | Jian-Kun Shen Gregory J Kubas Arnold L Rheingold |
| Institution: | a Department of Chemistry, Northwestern University, Evanston, IL 60208, USA b Material and Chemical Design Group, CST-10:MS-C346, Los Alamos National Laboratory, Los Alamos, NM 87545, USA c Department of Chemistry, University of Delaware, Newark, DE 19716, USA |
| Abstract: | Kinetic results are reported for intramolecular PPh3 substitution reactions of Mo(CO)2(η1-L)(PPh3)2(SO2) to form Mo(CO)2(η2-L)(PPh3)(SO2) (L = DMPE = (Me)2PC2H4P(Me)2 and dppe=Ph2PC2H4PPh2) in THF solvent, and for intermolecular SO2 substitutions in Mo(CO)3(η2-L)(η2-SO2) (L = 2,2′-bipyridine, dppe) with phosphorus ligands in CH2Cl2 solvent. Activation parameters for intramolecular PPh3 substitution reactions: ΔH≠ values are 12.3 kcal/mol for dmpe and 16.7 kcal/mol for dppe; ΔS≠ values are ?30.3 cal/mol K for dmpe and ?16.4 cal/mol K for dppe. These results are consistent with an intramolecular associative mechanism. Substitutions of SO2 in MO(CO)3(η2-L)(η2-SO2) complexes proceed by both dissociative and associative mechanisms. The facile associative pathways for the reactions are discussed in terms of the ability of SO2 to accept a pair of electrons from the metal, with its bonding transformations of η2-SO2 to η1-pyramidal SO2, maintaining a stable 18-e count for the complex in its reaction transition state. The structure of Mo(CO)2(dmpe)(PPh3)(SO2) was determined crystallographically: P21/c, A=9.311(1), B = 16.344(2), C = 18.830(2) Å, ß=91.04(1)°, V=2865.1(7) Å3, Z=4, R(F)=3.49%. |
| Keywords: | Kinetics and mechanism Ligand substitution reactions Crystal structures Molybdenum complexes Sulfur dioxide complexes |
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