An efficient method for the preparation of oxo molybdenum salalen complexes and their unusual use as hydrosilylation catalysts.
A number of molybdenum(VI) dioxo salalen complexes were prepared from the reaction of Mo(CO)(6) and salen ligands containing bulky substituents, providing a novel and facile entry to Mo-salalen compounds. Two of the complexes were characterized by single-crystal X-ray diffraction. Reduction with organic phosphines or silanes afforded the monooxo molybdenum(IV) complexes, along with dinuclear molybdenum(V) species featuring a bridged oxo ligand (mu-O). One of the dinuclear complexes as well as a molybdenum(VI) dioxo salan complex was characterized structurally. All of the molybdenum compounds except the monooxo molybdenum(IV) were fully characterized by NMR, mass spectrometry, and elemental analyses. Investigations of acetophenone and 4-Ph-2-butanone reduction with PhSiH(3) showed that all of these molybdenum oxo complexes could serve as catalysts at reasonably low loading (1 mol % Mo) and approximately 110 degrees C. The time profiles and efficacy of catalysis varied depending on the precursor form of the catalyst, Mo(VI)(O)(2) vs (O)Mo(V)-O-Mo(V)(O) vs Mo(IV)(O). Solvent effects, radical scavenger probes, and other mechanistic considerations reveal that the monooxo molybdenum(IV) is the most likely active form of the catalyst.
Brown Laboratory, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.
Jeanette E
JE
Ziegler
Guodong
G
Du
Philip E
PE
Fanwick
Mahdi M
MM
Abu-Omar